THERMODYNAMIC AND KINETIC STUDY OF HYDROGEN PEROXIDE SCAVENGING IN THE PRESENCE OF VITAMIN C AS AN ANTIOXIDANT IN DIFFERENT TEMPERATURES

The mechanism of oxidation of the ascorbic acid by hydrogen peroxide have been examined by using the 6-311++G(d,p) basis set of the density functional theory (DFT) method at the B3LYP level of theory. The thermodynamic characteristics of proton transfer from vitamin C molecule to hydrogen peroxide was calculated. Vitamin C is very easily decomposed by increases in the temperature, it will be oxidized to L-dehydroascorbat. Oxidation of vitamin C was measured at 298, 303, 308 and 313 K. The results of this research indicate that the Gibbs free energies of the oxidation of ascorbic acid at these temperatures are -59.96, -60.02, -60.03 and -60.04 kcal.mol-1, respectively. The rate constants of hydrogen peroxide scavenging in the presence of vitamin C are 59.0×1011, 60.0×1011, 61.1×1011 and 62.1×1011 s-1, respectively. The activation energy and the pre-exponential factor for the oxidation of ascorbic acid were found to be 0.62 kcal. mol-1 and 168.64 s-1. Global electron density transfer (GEDT) and the atomic charges given by the natural population analysis (NPA) at the most important points involved in this process have been calculated