Cover image for ChemPhysChem

December 15, 2003

Volume 4, Issue 12

Pages 1273–1380

    1. Cover Picture: Trends in Microfluidics with Complex Fluids (ChemPhysChem 12/2003) (page 1273)

      Thomas Pfohl, Frieder Mugele, Ralf Seemann and Stephan Herminghaus

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200390120

      The cover picture shows…‥individual F-actin filaments in lithographic microchannels (fluorescence microscopy image in the foreground, channel width 6 μm). Real-time observation of the fluctuations of the fluorescently labeled molecules within the channels yields insight into the statistical mechanics of biopolymers in confined geometry. The impact of various geometrical parameters, such as channel curvature, may be studied by means of more intricate microfluidic setups (bright-field microscopy image in the background). The goal is to understand the influence of geometric confinement, such as is present in microfluidic devices or in living cells, on the dynamics of complex matter. Find out more in the Concept Article by Herminghaus et al. on pp. 1291–1298.

    2. Graphical Abstract: ChemPhysChem 12/2003 (pages 1275–1281)

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200390121

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      Photon Counting Histogram for One-Photon Excitation (page 1280)

      Thomas D. Perroud, Bo Huang, Mark I. Wallace and Richard N. Zare

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200390122

    4. Experimental and Computational Investigations of the Properties of Fluorinated Single-Walled Carbon Nanotubes (pages 1283–1289)

      Holger F. Bettinger

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300854

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      Fluorinated tubes: Fluorination of single-walled carbon nanotubes (see picture) by reaction with elemental fluorine at elevated temperatures provides fluorinated single-walled carbon nanotubes (F-SWNT), which have the highest degree of functionalization (up to F/C=1/2) of any derivatized carbon-nanotube material reported to date. This Minireview covers experimental and computational investigations of F-SWNTs with a focus on the nature and the strength of the C–F linkage. Among the most interesting properties of F-SWNTs are their solubility in alcohols and their further derivatization with nucleophiles.

    5. Trends in Microfluidics with Complex Fluids (pages 1291–1298)

      Thomas Pfohl, Frieder Mugele, Ralf Seemann and Stephan Herminghaus

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300847

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      Miniaturization: a closer look. Microfluidics, the physics and technology of handling and moving small quantities of liquids (see picture), has recently attracted wide interest due to its potential for biotechnological applications. In this contribution, new concepts for microfluidic systems are presented, as well as new applications in biophysics and physical chemistry.

    6. Dynamics of Photoinduced Electron-Transfer Processes in Fullerene-Based Dyads: Effects of Varying the Donor Strength (pages 1299–1307)

      K. George Thomas, V. Biju, Prashant V. Kamat, M. V. George and Dirk M. Guldi

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200200561

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      The more you give, the more you get? Two classes of fullerene-based donor–bridge–acceptor (D–B–A) systems containing donors of varying oxidation potentials have been synthesized (see graphic). An increase in the rate constant and quantum yield of electron transfer (kET and ΦET) was observed for both classes of dyads, with decreasing oxidation potentials of the donor groups. The long-lived charge separation enabled the characterization of electron-transfer products, by using nanosecond transient absorption spectroscopy.

    7. The Low-Lying Excited States of 2,2′-Bithiophene: A Theoretical Analysis (pages 1308–1315)

      Mercedes Rubio, Manuela Merchán, Rosendo Pou-Amérigo and Enrique Ortí

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300790

      Exciting news: The low-energy region of the singlet[RIGHTWARDS ARROW]singlet, singlet[RIGHTWARDS ARROW]triplet, and triplet[RIGHTWARDS ARROW]triplet electronic spectra of 2,2′-bithiophene are studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbitals (ANO) basis sets. As regards the high triplet quantum yield of the molecule, an attempt to explain the intersystem crossing (ISC) process has been undertaken mainly on the basis of the computed singlet–triplet energy gaps and symmetry considerations. These results suggest that both triplet states can be populated by ISC, by starting from nonplanar singlet states.

    8. In-Plane Structures of Synthetic Oligolactose Lipid Monolayers—Impact of Saccharide Chain Length (pages 1316–1322)

      Motomu Tanaka, Matthias F. Schneider and Gerald Brezesinski

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300791

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      Sugar shapes: Grazing incidence X-ray diffraction study of synthetic oligolactose lipid monolayers (see graphic) revealed the impact of saccharide chain length on the in-plane molecular ordering.

