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|Title:||Kinetics and mechanism of protection of adenine from sulphate radical anion by caffeic acid under anoxic conditions|
|Authors:||Swaraga, M Sudha|
|Abstract:||The rates of photo-oxidation of adenine in the presence of peroxydisulphate (PDS) have been determined by measuring the absorbance of adenine at 260.5 nm spectrophotometrically. The rates and the quantum yields (φ) of oxidation of adenine by sulphate radical anion (SO<sup>4•-</sup> ) have been determined in the presence of different concentrations of caffeic acid. Increase in the concentration of caffeic acid is found to decrease the rate of oxidation of adenine suggesting that caffeic acid acts as an efficient scavenger of SO<sup>4•-</sup> and protects adenine from it; SO<sup>4•-</sup> competes for adenine as well as for caffeic acid. From competition kinetics, the rate constant of SO<sup>4•-</sup> with caffeic acid has been calculated to be 1.24 ± 0.2 Χ 10<sup>10</sup> mol<sup>-1</sup>dm<sup>3</sup>s<sup>-1</sup>. The quantum yields of photo-oxidation of adenine have been calculated from the rates of oxidation of adenine and the light intensity absorbed by PDS at 254 nm, the wavelength at which PDS is activated to SO<sup>4•-</sup> . The results of experimentally determined quantum yields (φ<sub>exptl</sub>) and the quantum yields calculated (φ<sub>cl</sub>) by assuming that caffeic acid acts only as a scavenger of SO<sup>4•-</sup> radicals show that φ<sub>exptl</sub> values are lower than φ<sub>cl</sub> values. The φ' values, which are experimentally found quantum yield values at each caffeic acid concentration and corrected for SO<sup>4•-</sup> scavenging by caffeic acid, are also found to be greater than φ<sub>exptl</sub> values. These observations suggest that the adenine radicals are repaired by caffeic acid, in addition to scavenging of sulphate radical anions.|
|Appears in Collections:||IJBB Vol.40(1) [February 2003]|
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