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PM7 AND DFT STUDY ON THE FREE RADICAL SCAVENGING MECHANISMS OF URIC ACID

It has been suggested that the rise in plasma antioxidant potency observed after the consumption of fruits and vegetables is not caused by the flavonoids (polyphenols), but is the consequence of increased uric acid levels. Polyphenol concentrations in human plasma are much lower ˂ 5 micromolar) than that of uric acid (~ 300 micromolar)[1]. Uric acid is the product of purine metabolism with both beneficial and harmful effects on human health [2]. This endogenous antioxidant may protect against oxidative stress by free radical scavenging [3]. Reaction enthalpies related to hydrogen atom transfer (HAT), single electron transfer- proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) mechanisms were studied using MOPAC2012 COSMO PM7 and Gaussian 09 DFT/M05-2X/6-311++G(d, p) SMD methods in water as a solvent [4]. Due to the lowest values of proton affinity (PA) and electron transfer enthalpy (ETE) both methods indicate double SPLET mechanism as thermodynamically preferred process. As the scavenging mechanisms are highly influenced by the properties of the scavenged free radical species, we used DFT method for calculating the free energy (∆G) of reactions of uric acid with ·OH, ·OOH, ·OCH3, ·O-O-CH=CH2, O2·- and ·OOCCl3 free radicals [5]. Exergonicity of double SPLET mechanism reactions in aqueous solution indicates that uric acid is efficient for scavenging of·OH and ·OOCCl3 free radicals.

Uric acid; free radicals; PM7; DFT

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