Ac voltammetric and square wave voltammetric study of the self-assembled monolayers of thiol-functionalized viologen derivative

Electroactive self-assembled monolayers (SAMs) containing viologen group are formed through the adsorption of thiol-functionalized viologen compound CH3(CH2)(9)V2+(CH2)(8)SH, where V2+ is N,N'-dialkylbipyridinium (i.e. a viologen group), onto gold electrodes from methanol/water solution and its electrochemical behavior is investigated ty Ac voltammetry and square wave voltammetry, which have the high sensitivity against background charging. The viologen SAM formed is a sub-monolayer and the normal potentials corresponding to the two successive one-electron transfer processes of the active centers (viologen) are -360 mV and -750 mV (vs. Ag/AgCl) in 0.1 mol/L phosphate buffer solutions (pH 6.96) respectively, and the standard electron transfer rate constant is 9.0 s(-1). The electrochemical behavior of this SAM in various solutions has been preliminarily discussed.

PHYSICAL AGING OF HIGH-PERFORMANCE THERMOPLASTICS - ENTHALPY RELAXATION IN PEK-C AND PES-C

The developments of physical aging in phenolphthalein poly(aryl-ether-ketone) (PEK-C) and poly(aryl-ether-sulfone) (PES-C) with time at two aging temperatures up to 20 K below their respective glass transition temperatures (T-g = 495 and 520 K) have been studied using differential scanning calorimetry (DSC). Substantial relaxation within the aging course of several hours were observed by detecting T-g decreasing during physical aging process at the two aging temperatures. The relaxation processes of both polymers are extremely nonlinear and self-retarding. The time dependencies of their enthalpies during the initial stages of annealing were approximately modeled using the Narayanaswamy-Tool model. The structure relaxation parameters obtained from this fitting were used to predict the possibility of physical aging occurring at their respective using temperatures. (C) 1995 John Wiley and Sons, Inc.

IN-SITU UV-VISIBLE SPECTROELECTROCHEMICAL AND CIRCULAR DICHROIC ELECTROCHEMICAL STUDY OF BILIRUBIN AND BILIRUBIN PLUS HUMAN SERUM-ALBUMIN COMPLEX

The electro-oxidation of bilirubin (BR) in aqueous solution was investigated by cyclic voltammetry and in-situ thin-layer spectroelectrochemical techniques, It was found that both oxidation processes of BR are two electron transfer reactions. A mechanism

PREFERENTIAL SORPTION OF MODIFIED PVA MEMBRANE IN PERVAPORATION

The swelling processes of an annealed poly (vinyl alcohol) membrane, a NaOH-crosslinked poly (vinyl alcohol) membrane, a poly (vinyl alcohol)-N,N'-methylene bisacrylamide irradiation-crosslinked membrane and a poly (vinyl alcohol)/poly(AMcoAANa) blend membrane were investigated. Water was preferentially sorbed by all four membranes. The selective sorption factor alpha(s) and the selective diffusion factor alpha(d) were defined, and were used to characterize the effects of sorption and diffusion on selectivity. The results have shown that preferential sorption has a marked effect on selectivity. The mean diffusion coefficients and pervaporation properties of the four membranes are also discussed.

INVESTIGATION OF THE ELECTROCHEMICAL-BEHAVIOR OF TRYPTOPHAN BY IN-SITU CIRCULAR DICHROIC SPECTROELECTROCHEMISTRY

The electrochemical redox processes of tryptophan were studied by in situ circular dichroic (CD) spectroelectrochemistry with a long optical path length thin-layer cell. The oxidation of tryptophan at low concentrations in basic aqueous solution is a two-electron irreversible electrochemical process which results from an irreversible subsequent chemical reaction. A method of treatment of CD spectral data for the irreversible electrochemical reaction is suggested, from which the values E(p/2) = 0.46 V, alphan(alpha) = 0.313 and k0 = 2.4 x 10(-4) cm s-1 (the standard heterogeneous reaction rate constant for tryptophan oxidation) were obtained.

