ChemPhysChem

Cover image for Vol. 7 Issue 5

May 12, 2006

Volume 7, Issue 5

Pages 973–1154

    1. Cover Picture: Hydrogen Electrocatalysis (ChemPhysChem 5/2006) (page 973)

      Ludwig A. Kibler

      Version of Record online: 3 MAY 2006 | DOI: 10.1002/cphc.200690016

      The cover picture shows an ordered array of 400 palladium clusters deposited onto a gold single-crystal surface in sulfuric acid solution (courtesy of F. Simeone and D. M. Kolb). This image (200 nm×200 nm, average cluster height around 1 nm) was not only recorded in situ by scanning tunneling microscopy, the palladium clusters were also fabricated with the tip of the microscope. The Minireview by Kibler on page 985 addresses relations between the local surface structure of noble metal surfaces and their activity for the hydrogen evolution reaction. Variations in the hydrogen chemisorption energy for different active centres have an impact on the overall reaction kinetics.

    2. Hydrogen Electrocatalysis (pages 985–991)

      Ludwig A. Kibler

      Version of Record online: 11 APR 2006 | DOI: 10.1002/cphc.200500646

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      Towards new electrocatalysts: The physical origin of the exchange current density j0 for cathodic hydrogen evolution is addressed in this Minireview. Variations in adsorption energies of atomic hydrogen on different electrodes (Pd and Au, see figure), including various catalytically active surface sites, play a crucial role for the explanation of so-called volcano curves.

    3. Water Formation on Pt and Pt-based Alloys: A Theoretical Description of a Catalytic Reaction (pages 992–1005)

      Timo Jacob and William A. Goddard III

      Version of Record online: 5 APR 2006 | DOI: 10.1002/cphc.200500613

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      Surface water: Many catalytic reactions can be studied on the atomic scale by computational modeling of strongly idealized systems. However, the seemingly simple formation of water from hydrogen and oxygen on Pt and Pt/Ni alloy surfaces has several reaction pathways (see picture). The reaction is influenced by changes in the environment (such as solvation) and/or by the structure of the catalyst surface (such as nanoparticles).

    4. Helium Atom Scattering from Oxide Surfaces (pages 1006–1013)

      Franziska Traeger

      Version of Record online: 20 APR 2006 | DOI: 10.1002/cphc.200500599

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      A gentle method for surface analysis: Helium atom scattering is an extremely surface-sensitive tool to study the structure and low-energy dynamics of surfaces (see figure; T=temperature, ΔE= energy loss; ΔK=momentum transfer). Due to the low energy and neutrality of the probe particles, it can be applied to any class of materials. Studies on MgO and for ZnO, where the sensitivity of the method to hydrogen is essential, are presented.

    5. Anomalously Low Probabilities for Rotational Excitation in HD–Surface Scattering (pages 1015–1018)

      Antonio Šiber, Ch. Boas, M. W. Cole and Christof Wöll

      Version of Record online: 3 APR 2006 | DOI: 10.1002/cphc.200500726

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      The H2–Cs surface interaction potential is directly investigated by scattering a rotationally cold beam of HD molecules from a Cs surface (see angular distribution diagram). The probability of rotational excitation is two orders of magnitude smaller than for Cu and other metal surfaces. Coupled channel calculations interpret the results, and the anomalous behaviour is linked to the peculiarities of the closed-shell alkali surface interactions.

    6. Modes of Action of a Weak Acid Modifier of Calcite Growth (pages 1019–1021)

      Phillip S. Dobson, Lucy A. Bindley, Julie V. Macpherson and Patrick R. Unwin

      Version of Record online: 24 MAR 2006 | DOI: 10.1002/cphc.200500469

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      Dynamics of crystallization processes: The simple dicarboxylic acid, maleic acid, is shown to have a dual mode of action on the calcite (104) surface (see left atomic force microscopy image of a single calcite microcrystal) in saturated and supersaturated solutions. The monoprotonated form of the acid promotes nanopitting, even in saturated solutions, before subsequently pinning the growth of steps in the acute crystallographic directions, at higher supersaturation (right image).

