Interactions between Ni2+ ions and tetrapeptides containing (Asp/Lys)HisGly(L/D)His sequence

A series of linear tetrapeptides containing two histidyl residues in positions 2 and 4 with different chirality: DHGH, DHG(D-His), KHGH, KHG(D-His), Ac-DHGH-NH2, Ac-DHG(D-His)-NH2, Ac-KHGH-NH2, and Ac-KHG(D-His)-NH2 were synthesized, characterized and their binding properties towards Ni2+ were investigated. To establish the stoichiometry and the stability of the resulting Ni2+ complexes, potentiometric titrations were carried out. The coordination mode of the complexes formed was investigated by performing extensive spectroscopic analyses (UV-Vis, CD) in strict correlation with the potentiometric results. The effects of the nature of the first amino acid (Lys versus Asp) and of the N-terminal amino group acetylation were determined. A careful comparison of the Ni2+ coordination abilities of the linear peptides provides a specific insight into the impact of the chirality of the C-terminal histidine residue (His(4)) on the metal binding properties. (C) 2010 Elsevier Ltd. All rights reserved.