ESR STUDIES OF COPPER(2) COMPLEX IONS

The bonding parameter a2 has been evaluated for several amino acid, peptide and trypsin complexes with copper (II) ions at liquid nitrogen temperatures. The changes in the nature of the metal to ligand bonding are reflected in changing values of a2 as the pH is varied. There appears to be a reasonable correlation between those structures proposed in the literature as determined by spectrophotometric and potentiometric techniques and the values of a2 as determined from ESR measurements. Of particular interest is the apparent change in the nature of the bonding in the trypsin-copper (II) complex over the range pH 5-6, which suggests a notable rearrangement from primarily amine-amide oxygen bonding sites to amine-amide nitrogen bonding sites. There does not appear to be any detectable change in ESR parameters on exposure of trypsin-copper(II) samples to magnetic fields of approximately 14,100 G. © 1969.