Electron spin resonance determination of formation constants of copper(II) dipeptide complexes

Abstract

Formation constants for complexes between copper(II) and a series of aliphatic dipeptides have been determined by e.s.r. spectroscopy. An iteration method for the evaluation of digitized e.s.r. spectra is introduced. The e.s.r. spectra and formation constants of all copper species obtained by this method are compared with the results of potentiometric titrations; thus the ambiguous formation of the complexes [CuL₂H₂] and [CuL₂]^2–(H₂L =⁺H₃N–CHR–CO–NH–CHR′–COO^–; R,R′= alkyl) could be excluded. The existence of the dimer species [Cu₂L₂(OH)]^– was confirmed. The influence of the side chains on the spectra of all complexes is discussed.