Cover image for Vol. 5 Issue 1

January 23, 2004

Volume 5, Issue 1

Pages 1–154

    1. You have free access to this content
      Cover Picture: In Situ Spectroscopic Analysis of Nanocluster Formation (ChemPhysChem 1/2004) (page 1)

      Jia Wang, Hans F. M. Boelens, Mehul B. Thathagar and Gadi Rothenberg

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200490000

      The cover picture shows an artist's impression of the formation of a metal nanocluster in a solution containing ions and atoms of two different metals. Nanoclusters are UV/Vis active, and in theory it should be possible to follow the exact kinetics of their formation by UV/Vis spectroscopy. In practice, however, the decomposition of the spectra presents a formidable problem. To read how Rothenberg et al. managed to solve this problem, turn to p. 93.

    2. You have free access to this content
      Editorial: The Fabulous Fifth! (pages 3–4)

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200490004

    3. How To Make Ohmic Contacts to Organic Semiconductors (pages 16–25)

      Yulong Shen, Ahmad R. Hosseini, Man Hoi Wong and George G. Malliaras

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300942

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      Making contact: The process of charge injection plays an important role in organic semiconductor devices. The authors discuss recent measurements of charge injection (see graphic) and outline ways to make ohmic contacts.

    4. Ultrafast Time-Resolved Transient Structures of Solids and Liquids by Means of Extended X-ray Absorption Fine Structure (pages 27–35)

      Ivan V. Tomov and Peter M. Rentzepis

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300917

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      Detection of ultrafast transient structures and the evolution of ultrafast structural intermediates during the course of reactions has been a long standing goal of chemists and biologists. This article presents means for the generation of short-nanosecond to femtosecond hard X-ray pulses by table-top high power laser induced plasma (see picture for a schematic representation of the experimental system). The experimental ystem for the detection of ultrafast time-resolved extended X-ray absorption fine structure (EXAFS) spectra of molecules in liquids is described and the method for the analysis of EXAFS spectra to yield transient structures is given. Such studies are expected to have a high impact in chemistry and biology.

    5. Cluster Assembled Nanostructures: Designing Interface Properties (pages 37–42)

      Bernhard Kaiser and Bert Stegemann

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300946

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      Just four atoms are enough to provide a wide variety of nanometer-size patterns and structures on various surfaces (see figure). In this Concept article, the authors present the Sb4 molecule as a model system for gas-phase deposition experiments with size-selected clusters. By careful adjustment of deposition parameters, they can control the morphology of the self-assembled nanostructures and their size over several orders of magnitude. The observed phenomena reach from the simple diffusion-limited aggregation (DLA) model to the formation and stabilization of new elemental modifications.

    6. Sense the Electrons that Come and Go (pages 43–45)

      Daniël Vanmaekelbergh and Zeger Hens

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300945

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      Electron tunneling dynamics: This highlight outlines how fluctuations in the electron number of a semiconductor quantum dot, connected to a source and drain electrode by tunneling barriers (see green circuit in the picture) and capacitively coupled to a gate electrode (black), can be measured by an independent single electron transistor (gray circuit). This allows to probe the tunneling dynamics between the quantum dot and the source and drain electrodes in the (green) quantum dot circuit with microsecond time resolution.

    7. Photoinduced Interactions Between Oxidized and Reduced Lipoic Acid and Riboflavin (Vitamin B2) (pages 47–56)

      Changyuan Lu, Götz Bucher and Wolfram Sander

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300687

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      Caught in a flash: Lipoic acid and dihydrolipoic acid quench the excited state of riboflavin derivatives such as vitamin B (both singlet and triplet) via electron transfer (see graphic). The intermediates were characterized by laser flash photolysis.

