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Yanxia Zhang - One of the best experts on this subject based on the ideXlab platform.

  • predicting au s Bond Breakage from the swelling behavior of surface tethered polyelectrolytes
    Soft Matter, 2011
    Co-Authors: Yanxia Zhang, Shen Zhang, Hong Chen
    Abstract:

    Surface tethered weak polyelectrolyte, carboxylated poly(OEGMA-r-HEMA), was prepared viasurface initiated polymerization (SIP) from metal (Au, Pt and Ag) surfaces functionalized with initiators through metal–S Bonds. The swelling behavior of carboxylated poly(OEGMA-r-HEMA) in phosphate buffered saline (PBS) was studied by quartz crystal microbalance (QCM) and was found to obey the following equation: Teff = (0.32ln([Na+]) + 2.53) × TCOOH,dry, where Teff and TCOOH,dry are the thicknesses of carboxylated poly(OEGMA-r-HEMA) in PBS measured by QCM and in air measured by ellipsometry, respectively. We also confirmed that the event of covalent Bond breaking (CBB) of Au–S Bonds occurred at a certain critical Teff, i.e. ∼255 nm. Thus, one could predict the CBB of Au–S or other metal–S Bonds from the swelling behavior of surface tethered carboxylated poly(OEGMA-r-HEMA).

  • directly observed au s Bond Breakage due to swelling of the anchored polyelectrolyte
    Chemical Communications, 2011
    Co-Authors: Ying Zhu, Yanxia Zhang, Hong Chen
    Abstract:

    A weak polyelectrolyte coating, carboxylated poly(oligo(ethylene glycol)methacrylate-co-2-hydroxyethylmethacrylate), was prepared via surface initiated polymerization (SIP) from initiators immobilized to gold surface through the Au-S Bonds. When dry thickness increased up to 75 nm, this polyelectrolyte coating was pulled off the Au substrate by simply exposing to phosphate buffer saline (PBS, pH = 7.4, [Na(+)] = 150 mM). This covalent Bond breaking (CBB) behavior was monitored in situ using a quartz crystal microbalance (QCM) and CBB was associated with the swelling of the anchored polyelectrolyte chains.

Hong Chen - One of the best experts on this subject based on the ideXlab platform.

  • predicting au s Bond Breakage from the swelling behavior of surface tethered polyelectrolytes
    Soft Matter, 2011
    Co-Authors: Yanxia Zhang, Shen Zhang, Hong Chen
    Abstract:

    Surface tethered weak polyelectrolyte, carboxylated poly(OEGMA-r-HEMA), was prepared viasurface initiated polymerization (SIP) from metal (Au, Pt and Ag) surfaces functionalized with initiators through metal–S Bonds. The swelling behavior of carboxylated poly(OEGMA-r-HEMA) in phosphate buffered saline (PBS) was studied by quartz crystal microbalance (QCM) and was found to obey the following equation: Teff = (0.32ln([Na+]) + 2.53) × TCOOH,dry, where Teff and TCOOH,dry are the thicknesses of carboxylated poly(OEGMA-r-HEMA) in PBS measured by QCM and in air measured by ellipsometry, respectively. We also confirmed that the event of covalent Bond breaking (CBB) of Au–S Bonds occurred at a certain critical Teff, i.e. ∼255 nm. Thus, one could predict the CBB of Au–S or other metal–S Bonds from the swelling behavior of surface tethered carboxylated poly(OEGMA-r-HEMA).

  • directly observed au s Bond Breakage due to swelling of the anchored polyelectrolyte
    Chemical Communications, 2011
    Co-Authors: Ying Zhu, Yanxia Zhang, Hong Chen
    Abstract:

    A weak polyelectrolyte coating, carboxylated poly(oligo(ethylene glycol)methacrylate-co-2-hydroxyethylmethacrylate), was prepared via surface initiated polymerization (SIP) from initiators immobilized to gold surface through the Au-S Bonds. When dry thickness increased up to 75 nm, this polyelectrolyte coating was pulled off the Au substrate by simply exposing to phosphate buffer saline (PBS, pH = 7.4, [Na(+)] = 150 mM). This covalent Bond breaking (CBB) behavior was monitored in situ using a quartz crystal microbalance (QCM) and CBB was associated with the swelling of the anchored polyelectrolyte chains.

J.w. Mcpherson - One of the best experts on this subject based on the ideXlab platform.

