ChemPhysChem

Cover image for Vol. 5 Issue 11

November 19, 2004

Volume 5, Issue 11

Pages 1637–1810

    1. Cover Picture: Probing Ligand–Protein Recognition with Sum-Frequency Generation Spectroscopy: The Avidin–Biocytin Case (ChemPhysChem 11/2004) (page 1637)

      Laurent Dreesen, Yannick Sartenaer, Christophe Humbert, Alaa A. Mani, Christophe Méthivier, Claire-Marie Pradier, Paul A. Thiry and André Peremans

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200490054

      The cover picture shows an artistic representation of the recognition of a protein (avidin) by a self-assembled monolayer of ligand molecules (biocytin) using sum- frequency generation (SFG) spectroscopy. This recognition is mainly highlighted by the occurrence of two additional SFG resonances denoted α and β on the cover picture. In the related Article on page 1719, Dreesen et al. discuss the origin of these two peaks and deduce information on the conformational order and orientation of the adsorbed biological species.

    2. Atmospheric Organic Aerosol Production by Heterogeneous Acid-Catalyzed Reactions (pages 1646–1661)

      Myoseon Jang, Nadine M. Czoschke and Amanda L. Northcross

      Version of Record online: 13 OCT 2004 | DOI: 10.1002/cphc.200301077

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      Climatic changes: Increased levels of secondary organic aerosol mass result from acid-catalyzed heterogeneous reactions of carbonyl compounds and their partitioning into the particle phase. This Review outlines fundamental chemistry of the particle-phase heterogeneous reactions (see graphic; R1,R2=H or alkyl, 3ROH=alcohol), which might have a much larger impact on climate-forcing effects than we now predict.

    3. Photochemistry of Molecules Relevant to the Atmosphere: Photodissociation of Nitric Acid in the Gas Phase (pages 1663–1669)

      J. Robert Huber

      Version of Record online: 21 OCT 2004 | DOI: 10.1002/cphc.200400071

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      Solar photolysis of nitric acid is of interest due to the important role of this molecule in atmospheric chemistry. This Minireview gives an account of the gas-phase photochemistry of HNO3, focussing on the regions around 300 and 200 nm, where solar photodissociation of HNO3 is expected to be efficient. The picture shows O(3P2) velocity profiles for three photochemical decay pathways, derived from resonance-enhanced multiphoton ionization time-of-flight data.

    4. Extraction of Kinetic Information from Single-Molecule Experiments (pages 1671–1678)

      Marcel O. Vlad and John Ross

      Version of Record online: 21 OCT 2004 | DOI: 10.1002/cphc.200300991

      Two simple approaches for extracting kinetic information from single-molecule experiments are discussed. The first is based on calculating correlation functions from measured fluorescence signals, and the second on studying the statistics of on and off times of the same fluorescence signal. In both cases it is possible to extract kinetic information about single-molecule intramolecular fluctuations, which produce stochastic memory effects.

    5. Infrared Absorption Features of Gaseous Isopropyl Carbocations (pages 1679–1685)

      Barbara Chiavarino, Maria E. Crestoni, Simonetta Fornarini, Joel Lemaire, Luke Mac Aleese and Philippe Maître

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400295

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      Multiphoton dissociation: The ground state iC3H7+ ion, which exists as a freely equilibrating mixture of chiral geometries (see picture), has been sampled by means of the wavelength-dependent multiphoton dissociation induced by the absorption of IR radiation from a high-fluence free-electron laser (FEL) source.

    6. Torsional Barriers in Aromatic Molecular Clusters as Probe of the Electronic Properties of the Chromophore (pages 1686–1694)

      Christoph Jacoby and Michael Schmitt

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400281

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      Hydrogen atom transfer from photoexcited phenol is discussed as a general mechanism, mostly independent of the nature of the clustering moiety. Evidence for this mechanism is given from the torsional properties of the complexed molecules ammonia, methanol, and water (see graphic). Early stages of the formation of methoxonium and ammonium radicals are observed. For a similar chromophore, naphthol, no such hydrogen atom transfer could be found.

    7. Spectroscopic Properties of Trapped Electrons on the Surface of MgO Nanoparticles (pages 1695–1703)

      Martin Sterrer, Thomas Berger, Slavica Stankic, Oliver Diwald and Erich Knözinger

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400266

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      Electron traps: Infrared (IR) and electron paramagnetic resonance (EPR) spectroscopic methods were used to study electron trapping on the surface of MgO nanoparticles (see picture). To characterise the electron-trapping sites, surface colour centres were generated using UV light in conjunction with selected hydrogen-based electron sources. Four different colour-centre species were identified.

    8. Singlet Excited-State Interactions in Naphthalene–Thymine Dyads (pages 1704–1709)

      Susana Encinas, Maria J. Climent, Salvador Gil, Urban O. Abrahamsson, Jan Davidsson and Miguel A. Miranda

      Version of Record online: 21 OCT 2004 | DOI: 10.1002/cphc.200400262

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      A physical deactivation process is the predominant pathway for the accelerated decay of the singlet excited state of a naphthalene dyad. This effect is strongly dependent on the relative spatial arrangement between the naphthalene and thymine units, together with the hydrogen-bonding ability of ROH molecules, which locks the dyad in a bridged conformation (see picture).

