Chemistry - A European Journal

Cover image for Vol. 13 Issue 22

July 27, 2007

Volume 13, Issue 22

Pages 6277–6517

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    1. Cover Picture: Aromaticity: Molecular-Orbital Picture of an Intuitive Concept (Chem. Eur. J. 22/2007) (page 6277)

      Simon C. A. H. Pierrefixe and F. Matthias Bickelhaupt

      Version of Record online: 17 JUL 2007 | DOI: 10.1002/chem.200790078

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      π Electrons decide about aromatic delocalization versus antiaromatic localization of the double bonds in benzene and cyclobutadiene, respectively. In their Full Paper on page 6321 ff., S. C. A. H. Pierrefixe and F. M. Bickelhaupt present a molecular-orbital (MO) model of aromaticity that augments the modern valence-bond picture available.

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  3. Corrigenda

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      Silyl Anions or Silylenoids?—A DFT Study of Silyllithium Compounds with π-Donating Substituents (page 6286)

      Michaela Flock and Christoph Marschner

      Version of Record online: 17 JUL 2007 | DOI: 10.1002/chem.200790083

      This article corrects:

      Silyl Anions or Silylenoids?—A DFT Study of Silyllithium Compounds with π-Donating Substituents

      Vol. 11, Issue 16, 4635–4642, Version of Record online: 15 JUN 2005

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  5. Concept

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    1. Heavy Grignard Reagents: Challenges and Possibilities of Aryl Alkaline Earth Metal Compounds (pages 6292–6306)

      Matthias Westerhausen, Martin Gärtner, Reinald Fischer, Jens Langer, Lian Yu and Markus Reiher

      Version of Record online: 19 JUN 2007 | DOI: 10.1002/chem.200700558

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      The challenges of preparing aryl compounds of the heavy alkaline earth metals are overcome and applications are in the process of being developed. Now, it is worthwhile to consider organic CaI compounds (an example of which is shown here: Ca orange, C blue, H grey) as active reagents.

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    1. Fully Fluorinated Imidodiphosphinate Shells for Visible- and NIR-Emitting Lanthanides: Hitherto Unexpected Effects of Sensitizer Fluorination on Lanthanide Emission Properties (pages 6308–6320)

      Peter B. Glover, Andrew P. Bassett, Peter Nockemann, Benson M. Kariuki, Rik Van Deun and Zoe Pikramenou

      Version of Record online: 15 JUN 2007 | DOI: 10.1002/chem.200700087

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      C[BOND]F substitution with care! Fluorinated ligand shells are reported that give rise to supreme NIR emission in lanthanide complexes, but are not so innocent for emission in the visible region (see illustration).

    2. Aromaticity: Molecular-Orbital Picture of an Intuitive Concept (pages 6321–6328)

      Simon C. A. H. Pierrefixe and F. Matthias Bickelhaupt

      Version of Record online: 19 JUN 2007 | DOI: 10.1002/chem.200700206

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      π Electrons decide: We present a molecular-orbital (MO) model of aromaticity that augments the modern valence-bond (VB) picture developed by Shaik and Hiberty. The propensity of the π electrons is always to localize double bonds against the delocalizing force of the σ electrons. Our MO model explains, through simple orbital-overlap considerations, why this is so and why the π system nevertheless decides about aromatic delocalization versus antiaromatic localization of the double bonds (see figure).

      Corrected by:

      Corrigendum: Aromaticity: Molecular-Orbital Picture of an Intuitive Concept

      Vol. 13, Issue 30, 8371, Version of Record online: 2 OCT 2007

    3. Highly Reduced, Polyoxo(alkoxo)vanadium(III/IV) Clusters (pages 6329–6338)

      Ian S. Tidmarsh, Rebecca H. Laye, Paul R. Brearley, Maheswaran Shanmugam, E. Carolina Sañudo, Lorenzo Sorace, Andrea Caneschi and Eric J. L. McInnes

      Version of Record online: 22 MAY 2007 | DOI: 10.1002/chem.200700247

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      High nuclearity, but low oxidation states: A family of high-nuclearity vanadium(III/IV/V) clusters (an example of which is shown here; green: vanadium; red: oxygen; grey: carbon) are reported, analogous to the polyoxo(alkoxo)vanadates but in uniquely low oxidation states.

