Cover image for ChemPhysChem

March 13, 2006

Volume 7, Issue 3

Pages 537–766

    1. Cover Picture: Linear and Two-Photon Absorption Properties of Interacting Polar Chromophores: Standard and Unconventional Effects (ChemPhysChem 3/2006) (page 537)

      Francesca Terenziani, Marika Morone, Said Gmouh and Mireille Blanchard-Desce

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200690008

      The cover picture shows the evolution of two-photon absorption (TPA) spectra for dimers of polar and polarisable chromophores, as a function of orientation and distance. Strong modulation of nonlinear optical responses can be attained through interchromophoric interactions. Important contributions from interaction terms beyond the standard excitonic model are demonstrated both experimentally and theoretically. Find out more in the Article by Terenziani et al. on page 685.

    2. Novel Insights into the Mechanism of the Ortho/Para Spin Conversion of Hydrogen Pairs: Implications for Catalysis and Interstellar Water (pages 551–554)

      Hans-Heinrich Limbach, Gerd Buntkowsky, Jochen Matthes, Stefan Gründemann, Tal Pery, Bernadeta Walaszek and Bruno Chaudret

      Article first published online: 22 FEB 2006 | DOI: 10.1002/cphc.200500559

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      Going for a spin: Exchange coupling is taken into account in the magnetic nuclear spin conversion between bound ortho- and para-dihydrogen (see picture). This coupling has to be reduced for a magnetic interaction to effectively induce a spin conversion. The implications for liquid water, ice, and the nuclear spin temperature of water vapor in comets are discussed. ΔEop is the energy difference between the two lowest states and ℋd is the Hamiltonian of dipole–dipole interactions.

    3. Analytical Assays Based on Detecting Conformational Changes of Single Molecules (pages 555–560)

      Giovanni Zocchi

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200400603

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      On target: A single DNA oligomer probe attached to a micron-sized bead forms the sensing element of a mechanical nanodevice, which performs a hybridization assay. When the target oligomer binds, the conformational change of the sensor molecule causes a nanometer-scale displacement of the bead, which is detected optically by evanescent-wave scattering (see picture).

    4. Relevance of Electron-Driven Proton-Transfer Processes for the Photostability of Proteins (pages 561–564)

      Andrzej L. Sobolewski and Wolfgang Domcke

      Article first published online: 22 FEB 2006 | DOI: 10.1002/cphc.200500604

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      Ultrafast coupled electron–proton transfer: The locally excited (LE) electronic state is deactivated via two sequential electron-transfer (ET) processes at conical intersections of the LE state (blue) and the electronic ground state (black) with a charge-transfer state (red). After each electron transfer, the proton follows the electron, thus accepting the energy deposited by the UV photon in the molecular system.

    5. Conformational Landscapes and Free-Jet Rotational Spectrum of Indan-1-ol (pages 565–568)

      Biagio Velino, Paolo Ottaviani, Walther Caminati, Anna Giardini and Alessandra Paladini

      Article first published online: 8 FEB 2006 | DOI: 10.1002/cphc.200500385

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      Nonbonding interactions: The most stable configuration of indanole as determined by rotational spectroscopy in supersonic expansions results in the hydroxyl group in the equatorial position, with the hydroxyl hydrogen pointing towards the cyclopentenyl ring (see figure). Five other rotamers, generated by the hydroxyl group rotation and by the five-membered ring puckering, relax to this one upon supersonic expansion.

    6. On the Protoporphyrin Monolayers Conformation (pages 569–571)

      Christophe Humbert, Laurent Dreesen, Yannick Sartenaer, André Peremans, Paul A. Thiry and Cédric Volcke

      Article first published online: 8 FEB 2006 | DOI: 10.1002/cphc.200500475

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      Challenging Characterisation: Precise determination of the conformation and electronic properties of haemoporphyrin–metal interfaces are important for device characterisation. The authors show that metalloporphyrins lie more planar on the substrate than the metal-free porphyrins, which are less tilted with respect to the surface normal direction (see sum-frequency generation, SFG, spectra).

