Density Functional Theory Calculations On The Antioxidant Activity Of Anthocyanins

The method by using density functional theory(Density Functional Theory, DFT) is the most widely used one of quantum chemistry calculation methods, as it has a high calculation accuracy and takes short time, the method has been widely applied in many fields for chemical theory research. Today the Density Functional Theory has been widely used in many aspects, such as the study of molecular structures and properties, transition state reaction mechanism, heat chemistry, spectrum, and etc, and at present it develops rapidly in the areas of the material science, life science, drug molecular design. With the development of society, the modern medical research shows that a lot of physical diseases damage is caused by excessive free radicals produced by the body, so it is particularly important to look for safe and non-toxic, highly effective natural antioxidants, and a lot of flavonoids(such as anthocyanidins) are natural functional antioxidants existed widely in plants, they have strong ability of scavenging free radicals and various beneficial physiological functions to human body, thus increasingly draw peoples’ concern and attention.Flavonoid is an important kind of plant polyphenols and distributed very widely in natural products,they are produced in the process of the plants metabolism, and hundreds of different types of them have been found today. Flavonoids have a wide range of bioactivities and pharmacological activities. chemical structure determines chemical properties, and that flavonoids have different antioxidant activities is closely related with their structures. A total of 38 kinds of flavonoids compounds of five categories and their corresponding free radicals had been structural optimized and energy calculated by using Density Functional Theory at the level of B3LYP/6-311+G(d, p)//6-311G(d, p). The results showed that the C ring structure had a great influence on the activity of flavonoids, C3(2)-OH, double bond C2=C3, C4 carbonyl in C ring had an enhancement effect on the activity of flavonoids; phenolic hydroxyl in A ring had little to the enhancement activity of flavonoids; C3’ phenolic hydroxyl in B ring had an obvious enhancement effect on the activity to its ortho C4’ phenolic hydroxyl. Of all the five flavonoids compounds, B ring had oxidation resistance activity and C4’ phenolic hydroxyl group was the main active site, the rest of the active sites were not the same in different kinds of compounds, in class A flavonoid compound, C7 and C3 phenolic hydroxyl groups in A ring also had some activity, so were the C7 phenolic hydroxyl group in Aring in class B dihydrogen flavonoid compounds, and the C5 phenolic hydroxyl group in A ring in class C flavan-3-alcohol compounds, and the rest of C3 and C5, C7 phenolic hydroxyl groups in class D anthocyanidins compounds, in class E isoflavones, C2 phenolic hydroxyl group had strong activity, the C7 in A ring also had some certain activity. At the same time, comprehensive analysis of flavonoids,isoflavones and anthocyanidins showed that they all had strong antioxidant activity as a whole, of all the 38 kinds of flavonoid compounds,the oxidation resistance activity of anthocyanidins 、A(3’,4’,5,7-OH)、A(3’,4’,5’,5,7-OH)、A(3’,4’,3,5,7-OH)、B(3’,4’,5,7-OH)、B(3’,4’,3,5,7-OH) 、B(3’,4’,5’,3,5,7-OH)、C(3’,4’,3,5,7-OH)、E(3’,4’,5,7-OH)、E(4’,2,5-OH)、E(4’,2,7-OH)、E(4’,2,5,7-OH)、E(3’,4’,2,5,7-OH)、E(3’,4’,5’,2,5,7-OH) were stronger, they could be used as potential highly effective antioxidants to provide certain theoretical reference for the screening and using of natural antioxidants.Anthocyanidins are water-soluble natural pigment widely existing in plants in nature, belonging to the flavonoid compounds, they are the main color material in the plant petals, widely existing in a variety of flowering plants, with a variety of physiological functions like the prevention against cancer, diabetes,cardiovascular disease and diseases associated with aging, and etc. The six anthocyanidins of pelargonidin,cyaniding, delphinidin, peonidin, petunidin, malvidin and their radicals were geometrically optimized by using the Density Functional Theory B3 LYP method with 6-311G(d, p) basis set. The antioxidant activity to scavenge harmful free radicals of the six anthocyanidins was discussed in detail based on their molecular structures, NBO charges on phenolic hydroxyl hydrogen atoms, the