recent journal articles: general chemistry




Recent Articles in Chemical Reviews

Fontecilla-Camps JC, Volbeda A, Cavazza C, Nicolet Y
Structure/Function Relationships of [NiFe]- and [FeFe]-Hydrogenases. (Chem. Rev. 2007, 107, 4273-4303. Published on the Web September 13, 2007.).
Chem Rev. 2007 Nov;107(11):5411. [Abstract]

Huynh MH, Meyer TJ
Proton-coupled electron transfer.
Chem Rev. 2007 Nov;107(11):5004-64. [Abstract]

Mezei G, Zaleski CM, Pecoraro VL
Structural and functional evolution of metallacrowns.
Chem Rev. 2007 Nov;107(11):4933-5003. [Abstract]

Ghosh SK, Pal T
Interparticle coupling effect on the surface plasmon resonance of gold nanoparticles: from theory to applications.
Chem Rev. 2007 Nov;107(11):4797-862. [Abstract]

Kamber NE, Jeong W, Waymouth RM, Pratt RC, Lohmeijer BG, Hedrick JL
Organocatalytic ring-opening polymerization.
Chem Rev. 2007 Dec;107(12):5813-40. [Abstract]

Akiyama T
Stronger brønsted acids.
Chem Rev. 2007 Dec;107(12):5744-58. [Abstract]

Beccalli EM, Broggini G, Martinelli M, Sottocornola S
C-C, C-O, C-N bond formation on sp2 carbon by Pd(II)-catalyzed reactions involving oxidant agents.
Chem Rev. 2007 Nov;107(11):5318-65. [Abstract]

Albu TV, Espinosa-García J, Truhlar DG
Computational chemistry of polyatomic reaction kinetics and dynamics: the quest for an accurate CH5 potential energy surface.
Chem Rev. 2007 Nov;107(11):5101-32. [Abstract]

Busca G
Acid catalysts in industrial hydrocarbon chemistry.
Chem Rev. 2007 Nov;107(11):5366-410. [Abstract]

Flynn AB, Ogilvie WW
Stereocontrolled synthesis of tetrasubstituted olefins.
Chem Rev. 2007 Nov;107(11):4698-745. [Abstract]

Kleparník K, Bocek P
DNA diagnostics by capillary electrophoresis.
Chem Rev. 2007 Nov;107(11):5279-317. [Abstract]

Li P, Sergueeva ZA, Dobrikov M, Shaw BR
Nucleoside and oligonucleoside boranophosphates: chemistry and properties.
Chem Rev. 2007 Nov;107(11):4746-96. [Abstract]

Enders D, Niemeier O, Henseler A
Organocatalysis by N-heterocyclic carbenes.
Chem Rev. 2007 Dec;107(12):5606-55. [Abstract]

de Vivie-Riedle R, Troppmann U
Femtosecond lasers for quantum information technology.
Chem Rev. 2007 Nov;107(11):5082-100. [Abstract]

Goldsmith EJ, Akella R, Min X, Zhou T, Humphreys JM
Substrate and docking interactions in serine/threonine protein kinases.
Chem Rev. 2007 Nov;107(11):5065-81. [Abstract]

Brackmann F, de Meijere A
Natural occurrence, syntheses, and applications of cyclopropyl-group-containing alpha-amino acids. 2. 3,4- and 4,5-methanoamino acids.
Chem Rev. 2007 Nov;107(11):4538-83. [Abstract]

Brackmann F, de Meijere A
Natural occurrence, syntheses, and applications of cyclopropyl-group-containing alpha-amino acids. 1. 1-aminocyclopropanecarboxylic acid and other 2,3-methanoamino acids.
Chem Rev. 2007 Nov;107(11):4493-537. [Abstract]

Mellah M, Voituriez A, Schulz E
Chiral sulfur ligands for asymmetric catalysis.
Chem Rev. 2007 Nov;107(11):5133-209. [Abstract]

Kaur H, Babu BR, Maiti S
Perspectives on chemistry and therapeutic applications of Locked Nucleic Acid (LNA).
Chem Rev. 2007 Nov;107(11):4672-97. [Abstract]

Mallat T, Orglmeister E, Baiker A
Asymmetric catalysis at chiral metal surfaces.
Chem Rev. 2007 Nov;107(11):4863-90. [Abstract]

Siegbahn PE, Tye JW, Hall MB
Computational studies of [NiFe] and [FeFe] hydrogenases.
Chem Rev. 2007 Oct;107(10):4414-35. [Abstract]

Vignais PM, Billoud B
Occurrence, classification, and biological function of hydrogenases: an overview.
Chem Rev. 2007 Oct;107(10):4206-72. [Abstract]

Kubas GJ
Fundamentals of H2 binding and reactivity on transition metals underlying hydrogenase function and H2 production and storage.
Chem Rev. 2007 Oct;107(10):4152-205. [Abstract]

Ockwig NW, Nenoff TM
Membranes for hydrogen separation.
Chem Rev. 2007 Oct;107(10):4078-110. [Abstract]

Kodama T, Gokon N
Thermochemical cycles for high-temperature solar hydrogen production.
Chem Rev. 2007 Oct;107(10):4048-77. [Abstract]

Esswein AJ, Nocera DG
Hydrogen production by molecular photocatalysis.
Chem Rev. 2007 Oct;107(10):4022-47. [Abstract]

Lubitz W, Tumas W
Hydrogen: an overview.
Chem Rev. 2007 Oct;107(10):3900-3. [Abstract]

Michl J
Editorial for the 100th Thematic Issue.
Chem Rev. 2007 Oct 10;107(10):3899. [Abstract]

Loudet A, Burgess K
BODIPY dyes and their derivatives: syntheses and spectroscopic properties.
Chem Rev. 2007 Nov;107(11):4891-932. [Abstract]

Najera C, Sansano JM
Catalytic asymmetric synthesis of alpha-amino acids.
Chem Rev. 2007 Nov;107(11):4584-671. [Abstract]

Recent Articles in Accounts of Chemical Research

Klingler FD
Asymmetric Hydrogenation of Prochiral Amino Ketones to Amino Alcohols for Pharmaceutical Use.
Acc Chem Res. 2007 Dec 6; .
This Account gives an overview of the homogeneously catalyzed asymmetric hydrogenation of prochiral amino ketones. The preparation of enantiopure arylalkanolamines, which are potent and economically very important pharmaceuticals, is described. Classical routes of synthesis are compared with the new asymmetric hydrogenation route for a number of compounds from the viewpoint of an industrial pharmaceutical chemist. [Abstract]

Moore JC, Pollard DJ, Kosjek B, Devine PN
Advances in the Enzymatic Reduction of Ketones.
Acc Chem Res. 2007 Dec 4;
Historically, biocatalytic ketone reductions involved the use of Baker's yeast. Within the last five years, a significant and growing number of isolated ketoreductases have become available that have rendered yeast-based reductions obsolete. The broad substrate range and exquisite selectivities of these enzymes repeatedly outperform other ketone reduction chemistries, making biocatalysis the general method of choice for ketone reductions. Presented here is a summary of our understanding of the capabilities and limitations of these enzymes. [Abstract]

Shultz CS, Krska SW
Unlocking the Potential of Asymmetric Hydrogenation at Merck.
Acc Chem Res. 2007 Nov 20;
This Account outlines the efforts of Merck scientists toward implementing asymmetric hydrogenation as a core competency within Merck Research Laboratories. Several key factors are discussed including (i) a focus on efficient chemical synthesis, (ii) implementation of high throughput screening (HTS) techniques, (iii) demonstration of robustness on scale, and (iv) diligence to ensure freedom of operation and catalyst supply for manufacturing. Several examples of the development of efficient asymmetric hydrogenation processes are described. [Abstract]

Castner EW, Wishart JF, Shirota H
Intermolecular dynamics, interactions, and solvation in ionic liquids.
Acc Chem Res. 2007 Nov;40(11):
Ionic liquids can simultaneously assume multiple solvent roles, because they are strongly polar and polarizable solvents and binary solutions and frequently contain very hydrophobic components. When the cation and anion functional groups are tuned appropriately, ionic liquids can be used as designer solvents for a broad range of applications. In this Account, we discuss our spectroscopic studies on the intermolecular interactions, dynamics, solvation, transport, and friction in ionic liquids, as compared with information obtained from macroscopic experiments including viscometry and calorimetry. [Abstract]

Ionic liquids.
Acc Chem Res. 2007 Nov;40(11): [Abstract]

Klosin J, Landis CR
Ligands for Practical Rhodium-Catalyzed Asymmetric Hydroformylation.
Acc Chem Res. 2007 Nov 13;
A series of bis-phosphite and bis-phosphine ligands for asymmetric hydroformylation reactions has been evaluated. Bis-phosphite ligands lead, in general, to high regioselectivities across a range of substrates while good enantioselectivities are limited to only a few examples. We found that bis-phospholane-type ligands, such as bis-diazaphospholanes and bis-phospholanes, can lead to very high regio- and enantioselectivities for several different substrates. [Abstract]

Smiglak M, Metlen A, Rogers RD
The Second Evolution of Ionic Liquids: From Solvents and Separations to Advanced MaterialsEnergetic Examples from the Ionic Liquid Cookbook.
Acc Chem Res. 2007 Nov;40(11):
In this Account of the small portion of the recent research in ionic liquids (ILs) by the Rogers Group, we fast forward through the first evolution of IL research, where ILs were studied for their unique set of physical properties and the resulting potential for tunable "green solvents", to the second evolution of ILs, where the tunability of the cation and anion independently offers almost unlimited access to targeted combinations of physical and chemical properties. This approach is demonstrated here with the field of energetic ionic liquids (EILs), which utilizes this design flexibility to find safe synthetic routes to ILs with high energy content and targeted physical properties. [Abstract]

Del Po?polo MG, Kohanoff J, Lynden-Bell RM, Pinilla C
Clusters, Liquids, and Crystals of Dialkyimidazolium Salts. A Combined Perspective from ab Initio and Classical Computer Simulations.
Acc Chem Res. 2007 Nov 20;40(11):
We summarize results obtained by a combination of ab initio and classical computer simulations of dialkylimidazolium ionic liquids in different states of aggregation, from crystals to liquids and clusters. Unusual features arising from the competition between electrostatic, dispersion, and hydrogen-bonding interactions are identified at the origin of observed structural patterns. We also discuss the way Brønsted acids interact with ionic liquids leading to the formation of hydrogen-bonded anions. [Abstract]

Angell CA, Byrne N, Belieres JP
Parallel developments in aprotic and protic ionic liquids: physical chemistry and applications.
Acc Chem Res. 2007 Nov;40(11):
This Account covers research dating from the early 1960s in the field of low-melting molten salts and hydrates,which has recently become popular under the rubric of "ionic liquids". It covers understanding gained in the principal author's laboratories (initially in Australia, but mostly in the U.S.A.) from spectroscopic, dynamic, and thermodynamic studies and includes recent applications of this understanding in the fields of energy conversion and biopreservation. Both protic and aprotic varieties of ionic liquids are included, but recent studies have focused on the protic class because of the special applications made possible by the highly variable proton activities available in these liquids. [Abstract]

Ohno H, Fukumoto K
Amino Acid ionic liquids.
Acc Chem Res. 2007 Nov;40(11):
The preparation of ionic liquids derived from amino acids, and their properties, are outlined. Since amino acids have both a carboxylic acid residue and an amino group in a single molecule, they can be used as either anions or cations. These groups are also useful in their ability to introduce functional group(s). Twenty different natural amino acids were used as anions, to couple with the 1-ethyl-3-methylimidazolium cation. The salts obtained were all liquid at room temperature. The properties of the resulting ionic liquids (AAILs) depend on the side groups of the amino acids involved. These AAILs, composed of an amino acid with some functional groups such as a hydrogen bonding group, a charged group, or an aromatic ring, had an increased glass transition (or melting) temperature and/or higher viscosity as a result of additional interactions among the ions. Viscosity is reduced and the decomposition temperature of imidazolium-type salts is improved by using the tetrabutylphosphonium cation. The chirality of AAILs was maintained even upon heating to 150 degrees C after acetylation of the free amino group. The amino group was also modified to introduce a strong acid group so as to form hydrophobic and chiral ionic liquids. Unique phase behavior of the resulting hydrophobic ionic liquids and water mixture is found; the mixture is clearly phase separated at room temperature, but the solubility of water in this IL increases upon cooling, to give a homogeneous solution. This phase change is reversible, and separation occurs again by raising the temperature a few degrees. It is extraordinary for an IL/water mixture to display such behavior with a lower critical solution temperature. Some likely applications are proposed for these amino acid derived ionic liquids. [Abstract]

Anderson JL, Dixon JK, Brennecke JF
Solubility of CO2, CH4, C2H6, C2H4, O2, and N2 in 1-Hexyl-3-methylpyridinium Bis(trifluoromethylsulfonyl)imide: Comparison to Other Ionic Liquids.
Acc Chem Res. 2007 Nov;40(11):
The solubilities of gases in ionic liquids are important in evaluating ionic liquids as solvents for reactions involving permanent gases, as gas storage media, and as solvents for gas separations. Gas solubilities are also important in developing methods to separate solutes from ionic liquid solutions. Here we describe our measurements of the solubilities of CO 2, CH 4, C 2H 6, C 2H 4, O 2, and N 2 in 1-hexyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide and compare these results to our previous investigations. In addition, focus is placed on efforts to tailor ionic liquids to enhance the solubilities of some gases, with particular emphasis on carbon dioxide. [Abstract]

Iwata K, Okajima H, Saha S, Hamaguchi HO
Local Structure Formation in Alkyl-imidazolium-Based Ionic Liquids as Revealed by Linear and Nonlinear Raman Spectroscopy.
Acc Chem Res. 2007 Nov;40(11):
We show several pieces of Raman spectroscopic evidence that are indicative of local structure formation in imidazolium-based ionic liquids. Low-frequency Raman spectra of C n mimX, where C n mim stands for 1-alkyl(C n H 2 n+1 )-3-methylimidazolium cation and X represents the anion, exhibit broad bands assignable to collective modes of local structures. Spatial distributions of coherent anti-Stokes Raman scattering (CARS) signals from C n mim[PF 6] are consistent with local structures whose size increases with increasing n. Picosecond Raman spectra of S 1 trans-stilbene as a "picosecond Raman thermometer" show microscopic thermal inhomogeneity ascribable to local structure formation in C 2mimTf 2N and C 4mimTf 2N. We also describe two novel phenomena that we believe are relevant to extraordinary nanoenvironments generated by local structures in a magnetic ionic liquid C 4mim[FeCl 4]. [Abstract]

Saudan LA
Hydrogenation Processes in the Synthesis of Perfumery Ingredients.
Acc Chem Res. 2007 Oct 26;
Homogeneous catalytic hydrogenation has played an important role in the development of modern organic synthesis. Indeed, the discovery of highly regio- and stereoselective catalysts for CC and CO bonds reductions has allowed the efficient synthesis of optically active compounds. As the fragrance industry has turned to synthetic ingredients to fulfill the need for novel, cost-effective, and environment-friendly products, the use of catalytic processes are more and more in demand. In this Account, we thus highlight the application of catalytic hydrogenation in the synthesis of fragrance ingredients. [Abstract]

Ikariya T, Blacker AJ
Asymmetric Transfer Hydrogenation of Ketones with Bifunctional Transition Metal-Based Molecular Catalysts.
Acc Chem Res. 2007 Oct 26;
Recent development of conceptually new chiral bifunctional transition metal based catalysts for asymmetric reductive transformations is described. The chiral bifunctional molecular catalyst promoted reduction is now realized to be a powerful tool to access chiral compounds in organic synthetic procedures in both academia and industry. Based on structural investigation of the actual catalyst and its intermediates and a deep understanding of the reaction mechanism, this asymmetric reduction system can be widely used to produce valuable chiral alcohols and is now is applicable to commercial scale production. [Abstract]

Maginn EJ
Atomistic simulation of the thermodynamic and transport properties of ionic liquids.
Acc Chem Res. 2007 Nov;40(11):
Atomistic simulations have emerged in recent years as an important compliment to experiment for understanding how the properties of ionic liquids are controlled by their underlying chemical structure. The ability to obtain reliable thermodynamic and transport properties from a simulation depends both on the quality of the force field and on the use of a proper simulation method. Properties such as densities and heat capacities may be obtained readily using standard techniques. With more effort and advanced simulation methods, solid-liquid and vapor-liquid phase equilibria may also be determined. Transport properties can also be computed, but the notoriously slow dynamics of many ionic liquid systems means that great care must be taken to ensure that the simulations are accurate. [Abstract]

Wildeman SM, Sonke T, Schoemaker HE, May O
Biocatalytic Reductions: From Lab Curiosity to "First Choice"
Acc Chem Res. 2007 Oct 18;
Enzyme-catalyzed reductions have been studied for decades and have been introduced in more than 10 industrial processes for production of various chiral alcohols, alpha-hydroxy acids and alpha-amino acids. The earlier hurdle of expensive cofactors was taken by the development of highly efficient cofactor regeneration methods. In addition, the accessible number of suitable dehydrogenases and therefore the versatility of this technology is constantly increasing and currently expanding beyond asymmetric production of alcohols and amino acids. Access to a large set of enzymes for highly selective CC reductions and reductive amination of ketones for production of chiral secondary amines and the development of improved d-selective amino acid dehydrogenases will fuel the next wave of industrial bioreduction processes. [Abstract]

Macfarlane DR, Forsyth M, Howlett PC, Pringle JM, Sun J, Annat G, Neil W, Izgorodina EI
Ionic liquids in electrochemical devices and processes: managing interfacial electrochemistry.
Acc Chem Res. 2007 Nov;40(11):
Many ionic liquids offer a range of properties that make them attractive to the field of electrochemistry; indeed it was electrochemical research and applications that ushered in the modern era of interest in ionic liquids. In parallel with this, a variety of electrochemical devices including solar cells, high energy density batteries, fuel cells, and supercapacitors have become of intense interest as part of various proposed solutions to improve sustainability of energy supply in our societies. Much of our work over the last ten years has been motivated by such applications. Here we summarize the role of ionic liquids in these devices and the insights that the research provides for the broader field of interest of these fascinating liquids. [Abstract]

Marciniec B
Catalytic coupling of sp2- and sp-hybridized carbon-hydrogen bonds with vinylmetalloid compounds.
Acc Chem Res. 2007 Oct;40(10):
In the Account given herein, it has been shown that silylative coupling of olefins, well-recognized as a new catalytic route for the activation of double bond C-H bond of olefins and double bond C-Si bond of vinylsilicon compounds with ethylene elimination, can be extended over both other vinylmetalloid derivatives (double bond C-E) (where E = Ge, B, and others) as well as the activation of triple bond C-H, double bond C aryl-H, and -O-H bond of alcohols and silanols. This general transformation is catalyzed by transition-metal complexes (mainly Ru and Rh) containing or initiating TM-H and/or TM-E bonds (inorganometallics). This new general catalytic route for the activation of double bond C-H and triple bond C-H as well as double bond C-E bonds called metallative coupling or trans-metalation (cross-coupling, ring-closing, and polycondensation) constitutes an efficient method (complementary to metathesis) for stereo- and regioselective synthesis of a variety of molecular and macromolecular compounds of vinyl-E (E = Si, B, and Ge) and ethynyl-E (E = Si and Ge) functionality, also potent organometallic reagents for efficient synthesis of highly pi-conjugated organic compounds. The mechanisms of the catalysis of this deethenative metalation have been supported by equimolar reactions of TM-H and/or TM-E with initial substances and reactions with deuterium-labeled reagents. [Abstract]

Wang Y, Jiang W, Yan T, Voth GA
Understanding Ionic Liquids through Atomistic and Coarse-Grained Molecular Dynamics Simulations.
Acc Chem Res. 2007 Nov;40(11):
Understanding the physical properties of ionic liquids (ILs) via computer simulation is important for their potential technological applications. The goal of our IL research is to obtain a unified understanding of the properties of ILs with respect to their underlying molecular structure. From atomistic molecular dynamics simulations, the many-body electronic polarization effect was found to be important for modeling ILs, especially their dynamics. The multiscale coarse-graining methodology has also been employed to increase the simulation speed by a factor of 100 or more, thereby making it possible to study the mesoscopic behavior of ILs by computer simulations. With these simulation techniques, ILs with an amphiphilic cation were found to exhibit a spatial heterogeneity due to the aggregation of their nonpolar alkyl tails. This spatial heterogeneity is a key feature in interpreting many physical phenomena of ILs, such as their heterogeneous self-diffusion and surface layering, as well as their surfactant-like micelles formed in IL/water mixtures. [Abstract]

