ChemPhysChem

Cover image for Vol. 5 Issue 5

May 17, 2004

Volume 5, Issue 5

Pages 589–762

    1. Cover Picture: Molecular Beams and Model Catalysis: Activity and Selectivity of Specific Reaction Centers on Supported Nanoparticles (ChemPhysChem 5/2004) (page 589)

      Jörg Libuda

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200490028

      The cover picture shows time-resolved surface IR spectra (top) acquired during a molecular beam experiment on a supported model catalyst (bottom). Using this approach, the microscopic role of different types of sites simultaneously present on a catalyst surface can be probed during a catalytic reaction. Moreover, detailed information on the activities and selectivities of specific reactive centers on the well-defined nanocrystallites of the catalyst can be obtained. Find out more in the Concept by Libuda on p. 625.

    2. Graphical Abstract: ChemPhysChem 5/2004 (pages 591–597)

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200490029

    3. Quantum Dynamics of Gas-Phase SN2 Reactions (pages 600–617)

      Stefan Schmatz

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301043

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      The nucleophilic bimolecular substitution (SN2) mechanism is a nice exemplary case for approaching one of the principal goals in chemistry: the understanding of the state-resolved dynamics of elementary chemical reactions that involve polyatomic molecules. The progress in the quantum mechanical treatment of SN2 reactions in the gas phase is reviewed. Although the calculations reported here are very demanding, the effort is rewarding because new and interesting insights into the details of multimode quantum dynamics of chemical reactions can be obtained (see graphic).

    4. Electronic Structure and Chemical Reactivity of Carbon Nanotubes: A Chemist's View (pages 619–624)

      Ernesto Joselevich

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301049

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      Why metallic and semiconducting carbon nanotubes are chemically different is explained from an unusual chemical perspective that merges the solid-state physics description of carbon nanotubes with the molecular orbitals picture of reaction mechanisms used in organic chemistry. Traditional concepts of aromaticity, orbital symmetry and frontier orbitals, applied to carbon nanotubes (see graphic), predict intriguing chemical selectivity based on electronic structure.

    5. Molecular Beams and Model Catalysis: Activity and Selectivity of Specific Reaction Centers on Supported Nanoparticles (pages 625–631)

      Jörg Libuda

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200400049

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      Nanoscale kinetics: What makes chemical reaction kinetics on nanometer-sized particles so different from those on extended surfaces? New approaches combining molecular-beam methods (see graphic) and model catalysts provide insights into this question, which lies at the heart of heterogeneous catalysis. By simple examples it is illustrated how the activity and selectivity of specific reaction centers can be probed at the microscopic level.

    6. Comparison of Properties of Aib-Rich Peptides in Crystal and Solution: A Molecular Dynamics Study (pages 633–641)

      Haibo Yu, Maaike Ramseier, Roland Bürgi and Wilfred F. van Gunsteren

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301026

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      Crystal versus solution: Molecular dynamics simulations show that large differences exist between properties of peptides in crystal and in solution. A shows peptide II in a crystal unit cell and B shows the most populated cluster of peptide I (in yellow) in dimethyl sulfoxide together with the crystal structure of peptide II (in purple).

    7. Probing the Basicity of Regular and Defect Sites of Alkaline Earth Metal Oxide Surfaces by BF3 Adsorption: A Theoretical Analysis (pages 642–651)

      Cristiana Di Valentin, Corrado Locati and Gianfranco Pacchioni

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200400006

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      The basicity of terrace, step, edge, and corner sites on the surface of MgO, CaO, SrO, and BaO was investigated theoretically by using BF3 as a probe molecule (the structure of a BF3 adduct adsorbed on a terrace oxide anion is shown in the picture). Many properties of adsorbed BF3, especially the experimentally accessible shifts in B[BOND]F vibrational frequency, in B and F 1s core levels, and in BF3 desorption temperature, exhibit a linear correlation with the surface basicity as measured by the vertical ionization potential of the oxide anions. However, shifts in the O 1s core-level binding energy are not quantitative indicators of surface basicity.