    7. Migration of Carbon into Subsurface Layers of Rh(100): A DFT Study (pages 1022–1025)

      Davy L. S. Nieskens, D. Curulla-Ferré and J. W. Niemantsverdriet

      Version of Record online: 5 APR 2006 | DOI: 10.1002/cphc.200500553

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      The driving force for migration of carbon into positions immediately below the Rh(100) surface is explored by DFT calculations. Carbon atoms adsorb on the Rh surface at low concentrations, whereas at coverages exceeding one C per two Rh atoms, strong repulsive interactions energetically favour C atom configurations in subsurface positions (see picture; the dark spheres correspond to C atoms in surface and octahedral subsurface sites).

    8. Adsorption Isotherms of ortho- and para-Water (pages 1026–1027)

      Vladimir I. Tikhonov and Alexander A. Volkov

      Version of Record online: 20 APR 2006 | DOI: 10.1002/cphc.200500627

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      Spin-modifyied water: Adsorption isotherms are measured separately for ortho- and para-water on a hydrophobic adsorbent (see picture; adsorbed molecules nO and nP as functions of partial pressures pO and pP) . In a closed volume filled with adsorbent the equilibrium gas-phase ortho:para ratio deviates noticeably from the statistical 3:1 in favor of the ortho component. Correspondingly, adsorbed water is formally para-enriched.

    9. Ligand Adsorption/Desorption on Sterically Stabilized InP Colloidal Nanocrystals: Observation and Thermodynamic Analysis (pages 1028–1031)

      Iwan Moreels, Jose C. Martins and Zeger Hens

      Version of Record online: 5 APR 2006 | DOI: 10.1002/cphc.200500659

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      Macroscopic characterisation: The adsorption/desorption equilibrium of trioctylphosphine oxide ligands at colloidal InP nanocrystals (see picture) is investigated with quantitative, one-dimensional 1H NMR spectroscopy. Thermodynamic analysis of the isotherm demonstrates that formation of the capping is driven by favorable adsorbate–substrate interactions and is strengthened by adsorbate–adsorbate interactions.

    10. Hydrogen Evolution Over Bimetallic Systems: Understanding the Trends (pages 1032–1035)

      Jeff Greeley, Jens K. Nørskov, Ludwig A. Kibler, Ahmed M. El-Aziz and Dieter M. Kolb

      Version of Record online: 24 MAR 2006 | DOI: 10.1002/cphc.200500663

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      Theory of evolution: Potential and solvent effects make the theoretical analysis of electrocatalytic phenomena more difficult than that for gas-phase catalysis. A simple model based on DFT gives a semiquantitative description of electrocatalytic reaction kinetics for the hydrogen evolution reaction. The figure shows the differential free energy of adsorption of hydrogen on overlayers of Pd on the surfaces of transition metal substrates.

    11. A New Type of In Situ Single-Molecule Rectifier (pages 1036–1040)

      Alexei A. Kornyshev and Alexander M. Kuznetsov

      Version of Record online: 3 MAY 2006 | DOI: 10.1002/cphc.200500685

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      Electrochemical nanojunctions: A theory of direct elastic electron tunneling under the potential barrier formed by a long molecule that is confined between two metallic electrodes in electrolyte solution is presented. This theory predicts a strong asymmetry of the dependence of the tunnel current on the electrode potentials which is due to the screening of the electric potential in the tunnel gap by the ions of the electrolyte.

      Corrected by:

      Corrigendum: A New Type of In Situ Single-Molecule Rectifier

      Vol. 9, Issue 8, 1092, Version of Record online: 26 MAY 2008

    12. Electrochemical Rate Constants in Room Temperature Ionic Liquids: The Oxidation of a Series of Ferrocene Derivatives (pages 1041–1045)

      Nicole Fietkau, Antony D. Clegg, Russell G. Evans, Constanza Villagrán, Christopher Hardacre and Richard G. Compton

      Version of Record online: 5 APR 2006 | DOI: 10.1002/cphc.200500709

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      The high-speed channel electrode has been used to measure heterogeneous electron-transfer rates, k0, for a series of ferrocene derivatives in room temperaure ionic liquids (RTILs) under steady-state conditions thus avoiding the problems of ohmic drop and capacitative currents associated with transient methods. The figure shows the three-dimensional surface plot for k0 versus the transfer coefficient, α.