    9. Ligand Dynamics in Myoglobin: Calculation of Infrared Spectra for Photodissociated NO (pages 1710–1718)

      David R. Nutt and Markus Meuwly

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400220

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      Infrared spectra from molecular dynamics simulations: The dynamics and infrared spectra of photodissociated nitric oxide (NO) in myoglobin have been calculated from simulations (see picture). Significant differences are observed when the results of this study are compared with those obtained for MbCO; these discrepancies are due to the different dipole moments of carbon monoxide (CO) and NO.

    10. Probing Ligand–Protein Recognition with Sum-Frequency Generation Spectroscopy: The Avidin–Biocytin Case (pages 1719–1725)

      Laurent Dreesen, Yannick Sartenaer, Christophe Humbert, Alaa A. Mani, Christophe Méthivier, Claire-Marie Pradier, Paul A. Thiry and André Peremans

      Version of Record online: 21 OCT 2004 | DOI: 10.1002/cphc.200400213

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      Biomolecular recognition: Due to its peculiar selection rules, sum-frequency generation spectroscopy, a valuable nonlinear optical technique, clearly reveals the specific recognition of a protein (avidin) by a self-assembled monolayer of a modified vitamin (biocytin; see picture).

    11. Oxygenolysis of Flavonoid Compounds: DFT Description of the Mechanism for Quercetin (pages 1726–1733)

      Sébastien Fiorucci, Jerôme Golebiowski, Daniel Cabrol-Bass and Serge Antonczak

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400186

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      Importance of electron transfer in specific antioxidative mechanisms: The mechanism of flavonoid oxygenolysis was investigated by means of DFT calculations on quercetin as a model compound. Results show that this reaction should proceed more easily when the substrate is oxidized, for example, by a metal center, and that 1,3-cycloaddition is preferred over 1,2-cycloaddition. The picture shows a dioxygen molecule approaching quercetin.

    12. Investigation of Redox Properties of Different PtSn/Al2O3 Catalysts (pages 1734–1744)

      Josette Olivier-Fourcade, Manfred Womes, Jean-Claude Jumas, Fabienne Le Peltier, Stéphane Morin and Blaise Didillon

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400184

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      Redox reaction: Alumina-supported Sn and PtSn particles are studied by 119Sn Mössbauer spectroscopy after oxidation and reduction under various conditions. It is shown that tin contributes to the oxygen uptake VO1 of a first titration cycle by platinum-catalysed transformation of SnII into an oxometallic phase PtxSn(O) (see graphic).

    13. Light-Scattering Study of the Aggregation of Syndiotactic Poly(methyl methacrylate) in Solution (pages 1745–1749)

      Wenna Chen, Yue Zhao, Yong Jiang, Dadong Yan and Charles C. Han

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400175

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      Sticking together at low temperatures: The aggregation behavior of syndiotactic poly(methyl methacrylate) (s-PMMA) was studied by a combination of static and dynamic laser-light-scattering experiments. s-PMMA may undergo aggregation in n-butyl chloride at temperatures below the θ temperature. The figure shows a plot of the weight-average molecular weight of the polymer (Mw) versus the radius of gyration (<Rg>).

    14. Multiple Refocusing in NMR Spectroscopy: Compensation of Pulse Imperfections by Scalar Couplings (pages 1750–1754)

      Jens Dittmer and Geoffrey Bodenhausen

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400073

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      Scalar couplings counteract pulse imperfections when applying multiple refocusing pulses to multiple-quantum coherences in NMR spectroscopy (depicted are simulations of the exchange between the operators 2NxHx , 2NzHx , and Hy). This surprising effect facilitates new experiments designed to characterize slow motions in proteins.

    15. Structural and Magnetic Investigations of the Mixed-Valence FeII,III Two-Dimensional Layer Complex, [Fe2IIFe2III(HCOO)10(C6H7N)6]n (pages 1755–1761)

      Jacob Overgaard, Eva Rentschler, Grigore A. Timco and Finn K. Larsen

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400027

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      Structural evidence for magnetic ordering: The title compound has an antiferromagnetic ordering temperature of 20 K. Single-crystal synchrotron X-ray diffraction studies on both sides of the transition temperature (see graphic) strongly indicate that the 90 ° rotation of one γ-picoline ligand is the main switching event for the onset of 3D long-range magnetic ordering.

    16. Intramolecular Charge Transfer in Pyrromethene Laser Dyes: Photophysical Behaviour of PM650 (pages 1762–1771)

      F. López Arbeloa, J. Bañuelos Prieto, V. Martínez Martínez, T. Arbeloa López and I. López Arbeloa

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400242

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      Improving lasing efficiency: The photophysical characteristics of pyrromethene 650 (PM650) dye in polar/protic and apolar media were studied by means of absorption and fluorescence techniques (see figure). The goal of the authors was to predict, from a photophysical point of view, the best environmental conditions for optimising the laser action of pyrromethene dyes.

