Voltammetric Study and Thermodynamic Parameters of [Zn^_L-Amino Acidate^_Vitamin-PP] Complexes vis-à-vis Kinetics of Electrode Reaction

 

Farid Khan,* Afroza Khanam

 

Electrochemical Laboratory, Department of Chemistry, Dr. H.S. Gour University, Sagar - 470 003, Madhya Pradesh, Índia

 

Received 12 June 2008; accepted 6 January 2009

 

Abstract

Voltammetric reduction of Zn (II) using L-lysine, L-ornithine, L-threonine, L-serine, L-phenylglycine, L-phenylalanine, L-glutamic acid, L-aspartic acid and vitamin-PP (nicotinamide, niacinamide) at pH = 7.30 ± 0.01, and µ = 1.0 M NaClO₄ was reported at 25 and 35 ºC. The nature of current voltage curves was quasireversible and diffusion controlled. Zn (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 L-lysine < L-ornithine < L-threonine < L-serine < L-phenylglycine < L-phenylalanine < L-glutamic acid < L-aspartic acid can be explained on the basis of size, basicity and steric hindrance of ligands. The thermodynamic parameters such as enthalpy (∆H), free energy (∆G) and entropy change (∆S) have also been reported. The kinetic parameters viz. transfer coefficient (a), degree of irreversibility (l), diffusion coefficient (D) and standard rate constant (k) were calculated. The values of ‘a’ confirmed the symmetric nature of ‘activated complex’ between oxidants and reductants response to applied potential between dropping mercury electrode and solution interface.

Keywords: voltammetry, thermodynamic parameters, electrode kinetics, [Zn^_L-amino acidate^_vitamin-PP] complexes.

 

 

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* Corresponding author. E-mail address: faridkhan58@yahoo.com; farid.fk@rediffmail.com