Adsorption of asparagine on the gold electrode and air/solution interface

Abstract

The adsorption of asparagine (Asn) on a gold electrode from 0.1 M LiClO 4 aqueous solutions was investigated. The experimental data obtained from ac impedance measurements were analyzed to determine the dependence of adsorption parameters, i.e. the standard Gibbs energy of adsorption (Δ G 0), maximal value of surface excess concentration ( Γ max) of Asn and parameter of interactions in the adsorbed layer ( A) on the electrode potential. The relatively large value of Gibbs energy of adsorption (∼ −47 kJ mol −1) gives the evidence of a very strong adsorption of Asn at the polycrystalline Au electrode. The comparison of the adsorption behavior of Asn at the air/solution and the Au/solution interfaces points out to the significant electronic interactions of adsorbate molecules with the Au electrode, since the adsorption of Asn on a free surface (from the same solutions) is very week. The analysis of the electrochemical data as well as the infrared reflection absorption spectroscopy (IRAS) results reveal that Asn molecules are anchored to the Au surface through oxygen atoms of the carboxylate group COO − and through the amide carbonyl group.