The Spectroelectrochemical And Electrochemical Studies Of Pharmaceutical Molecules

Spectroelectrochemistry (SEC) is a method allowing simultaneous acquisition of electrochemical and optical information in an electrochemical cell. The electrochemical reactions are initiated by applying potentials to the electrode, and the redox process that occur in the solution undergoing electrolysis are monitored by both electrochemical and spectroscopical techniques. Thus, SEC provides a convenient means for obtaining intermediate or product spectra and herein obtaining the redox potentials, the electron transfer number, the rate constants structural or conformational information on an intermediate product, and the diffusion coefficients of subsequent chemical reactions of electro-generated species, etc. Because of its unique characteristics, SEC has proved to be an effective approach for studying the redox chemistry of inorganic, organic and biological molecules, for investigating reaction mechanisms, for measuring reaction kinetics, and for exploring electrode surface phenomena . It has now been developed into an independent scientific branch in electrochemistry and has been widely applied. The adsorption phenomena occurs in most of the electrochemical reactions, so it is worthy for us to study the effective factors of the adsorption on electrode surface. The adsorption of reactant or product will affect the electrochemical signal (for example, I-E voltammetry curve) greatly. The theory of stationary electrode polarography for single scan and cyclic triangular wave experiments has been extended to describe electrochemical systems where either the reactant, the product, or both the reactant and product are adsorbed at the electrode-solution interface. Correlation of theoretical and experimental parameters made it possible to develop diagnostic criteria so that unknown systems could be characterized by studying the variation of peak shape and peak current as a function of scan rate and bulk concentration. This thesis work is mainly focused on using spectroelectrochemical methods combining with voltammetry to study: (1) the electrochemical reaction mechanism; (2) the electrode reaction and adsorption kinetics; (3) the structural or the conformational transition of pharmaceutical molecules during the electrochemical process. We also described the operation, the characters and the combination with electrochemical methods of the CD and UV-Vis-NIR spectrometer in detail. We treated the SEC data with the double logarithm method together with nonlinear regression program and obtained some parameters as the reaction kinetics, thermodynamics and adsorption constants. These constants will be helpful to us to learn the essence of the electrode reaction. ? Voltammetry and circular dichroic (CD) spectroelectrochemistry were used to study the electrochemical process of VB2 at glassy carbon (GC) electrode in neutral PBS solution. The adsorption conditions and the electroactive potential range of \/B2 at GC electrode were studied by cyclic voltammetry. The results showed that VB2 had weak adsorption on the electrode surface. We used SEC to learn the electrochemical process of VB2 in a long optical path length thin layer cell (LOPLTLC) for the first time. According to the change of CD spectra, we predicted the structural transition of VB2 and obtained some electrocheniical constants. The electrode reaction process of VD2 in ethanol solution were investigated using cyclic voltammetry and circular dichroic (CD) spectroelectrochemistry for the first time. We ad...