Formation constants and coordination thermodynamics for binary complexes of Cu(II) and some α-amino acids in aqueous solution

Abstract

In this study, the formation constants of 1 : 1 binary complexes of Cu(II) with L-glutamic acid, L-aspartic acid, glycine, L-alanine, L-valine, and L-leucine and 1 : 2 binary complexes of L-glutamic acid, glycine and the protonation macro- and microconstants of all these amino acids were determined potentiometrically in aqueous solutions at 5.0, 20.0, and 35.0°C at a constant ionic strength of I = 0.10 mol L⁻¹ (NaClO₄). The thermodynamic parameters ΔG _f°, ΔH _f°, and ΔS _f° were determined for the protonation of all amino acids used in this study and for the complex formation reactions of them with Cu(II). The results were analysed by means of Principle of hard and soft [Lewis] acids and bases. Additionally, in order to confirm the complex formation and determine the stability constants of complexes, UV-Vis spectroscopic studies were carried out. The stability constants obtained by spectrophotometrically are confirmed by those determined potentiometrically.

Keywords:

• Formation constants
• α-Amino acids
• Cu(II)
• Thermodynamics
• Hard and soft [Lewis] acids and bases principle

Acknowledgments

This study was financially supported by the Scientific Research Foundation of Marmara University (Project number SAĞ-BGS-080805-0171).