An electron spin resonance investigation of the nature of the complexes formed between copper(II) and glycylhistidine

Abstract

The pH dependence of the formation of complexes between copper(II) and the peptide glycylhistidine has been investigated for metal : ligand ratios of 1 : 1 and 1 : 2 by e.s.r. spectroscopy. Five complex species are seen with the 1 : 2 ratio solutions, 4 of which are also observed with the 1 : 1 ratio solutions. In each case ¹⁴N superhyperfine structure is resolved in fluid solution by working with the ⁶³Cu isotope and recording second-derivative spectra, thus producing a direct measurement of the number of nitrogen atoms bound to copper. Superhyperfine structure was also resolved in the frozen-solution spectra of several of the complexes, although this was not always consistent with the conclusions drawn from the fluid-solution spectra. The likely composition and coordination of the various species are discussed with reference to published results from electrochemical and u.v.-visible spectroscopic methods.