    4. A Concerted Approach for the Determination of Molecular Conformation in Ordered and Disordered Materials (pages 6339–6350)

      Jan Sehnert and Jürgen Senker

      Version of Record online: 11 MAY 2007 | DOI: 10.1002/chem.200601726

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      Local order in a molecular glass: Unraveling conformational distributions in various phases of triphenylphosphite (TPP); the combination of NMR spectroscopy (left), DFT structure models (bottom) and ab inito spectra simulation (right).

    5. Gold-Catalyzed Cyanosilylation Reaction: Homogeneous and Heterogeneous Pathways (pages 6351–6358)

      Woo Kyung Cho, Jungkyu K. Lee, Sung Min Kang, Young Shik Chi, Hee-Seung Lee and Insung S. Choi

      Version of Record online: 11 MAY 2007 | DOI: 10.1002/chem.200601791

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      Good as gold: Gold nanoparticles (AuNPs) were found to be catalytically active for a C[BOND]C bond-forming reaction, the cyanosilylation of aldehydes. The AuNP-catalyzed cyanosilylation proceeded smoothly at room temperature with 0.2 wt % loading of AuNPs (see scheme; TMS: trimethylsilyl). Detailed experiments indicate that the reaction occurs by a combined pathway of heterogeneous and homogeneous catalysis.

    6. Gold Nanoparticles in Organic Capsules: A Supramolecular Assembly of Gold Nanoparticles and Cucurbituril (pages 6359–6364)

      Avelino Corma, Hermenegildo García, Pedro Montes-Navajas, Ana Primo, José Juan Calvino and Susana Trasobares

      Version of Record online: 11 MAY 2007 | DOI: 10.1002/chem.200601900

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      Capturing gold: Gold nanoparticles (≤1.0 nm) were encapsulated in cucurbit[7]uril (see figure). The resulting supramolecular assembly shows shape selectivity towards organic probes.

    7. Synthetic Models of the Active Site of Cytochrome c Oxidase: Influence of Tridentate or Tetradentate Copper Chelates Bearing a His[BOND]Tyr Linkage Mimic on Dioxygen Adduct Formation by Heme/Cu Complexes (pages 6365–6378)

      Jin-Gang Liu, Yoshinori Naruta and Fumito Tani

      Version of Record online: 14 MAY 2007 | DOI: 10.1002/chem.200601884

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      Synthetic enzyme models: Two synthetic models (for example, 1 and 2) of the active site of cytochrome c oxidase have been designed and synthesized. The two models showed distinct oxygenation reactions at low temperature, which have been investigated in further detail.

    8. Stabilization of Parallel Triplexes by Twisted Intercalating Nucleic Acids (TINAs) Incorporating 1,2,3-Triazole Units and Prepared by Microwave-Accelerated Click Chemistry (pages 6379–6386)

      Imrich Géci, Vyacheslav V. Filichev and Erik B. Pedersen

      Version of Record online: 14 MAY 2007 | DOI: 10.1002/chem.200700053

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      Postsynthetic click reactions on fully deprotected oligonucleotides: Twisted intercalating nucleic acids (TINAs) prepared postsynthetically from unprotected oligonucleotides with the aid of microwave-accelerated click chemistry (see figure) formed stable Hoogsteen-type triplexes.

    9. Understanding Adsorption and Interactions of Alkane Isomer Mixtures in Isoreticular Metal–Organic Frameworks (pages 6387–6396)

      Li Zhang, Qi Wang, Tao Wu and Ying-Chun Liu

      Version of Record online: 16 MAY 2007 | DOI: 10.1002/chem.200700205

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      The preferential adsorption sites for alkanes in the isoreticular metal–organic frameworks IRMOF-1 and IRMOF-6 are the Zn4O clusters rather than the organic linkers according to calculations of the framework/adsorbate interactions. The interactions become stronger with increasing proximity to the Zn4O cluster, and it is more difficult for branched alkane molecules to approach the Zn4O cluster closely owing to the strong repulsive interaction caused by spatial hindrance, as illustrated for n-butane and 2-methylpropane.

    10. The First Direct Enzymatic Hydrolysis of Alicyclic β-Amino Esters: A Route to Enantiopure cis and trans β-Amino Acids (pages 6397–6401)

      Enikõ Forró and Ferenc Fülöp

      Version of Record online: 11 MAY 2007 | DOI: 10.1002/chem.200700257

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      Enzymes: Lipase-catalyzed enantioselective hydrolysis of β-amino esters in organic media (see scheme) leads to cyclic cis and trans β-amino acid enantiomers. When the Candida antarctica lipase B-catalyzed reactions were performed with H2O in iPr2O at 65 °C, high enantioselectivities (E usually >100) were observed. The present method was successfully used for the synthesis of cispentacin.