Lynden-Bell RM, Del Pópolo MG, Youngs TG, Kohanoff J, Hanke CG, Harper JB, Pinilla CC
Simulations of ionic liquids, solutions, and surfaces.
Acc Chem Res. 2007 Nov;40(11):
We have been using atomistic simulation for the last 10 years to study properties of imidazolium-based ionic liquids. Studies of dissolved molecules show the importance of electrostatic interactions in both aromatic and hydrogen-bonding solutes. However, the local structure strongly depends upon ion-ion and solute-solvent interactions. We find interesting local alignments of cations at the gas-liquid and solid-liquid interfaces, which give a potential drop through the surface. If the solid interface is charged, this charge is strongly screened over distances of a few nanometres and this screening decays on a fast time scale. We have studied the sensitivity of the liquid structure to force-field parameters and show that results from ab initio simulations can be used in the development of force fields. [Abstract]

Han X, Armstrong DW
Ionic liquids in separations.
Acc Chem Res. 2007 Nov;40(11):
Ionic liquids are liquids composed completely of ions. In the past two decades, ionic liquids have been widely used as "green solvents" replacing traditional organic solvents for organic synthesis and catalysis. In addition, ionic liquids are playing an increasingly important role in separation science. In this Account, the application of ionic liquids in all areas of separation science including extractions, gas chromatography, and supported liquid membrane processes are highlighted. [Abstract]

Zhou YG
Asymmetric Hydrogenation of Heteroaromatic Compounds.
Acc Chem Res. 2007 Sep 27;
Asymmetric hydrogenation of heteroaromatic compounds has emerged as a promising new route to saturated or partially saturated chiral heterocyclic compounds. In this Account, we outline recent advances in asymmetric hydrogenation of heteroaromatic compounds, including indole, quinoline, isoquinoline, furan, and pyridine derivatives, using chiral organometallic catalysts and organocatalysts. [Abstract]

Coradin T, Livage J
Aqueous silicates in biological sol-gel applications: new perspectives for old precursors.
Acc Chem Res. 2007 Sep;40(9):
Identification of silica sol-gel chemistry with silicon alkoxide hydrolysis and condensation processes is common in modern materials science. However, aqueous silicates exhibit several features indicating that they may be more suitable precursors for specific fields of research and applications related to biology and medicine. In this Account, we illustrate the potentialities of such aqueous precursors for biomimetic studies, bio-hybrid material design, and bioencapsulation routes. We emphasize that the natural relevance, the biocompatibility, and the low ecological impact of silicate chemistry may balance its lack of diversity, flexibility, and processability. [Abstract]

Dunn B, Zink JI
Sol-gel chemistry and materials.
Acc Chem Res. 2007 Sep;40(9): [Abstract]

Prato M, Kostarelos K, Bianco A
Functionalized Carbon Nanotubes in Drug Design and Discovery.
Acc Chem Res. 2007 Sep 15;
The development of functionalized carbon nanotubes as novel components of pharmaceutical agents (diagnostic or therapeutic) offers great potential for new drug design and discovery capabilities that will incorporate such nanotechnologies at an early stage. Conjugated with different therapeutic and diagnostic agents, carbon nanotubes can show improved efficacy. The current available examples include proof-of-principle studies using carbon nanotube-based conjugates with anticancer, antibiotic, and vaccination and gene therapeutic capacity. [Abstract]

Johnson NB, Lennon IC, Moran PH, Ramsden JA
Industrial-Scale Synthesis and Applications of Asymmetric Hydrogenation Catalysts.
Acc Chem Res. 2007 Sep 6;
This Account provides an overview of our activities in the area of asymmetric hydrogenation over the last 12 years. We discuss the manufacture of metal-containing precatalysts and their use in asymmetric hydrogenation processes. Many of the metal complexes have been made on a multikilogram scale for our own use and also provided to our customers. In addition, we review some of the applications that we have developed for our asymmetric hydrogenation catalysts, many of which have been operated on commercial scales. This all underlines that asymmetric hydrogenation is a mature technology that has been adopted for use in the pharmaceutical and fine-chemical industries. [Abstract]

Tomoda H, Doi T
Discovery and Combinatorial Synthesis of Fungal Metabolites Beauveriolides, Novel Antiatherosclerotic Agents.
Acc Chem Res. 2007 Sep 6;
Cyclodepsipeptic beauveriolides were isolated as inhibitors of lipid droplet synthesis using mouse macrophages from the culture broth of fungal Beauveria sp. FO-6979. The structures, including the absolute stereochemistry of beauveriolide III, were elucidated. Beauveriolides specifically inhibited macrophage acyl-CoA:cholesterol acyltransferase activity, resulting in the blockage of cholesteryl ester synthesis and leading to a reduction of lipid droplets in macrophages. Beauveriolides I and III exerted antiatherogenic activity in mouse models without any side effects. Furthermore, a focused library of beauveriolide analogues was prepared by a combinatorial synthesis with solid-phase assembly of linear depsipeptides followed by solution-phase cyclization to obtain more potent inhibitors. [Abstract]

Doctorovich F, Di Salvo F
Performing organic chemistry with inorganic compounds: electrophilic reactivity of selected nitrosyl complexes.
Acc Chem Res. 2007 Oct;40(10):
The inorganic nitrosyl (NO(+)) complexes [Fe(CN) 5NO](2-), [Ru(bpy)2(NO)Cl](2+), and [IrCl 5(NO)](-) are useful reagents for the nitrosation of a variety of organic compounds, ranging from amines to the relatively inert alkenes. Regarding [IrCl 5(NO)](-), its high electrophilicity and inertness define it as a unique reagent and provide a powerful synthetic route for the isolation and stabilization of coordinated nitroso compounds that are unstable in free form, such as S-nitrosothiols and primary nitrosamines. Related to the high electrophilicity of [IrCl 5(NO)](-), an unusual behavior is described for its PPh 4(+) salt in the solid state, showing an electronic distribution represented by Ir(IV)-NO(*) instead of Ir (III)-NO(+) (as for the K(+) and Na(+) salts). [Abstract]

Skucas E, Ngai MY, Komanduri V, Krische MJ
Enantiomerically Enriched Allylic Alcohols and Allylic Amines via C-C Bond-Forming Hydrogenation: Asymmetric Carbonyl and Imine Vinylation.
Acc Chem Res. 2007 Sep 5;
Hydrogenation of alkynes in the presence of carbonyl compounds and imines using cationic rhodium(I) and iridium(I) precatalysts enables the formation of allylic alcohols and allylic amines, respectively. Through the use of hydrogenation catalysts modified by chiral ligands, allylic alcohols and allylic amines may be generated in highly optically enriched forms. Hydrogenative fragment couplings of this type circumvent the use of preformed organometallic reagents and avoid the generation of stoichiometric byproducts. [Abstract]

Ghosh AK, Chapsal BD, Weber IT, Mitsuya H
Design of HIV Protease Inhibitors Targeting Protein Backbone: An Effective Strategy for Combating Drug Resistance.
Acc Chem Res. 2007 Aug 28;
The discovery of HIV protease inhibitors (PIs) followed by their incorporation into highly active antiretroviral therapy (HAART) was a major turning point for the management of HIV/AIDS. However, the rapid emergence of drug resistance has become a major concern. Our structure-based design of HIV-1 PIs that can specifically interact with the enzyme backbone atoms has led to the development of compounds with unprecedented potency and drug-resistance profiles. Particularly notable is the development of a stereochemically defined bis(tetrahydrofuranyl)urethane as the non-peptidic P 2 ligand. Incorporation of this ligand has provided a variety of exceedingly potent HIV-1 PIs with superior activity against multi-PI-resistant variants relative to other FDA-approved PIs. Darunavir, a PI recently approved for the treatment of drug-resistant HIV, directly resulted from this strategy. Our detailed protein-darunavir X-ray crystal structures have clearly demonstrated extensive interactions with the protein backbone in the enzyme active site. This present design concept targeting the protein backbone may serve as a powerful strategy to combat drug resistance. [Abstract]

Recent Articles in Chemical Society Reviews

Imrie CT, Henderson PA
Liquid crystal dimers and higher oligomers: between monomers and polymers.
Chem Soc Rev. 2007 Dec;36(12):2096-124.
The underlying theme of this Critical Review is the relationship between molecular structure and liquid crystalline behaviour in a class of materials referred to as liquid crystal oligomers. For the purposes of this review, a liquid crystal oligomer will be defined as consisting of molecules composed of semi-rigid mesogenic units connected via flexible spacers. Much of the review will be devoted to structure-property relationships in the simplest oligomers, namely dimers, in which just two mesogenic units are connected by a single spacer. Along the way we will see how this molecular architecture has been exploited to address issues in a range of quite different areas and has given rise to potential applications for these materials. On the whole, only compounds in which the mesogenic units are linked essentially in a linear fashion will be considered while structures such as liquid crystal dendrimers and tetrapodes fall outside the scope of this review. The review will be of interest not only to scientists working directly in this area but in particular to those interested in understanding the relationships between structure and properties in polymers, and those designing materials for new applications (231 references). [Abstract]

Hird M
Fluorinated liquid crystals - properties and applications.
Chem Soc Rev. 2007 Dec;36(12):2070-95.
This critical review begins with a brief, but essential, introduction to the special nature of liquid crystal materials, their peculiar properties, and their commercial applications, followed by an introductory insight into the remarkable nature of the fluoro substituent, and its fascinating influence on the properties of organic compounds. However, the main focus of the review is to discuss the enormous amount of exciting research on fluorinated liquid crystals that has been reported. The small size of the fluoro substituent enables its incorporation into all types of liquid crystal, including calamitic, discotic, banana, lyotropic, and polymers, without ruining the liquid crystalline nature of the material. However the fluoro substituent is larger than hydrogen, and hence causes a significant steric effect, which combined with the high polarity, confers many fascinating, and often remarkable, modifications to melting point, mesophase morphology and transition temperatures, and the many other very important physical properties, such as dielectric anisotropy, optical anisotropy, and visco-elastic properties. There are many different positions within a liquid crystal structure where a fluoro substituent can be located, including (i) a terminal position, (ii) within a terminal chain, as a semi-fluorinated or as a perfluorinated chain, or as one fluoro substituent at a chiral centre, (iii) as part of a linking group, and (iv) a lateral position in the core section. Such variety enables the interesting and advantageous tailoring of properties, both for the fundamental purposes of establishing structure-property relationships, and for materials targeted towards commercially-successful liquid crystal display applications. [Abstract]

Seed A
Synthesis of self-organizing mesogenic materials containing a sulfur-based five-membered heterocyclic core.
Chem Soc Rev. 2007 Dec;36(12):2046-69.
The majority of low molar mass calamitic mesogenic systems in the literature contain linear cores based on the 1,4-disubstituted phenyl ring. Heterocyclic cores such as thiophene impart unique physical properties as their slightly bent structure leads to features including a reduced packing ability (generally giving rise to lower melting points than their phenyl counterparts), a medium to strong lateral dipole, high anisotropy of the polarizability, low viscosity etc. This critical review describes the most recent synthetic methodology that has been used to prepare thiophene, 1,3-thiazole, and 1,3,4-thiadiazole-based mesogenic materials. (154 references). [Abstract]

Lemieux RP
Molecular recognition in chiral smectic liquid crystals: The effect of core-core interactions and chirality transfer on polar order.
Chem Soc Rev. 2007 Dec;36(12):2033-45.
This critical review focuses on the induction of polar order in smectic liquid crystal phases by dopants with axially chiral cores, and should be of interest to all practitioners of supramolecular chemistry. The variations in polarization power of these dopants with the core structure of the liquid crystal hosts is a manifestation of molecular recognition that reflects the nanosegregation of aromatic cores from paraffinic side-chains in smectic phases, and the collective effect of core-core interactions that enable the propagation of chiral perturbations. (76 references.). [Abstract]

Goodby JW, Görtz V, Cowling SJ, Mackenzie G, Martin P, Plusquellec D, Benvegnu T, Boullanger P, Lafont D, Queneau Y, Chambert S, Fitremann J
Thermotropic liquid crystalline glycolipids.
Chem Soc Rev. 2007 Dec;36(12):1971-2032.
Are the liquid crystalline properties of the materials of living systems important in biological structures, functions, diseases and treatments? There is a growing consciousness that the observed lyotropic, and often thermotropic liquid crystallinity, of many biological materials that possess key biological functionality might be more than curious coincidence. Rather, as the survival of living systems depends on the flexibility and reformability of structures, it seems more likely that it is the combination of softness and structure of the liquid-crystalline state that determines the functionality of biological materials. The richest sources of liquid crystals derived from living systems are found in cell membranes, of these glycolipids are a particularly important class of components. In this critical review, we will examine the relationship between chemical structure and the self-assembling and self-organising properties of glycolipids that ultimately lead to mesophase formation. [Abstract]

Tschierske C
Liquid crystal engineering - new complex mesophase structures and their relations to polymer morphologies, nanoscale patterning and crystal engineering.
Chem Soc Rev. 2007 Dec;36(12):1930-70.
This critical review focuses on recent progress in the field of T-shaped ternary amphiphiles. These molecules can self-assemble into a series of new liquid crystalline (LC) phases with polygonal cylinder structures, new lamellar phases and LC phases combining columns and layers. These structures are analyzed on the basis of symmetry, net topology and tiling pattern (Laves and Archimedean tilings) and discussed in relation to morphologies of multiblock copolymers, self organized DNA super-lattices, metal-organic frameworks, crystal-engineering and self-assembled periodic superstructures on surfaces (210 references). [Abstract]

Sergeyev S, Pisula W, Geerts YH
Discotic liquid crystals: a new generation of organic semiconductors.
Chem Soc Rev. 2007 Dec;36(12):1902-29.
Discotic (disc-like) molecules typically comprising a rigid aromatic core and flexible peripheral chains have been attracting growing interest because of their fundamental importance as model systems for the study of charge and energy transport and due to the possibilities of their application in organic electronic devices. This critical review covers various aspects of recent research on discotic liquid crystals, in particular, molecular design concepts, supramolecular structure, processing into ordered thin films and fabrication of electronic devices. The chemical structure of the conjugated core of discotic molecules governs, to a large extent, their intramolecular electronic properties. Variation of the peripheral flexible chains and of the aromatic core is decisive for the tuning of self-assembly in solution and in bulk. Supramolecular organization of discotic molecules can be effectively controlled by the choice of the processing methods. In particular, approaches to obtain suitable macroscopic orientations of columnar superstructures on surfaces, that is, planar uniaxial or homeotropic alignment, are discussed together with appropriate processing techniques. Finally, an overview of charge transport in discotic materials and their application in optoelectronic devices is given (234 references). [Abstract]

Marcos M, Martín-Rapún R, Omenat A, Serrano JL
Highly congested liquid crystal structures: dendrimers, dendrons, dendronized and hyperbranched polymers.
Chem Soc Rev. 2007 Dec;36(12):1889-901.
In this tutorial review we describe some studies concerning liquid crystal dendritic polymers. We have chosen to present several representative examples that illustrate the diverse kinds of LC dendritic structures, namely: dendrimers, dendrons, dendronized polymers and hyperbranched polymers. We review their synthesis, mesogenic properties and the way that they are arranged to form supramolecular liquid crystal assemblies. [Abstract]

Wilson MR
Molecular simulation of liquid crystals: progress towards a better understanding of bulk structure and the prediction of material properties.
Chem Soc Rev. 2007 Dec;36(12):1881-8.
This tutorial review covers recent progress in the field of computer simulation of liquid crystals. The development of the main "molecular-based" models for liquid crystals is described. These include lattice models, coarse-grained single site models based on hard and soft interaction potentials, atomistic models and multi-site coarse-grained models. A brief historical review is followed by an assessment of some of the new areas in this field, with an emphasis on understanding of molecular structure in liquid crystal phases and the prediction of bulk material properties. The article also looks to link the field of liquid crystal simulation with important developments in areas such as polymer simulation, lyotropic liquid crystals and model membranes. [Abstract]

Matharu AS, Jeeva S, Ramanujam PS
Liquid crystals for holographic optical data storage.
Chem Soc Rev. 2007 Dec;36(12):1868-80.
A tutorial review is presented to inform and inspire the reader to develop and integrate strong scientific links between liquid crystals and holographic data storage, from a materials scientist's viewpoint. The principle of holographic data storage as a means of providing a solution to the information storage demands of the 21st century is detailed. Holography is a small subset of the much larger field of optical data storage and similarly, the diversity of materials used for optical data storage is enormous. The theory of polarisation holography which produces holograms of constant intensity, is discussed.Polymeric liquid crystals play an important role in the development of materials for holographic storage and photoresponsive materials based on azobenzene are targeted for discussion due to their ease of photo-reversion between trans- and cis-states. Although the final polymer may not be liquid crystalline, irradiation can induce ordered domains. The mesogens act in a co-operative manner, enhancing refractive indices and birefringences. Surface relief gratings are discussed as a consequence of holographic storage.Cholesteric polymers comprising azobenzene are briefly highlighted. Irradiation causing cis-trans-isomerisation can be used to control helix pitch. A brief mention of liquid crystals is also made since these materials may be of future interest since they are optically transparent and amenable to photo-induced anisotropy. [Abstract]

Kato T, Hirai Y, Nakaso S, Moriyama M
Liquid-crystalline physical gels.
Chem Soc Rev. 2007 Dec;36(12):1857-67.
Liquid-crystalline (LC) physical gels are a new class of dynamically functional materials consisting of liquid crystals and fibrous aggregates of molecules that are called "gelators". Liquid-crystalline physical gels, which are macroscopically soft solids, exhibit induced or enhanced electro-optical, photochemical, electronic properties due to the combination of two components that form phase-separated structures. In this tutorial review, we describe the materials design and structure-property relationships of the LC physical gels. The introduction of self-assembled fibers into nematic liquid crystals leads to faster responses in twisted nematic (TN) mode and high contrast switching in light scattering mode. Furthermore, the LC physical gels can be exploited as a new type of materials for electro-optical memory. This function is achieved by the control of reversible aggregation processes of gelators under electric fields in nematic liquid crystals. Electronic properties such as hole mobilities are improved by the introduction of fibrous aggregates into triphenylene-based columnar liquid crystals. The incorporation of photochromic azobenzenes or electroactive tetrathiafulvalenes into the chemical structures of gelators leads to the preparation of ordered functional materials. [Abstract]

Goodby JW
Editorial - liquid crystals.
Chem Soc Rev. 2007 Dec;36(12):1855-6. [Abstract]

Angell YL, Burgess K
Peptidomimetics via copper-catalyzed azide-alkyne cycloadditions.
Chem Soc Rev. 2007 Oct;36(10):1674-89.
This critical review concerns the impact of copper-mediated alkyne-azide cycloadditions on peptidomimetic studies. It discusses how this reaction has been used to insert triazoles into peptide chains, to link peptides to other functionalities (e.g. carbohydrates, polymers, and labels), and as a basis for evolution of less peptidic compounds as pharmaceutical leads. It will be of interest to those studying this click reaction, peptidomimetic secondary structure and function, and to medicinal chemists. [Abstract]

Bowker M
Catalysis resolved using scanning tunnelling microscopy.
Chem Soc Rev. 2007 Oct;36(10):1656-73.
The technique of scanning tunnelling microscopy has revolutionised our understanding of surface chemistry, due to its ability to image at the atomic and molecular scale, the very realm at which chemistry operates. This critical review focuses on its contribution to the resolution of various problems in heterogeneous catalysis, including surface structure, surface intermediates, active sites and spillover. In the article a number of images of surfaces are shown, many at atomic resolution, and the insights which these give into surface reactivity are invaluable. The article should be of interest to catalytic chemists, surface and materials scientists and those involved with nanotechnology/nanoscience. (129 references.)The graphical abstract shows the reaction between gas phase methanol and oxygen islands on Cu(110), courtesy of Philip Davies of Cardiff University. The added-row island is shown as silver-coloured spheres (copper) and red (oxygen) on the copper surface. Methanol preferentially reacts with the terminal oxygen atoms in the island forming adsorbed methoxy and OH groups. Only the terminal oxygen atoms in the island are active sites for the reaction. [Abstract]