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      Generation of Iron Atoms in the Gas Phase by Microwave-Induced Plasma Afterglows (pages 1323–1327)

      Chris Vinckier and Kevin Cappan

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300860

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      From the microwave: Metal atoms can be generated at room temperature in a fast-flow reactor by the plasma-afterglow atomisation process (see picture of the set-up). The essential element of the technique is a microwave-induced hydrogen plasma, which is used as a source of hydrogen atoms. Reactions of these atoms with gaseous iron chloride yield iron atom concentrations on the order of 5×1010 atoms per cubic centimeter.

    10. Co-Conformational Distribution of Nanosized [2]Catenanes Determined by Pulse EPR Measurements (pages 1328–1334)

      Gunnar Jeschke and Adelheid Godt

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300890

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      Freely moving? The distance distribution of spin labels attached to the two macrocycles of [2]catenanes (see picture) can be characterized by EPR spectroscopy. Comparison to a theoretical model consisting of two perfect, infinitely thin circular rings reveals whether these molecules can be considered as an ensemble of simple geometric objects and whether all of the theoretically feasible co-conformations are accessible. It turns out that the answers depend strongly on the solvent.

    11. Single-Walled Carbon Nanotube Based Molecular Switch Tunnel Junctions (pages 1335–1339)

      Michael R. Diehl, David W. Steuerman, Hsian-Rong Tseng, Scott A. Vignon, Alexander Star, Paul C. Celestre, J. Fraser Stoddart and James R. Heath

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300871

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      Using a redox-switchable [2]catenane (see picture) as an approximately one-nanometer-cubic molecular switch, two-terminal molecular switch tunnel junctions (MSTJs), which incorporate a semiconducting single-walled carbon nanotube (SWNT) as the bottom electrode and a two-micrometer wide metallic top electrode, have been fabricated. Active and remnant current-voltage measurements demonstrated that these devices can be reconfigurably switched and repeatedly cycled between high and low current states under ambient conditions.

    12. Electron Attachment to “Naked” and Microsolvated Nucleotide Anions: Detection of Long-Lived Dianions (pages 1341–1344)

      Bo Liu, Shigeo Tomita, Jimmy Rangama, Preben Hvelplund and Steen Brøndsted Nielsen

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300885

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      In-flight reduction: In 50 keV collisions between gaseous nucleotide monoanions (e.g., see figure) and sodium vapour, electron transfer from sodium to the anion occurs. Dianions survive the long flight time to the detector (≈6 μs) despite being unstable to electron autodetachment. Based on B3LYP6–311++G(2d,p)//PM3 calculations, the electron binding energy of the dianion is negative but becomes positive after internal proton transfer from the sugar to the adenine.

    13. A Topological Analysis of the Electron Density in Anion–π Interactions (pages 1344–1348)

      Carolina Garau, Antonio Frontera, David Quiñonero, Pablo Ballester, Antoni Costa and Pere M. Deyà

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300886

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      Novel nonbonding interaction: The “atoms in molecules” (AIM) and the molecular interaction potential with polarization (MIPp) tools are successfully used i) to predict the energetic characteristics of π complexes of the chloride anion with electron-deficient aromatic rings (see graphic), which have a positive quadrupole moment and ii) to analyze the physical nature of this novel nonbonding interaction in detail.

    14. Trapping Electrochemical Oscillations between Self-Organized Potential Walls (pages 1348–1351)

      Hamilton Varela, Antoine Bonnefont and Katharina Krischer

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300922

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      Salient spatial structures: A hierarchy of spatial bifurcations during the electro-oxidation of hydrogen on platinum in the presence of negative global coupling leads to the formation of self-organized potential walls (see picture) of more than 1 V that separate oscillating active areas from high-potential passive domains.

    15. Biointerfacing Polyelectrolyte Microcapsules (pages 1351–1355)

      Liqin Ge, Helmuth Möhwald and Junbai Li

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200200631

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      Imitating nature: The authors attempted to assemble lipids on polyelectrolyte (PE) capsules (see graphic) to reduce the permeability of the capsules towards ions and small neutral molecules, thus imitating the barrier function of biological membranes. The lipid may form bilayer structures on the capsule surface, which provides the possibility to incorporate membrane-specific components such as channels and receptors for specific permeation and recognition.

