Equilibria and Stability in Glycine, Tartrate and Tryptophan Complexes, Investigation on Interactions in Cu(II) Binary and Ternary Systems in Aqueous Solution

S. A. A. Sajadi

Sharif University of Technology, Institute of Water & Energy, Tehran, Iran.

DOI: 10.4236/ojinm.2014.41001                

Abstract

The acidity and stability constants of M(Gly)¹, M(Ttr)¹, and M(Trp)¹ M: Cu²⁺, Cu(Bpy²)²⁺, and Cu(Phen³)²⁺ complexes, were determined by potentiometric pH titration. It is shown that the stability of the binary Cu(L), (L: Gly, Ttr, and Trp) complex is determined by the basicity of the carboxylate group on one side and amino group on the other side. It is demonstrated that the equilibrium, Cu(Ha⁴)²⁺ + Cu(L) Cu(Har)(L) + Cu²⁺, 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 possess increased stability. The stability constants of the 1:1 complexes formed between Cu²⁺, Cu(Bpy)²⁺ or Cu(Phen)²⁺ and L^2-, were determined by potentiometric pH titration in aqueous solution (I = 0.1 M, NaNO₃, 25?C). The order of the stability constants was reported. A comparative investigation between ternary complexes of Trp, Ttr, and Gly is made. The comparison of stability constants of these ternary complexes show that Cu(Har)(Trp) is found near 100% in closed form but Cu(Har)(Gly) exists in open form. The differences between the above mentioned stability constants are based on stacked form of Cu(Har)(Trp). The last provides increased stability.

Keywords

Glycine; Tartaric Acid; Tryptophan; Divalent Metal Ions; Potentiometric Titration; Acidity and Stability Constants

Conflicts of Interest

The authors declare no conflicts of interest.

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