Cover image for ChemPhysChem

April 10, 2006

Volume 7, Issue 4

Pages 769–970

    1. Cover Picture: Direct Observation of Single Protein Molecules in Aqueous Solution (ChemPhysChem 4/2006) (page 769)

      David Grünwald, Andreas Hoekstra, Thomas Dange, Volker Buschmann and Ulrich Kubitscheck

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200690011

      The cover picture shows a surface plot representation of the trajectories of a single quantum dot (larger signals in the back) and of a single fluorescent antibody (four smaller signals in the front) in aqueous buffer solution. In their Communication on page 812 Grünwald et al. show that imaging by an electron multiplying charge-coupled device is fast enough to obtain images of diffusing single molecules. The antibody signals are not as bright as the quantum dots, and slighty more smeared out due to movements during the 3-ms frame integration time.

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    3. Recent Progress in Ultrafast X-ray Diffraction (pages 783–792)

      M. Bargheer, N. Zhavoronkov, M. Woerner and T. Elsaesser

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500591

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      Expanding knowledge of condensed matter: The rapid progress in the generation of stable ultrashort X-ray pulses in both accelerator- and laser-based sources has enabled the time-resolved observation of small structural changes in bulk and nanostructured materials (see figure; ΔR/R0=relative reflectivity change; ΔΘ/Θ=relative angular shift). This Minireview details work on transient crystalline structures, focusing on laser-based experiments.

    4. Electronic and Crystal Engineering of Acenes for Solution-Processible Self-Assembling Organic Semiconductors (pages 793–797)

      Frank Würthner and Rüdiger Schmidt

      Version of Record online: 10 MAR 2006 | DOI: 10.1002/cphc.200600078

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      High charge-carrier mobility in bis- silylethynylated acenes: This article highlights new organic semiconductor materials (see figure) with pronounced p- and n-type charge-carrier mobilities. Particular emphasis is given to the evolution of the electronic properties with increasing number of annulated rings in the ascending bis-silylethynylated acene series as well as the rational supramolecular crystal engineering.

    5. Comment on “Disproving a Silicon Analog of an Alkyne with the Aid of Topological Analyses of the Electronic Structure and Ab Initio Molecular Dynamics Calculations” (pages 799–800)

      Gernot Frenking, Andreas Krapp, Shigeru Nagase, Nozomi Takagi and Akira Sekiguchi

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500689

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      Bond order of a silicon-silicon bond (1): The statement that the recently synthesized compound RSi[BOND]SiR (1) (R[DOUBLE BOND]Si[C(SiMe3)3]2CHMe2) has rather a double than a triple bond is challenged. Arguments are given which support the interpretation of the bonding situation in terms of two donor–acceptor bonds which are enhanced by one π bond (see picture).

    6. Reply to Comment on “Disproving a Silicon Analog of an Alkyne with the Aid of Topological Analyses of the Electronic Structure and Ab Initio Molecular Dynamics Calculations” (pages 801–802)

      Carlo A. Pignedoli, Alessandro Curioni and Wanda Andreoni

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200600025

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      Bond order of a silicon–silicon bond (2): Quantum chemical analysis of the central Si–Si bond in a recently synthesized compound, which was claimed to be the first stable silicon analog of an alkyne, led to the conclusion: the central Si[BOND]Si bond cannot be classified as a triple bond (see picture).

    7. Design of Improved Deep Eutectic Solvents Using Hole Theory (pages 803–806)

      Andrew P. Abbott, Glen Capper and Stephen Gray

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500489

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      Extraordinary solvents: The authors design deep eutectic solvents (DESs) based on small cations and fluorinated hydrogen-bond donors (see figure). These DESs display properties of decreased viscosity and increased conductivity with differences up to four orders of magnitude compared to ionic liquids.

    8. Ultrafast Chronoamperometry of Single Impact Events in Acoustically Agitated Solid Particulate Suspensions (pages 807–811)

      Antony D. Clegg, Neil V. Rees, Craig E. Banks and Richard G. Compton

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500589

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      Acoustically agitated suspensions of particles fired at an electrode placed directly opposite the ultrasonic horn have been explored. The authors demonstrate the potential analytical power of the technique for the determination of the number and size of particles in solution. The diagram illustrates the probable mechanism for the process occurring at the electrode and the effect on the measured current as a function of time.

