Potential modulated reflectance study of the electrooxidation of simple amino acids on Pt(111) in acidic media

The electroreflectance (ER) technique has been applied to the study of the electrooxidation of some simple amino acids (glycine, serine and alanine) on a Pt(111) surface in acid medium. A different behaviour in the 1/R∂R/∂E response as a function of applied potential has been observed during the positive and negative scans as consequence of the formation of adsorbed cyanide originating from the oxidation of glycine and serine. Alanine on the other hand does not readily form significant amounts of adsorbed cyanide on the first oxidation cycle. The integrated ER spectra (ΔR/R) of the three amino acids have also shown that the reversible adsorption of the glycinate, serinate and alaninate anions is initiated at ca. 0.35 V and reaches maximum coverage at ca. 0.7 V. This reversible adsorption produces changes in the reflectivity comparable to that displayed by bisulphate adsorption.