    8. Excitonic Coupling Strength and Coherence Length in the Singlet and Triplet Excited States of mesomeso Directly Linked Zn(II)porphyrin Arrays (pages 57–67)

      Jeong-Hyon Ha, Hyun Sun Cho, Jae Kyu Song, Dongho Kim, Naoki Aratani and Atsuhiro Osuka

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300758

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      Photosystem brought to light: Investigations of excitation-energy transport phenomena in mesomeso directly linked Zn(II)porphyrin arrays Zn and their bromo derivatives ZnBr2 by steady-state and time-resolved spectroscopy revealed coupling strengths of the Soret and Q bands of about 2 200 and 570 cm−1, respectively. The coherence length in the S1 state was determined to be 4–5 porphyrin units, which is comparable with that of the well-ordered two-dimensional circular structure B850 in the peripheral light-harvesting antenna (LH2) in photosynthetic purple bacteria.

    9. Synthesis of Silver and Gold Nanoparticles by a Novel Electrochemical Method (pages 68–75)

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

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300900

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      Plastic support for noble clusters: Poly(N-vinylpyrrolidone) (PVP) has a structure consisting of a polyvinyl skeleton with pendant polar pyrrolidone groups. Silver ions can anchor to the backbone of PVP by coordinating with the oxygen (or nitrogen) atoms of the lactim rings. During electrolysis, the Ag–PVP complex ions are reduced at the cathode surface, forming silver adatoms protected by the hydrophobic polyvinyl chains, which will form silver clusters shortly afterwards. The use of a rotating platinum cathode significantly accelerates the transfer rate of the silver clusters from the cathode vicinity to the bulk solution (see picture), thereby producing well-dispersed silver nanoparticles.

    10. Frequency-Switched Single-Transition Cross-Polarization: A Tool for Selective Experiments in Biomolecular NMR (pages 76–84)

      Fabien Ferrage, Thomas R. Eykyn and Geoffrey Bodenhausen

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300905

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      Protein NMR: A selective NMR scheme called frequency-switched single-transition cross-polarization (FS-ST-CP) is applied to study biological macromolecules. Structural and dynamic information concerning a single amino acid may be extracted by selecting relevant signals such as those of leucine 73 in the protein ubiquitin (magnified).

    11. Cell Shape Normalization, Dendrite Orientation, and Melanin Production of Normal and Genetically Altered (Haploinsufficient NF1)-Melanocytes by Microstructured Substrate Interactions (pages 85–92)

      Simon Jungbauer, Ralf Kemkemer, Hans Gruler, Dieter Kaufmann and Joachim P. Spatz

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300868

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      Microstripes enable normal cell function: Little is known about how functional regulation failure in genetically altered cells is influenced by topographical confinement of cells, a situation often present in tissues in vivo. Cultured melanocytes derived from human skin samples were used as a model system for such investigations. It is shown that morphology consequences of genetically altered melanocytes are canceled if cells interact with suitable substrates microstructured by stripes (see picture) that apply mechanophysical signals in the form of physical topography.

    12. In Situ Spectroscopic Analysis of Nanocluster Formation (pages 93–98)

      Jia Wang, Hans F. M. Boelens, Mehul B. Thathagar and Gadi Rothenberg

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300859

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      Check out the clustering: The reduction of palladium, gold, and silver ions and the formation of the corresponding clusters (see picture) are monitored by in situ UV/Vis spectroscopy. Analysis of the entire spectrum gives access to otherwise hidden mechanistic information in the clustering process. Implications towards the synthesis of multimetallic clusters by coreduction are discussed.

    13. Field-Induced Switching of the Layer Chirality in SmCP Phases of Novel Achiral Bent-Core Liquid Crystals and their Unusual Large Increase in Clearing Temperature under Electric Field Application (pages 99–103)

      Martin W. Schröder, Siegmar Diele, Gerhard Pelzl and Wolfgang Weissflog

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300904

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      Switching of chirality: A field-induced inversion of the layer chirality has been found in the SmCPA phase of novel bent-core mesogens. Furthermore, a field-induced enhancement of the clearing temperature (transition temperature SmCPA to isotropic) up to 4 K could be observed; this is obviously due to the field-induced alignment of ferroelectric clusters, which exist already in the isotropic liquid. The picture shows a texture of the SmCPA phase with circular domains.