    7. Photocatalytic Reforming of Methanol by Spatially Separated Pd Particles on Special TiO2 Layers (pages 572–574)

      Susann Meyer, Sarah Saborowski and Bernhard Schäfer

      Article first published online: 10 FEB 2006 | DOI: 10.1002/cphc.200500487

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      Photocatalytic hydrogen evolution: Spatially separated Pd particles on special flowery TiO2 layers (see picture) leads to interesting effects on the photocatalytic reforming of methanol. Furthermore in this context the authors deal with a new concept of palladium fixation to avoid agglomeration processes.

    8. Photoswitched Wettability on Inverse Opal Modified by a Self-Assembled Azobenzene Monolayer (pages 575–578)

      Hongli Ge, Guojie Wang, Yaning He, Xiaogong Wang, Yanlin Song, Lei Jiang and Daoben Zhu

      Article first published online: 3 FEB 2006 | DOI: 10.1002/cphc.200500496

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      Controllable wettability has been achieved in inverse opal, fabricated with a photoresponsive azobenzene monolayer. The surface undergoes reversible changes in wettability on UV/Vis irradiation due to photoisomerization of the monolayer. Adjustment of the air-sphere size of the inverse opal controls both structural color and contact angle (CA) [picture shows SEM image of modified inverse opal and water droplet shapes in the trans (CA=140.8°) and cis states (CA=121.8°)].

    9. Ordering Spatiotemporal Chaos in Small-World Neuron Networks (pages 579–582)

      Maosheng Wang, Zhonghuai Hou and Houwen Xin

      Article first published online: 3 FEB 2006 | DOI: 10.1002/cphc.200500499

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      Taming spatiotemporal chaos: The dynamics of chaotic Hindmarsh–Rose neurons in small-world networks have been investigated. An optimal but small number of random shortcuts can tame the spatiotemporal chaos observed in a regular neuron chain into an ordered state which is periodic in time and synchronized in space (see picture; the neurons fire in bright regions, and are quiescent in the dark ones).

    10. Fluorescent Hydroxyflavone–Zeolite Nanoparticles: Ship-in-a-Bottle Synthesis and Photophysical Properties (pages 583–589)

      Tristan Doussineau, Monique Smaïhi, Sébastien Balme and Jean-Marc Janot

      Article first published online: 10 FEB 2006 | DOI: 10.1002/cphc.200500363

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      Photochemically stable fluorescent colloids were obtained by using microporous zeolite nanoparticles as hosts for ship-in-a-bottle synthesis and confinement of 3-hydroxyflavone (3-OHF). N2 adsorption isotherms demonstrated the presence of 3-OHF in the microporous cavities and time-resolved fluorescence spectroscopy confirmed the stabilization of the normal N* form of excited hydroxyflavone in the zeolite cavities.

    11. Compression-Inhibited Pore Formation of Polyelectrolyte Multilayers Containing Weak Polyanions: A Scanning Force Microscopy Study (pages 590–596)

      Bo Wang, Lili Liu, Ke Chen, Lin Chen, Jie Feng and Changyou Gao

      Article first published online: 20 JAN 2006 | DOI: 10.1002/cphc.200500369

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      Polymer film formation: Layer-by-layer assembled poly(acrylic acid)/poly(diallyldimethylammonium chloride) multilayers are pattern-compressed by a rubber stamp. Upon compression the oppositely charged polyelectrolyte chains approach each other closer to produce a higher density of ion cross-linking and physical entanglement, which in turn effectively enhances their stability against chain rearrangement and/or phase separation.

    12. Spectral and Photophysical Properties of Thioxanthone in Protic and Aprotic Solvents: The Role of Hydrogen Bonds in S1-Thioxanthone Deactivation (pages 597–606)

      Ewa Krystkowiak, Andrzej Maciejewski and Jacek Kubicki

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500375

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      Time-resolved emission spectroscopy (TRES; see figure) used in this photophysical study, shows that the dominant deactivation process of the S1 state of thioxanthone in protic solvents involves a hydrogen bonded S1-complex. Important deactivation modes are fluorescence and intersystem crossing. The S1-complex[RIGHTWARDS ARROW]S0 internal conversion plays an insignificant role, which is evidenced by the absence of an isotope effect of protic solvents on the fluorescence lifetime and quantum yield.