    9. Direct Observation of Single Protein Molecules in Aqueous Solution (pages 812–815)

      David Grünwald, Andreas Hoekstra, Thomas Dange, Volker Buschmann and Ulrich Kubitscheck

      Version of Record online: 10 MAR 2006 | DOI: 10.1002/cphc.200500632

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      Real-time visualisation and tracking: Fluorescent labeled protein molecules are tracked using high-speed imaging systems. The figure shows the fluorescence signal from single quantum dots integrated over 2.7 ms. Diffusion coefficients deduced from single-molecule traces are consistent with those determined independently by fluorescence correlated spectroscopy, demonstrating in differnt distances to the focal plane the effectiveness of the technique.

    10. Solvents with Similar Bulk Properties Induce Distinct Supramolecular Architectures (pages 816–819)

      Thomas Pinault, Benjamin Isare and Laurent Bouteiller

      Version of Record online: 9 MAR 2006 | DOI: 10.1002/cphc.200500636

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      Thick or thin? Hydrogen-bonded bis-urea forms two distinct rodlike assemblies—thick or thin filaments—in a variety of aromatic solvents. The stability of each is dependent on the size of the solvent molecules and a simple viscosity test (see figure) differentiates between them.

    11. Excitation of the Asymmetric Stretch Vibration of CO2 in OH+CO[RIGHTWARDS ARROW]H+CO2 Reaction (pages 820–823)

      Congyun Shi, Li Ren and Fanao Kong

      Version of Record online: 10 MAR 2006 | DOI: 10.1002/cphc.200500695

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      CO2vibrations: High excitation in the asymmetric stretch (v3) mode of the CO2 product in the OH+CO reaction has been found (see picture). The strong IR emission was detected by time-resolved Fourier transform infrared (TR-FTIR) emission spectroscopy. The observed vibrational distribution is used for comparison with a variety of theoretical calculations on this reaction.

    12. A Lotus-Leaf-Like Superhydrophobic Surface Prepared by Solvent-Induced Crystallization (pages 824–827)

      Ning Zhao, Lihui Weng, Xiaoyan Zhang, Qiongdan Xie, Xiaoli Zhang and Jian Xu

      Version of Record online: 9 MAR 2006 | DOI: 10.1002/cphc.200500698

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      Natural inspiration: A lotus-leaf-like hierarchical structure is formed on a polycarbonate plate under mild conditions by successive plasticization and coagulation of the polymer surface. The resultant micron- and nanoscale rough structure, shown in the figure allows the common plastic to be superhydrophobic with a large water contact angle and less contact angle hysteresis.

    13. Coexistence of Dihydrogen, Blue- and Red-Shifting Hydrogen Bonds in an Ultrasmall System: Valine (pages 828–830)

      Wenbo Yu, Zijing Lin and Zhijian Huang

      Version of Record online: 9 MAR 2006 | DOI: 10.1002/cphc.200500721

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      Conformational space of valine: Dihydrogen, blue- and red-shifting H bonds coexist in the single molecule, valine (see picture). All functional groups of valine participate in H bonding and the amino and carboxyl group play the dual role of H-bond donor and acceptor. As all known H-bond types coexist in valine, a unifying concept of hydrogen bonding is depicted.

    14. Quenching Echo Modulations in NMR Spectroscopy (pages 831–836)

      Jens Dittmer  and Geoffrey Bodenhausen 

      Version of Record online: 10 MAR 2006 | DOI: 10.1002/cphc.200500403

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      Ideal decay: The amplitude of trains of spin echoes which are normally modulated by scalar couplings, are shown to be quenched by small pulse imperfections. When the refocusing pulses deviate slightly from ideal π rotations due to tilted effective radio-frequency fields, the modulations are cancelled and the transverse relaxation times can be accurately measured (blue curve).

    15. Conformational Reorientation of Immunoglobulin G During Nonspecific Interaction with Surfaces (pages 837–846)

      Michael Rankl, Thomas Ruckstuhl, Michael Rabe, Georg R. J. Artus, Andreas Walser and Stefan Seeger

      Version of Record online: 10 MAR 2006 | DOI: 10.1002/cphc.200500448

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      The nonspecific adsorption of proteins on solid surfaces is investigated by a model system comprising of immunoglobulin G and a set of chemically defined surfaces. The thermodynamics of bound proteins and a kinetic analysis of the adsorption process reveal two simple mechanisms: A) distinct reaction pathways for reversible and irreversible adsorption and B) the transition mechanism (see picture; k=respective reaction rate). The hydrophobic conformation favorably adsorbs onto the surfaces and a conformational reorientation of the protein occurs.