    11. Electrostatic Attachment of Gold and Poly(lactic acid) Nanoparticles onto ω-Aminoalkanoic Acid Self-Assembled Monolayers on 316L Stainless Steel (pages 6402–6407)

      Galit Shustak, Yulia Shaulov, Abraham J. Domb and Daniel Mandler

      Version of Record online: 16 MAY 2007 | DOI: 10.1002/chem.200601559

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      Gold plated: Gold and poly(lactic acid) nanoparticles were used to coat 316L stainless steel by means of electrostatic interactions (see figure). 12-Aminodecanoic acid electrochemically self-assembles to form a positively charged monolayer on stainless steel before the negatively charged nanoparticles are bound to the surface through electrostatic interactions.

    12. Structure of Ag Clusters Grown on Fs-Defect Sites of an MgO(1 0 0) Surface (pages 6408–6418)

      Giovanni Barcaro, Edoardo Aprà and Alessandro Fortunelli

      Version of Record online: 11 MAY 2007 | DOI: 10.1002/chem.200601796

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      A structural transition induced by the defect from noncrystalline fivefold symmetric structures to distorted face-centered cubic structures is found for AgN clusters adsorbed on an oxygen vacancy of an MgO(1 0 0) terrace at N=10 (see scheme).

    13. Highly Diastereoselective Lithiation and Substitution of an (S)-Prolinyl Thiocarbamate via Sterically Homogeneous Lithio(thiocarbamate): Synthesis of Enantiomerically Pure Prolinethiols (pages 6419–6429)

      Ravindra P. Sonawane, Christian Mück-Lichtenfeld, Roland Fröhlich, Klaus Bergander and Dieter Hoppe

      Version of Record online: 14 MAY 2007 | DOI: 10.1002/chem.200601853

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      A stereohomogeneous α-thiocarbanion: An (S)-prolinol-derived thiocarbamate 1 is deprotonated with high diastereoselectivity to form the (S,S)-lithium compound 2, which is substituted by several electrophiles with retention of the configuration.

    14. Chemical Anisotropies of Carbon Nanotubes and Fullerenes Caused by the Curvature Directivity (pages 6430–6436)

      Junqian Li, Guixiao Jia and Yongfan Zhang

      Version of Record online: 11 MAY 2007 | DOI: 10.1002/chem.200700067

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      Following the curves: The chemical reactivity of carbon nanotubes and fullerenes can be well explained by the concept of directional curvature KD (see figure), which covers the mean and directional properties of the curvatures of different carbon frameworks.

    15. [(NHC)AuI]-Catalyzed Formation of Conjugated Enones and Enals: An Experimental and Computational Study (pages 6437–6451)

      Nicolas Marion, Peter Carlqvist, Ronan Gealageas, Pierre de Frémont, Feliu Maseras and Steven P. Nolan

      Version of Record online: 25 MAY 2007 | DOI: 10.1002/chem.200700134

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      [(NHC)AuI] complexes catalyze the formation of α,β-unsaturated carbonyl compounds (enones and enals) from propargylic acetates in the presence of water. Based on calculations, a full catalytic cycle is proposed featuring an unprecedented transfer of the OH moiety bound to the gold center to the C[TRIPLE BOND]C bond (see scheme).

    16. Microwave-Assisted Transition-Metal-Catalyzed Synthesis of N-Shifted and Ring-Expanded Buflavine Analogues (pages 6452–6460)

      Prasad Appukkuttan, Wim Dehaen and Erik Van der Eycken

      Version of Record online: 16 MAY 2007 | DOI: 10.1002/chem.200700177

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      Buflavine analogues: The construction of the medium-sized ring system in N-shifted and ring-expanded buflavine analogues was achieved by using Suzuki–Miyaura biaryl coupling and ring-opening metathesis reactions as the key steps. The combination of the second-generation Grubbs catalyst and microwave irradiation was found to be highly useful in generating the otherwise difficult to obtain medium-sized ring system.

    17. A Sol–Gel-Modified Poly(methyl methacrylate) Electrophoresis Microchip with a Hydrophilic Channel Wall (pages 6461–6467)

      Gang Chen, Xuejiao Xu, Yuehe Lin and Joseph Wang

      Version of Record online: 16 MAY 2007 | DOI: 10.1002/chem.200700242

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      Isolated on a chip: A sol–gel method was employed to fabricate a poly(methyl methacrylate) (PMMA) electrophoresis microchip that contains a hydrophilic channel wall. The performance of the microchip was demonstrated by its ability to separate purines. The oblique views of a drop of water on the surfaces of sol–gel modified and pristine PMMA are shown in the figure to demonstrate their differing wettabilities.