dissociation enthalpy of phenolic hydroxyl bonds, the energies of the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO), the energy gap between HOMO and LUMO, and etc. The dissociation enthalpy of phenolic hydroxyl bonds and highest occupied molecular orbital could most explain the antioxidant activity. The 4’-OH had the highest antioxidation activity and the 3-OH was highly glycosylated. In the end, the transition state structure of the pelargonidin scavenging ?OH free radicals by its C4’ sites phenolic hydroxyl was optimized. The reaction activation energy of 14.6 KJ?mol-1 and reaction heat of-87.7KJ?mol-1 were obtained by this work.Blueberry was listed as one of the five human healthy foods by the United Nations food and agriculture organization, its nutrition and health care function increasingly caught the attention of people,and its consumer market was expanding year by year, it was called "the world’s third generation of fruit" after apple and citrus. Abundant of anthocyanins in blueberry had the functions of immunity enhancement,cardiovascular disease resistance, free radicals scavenging, anti-aging resistance, atherosclerosis preventant,cancer resistance, and ect. 15 different anthocyanins compounds and their respective dehydrogenation free radicals in blueberry were geometrically optimized by using Density Functional Theory method with B3LYP/6-311-g(d, p). The results of the analysis of molecular structure parameters, charge numbers of natural bond orbital(NBO), phenolic hydroxyl dissociation energy, the front rail related properties of 15 kinds of anthocyanins showed that, phenolic hydroxyl groups in A ring and B ring had some certain activity, the one of the C4’ was the strongest, then come the C5 phenolic hydroxyl and it was also stronger.Activity of phenolic hydroxyl in different parts of the 15 kinds of anthocyanins compounds affected by glycoside was different, activity of C5 phenolic hydroxyl was the weakest among galactoside anthocyanins,activity of C4’ phenolic hydroxyl in glucoside anthocyanins was stronger than in the other two kinds of glycosidic anthocyanins, activity of C5 phenolic hydroxyl in galactoside anthocyanins was stronger.Overall analysis showed that galactoside effect on the activity of anthocyanins molecules was bigger compared with the other two kinds of glycoside, antioxidant activity of these three kinds of glycosidic anthocyanins molecules was not that so different as a whole,as a whole the activity of molecules that had more substituents in B ring were relatively bigger among these three kinds of glycosidic anthocyanins.Cyanidin-3-glucoside is the most widely distributed anthocyanin in nature, it is a kind of flower pigment indican derivatives, with a variety of physiological functions like oxidation resistance,antibacterial and anti-inflammatory, immunity enhancement, cardiovascular disease prevent, anti-aging,glucolipid metabolism improvement, and etc, but how they to play a role in the body was not very clear, in recent years the absorption and metabolism of it has been a research hotspot. Metabolite molecules and their respective dehydrogenation free radicals of cyanidin-3-glucoside, Peonidin-3-glucoside, Cyanidin-3-glucuronide, cyanidin, protocatechuic acid in the body were geometrically optimized in circumstances of gas phase and the water solvent respectively by using the DFT/B3LYP/6-311+G(d, p)//B3LYP/6-311-G(d,p) method. Taking comprehensive consideration of the terms based on phenolic hydroxyl number and position, phenolic hydroxyl bond length, the number of NBO charge layout, the phenol hydroxyl solution from BDE, the frontier molecular orbital energy level, the five kinds of compounds in water solvent were relatively stable, and antioxidant activity of phenolic hydroxyl on the five kinds of compounds in watersolvent were stronger than those in the gas phase as a whole. In the gas phase and the water solvent, B ring of five kinds of compounds were main parts of the antioxidant activity, and activity of C4’ phenolic hydroxyl group was stronger, at the same time, phenolic hydroxyl groups in A ring and C ring of cyanidin-3-glucoside, Peonidin-3-glucoside, Cyanidin-3-glucuronide, cyanidin all had some certain activity,activity of cyanidin was stronger in the five kinds of compounds, the second were the cyanidin-3-glucoside’s and Cyanidin-3-glucuronide’s, the Peonidin-3-glucoside’s and protocatechuic acid’s come last, their activity showed weak.