Study On The Structure Activity Relationship Of Carotenoids And Flavanones Scavenging Free Radicals By Quantum Chemistry Calculation

Free radicals are the intermediate metabolites of various biochemical reactions in human life activities and play an important role in maintaining the normal life activities of the body.However,excessive free radicals can attack molecule it encounters through oxidation,that cause damage of the cells.Most common human diseasesarerelatedtofreeradicalsdamage.Asattractiveradical scavengers,carotenoids and flavanones are active substances that widely present in plants.Exploring the structure-activity relationship of carotenoid and flavanone scavenging free radicals has important practical significance for the development of corresponding antioxidant foods or auxiliary drugs.Therefore,the relationship between the structure of carotenoids and flavanones and their free radical scavenging capacity was studied by quantum chemistry calculation methods and a variety of free radical scavenging methods.For the study of carotenoids,a structural model of 13 carotenoids was constructed by GaussView5.0 and optimized through AM1 method.Then Density Functional Theory?DFT?was used in B3LYP/6-311?d,p?level for their further optimization.Meanwhile,the free radical scavenging activities of?-carotene,lutein,astaxanthin and lycopene were determined by ABTS radical scavenging method,DPPH radical scavenging method,superoxide anion radical scavenging method and hydroxyl radical scavenging method.?1?The results showed that carotenoids have different scavenging abilities of different free radicals;?2?according to the results of 4 radical scavenging methods,their radical scavenging ability from large to small:Lycopene>Lycopene>Lutein>?-carotene.?3?Through the differences in the energy levels of the frontal orbits and the NPA net charge distribution,the special structure of multiple conjugated double bonds of carotenoids is the vital reason for its ability to scavenge free radicals.The more conjugated double bonds,the higher free radical scavenging activity of carotenoids.?4?The groups on the ring also have an effect on the carotenoid activity.Carbon-carbon double bonds,hydroxyl groups,ketone groups,and epoxy groups can promote the activity of the molecule.On the ring,the carbon-carbon double bond and the keto group affect the conjugated system of the molecule and have the greatest effect on the carotenoid activity.It can be shown that the difference in energy levels in the frontal orbit and the NPA net charge distribution can be used as an important parameter to characterize the free radical scavenging capacity of carotenoids with rings.Regarding the study of flavanones,10 flavanones were optimized at the B3LYP/6-311?d,p?level by DFT to obtain the preferred conformation,while the ABTS radical scavenging method,DPPH radical scavenging method and hydroxyl radical scavenging method were used to determine the free radical scavenging ability of flavanones.?1?According to the net charge distribution of the NPA and the energy distribution of the frontier orbital track,the active site of the flavanone molecule is mainly the phenolic hydroxyl group of the B-ring.The amount of phenolic hydroxyl groups is correlated with the scavenging activity of the compound directly.?2?According to the distribution of energy in the frontier orbital track,it was found that along with increasing number of the hydroxyl groups on B-ring,the electron cloud distribution of the HOMO orbital of the flavanone shifts from the A-ring and the C-ring to the B-ring gradually,and the activity of the B-ring was improved.It indicates that the increasing number of hydroxyl groups on the B-ring enhances the free radical scavenging activity of the flavanones,which is consistent with the results of three radical scavenging methods.?3?Based on E_HOMO,ionization potential and?E,the structure-activity relationship of the free radical scavenging activity of flavanone molecules was analyzed from the single electron transfer mechanism.When the B-ring is monohydroxy,the activity of the site is R3-OH>R1-OH>R2-OH;When the B-ring is bishydroxyl,the molecular activity is related to the position of the two hydroxyl groups.?4?The structure-activity relationship of the free radical scavenging activity of flavanone molecules was analyzed based on the BDE and?HOF from the HAT mechanism.The Hydroxyl on B-rings,R1-OH has the greatest effect on its dehydrogenation capacity,followed by R3-OH,the last is R2-OH.The above studies provide a theoretical basis for the establishment of prediction methods for the active antioxidant sites and activity of carotenoids and flavanones,help to guide the molecular design of their highly active antioxidants and their production and application in practice.