J. Indian Chern. Soc., Vol. 86, July 2009, pp. 711-716 Electrode kinetics and thermodynamics of Mn 11 complexes with some amino acids and vitamin-B 7 Afroza Khanam and Farid Khan* Department of Chemistry, Dr. H. S. Gour University, Sagar-470 003, Madhya Pradesh, India E-mail : faridkhan58@yahoo.com; farid.fk@rediffmail.com Manuscript received 22 August 2008, revised 23 March 2009, accepted 24 March 2009 Abstract : The paper presents simple and highly sensitive direct voltammetric method developed for the determination of stability of the ternary complexes of Moll complexes with L-lysine, L-ornithine, L-threonine, L-serine, L-glutamic acid and L-aspartic acid as primary ligands and vitamln-8 7 (biotin) as secondary ligand at pH 7.30 ± 0.01 and 11. = 1.0 M NaCI0 4 at 25 •c and 35 •c. The nature of current voltage curves was quasireversible and diffusion controlled. Mn 11 formed I : 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-lyslne < 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 (AH), free energy change (AG) and entropy change (AS) respectively, The kinetic parameters viz. transfer coefficient (a), degree of Irreversibility (l), diffusion coefficient (DI/2) and standard rate constant (k) were calculated. The values of 'a' con- firmed that the 'activated complex' is formed in an exact intermediate between dropping mercury electrode and mer- cury solution interface. The study confirmed that L-amino acids or vitamin-8 7 or the combination of both could be used as antidote against Mn 11 toxicity. Keywords : Electrode kinetics, thermodynamics, [Mn-L-amino acidate-vltamin-87] system. Introduction Amino acids are well known chelating agents and play important role in biology, pharmacy and industry 1 - 3 . Com- plexes of some metal ions with amino acids can be used as models to study the pharmaco-dynamic effects of drugs or for increasing the biocompatibility and minimize the toxic effects of some metal ions 4 . Vitamin-B 7 (biotin or vitamin H) 5 is a member of the vitamin B complex and water-soluble. Biotin is involved in energy metabolism and plays a role in enabling the body to use glucose 6 . Biotin is sometimes chemically linked to a molecule or protein for biochemical assays 7 , earned a keen attention towards the studies of their metal complexes. Manganese is an essential trace element in biology 8 . Manganese works with vitamin K to support blood clotting, aids in diges- tion, and as antioxidant. It is a vital component of So- dium Oxide Dismutase 9 and it exhibits complex reduc- tion-oxidation (redox) chemistry 1 0-I3. Concern over pos- sible neurotoxic effects associated with chronic exposure to moderate levels of manganese in mixed oxidation states and by the growing use of methylcyclopentadienyl man- ganese tricarbonyl, a manganese-containing antiknock additive in gasoline is currently used in a number of de- veloped countries 14 . Furthermore, epidemiologic studies have suggested a relationship between elevated environ- mental manganese exposure and an increased risk for parkinsonian disturbances l5, 16. The elevated concentration of Mn 11 can be reduced by chelation therapy 17 . Therefore, the present study has been undertaken in which complexes of Mn 11 with L-amina acids and vitamin-B 7 has been studied. The specificity of the drugs and its amount is stability constants dependent therefore, the same has also been determined. Thermo- dynamic parameters play important role to confirm whether a particular reaction is feasible or not under the given set of conditions therefore, the same have also been under- taken. Kinetic parameters confirm the nature of electrode process at DME has also been discussed. Results and discussion Mn 11 gave two electron quasireversible reduction wave at pH 7.30 ± 0.01, Jl = 1.0 M NaC10 4 at 25 °C. The nature of current-voltage curves for complexes is also quasireversible. The E 112 values became more negative 711