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Transfer Kinetics (transfer + kinetics)

Distribution by Scientific Domains
Chemistry88%

Kinds of Transfer Kinetics

  • mass transfer kinetics
    		•

    Selected Abstracts

    Electron Transfer Kinetics of Ferrocene at Microcrystalline Boron-Doped Diamond Electrodes: Effect of Solvent and Electrolyte

    ELECTROANALYSIS, Issue 4 2003
    Shannon Haymond
    Abstract Cyclic voltammetric measurements were made using well-characterized microcrystalline boron-doped diamond thin-film electrodes to test the material's responsiveness for ferrocene as a function of scan rate, solvent, and electrolyte composition. Apparent heterogeneous electron transfer rate constants, k°app, of 0.042±0.015, 0.048±0.015, and 0.008±0.002,cm/s were observed in 0.1,M NaClO4/CH3CN, 0.1,M TBAClO4/CH3CN, and 0.1M TBAClO4/CH2Cl2, respectively. These rate constants, obtained using electrodes without any type of pretreatment, are similar to those observed for freshly polished glassy carbon. The results demonstrate that boron-doped diamond is a viable material for the electrochemical analysis of nonaqueous analytes. [source]

    Detecting Biorecognition Events at Blocked Interface Polymeric Membrane Ion-Selective Electrodes Using Electrochemical Impedance Spectroscopy and Atomic Force Microscopy

    ELECTROANALYSIS, Issue 3 2008
    Marco, Roland De
    Abstract Immobilization of a biorecognition element onto a polymeric membrane ion-selective electrode (ISE) using a self-assembly approach may provide scope for a novel biosensor technology platform based on the altered potentiometric response at the blocked ISE interface. In this paper, the authors have investigated the influence of solution adsorption of the model biorecognition element, avidin-biotin, on the electrode kinetics of a conventional polymeric membrane Ca2+ ISE using atomic force microscopy (AFM) coupled with electrochemical impedance spectroscopy (EIS). It is demonstrated that solution adsorption of avidin followed by biotin incorporation leads to a demonstrable biorecognition event characterized by an impediment in the Ca2+ ion transfer kinetics of the modified ISE surface. This kinetic principle is amenable to biosensing using pulsed chronopotentiometric polymeric ISEs, which is an established dynamic electrode technique for use with polymeric membrane ISEs. [source]

    Rate constants of mass transfer kinetics in reversed phase liquid chromatography

    AICHE JOURNAL, Issue 12 2005
    Lan Hong
    Abstract The parameters of the kinetics of mass transfer of several n -alkylbenzenes were measured by the method of moments on a series of columns prepared with different samples of the same RPLC packing material having widely different average particle diameters, from 3 to 50 ,m. These data were analyzed using the available models, and correlations. The best agreement between experimental and theoretical data was obtained under the assumption that the rate constant for the external mass transfer increases with increasing average particle size, an unexpected conclusion. It was also shown that the interpretation of the relative importance of the roles of pore diffusivity and surface diffusivity in the internal mass transfer kinetics is somewhat ambiguous and that the conclusion to be drawn from experimental results depends on the assumptions made regarding the tortuosity model and the relationship between kext and the average particle size. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source]

    Measurement of the parameters of the mass transfer kinetics in high performance liquid chromatography

    JOURNAL OF SEPARATION SCIENCE, JSS, Issue 3-4 2003
    Kanji Miyabe
    Abstract Fundamental studies of the mass transfer kinetics are as essential as those of the retention equilibrium for a detailed understanding of the characteristics and the mechanisms of chromatographic separations. The acquisition of a large amount of reliable experimental data and of meaningful results is necessary for any further progress of our knowledge of kinetics. The main goal of this review is to provide information on the methods used to perform accurate measurements and on the data analysis procedures used for deriving the kinetic parameters characterizing mass transfer in HPLC. First, the general characteristics of several methods of determination of some kinetic parameters are briefly reviewed. Secondly, we give detailed explanations of the experimental conditions of the pulse on a plateau method (i.e., elution chromatography on a plateau of finite concentration or pulse response method) and of the data analysis procedures based on moment analysis. Thirdly, we explain some important requirements for the acquisition of appropriate experimental data and discuss corrections to be applied when deriving several kinetic parameters. Fourthly, we discuss the accuracy of the kinetic parameters derived from the pulse on a plateau method and from moment analysis. Finally, some results concerning the mass transfer kinetics in RPLC systems are demonstrated as examples. [source]