STUDY OF THE ELECTRODE PROCESS OF HEMOGLOBIN AT A POLYMERIZED AZURE A FILM ELECTRODE

The electrochemically polymerized azure A film electrode is reported. The resulting film on a platinum electrode surface was analyzed with electron spectroscopy for chemical analysis (ESCA). The heterogeneous electron transfer processes of hemoglobin at the polymerized azure A film electrode have been investigated using in situ UV-visible spectroelectrochemistry. The formal potential (E-degrees') and electron transfer number (n) of hemoglobin were calculated as E = 0.088 V versus NHE (standard deviation +/- 0.5, N = 4) and n = 1.8 (standard deviation +/- 0.5, N = 4). Exhaustive reduction and oxidation electrolysis are achieved in 80 and 380 seconds, respectively, during a potential step between -0.3 and +0.3 V. A formal heterogeneous electron-transfer rate constant (k(sh)) of 3.54(+/- 0.12) X 10(-6) cm/s and a transfer coefficient (alpha) of 0.28(+/- 0.01) were obtained by cyclic voltabsorptometry, which indicated that the poly-azure A film electrode is able to catalyze the direct reduction and oxidation of hemoglobin.

THERMAL-DECOMPOSITION PROCESS OF SOME RARE-EARTH NITRILOTRIACETIC ACID SERINE MIXED COMPLEXES

Thermal decomposition processes of the mixed complexes of nitrilotriacetates of Pr, Sm, Tb, Ho and Tm with 2-amino-3-hydroxypropionic acid have been investigated. The results indicate that serine may coordinate to the rare earth ion via its hydroxyl group, not by means of its carboxyl group. From the thermogravimetric and the derivative thermogravimetric curves it can be deduced that there may be six or seven steps in the thermal decomposition process of these mixed complexes, and that not all thermal decomposition processes in these mixed complexes are the same. Some possible thermal decomposition reactions have been proposed, and the differences between the thermal decomposition processes of these complexes are also discussed.

A STUDY OF ION KINETIC-ENERGY SPECTROMETRY OF ORTHO-DICHLORO, META-DICHLORO AND PARA-DICHLORO BENZENE DOUBLY CHARGED IONS [C6H4CL2]2+ AND [C6H3CL]2+ IN GAS-PHASE

The unimolecular Charge separation reactions of the doubly charged ions [C6H4Cl2]2+, [C6H3Cl]2+ produced in the ion source by electron impact from o-, m-, and p-dichloro benzene have been studied using mass analysed ion kinetic energy spectrometry. The values of kinetic energy releases (T) can be calculated from the energy dispersion of product ions. As T essentially reflects the release of coulombic energy, which can be used to calculate the approximate distances R between the two charges immediately before decomposition of the ions. From these data, some structural information about transiton states could be provided. The ECID and CID processes of above doubly charged ions, have also been studied. We found that the CID reactions of (C6H4Cl2)2+ could be used to distinguish three dichloro benzene isomers.

STUDY ON ELECTRODE PROCESS OF MYOGLOBIN AT A POLYMERIZED AZURE A FILM ELECTRODE

The electrochemically polymerized azure A film electrode was firstly reported in this paper. A quasi-reversible electrode processes of myoglobin with the formal heterogeneous electron transfer rate constant (k(sh)) of 1.73 x 10(-4) cm.s-1 at the polymerized azure A modified electrode have been achieved using in-situ UV-visible spectroelectrochemistry. The adsorption of myoglobin on the polymerized azure A film electrode surface was confirmed by XPS. With simultaneously studying of cyclic voltammetry and in-situ cyclic voltabsorptometry, the attribution of the voltammetry responses of myoglobin at the film electrode has been studied. The mechanism for the heterogeneous electron transfer of myoglobin at the polymerized azure A film modified electrode has been proposed as well.

DIRECT ELECTRON-TRANSFER REACTION OF HEMEPROTEINS PROMOTED BY METHYLENE-BLUE MODIFIED ELECTRODE

The heterogeneous electron transfer reaction of hemeproteins including hemoglobin, myoglobin and cytochrome C at Pt mesh electrode adsorbed methylene blue has been investigated. Thin-layer spectroelectrochemical technique was used for observing the electron transfer processes of three kinds of proteins, and the corresponding electrode rate constants were measured.

