Adsorption And Oxidation Of Amino Acids On Au Electrodes Of Different Structures In Alkaline Solutions

Glycine is the simplest structural block of protein and the smallest amino acid molecule. A better understanding of adsorption and oxidation properties of amino acid on electrode surfaces is of significant importance to elucidate the mechanism of complex metal-protein interaction, and to explore fundamental of interaction of different functional groups (-COOH, -NH₂, -CHX, -OH, etc.) with electrocatalytic surfaces as well.The adsorption and oxidation of cyanide, glycine and serine on Au electrodes of different structures in alkaline solutions were studied using cyclic voltammetry (CV), in situ FTIR spectroscopy (in situ FTIRS) and electrochemical quartz crystal microbalance (EQCM). The main results are listed below.1. It has revealed that the electrodeposited nanostructured thin film of Au electrodes (nm-Au/GC) exhibit abnormal infrared effects (AIREs) for CN^- adsorption, which manifested 3 anomalous IR spectral features: the inversion of the IR band direction, the enhancement of IR absorption and the increase in the FWHM (full width at half maximum) of IR band. The study has extended the AIREs from Pt group and Fe group metals to coinage metal. Furthermore, the enhancement of IR absorption for CN- has increased significantly the sensitivity of determination of the interaction of amino acid with electrode surface.2. It has developed the knowledge concerning the reaction mechanism of amino acids. The C-C bond of glycine and serine can be broken at low potential (-0.8 V). The CN_ad^- species which derived from -CHxNH2 group are stable on Au electrodes in the potential region from -0.8 to 0.0 V, and can be oxidized to cyanate (OCN^-), and concomitantly, Au was oxidized to aurous cyanide (AuCN) and aurous di-cyanide (Au(CN)₂^-) species. The formation of Au(CN)₂^- anions may initiate a dissolution of Au(111) surface atoms, which has been confirmed by a loss of surface mass determined in EQCM studies. The -COO^- or -CH₂OH group was oxidized to CO₂ (HCO₃^- and CO₃^2-).3. It has found that the Au(111) electrode exhibited a much higher activity than the polycrystalline Au electrode for the oxidation of glycine and serine. The high electrocatalytic activity was promoted by the adsorption of OH- species and attributed to the orderly arrangement of adsorbed OH species on Au(111).The results obtained in this thesis have revealed the surface structure of Au electrocatalysts and their properties, and have thrown a light on elucidating the interaction mechanism of amino acid molecules with Au surfaces at molecule level. The current studies are also of importance in electrocatalysis, medication and bio-sensors applications.