    14. Can Nematic Transitions Be Predicted By Atomistic Simulations? A Computational Study of The Odd–Even Effect (pages 104–111)

      Roberto Berardi, Luca Muccioli and Claudio Zannoni

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300908

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      Predicting transition temperatures: The transition temperature, the key quantity for liquid crystals, has until now never been accurately predicted by computer simulation. The authors describe accurate predictions (within 15 K) of the nematic–isotropic transition temperature for a liquid crystal, starting from just the molecular structure, which show that a new level of predictive capability has now been reached. The picture shows typical equilibrium snapshots for the n=0 homologue of 4-(4′-cyanobenzylidene)aminocinnamate in the nematic phase.

    15. The Metastability of an Electrochemically Controlled Nanoscale Machine on Gold Surfaces (pages 111–116)

      Hsian-Rong Tseng, Dongmin Wu, Nicholas Xuanlai Fang, Xiang Zhang and J. Fraser Stoddart

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300992

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      Kick starting bistable rotaxanes on surfaces and in solid-state devices at ground zero produces the all-important metastability critical for operating ON/OFF switches in molecular electronics (see picture).

    16. Enhanced Biomacromolecule Encapsulation by Swelling and Shrinking Procedures (pages 116–120)

      Changyou Gao, Helmuth Möhwald and Jiacong C. Shen

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300761

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      Reversible growth: Microcapsules were fabricated by layer-by-layer assembly of poly(diallyldimethyl ammonium chloride)/poly(styrene sulfonate) onto removable melamine formaldehyde particles. The capsules with swelling and shrinking features (see graphic) provide a novel route for microencapsulation. Loading of biomacromolecules such as dextran with ultrahigh molecular weight is achieved by spontaneously opening the capsule during core removal procedure, followed by closing the capsule in salt solution.

    17. Theoretical Study of Anharmonic and Matrix Effects on the Molecular Structure and Vibrational Frequencies of GdF3 and GdCl3 (pages 120–123)

      Giuseppe Lanza and Camilla Minichino

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300766

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      Looking beyond standard quantum chemistry: Molecular properties of isolated lanthanide trihalides obtained from equilibrium structures differ significantly from those derived with inclusion of the effects of anharmonicity, temperature, and inert-gas matrices. Because of their exceptional fluxionality along the out-of-plane bending motion, GdF3 and GdCl3 are quasiplanar or planar at the equilibrium state, thermal average structures are pyramidal, while geometries are planar and stiff in an inert-gas matrix. This is exemplified in the picture by the potential energy curves of GdCl3 (—–) and GdCl3⋅(N2)2 (- - - -) as a function of the inversion coordinate s.

    18. High Pressure Effects on the Emission Properties and Crystal Structure of Coumarin 120 (pages 124–127)

      Hong Li, Liming He, Bo Zhong, Yi Li, Shikang Wu, Jing Liu and Guoqiang Yang

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300816

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      Under pressure: An organic crystal, 7-amino-4-methyl coumarin (C120), was squeezed in a diamond anvil cell and became condensed and amorphous above 7.0 GPa. A new crystal phase (see graphic) with novel fluorescence properties was formed from the condensed amorphous crystal after relaxation of the pressure.

    19. Alignment of Extremely Long Single Polymer Chains by Exploiting Hydrodynamic Flow (pages 128–130)

      Matthijs B. J. Otten, Christof Ecker, Gerald A. Metselaar, Alan E. Rowan, Roeland J. M. Nolte, Paolo Samorì and Jürgen P. Rabe

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300837

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      Lining up: Polyisocyanide derivatives bearing L-alanyl-D-alanine methyl ester side groups (PIAA) have been adsorbed on the surface of muscovite mica. Scanning force microscopy images reveal single polymer chains with contour lengths ranging from several hundred nanometers up to several micrometers. Their orientation on the micrometer scale is attributed to hydrodynamic flow during the sample preparation (see figure). These long and stiff polymers, which exhibit a persistence length of 76 nm if equilibrated on a surface, can possess an even higher anisometry when brought into nonequilibrium states.