    13. Protein Amyloidogenesis in the Context of Volume Fluctuations: A Case Study on Insulin (pages 1046–1049)

      Vytautas Smirnovas, Roland Winter, Theodor Funck and Wojciech Dzwolak

      Version of Record online: 5 APR 2006 | DOI: 10.1002/cphc.200500717

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      Unfolding and aggregation of insulin: Using ultrasound velocimetry, densimetry and pressure-perturbation calorimetry, the authors provide a precise description of the time-dependent aggregation process in insulin (see figure). Changes in the thermodymanic properties such as the coefficient of thermal expansion α and isothermal compressibility βT of the protein highlight the importance of volume fluctuations during the unfolding and fibrillation process.

    14. Luminescence Quenching by O2 of a Ru2+ Complex Attached to Zeolite L (pages 1050–1053)

      Rodrigo Q. Albuquerque, Zoran Popović, Luisa De Cola and Gion Calzaferri

      Version of Record online: 20 APR 2006 | DOI: 10.1002/cphc.200600020

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      Photonic antenna: Ru-based stopcocks are electrostatically bound to the negatively charged one-dimensional channels of zeolite L crystals (see figure). The authors show that the quenching of the luminescence of the stopcock molecule is much weaker when it is bound to zeolite L.

    15. Adsorption of Functionalized Benzoic Acids on MgSO4⋅H2O (100) (pages 1055–1061)

      Volodymyr Maslyuk, Christoph Tegenkamp, Herbert Pfnür and Thomas Bredow

      Version of Record online: 3 APR 2006 | DOI: 10.1002/cphc.200500486

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      Unraveling adsorption: Using a combination of ab initio and semiempirical methods, the geometry and electronic properties of benzoic acid (BA), salicylic acid (SA; see figure) and para-salicylic acid (p-SA) adsorbed on MgSO4⋅H2O (100) are studied. These molecules chemisorb—with binding energies ≈1.9 eV—forming bonds through the carboxylic O atom in a nonplanar geometry (b). The planar adsorption geometry (a) is nonbonding.

    16. Quantum-Dot-Labeled DNA Probes for Fluorescence In Situ Hybridization (FISH) in the Microorganism Escherichia coli (pages 1062–1067)

      Sheng-Mei Wu, Xiang Zhao, Zhi-Ling Zhang, Hai-Yan Xie, Zhi-Quan Tian, Jun Peng, Zhe-Xue Lu, Dai-Wen Pang and Zhi-Xiong Xie

      Version of Record online: 20 APR 2006 | DOI: 10.1002/cphc.200500608

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      Gone FISHing: Fluorescent semiconductor quantum dots are used to label single-stranded DNA sequences complementary to plasmid clusters. The bioconjugate probes have high dispersivity, bioactivity and specificity for hybridization. The subcellular location of plasmid pUC18 clusters in Escherichia coli (see figure) is successfully achieved by fluorescence in situ hybridization (FISH).

    17. Acetylene Decomposition on Rh(100): Theory and Experiment (pages 1068–1074)

      Davy L. S. Nieskens, Francisco Ample-Navarro, Maarten M. M. Jansen, Daniel Curulla-Ferré, Josep Ricart and Hans Niemantsverdriet

      Version of Record online: 11 APR 2006 | DOI: 10.1002/cphc.200500566

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      Which way? The decomposition of acetylene on a Rh(100) single crystal is studied using a combination of experimental techniques and a computational approach based on density functional theory (DFT). Acetylene adsorbs irreversibly on the Rh(100) surface and decomposes to atomic carbon and gas-phase hydrogen. The investigation enables the authors to determine the most likely reaction pathway for the decomposition process (see figure).