Grochala W
Atypical compounds of gases, which have been called 'noble'.
Chem Soc Rev. 2007 Oct;36(10):1632-55.
In this critical review I describe fascinating experimental and theoretical advances in 'noble gas' chemistry during the last twenty years, and have taken a somewhat unexpected course since 2000. I also highlight perspectives for further development in this field, including the prospective synthesis of compounds containing as yet unknown Xe-element and element-Xe-element bridging bonds, peroxide species containing Xe, adducts of XeF(2) with various metal fluorides, Xe-element alloys, and novel pressure-stabilized covalently bound and host-guest compounds of Xe. A substantial part of the essay is devoted to the-as yet experimentally unexplored-behaviour of the compounds of Xe under high pressure. The blend of science, history, and theoretical predictions, will be valued by inorganic and organic chemists, materials scientists, and the community of theoretical and experimental high-pressure physicists and chemists (151 references). [Abstract]

Ritch JS, Chivers T, Afzaal M, O'Brien P
The single molecular precursor approach to metal telluride thin films: imino-bis(diisopropylphosphine tellurides) as examples.
Chem Soc Rev. 2007 Oct;36(10):1622-31.
Interest in metal telluride thin films as components in electronic devices has grown recently. This tutorial review describes the use of single-source precursors for the preparation of metal telluride materials by aerosol-assisted chemical vapour deposition (AACVD) and acquaints the reader with the basic techniques of materials characterization. The challenges in the design and synthesis of suitable precursors are discussed, focusing on metal complexes of the recently-developed imino-bis(diisopropylphosphine telluride) ligand. The generation of thin films and nanoplates of CdTe, Sb(2)Te(3) and In(2)Te(3) from these precursors are used as illustrative examples. [Abstract]

Aucouturier M, Darque-Ceretti E
The surface of cultural heritage artefacts: physicochemical investigations for their knowledge and their conservation.
Chem Soc Rev. 2007 Oct;36(10):1605-21.
This tutorial review intends to show, through demonstrative examples chosen from the recent literature, how surface characterisation conducted by modern investigation methods leads to very rich information on a cultural heritage artefact's history, fabrication techniques and conservation state. Application of surface science to conservation science is of great help for the definition of a conservation and restoration policy for museum and archaeological objects. A brief description of the investigation methods is given, together with relevant references for more detailed information. [Abstract]

Rosillo M, Domínguez G, Pérez-Castells J
Chromium arene complexes in organic synthesis.
Chem Soc Rev. 2007 Oct;36(10):1589-604.
The complexation of an arene to a chromium tricarbonyl unit changes its chemical behavior, giving rise to unprecedented transformations. The electron-withdrawing effect of the unit allows efficient nucleophilic attack (S(N)Ar and dearomatization reactions), stabilizes negative charges in benzylic positions and activates C(Ar)-halogen bonds for cross-coupling reactions. In addition, the Cr(CO)(3) moiety exerts great facial control so it can be used as an auxiliary that can easily be removed. The 1,2- and 1,3-unsymmetrically disubstituted complexes are planar chiral and there are various ways to prepare them in enantiomerically pure form. Planar chiral chromium complexes are becoming useful intermediates and ligands for asymmetric catalysis. This mature field of organometallic chemistry has given rise to several synthetic applications of chromium arene complexes in the synthesis of natural products. This chemistry is overviewed in this tutorial review, giving special attention to the most recent and outstanding contributions in the area. [Abstract]

Basavaiah D, Venkateswara Rao K, Jannapu Reddy R
The Baylis-Hillman reaction: a novel source of attraction, opportunities, and challenges in synthetic chemistry.
Chem Soc Rev. 2007 Oct;36(10):1581-8.
The Baylis-Hillman reaction is a successful, useful, and atom-economical carbon-carbon bond forming reaction, which has grown from an obscure level to the level of high synthetic popularity due to its operational simplicity and also due to the enormous applications of the Baylis-Hillman adducts in organic synthesis. In this tutorial review, we briefly describe the way this reaction has grown to its present heights and the opportunities, attractions, and challenges the reaction offers with respect to its asymmetric and intramolecular versions, and mechanistic aspects. [Abstract]

Williams CK
Synthesis of functionalized biodegradable polyesters.
Chem Soc Rev. 2007 Oct;36(10):1573-80.
This tutorial review summarizes recent developments in the syntheses of functionalized aliphatic polyesters. These polymers are attracting attention as sustainable alternatives to petrochemicals and for applications in medicine. Two main syntheses are described: step polymerization using mild chemo/enzymatic catalysis and ring opening polymerization, which is usually initiated by metal complexes. The methods are compared and their utility illustrated with reference to interesting new materials. [Abstract]

Satoh T
Recent advances in the chemistry of magnesium carbenoids.
Chem Soc Rev. 2007 Oct;36(10):1561-72.
This tutorial review deals with recent advances in the chemistry and synthetic use of magnesium carbenoids. The reactivity of traditional carbenoids (alpha-haloalkyllithium species) was successfully reduced by using magnesium as the metal instead of lithium. Properties of these relatively stable carbenoids, magnesium carbenoids, were widely investigated and it was found that the magnesium carbenoids have very interesting reactivity toward several nucleophiles. The magnesium carbenoids, magnesium cyclopropylidenes, magnesium alkylidene carbenoids, and magnesium beta-oxido carbenoids are generated from alpha-chloroalkyl (or alpha-chloroalkenyl) aryl sulfoxides with a Grignard reagent at low temperature by sulfoxide-magnesium exchange reaction. The stability of the generated magnesium carbenoids and several new reactions based on the electrophilicity of the magnesium carbenoids, including 1,3-CH insertion, are reviewed. Magnesium carbenoids open up the new world of the chemistry of carbenoids. [Abstract]

Liu S, Han YF, Jin GX
Formation of direct metal-metal bonds from 16-electron "pseudo-aromatic" half-sandwich complexes Cp''M[E2C2(B10H10)].
Chem Soc Rev. 2007 Oct;36(10):1543-60.
Continuous study on preparation of multimetallic clusters is stimulated by their rich coordination chemistry and promising applications in a variety of interesting fields. Although numerous efforts have been devoted to this field, the rational design of homo- and hetero-multimetallic compounds with direct metal-metal bonding supported by 1,2-dicarba-closo-dodecarborane-1,2-dichalcogenolates will still be an important step forward. This tutorial review focuses on the synthetic approach via redox reactions between the pseudo-aromatic half-sandwich oraganometallic carborane precursors and low-valent transition metal reagents. The tailoring of reaction conditions and the structural information from the resulting products are discussed extensively. [Abstract]

Spivey JJ, Egbebi A
Heterogeneous catalytic synthesis of ethanol from biomass-derived syngas.
Chem Soc Rev. 2007 Sep;36(9):1514-28.
The selective catalytic conversion of biomass-derived syngas into ethanol is thermodynamically feasible at temperatures below roughly 350 degrees C at 30 bar. However, if methane is allowed as a reaction product, the conversion to ethanol (or other oxygenates) is extremely limited. Experimental results show that high selectivities to ethanol are only achieved at very low conversions, typically less than 10%. The most promising catalysts for the synthesis of ethanol are based on Rh, though some other formulations (such as modified methanol synthesis catalysts) show promise. [Abstract]

Donnio B, Buathong S, Bury I, Guillon D
Liquid crystalline dendrimers.
Chem Soc Rev. 2007 Sep;36(9):1495-513.
In recent years, there has been an increasing interest in the field of liquid crystalline dendrimers. Such a fast development is, among other things, driven by the multiple possibilities offered by combining the mesomorphic properties of single mesogenic subunits with the supermolecular and versatile architectures of dendrimers to yield a new class of highly functional materials. The induction and the control of the mesomorphic properties (phase type and stability) in dendrimers can be achieved by a dedicated molecular design which depends on the chemical nature and structure of both the functional groups and the dendritic matrix. In particular, the intrinsic connectivity of the dendrimer such as the multivalency of the focal core and the multiplicity of the branches, both controlling the geometrical rate of growth, or the dendritic generation, plays a crucial role and influences at various stages the subtle relationships between the supermolecular structure and the mesophase structure and stability. In this critical review article, an account of the various types of dendritic systems that form liquid-crystalline mesophases along with a description of the self-organization of representative case-study supermolecules into liquid crystalline mesophases will be discussed. Some basics of thermotropic liquid crystals and dendrimers will be given in the introduction. Then, in the following sections, selected examples including side-chain, main-chain, fullerodendrimers, shape-persistent dendrimers, supramolecular dendromesogens and metallodendrimers, as representative families of LC dendrimers, will be described. In the conclusion some further developments will be highlighted. This review will not cover liquid crystalline hyperbranched and dendronized polymers that might be considered as being somehow less structurally "perfect". [Abstract]

Midgley PA, Ward EP, Hungría AB, Thomas JM
Nanotomography in the chemical, biological and materials sciences.
Chem Soc Rev. 2007 Sep;36(9):1477-94.
Nanotomography is a technique of growing importance in the investigation of the shape, size, distribution and elemental composition of a wide variety of materials that are of central interest to investigators in the physical and biological sciences. Nanospatial factors often hold the key to a deeper understanding of the properties of matter at the nanoscale level. With recent advances in tomography, it is possible to achieve experimental resolution in the nanometre range, and to determine with elemental specificity the three-dimensional distribution of materials. This critical review deals principally with electron tomography, but it also outlines the power and future potential of transmission X-ray tomography, and alludes to other related techniques. [Abstract]

Cooke MW, Hanan GS
Luminescent polynuclear assemblies.
Chem Soc Rev. 2007 Sep;36(9):1466-76.
This tutorial review consists of five main sections. The first gives a general introduction and then a discussion about the need for luminescent assemblies. The next four sections present the various assemblies based on the metal ions used to assemble the final structures. Each of these sections gives a brief overview of the design principles, synthesis, and ground and excited-state properties of the ligands and complexes in question. The review concludes with some suggestions for future avenues of research. [Abstract]

Althues H, Henle J, Kaskel S
Functional inorganic nanofillers for transparent polymers.
Chem Soc Rev. 2007 Sep;36(9):1454-65.
The integration of inorganic nanoparticles into polymers has been used for the functionalization of polymer materials with great success. Whereas in traditional polymer composites, micron sized particles or agglomerates typically cause significant light scattering hampering optical applications, in nanocomposites the particle dimensions are small enough for the production of highly transparent composites. A challenge for the generation of such materials is to develop an integrated synthesis strategy adapting particle generation, surface modification and integration inside the polymer. Surface grafting using polymerizable surfactants or capping agents allows for linking the particles to the polymer. Novel techniques such as in situ polymerization and in situ particle processing are beneficial to avoid aggregation of inorganic particles inside the polymer matrix. The functions associated with inorganic fillers are widespread. Layered silicates and related materials are nowadays commercially available for improving mechanical and barrier properties in packaging. With the availability of highly transparent materials, the focus has shifted towards optical functions such as luminescence and UV-protection in transparent polymers. IR-active fillers are used in laser-holography for transparent poly(methyl methacrylate) (PMMA) nanocomposites. Refractive index modulation and ultrahigh refractive index films were developed based on inorganic materials such as PbS. The integration of magnetic nanoparticles has a great potential for applications such as electromagnetic interference shielding and magneto-optical storage.This tutorial review will summarize functions associated with the integration of inorganic nanofillers in polymers with a focus on optical properties. [Abstract]

Pitt MA, Johnson DW
Main group supramolecular chemistry.
Chem Soc Rev. 2007 Sep;36(9):1441-53.
Metal directed self-assembly has yielded a wide array of two- and three-dimensional structures with fascinating new chemical properties. These structures have typically been prepared utilizing transition metals as directing units, owing to the well-defined coordination preferences these metals exhibit. An area of growing research interest involves the preparation of structures containing main group elements as directing units. This tutorial review surveys the wide range of structure types available through this approach, specifically covering unique structure types accessible from the unusual coordination geometries often exhibited by the elements in Groups 12-17 of the periodic table. This review should be of interest to supramolecular and main group chemists, and researchers in the fields of crystal engineering, host-guest chemistry, and molecular recognition. [Abstract]

Fisk JS, Mosey RA, Tepe JJ
The diverse chemistry of oxazol-5-(4H)-ones.
Chem Soc Rev. 2007 Sep;36(9):1432-40.
The assembly of structurally diverse scaffolds via substrate controlled diversity oriented synthesis (DOS) has proven to be an effective tool in the discovery of novel biologically important compounds. This tutorial review aims to summarize some of the more recent applications of oxazolones as a general template for the stereoselective syntheses of amino acids and heterocyclic scaffolds. A brief introduction covers a short history, nomenclature and general reactivity of oxazolones. The main body of this tutorial review highlights several applications of oxazolones as starting blocks for the diverse and stereoselective synthesis of amino acids, oxazoles, beta-lactams, pyrroles, imidazolines, pyrrolines, and imidazoles. [Abstract]

Chi Y, Chou PT
Contemporary progresses on neutral, highly emissive Os(II) and Ru(II) complexes.
Chem Soc Rev. 2007 Sep;36(9):1421-31.
This tutorial review highlights recent and current advances in Os(II) and Ru(II) based luminescent complexes in view of their potential in providing models for photophysical properties and in serving as active materials in optoelectronic devices. It starts with a discussion of the fundamentals of pyridyl azolate chromophores and presents several prototypical designs that allow subtle variation of their basic properties. The third section of this article concerns the preparation of Os(II) and Ru(II) metal complexes and discusses the key factors that control their phosphorescence efficiencies and peak wavelengths. Attention is focused on the properties of their lowest lying excited states. In the last section, we present a series of related Os(II) complexes possessing pyridyl azolate, cyclometalated benzo[h]quinoline, beta-diketonates and quinolinates to demonstrate the power of fundamental basis to chemistry and theoretical approaches in rationalizing the corresponding photophysical behavior and hence to discuss the implications regarding their possible routes for future research. [Abstract]

Recent Articles in Angewandte Chemie International Edition

Avenier F, Gouré E, Dubourdeaux P, Sénèque O, Oddou JL, Pécaut J, Chardon-Noblat S, Deronzier A, Latour JM
Multiple Aromatic Amination Mediated by a Diiron Complex.
Angew Chem Int Ed Engl. 2007 Dec 10; . [Abstract]

Guin J, Fröhlich R, Studer A
Thiol-Catalyzed Stereoselective Transfer Hydroamination of Olefins with N-Aminated Dihydropyridines.
Angew Chem Int Ed Engl. 2007 Dec 10; [Abstract]

Voss CV, Gruber CC, Kroutil W
Deracemization of Secondary Alcohols through a Concurrent Tandem Biocatalytic Oxidation and Reduction.
Angew Chem Int Ed Engl. 2007 Dec 10; [Abstract]

Soderholm L, Almond PM, Skanthakumar S, Wilson RE, Burns PC
The Structure of the Plutonium Oxide Nanocluster [Pu(38)O(56)Cl(54)(H(2)O)(8)](14-).
Angew Chem Int Ed Engl. 2007 Dec 10; [Abstract]

Zhu SS, Staats H, Brandhorst K, Grunenberg J, Gruppi F, Dalcanale E, Lützen A, Rissanen K, Schalley CA
Anion Binding to Resorcinarene-Based Cavitands: The Importance of C--HAnion Interactions.
Angew Chem Int Ed Engl. 2007 Dec 11; [Abstract]

Walther A, Hoffmann M, Müller AH
Emulsion Polymerization Using Janus Particles as Stabilizers.
Angew Chem Int Ed Engl. 2007 Dec 11; [Abstract]

Morris RE
Ionic Liquids and Microwaves-Making Zeolites for Emerging Applications.
Angew Chem Int Ed Engl. 2007 Dec 11; [Abstract]

Miller JJ, Sigman MS
Quantitatively Correlating the Effect of Ligand-Substituent Size in Asymmetric Catalysis Using Linear Free Energy Relationships.
Angew Chem Int Ed Engl. 2007 Dec 11; [Abstract]

Wöll D, Uji-I H, Schnitzler T, Hotta JI, Dedecker P, Herrmann A, De Schryver FC, Müllen K, Hofkens J
Radical Polymerization Tracked by Single Molecule Spectroscopy.
Angew Chem Int Ed Engl. 2007 Dec 11; [Abstract]

Shin HS, Yoon SM, Tang Q, Chon B, Joo T, Choi HC
Highly Selective Synthesis of C(60) Disks on Graphite Substrate by a Vapor-Solid Process.
Angew Chem Int Ed Engl. 2007 Dec 11; [Abstract]

Guo J, Wang J, Anderson JC, Schultz PG
Addition of an alpha-Hydroxy Acid to the Genetic Code of Bacteria.
Angew Chem Int Ed Engl. 2007 Dec 11; [Abstract]

Yu XQ, Yoshimura F, Ito F, Sasaki M, Hirai A, Tanino K, Miyashita M
Palladium-Catalyzed Stereospecific Substitution of alpha,beta-Unsaturated gamma,delta-Epoxy Esters by Alcohols with Double Inversion of Configuration: Synthesis of 4-Alkoxy-5-hydroxy-2-pentenoates.
Angew Chem Int Ed Engl. 2007 Dec 11; [Abstract]

Sussman VJ, Ellis JE
From Storable Sources of Atomic Nb(-) and Ta(-) Ions to Isolable Anionic Tris(1,3-butadiene)metal Complexes: [M(eta(4)-C(4)H(6))(3)](-), M=Nb, Ta.
Angew Chem Int Ed Engl. 2007 Dec 11; [Abstract]

Foley NA, Gunnoe TB, Cundari TR, Boyle PD, Petersen JL
Activation of sp(3) Carbon-Hydrogen Bonds by a Ruthenium(II) Complex and Subsequent Metal-Mediated C--C and C--N Bond Formation.
Angew Chem Int Ed Engl. 2007 Dec 7; [Abstract]

Clegg W, Dale SH, Hevia E, Hogg LM, Honeyman GW, Mulvey RE, O'Hara CT, Russo L
Structurally Defined Reactions of Sodium TMP-Zincate with Nitrile Compounds: Synthesis of a Salt-Like Sodium Sodiumdizincate and Other Unexpected Ion-Pair Products.
Angew Chem Int Ed Engl. 2007 Dec 7; [Abstract]

Xiao CX, Cai ZP, Wang T, Kou Y, Yan N
Aqueous-Phase Fischer-Tropsch Synthesis with a Ruthenium Nanocluster Catalyst.
Angew Chem Int Ed Engl. 2007 Dec 7; [Abstract]

Xu B, Hammond GB
Thermodynamically Favored Aldol Reaction of Propargyl or Allenyl Esters: Regioselective Synthesis of Carbinol Allenoates.
Angew Chem Int Ed Engl. 2007 Dec 6; [Abstract]

Chase PA, Welch GC, Jurca T, Stephan DW
Metal-Free Catalytic Hydrogenation.
Angew Chem Int Ed Engl. 2007 Dec 10;46(48): [Abstract]

Shi L, Lundberg D, Musaev DG, Menger FM
[12]Annulene Gemini Surfactants: Structure and Self-Assembly.
Angew Chem Int Ed Engl. 2007 Dec 10;46(48): [Abstract]

Kögl M, Brecker L, Warrass R, Mulzer J
Inside cover: total synthesis and configurational assignment of pasteurestin a and B (Angew. Chem. Int. Ed. 48/2007).
Angew Chem Int Ed Engl. 2007;46(48): [Abstract]

Vaupel E
Interconnections and independence: Heinrich Wieland (1877-1957) and his era.
Angew Chem Int Ed Engl. 2007;46(48): [Abstract]

Bioorganic Chemistry: Awards to C. Bertozzi, M. Movassaghi, and K. A. Scheidt.
Angew Chem Int Ed Engl. 2007 Dec 10;46(48): [Abstract]