    13. The Leading Role of Association in Framework Modification of Highly Siliceous Zeolites with Adsorbed Methylamine (pages 607–613)

      Ai-Jie Han, Juan Guo, Hui Yu, Yu Zeng, Yue-Fang Huang, He-Yong He and Ying-Cai Long

      Article first published online: 3 FEB 2006 | DOI: 10.1002/cphc.200500389

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      Hybrid zeolites: Adsorbed methylamine (MA) strongly interacts with the framework of highly siliceous MFI, FAU, and FER zeolites. At 298 K the H atom of the amine group attacks the Si[BOND]O[BOND]Si framework to form Si[BOND]OH and O⋅⋅⋅H⋅⋅⋅N bonds, which leads to great variations in the 29Si magic-angle spinning NMR spectra of the zeolites (see spectra for MFI: a=raw zeolite, b=after MA adsorption).

    14. Exploring Two-State Reaction Pathways in the Photodimerization of Cyclohexadiene (pages 614–618)

      Luis R. Domingo and Julia Pérez-Prieto

      Article first published online: 6 FEB 2006 | DOI: 10.1002/cphc.200500431

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      Bis-allylic biradical intermediates are involved in the stepwise mechanism of the photodimerization of cyclohexadiene (see picture) according to DFT calculations. The first C[BOND]C bond formation in the lowest triplet state (T1) leading to intermediate IN(T1) has a low activation enthalpy, but the subsequent ring-closure has a very large activation enthalpy. Triplet-to-singlet intersystem crossing (ISC) from IN(T1 ) to IN(S0 ) favors cyclization to give the corresponding [2+2] and [4+2] cycloadducts.

    15. Binding Interactions and Raman Spectral Properties of Pyridine Interacting with Bimetallic Silver–Gold Clusters (pages 619–628)

      De-Yin Wu, Bin Ren and Zhong-Qun Tian

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500439

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      Bimetallic colloidal particles: Active surface sites and surface Raman spectra of probe pyridine molecules on a gold–silver bimetallic surface (see figure) are investigated by hybrid density functional theory. Electrostatic interactions result in pyridine molecules preferring to bind to the silver active sites. Raman spectra of adsorbed pyridine depend on the binding interactions at the adsorption site on the bimetallic surface.

    16. The Properties of Weak and Strong Dihydrogen-Bonded D[BOND]H⋅⋅⋅H[BOND]A Complexes (pages 629–639)

      Hubert Cybulski, Elwira Tymińska and Joanna Sadlej

      Article first published online: 14 FEB 2006 | DOI: 10.1002/cphc.200500462

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      Dihydrogen bonding in complexes is investigated using a number of ab initio methods. Study of the structural, energetic and spectroscopic parameters divides the studied D[BOND]H⋅⋅⋅H[BOND]A complexes into three groups and allows a comparison with conventional hydrogen bonding. The figure shows the dependence of the reduced intermolecular spin–spin coupling constant, 1hKH[BOND]H , on H⋅⋅⋅H intermolecular distances in particular BeH2 complexes.

    17. Theoretical Investigations into the Blue-Shifting Hydrogen Bond in Benzene Complexes (pages 640–643)

      Vladimír Špirko and Pavel Hobza

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500565

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      Bond contraction: Optimization of benzene⋅⋅⋅X complexes where X=benzene, antracene, ovalene (see figure) shows that the C[BOND]H bond of the proton donor is contracted. This contraction is accompanied by a blue-shifting in the C[BOND]H stretching frequency which arises due to the compensation of the exchange repulsion and London dispersion energies.

    18. Photoisomerizable Bipyridine Ligands and Macroligands: Absorption, Photoisomerization Properties and Theoretical Study (pages 644–657)

      Lydie Viau, Itamar Malkowsky, Karine Costuas, Stéphanie Boulin, Loïc Toupet, Eléna Ishow, Keitaro Nakatani, Olivier Maury  and Hubert Le Bozec

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500473

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      Azo-containing polymers: 4,4′-Dibutylaminophenylazostyryl-2,2′-bipyridine and its corresponding macroligand are prepared by copper-catalyzed atom-transfer radical polymerization of methyl methacrylate. Photoisomerization experiments are carried out in both solution and film, and the kinetics of photochemical (E/Z) and thermal (Z/E) isomerization are investigated (see picture).