    20. Conformers of Guanosines and their Vibrations in the Electronic Ground and Excited States, as Revealed by Double-Resonance Spectroscopy and Ab Initio Calculations (pages 131–137)

      Eyal Nir, Isabel Hünig, Karl Kleinermanns and Mattanjah S. de Vries

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300862

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      Strong intramolecular 5′-OH⋅⋅⋅3-N hydrogen bonds stabilize guanosine, 2′-deoxyguanosine, and 3′-deoxyguanosine and fold them into a single preferred conformation (see picture), even in the absence of solvent interactions or DNA backbones. This conclusion was reached by means of a study combining UV–UV and IR–UV double-resonance laser spectroscopy and ab initio calculations.

    21. Tetrachloro-substituted Perylene Bisimide Dyes as Promising n-Type Organic Semiconductors: Studies on Structural, Electrochemical and Charge Transport Properties (pages 137–140)

      Zhijian Chen, Michael G. Debije, Tony Debaerdemaeker, Peter Osswald and Frank Würthner

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300882

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      Twisted π-systems: The highly twisted 1,6,7,12-tetrachloro-substituted perylene bisimides possess an improved electron affinity. The nonplanar nature of these molecules facilitates a slipped brickstone-type rather than a columnar stacking of the π-systems, with a potentially useful two dimensional contact feature. These compounds show isotropic charge carrier mobilities as high as up to 0.14 cm2 V−1 s−1 (see graphic).

    22. Microwave Driven Bray–Liebhafsky Oscillatory Reaction (pages 140–144)

      Dragomir R. Stanisavljev, Antonije R. Djordjević and Vladana D. Likar-Smiljanić

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300899

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      Microwaves alter dynamics: Oscillatory reactions are important in controlling processes in living organisms, in the same way that a clock controls processes in modern computers. Investigations of the microwave heating of the Bray–Liebhafsky oscillatory reaction revealed nonthermal effects by the favoring of monotonic dynamics (see graphic). The important role of bulk water is discussed.

    23. Energy–Entropy Compensation in the Transfer of Nonpolar Solutes from Water to Cosolvent/Water Mixtures (pages 144–147)

      Nico F. A. van der Vegt, Daniel Trzesniak, Besnik Kasumaj and Wilfred F. van Gunsteren

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300918

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      Microscopic view on solvation: Preferential interactions between solutes and cosolvent molecules in binary solvents are determined by using molecular dynamics computer simulations. The picture shows the solvent molecules water (red) and urea (blue) in the first solvation shell of a propane molecule. Urea preferentially interacts with propane driven by the solute-solvent van der Waals energy. The interaction is entropically opposed because urea hydration water molecules impose an excluded volume restriction upon formation of urea-propane contacts.

    24. Electrografting of Polymers onto AFM Tips: A Novel Approach for Chemical Force Microscopy and Force Spectroscopy (pages 147–149)

      Christine Jérôme, Nicolas Willet, Robert Jérôme and Anne-Sophie Duwez

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200300924

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      Grafting makes versatile probes: Polymer-modified AFM tips have been prepared through an easily implemented and versatile electrochemical method (see graphic). The authors describe the electropolymerization process of acrylic-based monomers onto gold-coated tips (see graphic) and show force curves obtained during approach–retraction cycles between the modified tips and a bare silicon surface. This direct chemical grafting creates new possibilities for single-molecule force spectroscopy.

    25. Preview: ChemPhysChem 1/2004 (page 154)

      Version of Record online: 19 JAN 2004 | DOI: 10.1002/cphc.200490003