    Spheroidization of Titanium Carbide Powders by Induction Thermal Plasma Processing

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001
    Ya-Li Li
    Highly spherical particles of titanium carbide (TiC) have been produced by in-flight heat processing of irregularly shaped TiC powders in an aerosol reactor under argon-hydrogen and argon-helium induction thermal plasma. The spherical powders obtained by the plasma treatment consist of unagglomerated and uniform particles with mean diameters between 25 and 28.5 ,m, which is smaller than the original TiC particle mean diameters (29.5 ,m) because of partial evaporation of the particles during the plasma treatment. The spheroidization ratio of the treated TiC powders increases with the increase of hydrogen flow rate in plasma gases and the reduction of powder feeding carrier gas flow rate. Under certain processing conditions, the TiC powders have been completely spheroidized. The morphology and structure of individual spherical particles were examined and their formation mechanism was discussed based on calculation of heat transfer kinetics of the particles in the thermal plasma. [source]

    Protein dynamics control proton transfer from bulk solvent to protein interior: A case study with a green fluorescent protein

    PROTEIN SCIENCE, Issue 7 2005
    Anoop M. Saxena
    Abstract The kinetics of proton transfer in Green Fluorescent Protein (GFP) have been studied as a model system for characterizing the correlation between dynamics and function of proteins in general. The kinetics in EGFP (a variant of GFP) were monitored by using a laser-induced pH jump method. The pH was jumped from 8 to 5 by nanosecond flash photolysis of the "caged proton," o -nitrobenzaldehyde, and subsequent proton transfer was monitored by following the decrease in fluorescence intensity. The modulation of proton transfer kinetics by external perturbants such as viscosity, pH, and subdenaturing concentrations of GdnHCl as well as of salts was studied. The rate of proton transfer was inversely proportional to solvent viscosity, suggesting that the rate-limiting step is the transfer of protons through the protein matrix. The rate is accelerated at lower pH values, and measurements of the fluorescence properties of tryptophan 57 suggest that the enhancement in rate is associated with an enhancement in protein dynamics. The rate of proton transfer is nearly independent of temperature, unlike the rate of the reverse process. When the stability of the protein was either decreased or increased by the addition of co-solutes, including the salts KCl, KNO3, and K2SO4, a significant decrease in the rate of proton transfer was observed in all cases. The lack of correlation between the rate of proton transfer and the stability of the protein suggests that the structure is tuned to ensure maximum efficiency of the dynamics that control the proton transfer function of the protein. [source]

    Photoelectron Generation by Photosystem,II Core Complexes Tethered to Gold Surfaces

    CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 4 2010
    Michele Vittadello, Prof.
    Abstract By using a nondestructive, ultrasensitive, fluorescence kinetic technique, we measure in,situ the photochemical energy conversion efficiency and electron transfer kinetics on the acceptor side of histidine-tagged photosystem,II core complexes tethered to gold surfaces. Atomic force microscopy images coupled with Rutherford backscattering spectroscopy measurements further allow us to assess the quality, number of layers, and surface density of the reaction center films. Based on these measurements, we calculate that the theoretical photoelectronic current density available for an ideal monolayer of core complexes is 43,,A,cm,2 at a photon flux density of 2000,,mol,quanta,m,2,s,1 between 365 and 750,nm. While this current density is approximately two orders of magnitude lower than the best organic photovoltaic cells (for an equivalent area), it provides an indication for future improvement strategies. The efficiency could be improved by increasing the optical cross section, by tuning the electron transfer physics between the core complexes and the metal surface, and by developing a multilayer structure, thereby making biomimetic photoelectron devices for hydrogen generation and chemical sensing more viable. [source]