Surface electrochemistry of the oxidation of glycine at Pt

Abstract

The electrochemical oxidation of glycine at a Pt electrode was investigated in aqueous solutions at pH 1 and 13 using steady-state current–potential measurements, cyclic voltammetry, and open circuit potential decay. The capacitance behaviour and the high Tafel slopes suggest the production of free radicals at the surface of the electrode accompanied by a second reaction involving loss of CO2 which is the rate determining step. In the electro-oxidation of glycine, it appears that the adsorbed intermediate species is either hydrolyzed anodically to formaldehyde and ammonia, or is oxidized to a carbonium ion which is subsequently hydrolyzed to formaldehyde and ammonia in solution. This behaviour differs from the dimerization process typical of the radical reactions associated with the Kolbe mechanism. Keywords: glycine, amino acid, electrochemical oxidation, surface electrochemistry, Kolbe mechanism.

In Situ FTIR Studies of an Oxidation Product from Protein Adsorption at the Platinum Electrode

“…A similar mechanism has been previously proposed for the adsorption and oxidation mechanisms of amino acids at platinum by electrochemical steady-state potentiodynamic and cyclic voltammetric measurements, accompanied by product analysis (15)(16)(17)(18). The findings reported in this work have shown that SNIFTIRS provides a valuable tool for confirming the production of CO 2 from the adsorption and subsequent oxidation of ribonuclease at anodic potentials at the platinum electrode.…”

A comparative study of electrochemical techniques in investigating the adsorption behaviour of fibrinogen on platinum

“…At anodic potentials of 0.60 V the onset of production of CO 2 is just beginning to be evident from our in situ FTIR measurements, and this process increases with further anodic potentials [44]. Following decarboxylation, at anodic potentials P0.60 V, it is expected that oxidation of the acidic amino acid residues accompanied by electron transfer would continue to proceed to form the next lower aldehyde in the homologous series, consistent with our studies with amino acids [48][49][50]. From the number of carboxylate groups on the protein (number of acidic residues plus the C-terminal), the number of electrons transferred per protein molecule can be determined and then compared to the measured surface charge related to the adsorption of the protein, Q ADS (in C cm À2 ), which in turn can be related to the surface concentration of the protein.…”

“…The initial step of adsorption involves an electron transfer process as follows: P þ nM PðMÞ n þ ne where P represents the protein, M represents the metal electrode, and n represents the number of carboxylate groups on the protein and hence the number of electrons transferred to the electrode. It may be noted that the electron transfer process, which occurs directly from the adsorbed carboxylate on the electrode surface for amino acids [46][47][48], appears also to be an electrolyte-assisted mechanism with proteins in the high anodic potential fields, and hence does not require all the carboxylate groups to physically contact the electrode surface.…”

FTIR studies of tyrosine oxidation at polycrystalline Pt and Pt(111) electrodes

“…The adsorption and differentiation of various amino acids on biomembranes and solid surfaces have been experimentally approached by the application of different in situ electrochemical [5][6][7][8][9][10][11][12][13][14][15][16][17][18] and non-electrochemical techniques [19]. In particular, the combination of cyclic voltammetry (CV), current transients and in situ Fourier-transform infrared spectroscopy (FTIRS) have demonstrated to be powerful tools to study the adsorption, nature and configuration of amino acids [20][21][22][23][24][25][26][27].…”