Research On Quantum Chemistry And Antioxidant Activity Study Of 4 Natural Antioxidants

At present, people gradually realize that antioxidant is closely related to our health. Medical research results show that the overmuch free radicals in the human body may cause a variety of diseases, such as atherosclerosis, cancer, neurological diseases. Therefore, the antioxidants in the diet more and more aroused people's attention. Lycopene and ?- carotene belongs to carotenoids. Delphinidin and petunidin belongs to anthocyanin. They are four typical natural antioxidant, which exists widely in various kinds of fruits and vegetables. They have certain health function about scavenging free radicals, anti-cancer anti-cancer, enhance immunity, anti-aging and preventing cardiovascular disease. But for now, there are various method determined antioxidant activity and different standards. In addition, because of the limitations of research methods, the antioxidant mechanism in the theoretical research is still not clear. So new method is needed. Therefore, the density functional theory in the quantum chemistry can make the calculation and simulation of the antioxidant, so that the antioxidant mechanism can be explored in thoery.In this paper, Chemdraw 2D and 3D was used to build the model of lycopene, ?-carotene, delphinidin and petunidin. Using the density functional theory(DFT) method in quantum with Gaussian software, these four antioxidants were studied on the mechanism of antioxidant and hydroxyl radical scavenging activity. The compound molecular structure parameters, spectral properties, frontier orbital energy and transition state energy barrier were obtained, which was used in the research of activity of the compound and explore the mechanism of reaction.lycopene, ?-carotene, delphinidin and petunidin, were calculated using DFT B3 LYP method with 6-311 G basis set. Their activities were analyzed based on bond length, IR spectrum, and the frontier orbitals, respectively. The results showed that lycopene in the C2-H43, C34-H81, C35-H83 and C35-H84 are longer and more active than other bond. ?-carotene in C1-H41, C3-H45, C31-H79 and C34-H83 are longer and more active than other bond. The O-H bond length of O21 and O22 in delphinidin and petunidin are longer and more active than other bond. This paper gained the infrared spectroscopy of lycopene, ?- carotene, delphinidin and petunidin, which were compared with experiment IR spectrum in experiment of lycopene, ?-carotene, delphinidin and petunidin. The result shows that the optimization results were reasonable. Through the result of HOMO and LUMO, the order of reactivity activity might be: lycopene >?- carotene, delphinidin > petunidin. In this paper, the figure of the highest occupied orbital of lycopene, ?- carotene, delphinidin and petunidin were analyzed through electron cloud density distribution. The anti-reduction of lycopene and ?- carotene were mainly on the double bond. The anti-reduction of delphinidin and petunidin were mainly on the B ring and phenol hydroxyl in B ring.Free radicals is the molecular groups with unpaired electron. Hydroxyl free radical(· OH) is active and electronegative in the human body. Scavenging this free radicals, ·OH has very important influence on people's health. Therefore, this paper using density functional method(DFT) B3 LYP under 6-311 G basis set to calculate the transition state of the active site of lycopene, ?- carotene, delphinidin and petunidin react with hydroxyl free radical. The results showed that the activation energy of lycopene C2-H43, C34-H81, C35-H83 and C35-H84 reacting with · OH free radical were 1.324 kcal·mol-1? 1.318 kcal·mol-1 ? 0.954 kcal·mol-1 ? 0.853 kcal·mol-1, respectively. The calculation results of the active sites are consistent with calculation results of bond length. The activation energy of ?- carotene C1-H41, C3-H45, C31-H79 and C34-H83 reacting with · OH free radical were 0.691 kcal·mol-1?0.628 kcal·mol-1?0.621 kcal·mol-1?0.634 kcal·mol-1, respectively. The result of transition state of active site is consistant with bond length. In addition, the activation energy of O21 and O22 in delphinidin and petunidin were lower than other sites.Finally, this paper made scavenging hydroxyl free radical experiment of lycopene, ?-carotene, delphinidin and petunidin. The result showed that the active order was lycopene >?- carotene, delphinidin > petunidin, which was consistent with density functional theory calculations. This result further proved the result of density functional theory calculations.