    18. Atom–Molecule Interactions on Transition Metal Surfaces: A DFT Study of CO and Several Atoms on Rh(100), Pd(100) and Ir(100) (pages 1075–1080)

      Davy L. S. Nieskens, Daniel Curulla-Ferré and J. W. Niemantsverdriet

      Version of Record online: 20 APR 2006 | DOI: 10.1002/cphc.200600005

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      On the surface: Trends in the interaction energy between CO and all atoms from the first three rows of the periodic table coadsorbed on Rh(100), Pd(100) and Ir(100) surfaces have been studied. The results indicate that the strength of the interaction energy between CO and a coadsorbed atom on a certain catalyst surface is specific for the particular combination and the coverages of all the species involved (see picture for Rh; ML=monolayer).

    19. Nano-Electrochemical Detection of Hydrogen or Protons Using Palladium Nanoparticles: Distinguishing Surface and Bulk Hydrogen (pages 1081–1085)

      Christopher Batchelor-McAuley, Craig E. Banks, Andrew O. Simm, Timothy G. J. Jones and Richard G. Compton

      Version of Record online: 24 MAR 2006 | DOI: 10.1002/cphc.200500571

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      A deeper insight into the Pd/H2/H+system: The electrochemical response of a palladium-nanoparticle-modified boron-doped diamond (BDD) electrode for the electrochemical detection of protons and/or hydrogen (see cyclic voltammogram for the reduction of PdCl2 in H2SO4 at a BDD electrode) is explored. The roles played by the surface- and bulk-absorbed hydrogen, which cannot be observed at palladium macro- or microelectrodes, are identified.

    20. X-ray Absorption Spectroscopic Study of LiCoO2 as the Negative Electrode of Lithium-Ion Batteries (pages 1086–1091)

      Alan V. Chadwick, Shelley L. P. Savin, Ricardo Alcántara, Diego Fernández Lisbona, Pedro Lavela, Gregorio F. Ortiz and José L. Tirado

      Version of Record online: 12 APR 2006 | DOI: 10.1002/cphc.200500619

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      Positively different: Lithium cobalt oxide, a widely used positive electrode material in lithium-ion cells, is studied here as the negative electrode. The changes in the oxidation state and local environment of the cobalt atoms are resolved by using X-ray absorption spectroscopy (see figure). The formation of cobalt nanoparticles by electrochemical reduction is unfolded.

    21. Computational Study of 19F NMR Spectra of Double Four Ring-Containing Si/Ge-Zeolites (pages 1092–1099)

      Angeles Pulido, German Sastre and Avelino Corma

      Version of Record online: 12 APR 2006 | DOI: 10.1002/cphc.200500634

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      Rationalising spectra:19F NMR spectroscopy is a useful tool for studying the F location in zeolites. However, different assignments of 19F NMR chemical shifts have been reported in Si/Ge-zeolites containing double four rings (D4R). Computational chemistry techniques are used to simulate 19F NMR chemical shifts in Si/Ge-zeolites, providing a greater knowledge about the F environment and Ge distributions in D4R-containing zeolites.

    22. Interaction of Carboranes with Biomolecules: Formation of Dihydrogen Bonds (pages 1100–1105)

      Jindřich Fanfrlík, Martin Lepšík, Dominik Horinek, Zdeněk Havlas and Pavel Hobza

      Version of Record online: 3 MAY 2006 | DOI: 10.1002/cphc.200500648

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      Noncovalent interactions between polyhedral carborane 1-carba-closo-dodecaborane (CB11H12) and building blocks of biomolecules are investigated by molecular dynamic simulations and ab initio quantum chemical procedures. Carboranes are shown to interact with biomolecules such as arginine (see picture) by forming dihydrogen bond (dashed lines) complexes with large stabilization energies (8–15 kcal mol−1).

    23. ESR Spin Probes in Ionic Liquids (pages 1106–1111)

      Reinhard Stoesser, Werner Herrmann, Andrea Zehl, Veronika Strehmel and André Laschewsky

      Version of Record online: 5 APR 2006 | DOI: 10.1002/cphc.200500651

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      Spin probes in ionic liquids are compared to water/glycerol and organic-solvent reference systems, revealing the presence of salt effects and spin exchange. The picture shows an electron spin resonance (ESR) spectrum of the spin probe 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in 1-hexyl-3-methylimidazoliumtetrafluoroborate.

