Spectroscopic and Thermodynamic Studies of Metal Ligand Interaction

Abstract

The present investigation reports a comprehensive spectroscopic and thermodynamic study of metal-ligand interactions involving divalent transition metal ions — Cu(II), Ni(II), Co(II), and Zn(II) — with biologically significant amino acid ligands, namely glycine, alanine, and histidine, in aqueous medium. Stability constants were determined at varying temperatures (25°C, 35°C, and 45°C) and ionic strength (I = 0.1 M NaClO4) using UV-Vis spectrophotometry and potentiometric titration methods. Thermodynamic parameters including Gibbs free energy change (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) were evaluated from the temperature dependence of stability constants using the van't Hoff equation. The spectral studies using FTIR and electronic spectra provided insight into the mode of coordination and geometry around the metal centres. The results indicate that complex formation is spontaneous, enthalpy-driven, and favoured by a decrease in Gibbs free energy. Cu(II) complexes exhibited the highest stability, consistent with the Irving-Williams series. The study has implications for understanding metal-biomolecule interactions in biological and pharmaceutical systems.