Coordination of di-Histidine-containing hexapeptides with cupric ion and its application in electrochemical detection

The lone pair electrons of nitrogen in imidazole ring enable His residue served as an anchor to bind metal ion or as a connector to regulate peptide-metal ions self-assembly. In this paper, a series of hexapeptides with two His residues of different locations in the sequences were synthesized and their coordination performance with Cu2+ were explored. The stoichiometric ratio, binding ability and coordination structures of the peptides with Cu2+ in aqueous solutions were characterized with isothermal titration calorimetry (ITC), 1H nuclear magnetic resonance (1H NMR), ultraviolet visible (UV–Vis) and visible circular dichroism (Vis-CD) spectroscopies. Furthermore, the di-His-containing peptides were immobilized on gold electrodes to detect Cu2+ through the high-efficiency complexation. The results indicated that the binding ability and coordination structures of di-His-containing peptides with Cu2+ were determined by the sequence. GHGGGH showed the highest binding constant with Cu2+ and formed a stable 4 N complex of {NH2, N-, 2Nim}. GHGGGH modified electrodes had the highest sensitivity in the electrochemical detection of Cu2+ in aqueous solutions at neutral pH. This work provides us with a better understanding of the interaction of functional amino acids in peptide sequences with metal ions and offers constructive guidance in designing metal ion binding peptides.