    8. Effects of Ion-Carrier Substituents on the Potentiometric-Response Characteristics in Anion-Selective Membrane Electrodes Based on Iron Porphyrins (pages 652–660)

      Saeed Shahrokhian, Hassan Seifi, Mojtaba Bagherzadeh and S. Reza Mousavi

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301025

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      Sensitive salicylate sensors: Iron porphyrin complexes in polyvinylchloride membranes can act as anion carriers with a relatively high selectivity for salicylate (see graphic). The mechanism of the ionophore response is strongly dependent on the substituents of the porphyrin and also on the pH of the solution in which the response is measured. The introduction of highly electrophilic substituents into the porphyrin improves the sensitivity and, to some extent, the selectivity of porphyrin-based membrane electrodes.

    9. Kinetics and Mechanism of the C6H5 + CH3CHO Reaction: Experimental Measurement and Theoretical Prediction of the Reactivity toward Four Molecular Sites (pages 661–668)

      Y. M. Choi, J. Park and M. C. Lin

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301201

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      Radical reaction rates: The kinetics and mechanism of the reaction of C6H5 with CH3CHO (see potential energy diagram) have been investigated experimentally and theoretically. The reactions of the phenyl radical with aldehydes may occur under sooting conditions. The theories predict that the reaction may occur by two hydrogen-abstraction and two addition channels, with the aldehydic hydrogen-abstraction reaction being dominant. The rate constant calculated by the transition-state theory for the aldehydic hydrogen-abstraction reaction is in good agreement with the experimental result after a very small adjustment of the predicted reaction barrier.

    10. Abrasively Immobilised Multiwalled Carbon Nanotube Agglomerates: A Novel Electrode Material Approach for the Analytical Sensing of pH (pages 669–677)

      Gregory G. Wildgoose, Henry C. Leventis, Ian Streeter, Nathan S. Lawrence, Shelley J. Wilkins, Li Jiang, Timothy G. J. Jones and Richard G. Compton

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200400030

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      Many three-phase boundaries: The authors demonstrate for the first time that agglomerates of multiwalled carbon nanotubes can be formed in which the binder in the agglomerate is itself a redox-active molecular solid (see picture). The nature of this structure, when immobilised on a substrate electrode and in contact with aqueous electrolyte solutions, gives rise to many three-phase boundaries, which imparts a larger electroactive surface area than other modified carbon electrodes.

    11. Photophysical Aspects of Single-Molecule Detection by Two-Photon Excitation with Consideration of Sequential Pulsed Illumination (pages 678–687)

      R. Niesner, W. Roth and Karl-Heinz Gericke

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200300881

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      Calculation of fluorescence autocorrelation functions by a suitably designed model is an important step in the evolution of fluorescence correlation spectroscopy (FCS). Recently, FCS has been increasingly performed in combination with multiphoton pulsed excitation, and the development of models which apply a time-dependent treatment of the molecular photoprocesses illustrated in the picture has become particularly significant. Here, the molecular photodynamics are described by a linear set of differential equations with time-dependent prefactors.

    12. Dissolution of Crystallites: Surface Energetic Control and Size Effects (pages 688–696)

      Ruikang Tang, Christine A. Orme and George H. Nancollas

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200300956

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      Dissolving mechanism: Dissolution of crystallites is accompanied by the formation and growth of surface pits (see picture). The development of a pit is not always spontaneous and there is a critical pit size due to surface energy control. Only large pits contribute to the reaction. When crystallites are reduced to a size similar to that of a critical pit, dissolution is inhibited or even suppressed.

    13. Reactive Ion Surface Scattering as an Eley–Rideal Process: A Molecular Dynamics Study into the Abstraction Reaction Mechanism by Low Energy Cs+ From Pt(111) (pages 697–705)

      Rob J. W. E. Lahaye and Heon Kang

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200300983

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      Attraction aids pick-up: Reactive ion scattering from surfaces is a technique for determining neutral adsorbates on a surface. When a Cs+ projectile scatters from a surface in the vicinity of an adsorbate (see graphic), the adsorbate may desorb and form an ion–adsorbate product in the outgoing trajectory, due to the ion–dipole attraction between the two particles. Using classical molecular dynamics simulations, the authors introduce a new mechanism that explains the high efficiencies for such product formations as observed in recent experiments. Critical factors appear to be the adsorbate binding energy to the surface and the inertia of the adsorbate mass.