    16. Nanoscale Structural and Electronic Properties of Ultrathin Blends of Two Polyaromatic Molecules: A Kelvin Probe Force Microscopy Investigation (pages 847–853)

      Vincenzo Palermo, Susanna Morelli, Matteo Palma, Christopher Simpson, Fabian Nolde, Andreas Herrmann, Klaus Müllen and Paolo Samorì

      Version of Record online: 10 MAR 2006 | DOI: 10.1002/cphc.200500480

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      Blend not a simple sum: A phase-segregated blend composed of electron-donor nanofibers embedded in an electron-acceptor ultrathin film is obtained by self-assembly of large polyaromatic molecules from solution. Kelvin probe force microscopy (see figure) probes simultaneously the structural and electronic properties of both the fibers and the surrounding layer. Each component in the blend revealed significantly different nanoscale electronic properties from its neat film.

    17. Electrochemical Characterization of Self-Assembled Thiol-Porphyrin Monolayers on Gold Electrodes by SECM (pages 854–862)

      Xiaoquan Lu, Limin Zhang, Minrui Li, Xiaoqiang Wang, Yan Zhang, Xiuhui Liu and Guofang Zuo

      Version of Record online: 6 MAR 2006 | DOI: 10.1002/cphc.200500492

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      Influencing electron transfer: Thiol-porphyrin self-assembled monolayers on gold electrodes, investigated using cyclic voltammetry and scanning electrochemical microscopy (SECM), influence the electron-transfer process. The substrate potential, the solution properties and the structure of the probe molecules [see figure showing reaction scheme of probe molecule and metalloporphyrin (M)] all play an important role.

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      Thiophene–Thiophene versus Phenyl–Phenyl Coupling in 2-(Diphenylamino)-Thiophenes: An ESR-UV/Vis/NIR Spectroelectrochemical Study (pages 863–870)

      Peter Rapta, Olaf Zeika, Dirk Rohde, Horst Hartmann and Lothar Dunsch

      Version of Record online: 7 MAR 2006 | DOI: 10.1002/cphc.200500533

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      Substitution variety: The oxidative coupling mechanism of different substituted 2-diphenylaminothiophenes is investigated. The stability and reactivity of the radical cations depend strongly on the substitution pattern in the thiophene moieties and give rise to different consecutive reactions: thiophene–thiophene versus phenyl–phenyl coupling (see scheme).

    19. Highly Anisotropic Orbitally Dependent Superexchange in Cyano-Bridged Clusters Containing Mn(III) and Mn(II) Ions (pages 871–879)

      Andrew Palii, Sergey M. Ostrovsky, Sophia I. Klokishner, Boris. S. Tsukerblat and Kim R. Dunbar

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500549

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      Magnetic metal clusters: Cyano-bridged manganese-containing dimers and trimers (see picture) are analyzed theoretically. The energy levels are shown to be dependent on both spin and orbital quantum numbers, thus providing direct information of the magnetic anisotropy of the system. Under certain conditions an appreciable barrier for the reversal of magnetization is created which significantly increases when passing from the dimer to the trimer.

    20. The “Non-Reaction” of Ground-State Triplet Carbon Atoms with Water Revisited (pages 880–885)

      Peter R. Schreiner and H. Peter Reisenauer

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500555

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      Triplet carbon atoms do not react with water, despite their high energy, as is revealed by generating ground-state triplet carbon atoms by laser ablation, condensation with Ar, annealing of the matrix, recooling, and spectral recording. For the first time the reactivity of triplet and singlet carbon atoms towards water is distinguished (see scheme) with the results consistent with earlier lower-level and present high-level computational predictions. This has implications for the formation of aldoses in extraterrestrial environments, which, based on the current findings, can only derive from “hot” carbon atoms or through photoreactions.

    21. Fingerprints of Damped Quantum Rotation Observed in Solid-State Proton NMR Spectra (pages 886–893)

      Peter Gutsche, Heike Schmitt, Ulrich Haeberlen, Tomasz Ratajczyk and Slawomir Szymanski

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500572

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      Molecular rate processes observed in NMR spectra are not necessarily classical. The hindered rotation of the methyl group is a quantum mechanical process at all temperatures which is controlled by two quantum rate constants, kt and kK. The phenomenological behaviour becomes classical only when kt=kK. NMR spectra of the methyl protons in a single crystal of methylmalonic acid provide evidence that in this material kt and kK are substantially different (see figure).

    22. Alternative Low-Energy Mechanisms for Isotopic Exchange in Gas-Phase D2O–H+(H2O)n Reactions (pages 894–903)

      Massimo Mella and Alessandro Ponti

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500575

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      H/D scrambling in gas-phase clusters: Computational results provide support to a detailed mechanism for isotopic scrambling in energized H+(H2O)nD2O clusters (n=2–5). The mechanism, composed of a sequence of single-water-molecule migrations, allows interconversion to different isomers. A few of the possible migrations (see diagram) also involve proton exchange between two neighboring molecules, therefore allowing the transfer of D.