Spotlights on our sister journals: Angew. Chem. Int. Ed. 48/2007.
Angew Chem Int Ed Engl. 2007 Dec 10;46(48): [Abstract]

Diéguez-Vázquez A, Tzschucke CC, Lam WY, Ley SV
PtCl(4)-Catalyzed Domino Synthesis of Fused Bicyclic Acetals.
Angew Chem Int Ed Engl. 2007 Dec 5; [Abstract]

Preview: Angew. Chem. Int. Ed. 1/2008.
Angew Chem Int Ed Engl. 2007 Dec 10;46(48): [Abstract]

Index: Angew. Chem. Int. Ed. 2007.
Angew Chem Int Ed Engl. 2007 Dec 10;46(48): [Abstract]

Koh K, Wong-Foy AG, Matzger AJ
A Crystalline Mesoporous Coordination Copolymer with High Microporosity.
Angew Chem Int Ed Engl. 2007 Dec 4; [Abstract]

Wang F, Xue X, Liu X
Multicolor Tuning of (Ln, P)-Doped YVO(4) Nanoparticles by Single-Wavelength Excitation.
Angew Chem Int Ed Engl. 2007 Dec 4; [Abstract]

Marciniec B, Szubert K, Potrzebowski MJ, Kownacki I, Le Szczak K
Synthesis, Characterization, and Catalytic Activity of a Well-Defined Rhodium Siloxide Complex Immobilized on Silica.
Angew Chem Int Ed Engl. 2007 Dec 4; [Abstract]

Aelvoet K, Batsanov AS, Blatch AJ, Grosjean C, Patrick LG, Smethurst CA, Whiting A
A Catalytic Aldol Reaction and Condensation through In Situ Boron "Ate" Complex Enolate Generation in Water.
Angew Chem Int Ed Engl. 2007 Dec 4; [Abstract]

Recent Articles in Journal of the American Chemical Society

Thompson DB, Brook MA
Rapid Assembly of Complex 3D Siloxane Architectures.
J Am Chem Soc. 2007 Dec 11; .
Few routes to well-defined 3D silicone structures exist because of their susceptibility to depolymerization/metathesis in the presence of acids or bases. The Lewis acid B(C6F5)3 can be employed to condense hydrosilanes with alkoxysilanes, producing siloxanes and alkanes (R3SiH+R'OSiR' '3 --> R3SiOSiR' '3 + R'H). We demonstrate that balancing the steric demands at both the hydrosilane and alkoxysilanes, and the careful control of reaction conditions, permits clean condensation reactions to occur in the absence of competing metathesis processes. The resulting linear or highly branched siloxane compounds can be rapidly and easily assembled into explicit, complex 3D silicone structures in high yield. [Abstract]

Gong XQ, Selloni A, Dulub O, Jacobson P, Diebold U
Small Au and Pt Clusters at the Anatase TiO(2)(101) Surface: Behavior at Terraces, Steps, and Surface Oxygen Vacancies.
J Am Chem Soc. 2007 Dec 11;
The adsorption properties of Au and Pt metal nanoclusters on TiO2 anatase (101) were calculated using density functional theory. Structures and energetics of adsorbed Au and Pt monomers, dimers, and trimers at clean anatase TiO2(101) terraces and two major step edges, as well as O-vacancies, were systematically determined. The theoretical predictions were tested by vapor-depositing small coverages of Au and Pt on anatase (101) and investigating the resulting clusters with Scanning Tunneling Microscopy. On the clean surface, Au shows a strong tendency to form large clusters that nucleate on step edges. A preference for adsorption at type D-(112) steps is observed, which is probably a result of kinetic effects. For Pt, clusters as small as monomers are observed on the terraces, in agreement with the predicted large binding energy of 2.2 eV. Step edges play a less important role than in the case of Au. Oxygen vacancies, produced by electron irradiation, dramatically influence the growth of Au, while the nucleation behavior of Pt was found to be less affected. [Abstract]

Desnous C, Babu BR, Moriou C, Mayo JU, Favre A, Wengel J, Clivio P
The Sugar Conformation Governs (6-4) Photoproduct Formation at the Dinucleotide Level.
J Am Chem Soc. 2007 Dec 11;
The LNA dinucleotide mimic of TpT whose two-sugar puckers are locked in the C3'-endo conformation selectively produces the corresponding cyclobutane pyrimidine dimer under 254 nm irradiation. In the natural series (TpT) the sugar puckers are in a major C2'-endo sugar conformation and the (6-4) photoproduct is also produced. Consequently, this study demonstrates that the C2'-endo conformation of the sugar pucker is necessary for (6-4) photoproduct formation. [Abstract]

Scott SL
Spectroscopy in Catalysis: An Introduction, Third, Completely Revised and Enlarged Edition By J. W. Niemantsverdriet (Eindhoven University of Technology, The Netherlands). Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim. 2007. xviii + 326 pp. $135. ISBN 978-3-527-31651-9.
J Am Chem Soc. 2007 Dec 11; [Abstract]

Billups WE
Fullerenes: Principles and Applications Edited by Fernando Langa (University of Castilla La Mancha, Toledo, Spain) and Jean-François Nierengarten (CNRS, Toulouse, France). Royal Society of Chemistry: Cambridge. 2007. xii + 398 pp. $169. ISBN 978-0-85404-551-8.
J Am Chem Soc. 2007 Dec 11; [Abstract]

Detellier C
Analytical Methods in Supramolecular Chemistry Edited by Christoph A. Schalley (Universität Berlin). Wiley-VCH Verlag GmbH & Co. KgaA: Weinheim. 2007. xvi + 484 pp. $190.00. ISBN 978-3-527-31505-5.
J Am Chem Soc. 2007 Dec 11; [Abstract]

Murata H, Miyazaki Y, Inaba A, Paduan-Filho A, Bindilatti V, Jr NF, Delen Z, Lahti PM
2-(4,5,6,7-Tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1- H-imidazole-3-oxide-1-oxyl, A Hydrogen-Bonded Organic Quasi-1D Ferromagnet.
J Am Chem Soc. 2007 Dec 11;
The title radical (F4BImNN) is a stable nitronylnitroxide that forms hydrogen-bonded NH...ON chains in the solid state. The chains assemble the F4BImNN molecules to form stacked contacts between the radical groups, in a geometry that is expected to exhibit ferromagnetic (FM) exchange based on spin polarization (SP) models. The experimental magnetic susceptibility of F4BImNN confirms the expectation, showing 1-D Heisenberg chain FM exchange behavior over 1.8-300 K with an intrachain exchange constant of Jchain/k = +22 K. At lower temperatures, ac magnetic susceptibility and variable field heat capacity measurements show that F4BImNN acts as a quasi-1-D ferromagnet. The dominant ferromagnetic exchange interaction is attributable to overlap between spin orbitals of molecules within the hydrogen-bonded chains, consistent with the SP model expectations. The chains appear to be antiferromagnetically exchange coupled, giving cusps in the ac susceptibility and zero field heat capacity at lower temperatures. The results indicate that the sample orders magnetically at about 0.7 K. The magnetic heat capacity ordering cusp shifts to lower temperatures as external magnetic field increases, consistent with forming a bulk antiferromagnetic phase below a Néel temperature of TN(0) = 0.72 K, with a critical field of Hc approximately 1800 Oe. The interchain exchange is estimated to be zJ/k congruent with (-)0.1 K. [Abstract]

Ko?aski M, Lee HM, Pak C, Kim KS
Charge-Transfer-to-Solvent-Driven Dissolution Dynamics of I(-)(H(2)O)(2-5) upon Excitation: Excited-State ab Initio Molecular Dynamics Simulations.
J Am Chem Soc. 2007 Dec 11;
In contrast to the extensive theoretical investigation of the solvation phenomena, the dissolution phenomena have hardly been investigated theoretically. Upon the excitation of hydrated halides, which are important substances in atmospheric chemistry, an excess electron transfers from the anionic precursor (halide anion) to the solvent and is stabilized by the water cluster. This results in the dissociation of hydrated halides into halide radicals and electron-water clusters. Here we demonstrate the charge-transfer-to-solvent (CTTS)-driven femtosecond-scale dissolution dynamics for I-(H2O)n=2-5 clusters using excited state (ES) ab initio molecular dynamics (AIMD) simulations employing the complete-active-space self-consistent-field (CASSCF) method. This study shows that after the iodine radical is released from I-(H2O)n=2-5, a simple population decay is observed for small clusters (2 </= n </= 4), while rearrangement to stabilize the excess electron to an entropy-driven structure is seen for n = 5. These results are in excellent agreement with the previous ultrafast pump-probe experiments. For the first approximately 30 fs of the simulations, the iodine plays an important role in rearranging the hydrogen orientations (although the water network hardly changes), which increases the kinetic energy of the cluster. However, approximately 50 fs after the excitation, the role of the iodine radical is no longer significant. After approximately 100 fs, the iodine radical is released, and the solvent molecules rearrange themselves to a lower free energy structure. The CTTS-driven dissolution dynamics could be useful in designing the receptors which are able to bind and release ions in host-guest chemistry. [Abstract]

Larivée A, Mousseau JJ, Charette AB
Palladium-Catalyzed Direct C-H Arylation of N-Iminopyridinium Ylides: Application to the Synthesis of (+/-)-Anabasine.
J Am Chem Soc. 2007 Dec 8;
Palladium-catalyzed direct C-H arylation of N-iminopyridinium ylides provides a powerful and versatile method for the synthesis of functionalized piperidines in good yields. Chemoselective functionalization of the pyridinium ring in the presence of a pyridine substituent is possible as exemplified by the expedient synthesis of anabasine in 61% overall yield over three steps. [Abstract]

Pita M, Katz E
Multiple Logic Gates Based on Electrically Wired Surface-Reconstituted Enzymes.
J Am Chem Soc. 2007 Dec 8;
The electrode functionalized with glucose oxidase (GOx) and microperoxidase-11 (MP-11) performs various Boolean logic operations (OR, XOR, AND-OR) upon addition of glucose and/or H2O2 and application of different potentials. The output signal coming from the electrically wired enzymes is electrochemically readable, allowing interfacing of biochemical computing systems with ordinary electronics. [Abstract]

Bandaria JN, Dutta S, Hill SE, Kohen A, Cheatum CM
Fast Enzyme Dynamics at the Active Site of Formate Dehydrogenase.
J Am Chem Soc. 2007 Dec 8;
The role of femtosecond-picosecond structural dynamics of proteins in enzyme-catalyzed reactions is a hotly debated topic. We report infrared photon echo measurement of the formate dehydrogenase-NAD+-azide ternary complex. In contrast to earlier studies of protein dynamics, the data show complete spectral diffusion on the femtosecond-picosecond time scale with no static heterogeneity. This result indicates that this transition-state analogue complex completely samples the distribution of structures that determine the distribution of azide vibrational frequencies within a few picoseconds and that there are no slower motions that perturb the H-bond network at the active site. [Abstract]

Dublin SN, Conticello VP
Design of a Selective Metal Ion Switch for Self-Assembly of Peptide-Based Fibrils.
J Am Chem Soc. 2007 Dec 8;
The self-assembling peptide TZ1H, a structural variant of the trimeric isoleucine zipper GCN4-pII, contains histidine residues at core d-positions of alternate heptads that define three trigonal coordination sites within the coiled-coil trimer. Circular dichroism spectropolarimetry indicated that peptide TZ1H undergoes a random coil to alpha-helical conformational change upon binding of 1 equiv of silver(I) ion, but not zinc(II), copper(II), or nickel(II) ions. Isothermal titration calorimetry provided evidence for a single binding-site model in which each peptide contributes one net silver(I) coordination site, in agreement with the proposed structural model. Transmission electron microscopy revealed that TZ1H self-assembles into long aspect ratio helical fibers in the presence of silver(I) ion. These results demonstrate that the rational design of selective metal ion binding sites within de novo designed peptides represents a promising approach to the controlled fabrication of nanoscale, self-assembled materials. [Abstract]

Grotjahn DB, Miranda-Soto V, Kragulj EJ, Lev DA, Erdogan G, Zeng X, Cooksy AL
Hydrogen-Bond Acceptance of Bifunctional Ligands in an Alkyne-Metal pi Complex.
J Am Chem Soc. 2007 Dec 8;
Experiment and theory have been used to study reactive alkyne pi complexes, intermediates in anti-Markovnikov alkyne hydration by CpRu bis(phosphine) catalysts with heterocyclic substituents. Each heterocycle accepts a hydrogen bond from an acetylene C-H, as revealed by NMR coupling constants between alkyne 13C and 1H nuclei as well as between alkyne 13C and pyridine 15N (2hJCN). Moreover, further alkyne transformations occur at temperatures from 50 to 90 degrees C below what is needed to convert a control compound without the heterocycles. [Abstract]

Evans WJ, Montalvo E, Champagne TM, Ziller JW, Dipasquale AG, Rheingold AL
Organolanthanide-Based Synthesis of 1,2,3-Triazoles from Nitriles and Diazo Compounds.
J Am Chem Soc. 2007 Dec 8;
The reaction of [(C5Me5)2Ln][(mu-Ph)2BPh2] complexes with the lithium salt of (trimethylsilyl)diazomethane, Li[Me3SiCN2], gave products formulated as the dimeric isocyanotrimethylsilyl amide complexes {(C5Me5)2Ln[mu-N(SiMe3)NC]}2 (Ln = Sm, 1; La, 2). Reactions of (C5Me5)2Sm and [(C5Me5)2Sm(mu-H)]2 with Me3SiCHN2 also form 1. Complexes 1 and 2 react with Me3CCN to form the 1,2,3-triazolato complexes (C5Me5)2Ln(NCCMe3)[NNC(SiMe3)C(CMe3)N] (Ln = Sm, 3; La, 4). Complex 2 reacts with Me3SiN3 to make the isocyanide ligated azide complex {(C5Me5)2La[CNN(SiMe3)2](mu-N3)}3, 5. [Abstract]

Turner DL, Vaid TP, Stephens PW, Stone KH, Dipasquale AG, Rheingold AL
Semiconducting Lead-Sulfur-Organic Network Solids.
J Am Chem Soc. 2007 Dec 8;
The reactions of Pb(OAc)2 with 1,2,4,5-benzenetetrathiol, 1,4-benzenedithiol, and benzenehexathiol in ethylenediamine yield bright yellow [Pb2(S2C6H2S2)(en)]n, orange-red [Pb3(SC6H4S)3(en)2]n, and brown [Pb3C6S6]n, respectively. The structures of [Pb2(S2C6H2S2)(en)]n and [Pb3C6S6]n were solved by synchrotron X-ray powder diffraction, while the structure of [Pb3(SC6H4S)3(en)2]n was solved by single-crystal X-ray diffraction. The bonding in [Pb2(S2C6H2S2)(en)]n indicates the presence of "molecular" units, while in [Pb3C6S6]n, the bonding most resembles that in an inorganic solid such as PbS. The differences in bonding are reflected in the optical and electrical properties of the materials; [Pb3C6S6]n is a semiconductor. [Abstract]

Tian Z, Lis L, Kass SR
Hydrogen-Deuterium Exchange and Selective Labeling of Deprotonated Amino Acids and Peptides in the Gas Phase.
J Am Chem Soc. 2007 Dec 8;
Hydrogen-deuterium exchange reactions of deprotonated amino acids and small peptides were studied. Selective labeling can be carried out at the alpha-amino group of lysine (2 of 4 labile hydrogens undergo exchange with CF3CH2OD) and the guanidine side chain of arginine (3 of 6 labile hydrogens undergo exchange with CH3CH2OD and C6H5CH2OD). Differential labeling of peptides also was accomplished, and the extent of H/D exchange is dependent on the amino acids which are present as well as their order in the chain. [Abstract]

Stubbs KA, Scaffidi A, Debowski AW, Mark BL, Stick RV, Vocadlo DJ
Synthesis and Use of Mechanism-Based Protein-Profiling Probes for Retaining beta-d-Glucosaminidases Facilitate Identification of Pseudomonas aeruginosa NagZ.
J Am Chem Soc. 2007 Dec 8;
The NagZ class of retaining exo-glucosaminidases play a critical role in peptidoglycan recycling in Gram-negative bacteria and the induction of resistance to beta-lactams. Here we describe the concise synthesis of 2-azidoacetyl-2-deoxy-5-fluoro-beta-d-glucopyranosyl fluoride as an activity-based proteomics probe for profiling these exo-glycosidases. This active-site directed reagent covalently inactivates this class of retaining N-acetylglucosaminidases with exquisite selectivity by stabilizing the glycosyl-enzyme intermediate. Inactivated Vibrio cholerae NagZ can be elaborated with biotin or a FLAG-peptide epitope using the Staudinger ligation or the Sharpless-Meldal click reaction and detected at nanogram levels. This ABPP enabled the profiling of the Pseudomonas aeruginosa proteome and identification at endogenous levels of a tagged protein with properties consistent with those of PA3005. Cloning of the gene encoding this hypothetical protein and biochemical characterization enabled unambiguous assignment of this hypothetical protein as a NagZ. The identification and cloning of this NagZ may facilitate the development of strategies to circumvent resistance to beta-lactams in this human pathogen. As well, this general strategy, involving such 5-fluoro inactivators, may prove to be of general use for profiling proteomes and identifying glycoside hydrolases of medical importance or having desirable properties for biotechnology. [Abstract]

Ratnakar SJ, Woods M, Lubag AJ, Kovacs Z, Sherry AD
Modulation of Water Exchange in Europium(III) DOTA-Tetraamide Complexes via Electronic Substituent Effects.
J Am Chem Soc. 2007 Dec 8;
The chemical exchange saturation transfer (CEST) efficiency for a series Eu3+-based tetraamide complexes bearing p-substituents on a single coordinating pendant arm is highly sensitive to water exchange rates. The CEST effect increases in the order Me < MeO < F approximately CO2tBu < CN < H. These results show that CEST contrast can be modulated by changes in electron density at a single ligating atom, and this forms the basis of creating imaging agents that respond to chemical oxidation and reduction. [Abstract]

Shashilov VA, Lednev IK
2D Correlation Deep UV Resonance Raman Spectroscopy of Early Events of Lysozyme Fibrillation: Kinetic Mechanism and Potential Interpretation Pitfalls.
J Am Chem Soc. 2007 Dec 8;
The early stages of hen egg white lysozyme (HEWL) fibrillation were quantitatively characterized by two-dimensional correlation deep UV resonance Raman spectroscopy (2D-DUVRR) in terms of the sequential order of events and their characteristic times. The evolution of individual secondary structural elements was established through the correlation between Amide I, Amide III, and Calpha-H bending Raman bands. The temporal order of tertiary and individual secondary structural changes was probed through the cross-correlation of phenylalanine and Amide Raman bands. Both the sequential order and the characteristic times of tertiary and secondary structural changes allowed for reconstructing the molecular mechanism of lysozyme structural changes at the early stages of fibrillation. The 2D-DUVRR analysis of our data indicated that melting of the alpha-helix happened after the formation of the disordered structure, which was termed as apparent inverse order of secondary structural changes. We demonstrated that this apparent inverse order of events is typical for all chemical reactions involving the formation of intermediate(s), which may lead to the serious misinterpretation of 2D correlation results. We proposed a new simulation-aided approach for reconstructing and quantitatively characterizing the reaction mechanism of a (bio)chemical reaction that accounts for the apparent inverse order of events. [Abstract]

He W, Huang J, Sun X, Frontier AJ
Total Synthesis of (+/-)-Merrilactone A.
J Am Chem Soc. 2007 Dec 8;
The total synthesis of racemic merrilactone A (a neurotrophic agent) is described, featuring simultaneous and stereospecific creation of the C4 and C5 stereocenters via a notable silyloxyfuran Nazarov cyclization. Full details of the successful synthetic strategy are given, as well as several examples of the interesting reactivity of intermediates that were prepared and studied during the execution of the total synthesis. A detailed investigation of the Lewis acid-catalyzed Nazarov cyclization of silyloxyfurans was conducted, including a systematic study of substrate scope and limitations. In addition, experiments were conducted that suggest the participation of Lewis acidic silicon species in the Nazarov cyclization. [Abstract]

