Chemistry - A European Journal

Cover image for Vol. 13 Issue 24

August 17, 2007

Volume 13, Issue 24

Pages 6769–7023

  1. Cover Picture

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    1. Cover Picture: Improved Cyclodextrin-Based Receptors for Camptothecin by Inverse Virtual Screening (Chem. Eur. J. 24/2007) (page 6769)

      Andreas Steffen, Carolin Thiele, Simon Tietze, Christian Strassnig, Andreas Kämper, Thomas Lengauer, Gerhard Wenz and Joannis Apostolakis

      Article first published online: 7 AUG 2007 | DOI: 10.1002/chem.200790088

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      Design of a synthetic receptor for a given ligand, in this case the anti-cancer drug camptothecin, is generally a very tedious task. Many receptor candidates have to be synthesized and checked to find a few hits with high affinities. Therefore it is more efficient to perform the most part of receptor screening in the virtual space of a computer as visualized on the cover picture. In their Full Paper on page 6801 ff., G. Wenz, J. Apostolakis et al. demonstrate that the resulting top-ranking candidates, derivatives of β-cyclodextrin, indeed exhibit exceptional binding potential for camptothecin and are promising excipients for drug delivery.

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  3. News

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  4. Concept

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    1. Recent Advances in the Benzannulation of Substituted 3-Alkoxycarbonyl-3,5-hexadienoic Acids and 3-Alkoxycarbonylhex-3-en-5-ynoic Acids to Polysubstituted Aromatics (pages 6782–6791)

      Stefano Serra, Claudio Fuganti and Elisabetta Brenna

      Article first published online: 17 JUL 2007 | DOI: 10.1002/chem.200700735

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      Polysubstituted aromatics: The specific preparation of different polysubstituted aromatics can be achieved by the benzannulation reaction of substituted hexadienoic acids precursors. The process is very flexible, and can be applied to the regiospecific preparation of oligoaryls, naphthalenes, ring-fused heterocycles, chiral tetrahydronaphthalenes, C-aryl-glycosides and many natural products of different structure (some examples are illustrated here).

  5. Full Papers

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    1. Constitutional Self-Organization of Adenine–Uracil-Derived Hybrid Materials (pages 6792–6800)

      Carole Arnal-Hérault, Mihai Barboiu, Andreea Pasc, Mathieu Michau, Pascal Perriat and Arie van der Lee

      Article first published online: 17 JUL 2007 | DOI: 10.1002/chem.200700739

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      Dynamic polyfunctional diversity: The formation and the interconversion of hydrogen-bond architectures derived from the alkoxysilane adenine (A) and uracil (U) nucleobase precursors that are subsequently fixed in the hybrid organic–inorganic materials (M) by means of a sol–gel transcription process is described.

    2. Improved Cyclodextrin-Based Receptors for Camptothecin by Inverse Virtual Screening (pages 6801–6809)

      Andreas Steffen, Carolin Thiele, Simon Tietze, Christian Strassnig, Andreas Kämper, Thomas Lengauer, Gerhard Wenz and Joannis Apostolakis

      Article first published online: 3 JUL 2007 | DOI: 10.1002/chem.200700661

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      High-throughput screening in silico! High-throughput docking calculations have been used to select receptors for the anti-cancer drug camptothecin from a virtual library of cyclodextrin derivatives. The top-ranking candidates indeed showed exceptional binding potential for camptothecin (an example is shown here) and are interesting excipients for drug delivery.

    3. Ligand and Substrate Effects in Gas-Phase Reactions of NiX+/RH Couples (X=F, Cl, Br, I; R=CH3, C2H5, nC3H7, nC4H9) (pages 6810–6816)

      Maria Schlangen, Detlef Schröder and Helmut Schwarz

      Article first published online: 25 JUN 2007 | DOI: 10.1002/chem.200700506

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      Activate and transfer! Both the ligand X and the substrate RH control the competitive bond activations of saturated hydrocarbons by gaseous nickel cations NiX+ (see scheme). Labeling experiments reveal unprecedentedly large preferences for secondary C[BOND]H bond activation.

