Speciation of nickel(II) complexes of L-glutamine and succinic acid in DMF-water mixtures

The speciation of NiII complexes of glutamine (Gln) and succinic acid (Sue) has been investigated pH metrically in varying concentrations (0-60%, v/v) of DMF-water mixtures at an ionic strength of 0.16 M dm(-3) and temperature 303 K. Various models for the speciation of these complexes are refined by using the computer programs SCPHD and MINIQUAD75. The active forms of the ligands are LH2 and LH in the pH range of study. The predominant species detected for Gln complexes are ML and ML2 and that for Sue is MLH The trend in the variation of stability constants of the complexes with dielectric constant is explained on the basis of electrostatic and non-electrostatic forces. The species distribution with pH at different solvent compositions, the plausible equilibria for the formation of the species and the structures of the species are also presented.