Study On The Structure Activity Relationship Of Polyphenols And Peptides Scavenging Free Radicals By Quantum Chemistry Calculation

Free radicals are with no unpaired electrons of the molecules, ions or groups,and can be produced through a variety of ways in vivo. Since the free radical theory is generally accepted in academic circles, people began to realize the body distribution of free radicals are the cause of human aging and one of the main causes of many diseases. The body excess free radicals can damage the cell membrane, attack proteins, damage DNA, is important inducement of many diseases such as cancer,cardiovascular and cerebrovascular diseases, neurodegenerative diseases and aging.Due to free radicals in organism at any moment are in produce, we can not use drugs to thoroughly eliminate or control for a long time. Therefore, through daily diet to control the cumulative excess is the most effective way to prevent free radical damage. And from food to find an efficient and safe free radical scavenger has been one of the important research content of food nutrition and health. Therefore, get rid of excessive free radical damage to the human body is concern of a scientific problem.Based on quantum chemistry angle, Using the quantum chemistry calculation method to analyze mechanism of several polyphenolic antioxidants and antioxidative peptides scavenging free radical. In the study of mechanism, quantum chemistry calculation method calculated the relevant theoretical parameters, then quantitative to explore the scavenging free radical chemistry nature. In the study of structure activity relationship, especially antioxidant peptides, it is the first time that antioxidation mechanism was studied from the level of amino acid into chemical group level.On flavonoids polyphenolic antioxidants research, firstly constructing molecular model of four flavonoids of naringenin, naringin, hesperetin and hesperidin, then optimize configuration to get the stable conformations and the related theory of quantum chemical parameters were calculated using density functional method with high accuracy. By controlling experiments the order of antioxidant activity was found,the atomic charge difference of hydroxyls OH can reflect the size of the activehydroxyl of the B and C rings, frontier molecular orbital distribution maps can intuitively display the reactive groups on the molecular, energy difference of frontier molecular orbitals is the effective characterization of scavenging activity of four flavonoids, the hydroxyl O-H bond dissociation enthalpies can effectively characterize the antioxidant activity of different hydroxyl O-H site in same molecule.Naringin and its aglycone(naringenin) active site is mainly 4’-OH, 5-OH and 7-OH groups, including 4’-OH of the activity was greater than 5-OH, 7-OH activity,hesperidin and its aglycone(hesperetin) antioxidant activity site is 5’-OH, 5-OH and7-OH, of which 5’-OH group activity was stronger in 5-OH, 7-OH groups; finally, by the characterization of bond dissociation enthalpy, 4’-OH groups is the main site of the antioxidant activity of naringenin and naringin, 5’-OH groups is the main site of the antioxidant activity of hesperetin and hesperidin, the quantitative parameters of the two groups can be respectively as a main index of predicting the antioxidant activity of four flavonoids, then the predicted sequence and the experimental results are consistent.On isoflavone polyphenol antioxidants research, firstly, the molecular simulation of the four molecules of genistein, daidzein, pomiferin, osajin were carried out and the stable dominant conformation was obtained, finally the related quantum chemistry calculation was carried out. It was found that four kinds of isoflavones scavenging free radicals ability and phenolic hydroxyl position of electron transfer and dehydrogenation ability, frontier molecular orbital can intuitively show the activity of antioxidant molecular parts, energy gap and free radical heat of formation are the accurate characterization of four isoflavone molecular antioxidant activity sequence,for the polyhydroxy heat of formation of four molecules analysis showed that, 4’-OH is Genistein and Daidzein main hydroxyl active site, 4’-OH can be as a representation of the two molecular scavenging free radical activity sites. 3’-OH is Pomiferin and Osajin main hydroxyl groups active site, 4’-OH and 3’-OH can be used as a representation of the two molecular scavenging free radical activity sites respectively.On non flavonoid polyphenols antioxidants research. First of all, to design 7kinds of resveratrol and its hydroxyl derivatives structure, then constructed the molecular model and optimized geometries obtained dominant conformation,quantum chemistry calculation of 7 kinds of resveratrol and its polyhydroxyl derivatives by using DFT method, then obtained a series of quantum chemical theoretical parameters. Analysis found that atomic charge distribution and frontier molecular orbital diagram can directly show active groups of resveratrol and its hydroxyl derivatives; hydroxyls OH charge difference and frontier molecular orbitalπ electron cloud density can well characterize the hydroxyls on the order of activity.According to the frontier molecular orbital energy difference△E also confirmed that the magnitude of the activity of resveratrol and its hydroxyl derivatives and the activity order of the hydroxy groups. According to the energy gap Egap of the seven kinds of molecular design can effectively characterize the molecular order of antioxidant activity. For resveratrol and its polyhydroxyl derivatives scavenging free radical mechanism of quantum chemistry computation results shows that, the hydroxyl groups of the activity order is 4,4’ hydroxy > 3,3’ hydroxy > 5,5’ hydroxy and 4,4’ hydroxyl position is the main active sites, the corresponding quantitative indicators can be the main parameters of the predicting molecular antioxidant activity.The final prediction of 3,3’, 4,4’, 5,5’- hydroxystilbene has the highest antioxidant activity of 7 kinds of resveratrol and its derivatives.Research on polypeptide antioxidants, mainly through the VPW and VFPW,LHY and PHYL four kinds of polypeptide molecules with reasonably high accuracy quantum chemical method was used to optimize the structure, then obtained dominant conformation of polypeptide molecules. Compare quantisation parameter and the measured results, by atomic net charge distribution in the active site of VPW and VFPW mainly concentrated in the Trp indole ring N-H structure, active site of LHY and PHYL concentrated on Tyr phenolic O-H structure. And the frontier molecular orbital to differential can effectively predict the four polypeptides of free radical scavenging activity, in the dehydrogenation reaction of same active groups, molecular energy and hydrogen free radical antioxidant activity level difference can effectively characterize polypeptides.Through the above research, we make active groups on these types of polyphenols and polypeptide of natural antioxidants in the qualitative judgment, and reveal the active groups of scavenging free radicals in the specific mechanism ofaction. The results provides theoretical basis for the establishment of polyphenols and polypeptide natural antioxidant active sites and activity prediction method, and be beneficial to the molecular design of guidance of antioxidant peptides with higher activity and polyphenol antioxidants and its production and application in practice.