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Portugaliae Electrochimica Acta
Print version ISSN 0872-1904
Abstract
KHAN, Farid and KHANAM, Afroza. Voltammetric Study and Thermodynamic Parameters of [Zn_L-Amino Acidate_Vitamin-PP] Complexes vis-à-vis Kinetics of Electrode Reaction. Port. Electrochim. Acta [online]. 2009, vol.27, n.2, pp.87-98. ISSN 0872-1904.
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.