ChemPhysChem

Cover image for Vol. 5 Issue 4

April 19, 2004

Volume 5, Issue 4

Pages 429–586

    1. Cover Picture: Modulation of the Work Function in Layer-by-Layer Assembly of Metal Nanoparticles and Poly-L-lysine on Modified Au Surfaces (ChemPhysChem 4/2004) (page 429)

      Michel Carrara, Joseph J. Kakkassery, Jean-Pierre Abid and David J. Fermín

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200490021

      The cover picture shows the modulation of the work function in the layer-by-layer growth of assemblies of Au nanoparticles of 19±2 nm diameter and poly-L-lysine on Au surfaces. The decrease in the amplitude of modulation with increasing number of layers is associated with disordering in the 3D assembly. This disordering manifests itself in the increment of the surface roughness as illustrated in the 500×500 nm2 AFM images of the first and fifth layer of particles. On page 571, Carrara et al. demonstrate that the modulation of the work function in multilayered materials is dependent on the size and nature of the metal nanoparticles.

    2. Graphical Abstract: ChemPhysChem 4/2004 (pages 431–437)

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200490022

    3. Single Bubble Sonoluminescence–A Chemist's Overview (pages 439–448)

      Muthupandian Ashokkumar and Franz Grieser

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200300926

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      Acoustically driven bubbles: Sound waves of optimal frequency and power can levitate and oscillate a single bubble in a liquid medium. The growth and collapse of this bubble (see picture) occurs during every acoustic cycle. The near-adiabatic and inertial collapse of this bubble can heat the contents of the bubble to over 20 000 K. This extreme thermal conditions leads to light emission from the bubble (sonoluminescence) and chemical reactions within the bubble and in the surround medium (sonochemistry). The chemical aspects of single bubble sonoluminescence are discussed.

    4. Hybrid Integral-Equation/Simulation Models: From Complexation Thermodynamics to Direct Free Energies (pages 449–455)

      Stefan M. Kast

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200300990

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      Hybrid models methodology: Combinations of statistical-mechanical integral equation theory with molecular simulations are shown to complement either methodology's inherent limitations. This concept is applied to solvent effects on complexation reactions (see in the picture K+/[18]crown-6 reaction pathways in acetonitrile) the correction of artefacts induced by truncated potentials, and to the direct computation of free energies from a simulation of a single state.

    5. Dissipative Particle Dynamics Simulations in the Grand Canonical Ensemble: Applications to Polymer Brushes (pages 457–464)

      Florent Goujon, Patrice Malfreyt and Dominic J. Tildesley

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200300901

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      Polymers grafted onto surfaces form brushes (see picture) only if the grafting density is sufficiently high to force the chains to stretch away from the grafting surface. The amount of stretching is determined both by the quality of the solvent and by the polymer chain length. The authors use a mesoscopic simulation technique in the grand canonical ensemble to calculate the force between compressed brushes in a good solvent as a function of the separation between the grafting surfaces.

    6. Solvate-Supported Proton Transport in Zeolites (pages 465–472)

      Marion E. Franke and Ulrich Simon

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301011

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      Enhanced proton transport in ZSM zeolites due to the presence of NH3 and H2O guest molecules was studied by complex impedance spectroscopy. The proton mobility (and hence the impedence Z*, see picture) depends on the NH3 or H2O concentration, temperature, and the SiO2/Al2O3 ratio of the zeolite. These findings are relevant to the development of NH3 and H2O sensor devices for high-temperature applications, such as automotive exhaust control with SCR DeNOx catalysts.

    7. Ground and Excited-State Electronic Interactions in Poly(propylene amine) Dendrimers Functionalized with Naphthyl Units: Effect of Protonation and Metal Complexation (pages 473–480)

      Fernando Pina, Paolo Passaniti, Mauro Maestri, Vincenzo Balzani, Fritz Vögtle, Marius Gorka, Sang-Kyu Lee, Jeroen van Heyst and Hassan Fakhrnabavi

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301030

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      Quenching and revival: The intense fluorescence band of the 2-naphthalene-1-sulfonamide is strongly quenched when the naphthyl unit is covalently linked at the periphery of poly(propylene amine) dendrimers. The quenching effect, which increases with increasing the dendrimer generation, is attributed to dimer/excimer (between naphthyl units) and charge-transfer/exciplex (between naphthyl and amine units of the branches) excited states, as shown in the cartoon. Protonation and metal (Zn2+ and Co3+) coordination revive the fluorescence intensity, although to a different extent, erasing the charge-transfer/exciplex formation pathway.

    8. Hydrogen Bonding in Mimics of Watson–Crick Base Pairs Involving C[BOND]H Proton Donor and F Proton Acceptor Groups: A Theoretical Study (pages 481–487)

      Célia Fonseca Guerra, F. Matthias Bickelhaupt and Evert Jan Baerends

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301069

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      Characteristic geometrical changes: Replacing N[BOND]H ⋅ ⋅ ⋅ O and N ⋅ ⋅ ⋅ H[BOND]N hydrogen bonds in Watson–Crick pairs with N[BOND]H ⋅ ⋅ ⋅ F and N ⋅ ⋅ ⋅ H[BOND]C causes characteristic geometrical changes that depend on how many and on which hydrogen bonds are substituted (see picture). Unexpectedly, orbital interactions are found to be essential even in the weakly bound Watson–Crick mimics that result from the above substitutions.