    24. Dynamic Light-Scattering Analysis of the Electrostatic Interaction of Hexahistidine-Tagged Cytochrome P450 Enzyme with Semiconductor Quantum Dots (pages 1112–1118)

      Binil Itty Ipe, Anuj Shukla, Huachang Lu, Bo Zou, Heinz Rehage and Christof M. Niemeyer

      Version of Record online: 11 APR 2006 | DOI: 10.1002/cphc.200500660

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      Stoichiometry investigation: The authors use the fast and convenient dynamic light scattering technique to probe the electrostatic interactions in enzyme–quantum dot (QD) conjugates. The dramatic enhancement of the light scattering intensity, when the enzyme binds to the functionalised QDs, monitors changes in the size of the nanohybrids enabling the stoichiometry of the conjugate to be determined.

    25. Thermodynamic and Ab Initio Analysis of the Controversial Enthalpy of Formation of Formaldehyde (pages 1119–1126)

      Gabriel da Silva, Joseph W. Bozzelli, Nadia Sebbar and Henning Bockhorn

      Version of Record online: 5 APR 2006 | DOI: 10.1002/cphc.200500667

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      Accurate enthalpy: Despite the importance of formaldehyde (see figure) in atmospheric and combustion chemistry, its standard enthalpy of formation is not accurately known. This study provides a new enthalphy value for formaldehyde from an analysis of existing thermochemical data, with the assistance of ab initio calculations.

    26. Photoexcitation and Relaxation Dynamics of Catecholato–Iron(III) Spin-Crossover Complexes (pages 1127–1135)

      Cristian Enachescu, Andreas Hauser, Jean-Jacques Girerd and Marie-Laure Boillot

      Version of Record online: 3 APR 2006 | DOI: 10.1002/cphc.200500671

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      Spin density in iron(III) systems: Low-temperature tunneling and thermally activated intersystem crossing is evidenced in catecholato–iron(III) spin-crossover complexes using laser pump–probe techniques (see figure; OD=optical density). In particular, the low-temperature rate constant depends critically on structural, energetic, and electronic parameters.

    27. Novel Superalkali Superhalogen Compounds (Li3)+(SH) (SH=LiF2, BeF3, and BF4) with Aromaticity: New Electrides and Alkalides (pages 1136–1141)

      Fang-Fang Wang, Zhi-Ru Li, Di Wu, Xiao-Ying Sun, Wei Chen, Ying Li and Chia-Chung Sun

      Version of Record online: 5 APR 2006 | DOI: 10.1002/cphc.200600014

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      Aromatic superatoms: Compared with alkali halide salts, such as LiF, the novel superalkali superhalides (Li3)+(SH) (SH=LiF2, BeF3, and BF4) have special characteristics. They have low vertical ionization energies and the delocalized σ-bonding highest occupied molecular orbital (HOMO) on the Li3+ ring is repulsed by the (SH) anion leading to the formation of excess electrons (see figure).

    28. Enhanced Activity and Selectivity in Cyclohexane Autoxidation by Inert H-Bond Acceptor Catalysts (pages 1142–1148)

      Ive Hermans, Jozef Peeters and Pierre A. Jacobs

      Version of Record online: 20 APR 2006 | DOI: 10.1002/cphc.200600074

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      H-bond acceptors, X, catalyse the rate-determining initiation of radical-chain autoxidations (see figure). Compounds such as Teflon and perfluorodecaline significantly boost the selectivity of cyclohexane autoxidation. The enhanced cyclohexanone and reduced hydroperoxide and cyclohexanol selectivity, fully sustains the authors' previous reports on a new autoxidation scheme which associates the formation of ketone and alcohol with the propagation of cyclohexyl hydroperoxide (CyOOH).

    29. Molecular Orbitals of Transition Metal Complexes. By Yves Jean. (pages 1149–1150)

      Latévi Max Lawson Daku

      Version of Record online: 3 MAY 2006 | DOI: 10.1002/cphc.200500696

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      Preview: ChemPhysChem 5/2006 (page 1154)

      Version of Record online: 3 MAY 2006 | DOI: 10.1002/cphc.200690015

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