    17. Molecular Complexes of Organometallic Molecules with Noble Gases: The Rotational Spectrum of Dimethylsilane–Argon (pages 1772–1778)

      Paolo Ottaviani, Sonia Melandri, Walther Caminati, Deike Banser, Melanie Schnell and Jens-Uwe Grabow

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400191

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      The most stable configuration of dimethylsilane–argon (see picture) was determined by means of rotational spectroscopy under the conditions of very low pressure and temperature following a supersonic expansion. In addition, the potential energy surface that describes the motion of Ar was modeled from the very small (28 kHz) inversion splitting.

    18. Bifurcated CH2⋅⋅⋅O and (C[BOND]H)2⋅⋅⋅F[BOND]C Weak Hydrogen Bonds: The Oxirane–Difluoromethane Complex (pages 1779–1782)

      Susana Blanco, Juan C. López, Alberto Lesarri, Walther Caminati and José L. Alonso

      Version of Record online: 20 OCT 2004 | DOI: 10.1002/cphc.200400360

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      Bifurcated hydrogen bonds: The oxirane–difluoromethane molecular complex, generated in a supersonic jet, is stabilized by two bifurcated weak hydrogen bonds (see picture). The binding energy of the complex was estimated to be 9.6 kJ mol−1.

    19. Photon Antibunching Proves Emission from a Single Subunit in the Autofluorescent Protein DsRed (pages 1782–1785)

      Gabriel Sánchez-Mosteiro, Majolein Koopman, Erik M. H. P. van Dijk, Jordi Hernando, Niek F. van Hulst and María F. García-Parajó

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400216

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      Many colors red: Photon antibunching provides a unique way of revealing the single quantum character in a multichromophoric system. Here, it is demonstrated that the fluorescence emission in the DsRed tetramer (see picture) proceeds dominantly from one emitter at a time. This approach has equal potential for the investigation of conformational fluctuations and intermolecular interactions of complex (bio)systems at room temperature.

    20. Higher-Excited-State Photophysical Pathways in Multichromophoric Systems Revealed by Single-Molecule Fluorescence Spectroscopy (pages 1786–1790)

      Philip Tinnefeld, Johan Hofkens, Dirk-Peter Herten, Sadahiro Masuo, Tom Vosch, Mircea Cotlet, Satoshi Habuchi, Klaus Müllen, Frans C. De Schryver and Markus Sauer

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400325

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      Singlets annihilated: A single-molecule fluorescence spectroscopic study of multichromophoric peryleneimide-substituted polyphenylene-core dendrimers under various conditions indicates that increased intersystem crossing (see graphic) as a consequence of an annihilation process might represent a general motif for increased photobleaching of the first intensity levels in multichromophoric systems.

    21. A Numerical Evidence for Nonframework Cation Redistribution Upon Water Adsorption in Faujasite Zeolite (pages 1791–1793)

      Christèle Beauvais, Anne Boutin and Alain H. Fuchs

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400195

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      Trace amounts of water are sufficient to produce cation redistribution in zeolites. Monte Carlo simulations of zeolite faujasite NaY reveal a spontaneous redistribution of site-I and site-I′ cations upon water adsorption. When aromatics are coadsorbed in the zeolite, cation redistribution takes place for a very small amount of water (full dots in the figure).

    22. Chemical Derivatisation of Multiwalled Carbon Nanotubes Using Diazonium Salts (pages 1794–1799)

      Charles G. R. Heald, Gregory G. Wildgoose, Li Jiang, Timothy G. J. Jones and Richard G. Compton

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400369

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      A facile and versatile modification strategy: A chemically activated method of covalently derivatising carbon powder, via the chemical reduction of aryl diazonium salts with hypophosphorous acid, to include the covalent derivatisation of multiwalled carbon nanotubes (MWCNTs) is demonstrated. The specific molecular environments of 1-anthraquinonyl moieties attached to MWCNTs (see picture) produce interesting effects.

    23. Equilibria between Peroxo and Hydroperoxo Species in the Titanosilicates: An In Situ High-Resolution XANES Investigation (pages 1799–1804)

      Carmelo Prestipino, Francesca Bonino, Sandro Usseglio, Alessandro Damin, Andrea Tasso, Mario G. Clerici, Silvia Bordiga, Francesco D′Acapito, Adriano Zecchina and Carlo Lamberti

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200400427

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      Water is the key factor: For titanium-silicalite-1 in aqueous H2O2, the driving force that governs the equilibrium between the uncolored end-on η1-titanium–hydroperoxo complex and the yellow-colored side-on η2-Ti-peroxo complex (see picture) is the amount of water present in the system, as proven by in situ X-ray absorption near edge structure spectroscopy performed at 77 K.

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      Preview: ChemPhysChem 11/2004 (page 1810)

      Version of Record online: 5 NOV 2004 | DOI: 10.1002/cphc.200490056

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