PH-Metric evidence on Metal-Peptide Nitrogen Linkage in Some Oligopeptide Complexes

Abstract

Already  reported pH-metric experimental data by Martell et al. on metal
(Cu²⁺, Ni²⁺, and Co²⁺) complexes of oligopeptide derivatives (H₃L),
diglycine-N,  N-diacetic acid (2GDA),  triglycine-N, N-diacetic acid
(3GDA), tetraglycine-N, N-diacetic acid (4GDA) has been analysed, for
obtaining the structural information on the complexes formed at higher pH,
using the previously described procedure with little modifications, Comparing
the results obtained in this  work with those of IR study (by Martell
et al.),  participation of peptide nitrogen in coordination with metal ions has
been confirmed.  Along with the earlier reported protonated complexes,
formation of NiH_₁L^2- instead of NiL(OH)^2- [with 2GDA], mixed
protonated hldroxo complexes NiH_₁L(OH)^3- [with3GDA] and
CuH_₂L(OH)^4- , CoH_₂L(OH)^4- [with 4GDA] has been characterized.