Kinetics and Mechanistic Studies of Oxidation of a Ternary Nitrilotri-Acetatocobalt(II) Complexes Involving DL-valine and DL-aspartic Acid as a Secondary Ligands by Periodate

Ahmed A Abdel-Khalek

doi:10.11648/j.wjac.20170201.14

Abstract

Oxidation of ternary complexes, [CoII (NTA)(L)(H2O)X]-n by periodate in aqueous medium has been studied spectrophotometrically over the (25.0 – 45.0) ± 0.1°C range. The reaction show first order kinetics with respect to both [IO4-] and the complexes, and the rate of the reaction increases over the [H+] range (1.05 – 28.20) x 10-5 mol dm-3 in both cases. Preparation and characterization of [CoII (NTA)(Asp)(H2O)2]-3 and [CoII (NTA)Val(H2O)2]2- is performed. Conformation of the formation of the ternary complexes has been done using IR spectrum, TGA, UV‐visible spectroscopic and cyclic voltammetry measurements. The thermodynamic activation parameters have been calculated. It is assumed that electron transfer takes place via an inner-sphere mechanism.

Highlights

The aim of the present study is to propose the most probable reaction path for the kinetics of oxidation of biologically important ternary nitrilotri-acetatocobalt(II) complexes involving DL-valine and DL-aspartic acid as a secondary ligands. [CoII(NTA)(L)(H2O)X]-n where (NTA = nitrilotriactate acid, L= aspartic acid, Val = DL-valin, x= no of coordinated water molecule, and n = no of negative charge)
The kinetics of the reaction was studied over [H+] range (1.05 –28.20) x 10-5 mol dm-3 at different temperatures Table (4 & 5) lists the variation of k1 with [H+] at different temperatures which indicate that the reaction rate increased gradually with decreasing [H+]
This proposal seems to be supported for the following reasons: Formation of the initial cobalt (III) products, which were slowly converted to the final cobalt products [13, 15, 24]

Summary

Introduction

Amino acid residues are the main constituents of proteins and the study of its sensitivity towards oxidation open up a new area to understand the mechanism involved in the protein and amino acid modification [1].The use of transition metal complexes of nitrilotriacetic acid have been widely adopted in biology, and are gaining increasing use in biotechnology, in the protein purification technique known as immobilized metal-ion [2].Ternary complexes of oxygen-donor ligands and heteroaromatic N-bases have attracted much interest as they can display exceptionally high stability and biological important [3, 4].Periodate oxidation exerts a number of biological effects including the enhancement of lymphocyte activation and increased the frequency of effecter to target cell binding [5]. Amino acid residues are the main constituents of proteins and the study of its sensitivity towards oxidation open up a new area to understand the mechanism involved in the protein and amino acid modification [1]. The use of transition metal complexes of nitrilotriacetic acid have been widely adopted in biology, and are gaining increasing use in biotechnology, in the protein purification technique known as immobilized metal-ion [2]. Periodate oxidation exerts a number of biological effects including the enhancement of lymphocyte activation and increased the frequency of effecter to target cell binding [5]. Oxidation of caffeic acid (3,4-dihydroxycinnamic acid) by means of sodium periodate was reported, that mimics the mechanism of polyphenyleoxidase. The reaction leads to the formation of the antioxidant product 2-S-cysteinylecaffeic adduct which exhibits slightly improved antiradical activity in relation with the parent molecule (caffeic acid) [7]. Kinetics studies of periodate oxidations on a series of dextran oligomers, polymers, some dimeric carbohydrates [8] and of chitosans with different chemical composition [9] were investigated to show the dependence of the kinetics on the molecular weight

Objectives

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Results

Discussion

Conclusion