Cover image for ChemPhysChem

March 17, 2003

Volume 4, Issue 3

Pages 225–318

    1. You have free access to this content
    2. Overcharging in Colloids: Beyond the Poisson–Boltzmann Approach (pages 234–248)

      Manuel Quesada-Pérez, Enrique González-Tovar, Alberto Martín-Molina, Marcelo Lozada-Cassou and Roque Hidalgo-Álvarez

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390040

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      Getting on with the neighbors: The Poisson–Boltzmann equation has for decades been a keystone in the theoretical description of the electric double layer of colloids. However, there are some fascinating phenomena that challenge this traditional approach, such as overcharging, which can come about for highly charged macroions in the presence of multivalent counterions. Why does the classical picture fail under such conditions? The figure illustrates the quantitative and qualitative differences that can be found for the macroion–ion radial distribution functions predicted by the Poisson–Boltzmann theory (••••) and a modern integral equation theory (—).

    3. The Influence of σ and π Acceptors on Two-Photon Absorption and Solvatochromism of Dipolar and Quadrupolar Unsaturated Organic Compounds (pages 249–259)

      Bernd Strehmel, Ananda M. Sarker and Heiner Detert

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390041

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      Chemical chameleons: Two-photon absorption cross sections of unsaturated organic compounds such as distyrylbenzenes with donor–acceptor–donor (D–A–D) substitution patterns can be tuned by means of electron-donating and -withdrawing groups. The intense fluorescence of these compounds and the intramolecular charge transfer (ICT) state formed on excitation makes them attractive for sensing applications. The ICT energy depends on the surrounding environment, which results in a change in emission color, for example (see picture), from blue (cyclohexane) to yellow (toluene) to orange (butyronitrile).

    4. Photoluminescence Intensity Fluctuations and Electric-Field-Induced Photoluminescence Quenching in Individual Nanoclusters of Poly(phenylenevinylene) (pages 260–267)

      Ivan Scheblykin, George Zoriniants, Johan Hofkens, Steven De Feyter, Mark Van der Auweraer and Frans C. De Schryver

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390042

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      Blinking nanoclusters: Single clusters of PPV containing more than 75 polymer chains, or 30 000 monomer units, have been found to exhibit fluorescence intensity fluctuations that resemble the “blinking” observed in single-molecule fluorescence. In addition to distinct jumps, smooth fluctuations of the fluorescence intensity were observed (see graph). We propose that quenching of the light-emitting excitons by polarons plays an important role in these unusual fluctuations.

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      Reversible Immobilization of Peptides: Surface Modification and In Situ Detection by Attenuated Total Reflection FTIR Spectroscopy (pages 268–275)

      Per Rigler, Wolf-Peter Ulrich, Patrik Hoffmann, Michael Mayer and Horst Vogel

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390043

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      The surface of the story: Highly sensitive and accurate detection of reversibly surface-immobilized peptides is possible by ATR–FTIR spectroscopy. Using self-assembly of chelating molecules on inorganic IR-transparent substrates covered with either gold or SiO2, surface-tethered peptide layers with high surface concentration were obtained (see picture). The developed methods are generally applicable for the reversible, unidirectionally oriented immobilization of functional proteins on planar surfaces, which is a prerequisite for the efficient screening of protein–ligand and protein–protein interactions.

    6. On the Preparation of High-Surface-Area Nano-Zirconia by Reflux-Digestion of Hydrous Zirconia Gel in Basic Solution (pages 277–281)

      Shuang-Feng Yin and Bo-Qing Xu

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390044

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      Making a meal of it: Reflux-digestion of ZrO(OH)2 in basic solution results in an incorporation into the solid of Si4+ ions from the glass vessel, which induces texture and crystal stabilization of the zirconia product (see graph; S=surface area).

    7. The Potential of Ordered Mesoporous Silica for the Storage of Drugs: The Example of a Pentapeptide Encapsulated in a MSU-Tween 80 (pages 281–286)

      Corine Tourné-Péteilh, Dan A. Lerner, Clarence Charnay, Lionel Nicole, Sylvie Bégu and Jean-Marie Devoisselle

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390045

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      Checking the dosage! Carrying a drug adsorbed on a mesoporous silica material may become a standard to deliver drugs. But how can you be sure that the drug is safely tucked inside the channels (see graphic)? The authors tackle this tricky problem.