    14. Ultrafast Proton-Coupled Electron-Transfer Dynamics in Pyrene-Modified Pyrimidine Nucleosides: Model Studies towards an Understanding of Reductive Electron Transport in DNA (pages 706–712)

      Milen Raytchev, Elke Mayer, Nicole Amann, Hans-Achim Wagenknecht and Torsten Fiebig

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301205

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      Charge carriers: PydX (Py=pyrenyl, dX=deoxyuridine or deoxycytidine) serve as nucleoside models to study the properties of the intermediate charge carriers of electron transport in DNA. Excitation of the pyrene moiety in PydX leads to an intramolecular proton-coupled electron transfer (PCET) that yields the pyrenyl radical cation and the corresponding pyrimidine radical anion (illustrated in graphic).

    15. Spontaneous Organization of Individual Silver Nanoparticles into One-Dimensionally Ordered Nanostructures (pages 713–716)

      Houyi Ma, Yongli Jiao, Bingsheng Yin, Shuyun Wang, Shiyong Zhao, Shaoxin Huang, Wei Pan, Shenhao Chen and Fanjun Meng

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301007

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      Stretching shapes structures: The interaction between poly(N-vinylpyrrolidone) (PVP) and sodium dodecyl benzene sulfonate (SDBS) can make the PVP coil polyvinyl skeleton stretch to a considerable degree. Silver nanoparticles produced by photoreduction are anchored onto the backbone of PVP (see graphic); they then spontaneously organize into one-dimensionally ordered nanoaggregates along the stretched PVP chain.

    16. A Novel and Efficient System of a Visible-Light-Responsive Organic Photoelectrocatalyst Working in a Water Phase (pages 716–720)

      Toshiyuki Abe, Keiji Nagai, Masao Kaneko, Takashi Okubo, Kouki Sekimoto, Akio Tajiri and Takayoshi Norimatsu

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301060

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      The best of both worlds: An organic bilayer, composed of a perylene derivative (PV) and a phthalocyanine (H2Pc), was found to be a novel example of a photoanode involving a catalytic oxidation in water (see graphic). Based on the action spectrum for photocurrent, it is noted that the widespread visible light absorption (<750 nm) by only the PV can efficiently induce the photoanodic current generation at the interface of H2Pc/water coupled with the hole-conducting character of H2Pc.

    17. Gold-Colloid-Modified AgCl Photocatalyst for Water Oxidation to O2 (pages 720–724)

      Antonio Currao, Vanga Raja Reddy and Gion Calzaferri

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301211

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      Better with gold! Gold nanoparticles have a deep red color and an absorption maximum at about 530 nm. They have been used to remarkably improve the performance of silver chloride photoanodes for photoelectrochemical water oxidation to dioxygen. The Figure shows O2 production versus time for an AgCl electrode modified with Au colloids.

    18. An Anhydrous Proton Conductor Based on Lactam–Lactim Tautomerism of Uracil (pages 724–728)

      Masanori Yamada and Itaru Honma

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301015

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      Proton-conducting composite salts were obtained by doping uracil (U) with monodecyl phosphate (MDP). The proton-transfer reaction of the composite salt involves the lactam form of U at low MDP doping ratios, and the lactim form at high ratios (see picture). A proton conductivity of 6×10−4 S cm−1 was achieved at 160 °C under anhydrous conditions, and the material is thus of interest for applications in polymer electrolyte membrane fuel cells.

    19. DNA-Based Formation of a Supported, Three-Dimensional Lipid Vesicle Matrix Probed by QCM-D and SPR (pages 729–733)

      Annette Granéli, Malin Edvardsson and Fredrik Höök

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301061

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      Resonance in soft films: The formation of multilayers of DNA-modified lipid vesicles (see graphic) was investigated with a quartz crystal microbalance and surface plasmon spectroscopy to investigate the assembly process, with specific attention placed on analyzing soft films approaching the sensing depth of these techniques.

