Adsorption of some aliphatic α-amino acids at the mercury—Aqueous solution interface

Abstract

The adsorption of four aliphatic α-amino acids, DL-norleucine(NL), DL-norvaline(NV), DL-α-amino- n-butyric acid(ABA) and DL-α-alanine(AL), at the mercury—neutral aqueous solution interface has been studied by means of double layer capacity, potential of zero charge and surface tension at pzc. The capacity curves are interpreted in terms of two factors, the contribution of the zwitterion group and that of the hydrocarbon group. Two common intersection points observed on the capacity curves of NL, NV and ABA at various concentrations are verified to correspond to the inflection points of the surface excess vs. potential curves. The adsorption of NL, NV and ABA obeys the Frumkin isotherm. The interaction parameter and the potential dependence of the adsorption energy are discussed in terms of the two factors. The shifts of pzc with surface coverage are negative for AL and positive for ABA, NV and NL, which can be explained by assuming the existence of a small dipole component perpendicular to the mercury surface.