Electrochemical study of tryptophan-containing peptides-Cu(II) complexes

This article presents rotating ring-disc electrode investigations of (A = alanine, F = phenylalanine, G = glycine, L = leucine, W = tryptophan) W, GW, WGG, GWG, GGW, GWGG, and GGWA. In addition, the analyses of the copper complexes of the same peptides plus GF, FGG, GFG, FGG, GGFL, GGGG, AAAA, and GGGGGG have been carried out. The results suggest that an influential step in the reaction mechanism of the copper complexes of the tryptophan-containing peptides (W-peptides) is the alteration of the peptide structure after the one-electron oxidation of tryptophan. This change in structure leads to a positive shift in redox potential for the Cu(III)/Cu(II) couple. The analytical implications for the electrochemical detection of W-peptides as their copper complexes are applied for detection of W-containing bioactive peptides. Application of the optimized detection conditions of peptides as their Cu(II) complexes are as follows: (1) If sensitivity is paramount, detect the copper complexes at a relatively high potential, around 0.7 V vs. Ag/AgCl. (2) If selectivity is paramount, use a dual electrode detector, oxidize at an upstream anode at 0.4 V, and detect at the downstream cathode at 0-0.1 V.