Complexes of metal ions with N-acylpeptides: Part I - preparation, spectroscopic & magnetic properties of complexes of nickel(II) and copper(II) with N-protected dipeptides and their amine adducts

Abstract

Mixed-ligand complexes of the type ML₂D_yxH₂O [where M = Cu²⁺ and Ni²⁺, LH = N-acetyl-L-phenylalanylglycine, N-monochloroacetyl- L-phenylalanylglycine, N-trifluoroacetyl- L- phenylalanylglycine, D = imidazole, 2-methylimidazole, 1,2-dimethylimidazole, y = 0 or 2 and x = 0 to 4] have been prepared and characterized by physicochemical as well as spectroscopic techniques. The infrared data suggest coordination through the carboxylate group in a bidentate manner and peptide CO (complexes <strong>1-3</strong>, <strong>10-12</strong>). But in the adducts (<strong>4-9</strong>, <strong>13-21</strong>) the site of peptide CO is occupied by the amine molecule. The electron spin resonance spectra of CuL₂D_y.xH₂O (where y = 0) indicate dimeric copper (<em>S</em> = 1) with an antiferromagnetic exchange, monomeric copper (<em>S</em> = 1/2) and a signal due to <img src='http://www.niscair.res.in/jinfo/delta.gif' border=0>ms = ± 2 transition. The data suggest an octahedral or pseudooctahedral structure. Coordination number is six in these complexes [except in dimeric copper(II) complexes].