    4. Choline-Derivative-Based Ionic Liquids (pages 6817–6827)

      Juliusz Pernak, Anna Syguda, Ilona Mirska, Anna Pernak, Jan Nawrot, Aleksandra Pra̧dzyńska, Scott T. Griffin and Robin D. Rogers

      Article first published online: 30 MAY 2007 | DOI: 10.1002/chem.200700285

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      Ionic liquids as insect feeding deterrents, soft tissue fixatives, and blood preservatives: Choline-derivative-based ionic liquids (depicted) have been prepared, their physical properties and crystal structures have been determined, and the antimicrobial activities of the hydrophilic acesulfamate-based ILs have been measured. Quaternary ammonium acesulfamates have been shown to be insect feeding deterrents (one example shown), opening up a new generation of synthetic deterrents based on ionic liquids.

    5. Towards a Rational Design of Ruthenium CO2 Hydrogenation Catalysts by Ab Initio Metadynamics (pages 6828–6840)

      Atsushi Urakawa, Marcella Iannuzzi, Jürg Hutter and Alfons Baiker

      Article first published online: 13 JUN 2007 | DOI: 10.1002/chem.200700254

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      Metadynamic insights: The rate-limiting step of ruthenium-catalyzed CO2 hydrogenation has been clarified by elucidating complete reaction pathways and intermediates by ab initio metadynamics (see figure). The insight gained correlates well with the ligand effects observed experimentally.

    6. The Stuffed Framework Structure of SrP2N4: Challenges to Synthesis and Crystal Structure Determination (pages 6841–6852)

      Friedrich W. Karau, Lena Seyfarth, Oliver Oeckler, Jürgen Senker, Kai Landskron and Wolfgang Schnick

      Article first published online: 13 JUN 2007 | DOI: 10.1002/chem.200700216

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      A complementary approach employing neutron, synchrotron, and X-ray powder diffraction, electron microscopy, and solid-state NMR techniques enabled the elucidation of the complex structure and superstructure of the novel nitridophosphate SrP2N4 (see picture).

    7. Discotic Liquid-Crystalline Materials Based on Porphycenes: A Mesogenic Metalloporphycene–Tetracyanoquinodimethane (TCNQ) Adduct (pages 6853–6863)

      Marcin Stępień, Bertrand Donnio and Jonathan L. Sessler

      Article first published online: 14 JUN 2007 | DOI: 10.1002/chem.200700125

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      Mesogenic porphyrin isomers: New liquid crystalline materials may be prepared by using the quintessential porphyrin isomer, porphycene, as the central core. A particularly stable mesophase is formed in the presence of the electron-acceptor tetracyanoquinodimethane (TCNQ).

    8. Artificial Ditopic Arg-Gly-Asp (RGD) Receptors (pages 6864–6873)

      Carsten Schmuck, Daniel Rupprecht, Matthias Junkers and Thomas Schrader

      Article first published online: 12 JUN 2007 | DOI: 10.1002/chem.200601821

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      Two attachments are better than one: Covalent fusion of two artificial recognition motifs for arginine and aspartate through a rigid aromatic spacer allows selective binding of the Ac-RGD-NH2 (RGD=Arg-Gly-Asp) tripeptide over other tripeptides, even in buffered water. The model shows the complex between the artificial receptor and the Ac-RGD-NH2 tripeptide.

    9. Bis-alkynyl Diruthenium Compounds with Built-in Electronic Asymmetry: Toward an Organometallic Aviram–Ratner Diode (pages 6874–6882)

      Jie-Wen Ying, Antoinette Cordova, Tony Y. Ren, Guo-Lin Xu and Tong Ren

      Article first published online: 6 JUL 2007 | DOI: 10.1002/chem.200700655

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      Single-molecule rectification: A strategy to prepare unsymmetric diruthenium bis-alkynyl compounds has been developed, and the push-pull electron asymmetry has been probed by voltammetric studies; the possibility of electrical rectification along the alknyl–Ru2–alkynyl backbone is discussed (see figure).

