Speciation and structure of copper(II) complexes with histidine-containing peptides in aqueous medium: a combined potentiometric and spectroscopic study

The complex formation between copper(II) and some histidine-containing peptides has been investigated by means of potentiometric and spectroscopic measurements. Due to the interesting co-ordination mode towards copper(II), peptides with histidyl residue located in second position from the N-terminal amino group have been chosen. The stability constants evaluation has been performed by both pH-metric and ESR (room temperature) measurements; in this context a suitable computer program for the calculation of both stability constant values and the ESR spectrum for each complex has been written. Visible spectrophotometric and circular dichroism spectra, together with the isotropic ESR parameters, were used in order to propose a structure for each complex having a significant percentage of formation in solution.