    20. Oxide Surfaces that Catalyse an Acid–Base Reaction with Surface Lattice Oxygen Exchange: Evidence of Nucleophilicity of Oxide Surfaces (pages 733–736)

      Hideto Tsuji and Hideshi Hattori

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200400009

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      Moving the labels: The dynamics of surface lattice oxygen atoms is demonstrated using 18O-labeled MgO and CaO catalysts. The incorporation of 18O into the products of the pseudo-Canizzaro reaction under mild conditions (see Figure) illustrates the nucleophilicity of the oxide surfaces and indicates a reaction mechanism involving surface restructuring.

    21. Structural Distortion of Pyridazine in the 1(n,π*) Excited State: Evidence for Local Excitation (pages 737–739)

      Kyo-Won Choi, Doo-Sik Ahn, Sungyul Lee, Heechol Choi, Kyoung-Koo Baeck, Seong-Ung Heo, Sun Jong Baek, Young S. Choi and Sang Kyu Kim

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200400053

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      Exciting results: The graphic shows the calculated structure of pyridazine in the S1 state, demonstrating the distorted CS geometry due to the local 1(n,π*) excitation—the nature of vibronic states of the S1 pyridazine has been clearly identified for the first time.

    22. Probing the Vibrations of Shared, OH+O-Bound Protons in the Gas Phase (pages 740–743)

      David T. Moore, Jos Oomens, Lex van der Meer, Gert von Helden, Gerard Meijer, Jose Valle, Alan G. Marshall and John R. Eyler

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200400062

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      Spectral signature of a proton bridge? Gas-phase infrared spectra are reported in the range of 500–1800 cm−1 for three species with short, strong hydrogen bonds, namely the proton-bound dimers of dimethyl ether (shown in the picture) and diethyl ether, and protonated 1,1′-oxybis[2-methoxyethane] (diglyme). The spectra are all quite similar, and furthermore they also strongly resemble the spectrum of the proton-bound water dimer (H5O2+), suggesting that there may be a conserved “spectral signature” for a proton bound between two oxygen atoms.

    23. Sensitized Emission in Ln3+-Doped TiO2 Semiconductor Nanoparticles (pages 743–746)

      Jan W. Stouwdam and Frank C. J. M. van Veggel

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200300967

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      The doping of lanthanide ions in semiconductor TiO2 nanoparticles is studied. The presence of the TiO2 absorption band in the excitation spectrum of the lanthanide (see graphic; excitation and emission) proves the existence of energy transfer from the host material to the lanthanide ion. Energy transfer to several lanthanide ions occurs, including to Er3+, Nd3+, Yb3+, and Eu3+.

    24. Parallel β-Sheet Assemblies at Interfaces (pages 747–750)

      Ronit Sneer, Markus Jan Weygand, Kristian Kjaer, David A. Tirrell and Hanna Rapaport

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200301046

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      Electrostatic tuning: Parallel β-sheet assemblies at interfaces were obtained via designed complementary electrostatic interactions. A system composed of an equimolar mixture of two amphiphilic peptides PA (see picture) and PB, which are identical in sequence but for the two amino acids, lysine and glutamic acid, reversed in positions along the strands, demonstrates the prevailing effect of cross-strand pair electrostatic interactions on tuning the assembly of β-strands.

    25. Large-Area Fabrication of a Nanostructure-Induced Hydrophobic Surface from a Hydrophilic Polymer (pages 750–753)

      Chaowei Guo, Lin Feng, Jin Zhai, Guojie Wang, Yanlin Song, Lei Jiang and Daoben Zhu

      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200400013

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      Wet and dry? The ability to control wettability of a solid surface is essential in many fields. A simple and effective “template rolling press” method for preparing large-area patterned surfaces with controlled wetting properties (see picture) on the nanometer scale is demonstrated. It is believed that reorientation of polymer molecules occurs when the polymer is heated and compressed into the nanopore of the template.

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      Article first published online: 14 MAY 2004 | DOI: 10.1002/cphc.200490033

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