    18. Cucurbit[8]uril/Cucurbit[7]uril Controlled Off/On Fluorescence of the Acridizinium and 9-Aminoacridizinium Cations in Aqueous Solution (pages 6468–6473)

      Ruibing Wang, Lina Yuan, Heiko Ihmels and Donal H. Macartney

      Version of Record online: 16 MAY 2007 | DOI: 10.1002/chem.200700199

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      Quenched by the host: The fluorescence of acridizinium and 9-aminoacridizinium cations is turned off, and then on again, by the sequential addition of cucurbit[8]uril and cucurbit[7]uril hosts in aqueous solutions (see figure).

    19. On the Coherent Description of Diffusion-Influenced Fluorescence Quenching Experiments (pages 6474–6483)

      Arnulf Rosspeintner, Daniel R. Kattnig, Gonzalo Angulo, Stephan Landgraf, Günter Grampp and Alejandro Cuetos

      Version of Record online: 10 MAY 2007 | DOI: 10.1002/chem.200700106

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      Remoteness of electron transfer, solvent structure and distance-dependent diffusion coefficients are crucial to consistently describe the huge deviations from linearity observed in Stern–Volmer plots (see figure) at varying viscosities.

    20. Highly Efficient Synthesis of Stereodefined Multisubstituted 1,4-Dicyano- and 1-Cyano-1,3-butadienes and Their Reactions with Organolithium Reagents (pages 6484–6494)

      Congyang Wang, Chao Wang, Qifeng Wang, Zhihui Wang, Hui Sun, Xiangyu Guo and Zhenfeng Xi

      Version of Record online: 11 MAY 2007 | DOI: 10.1002/chem.200700028

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      New building blocks: Multi-substituted stereodefined 1-cyano- and 1,4-dicyano-1,3-dienes are prepared from readily available starting materials and CuCN in yields of 81–98 % with excellent stereoselectivity. The application of these unsaturated nitriles is demonstrated by their interesting and useful reactions with organolithium reagents (see scheme). An unprecedented reduction–cyclization process occurs when these unsaturated nitriles are treated with LiAlH4.

    21. Eutectic-Based Ionic Liquids with Metal-Containing Anions and Cations (pages 6495–6501)

      Andrew P. Abbott, John C. Barron, Karl S. Ryder and David Wilson

      Version of Record online: 4 MAY 2007 | DOI: 10.1002/chem.200601738

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      Zinc chloride can disproportionate to give ZnCl3 (right-hand side) and ZnCl+ when mixed with suitable donor molecules, for example, acetamide, urea or ethylene glycol. This gives rise to a new class of ionic liquids, such as depicted on the left-hand side ([ZnCl(urea)]+).

    22. Low-Temperature Adsorption/Storage of Hydrogen on FAU, MFI, and MOR Zeolites with Various Si/Al Ratios: Effect of Electrostatic Fields and Pore Structures (pages 6502–6507)

      Sung Hwa Jhung, Ji Woong Yoon, Ji Sun Lee and Jong-San Chang

      Version of Record online: 11 MAY 2007 | DOI: 10.1002/chem.200700148

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      Hydrogen adsorption on zeolites: Irrespective of the zeolite structure, the adsorption capacity, isosteric heat of adsorption (−ΔHads), surface coverage, and micropore occupancy increase when increasing the aluminum content of a zeolite (see figure). For zeolites with similar aluminum contents, the adsorption capacities are in the order of mordenite>ZSM-5>faujasite. Zeolites with strong electrostatic fields and narrow pores without intersections are beneficial for high hydrogen uptake.

    23. Preparation of a Polymer-Supported Fluorene-Based Receptor for Quantitative and Efficient Binding of Silver Cations (pages 6508–6513)

      Vincent J. Chebny, Moloy Banerjee and Rajendra Rathore

      Version of Record online: 16 MAY 2007 | DOI: 10.1002/chem.200601776

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      A simple C[BOND]C bond rotation (see picture) was found to enable a polymer-supported fluorene-p-xylene-based receptor to adopt a π-prismand-like conformation; this allowed it to bind quantitatively one single silver cation per receptor site with remarkable efficiency. The synthesis and binding studies of the receptor are described.

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      Preview: Chem. Eur. J. 23/2007 (page 6517)

      Version of Record online: 17 JUL 2007 | DOI: 10.1002/chem.200790082

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