  • thermochemical description of dielectric breakdown in high dielectric constant materials
    Applied Physics Letters, 2003
    Co-Authors: J.w. Mcpherson, A. Shanware, H. Mogul
    Abstract:

    A thermochemical/molecular model is developed for breakdown in high dielectric constant materials and the model suggests that a fundamental relationship exists between dielectric breakdown strength (Ebd) and dielectric constant (k). The model indicates that Ebd should show an approximate (k)−1/2 dependence over a wide range of high dielectric constant materials. The model also predicts that the field-acceleration parameter (γ), from time-dependent dielectric breakdown (TDDB) testing, should increase with dielectric constant. TDDB and Ebd data are presented for model support. The thermochemical model suggests that the very high local electric field (Lorentz-relation/Mossotti-field) in high-k dielectrics tends to distort/weaken the polar molecular Bonds making them more susceptible to Bond Breakage by standard Boltzmann processes and/or by hole capture and thus lowers the breakdown strength.

  • field enhanced si si Bond Breakage mechanism for time dependent dielectric breakdown in thin film sio2 dielectrics
    Applied Physics Letters, 1997
    Co-Authors: J.w. Mcpherson, V K Reddy, H C Mogul
    Abstract:

    A field-enhanced Si–Si Bond-Breakage mechanism is presented which accurately describes the time-dependent dielectric breakdown behavior recently reported for thin-film SiO2 dielectrics over a wide range of fields and temperatures. The breakdown kinetics (both the field and temperature dependence) are shown to be consistent with a field-dependent dipolar energy term associated with an oxygen vacancy which serves to reduce the activation energy required for Si–Si Bond Breakage.

Andreas Janshoff - One of the best experts on this subject based on the ideXlab platform.

  • Mechanically interlocked calix[4]arene dimers display reversible Bond Breakage under force
    Nature Nanotechnology, 2009
    Co-Authors: Matthias Janke, Gregor Diezemann, Yuliya Rudzevich, Olena Molokanova, Thorsten Metzroth, Piotr E. Marszalek, Jürgen Gauss, Volker Böhmer, Andreas Janshoff
    Abstract:

    The physics of nanoscopic systems is strongly governed by thermal fluctuations that produce significant deviations from the behaviour of large ensembles^ 1 , 2 . Stretching experiments of single molecules offer a unique way to study fundamental theories of statistical mechanics, as recently shown for the unzipping of RNA hairpins^ 3 . Here, we report a molecular design based on oligo calix[4]arene catenanes—calixarene dimers held together by 16 hydrogen bridges—in which loops within the molecules limit how far the calixarene nanocapsules can be separated. This mechanically locked structure tunes the energy landscape of dimers, thus permitting the reversible rupture and rejoining of the individual nanocapsules. Experimental evidence, supported by molecular dynamics simulations, reveals the presence of an intermediate state involving the concerted rupture of the 16 hydrogen bridges. Stochastic modelling using a three-well potential under external load allows reconstruction of the energy landscape. Stretching experiments on single molecules offer a unique way to study the fundamental theories of statistical mechanics. Researchers have now shown that entangled calix[4]arene dimers can be used in such experiments as a tuneable model system for investigating the strength of hydrogen Bonds on a single-molecule level.

  • force clamp spectroscopy of reversible Bond Breakage
    Journal of Chemical Physics, 2009
    Co-Authors: Gregor Diezemann, Andreas Janshoff
    Abstract:

    We consider reversible breaking of adhesion Bonds or folding of proteins under the influence of a constant external force. We discuss the statistical properties of the unbinding/rebinding events and analyze their mean number and their variance in the framework of simple kinetic models. In the calculations, we explicitly exploit the analogy to single molecule fluorescence and particularly between unbinding/rebinding and photon emission events. Whereas for two-state behavior Poisson or sub-Poisson statistics of the events is found, we show that for more general kinetic schemes also super-Poisson statistics can occur. Temporal fluctuations of the transition rates, a hallmark for the presence of dynamic disorder, should become experimentally accessible via the determination of the second moment of the event-number distribution.

  • force clamp spectroscopy of reversible Bond Breakage
    arXiv: Soft Condensed Matter, 2008
    Co-Authors: Gregor Diezemann, Andreas Janshoff
    Abstract:

    We consider reversible breaking of adhesion Bonds or folding of proteins under the influence of a constant external force. We discuss the stochastic properties of the unbinding/rebinding events and analyze their mean number and their variance in the framework of simple two-state models. In the calculations, we exploit the analogy to single molecule fluorescence and particularly between unbinding/rebinding and photon emission events. Environmental fluctuation models are used to describe deviations from Markovian behavior. The second moment of the event-number distribution is found to be very sensitive to possible exchange processes and can thus be used to identify temporal fluctuations of the transition rates.

