TITLE:
Equilibria and Stability in Glycine, Tartrate and Tryptophan Complexes, Investigation on Interactions in Cu(II) Binary and Ternary Systems in Aqueous Solution
AUTHORS:
S. A. A. Sajadi
KEYWORDS:
Glycine; Tartaric Acid; Tryptophan; Divalent Metal Ions; Potentiometric Titration; Acidity and Stability Constants
JOURNAL NAME:
Open Journal of Inorganic Non-metallic Materials,
Vol.4 No.1,
December
25,
2013
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 L2-, 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.