    19. Slater-Like Model for Carbon 1s Core Ionization Energies of Halomethanes (pages 658–663)

      Chenzhong Cao

      Article first published online: 22 FEB 2006 | DOI: 10.1002/cphc.200500490

      Computing core ionization energies: The carbon 1s core ionization energy E1,C of halomethanes can be calculated by a Slater-like model, in which the electrostatic–relaxation shielding of the carbon 1s electron is expressed by the charge effect together with the relaxation effect. The proposed model lays a good foundation for computing the core ionization energies of various atoms in more complex molecules.

    20. Oriented Attachment Mechanism in Anisotropic Nanocrystals: A “Polymerization” Approach (pages 664–670)

      Caue Ribeiro, Eduardo J. H. Lee, Elson Longo and Edson R. Leite

      Article first published online: 13 FEB 2006 | DOI: 10.1002/cphc.200500508

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      Growing Colloids: Oriented attachment mechanisms in nanostructures (e.g. nanowires, nanoribbons, nanorods) are experimentally correlated to the tailoring of these structures (see figure); this differs from coarsening as it is not a solubilization–precipitation process. The authors propose a physical model based on a polymerization approach to aid a deeper understanding of anisotropic growth on the nanoscale.

    21. Force Field Evaluation for Biomolecular Simulation: Free Enthalpies of Solvation of Polar and Apolar Compounds in Various Solvents (pages 671–678)

      Daan P. Geerke and Wilfred F. van Gunsteren

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500510

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      Biomolecular simulations: The performance of the GROMOS 53A6 biomolecular force field has been investigated by calculating the free enthalpy of solvation of a set of apolar and polar compounds representative for biomolecular moieties in a variety of solvents (see figure). Calculated values for and obtained trends in the solvation free enthalpy are in good agreement with the experimental data.

    22. Critique of the Multipath Model for 1J(C,C) Nuclear Spin–Spin Coupling via Electron Current Induced by 13C Nuclear Magnetic Dipoles (pages 679–684)

      A. Soncini and P. Lazzeretti

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500517

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      Spin–spin coupling in cyclic systems: The topology of maps of the electonic current density induced by nuclear magnetic dipoles in ethane, cyclopropane and bicyclobutane is used to interpret 1J(C,C) values in terms of classical electromagnetic theory. The results are not affected by the multipath coupling processes typically invoked in the literature. A contour plot of the Fermi-contact coupling density for 1J(C,C) in cyclopropane is depicted in the figure.

    23. Linear and Two-Photon Absorption Properties of Interacting Polar Chromophores: Standard and Unconventional Effects (pages 685–696)

      Francesca Terenziani, Marika Morone, Said Gmouh and Mireille Blanchard-Desce

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500536

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      Interchromophore interactions can play a crucial role (either beneficial or detrimental) in the linear and nonlinear optical properties of polar molecules, as illustrated in the figure, where the two-photon absorption cross section σ2 of a dimer of polar chromophores is compared with the response of the corresponding monomer. Such remarkable effects stemming from purely electrostatic interactions are shown to be strongly determined by contributions beyond the standard exciton model.

    24. Mathematical Modelling and Simulation of Adsorption Processes at Spherical Microparticles (pages 697–703)

      François G. Chevallier, Biljana Šljukić, Gregory G. Wildgoose, Li Jiang, Timothy G. J. Jones and Richard G. Compton

      Article first published online: 3 FEB 2006 | DOI: 10.1002/cphc.200500546

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      Adsorption at microparticles: A model for the adsorption process at spherical microparticles was developed and solved using numerical simulation. The properties of the system were studied for both the case where mass transport is described by diffusion only and the case where it is the result of a coupled diffusion/convection process (see figure).

    25. AFM Studies of Metal Deposition: Instantaneous Nucleation and the Growth of Cobalt Nanoparticles on Boron-Doped Diamond Electrodes (pages 704–709)

      Andrew O. Simm, Xiaobo Ji, Craig E. Banks, Michael E. Hyde and Richard G. Compton

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500557

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      The bare neccessities: The high degree of flatness and uniformity on the bare surface of boron-doped diamond electrodes provides the desirable starting point for the nucleation of cobalt nanoparticles. Using an in situ atomic force microscopy cell, real-time images are collected after sequential potentials are applied, recording the growth of cobalt nuclei (see diagram).