    16. Self-Organization of an L-Ether-amide Phospholipid in Large Two-Dimensional Chiral Crystals (pages 1355–1358)

      Xiuhong Zhai, Qiang He, Junbai Li, Gerald Brezesinski and Helmuth Möhwald

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300912

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      Large two-dimensional chiral crystals are obtained in monolayers of 1-O-hexadecyl-2-N-palmitoyl-2-amino-2-deoxy-sn-glycero-3-phosphocholine by a pressure-induced 2D transition from a fluid to a condensed phase. The chiral domain growth in two dimensions (see Brewster angle microscopy image) exceeds over 400 micrometer, which was not observed before for phospholipids. Grazing incidence X-ray diffraction clearly shows the formation of a chiral lattice that is barely changed during compression. Therefore, the chiral discrimination forces must be enhanced by other directed interactions such as hydrogen bonds.

    17. One-Bond 15N[BOND]13C′ Nuclear Spin–Spin Coupling in N-Methylacetamide: a Model for Hydrogen-Bonded Peptides (pages 1358–1360)

      Predrag Ilich and Nenad Juranić

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300647

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      New insight into hydrogen bonds: The authors present a new approach to the analysis of the polypeptide and polynucleotide secondary structures that is based on the observation of the “through-hydrogen-bond” nuclear spin–spin coupling in a simple peptide-model molecule, N-methylacetamide. The geometry of N-methylacetamide is gradually changed (see picture) to mimic the response to the major energy components of hydrogen-bonded interactions, and the associated changes in the one-bond 15N[BOND]13C′ nuclear spin–spin coupling are estimated by calculating the Fermi contact term.

    18. Noncontact Surface Force Microscopy of Protein Molecules (pages 1361–1364)

      Takaaki Aoki, Yoshiyuki Sowa and Toshio Yanagida

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300796

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      Using intermolecular force microscopy, the forces in the sub-piconewton order between the probe stylus and the sample surfaces can be measured with a gap distance controlled with nanometer accuracy. In this study, electrostatic features of the protein surface were visualized as 2D electrostatic force maps (see picture). Furthermore, the interaction between motor proteins in the noncontact region was measured.

    19. Wiring Electrons of Cytochrome c with Silver Nanoparticles in Layered Films (pages 1364–1366)

      Tao Liu, Jun Zhong, Xin Gan, Chunhai Fan, Genxi Li and Naoki Matsuda

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300817

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      Pass it on! Highly conductive silver nanoparticles (NPs; see picture) act as efficient electron relays on a pyrolytic graphite (PG) electrode, and heavily negatively charged silver NPs provide suitable docking sites for positively charged cytochrome c (cyt c). Direct, well-defined electrochemistry of cyt c is obtained at an assembled silver NPs/PG electrode surface, which results in an electron-transfer rate of 15.8 s−1 for cyt c. The usage of silver NPs will open new opportunities for studying in vitro electron-transfer processes of heme protein and for fabrication of bioelectronic devices.

    20. Covalent Immobilization of Single Proteins on Mica for Molecular Recognition Force Microscopy (pages 1367–1371)

      Dionne C. G. Klein, Cordula M. Stroh, Henriette Jensenius, Maarten van Es, A. S. M. Kamruzzahan, Amalia Stamouli, Hermann J. Gruber, Tjerk H. Oosterkamp and Peter Hinterdorfer

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300844

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      Tether them! A matrix of proteins that are covalently bound to mica with only one short tether per protein was created in order to fulfil all requirements for molecular recognition force microscopy of single proteins (see picture). This immobilization technique produces a high density of individual proteins on a flat surface in liquid with extremely low surface roughness.

    21. Probing Nanomagnets' Interactions inside Colloidal Superparamagnetic Composites: Aerosol versus Surface Template Methods (pages 1371–1375)

      Pedro Tartaj

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200300866

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      An alternative surface template method is reported for the preparation of colloidal superparamagnetic composites (see TEM micrographs) that could be useful for biomedical applications. The magnetic behavior of colloidal superparamagnetic composites prepared by the surface template method is compared with that of colloidal superparamagnetic composites prepared by aerosol pyrolysis. The author is able to find evidences of an interacting superparamagnetic regime at low packing fractions in the composites prepared by the template method.

    22. Preview: ChemPhysChem 12/2003 (page 1380)

      Article first published online: 8 DEC 2003 | DOI: 10.1002/cphc.200390124