Peter Vohringer - One of the best experts on this subject based on the ideXlab platform.

  • unravelling the ultrafast photodecomposition mechanism of dibenzoyl peroxide in solution by time resolved ir spectroscopy
    Physical Chemistry Chemical Physics, 2008
    Co-Authors: Christian Reichardt, Peter Vohringer, J Schroeder, Dirk Schwarzer
    Abstract:

    The ultrafast photo-fragmentation of dibenzoyl peroxide (DBPO) is studied using femtosecond UV excitation at 266 nm and mid-infrared broadband probe pulses to elucidate the dissociation mechanism. With the help of 13C-labeled DBPO it was possible to unambiguously assign transient IR bands in the fingerprint region to the benzoyloxy radical. Our experiments show that the fragmentation is controlled by the S1-lifetime of DBPO and within 0.4 ± 0.2 ps leads to a benzoyloxy/phenyl radical pair plus CO2via concerted Bond Breakage of the O–O and the phenyl–C(carbonyl) Bond. 20% of the radical pairs geminately recombine to phenyl benzoate on a timescale of 70 ps.

  • energy relaxation versus spectral diffusion of the oh stretching vibration of hod in liquid to supercritical deuterated water
    Journal of Chemical Physics, 2005
    Co-Authors: Dirk Schwarzer, Jorg Lindner, Peter Vohringer
    Abstract:

    The dynamics of vibrational energy relaxation (VER) of the OH-stretching vibration of HOD in liquid-to-supercritical heavy water is studied as a function of temperature and solvent density by femtosecond mid-infrared spectroscopy. Using the dielectric constant of the fluid both, the OH-stretching absorption frequency and the VER rate, can be correlated phenomenologically with the average hydrogen-Bond connectivity within the random D2O network. This correlation enables the identification of thermodynamic conditions under which spectral diffusion due to hydrogen-Bond Breakage/formation is much faster than VER.

  • transition state probing and fragment rotational dynamics following impulsive Bond Breakage of hgi2
    Physical Chemistry Chemical Physics, 2000
    Co-Authors: Helge Bursing, Peter Vohringer
    Abstract:

    The optical anisotropic response following 30 fs, 266 nm photolysis of mercuric diiodide in ethanol solution was measured to explore transition state dynamics leading to Bond fission as well as fragment rotational dynamics in the asymptotic limit for two-body dissociation. The reactive motion in the vicinity of the transition state is accompanied by modifications of the nature of the electronic transition utilized for optical detection. The initial motion away from the originally prepared Franck–Condon region through the transition state toward the fragments effectively rotates the transition moment of the electronic probe resonance in the molecular frame of the dynamically evolving system. After the reactive portion including Bond Breakage is complete, the anisotropy reveals an inertial component on ultrafast time scales well below 1 ps. The time constant associated with this inertial decay is much faster than the free-rotor time constant of HgI implying that impulsive Bond Breakage of the parent molecule results in rotational excitation of the diatomic fragment. It is argued that excitation of fragment rotational degrees of freedom presumably arises from pronounced anisotropies of the excited state potential which is known to be bent for isolated HgI2. Furthermore, coherent vibrational motion of the diatomic product gives rise to periodic modulations of the anisotropy due to stretch–bend coupling in the dynamically evolving system.

  • vibrational relaxation and geminate recombination in the femtosecond photodissociation of triiodide in solution
    Journal of Chemical Physics, 1996
    Co-Authors: Thomas Kuhne, Peter Vohringer
    Abstract:

    The dynamics of product vibrational deactivation and subsequent geminate recombination of diiodide ions with atomic iodine following 400‐nm photolysis of triiodide in ethanol solution has been studied using femtosecond transient absorption spectroscopy. The excess vibrational energy of the diatomic product was found to decay on two distinct time scales. An ultrafast subpicosecond component, which accounts for the dissipation of most of the energy that is initially deposited into fragment vibrations, is followed by thermalization near the bottom of the I−2 potential on a time scale of several picoseconds. The former process is associated with recoil of the fragments in the exit channel of the potential energy surface relevant to Bond Breakage whereas the latter process represents relaxation in the asymptotic limit where interaction between the atom–diatom fragments becomes negligible. Transient product vibrational distributions are determined for delay times larger than the dephasing time of nuclear cohere...