Ahmad G, Dickerson MB, Cai Y, Jones SE, Ernst EM, Vernon JP, Haluska MS, Fang Y, Wang J, Subramanyam G, Naik RR, Sandhage KH
Rapid Bioenabled Formation of Ferroelectric BaTiO(3) at Room Temperature from an Aqueous Salt Solution at Near Neutral pH.
J Am Chem Soc. 2007 Dec 8;
A 12-mer peptide, identified through phage display biopanning, has been used for the first time to induce the rapid formation of ferroelectric (tetragonal) nanocrystalline BaTiO3 at room temperature from an aqueous salt precursor solution at near neutral pH. BaTiO3 is widely used in capacitors, thermistors, displays, and sensors owing to its attractive dielectric, ferroelectric, pyroelectric, optical, and electrochemical properties. Two 12-mer peptides (BT1 and BT2) were selected from a phage-displayed peptide library via binding to tetragonal BaTiO3 powder. While these peptides possessed various types of amino acids, 8 of the 12 amino acids were common to both peptides. Each of these peptides induced the formation of faceted nanoparticles (50-100 nm diameter) from an aqueous precursor solution. X-ray diffraction and selected area electron diffraction patterns obtained from these faceted nanoparticles were consistent with the BaTiO3 compound. Rietveld analyses of the X-ray diffraction patterns yielded good fits to tetragonal crystal structures, with the BaTiO3 formed in the presence of the BT2 peptide exhibiting the most tetragonal character. A coating of the latter BaTiO3 nanoparticles exhibited polarization hysteresis (a well-known characteristic of ferroelectric materials) at room temperature and a relative permittivity of 2200. Such rapid, peptide-induced precipitation at room temperature provides new opportunities for direct BaTiO3 formation on low-melting or reactive materials (e.g., plastics, cloths, bio-organics) and the low temperature integration of BaTiO3 into electronic devices (e.g., on silicon or flexible polymer substrates). [Abstract]

Graziano JJ, Liu W, Perera R, Geierstanger BH, Lesley SA, Schultz PG
Selecting Folded Proteins from a Library of Secondary Structural Elements.
J Am Chem Soc. 2007 Dec 8;
A protein evolution strategy is described by which double-stranded DNA fragments encoding defined Escherichia coli protein secondary structural elements (alpha-helices, beta-strands, and loops) are assembled semirandomly into sequences comprised of as many as 800 amino acid residues. A library of novel polypeptides generated from this system was inserted into an enhanced green fluorescent protein (EGFP) fusion vector. Library members were screened by fluorescence activated cell sorting (FACS) to identify those polypeptides that fold into soluble, stable structures in vivo that comprised a subset of shorter sequences ( approximately 60 to 100 residues) from the semirandom sequence library. Approximately 108 clones were screened by FACS, a set of 1149 high fluorescence colonies were characterized by dPCR, and four soluble clones with varying amounts of secondary structure were identified. One of these is highly homologous to a domain of aspartate racemase from a marine bacterium (Polaromonas sp.) but is not homologous to any E. coli protein sequence. Several other selected polypeptides have no global sequence homology to any known protein but show significant alpha-helical content, limited dispersion in 1D nuclear magnetic resonance spectra, pH sensitive ANS binding and reversible folding into soluble structures. These results demonstrate that this strategy can generate novel polypeptide sequences containing secondary structure. [Abstract]

Han YK, Jung J
Does the "Superatom" Exist in Halogenated Aluminum Clusters?
J Am Chem Soc. 2007 Dec 8;
We have shown that Aln clusters do not show any characteristics of a superatom in halogenated aluminum clusters. The enhanced stability of halogenated Al clusters can be explained by the magic nature of the clusters, not by superatom chemistry. The presence of even a few electronegative elements provides significant perturbation to the molecular orbitals of Al clusters and stabilizes the electropositive Al cluster cores, closely correlating with metal cluster-ligand chemistry. Our work provides significant chemical insights into the understanding of the structure and stability of halogenated aluminum clusters, and these new insights are applicable to other metal cluster-ligand systems. [Abstract]

Herranz MA, Ehli C, Campidelli S, Gutiérrez M, Hug GL, Ohkubo K, Fukuzumi S, Prato M, Martín N, Guldi DM
Spectroscopic Characterization of Photolytically Generated Radical Ion Pairs in Single-Wall Carbon Nanotubes Bearing Surface-Immobilized Tetrathiafulvalenes.
J Am Chem Soc. 2007 Dec 8;
We succeeded in establishing for the first time a conclusive spectroscopic signature for reduced single-wall carbon nanotubes (SWNT), which evolves from electron donor-acceptor interactions between SWNT and electron-donating pi-extended tetrathiafulvalene (exTTF). In particular, pi-pi interactions were employed to anchor the electron donor to the surface of SWNT. New conduction band electrons, injected from photoexcited exTTF, shift the transitions that are associated with the van Hove singularities to lower energies. [Abstract]

McDaniel ND, Coughlin FJ, Tinker LL, Bernhard S
Cyclometalated Iridium(III) Aquo Complexes: Efficient and Tunable Catalysts for the Homogeneous Oxidation of Water.
J Am Chem Soc. 2007 Dec 7;
A series of bis-phenylpyridine, bis-aquo iridium(III) complexes is herein shown to robustly and efficiently catalyze the oxidation of water to dioxygen in the presence of a sacrificial oxidant. Through substitution on the cyclometalating ligands of these complexes, it is shown that a broad range of oxidation potentials can be achieved within this class of catalyst. Parallel, dynamic monitoring of oxygen evolution, made possible by equipping reaction vessels with pressure-voltage transducers, facilitates correlation of these complexes' ionization potentials with their respective activity toward water oxidation. The importance of these catalysts lies in (A) their ability to oxidize water in a purely aqueous medium, (B) their simplicity of design, (C) their durability, and (D) the ease with which they can be tuned to accommodate the electrochemical needs of photosensitizers in hypothetical photochemical water oxidation and full artificial photosynthetic schemes. [Abstract]

Doonan CJ, Rubie ND, Peariso K, Harris HH, Knottenbelt SZ, George GN, Young CG, Kirk ML
Electronic Structure Description of the cis-MoOS Unit in Models for Molybdenum Hydroxylases.
J Am Chem Soc. 2007 Dec 7;
The molybdenum hydroxylases catalyze the oxidation of numerous aromatic heterocycles and simple organics and, unlike other hydroxylases, utilize water as the source of oxygen incorporated into the product. The electronic structures of the cis-MoOS units in CoCp2[TpiPrMoVOS(OPh)] and TpiPrMoVIOS(OPh) (TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate), new models for molybdenum hydroxylases, have been studied in detail using S K-edge X-ray absorption spectroscopy, vibrational spectroscopy, and detailed bonding calculations. The results show a highly delocalized Mo=S pi* LUMO redox orbital that is formally Mo(dxy) with approximately 35% sulfido ligand character. Vibrational spectroscopy has been used to quantitate Mo-Ssulfido bond order changes in the cis-MoOS units as a function of redox state. Results support a redox active molecular orbital that has a profound influence on MoOS bonding through changes to the relative electro/nucleophilicity of the terminal sulfido ligand accompanying oxidation state changes. The bonding description for these model cis-MoOS systems supports enzyme mechanisms that are under orbital control and dominantly influenced by the unique electronic structure of the cis-MoOS site. The electronic structure of the oxidized enzyme site is postulated to play a role in polarizing a substrate carbon center for nucleophilic attack by metal activated water and acting as an electron sink in the two-electron oxidation of substrates. [Abstract]

Rümmeli MH, Schäffel F, Kramberger C, Gemming T, Bachmatiuk A, Kalenczuk RJ, Rellinghaus B, Büchner B, Pichler T
Oxide-Driven Carbon Nanotube Growth in Supported Catalyst CVD.
J Am Chem Soc. 2007 Dec 6;
Detailed HREM studies on carbon nanotubes (CNTs) synthesized via chemical vapor deposition (CVD) using nanoengineered Fe particles on oxide supports show capped tops and open-ended roots. We demonstrate that the pristine catalyst particle dictates the CNT diameter and number of walls at nucleation. The consecutive inward formation of concentric graphene caps during nucleation constricts and elongates the catalyst particle within the tube core. Continued growth stems from the oxide support. [Abstract]

Nagy P, Wang X, Lemma K, Ashby MT
Reactive Sulfur Species: Hydrolysis of Hypothiocyanite To Give Thiocarbamate-S-oxide.
J Am Chem Soc. 2007 Dec 6;
Hypothiocyanite (OSCN-) hydrolyzes under alkaline conditions to give thiocarbamate-S-oxide (H2NC(=O)SO-, the conjugate base of carbamothioperoxoic acid) via a mechanism that involves rate-limiting nucleophilic attack of OH- on OSCN-, followed by fast protonation (with no net consumption of H+/OH- at pH 11.7). Thiocarbamate-S-oxide has been characterized by 13C NMR, 15N NMR, UV spectroscopy, and ion chromatography. It has also been independently synthesized by the reaction of thiocarbamate (H2NC(=O)S-) and hypochlorite (OCl-). The properties of thiocarbamate-S-oxide that is produced by hydrolysis of OSCN- and by oxidation of H2NC(=O)S- are the same. The possible relevance of thiocarbamate-S-oxide in human peroxidase defense mechanisms remains to be explored. [Abstract]

Explosives: Completely Revised 6th ed By Rudolf Meyer (formerly of WASAG Chemie, Essen, Germany), Josef Köhler (Schardenberg, Austria), and Axel Homburg (Dynamit Nobel GmbH, Troisdorf, Germany) Wiley-VCH Verlag GmbH: Weinheim. 2007.viii + 422 pp. $240. ISBN 978-3-527- 31656-4.
J Am Chem Soc. 2007 Dec 6; [Abstract]

Perera H, Shvarev A
Unbiased Selectivity Coefficients Obtained for the Pulsed Chronopotentiometric Polymeric Membrane Ion Sensors.
J Am Chem Soc. 2007 Dec 6;
We report here on the successful observation of the unbiased thermodynamic selectivity of ion-selective sensors working in normal pulse chronopotentiometric mode (pulstrodes). In contrast to ion-selective electrodes, the pulstrodes do not require careful counterbalancing of the transmembrane ionic fluxes to achieve unbiased thermodynamic selectivity. The pulstrodes can work under asymmetric conditions, which are often encountered in practice. The composition of the inner filling solution did not affect the sensor response, indicating that the transmembrane flux of primary ions was indeed effectively suppressed in the absence of ion exchanger. For the K-selective sensor considered here, an improvement of Mg discrimination by a factor of 1000 was demonstrated. [Abstract]

Recent Articles in Chemistry - A European Journal

Estévez MC, Galve R, Sánchez-Baeza F, Marco MP
Disulfide Symmetric Dimers as Stable Pre-Hapten Forms for Bioconjugation: A Strategy to Prepare Immunoreagents for the Detection of Sulfophenyl Carboxylate Residues in Environmental Samples.
Chemistry. 2007 Dec 10; .
A convenient, generic synthesis of bioconjugates from haptens with a thiol group has been established. The corresponding haptens are synthesized as stable symmetric dimmers through a disulfide bond that is reduced immediately before conjugation with the aid of a di(n-butyl)phenylphosphine polystyrene (DBPP) resin. This strategy was used to prepare haptenized biomolecules and to raise antibodies against short-alkyl-chain sulfophenyl carboxylates (X-C(z)-SPCs; X is the position of the benzylic group and z is the alkyl-chain length) formed after degradation of the widely used domestic and industrial linear alkylbenzene sulfonates (LASs) surfactants. Because of the complexity of the LASs technical mixture, homologous and pseudo-heterologous immunization strategies have been studied with the aim of broadening antibody recognition of the SPC family. With this purpose, two types of immunizing haptens have been synthesized and used to prepare bioconjugates and raise antibodies. Type-A bioconjugates (SPC(A)-protein) were prepared by synthesizing type-A haptens as stable symmetric dimers, generically 2,2'-dithiobis[5-{4-(N-ethylsulfamoyl)}phenylalkanoic acids] (X-C(z)-S-SPC). On the other hand, type-B bioconjugates (SPC(B)-protein) were prepared by treating the carboxylic groups of the corresponding 4-sulfophenylalkanoic acids (X-C(z)-SPC) with the amino groups of the lysine residues by using classical carbodiimide procedures. Type-A haptens produced antibodies with a much higher avidity for the target analyte. Under competitive immunochemical configurations (As112/2-C(5)-ovalbumin), these antibodies can reach a limit of detection (LOD) of 40 ng L(-1) with an IC(50) value of 200 ng L(-1) for 3-C(6)-SPC, which opens up the possibility of trace contamination of edible waters by surfactants with 3-C(6)-SPC as a marker of LAS pollution. A comparative study of the properties of the three families of polyclonal antibodies produced revealed that antibodies raised through pseudo-heterologous immunization strategies produced antibodies with a broader specificity versus the SPC family. These results indicate that this approach could be useful in avoiding synthetic difficulties associated with preparing haptens that preserve all the most important chemical functionalities of the molecule. [Abstract]

Venkatasubbaiah K, Doshi A, Nowik I, Herber RH, Rheingold AL, Jäkle F
Examination of the Mixed-Valence State of the Doubly Boron-Bridged Diferrocene Cation [(FeCp)(2){mu-C(10)H(6)(BPh)(2)}](+).
Chemistry. 2007 Dec 10;
A series of mixed-valent (MV) complexes [(FeCp)(2)(mu-C(10)H(6)(BPh)(2))](+)X ([1(+)]X; X=I(5), PF(6), SbF(6), B(C(6)F(5))(4)) were prepared by oxidation of diboradiferrocene [(FeCp)(2)(mu-C(10)H(6)(BPh)(2))] (1) with I(2), AgPF(6), and AgSbF(6), respectively, and through anion exchange of the I(5) (-) salt with [Li(Et(2)O)(x)][B(C(6)F(5))(4)] in the case of X=B(C(6)F(5))(4). The MV state of the cation was investigated in solution by multinuclear NMR spectroscopy, CV, and UV/Vis-NIR absorption spectroscopy, and in the solid state by IR spectroscopy, single-crystal X-ray crystallography, and Mössbauer spectroscopy. The cyclic voltammogram of 1 shows two distinct redox waves with a large redox splitting of DeltaE=510 mV in CH(2)Cl(2) and the NIR spectrum for the mono-oxidized species displays an intervalence charge-transfer band at around 1500 to 1700 nm depending on the specific counterion present. The X-ray crystal structures of [1(+)]X show inversion-symmetric cations with X=I(5) and B(C(6)F(5))(4) and unsymmetric valence-trapped structures composed of one ferrocene and one ferrocenium moiety with X=PF(6) and SbF(6). Mössbauer data for X=PF(6) are consistent with valence trapping at all temperatures between 90 and 343 K. In comparison, fast electron transfer is evident on the Mössbauer timescale for X=I(5) and temperature-dependent behavior is observed for X=B(C(6)F(5))(4). The anion dependence of the X-ray structural and Mössbauer data is discussed in the context of crystal symmetry and the possibility of static and dynamic disorder effects is considered. [Abstract]

Jiang HL, Huang SP, Fan Y, Mao JG, Cheng WD
Explorations of New Types of Second-Order Nonlinear Optical Materials in Cd(Zn)-V(V)-Te(IV)-O Systems.
Chemistry. 2007 Dec 11;
Solid-state reactions of zinc(II) or cadmium(II) oxide, V(2)O(5), and TeO(2) at high temperature led to two novel quaternary compounds, namely, Zn(3)V(2)TeO(10) and Cd(4)V(2)Te(3)O(15). The structure of Zn(3)V(2)TeO(10) is a complicated three-dimensional (3D) network constructed by the interconnection of ZnO(5), ZnO(6), VO(4), and TeO(4) polyhedra via corner- and edge-sharing. Cd(4)V(2)Te(3)O(15) with an acentric structure features a 3D network in which the cadmium tellurite layers are further interconnected by both "isolated" VO(4) tetrahedra and one-dimensional (1D) vanadium oxide helical chains. Cd(4)V(2)Te(3)O(15) displays a second harmonic generation (SHG) efficiency of about 1.4 times that of KH(2)PO(4) (KDP). Both compounds are direct band-gap semiconductors and are transparent in the range of 0.6-10.0 mum. Measurements of luminescence indicate that both compounds exhibit broad emission bands in the blue-light region. [Abstract]

Barros N, Schappacher M, Dessuge P, Maron L, Guillaume SM
New Insights into the Polymerization of Methyl Methacrylate Initiated by Rare-Earth Borohydride Complexes: A Combined Experimental and Computational Approach.
Chemistry. 2007 Dec 11;
Polymerization of methyl methacrylate (MMA) initiated by the rare-earth borohydride complexes [Ln(BH(4))(3)(thf)(3)] (Ln=Nd, Sm) or [Sm(BH(4))(Cp*)(2)(thf)] (Cp*=eta-C(5)Me(5)) proceeds at ambient temperature to give rather syndiotactic poly(methyl methacrylate) (PMMA) with molar masses M (n) higher than expected and quite broad molar mass distributions, which is consistent with a poor initiation efficiency. The polymerization of MMA was investigated by performing density functional theory (DFT) calculations on an eta-C(5)H(5) model metallocene and showed that in the reaction of [Eu(BH(4))(Cp)(2)] with MMA the borate [Eu(Cp)(2){(OBH(3))(OMe)C==C(Me)(2)}] (e-2) complex, which forms via the enolate [Eu(Cp)(2){O(OMe)C==C(Me)(2)}] (e), is calculated to be exergonic and is the most likely of all of the possible products. This product is favored because the reaction that leads to the formation of carboxylate [Eu(Cp)(2){OOC--C(Me)(==CH(2))}] (f) is thermodynamically favorable, but kinetically disfavored, and both of the potential products from a Markovnikov [Eu(Cp)(2){O(OMe)C--CH(Me)(CH(2)BH(3))}] (g) or anti-Markovnikov [Eu(Cp)(2){O(OMe)C--C(Me(2))(BH(3))}] (h) hydroboration reaction are also kinetically inaccessible. Similar computational results were obtained for the reaction of [Eu(BH(4))(3)] and MMA with all of the products showing extra stabilization. The DFT calculations performed by using [Eu(Cp)(2)(H)] to model the mechanism previously reported for the polymerization of MMA initiated by [Sm(Cp*)(2)(H)](2) confirmed the favorable exergonic formation of the intermediate [Eu(Cp)(2){O(OMe)C==C(Me)(2)}] (e'') as the kinetic product, this enolate species ultimately leads to the formation of PMMA as experimentally observed. Replacing H by BH(4) thus prevents the 1,4-addition of the [Eu(BH(4))(Cp)(2)] borohydride ligand to the first incoming MMA molecule and instead favors the formation of the borate complex e-2. This intermediate is the somewhat active species in the polymerization of MMA initiated by the borohydride precursors [Ln(BH(4))(3)(thf)(3)] or [Sm(BH(4))(Cp*)(2)(thf)]. [Abstract]

Yuasa J, Yamada S, Fukuzumi S
Accelerating and Decelerating Effects of Metal Ions on Electron-Transfer Reduction of Quinones as a Function of Temperature and Binding Modes of Metal Ions to Semiquinone Radical Anions.
Chemistry. 2007 Dec 11;
The accelerating effect of Sc(3+) on the electron-transfer (ET) reduction of the p-benzoquinone derivative 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ) by 10,10'-dimethyl-9,9'-biacridine ((AcrH)(2)) at 233 K changes to a decelerating effect with increasing reaction temperature; the observed second-order rate constant k(et) decreases with increasing Sc(3+) concentration at high concentrations of Sc(3+) at 298 K. At 263 K the k(et) value remains constant with increasing Sc(3+) concentration. Such a remarkable difference with regard to dependence of k(et) on [Sc(3+)] between low and high temperatures results from the difference in relative activity of two ET pathways that depend on temperature, one of which affords 1:1 complex TolSQ(.) (-)-Sc(3+), and the other 1:2 complex TolSQ(.) (-)-(Sc(3+))(2) with additional binding of Sc(3+) to TolSQ(.) (-)-Sc(3+). The formation of TolSQ(.) (-)-Sc(3+) and TolSQ(.) (-)-(Sc(3+))(2) complexes was confirmed by EPR spectroscopy in the ET reduction of TolSQ in the presence of low and high concentrations of Sc(3+), respectively. The effects of metal ions on other ET reactions of quinones to afford 1:1 and 1:2 complexes between semiquinone radical anions and metal ions are also reported. The ET pathway affording the 1:2 complexes has smaller activation enthalpies DeltaH( not equal) and more negative activation entropies DeltaS( not equal) because of stronger binding of metal ions and more restricted geometries of the ET transition states as compared with the ET pathway to afford the 1:1 complexes. [Abstract]

