Investigation of Extent of Interaction of Thiobarbituric Acid and Two Selected Amino Acids with Three Divalent Metal Ions in Aqueous-organic Medium at Different Temperatures

Abstract

The formation constants of binary and ternary complexes of Thiobarbituric acid as primary ligand and L-tyrosine and L-histidine as secondary ligands have been examined in 40% (v/v) ethanol-water mixture at 27oC and 35oC and at ionic strength of 0.02 NaNO3 by potentiometric method. The ligands formed 1:1 binary complexes with the metal ions. The primary and secondary ligands simultaneously coordinated to the metal ions to form 1:1:1 ternary complexes. The difference in stability constants of binary and ternary complexes were determined by DlogK and RS%. Ternary complexes exhibited enhanced stability than the binary complexes. The stability of the complexes decrease with increase in temperature. The thermodynamic parameters such as Gibb’s free energy change (ΔG), entropy change (ΔS) and enthalpy change (ΔH) accompany the interactions were evaluated. The interactions were found to be spontaneous, exothermic, and entropically favoured.

Complex Equilibria and Distribution of Metal (II) Ions with Biologically Active Chelating Agents in Aqueous and Aqueous-organic Media

“…conformity with the effects of the polarizability and dipole moment of the ligands. This order could be ascribed to the basicity of the lugand and M→ L π -formation in the Urc complex in addition to L → M σ -bond by the back donation of electrons from the metal dπ orbitals to the vacant pπ orbitals of the Urc[41,42].Urc interacts with the metal ions in water medium with the formation constants in the order of LogK attributed to the covalent index of the metal ions(Nieboer & Richardson [10]; Oladipo et al[43]). Met in water medium and the ligands in ethanol-water medium formed binary complexes with the metal ions in the order of LogK CuMet…”