Content area
Full text
KEYWORDS
Ternary complexes; Divalent metal ions; Potentiometric titration; Acidity and stability constants.
Abstract. The acidity and stability constants of M (MNPPAP) (MNPPAP: 2((4-methyl-5-nitro-6-(pyrrolidine-1-yl)pyrimidine-2-yl)amino)propionic acid) M: Cu^sup 2+^, Cu (Bpy)^sup 2+^ (Bpy: 2,2'-Bipyridine), or Cu(Phen)^sup 2+^ (Phen: 1,10-Phenanthroline) complexes were determined by potentiometric pH titration. It is shown that the stability of the binary Cu (MNPPAP) complex is determined by the basicity of the carboxylate group on one side and amine group on the other side. It is demonstrated that the equilibrium, Cu(Har)^sup 2+^ (Har: Heteroaromatic ligand such as Bpy or Phen) + Cu(MNPPAP) Cu(Har)(MNPPAP) + Cu^sup 2+^, is displacement due to the well known experience that mixed ligand complexes formed by a divalent 3d ion, a heteroaromatic N base, and an O donor ligand possessing increased stability. The other part of this displacement amounts, on average, to no increased stability of the mixed ligand Cu (Bpy)(MNPPAP) and Cu(Phen)(MNPPAP) complexes. The stability constants were determined by potentiometric pH titration in aqueous solution. The order of the stability constants was reported. A comparative investigation between ternary complexes of MNPPAP, Trp (Trp: L-Tryptophan) and Gly (Gly: Glycine) is made. The comparison of stability constants of these ternary complexes show that Cu (Har) (MNPPAP) and Cu (Har) (Gly) exist in open form, but Cu (Har)(Trp) is found near 100% in closed form. The differences between the above mentioned stability constants are based on stacked form of Cu (Har) (Trp), and provide increased stability compared with Cu (Har)(MNPPAP).
© 2014 Sharif University of Technology. All rights reserved.
(ProQuest: ... denotes formulae omitted.)
1. Introduction
Peptides interact with metal ions primarily through side chain functional groups, although there are many examples of peptide amide nitrogens functioning as donor atoms with certain metal ions. Many physiologically important peptides function as metal complexes [1,2]. The chemical structure of MNPPAP is shown in Figure 1. MNPPAP contains identical chemical structure like amino acids, so that we expect similar chemical properties [3].
Among the side chains of amino acids, the indole moiety is the most potent electron donor [4]. Indeed, charge-transfer-type interactions between tryptophan or other indole derivatives and nucleosides or nucleotides occur in aqueous solution [5-9]. Based on the above mentioned essential role of amino acids, it is interesting to study the...