Justus E, Rischka K, Wishart JF, Werner K, Gabel D
Trialkylammoniododecaborates: Anions for Ionic Liquids with Potassium, Lithium and Protons as Cations.
Chemistry. 2007 Dec 7;
Herein we report a new class of low-melting ionic liquids (IL) that consist of N,N,N-trialkylammonioundecahydrododecaborates(1-) as the anion and a range of cations. The cations include the common cations of conventional ILs such as tetraalkylammonium, N-alkylpyridinium, and N-methyl-N'-alkylimidazolium. In addition, their salts with lithium, potassium, and proton cations also exist as ILs. Pulse radiolysis studies indicate that the anions do not react with solvated electrons. [Abstract]

Mora F, Tran DH, Oudry N, Hopfgartner G, Jeannerat D, Sakai N, Matile S
Interface Engineering of Synthetic Pores: Towards Hypersensitive Biosensors.
Chemistry. 2007 Dec 7;
Hydrophilic anchoring is introduced as a promising strategy to constructively control the various interactions of synthetic pore sensors with the surrounding biphasic environment. Artificial rigid-rod beta barrels are selected as classical synthetic multifunctional pores and random-coil tetralysines are attached as hydrophilic anchors. The synthesis of this advanced pore is accomplished in 32 steps from commercially available starting materials. With regard to pore activity as such, the key impact of hydrophilic anchoring is a change from a Hill coefficient n<1 to n=4. This change confirms successful suppression of the competing self-assembly with precipitation from the aqueous phase as the origin of the accomplished increase in pore activity. The hydrophilic anchors do not interfere with the blockage of the synthetic pore sensors by anionic analytes. In the case of stoichiometric binding of blockers (K(D)=EC(50) of the pore; EC(50)=concentration needed to observe 50 % pore activity), however, the increase in pore activity achieved by hydrophilic anchoring results in improved pore blockage under high dilution conditions. Controls confirm that this increase does not occur with analytes that do not exhibit stoichiometric binding (K(D)>EC(50)). These results not only reveal stoichiometric binding as the expected origin of the sensitivity limit of synthetic pore sensors, they also provide promising solutions for this problem. The combination of hydrophilic anchoring with targeted pore formation emerges as a particularly promising strategy to further reduce effective pore concentrations. The scope and limitations of this approach are exemplified with pertinent analyte pairs that are essential for the sensing of sucrose, lactose, acetate, and glutamate with synthetic pores in samples from the supermarket. [Abstract]

Capon JF, Ezzaher S, Gloaguen F, Pétillon FY, Schollhammer P, Talarmin J
Electrochemical Insights into the Mechanisms of Proton Reduction by [Fe(2)(CO)(6){mu-SCH(2)N(R)CH(2)S}] Complexes Related to the [2Fe](H) Subsite of [FeFe]Hydrogenase.
Chemistry. 2007 Dec 7;
Electrochemical investigations on a structural analogue of the [2Fe](H) subsite of [FeFe]H(2)ases, namely, [Fe(2)(CO)(6){mu-SCH(2)N(CH(2)CH(2)- OCH(3))CH(2)S}] (1), were conducted in MeCN/NBu(4)PF(6) in the presence of HBF(4)/Et(2)O or HOTs. Two different catalytic proton reduction processes operate, depending on the strength and the concentration of the acid used. The first process, which takes place around -1.2 V for both HBF(4)/Et(2)O and HOTs, is limited by the slow release of H(2) from the product of the {2 H(+)/2 e} pathway, 1-2H. The second catalytic process, which occurs at higher acid concentrations, takes place at different potentials depending on the acid present. We propose that this second mechanism is initiated by protonation of 1-2H when HBF(4)/Et(2)O is used, whereas the reduction of 1-2H is the initial step in the presence of the weaker acid HOTs. The potential of the second process, which occurs around -1.4 V (reduction potential of 1-3H(+)) or around -1.6 V (the reduction potential of 1-2H) is thus dependent on the strength of the available proton source. [Abstract]

Montes-Navajas P, Teruel L, Corma A, Garcia H
Specific Binding Effects for Cucurbit[8]uril in 2,4,6-Triphenylpyrylium-Cucurbit[8]uril Host-Guest Complexes: Observation of Room-Temperature Phosphorescence and their Application in Electroluminescence.
Chemistry. 2007 Dec 7;
2,4,6-Triphenylpyrylium (TP(+)) forms host-guest complexes with cucurbiturils (CBs) in acidic aqueous solutions. (1)H NMR spectroscopic data indicates that complexation takes place by encapsulation of the phenyl ring at the four position within CB. Formation of the complex with CB[6] and CB[7] leads to minor shifts in the fluorescence wavelength maximum (lambda(fl)) or quantum yield (Phi(fl)). In sharp contrast, for complexes with CB[8], the emission results in the simultaneous observation of fluorescence (lambda(fl)=480 nm, Phi(fl)=0.05) and room-temperature phosphorescence (lambda(ph)=590 nm, Phi(ph)=0.15). The occurrence of room-temperature phosphorescence can be used to detect the presence of CB[8] visually in solution. Molecular modeling and MM2 molecular mechanics calculations suggest that this effect arises from locking the conformational mobility of the 2- and 6-phenyl rings as a result of CB[8] encapsulation. The remarkably high room-temperature phosphorescence quantum yield of the TP(+)@CB[8] complex has been advantageously applied to develop an electroluminescent cell that contains this host-guest complex. In contrast, analogous cells prepared with TP(+) or TP(+)@CB[7] fail to exhibit electroluminescence. [Abstract]

Bringmann G, Mutanyatta-Comar J, Maksimenka K, Wanjohi JM, Heydenreich M, Brun R, Müller WE, Peter MG, Midiwo JO, Yenesew A
Joziknipholones A and B: The First Dimeric Phenylanthraquinones, from the Roots of Bulbine frutescens.
Chemistry. 2007 Dec 7;
From the roots of the African plant Bulbine frutescens (Asphodelaceae), two unprecedented novel dimeric phenylanthraquinones, named joziknipholones A and B, possessing axial and centrochirality, were isolated, together with six known compounds. Structural elucidation of the new metabolites was achieved by spectroscopic and chiroptical methods, by reductive cleavage of the central bond between the monomeric phenylanthraquinone and -anthrone portions with sodium dithionite, and by quantum chemical CD calculations. Based on the recently revised absolute axial configuration of the parent phenylanthraquinones, knipholone and knipholone anthrone, the new dimers were attributed to possess the P-configuration (i.e., with the acetyl portions below the anthraquinone plane) at both axes in the case of joziknipholone A, whereas in joziknipholone B, the knipholone part was found to be M-configured. Joziknipholones A and B are active against the chloroquine resistant strain K1 of the malaria pathogen, Plasmodium falciparum, and show moderate activity against murine leukemic lymphoma L5178y cells. [Abstract]

Zhang X, Bureau B, Lucas P, Boussard-Pledel C, Lucas J
Glasses for Seeing Beyond Visible.
Chemistry. 2007 Dec 7;
Conventional glasses based on oxides have a transparency limited by phonon absorption in the near IR region and have a limited interest for analyzing information located far beyond the visible. The IR spectral domain is nevertheless of prime interest, since it covers fundamental wavelength ranges used for thermal imaging as well as molecular vibrational signatures. Besides spectacular advances in the field of IR detectors, the main significant progresses are related to the development of IR glass optics, such as lenses or IR optical fibres. The field of IR glasses is almost totally dominated by glasses formed from heavy atoms such as the chalcogens S, Se and Te. Their transparency extends up to 12, 16 and 28 mum for sulfide-, selenide- and the new generation of telluride-based glasses, respectively. They cover the atmospheric transparency domains, 3-5 and 8-13 mum, respectively, at which the IR radiation can propagate allowing thermal imaging and night-vision operations through thick layers of atmosphere. The development of new glass compositions will be discussed on the basis of structural consideration with the objective of moulding low-cost lenses for IR cameras used, for instance, in car-driving assistance. Additionally, multimode, single-index, optical fibres operating in the 3 to 12 mum window developed for in situ remote evanescent-wave IR spectroscopy will also be mentioned. The detection of molecular IR signatures is applied to environmental monitoring for investigating the pollution of underground water with toxic molecules. The extension of this technique to the investigation of biomolecules in three different studies devoted to liver tissues analysis, bio-film formation, and cell metabolism will also be discussed. Finally we will mention the developments in the field of single-mode fibres operating around 10 mum for the Darwin space mission, which is aiming at discovering, signs of biological life in telluric earth-like exoplanets throughout the universe. [Abstract]

Preview: Chem. Eur. J. 1/2008.
Chemistry. 2007 Dec 7;13(36): [Abstract]

Index: Chem. Eur. J. 36/2007.
Chemistry. 2007 Dec 7;13(36): [Abstract]

Spotlights on our sister journals: Chem. Eur. J. 36/2007.
Chemistry. 2007 Dec 7;13(36): [Abstract]

Krebs A, Ludwig V, Pfizer J, Dürner G, Göbel MW
Enantioselvctive Synthesis of Non- Natural Aromatic alpha-Amino Acids.
Chemistry. 2007 Dec 7;13(36): [Abstract]

Jagesar DC, Hartl F, Buma WJ, Brouwer AM
Infrared Study of Intercomponent Interactions in a Switchable Hydrogen-Bonded Rotaxane.
Chemistry. 2007 Dec 6;
The macrocycle in rotaxane 1 is preferentially hydrogen bonded to the succinamide station in the neutral form, but can be moved to the naphthalimide station by one-electron reduction of the latter. The hydrogen bonding between the amide NH groups of the macrocycle and the C==O groups in the binding stations in the thread was studied with IR spectroscopy in different solvents in both states. In addition, the solvent effect on the vibrational frequencies was analyzed; a correlation with the solvent acceptor number (AN) was observed. The conformational switching upon reduction could be detected by monitoring the hydrogen-bond-induced shifts of the nu(CO) frequencies of the C==O groups of the succinamide and the reduced naphthalimide stations. The macrocycle was found to shield the encapsulated station from the solvent: wavenumbers of nu(CO) bands of the C==O groups residing inside the macrocycle cavity remain unaffected by the solvent polarity. [Abstract]

Westermaier M, Mayr H
Regio- and Stereoselective Ring-Opening Reactions of Epoxides with Indoles and Pyrroles in 2,2,2-Trifluoroethanol.
Chemistry. 2007 Dec 6;
Aliphatic and aromatic epoxides react regio- and stereoselectively with indoles and pyrroles in 2,2,2-trifluoroethanol without the use of a catalyst or any other additive. While aromatic epoxides are selectively attacked at the benzylic position, aliphatic epoxides react at the less-substituted position. Chiral epoxides react with >99 % ee (ee=enantiomeric excess). [Abstract]

Bieniek M, Michrowska A, Usanov DL, Grela K
In an Attempt to Provide a User's Guide to the Galaxy of Benzylidene, Alkoxybenzylidene, and Indenylidene Ruthenium Olefin Metathesis Catalysts.
Chemistry. 2007 Dec 6;
The data reported in this paper demonstrate that great care must be taken when choosing an appropriate catalyst for a given metathesis reaction. First-generation catalysts were found to be useful in the metathesis of sterically unhindered substrates. Second-generation catalysts (under optimised conditions) showed good to excellent activities toward sterically hindered and electron-withdrawing group (EWG)-substituted alkenes that do not react using the first-generation complexes. A strong temperature effect was noted on all of the reactions tested. Interestingly, attempts to force a reaction by increasing the catalyst loading were much less effective. Therefore, when possible, it is suggested that metathesis transformations should be carried out with a second-generation catalyst at 70 degrees C in toluene. However, different second-generation catalysts proved to be optimal for different applications and no single catalyst outperformed all others in all cases. Nevertheless, some empirical rules can be deduced from the model experiments, providing preliminary hints for the selection of the optimal catalysts. [Abstract]

Zhang Y, Chen P, Liu M
A General Method for Constructing Optically Active Supramolecular Assemblies from Intrinsically Achiral Water-Insoluble Free-Base Porphyrins.
Chemistry. 2007 Dec 6;
We have developed a general method to construct optically active porphyrin supramolecular assemblies by using a simple air-water interfacial assembly process. The method involved the in situ diprotonation of the free-base porphyrins at the air-water interface and subsequent assembly under compression. We showed that two intrinsically achiral water-insoluble free-base porphyrin derivatives, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (H(2)OEP) and 5,10,15,20-tetra-p-tolyl-21H,23H-porphine (H(2)TPPMe), could be diprotonated when spread onto a 2.4 M hydrochloric acid solution surface, and the Langmuir-Schaefer (LS) films fabricated from the subphase exhibited strong circular dichroism (CD) absorption, whereas those fabricated from pure Milli-Q water subphase did not. The experimental data suggested that the helical stacking of the achiral porphyrin building blocks was responsible for the supramolecular chirality of the assemblies. Interestingly, such a method was successfully applied to a series of other intrinsically achiral free-base porphyrins such as 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine (H(2)TPPOMe), 5,10,15,20-tetraphenyl-21H,23H-porphine (H(2)TPP), 5,10,15,20-tetrakis(4-(allyloxy)phenyl)-21H,23H-porphine (H(2)TPPOA), and 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)-21H,23H-porphine (H(2)TPPDOMe). A possible mechanism has been proposed. The method provides a facile way to obtain optically active porphyrin supramolecular assemblies by using intrinsically achiral water-insoluble free-base porphyrin derivatives. [Abstract]

Camerano JA, Casado MA, Ciriano MA, Tejel C, Oro LA
Coordination Features of a Hybrid Scorpionate/Phosphane Ligand Exemplified with Iridium.
Chemistry. 2007 Dec 6;
Although the pentacoordinated complex [Ir{(allyl)B(CH(2)PPh(2))(pz)(2)}(cod)] (1; pz=pyrazolyl, cod=1,5-cyclooctadiene), isolated from the reaction of [{Ir(mu-Cl)(cod)}(2)] with [Li(tmen)][B(allyl)(CH(2)PPh(2))- (pz)(2)] (tmen=N,N,N',N'-tetramethylethane-1,2-diamine), shows behavior similar to that of the related hydridotris(pyrazolyl)borate complex, the carbonyl derivatives behave in a quite different way. On carbonylation of 1, the metal--metal-bonded complex [(Ir{(allyl)B(CH(2)PPh(2))(pz)(2)}CO)(2)(mu-CO)] (2) that results has a single ketonic carbonyl bridge. This bridging carbonyl is labile such that upon treatment of 2 with PMe(3) the pentacoordinated Ir(I) complex [Ir(CO){(pz)B(eta(2)-CH(2)CH==CH(2))(CH(2)PPh(2))(pz)}(PMe(3))] (3) was isolated. Complex 3 shows a unique fac coordination of the hybrid ligand with the allyl group eta(2)-bonded to the metal in the equatorial plane of a distorted trigonal bipyramid with one pyrazolate group remaining uncoordinated. This unusual feature can be rationalized on the basis of the electron-rich nature of the metal center. The related complex [Ir(CO){(pz)B(eta(2)-CH(2)CH==CH(2))(CH(2)PPh(2))(pz)}(PPh(3))] (4) was found to exist in solution as a temperature-dependent equilibrium between the cis-pentacoordinated and trans square planar isomers with respect to the phosphorus donor atoms. Protonation of 3 with different acids is selective at the iridium center and gives the cationic hydrides [Ir{(allyl)B(CH(2)PPh(2))(pz)(2)}(CO)H(PMe(3))]X (X=BF(4) (5), MeCO(2) (6), and Cl (7)). Complex 7 further reacts with HCl to generate the unexpected product [Ir(CO)Cl{(Hpz)B(CH(2)PPh(2))(pz)CH(2)CH(Me)}(PMe(3))]Cl (9; Hpz=protonated pyrazolyl group) formed by the insertion of the hydride into the Ir--(eta(2)-allyl) bond. In contrast, protonation of complex 4 with HCl stops at the hydrido complex [Ir{(allyl)B(CH(2)PPh(2))(pz)(2)}(CO)H(PPh(3))]Cl (8). X-ray diffraction studies carried out on complexes 2, 3, and 9 show the versatility of the hybrid scorpionate ligand in its coordination. [Abstract]

Zuidema E, Escorihuela L, Eichelsheim T, Carbó JJ, Bo C, Kamer PC, van Leeuwen PW
The Rate-Determining Step in the Rhodium-Xantphos-Catalysed Hydroformylation of 1-Octene.
Chemistry. 2007 Dec 5;
The rate-determining step in the hydroformylation of 1-octene, catalysed by the rhodium-Xantphos catalyst system, was determined by using a combination of experimentally determined (1)H/(2)H and (12)C/(13)C kinetic isotope effects and a theoretical approach. From the rates of hydroformylation and deuterioformylation, a small (1)H/(2)H isotope effect of 1.2 was determined for the hydride moiety of the rhodium catalyst. (12)C/(13)C isotope effects of 1.012(1) and 1.012(3) for the alpha-carbon and beta-carbon atoms of 1-octene were determined, respectively. Both quantum mechanics/molecular mechanics (QM/MM) and full quantum mechanics calculations were carried out on the key catalytic steps, for "real-world" ligand systems, to clarify whether alkene coordination or hydride migration is the rate-determining step. Our calculations (21.4 kcal mol(-1)) quantitatively reproduce the experimental energy barrier for CO dissociation (20.1 kcal mol(-1)) starting at the (bisphosphane)RhH(CO)(2) resting state. The barrier for hydride migration lies 3.8 kcal mol(-1) higher than the barrier for CO dissociation (experimentally determined trend ~3 kcal mol(-1)). The computed (1)H/(2)H and (12)C/(13)C kinetic isotope effects corroborate the results of the energy analysis. [Abstract]

Lu X, Tuan HY, Korgel BA, Xia Y
Facile Synthesis of Gold Nanoparticles with Narrow Size Distribution by Using AuCl or AuBr as the Precursor.
Chemistry. 2007 Dec 4;
Gold(I) halides, including AuCl and AuBr, were employed for the first time as precursors in the synthesis of Au nanoparticles. The synthesis was accomplished by dissolving Au(I) halides in chloroform in the presence of alkylamines, followed by decomposition at 60 degrees C. The relative low stability of the Au(I) halides and there derivatives eliminated the need for a reducing agent, which is usually required for Au(III)-based precursors to generate Au nanoparticles. Controlled growth of Au nanoparticles with a narrow size distribution was achieved when AuCl and oleylamine were used for the synthesis. FTIR and mass spectra revealed that a complex, [AuCl(oleylamine)], was formed through coordination between oleylamine and AuCl. Thermolysis of the complex in chloroform led to the formation of dioleylamine and Au nanoparticles. When oleylamine was replaced with octadecylamine, much larger nanoparticles were obtained due to the lower stability of [AuCl(octadecylamine)] complex relative to [AuCl(oleylamine)]. Au nanoparticles can also be prepared from AuBr through thermolysis of the [AuBr(oleylamine)] complex. Due to the oxidative etching effect caused by Br(-), the nanoparticles obtained from AuBr exhibited an aspect ratio of 1.28, in contrast to 1.0 for the particles made from AuCl. Compared to the existing methods for preparing Au nanoparticles through the reduction of Au(III) compounds, this new approach based on Au(I) halides offers great flexibility in terms of size control. [Abstract]

Shen ZL, Cheong HL, Loh TP
Indium-Silver- and Zinc-Silver-Mediated Barbier-Grignard-Type Alkylation Reactions of Imines by Using Unactivated Alkyl Halides in Aqueous Media.
Chemistry. 2007 Dec 4;
In the presence of In or Zn/AgI/InCl(3), an efficient and practical method for the Barbier-Grignard-type alkylation reactions of simple imines by using a one-pot condensation of various aldehydes, amines (including the aliphatic and chiral version), and secondary alkyl iodides has been developed. The reaction proceeded more efficiently in water than in organic solvents. Without the use of CuI, it mainly gave the imine self-reductive coupling product, which was not the alkylated product. Good diastereoselectivities (up to 92:8 dr) were obtained when L-valine methyl ester was used as the substrate. [Abstract]