    26. Cyanomethylidyne: A Reactive Carbyne Radical (pages 710–722)

      Jian Wang, Yi-hong Ding and Chia-chung Sun

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500548

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      A carbyne insertion–dissociation mechanism is followed by the cyanomethylidyne radical (CCN) in its reaction with CH4 as opposed to the direct H-abstraction mechanism proposed by a recent experimental study and other σ-bonded molecules HX (X=OH, NH2, and F) according to ab initio calculations. These results, as well as the formation of a three-membered cyclic intermediate by barrierless carbenoid addition to the C[TRIPLE BOND]C bond of acetylene, lead to the conclusion that CCN is a reactive carbyne radical.

    27. Importance of Spin–Orbit Coupling for the Assignment of the Photodetachment Spectra of AuX2 (X=Cl, Br, and I) (pages 723–727)

      Sabyashachi Mishra, Valerie Vallet and Wolfgang Domcke

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500554

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      Spin–orbit effects: The photodetachment spectra of AuX2, X=Cl, Br, and I are reassigned, taking spin–orbit coupling into account and employing relativistic-effective core potentials for gold and the halogen atoms (see highest occcupied molecular orbitals in AuCl2 and AuI2). The results of this work are compared with experiment and with other scalar-relativistic theoretical studies.

    28. Electron Traps on Oxide Surfaces: (H+)(e) Pairs Stabilized on the Surface of 17O Enriched CaO (pages 728–734)

      Mario Chiesa, Maria Cristina Paganini, Elio Giamello, Cristiana Di Valentin and Gianfranco Pacchioni

      Article first published online: 14 FEB 2006 | DOI: 10.1002/cphc.200500564

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      Dissolving H atoms on oxide surfaces: H atoms react with alkaline-earth oxide surfaces to give unusual (H+)(e) ion pairs stabilized at low coordinated sites. The process, which can be thought of as the dissolution of the H atom over a bidimensional solvent, is monitored by electron paramagnetic resonance spectroscopy on the 17O enriched CaO surface and modeled by ab initio quantum chemical calculations (see figure).

    29. Spectroscopic Study of a UV-Photostable Organic–Inorganic Hybrids Incorporating an Eu3+ β-Diketonate Complex (pages 735–746)

      Patricia P. Lima, Rute A. Sá Ferreira, Ricardo O. Freire, Filipe A. Almeida Paz, Lianshe Fu, Severino Alves Jr., Luis D. Carlos and Oscar L. Malta

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500588

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      Photostable hybrids: A highly luminescent Eu3+ β-diketonate complex was synthesized and incorporated in organic–inorganic hybrids, named ‘di-ureasils’. The hybrid is photostable under UVA excitation compared with the isolated complex (see picture), and has potential for use in organic light-emitting diodes and UVB and UVC dosimeters.

    30. Clean Diesel Power via Microwave Susceptible Oxidation Catalysts (pages 747–755)

      Jurriaan Beckers, Lars M. van der Zande and Gadi Rothenberg

      Article first published online: 10 FEB 2006 | DOI: 10.1002/cphc.200500420

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      A cleaner, greener exhaust: Regenerating diesel soot filters is easy if one uses mixed perovskite oxides that combine high microwave susceptibility with selective oxidation catalysis. These crystalline materials heat fast under microwave irradiation, giving “hot spots” where the catalysis takes place (see figure). The catalysts can be tuned for high SO2 tolerance. Preliminary tests show the concept is feasible in a practical application.

    31. Long-Range Molecular Organization of an Organic Monolayer Grafted on a Mineral Substrate (pages 756–761)

      Bernd Struth, Pierre Terech and François Rieutord

      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200500501

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      The regular array of reactive sites present at the single-crystal surface of topaz is exploited to perform a liquid-phase silanization reaction with a trialkylchlorosilane. By using the grazing-incidence X-ray diffraction technique the bare and covalently coated surfaces are characterized, and the ordering of the monomolecular organic layer (C18 alkane chains in diagram represented as cylinders) reproduces the perfect single-crystal structure of the cleaved surface over millimeter distances.

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      Article first published online: 3 MAR 2006 | DOI: 10.1002/cphc.200690010