    23. Kinetic Model of Energy Transfer Processes Between Low-Coordinated Ions on MgO by Photoluminescence Decay Measurements (pages 904–911)

      Céline Chizallet, Guylène Costentin, Jean-Marc Krafft, Hélène Lauron-Pernot and Michel Che

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500580

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      Surface phosphorescence: The kinetics of intrinsic emission and energy transfer processes for the surface species on MgO nanocubes (see figure) are reported. A simple numerical model, which fits the experimental data, is presented and identifies the emitting species as O2−4 C (edge) and O2−3C (corner and kink) surface oxide ions.

    24. Mechanism of Cysteine Oxidation by a Hydroxyl Radical: A Theoretical Study (pages 912–919)

      Mironel Enescu and Bruno Cardey

      Version of Record online: 6 MAR 2006 | DOI: 10.1002/cphc.200500585

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      Fast dissociating intermediate states: Thiols are very efficiently oxidized by hydroxyl radicals. The question how the diversity of the thiol molecular environment could affect this efficiency is of great biological interest. To answer this question the mechanism of cysteine oxidation (see picture of cysteine–HO. interaction) is theoretically analyzed.

    25. Linked Crystallites in the Conducting Topmost Layer of Polymer Bilayer Films Controlled by Temperature: From Micro- to Nanocrystallites (pages 920–923)

      Elena Laukhina, Vladislava Tkacheva, Salavat Khasanov, Leokadia Zorina, Jordi Gómez-Segura, Angel Pérez del Pino, Jaume Veciana, Vladimir Laukhin and Concepció Rovira

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500600

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      Conducting surface layers in polymer bilayer films are formed with micro- or nanocrystallites (see AFM images) of α′-(BEDT-TTF)2(IxBr1−x)3 (BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene) by fine temperature control of the crystallization process. The conducting properties of the films do not vary significantly with the size of the crystallites, and their uniform nanoscale conducting properties suggest potential application as miniaturized conducting plastic materials.

    26. Conformational Effects on Circular Dichroism in the Photoelectron Angular Distribution (pages 924–934)

      Devis Di Tommaso, Mauro Stener, Giovanna Fronzoni and Piero Decleva

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500602

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      Fingerprints of conformers: A theoretical investigation of the influence of conformational factors on photoionization dynamical parameters, with special attention to circular dichroism in the photoelectron angular distribution is presented. The sensitivities to selected conformers of the chiral molecules shown in the figure, prove useful for conformational analysis.

    27. Optical-Limiting and Photophysical Properties of Two Soluble Chloroindium Phthalocyanines with α- and β-Alkoxyl Substituents (pages 935–941)

      Shuangqing Wang, Quan Gan, Yongfang Zhang, Shayu Li, Huijun Xu and Guoqiang Yang

      Version of Record online: 9 MAR 2006 | DOI: 10.1002/cphc.200500595

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      Enhanced optical limiting in heavy-metal phthalocyanines is obtained by substitution in the α and β positions. Tetra-α-(2-ethylbutoxy) chloroindium phthalocyanine (α-InPcCl, see picture) is superior to its β counterpart, due to its larger triplet quantum yield and is therefore a more suitable optical-limiting material.

    28. Binding Modes in Metal Ion Complexes of Quinones and Semiquinone Radical Anions: Electron-Transfer Reactivity (pages 942–954)

      Junpei Yuasa, Tomoyoshi Suenobu and Shunichi Fukuzumi

      Version of Record online: 7 MAR 2006 | DOI: 10.1002/cphc.200500640

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      Mechanistic insights: Only o-quinones form complexes with metal ions; p-quinones do not. However, when semiquinone radical anions are generated, both o- and p-types form metal-ion complexes. The binding modes (see figure) in these complexes are characterized by electron spin resonance (ESR) and absorption, and provide valuable mechanistic insights into the metal ion-promoted electron-transfer reduction of quinones.

    29. Spin–Orbit Ab Initio Investigation of the Photolysis of Bromoiodomethane (pages 955–963)

      Ya-Jun Liu, Devarajan Ajitha, Jesper Wisborg Krogh, Alexander N. Tarnovsky and Roland Lindh

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200500654

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      Affairs of state: CH2BrI and the isomers CH2Br-I and CH2I-Br, with two different carbon–halogen bonds, are excellent candidates for investigating selective bond dissociations upon electronic excitation (see figure). The ground- and excited-state geometries of all three compounds were optimized and the corresponding photoproducts were assigned by multistate second-order multiconfigurational perturbation theory.

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      Preview: ChemPhysChem 4/2006 (page 970)

      Version of Record online: 4 APR 2006 | DOI: 10.1002/cphc.200690014