    9. Structure and Dynamics of Self-Assembled Poly(ethylene glycol) Based Coiled-Coil Nano-Objects (pages 488–494)

      Guido W. M. Vandermeulen, Dariush Hinderberger, Hui Xu, Sergei S. Sheiko, Gunnar Jeschke and Harm-Anton Klok

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301079

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      Parallel peptide helices: Due to their nanosized dimensions and complex structures, supramolecular objects are often difficult to characterize by X-ray or neutron scattering and NMR spectroscopy. This contribution discusses the use of electron paramagnetic resonance spectroscopy and demonstrates that this technique is a very powerful tool which can provide detailed insight into the solution structure of nano-objects generated from protein-inspired hybrid block copolymers (see picture).

    10. Thioacetylacetone: Structural and Vibrational Assignments (pages 495–502)

      Yevgen Posokhov, Alexander Gorski, Jens Spanget-Larsen, Fritz Duus, Poul Erik Hansen and Jacek Waluk

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200404016

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      Light conversion: Upon irradiation with light, the dominant ground-state species of thioacetylacetone, chelated (Z)-enol, is converted into the nonchelated SH exo-rotamer of the (Z)-enethiol tautomeric form (see graphic). Detailed vibrational assignments for both forms were obtained, based on matrix isolation and polarization experiments, and on quantum chemical calculations.

    11. Discovery of the New Metastable HONF. Radical (pages 503–508)

      Fulvio Cacace, Giulia de Petris, Marzio Rosi and Anna Troiani

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200400020

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      Energetic molecules: The cis (——) and trans (⋅⋅⋅⋅⋅) HONF. radicals (see graphic) have been detected for the first time as isolated species in the gas-phase. Obtained by neutralization of HONF+ ions, they prove to be high-energy, kinetically stable molecules, which live at least 1 μs. Their dissociation into HF and NO releases about 90 kcal mol−1.

    12. Local Structure of Amorphous Ice as Revealed by O K-Edge EXAFS (pages 509–514)

      Yan Zubavichus, Yongjie Yang, Michael Zharnikov, Oliver Fuchs, Thomas Schmidt, Clemens Heske, Eberhard Umbach, George Tzvetkov, Falko P. Netzer and Michael Grunze

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200300842

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      EXAFS in the ultrasoft X-ray range: Several peaks attributable to covalent and H-bridging O[BOND]H bonds, as well as to O⋅⋅⋅O intermolecular separations in the distance range of 1–7 Å, have been revealed in the Fourier transform (FT) of an O K-edge EXAFS spectrum measured on a submicron amorphous ice film deposited onto a gold substrate under UHV conditions at 100 K. Unexpectedly, the experimental pattern of interatomic distances appeared similar to that of high-density crystalline ice II (see graphic).

    13. The Ground and Excited States of Polyenyl Radicals C2n−1H2n+1 (n=2–13): A Valence Bond Study (pages 515–528)

      Yan Luo, Lingchun Song, Wei Wu, David Danovich and Sason Shaik

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200300935

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      Radical findings: VBDFT(s) is applied to the ground and excited states of polyenyl radicals C2n−1H2n+1 (n=2–13; see graphic). This simple VB theory provides not only good numerical values but also lucid wave functions, which help the understanding of physical properties of the ground and excited states. The computational results, along with previous ones, further show that VBDFT(s) is an efficient VB method for studying the excited states of conjugated molecules.

    14. Spectroscopic and Theoretical Study of the Molecular and Electronic Structures of a Terthiophene-Based Quinodimethane (pages 529–539)

      Juan Casado, Ted M. Pappenfus, Kent R. Mann, Enrique Ortí, Pedro M. Viruela, Begoña Milián, Víctor Hernández and Juan T. López Navarrete

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200300963

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      Quinoid terthiophene: Bu2(DCM)2TTH has a quinoid molecular structure, shows a strong optical absorption in the red (see spectrum), and exhibits ambipolar (p- and n-type) transport in organic TFT devices. Furthermore, Bu2(DCM)2TTH mimics the structural and electronic properties of dication species (bipolarons) in doped oligothiophenes (polythiophenes).

    15. Simulated Annealing Study of Diblock Copolymer Thin Films Confined between Two Homogeneous Surfaces (pages 540–548)

      Yuhua Yin, Pingchuan Sun, Tiehong Chen, Baohui Li, Qinghua Jin, Datong Ding and An-Chang Shi

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200300999

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      Diblock copolymer sandwiches: Simulated annealing is used for the first time to study the self-assembly of diblock copolymers confined between walls. Systems with a dozen of film thicknesses and three types of surfaces are studied systematically. Very regular equilibrium morphologies (see picture) are formed in all cases. The quantitative calculations of the interfacial energy, conformational entropy, and free energy of the systems show that the selected structures are correlated with the morphologies of lowest free energy.