    10. Mechanisms for the Dehydrogenation of Alkanes on Platinum: Insights Gained from the Reactivity of Gaseous Cluster Cations, Ptn+n=1–21 (pages 6883–6890)

      Christian Adlhart and Einar Uggerud

      Article first published online: 31 MAY 2007 | DOI: 10.1002/chem.200700501

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      Platinum favors alpha: Gase-phase reactions of size-selected platinum cluster cations with hydrocarbons reveal a preference for α-hydrogen atoms upon dihydrogen elimination (see scheme). These observations are in strong contrast to rhodium, which favors 1,2-elimination and explains why platinum is reactive towards methane whilst rhodium is not.

    11. Self-Assembly of Nanosize Coordination Cages on Si(100) Surfaces (pages 6891–6898)

      Marco Busi, Marco Laurenti, Guglielmo G. Condorelli, Alessandro Motta, Maria Favazza, Ignazio L. Fragalà, Marco Montalti, Luca Prodi and Enrico Dalcanale

      Article first published online: 30 MAY 2007 | DOI: 10.1002/chem.200700496

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      Nanoscale molecular containers on silicon: Bottom-up fabrication of 3D organic nanostructures on Si(100) surfaces has been achieved through metal-directed self-assembly by using alternately designed cavitand ligands. Formation and distribution on the Si surface of the coordination cages (see picture) is supported by XPS (X-ray photoelectron spectroscopy), AFM (atomic force microscopy), and fluorescence spectroscopy.

    12. Atom-Transfer Radical Addition (ATRA) and Cyclization (ATRC) Reactions Catalyzed by a Mixture of [RuCl2Cp*(PPh3)] and Magnesium (pages 6899–6907)

      Katrin Thommes, Burçak Içli, Rosario Scopelliti and Kay Severin

      Article first published online: 4 JUN 2007 | DOI: 10.1002/chem.200700442

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      Radical reactions: A combined catalyst system of the Ru complex [RuCl2Cp*(PPh3)] (Cp*: pentamethylcyclopentadienyl) with magnesium allows atom-transfer radical addition (ATRA) and cyclization (ATRC) reactions to be performed with exceptional efficiency under mild conditions (see scheme).

    13. Ion- and Atom-Leaching Mechanisms from Palladium Nanoparticles in Cross-Coupling Reactions (pages 6908–6913)

      Anil V. Gaikwad, Alexandre Holuigue, Mehul B. Thathagar, Johan E. ten Elshof and Gadi Rothenberg

      Article first published online: 31 MAY 2007 | DOI: 10.1002/chem.200700105

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      Palladium leaching: The mechanism of catalysis for Heck and Suzuki coupling reactions by using palladium nanoparticles has been invesigated by using a special membrane reactor (see figure). Pd0 atoms or PdII ions that have leached in solution were shown to be the active catalytic species.

    14. Towards a Bio-Based Industry: Benign Catalytic Esterifications of Succinic Acid in the Presence of Water (pages 6914–6919)

      Vitaly Budarin, Rafael Luque, Duncan J. Macquarrie and James H. Clark

      Article first published online: 30 MAY 2007 | DOI: 10.1002/chem.200700037

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      Catalysing change: Unlocking the biorefinery. A new family of tuneable mesoporous carbonaceous acid catalysts derived from starch can be used to accomplish efficient chemistry in aqueous solution. The reactions of succinic acid (platform molecule) in aqueous alcohol demonstrate the outstanding activities of these new catalysts (see figure).

