Electrode kinetics and thermodynamics of MnII complexes with some amino acids and vitamin-B7

Abstract

The paper presents simple and highly sensitive direct voltammetric method developed for the determination of stability of the ternary complexes of Mn II complexes with L -lysine, L -ornithine, L -threonine, L -serine, L -glutamic acid and L -aspartic acid as primary ligands and vitamin-B 7 (biotin) as secondary ligand at pH 7.30 ± 0.01 and μ = 1.0 M NaClO 4 at 25 °C and 35 °C. The nature of current voltage curves was quasireversible and diffusion controlled. Mn II formed 1: 1: 1, 1: 1: 2 and 1: 2: 1 complexes with these drugs as confirmed by Schaap and McMaster method. The sequence of stability constant of complexes was L-lysine < L -ornithine < L -threonine < L -serine < L -glutamic acid < L-aspartic acid can be explained on the basis of size, basicity and steric hindrance of ligands. The study has been carried out at 35 °C also to determine the thermodynamic parameters such as enthalpy change (ΔH), free energy change (ΔG) and entropy change (ΔS) respectively. The kinetic parameters viz. transfer coefficient (α), degree of irreversibility (λ), diffusion coefficient (D 1/2 ) and standard rate constant (k) were calculated. The values of 'α' confirmed that the 'activated complex' is formed in an exact intermediate between dropping mercury electrode and mercury solution interface. The study confirmed that L-amino acids or vitamin-B 7 or the combination of both could be used as antidote against Mn II toxicity.