Pierrefixe SC, Fonseca Guerra C, Bickelhaupt FM
Hypervalent Silicon versus Carbon: Ball-in-a-Box Model.
Chemistry. 2007 Dec 4;
Why is silicon hypervalent and carbon not? Or why is [Cl--CH(3)--Cl](-) labile with a tendency to localize one of its axial C--Cl bonds and to largely break the other one, while the isostructural and isoelectronic [Cl--SiH(3)--Cl](-) forms a stable pentavalent species with a delocalized structure featuring two equivalent Si--Cl bonds? Various hypotheses have been developed over the years focusing on electronic and steric factors. Here, we present the so-called ball-in-a-box model, which tackles hypervalence from a new perspective. This model reveals the key role of steric factors and provides a simple way of understanding the above phenomena in terms of different atom sizes. Our bonding analyses are supported by computation experiments in which we probe, among other things, the shape of the S(N)2 potential-energy surface of Cl(-) attacking a carbon atom in the series of substrates CH(3)Cl, (.)CH(2)Cl, (.) (.)CHCl, and (.) (.) (.)CCl. Our findings for ClCH(3)Cl(-) and ClSiH(3)Cl(-) are generalized to other Group 14 central atoms (Ge, Sn, and Pb) and axial substituents (F). [Abstract]

Roth A, Buchholz A, Rudolph M, Schütze E, Kothe E, Plass W
Directed Synthesis of a Heterobimetallic Complex Based on a Novel Unsymmetric Double-Schiff-Base Ligand: Preparation, Characterization, Reactivity and Structures of Hetero- and Homobimetallic Nickel(II) and Zinc(II) Complexes.
Chemistry. 2007 Dec 4;
A series of bimetallic zinc(II) and nickel(II) complexes based on the novel dinucleating unsymmetric double-Schiff-base ligand benzoic acid [1-(3-{[2-(bispyridin-2-ylmethylamino)ethylimino]methyl}-2-hydroxy-5-methylphenyl)methylidene]hydrazide (H(2)bpampbh) has been synthesized and structurally characterized. The metal centers reside in two entirely different binding pockets provided by the ligand H(2)bpampbh, a planar tridentate [ONO] and a pentadentate [ON(4)] compartment. The utilized ligand H(2)bpampbh has been synthesized by condensation of the single-Schiff-base proligand Hbpahmb with benzoic acid hydrazide. The reaction of H(2)bpampbh with two equivalents of either zinc(II) or nickel(II) acetate yields the homobimetallic complexes [Zn(2)(bpampbh)(mu,eta(1)-OAc)(eta(1)-OAc)] (ZnZn) and [Ni(2)(bpampbh)(mu-H(2)O)(eta(1)-OAc)(H(2)O)](OAc) (NiNi), respectively. Simultaneous presence of one equivalent zinc(II) and one equivalent nickel(II) acetate results in the directed formation of the heterobimetallic complex [NiZn(bpampbh)(mu,eta(1)-OAc)(eta(1)-OAc)] (NiZn) with a selective binding of the nickel ions in the pentadentate ligand compartment. In addition, two homobimetallic azide-bridged complexes [Ni(2)(bpampbh)(mu,eta(1)-N(3))]ClO(4) (NiNi(N(3))) and [Ni(2)(bpampbh)(mu,eta(1)-N(3))(MeOH)(2)](ClO(4))(0.5)(N(3))(0.5) (NiNi(N(3))(MeOH)(2)) were synthesized. In all complexes, the metal ions residing in the pentadentate compartment adopt a distorted octahedral coordination geometry, whereas the metal centers placed in the tridentate compartment vary in coordination number and geometry from square-planar (NiNi(N(3))) and square-pyramidal (ZnZn and NiZn), to octahedral (NiNi and NiNi(N(3))(MeOH)(2)). In the case of complex NiNi(N(3)) this leads to a mixed-spin homodinuclear nickel(II) complex. All compounds have been characterized by means of mass spectrometry as well as IR and UV/Vis spectroscopies. Magnetic susceptibility measurements show significant zero-field splitting for the nickel-containing complexes (D=2.9 for NiZn, 2.2 for NiNi(N(3)), and 0.8 cm(-1) for NiNi) and additionally a weak antiferromagnetic coupling (J=-1.4 cm(-1)) in case of NiNi. Electrochemical measurements and photometric titrations reveal a strong Lewis acidity of the metal center placed in the tridentate binding compartment towards external donor molecules. A significant superoxide dismutase reactivity against superoxide radicals was found for complex NiNi. [Abstract]

Boyarskiy VP, Belov VN, Medda R, Hein B, Bossi M, Hell SW
Photostable, Amino Reactive and Water-Soluble Fluorescent Labels Based on Sulfonated Rhodamine with a Rigidized Xanthene Fragment.
Chemistry. 2007 Dec 4;
Highly water soluble fluorescent dyes were synthesized and transformed into new amino reactive fluorescent labels for biological microscopy. To this end, rhodamine 8 (prepared from 7-hydroxy-1,2,3,4-tetrahydroquinoline (7) and phthalic anhydride in 85 % aq. H(3)PO(4)) was sulfonated with 30 % SO(3) in H(2)SO(4) and afforded the water soluble disulfonic acid 3 a (64 %). Amidation of the carboxy group in 3 a with 2-(methylamino)ethanol in the presence of O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluroniumPF(6) (-) (HATU) led to alcohol 3 b (66 %), which was transformed into the amino reactive mixed carbonate 3 d with di(N-succinimidyl)carbonate and Et(3)N. Reaction of the carboxy group in 3 a with MeNH(CH(2))(2)CO(2)Me and N,N,N',N'-tetramethyl-O-(N-succinimidyl)-uroniumBF(4) (-) (TSTU) yielded methyl ester 13. After saponification of the aliphatic carboxy group in 13, the compound was converted into NHS-ester 3 e (using HATU and Et(3)N). Heating of 7 with trimellitic anhydride in H(3)PO(4) gave a mixture of dicarboxylic acids 14 and 15 (1:1). Regioisomer 15 was isolated, sulfonated with 30 % SO(3) in H(2)SO(4), and disulfonic acid 3 f was used for the synthesis of the mono NHS-ester 3 g, in which the sterically unhindered carboxy group was selectively activated (with N-hydroxysuccinimide, HATU, and Et(3)N). The sulfonated rhodamines 3 b, c and f are soluble in water (up to 0.1 M), have excellent photostabilities and large fluorescence quantum yields. Subdiffraction resolution images of tubulin filaments of mammalian cells stained with these dyes illustrate their applicability as labels for stimulated emission depletion microscopy and other fluorescence techniques. [Abstract]

Lestini E, Nikitin K, Müller-Bunz H, Fitzmaurice D
Introducing Negative Charges into Bis-p-phenylene Crown Ethers: A Study of Bipyridinium-Based [2]Pseudorotaxanes and [2]Rotaxanes.
Chemistry. 2007 Dec 4;
This paper describes novel host-guest systems comprising viologen cations (guests) and the derivatives of bis-para-phenylene-34-crown-10 (hosts) with anionic groups COO(-) or SO(3) (-). The structure of the resulting charge-compensated host-guest complexes, their association constants and their electrochemical behaviour have been studied. In the solid state, the viologen cations thread the negatively charged crown ethers forming electroneutral zwitterion-like [2]pseudorotaxane salts; in solution this threaded geometry is preserved. The association constants of [2]pseudorotaxane salts incorporating the 1,1'-diethylviologen moiety in solution are significantly higher than those of previously reported analogues. The extrapolated association free energies in non-aqueous media exceed -40 kJ mol(-1) at 25 degrees C. This significant increase of the interaction free energy makes these compounds stable even in aqueous solutions. The association constants of [2]pseudorotaxane salts incorporating sterically more hindered 1,1'-diethyl-3,3'-dimethylviologen moieties are significantly lower. Structurally related [2]rotaxane salts, in which the oppositely charged ionic components are mechanically interlocked, have been prepared in good yields. It has been shown that [2]rotaxane salts incorporating anti-isomers of bisfunctionalised crown ethers are cycloenantiomeric. In both [2]pseudorotaxane and [2]rotaxane salts, the electrostatic interactions between the viologen moieties and the negatively charged crown ethers lead to very significant negative shifts of viologen reduction potentials up to 450 mV. The findings of the present study are valuable for the design of nanoscale molecular electronic devices. [Abstract]

Huang YX, Prots Y, Kniep R
Zn[BPO(4)(OH)(2)]: A Zinc Borophosphate with the Rare Moganite-Type Topology.
Chemistry. 2007 Dec 3;
A novel zinc borophosphate Zn[BPO(4)(OH)(2)] with moganite-type topology (a rare polymorph of silica) has been prepared from a mixture of ZnO, B(2)O(3), and P(2)O(5) by hydrothermal treatment at 443 K. The crystal structure was determined from single-crystal X-ray data (orthorhombic, Pbcn (no. 60), a=915.07(3), b=897.22(3), c=1059.19(3) pm, V=869.62(5)x10(6) pm(3), Z=8, R1=0.028, wR2=0.075). The crystal structure comprises unbranched vierer-single borophosphate chains running along [010] and interconnected via ZnO(2)(OH)(2)-tetrahedra by sharing common vertices. The resulting topology of the three-dimensional tetrahedral framework structure is described by the Schläfli symbol (4(2).6(2).8(2))(4.6(4).8)(2). Although showing Zn in a tetrahedral coordination, the title compound does not belong to the group of zincoborophosphates but is a special case of a borophosphate containing vierer single rings of tetrahedra with the sequence Zn-B-Zn-P. [Abstract]

Zeuner M, Pagano S, Schnick W
Precursor Approach to Lanthanide Dioxo Monocarbodiimides Ln(2)O(2)CN(2) (Ln=Y, Ho, Er, Yb) by Insertion of CO(2) into Organometallic Ln-N Compounds.
Chemistry. 2007 Dec 3;
We present two organometallic precursor approaches leading to the hitherto-unknown dioxo monocarbodiimides (Ln(2)O(2)CN(2)) of the late lanthanides Ho, Er, and Yb as well as yttrium. One involves insertion of CO(2), and the other one is a straightforward route using a molecular single-source precursor. To this end the reactivity of the activated amido lanthanide compound [(Cp(2)ErNH(2))(2)] towards carbon dioxide absorption under supercritical conditions was studied. Selective insertion of CO(2) into the amido complex yielded the single-source precursor [Er(2)(O(2)CN(2)H(4))Cp(4)], which was characterized by vibrational spectroscopy and thermal and elemental analyses. Ammonolysis of this amorphous compound at 700 degrees C affords Er(2)O(2)CN(2). To gain deeper insight into the structural characteristics of the amorphous precursor, a similar molecular carbamato complex was synthesized and fully characterized. X-ray structure analysis of the dimeric complex [Cp(4)Ho(2){mu-eta(1):eta(2)-OC(OtBu)NH}] shows an unusual bonding mode of the tert-butylcarbamate ligand, which acts as both a bridging and side-on chelating group. Ammonolysis of this compound also yielded dioxo monocarbodiimides, and therefore the crystalline carbamato complex turned out to be an alternative precursor for the straightforward synthesis of Ln(2)O(2)CN(2). Analogously, the dioxo monocarbodiimides of Y, Ho, Er, and Yb were synthesized by this route. The crystal structures were determined from X-ray powder diffraction data and refined by the Rietveld method (Ln=Ho, Er). Further spectroscopic characterization and elemental analysis evidenced the existence of phase-pure products. The dioxo monocarbodiimides of holmium and erbium crystallize in the trigonal space group P3 m1. According to X-ray powder diffraction, they adopt the Ln(2)O(2)CN(2) (Ln=Ce-Gd) structure type. [Abstract]

Beni A, Dei A, Laschi S, Rizzitano M, Sorace L
Tuning the Charge Distribution and Photoswitchable Properties of Cobalt-Dioxolene Complexes by Using Molecular Techniques.
Chemistry. 2007 Dec 3;
A series of cobalt complexes [Co(Me(n)tpa)(diox)]PF(6)sol (diox=3,5-di-tert-butyl-1,2-dioxolene; sol=ethanol, toluene; tpa=tris(2-pyridylmethyl)amine) were prepared by using tripod-like Me(n)tpa (n=0, 1, 2, 3), derived from tpa by successive introduction of methyl groups into the 6-position of the pyridine moieties, as an ancillary ligand. The steric hindrance induced by this substitution modulates the redox properties of the metal acceptor, thus determining the charge distribution of the metal-dioxolene moiety at room temperature. All of these complexes were characterised by using diffractometric studies, electronic spectroscopic analysis, and magnetic susceptibility measurements. In the solid state, the [Co(Me(n)tpa)(diox)](+) ions (n=0, 1) can be described as diamagnetic cobalt(III)-catecholato derivatives, whereas a cobalt(II)-semiquinonato description seems appropriate for the paramagnetic [Co(Me(3)tpa)(diox)](+) complex. The complex [Co(Me(2)tpa)(diox)]PF(6)C(2)H(5)OH undergoes entropy-driven valence tautomeric interconversion at room temperature. Optically induced valence tautomerism was observed by irradiation of [Co(Me(n)tpa)(diox)]PF(6) complexes (n=0, 1, 2) at cryogenic temperatures. The different relaxation kinetics of the photoinduced metastable phases are related to the respective free-energy changes of the interconversion, as estimated by cyclic voltammetric experiments at room temperature, and to the different lattice interactions, as supported by structural data. These results show the importance of molecular techniques for controlling the relaxation properties of photoinduced metastable species. At the same time, this behaviour strongly suggests that this paradigm exhibits intrinsic limits because of the less controllable factors that affect the process. [Abstract]

Recent Articles in Journal of Combinatorial Chemistry

Krchn?ák V, Moellmann U, Dahse HM, Miller MJ
Solid-Supported Nitroso Hetero Diels-Alder Reactions. 1. Acylnitroso Dienophiles: Scope and Limitations.
J Comb Chem. 2007 Dec 8;
Polymer-supported acylnitroso dienophiles were prepared and used in hetero Diels-Alder (HDA) reactions with a variety of dienes. The transient acylnitroso dienophiles were prepared in situ from immobilized hydroxamates, which were attached to solid supports via several linkers each cleavable by different cleavage reagents, and served for the synthesis of both N-unsubstituted and N-derivatized HDA adducts. Model compounds were used to (i) optimize reaction conditions for solid-supported HDA reactions, (ii) evaluate the outcome of the reactions with various dienes, (iii) compare relative reactivities of dienes, and (iv) assess the stability of HDA adducts toward cleavage conditions typically used in solid-phase syntheses. Cleaved products were submitted to biological assays, and the results are reported. The accompanying paper, focused on complementary arylnitroso HDA reactions, includes a comparison of both HDA reactions. [Abstract]

Krchn?ák V, Moellmann U, Dahse HM, Miller MJ
Solid-Supported Nitroso Hetero-Diels-Alder Reactions. 3. Acid-Mediated Transformation of Cycloadducts by Scission of the Oxazine C-O Bonds.
J Comb Chem. 2007 Dec 8;
Polymer-supported dihydro[1,2]oxazine derivatives were prepared by acyl- and arylnitroso hetero-Diels-Alder reactions and exposed to strong (trifluoroacetic) acid during cleavage from resin-bound linkers. Cycloadducts prepared from cyclic dienes containing electron-donating substituents at the C6 oxazine carbon promoted formation of carbocations by cleavage of the C-O bond. The carbocations were quenched by nucleophilic reagents including triethylsilane, water, and alcohols and provided access to novel derivatives of N-alkyl hydroxamates. Products were submitted to biological assays, and the results are reported. [Abstract]

Doan ND, Bourgault S, Létourneau M, Fournier A
Effectiveness of the Suzuki-Miyaura Cross-Coupling Reaction for Solid-Phase Peptide Modification.
J Comb Chem. 2007 Dec 8;
The Suzuki-Miyaura (SM) cross-coupling reaction has recently become one of the most efficient methods for C-C bond construction opening a wide range of opportunities in organic synthesis. This study focused on the evaluation of the use of the SM reaction to modify peptides using a solid-phase synthesis approach, an avenue that was still not investigated intensively. We used as a peptide model [Ala (1,2,3), Leu (8)]Enk linked to a polystyrene support on which it was previously assembled. The aromatic residues Tyr (4) and Phe (7) of [Ala (1,2,3), Leu (8)]Enk were respectively substituted with p-iodo-Phe, and an SM-related strategy was developed. Results indicated that the reaction conditions involving K 3PO 4 or Na 2CO 3 (base), DMF (solvent), Pd(PPh 3) 4 (catalyst), and temperatures ranging from 50 to 80 degrees C during 20 h were found as optimal. Finally applying those optimal conditions, a series of [Ala (1,2,3), Leu (8)]Enk analogs modified at Tyr (4) or Phe (7) positions was synthesized using diverse boronic acid derivatives. [Abstract]

Houghten RA, Pinilla C, Giulianotti MA, Appel JR, Dooley CT, Nefzi A, Ostresh JM, Yu Y, Maggiora GM, Medina-Franco JL, Brunner D, Schneider J
Strategies for the Use of Mixture-Based Synthetic Combinatorial Libraries: Scaffold Ranking, Direct Testing In Vivo, and Enhanced Deconvolution by Computational Methods.
J Comb Chem. 2007 Dec 8; [Abstract]

Bremner WS, Organ MG
Formation of Substituted Pyrroles via an Imine Condensation/Aza-Claisen Rearrangement/Imine-Allene Cyclization Process by MAOS.
J Comb Chem. 2007 Dec 7;
A diverse collection of pyrroles has been prepared using a one-pot, domino aldehyde/amine condensation, [3,3]-aza-Claisen rearrangement, imine-allene cyclization strategy. This protocol was accelerated by microwave irradiation and provided very good levels of conversion after reacting for only 30 min. [Abstract]

Yu HL, Xu JH, Wang YX, Lu WY, Lin GQ
Assembly of a Three-Dimensional Array of Glycoconjugates by Combinatorial Biocatalysis in Nonaqueous Media.
J Comb Chem. 2007 Dec 7;
Glycoconjugates can be artificially synthesized by combinatorial biocatalysis. An example is given in this paper describing the construction of glycoconjugates array by using glycosidase and lipase in nonaqueous media. This array was started from glucose, with three aryl alcohols as the aglycone moiety of glycosides and five acids or esters as acyl donors for combinatorial acylation of glycosides, affording a three-dimensional array containing about 30 members with diverse structures. The array would be more abundant if more aglycones and acyl donors with other structures were filled in. Indeed, diverse classes of carbohydrates besides glucose can also be employed for generating diverse glycoconjugates due to their different roles in numerous physiological responses. The composition and distribution of the demonstration glycoconjugates array was detected and evaluated by HPLC-MS with electrospray ionization. And also, the distribution of the artificial array can be adjusted by changing the molar ratio of the auxiliary materials. [Abstract]

Krchn?ák V, Moellmann U, Dahse HM, Miller MJ
Solid-Supported Nitroso Hetero Diels-Alder Reactions. 2. Arylnitroso Dienophiles: Scope and Limitations.
J Comb Chem. 2007 Dec 7;
Immobilized arylnitroso dienophiles were prepared and used in hetero Diels-Alder (HDA) reactions with a variety of dienes. Polymer-supported arylnitroso species were prepared on several linkers cleavable by different cleavage reagents and used for (i) optimization of reaction conditions for HDA reactions, (ii) evaluation of the reaction outcome with various dienes, (iii) comparison of relative reactivities of dienes, and (iv) assessment of the stability of HDA adducts toward cleavage conditions typically used in solid-phase preparation (TFA). The outcome of the HDA reactions has been evaluated for a set of 19 dienes, and the relative reactivities of dienes that yielded the expected HDA adducts were compared. Cleaved products were submitted to biological assays, and the results are reported. [Abstract]