    15. Investigation of the Stability of the M-H-B Bond in Borane σ Complexes [M(CO)51-BH2R⋅L)] and [CpMn(CO)21-BH2R⋅L)] (M=Cr, W; L=Tertiary Amine or Phosphine): Substituent and Lewis Base Effects (pages 6920–6931)

      Yasuro Kawano, Kazunori Yamaguchi, Shun-ya Miyake, Taeko Kakizawa and Mamoru Shimoi

      Article first published online: 24 MAY 2007 | DOI: 10.1002/chem.200601883

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      Enhanced stability of borane σ complexes has been achieved by introduction of a more donating substituent or a stronger Lewis base into the borane adduct in both [M(CO)51-BH2RL)] (M=Cr, W) and [CpMn(CO)21-BH2RL)] systems. This indicates that the borane[BOND]metal interaction consists of the predominant ligand-to-metal electron donation and little back donation.

    16. The Mechanism of C[BOND]X (X=F, Cl, Br, and I) Bond Activation in CX4 by a Stabilized Dialkylsilylene (pages 6932–6941)

      Chi-Hui Chen and Ming-Der Su

      Article first published online: 31 MAY 2007 | DOI: 10.1002/chem.200601736

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      In the reaction of a dialkylsilylene with carbon tetrahalides, density functional calculations suggest that of the three possible reaction paths, halogen (X)-atom abstraction, CX3-group abstraction, and insertion (see scheme), X abstraction is the most favorable. For a stable dialkylsilylene, the chemical reactivity has been found to increase in the order CF4≪CCl4<CBr4<CI4.

    17. Progress in the Understanding of Drug–Receptor Interactions, Part 2: Experimental and Theoretical Electrostatic Moments and Interaction Energies of an Angiotensin II Receptor Antagonist (C30H30N6O3S) (pages 6942–6956)

      Raffaella Soave, Mario Barzaghi and Riccardo Destro

      Article first published online: 31 MAY 2007 | DOI: 10.1002/chem.200601516

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      Drug–receptor interactions: A combined experimental and theoretical charge density study of an AT1 selective angiotensin II receptor antagonist named LR-B/081 (see picture) is presented, focusing on electrostatic properties such as molecular electrostatic moments up to the fourth rank and the energies of the intermolecular interactions. In this way, the key pharmacophoric features responsible for the high activity of LR-B/081 are elucidated and quantitatively characterised.

    18. Characterization of Titanium Dioxide Nanoparticles Dispersed in Organic Ligand Solutions by Using a Diffusion-Ordered Spectroscopy-Based Strategy (pages 6957–6966)

      Luk Van Lokeren, Géraldine Maheut, François Ribot, Virginie Escax, Ingrid Verbruggen, Clément Sanchez, José C. Martins, Monique Biesemans and Rudolph Willem

      Article first published online: 12 JUN 2007 | DOI: 10.1002/chem.200601722

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      Particles get DOSY! Diffusion-ordered NMR spectroscopy (DOSY NMR) is presented as a tool for the determination of diffusion coefficients of ligands in the unbound state and bound to TiO2 nanoparticles (for example, a redispersed xerosol, see picture). The technique allows the assessment of particle size and ligand involvement in interactions with nanoparticles.

    19. Evidence for a SN2-Type Pathway for Phosphine Exchange in Phosphine–Phosphenium Cations, [R2P[BOND]PR′3]+ (pages 6967–6974)

      John M. Slattery, Cheryl Fish, Michael Green, Thomas N. Hooper, John C. Jeffery, Richard J. Kilby, Jason M. Lynam, John E. McGrady, Dimitrios A. Pantazis, Christopher A. Russell and Charlotte E. Willans

      Article first published online: 31 MAY 2007 | DOI: 10.1002/chem.200601742

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      Tuning the properties of electron-deficient phosphorus: Experiment and theory are used to explore the properties of two distinct classes of phosphenium cation and their phosphine adducts. Both electronic and steric properties of substituents bonded to the phosphorus centers prove to have a profound influence on the structure and reactivity of these systems.

