Equilibria Studies on Nickel(II) Complexes with 1,10-Phenanthroline Derivatives and Some Amino Acids in Aqueous Solution

Abstract

In recent years, an increase in the biological applications of metal complexes of biologically active ligands has been observed due to their key role in clinical treatments. A potentiometric titration technique has been used to determine the protonation constants of biologically active ligands {glycine (gly), leucine (leu), methionine (met), phenylalanine (phe), tryptophan (trp), asparagine (asn), glutamine (gln), 1,10-phenanthroline (phen), 4-methyl-phenanthroline (4-mphen), 5-methyl-phenanthroline (5-mphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (3,4,7,8-tmphen), 5-nitro-phenanthroline (5-nphen)} and the stability constants of their (1:1) and (1:1:1) complexes with Ni(II) ion (I = 0.100 mol·L–1 KCl and T = 298.15 K). The protonation constants of the biologically active ligands and the stability constants of the (1:1) and (1:1:1) complexes of Ni(II) with the biologically active ligands have been computed by using the BEST program. Moreover, the SPE program has been used to determine the distribution of the species that occurred in the aqueous solution medium. The relative stabilities of the (1:1:1) Ni(II) complexes are compared with those of the corresponding (1:1) Ni(II) complexes in terms of Δlog10K values. The effect of phenanthroline substituents (4-methyl, 5-methyl, 3,4,7,8-tetramethyl, 5-nitro) on the nature of the Ni(II) complexes is evaluated.