    8. An Explanation of Anomalous Diffusion Patterns Observed in Electroactive Materials by Impedance Methods (pages 287–292)

      Juan Bisquert, Germà Garcia-Belmonte and Ángeles Pitarch

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390046

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      Hop, skip, and jump? Diffusion impedance in disordered systems was used to consider some physical aspects of carrier diffusion in electroactive films. Energy dispersion of ion sites or a distribution of electron sites (traps) is a common feature of these systems. The implications for transport are analyzed with a view to interpreting electrochemical impedance spectra. An explanation is given for anomalous diffusion patterns observed in electroactive materials, and structured impedance spectra (see figure) are described in terms of carrier hopping, trapping, and relaxation in the solid state.

    9. Substantial Errors from Time-Dependent Density Functional Theory for the Calculation of Excited States of Large π Systems (pages 292–295)

      Stefan Grimme and Maja Parac

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390047

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      A warning to TDDFT users: Unexpected failures of the popular time-dependent DFT (TDDFT) method for the π[RIGHTWARDS ARROW]π* excited states (see figure) of large aromatic molecules are reported. A very probable reason for this behaviour is the underestimated interaction of important ionic components in the corresponding La-state wavefunctions with current standard functionals.

    10. Characterization of Diffusion Processes of Pharmacologically Relevant Molecules through Polydimethylsiloxane Membranes by Confocal Micro-resonance Raman Spectroscopy (pages 296–299)

      Michael Schmitt, Belinda Leimeister, Lucian Baia, Barbara Weh, Ingfried Zimmermann, Wolfgang Kiefer and Jürgen Popp

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390048

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      Focus on diffusion. Confocal micro resonance Raman spectroscopy (see picture) was applied to investigate the kinetics of diffusion processes of β-carotene dissolved in DMSO through polydimethylsiloxane membranes. By using this technique the dynamics of the diffusion process at well-defined points inside the membrane and the formation of a concentration gradient before reaching steady-state conditions at specific points inside the membrane can be observed.

    11. Vacuum Preparation and Ionization Energies of FN3 and IN3 (pages 300–303)

      Che Huijuan, Bi Huimin, Zeng Yanli, Meng Lingpeng, Zheng Shijun, Chau Foo-tim and Wang Dianxun

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390049

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      Reactions in the pipeline: Flowing beams of FN3 and IN3 gas were directly prepared on-line to a HeI photoelectron spectrometer. The ionization energies corresponding to removing electrons from different molecular orbitals of both FN3 and IN3 were determined by photoelectron spectroscopy experiments and by both restricted outer valence Green's function (ROVGF) and ab initio Gaussian 2 (G2) calculations. The experimental results (see graphic) are in excellent agreement with the theoretical ones. The first PES ionization energies of FN3 and IN3 are 10.86 and 9.34 eV, respectively.

    12. The Effect of Molecular Organisation in DNA Oligomers Studied by Femtosecond Fluorescence Spectroscopy (pages 303–305)

      Dimitra Markovitsi, Alexei Sharonov, Delphine Onidas and Thomas Gustavsson

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390050

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      Organisation lengthens life! The first fluorescence investigation of DNA oligomers performed with femtosecond resolution revealed that organisation of nucleotides into single strands, and further into double strands, makes the fluorescence decays slower and slower (see graph). This is important because a longer lifetime increases the reactivity of the excited states and, thus, the probability of inducing damage to the double helix.

    13. The Potential of the Xenon “Spin-Spy” Methodology for the Study of Configurational Equilibria in Solution (pages 305–308)

      Emanuela Locci, Jacques Reisse and Kristin Bartik

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390051

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      Xenon, a gas of rare ability: The mutarotation of D-glucose (see structure) was monitored using 129Xe NMR spectroscopy. This is the first example of the use of xenon NMR spectroscopy to probe a configurational equilibrium in solution of a system which does not complex xenon.

    14. Direct Observation of Charge-Transfer Reactions in Nanoscopic Test Tubes: Self-Ionization in HNO3 Clusters (pages 308–312)

      Christoph R. Gebhardt, Thomas Witte and Karl L. Kompa

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390052

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      Cluster busting: The direct mass spectrometric observation of solution-phase charge-transfer reactions is demonstrated for the self-ionization reaction of pure nitric acid by employing molecular clusters as nanoscopic test tubes (see picture).

    15. Preview: ChemPhysChem 3/2003 (page 318)

      Article first published online: 11 MAR 2003 | DOI: 10.1002/cphc.200390055