    20. Synthesis, Characterization, and Electrochemiluminescence of Luminol-Reduced Gold Nanoparticles and Their Application in a Hydrogen Peroxide Sensor (pages 6975–6984)

      Hua Cui, Wei Wang, Chun-Feng Duan, Yong-Ping Dong and Ji-Zhao Guo

      Article first published online: 31 MAY 2007 | DOI: 10.1002/chem.200700011

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      Guiding light: Electrochemiluminescent gold nanoparticles (AuNPs) have been synthesized by the direct reduction of HAuCl4 with the luminescent reagent luminol in an aqueous solution. An as-prepared luminol-capped AuNP-modified electrode exhibited an electrochemiluminescence (ECL) response in alkaline aqueous solution under a double-step potential (see picture). H2O2 enhanced the ECL and thus an ECL sensor for the detection of H2O2 was developed.

    21. Cytotoxic Polyketides Containing Tetramic Acid Moieties Isolated from the Fungus Myceliophthora Thermophila: Elucidation of the Relationship between Cytotoxicity and Stereoconfiguration (pages 6985–6991)

      Yu-Liang Yang, Chun-Ping Lu, Mao-Yen Chen, Kuei-Yu Chen, Yang-Chang Wu and Shih-Hsiung Wu

      Article first published online: 14 MAY 2007 | DOI: 10.1002/chem.200700038

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      Fungus kills cancer! New polyketides containing tetramic acid moieties were isolated from the thermophilic fungus Myceliophthora thermophila. The elucidation of the structure, relative configurations, and the cytotoxic effects of five myceliothermophins (example figure right) are described. A microscopic picture of mature spores of Myceliophthora thermophila is shown on the left.

    22. Cycloaddition of CO2 to Epoxides Catalyzed by Polyaniline Salts (pages 6992–6997)

      Jinling He, Tianbin Wu, Zhaofu Zhang, Kunlun Ding, Buxing Han, Ye Xie, Tao Jiang and Zhimin Liu

      Article first published online: 31 MAY 2007 | DOI: 10.1002/chem.200700210

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      Keeping up with catalysis! Polyaniline-HI is a very active, stable, selective, and inexpensive heterogeneous catalyst for the cycloaddition of CO2 to epoxides (see scheme).

    23. Scope and Limitations of Baird's Theory on Triplet State Aromaticity: Application to the Tuning of Singlet–Triplet Energy Gaps in Fulvenes (pages 6998–7005)

      Henrik Ottosson, Kristine Kilså, Khalil Chajara, Mari Carmen Piqueras, Raül Crespo, Haruhisa Kato and Daniel Muthas

      Article first published online: 11 JUN 2007 | DOI: 10.1002/chem.200700362

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      Exploiting aromatic chameleons: The singlet–triplet energy gaps (ΔEST) of fulvenes are easily varied by substitution, as shown schematically for the parent fulvene (X=H) and fulvenes in which X is an electron-withdrawing or electron-donating group (X=EWG and EDG, respectively). This exploits the aromatic-chameleon nature of fulvenes, that is, they reverse their dipoles on going from the singlet ground state to the lowest triplet excited state and thus adapt their electron distributions to achieve a degree of aromaticity in both states.

    24. Oxovanadium(V) Tetrathiacalix[4]arene Complexes and Their Activity as Oxidation Catalysts (pages 7006–7016)

      Elke Hoppe and Christian Limberg

      Article first published online: 13 JUN 2007 | DOI: 10.1002/chem.200700354

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      An alkoxo-bridged intermediate involved in the catalytic cycle for oxidative dehydrogenation of alcohols with a dinuclear oxovanadium tetrathiacalixarene catalyst has been isolated (see scheme). It provides hints to why dinuclear complexes are more efficient in this catalytic process than mononuclear ones and may stimulate discussions concerning the active species in corresponding heterogeneously catalyzed processes.

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      Preview: Chem. Eur. J. 25/2007 (page 7023)

      Article first published online: 7 AUG 2007 | DOI: 10.1002/chem.200790091

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