    16. Dual-Color Fluorescence Cross-Correlation Spectroscopy Using Single Laser Wavelength Excitation (pages 549–551)

      Ling Chin Hwang and Thorsten Wohland

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301057

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      Spotlight on interactions: The authors show that single wavelength excitation fluorescence cross-correlation spectroscopy (SW-FCCS) is possible using only one laser beam to excite a combination of labels, in work performed with studied FRET (fluorescence resonance energy transfer) dyes and quantum dots. They demonstrate that equilibrium binding and stoichiometry can easily be determined (see graphic; QR = quantum red dye, BF = fluorescein-labeled biotin). SW-FCCS is a promising tool for high-throughput screening applications as well as for the measurement of molecular interactions.

    17. Biofunctionalized Polymer Surfaces Exhibiting Minimal Interaction towards Immobilized Proteins (pages 552–555)

      Elza V. Amirgoulova, Jürgen Groll, Colin D. Heyes, Thomas Ameringer, Carlheinz Röcker, Martin Möller and G. Ulrich Nienhaus

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200400024

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      An invisible surface: Single protein molecules were immobilized on a cross-linked polymer surface (see cartoon), and imaged using fluorescence resonance energy transfer (FRET). The surface not only maintained the correct conformation of the protein molecules, but also allowed them to be unfolded and refolded fifty times consecutively. Moreover, the measured δG, cooperativity and the transition midpoint in guanidinium chloride of the unfolding-folding transition on the surface was identical to the protein in solution. Thus, the surface is energetically ‘invisible’ to the folding protein.

    18. Large Solvent and Potential Effects on the Collective Surface Plasmon Band of Gold Nanoparticle Films (pages 555–559)

      Mami Yamada and Hiroshi Nishihara

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301013

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      Spectroscopic shifts: Gold nanoparticle films (see picture), modified with biferrocene-terminated alkyl thiolates (Aun-BFc), with average core diameters of 2.2, 4.3 and 6.4 nm, exhibit a collective surface plasmon (SP) band that includes interparticle interactions and results in peculiar spectroscopic shifts with applied potential and surrounding solvent. These shifts are different from those of single particles.

    19. Dynamics of a Ferroelectric Liquid Crystal by means of 2H NMR Spectroscopy: A Multifrequency Relaxation Study (pages 559–563)

      Valentina Domenici, Marco Geppi, Carlo Alberto Veracini, Robert Blinc, Andrija Lebar and Bostjan Zalar

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301019

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      Spinning and tumbling motions in liquid crystals: Measurements of deuterium quadrupolar (T1Q) and spin-lattice (T1Z) relaxation times of selectively deuterated ferroelectric liquid crystals can be suitably analysed in terms of dynamic models to get detailed information on collective, overall (molecular spinning and tumbling) and internal motions (see picture). The availability of relaxation times measured at three Larmor frequencies and for two different molecular sites results in a remarkably improved reliability in the determination of the diffusion coefficients.

    20. A Selective, Fluorescent Sensor for Zn2+ (pages 564–566)

      Yi Chen and De X. Zeng

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301021

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      Standing out from the crowd: The fluorescence intensity increases remarkably when a diarylethene ligand binds with Zn2+. By contrast, the fluorescence intensity is quenched when the ligand binds with other metal ions (see graphic) that compete with the zinc ion for binding sites.

    21. Pressure Perturbation Calorimetry: A New Technique Provides Surprising Results on the Effects of Co-solvents on Protein Solvation and Unfolding Behaviour (pages 566–571)

      Revanur Ravindra and Roland Winter

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301080

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      Exquisitely sensitive, pressure perturbation calorimetry was used by the authors to study the solvation and volumetric properties of proteins in their native and unfolded states. The magnitude and even sign of the volume change on unfolding drastically depends on the co-solvent concentration (see graphic).

    22. Modulation of the Work Function in Layer-by-Layer Assembly of Metal Nanoparticles and Poly-L-lysine on Modified Au Surfaces (pages 571–575)

      Michel Carrara, Joseph J. Kakkassery, Jean-Pierre Abid and David J. Fermín

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301212

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      Layered surface: Particles with a diameter smaller than 10 nm can be organised in ordered multilayers that feature regular fluctuations of the work function. While the amplitude of the modulation is determined by the properties of the polypeptide and the layer-by-layer ordering, the work function of the nanoparticle-terminated surface is determined by the nature of the metal particle and its surface functionalisation (see graphic).

    23. Computer Simulation of Ionic and Nonionic Mixed Surfactants in Aqueous Solution (pages 575–580)

      Ming-Yu Kuo, Hsiao-Ching Yang, Chih-Yu Hua, Cheng-Lung Chen, Shi-Zhe Mao, Feng Deng, Han-Hui Wang and You-Ru Du

      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200301036

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      Micellar phases: The phase diagram of aqueous sodium tetradecyl sulfate (STS) at different concentration was predicted successfully by means of the dissipative particle dynamics (DPD) method. The typical hexagonal phase (shown) was formed in an aqueous solution of 45 mol% STS at room temperature.

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      Article first published online: 14 APR 2004 | DOI: 10.1002/cphc.200490027

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