VOLTAMMETRIC STUDY OF IMMUNOMODULATORY COMPLEXES OF Mn(II) WITH SOME L-AMINO ACIDS AND VITAMIN C IN RELATION TO ELECTRODE KINETICS

A simple and highly sensitive direct polarographic method was 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 ligand and vitamin C (ascorbic acid) as secondary ligand at pH=7.30 +/- 0.01 and mu=1.0 M NaClO4 at 25 and 35 degrees C. The nature of current voltage curves was quasi-reversible and diffusion-controlled. Mn(II) formed 1: 1: 1, 1: 1:2 and 1:2:1 complexes with these drugs as confirmed by the Schaap and McMaster method. The sequence of stability constants 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 degrees C also to determine the thermodynamic parameters such as enthalpy (Delta H), free energy change (Delta G) and entropy change (Delta S), respectively. The kinetic parameters viz. transfer coefficient (alpha), degree of irreversibility (lambda), diffusion coefficient (D) and standard rate constant (k) were calculated. The values of 'alpha' confirmed that the 'activated complex' is formed in an exact intermediate between dropping mercury electrode and mercury solution interface.