RESEARCHES ON CHEMICALLY MODIFIED ELECTRODES - ELECTROCHEMISTRY OF 1-12 PHOSPHOMOLYBDIC HETEROPOLY ANION FILM MODIFIED ELECTRODE

A monolayer of 1:12 phosphomolybdic anion (PMo_(12)) was modified electrochemically on a glassy carbon electrode and its electrochemical behavior was studied with cyclic voltammetry (CV). It is shown that PMo_(12) film is adsoibed strongly on the surface of glassy carbon electrodes, H~+ ions in the solution plays an important role in the electrochemical processes of PMo_(12) film modified electrodes, whereas other anions, such as Cl~-, NO_3~-, SO_4~(2-), ClO_4~- and PO_4~(3-) etc., do not take par...

SYNTHESIS OF TETRAPHENYLBUTADIENE LANTHANIDE METALLACYCLES

The cyclic derivatives of transition metals have been extensively investigated in recent years since they are believed to serve as key intermediates in various homogeneous catalytic processes of olefine and alkyne metathesis. The synthesis of the title compounds has not been reported before.

Dynamics of the buoyant plume off the Pearl River Estuary in summer

Field measurements of salinity, wind and river discharge and numerical simulations of hydrodynamics from 1978 to 1984 are used to investigate the dynamics of the buoyant plume off the Pearl River Estuary (PRE), China during summer. The studies have shown that there are four major horizontal buoyant plume types in summer: Offshore Bulge Spreading (Type I), West Alongshore Spreading (Type II), East Offshore Spreading (Type III), and Symmetrical Alongshore Spreading (Type IV). River mouth conditions, winds and ambient coastal currents have inter-influences to the transport processes of the buoyant plume. It is found that all of the four types are surface-advected plumes by analysing the vertical characteristic of the plumes, and the monthly variations of the river discharge affect the plume size dominantly. The correlation coefficient between the PRE plume size and the river discharge reaches 0.85 during the high river discharge season. A wind strength index has been introduced to examine the wind effect. It is confirmed that winds play a significant role in forming the plume morphology. The alongshore wind stress and the coastal currents determine the alongshore plume spreading. The impact of the ambient currents such as Dongsha Current and South China Sea (SCS) Warm Current on the plume off the shelf has also assessed. The present study has demonstrated that both the river discharge and wind conditions affect the plume evolution.

Physical mechanism and numerical simulations of surface layer temperature inversion in tropical ocean

The one-dimensional Kraus-Turner mixed layer model improved by Liu is developed to consider the effect of salinity and the equations of temperature and salinity under the mixed layer. On this basis, the processes of growth and death of surface layer temperature inversion is numerically simulated under different environmental parameters. At the same time, the physical mechanism is preliminarily discussed combining the observations at the station of TOGA-COARE 0 degrees N, 156 degrees E. The results indicate that temperature inversion sensitively depends on the mixed layer depth, sea surface wind speed and solar shortwave radiation, etc., and appropriately meteorological and hydrological conditions often lead to the similarly periodical occurrence of this inversion phenomenon.

Bacterial roles in the formation of high-molecular-weight dissolved organic matter in estuarine and coastal waters: Evidence from lipids and the compound-specific isotopic ratios

High-molecular-weight dissolved organic matter (HMW-DOM, > 1,000 Daltons) is actively involved in the global biogeochemical cycling of many elements, but its carbon sources and detailed formation pathways are still not well understood. In this study, we measured bulk stable carbon and nitrogen isotopic ratios, lipid composition, and compound-specific carbon isotopic ratios of HMW-DOM samples collected from four U.S. estuaries (Boston Harbor/Massachusetts Bay, Delaware/Chesapeake Bay, San Diego Bay, and San Francisco Bay). Analytical results show (1) a fraction of HMW-DOM (lipid associated) in estuarine and coastal waters is derived from bacteria and phytoplankton; (2) this fraction of HMW-DOM is formed by various release processes of bacterial membrane components and bacterial reworking of phytoplankton-derived material; (3) this fraction of HMW-DOM is generally present in all samples from different coastal systems despite variable organic matter inputs and environmental conditions, suggesting an important bacterial role in HMW-DOM formation.