A Theoretical Study On The Reaction Mechanisms Of Several Plant Polyphenols Scavenging Radical In Vivo

Radicals are byproducts in the process of auto-oxidation of organism,which have strong oxidation.In vivo environment,the generation and clearing of radicals are keeping balance.Once the antioxidant systems of body are destroyed,the metabolism balance of radicals will be broken,leading to cell damage,chronic disease and aging.At this time,taking some extra antioxidants is very helpful for keeping the balance of radical metabolism,preventing diseases and maintaining the health of body.Therefore,the research of antioxidant has become focus in the biological and medical fields.Due to the side effect of synthetic antioxidant,finding safe and effective natural antioxidant has become an inevitable trend.Plant polyphenol is a kind of natural compound existing in various plants,which is the largest source of antioxidants in diet.In recent years,plant polyphenol is a hot issue of research,because it has many biological activities,such as antioxidant,antiviral,anti-inflammatory,antibacterial and etc.Plant polyphenol is various,the antioxidant activity and mechanism of them are very different,thus the study on the reaction mechanism of plant polyphenols scavenging radicals is very important to develop efficient natural antioxidants.In this study,we carried out a theoretical research on the antioxidant mechanisms of two plant polyphenols（piceatannol and isorhapontigenin）scavenging ·OH,·OOH,·NO and ·NO₂ in vivo.Using M05-2X functional and6-311++G（d,p）basis set of the density functional theory（DFT）method,the thermodynamic and kinetic parameters of all pathways for hydrogen atom transfer（HAT）and radical adduct formation（RAF）mechanisms were calculated,the potential energy surfaces for all pathways were also obtained.The solvent effects were researched in the framework of the continuum solvation model based on solute electron density（SMD）,and water was taken as the solvent to simulate theinner environment of human body.The main mechanisms and major active sites of piceatannol and isorhapontigenin scavenging four radicals were identified.The racial scavenging activities of piceatannol and isorhapontigenin were compared.The results show that HAT is the main mechanism of piceatannol and isorhapontigenin scavenging ·OH,·OOH and ·NO₂,while RAF is the main mechanism of scavenging ·NO.A-4/A’-4 hydroxyl groups are the major active sites of piceatannol and isorhapontigenin scavenging radicals.For scavenging ·OH and ·NO₂,piceatannol is more efficient than isorhapontigenin,while for scavenging ·OOH and ·NO,isorhapontigenin is more efficient.The antioxidant mechanisms of another plant polyphenol（sinapic acid）scavenging ·OH and ·NO₂ in vivo were also studied,using the DFT.Under the level of M05-2X/6-311++G（d,p）and SMD solvent model,the thermodynamic and kinetic parameters of all pathways in water solution were obtained,the potential energy surfaces for all pathways in water solution were also calculated.Using the Polyrate9.7 program,the rate constant and the branching ratio of every pathway,together with the total rate constants of sinapic acid scavenging ·OH and ·NO₂ in water solution,under 298 K,were obtained.The results show that the hydroxyl group on the benzene ring is the major active site of sinapic acid scavenging ·OH and ·NO₂ in vivo.At 298 K,the total rate constants of sinapic acid with ·OH and ·NO₂ in water solution are 9.2×109 M-1·s-1and 1.3×108 M-1·s-1,agreed well with the experimental values reported in previous literature.In this study,the main mechanisms of piceatannol,isorhapontigenin and sinapic acid scavenging radicals in vivo were identified.The calculated data of potential energy surfaces,rate constants and branching ratios can provide the information which is very difficult to get by the experimental approach.This research is a reliable reference for developing effective plant polyphenols antioxidants.