Shin DS, Kim YG, Kim EM, Kim M, Park HY, Kim JH, Lee BS, Kim BG, Lee YS
Solid-Phase Peptide Library Synthesis on HiCore Resin for Screening Substrate Specificity of Brk Protein Tyrosine Kinase.
J Comb Chem. 2007 Dec 6; [Abstract]

Doi T, Inoue H, Tokita M, Watanabe J, Takahashi T
Sequential Palladium-Catalyzed Coupling Reactions on Solid-Phase.
J Comb Chem. 2007 Dec 6;
Six-types of palladium-catalyzed coupling, Mizoroki-Heck, Migita-Stille, Sonogashira, carbonylative esterification, carbonylative Stille, and carbonylative Sonogashira reactions, were performed on a polymer support. The above coupling reactions of m- and p-substituted aromatic rings, followed by carbonylative esterification with m- and p-substituted anisol derivatives were carried out in a combinatorial manner. Acid cleavage from the polymer-support provided the conjugated aromatic ring systems 1 and 2, which are the core parts of rodlike liquid crystals. [Abstract]

Fenniri H, Chun S, Terreau O, Bravo-Vasquez JP
Preparation and Infrared/Raman Classification of 630 Spectroscopically Encoded Styrene Copolymers.
J Comb Chem. 2007 Nov 21;
The barcoded resins (BCRs) were introduced recently as a platform for encoded combinatorial chemistry. One of the main challenges yet to be overcome is the demonstration that a large number of BCRs could be generated and classified with high confidence. Here, we describe the synthesis and classification of 630 polystyrene-based copolymers prepared from the combinatorial association of 15 spectroscopically active styrene monomers. Each of the 630 copolymers displayed a unique vibrational fingerprint (infrared and Raman), which was converted into a spectral vector. To each of the 630 copolymers, a vector of the known (reference) composition was assigned. Unknown (prediction) vectors were decoded using multivariate data analysis. From the inner product of the reference and prediction vectors, a correlation map comparing 396 900 copolymer pairs (630 x 630) was generated. In 100% of the cases, the highest correlation was obtained for polymer pairs in which the reference and prediction vectors correspond to copolymers prepared from identical styrene monomers, thus demonstrating the high reliability of this encoding strategy. We have also established that the spectroscopic barcodes generated from the Raman and infrared spectra are independent of the copolymers' morphology (beaded versus bulk polymers). Besides the demonstration of the generality of the polymer barcoding strategy, the analytical methods developed here could in principle be extended to the investigation of the composition and purity of any other synthetic polymer and biopolymer library, or even scaffold-based combinatorial libraries. [Abstract]

Marcucci E, Bayó-Puxan N, Tulla-Puche J, Spengler J, Albericio F
Cysteine-S-trityl a Key Derivative to Prepare N-Methyl Cysteines.
J Comb Chem. 2007 Nov 20;
S-Trt Cys are used as precursors for the synthesis of protected NMe-Cys. N-Methylation of Alloc-Cys(Trt)-OH and Boc-Cys(Trt)-OH gives the corresponding N-methylated derivatives in good yields and purities, which can be further derivatized in solution to obtain a myriad of S-protected derivatives. To further broaden the scope of this methodology, the N (alpha)-amino protecting group of the NMe- S-protected Cys can be replaced easily either on the solid phase (from the Alloc precursor) or in solution (from the Boc precursor). Thus, this convenient route allows us to obtain many different protected NMe-Cys, which were of limited accessibility until now. [Abstract]

Le Quement ST, Nielsen TE, Meldal M
Scaffold diversity through intramolecular cascade reactions of solid-supported cyclic N-acyliminium intermediates.
J Comb Chem. 2007 Nov-Dec;9(6):1060-72.
The solid-phase synthesis of pharmacologically interesting heterocycles is presented. The formation of a series of (5,5)-, (5,6)-, (6,5)-, and (6,6)-fused bicyclic ring systems was systematically studied by implementation of a common strategy involving N-acyliminium intermediates. These are highly reactive and transformed further in intramolecular cascade reactions with strong as well as weak C, N, S, and O-nucleophiles. The methodology was successfully applied to the conversion of peptidomimetics into constrained small molecule core structures, such as the hexahydropyrrolo[2,1- b][1,3]oxazines, generally with full control of diastereoselectivity (>20:1) and in purities above 90%. [Abstract]

Cavallaro CL, Harikrishnan LS, Chi F, Dodd D, Purandare A
Preparation of 2,7-Diaminosubstituted-[1,2,4]triazolo[1,5-a]pyrimidine-6-Carbonitriles by Solid-Phase Synthesis.
J Comb Chem. 2007 Nov 10; [Abstract]

Vaccaro HA, Zhao Z, Clader JW, Song L, Terracina G, Zhang L, Pissarnitski DA
Solution-Phase Parallel Synthesis of Carbamates as gamma-Secretase Inhibitors.
J Comb Chem. 2007 Nov 8;
A novel methodology for parallel liquid-phase synthesis of carbamates suitable for the preparation of sterically hindered molecules is disclosed. The alcohols are converted to 4-nitrophenylcarbonates, followed by the reaction with amines. Side product 4-nitrophenol and the unreacted excess amines are scavenged by appropriately chosen cleanup resins, selected among Amberlyst A26 (hydroxide form) and macroporous sulfonic acid (MP-TsOH) or polystyrene isocyanate (PS-NCO) and polystyrene benzaldehyde (PS-PhCHO) resins. As a part of a medicinal chemistry program directed toward finding gamma-secretase inhibitors as prospective drug candidates for Alzheimer's disease, a 6 x 24 library of carbamates was prepared. Out of 144 library members, 133 had a purity for the targeted compound of 80% or better. The prepared compounds were assessed in the gamma-secretase inhibition assay and demonstrated activity with IC 50 values in the range from 1 microM to 5 nM, with the activity of 7 compounds being better than 10 nM. [Abstract]

Benali O, Davies G, Deal M, Farrant E, Guthrie D, Holden J, Wheeler R
Fully Automated Open Access Platform for Rapid, Combined Serial Evaporation and Sample Reformatting.
J Comb Chem. 2007 Nov 3;
This paper reports a novel evaporator and its integration with an automated sample handling system to create a high throughput evaporation platform. The Vaportec V-10 evaporator uses a high speed rotation motor ( approximately 6000 rpm) to spin the vial containing a sample, creating a thin film of solvent which can be readily evaporated by the application of heat to the vial, while the consequent centrifugal force prevents "bumping". An intelligent algorithm controls pressure and temperature for optimum solvent removal conditions and end of run detection, critical for automation. The system allows the option of evaporation directly from a sample source vial, or alternatively, integrated liquid handling facilities provide the capability of transferring samples portionwise from a (large) source vial or bottle to a (small) daughter container, enabling efficient sample reformatting, with minimum user intervention. The open access system makes significant advances over current vacuum centrifugal evaporators in terms of evaporation rate and ease of automation. The evaporator's main features, the integration of robotics to provide automation, and examples of evaporation rates of a wide range of solvents from a variety of containers are described. [Abstract]

Yi JP, Fan ZG, Jiang ZW, Li WS, Zhou XP
High-throughput parallel reactor system for propylene oxidation catalyst investigation.
J Comb Chem. 2007 Nov-Dec;9(6):1053-9.
A high-throughput reactor system was designed for catalyst testing, which includes two important sections: the gas flow splitters and the parallel reactor. Each gas flow splitter could split one gas stream to 64 streams (8 x 8). The current system has two gas splitters that could feed two kinds of gases (from mass flow controllers) to a 64-channel (8 x 8) parallel fixed-bed reactor. The reactor is composed of tube connectors, a reactor tube array, a heating block, a product collector, and a temperature controller. The reactor system could test 64 catalysts simultaneously and give results, which are comparable with a regular single-channel microreactor. For the purpose of verifying the validity of the reactor system, propylene oxidation to prepare acrolein was used as the probing reaction. In order to analyze the reaction products, a high-throughput colorimetric diffusion-reflection imaging method was developed for the analysis of acrolein. By comparing the results from colorimetric diffusion-reflection imaging analysis with that from the traditional gas chromatography spectrometer with thermal conductivity detectors, a colorimetric diffusion-reflection imaging method was confirmed to be reliable and accurate in acrolein analysis. [Abstract]

Zhang CX, Tong HB, Yan CG
First soluble multipolymer MPEG-supported liquid-phase convergent synthesis of tripeptide Fmoc-GlyVal-GlyOH.
J Comb Chem. 2007 Nov-Dec;9(6):924-5. [Abstract]

Zimmermann V, Bräse S
Hartwig-Buchwald amination on solid supports: a novel access to a diverse set of 1H-benzotriazoles.
J Comb Chem. 2007 Nov-Dec;9(6):1114-37.
Hartwig-Buchwald amination reactions of bromo- and chloroarenes were performed on solid supports with triazene-linked arenes. Immobilized 2-haloarenes were treated with diverse primary amines and anilines at 100 degrees C under palladium catalysis to yield N-substituted 2-aminoarenes. The latter were alternatively formed through reaction of bromo- and chloroarenes with immobilized primary 2-aminobenzenes. Subsequent acidic cleavage furnished 1H-benzotriazoles in high purities. The two described routes allow a broad range of the substitution pattern of N-substituted 1H-benzotriazoles. [Abstract]

Gray BL, Schreiber SL
Skeletal diversity in small-molecule synthesis using ligand-controlled catalysis.
J Comb Chem. 2007 Nov-Dec;9(6):1028-35.
Two Pd-catalyzed reductive transformations of diynes tethered through a silyl ether linkage were developed, where the reaction outcomes were controlled solely by selection of phosphine ligand. We screened Pd precatalysts, ligands, and additives to optimize conditions selective either for reductive cyclization or hydrogenation of this substrate class. Sixteen silyl ether-tethered diynes were prepared and subjected to the best catalyst/ligand combinations for each pathway. Silacyclic dienes and silyl-tethered enyne products of these reactions were elaborated to densely substituted, stereochemically- and appendage-rich, bicyclic and tricyclic small molecules in 1-3 synthetic steps. These studies illustrate how small modifications to a transition-metal catalyst can be used to access a diverse set of small molecules, in a fashion analogous to biosynthetic pathways such as terpene biosynthesis, where minor changes to enzyme structure direct skeletal differentiation. [Abstract]

Koesdjojo MT, Rasmussen HT, Fermier AM, Patel P, Remcho VT
The development of a semiautomated procedure for the synthesis and screening of a large group of molecularly imprinted polymers.
J Comb Chem. 2007 Nov-Dec;9(6):929-34.
A method for synthesis and evaluation of molecularly imprinted polymers (MIPs) on a semiautomated miniature scale is reported. This technique combines molecular imprinting with the combinatorial chemistry approach, allowing rapid screening and optimizations of libraries of MIPs. The polymers were prepared and evaluated in situ by rebinding utilizing powder dispensing and liquid handling systems. MIPs were prepared by a combinatorial approach using methacrylic acid (MAA), 4-vinylpyridine (4-VP), acrylamide, and styrene as functional monomers, and acetonitrile and toluene as porogenic solvents. A drug substance having aromatic, hydroxyl, -O-CONH2 functional groups was selected as the template molecule for this study. The MIP library results demonstrated that the polymer prepared with MAA as functional monomer shows the strongest binding affinity, and therefore, is preferred for the preparation of this particular template molecule. Due to the low consumption of reagents, and more importantly, the demonstrated ability of this method to effectively identify optimal imprinting conditions, this small-scale combinatorial protocol is well suited for fast and efficient screening and optimizations of MIPs. [Abstract]

Johnson PM, Stansbury JW, Bowman CN
Alkyl chain length effects on copolymerization kinetics of a monoacrylate with hexanediol diacrylate.
J Comb Chem. 2007 Nov-Dec;9(6):1149-56.
Copolymerizations of hexanediol diacrylate with three monoacrylates were analyzed using high-throughput conversion analysis to elucidate the effects of varying alkyl pendant groups at different compositions. Each analyzed copolymerization system contained hexanediol diacrylate (HDDA), and copolymerizations with 30-60 wt % monoacrylate reached nearly complete conversion after 30 s of exposure time. For higher amounts of monoacrylate, the photopolymerization kinetics of the hexyl acrylate (HA) copolymerization were significantly slower than the copolymerization with either ethylhexyl acrylate (EHA) or dodecyl acrylate (DDA). With 20 wt % HDDA, conversion at 30 s with a comonomer of HA was 62+/-3%, as compared to 76+/-3% and 84+/-3% when copolymerized with EHA and DDA, respectively. Model kinetic parameters were estimated for all four monomer systems, with HDDA monomer parameters found to be within the same error when estimated from any of the copolymerizations. With kinetic parameters for each monomer, comparison maps showing the difference in conversion between two copolymerizations were generated. These comparison maps allow for an assessment of two comonomer systems to determine the optimal photopolymerization conditions. Slower photopolymerization kinetics for HA occur at nearly all compositions containing monoacrylate, with the largest reduction occurring between 20 and 40 wt % monoacrylate. [Abstract]

Tu S, Li C, Li G, Cao L, Shao Q, Zhou D, Jiang B, Zhou J, Xia M
Microwave-assisted combinatorial synthesis of polysubstituent imidazo[1,2-a]quinoline, pyrimido[1,2-a]quinoline and quinolino[1,2-a]quinazoline derivatives.
J Comb Chem. 2007 Nov-Dec;9(6):1144-8.
A series of unusual fused heterocyclic compound derivatives, consisting of a pyridine and a imidazole or pyrimidine core, with a bridgehead nitrogen, were successfully synthesized by a microwave-assisted, three-component domino reaction of aldehydes, enaminones, and malononnitrile. In this one-pot reaction, up to five new bonds were formed accompanied by generating the lactam group. This method has the advantages of short synthetic route, operational simplicity, increased safety for small-scale high-speed synthesis, and minimal environment impact. [Abstract]

Li L, Wang Z, Chen Y, Yuan Y, Liu G
Design and synthesis of novel tricycles based on 4H-benzo[1,4]thiazin-3-one and 1,1-dioxo-1,4-dihydro-2H-1lambda6-benzo[1,4]thiazin-3-one.
J Comb Chem. 2007 Nov-Dec;9(6):959-72.
This paper reports our recent efforts to develop novel tricycles based on 4H-benzo[1,4]thiazin-3-one ( 2) and 1,1-dioxo-1,4-dihydro-2H-1lambda(6)-benzo[1,4]thiazin-3-one (3) using 1,5-difluoro-2,4-dinitrobenzene (1). All of these tricycles integrate two privileged structures into one skeleton, including 3,8-dihydro-5-thia-1,3,8-triaza-cyclopenta[b]naphthalene-7-one (4, 10, 12), 5,5-dioxo-3,5,6,8-tetrahydro-5lambda(6)-thia-1,3,8-triaza-cyclopenta[b]naphthalene-7-one (5, 11), 3,8-dihydro-5-thia-1,2,3,8-tetraaza-cyclopenta[b]naphthalene-7-one (6), 5,5-dioxo-3,5,6,8-tetrahydro-5lambda(6)-thia-1,2,3,8-tetraaza-cyclopenta[b]naphthalene-7-one (7), 3,8-dihydro-1H-5-thia-1,3,8-triaza-cyclopenta[b]naphthalene-2,7-dione (8), and 5,5-dioxo-3,5,6,8-tetrahydro-1H-5lambda(6)-thia-1,3,8-triaza-cyclopenta[b]naphthalene-2,7-dione (9). A typical library of scaffold 5 was synthesized in a parallel solution-phase manner and analyzed by HPLC-UV-MS or HPLC-UV-ELSD method. [Abstract]

Prakash GK, Weber C, Chacko S, Olah GA
New solid-phase bound electrophilic difluoromethylating reagent.
J Comb Chem. 2007 Nov-Dec;9(6):920-3. [Abstract]

Broussy S, Waldmann H
Solid phase synthesis of highly substituted tetrahydropyrans by tandem ene-reaction/intramolecular Sakurai cyclization.
J Comb Chem. 2007 Nov-Dec;9(6):1138-43.
A solid-phase tandem ene-reaction/intramolecular Sakurai cyclization sequence has been developed to synthesize highly substituted tetrahydropyran derivatives in two steps from aldehydes and with complete control of the relative stereochemistry of the three newly formed stereocenters. The compounds are obtained with high purity after release from the solid support and can be easily isolated in multimilligram amounts. Moreover, we have shown that asymmetric induction is possible on solid phase and that enantiomerically pure tetrahydropyrans containing four stereocenters can be effectively synthesized with this method. [Abstract]

Zhang A, Ding C, Cheng C, Yao Q
Convenient synthesis of 2,7-naphthyridine Lophocladines A and B and their analogues.
J Comb Chem. 2007 Nov-Dec;9(6):916-9. [Abstract]

Kofoed J, Reymond JL
A general method for designing combinatorial peptide libraries decodable by amino acid analysis.
J Comb Chem. 2007 Nov-Dec;9(6):1046-52.
Herein we describe an algorithm for designing combinatorial peptide libraries for split-and-mix synthesis on solid support that are decodable by amino acid analysis (AAA) of the beads. AAA is a standard service analysis available in most biochemical laboratories, and it allows one to control the quality of the peptide on each bead, an important feature that is missing from most library decoding protocols. In the algorithm, each AA is assigned to two variable positions in the sequence grouped in a "unique pair". This arrangement limits sequence design because both the number of unique pairs U (setting the maximum number of variable AA) and the maximum number S of different AA per variable position depend on the peptide length N (U=N(N-1)/2), S=N-1). The method is therefore only suitable for focused libraries. An application example is shown for the selection of peptides with N-terminal proline or hydroxyproline catalyzing an aldol reaction from a combinatorial library of 65536 octapeptides. A simple enumeration program is available to help design combinatorial libraries decodable by amino acid analysis. The method applies to linear and cyclic peptides, can be used for nonnatural building blocks, including beta-amino acids, and should help to explore the vast chemistry of linear and cyclic peptide for catalysis and bioactivity. [Abstract]

Zhao HY, Liu G
Solution-phase parallel synthesis of diverse 1,5-benzodiazepin-2-ones.
J Comb Chem. 2007 Nov-Dec;9(6):1164-76.
A practical and efficient parallel method has been developed for the synthesis of 1,5-benzodiazepin-2-ones with a large variety of substituents at the 3-, 4-, 5-, 7-, and 8-positions using 1,5-difluoro-2,4-dinitrobenzene as the starting material. All the reactions involved here are highly effective in giving the desired products under mild conditions. [Abstract]

Laustsen LS, Sams CK
Parallel synthesis of 1,3-dihydro-1,4-benzodiazepine-2-ones employing catch and release.
J Comb Chem. 2007 Nov-Dec;9(6):1094-103.
An efficient solid-phase method has been developed for the parallel synthesis of 1,3-dihydro-1,4-benzodiazepine-2-one derivatives. A key step in this procedure involves catching crude 2-aminobenzoimine products 4 on an amino acid Wang resin 10. Mild acidic conditions then promote a ring closure and in the same step cleavage from the resin to give pure benzodiazepine products 12. The 2-aminobenzoimines 4 can be synthesized from either 2-aminobenzonitriles 1 and Grignard reagents 2 or from iodoanilines 5 and nitriles 7 allowing a range of diversification. Further diversification can be introduced to the benzodiazepine products by N-alkylation promoted by a resin bound base and alkylating agents 13. [Abstract]

Lin MJ, Zhang W, Sun CM
Fluorous and traceless synthesis of substituted indole alkaloids.
J Comb Chem. 2007 Nov-Dec;9(6):951-8.
The fluorous traceless synthesis of substituted indole alkaloids is carried out first by attaching the 3-(perfluorooctyl)propanol with Boc protected L-tryptophan. The reaction of perfluoroalkyl (Rfh)-tagged tryptophan esters with various aldehydes undergoes Pictet-Spengler reaction to give cis and trans stereoisomers of tetrahydro-beta-carbolines. The nucleophilic addition of the piperidine nitrogen across various isocyanates is followed by the cyclization of ureas and simultaneous rupture of the fluorous tag to afford the hydantoin ring fused tetrahydro-beta-carbolines. All the fluorous-tag compounds are purified by solid-phase extraction (SPE) through Fluoro Flash cartridges. [Abstract]