| Structure Identification: |
| Computers & Applied Chemistry, 2012,29(6):656-660. | | Density functional theory calculations on antioxidation activity of four flavones from radix glycyrrhizae.[Reference: WebLink] |
METHODS AND RESULTS:
The geometrical structures of the four main compounds of glycyrrhiza flavonoids,liquiritigenin,liquiritin,isoliquiritigenin and Isoliquiritoside,which have potential medicinal value of antioxidant activity,remarkable anti-tumor and anti-HIV effects,have been calculated by using the Density Functional Theory(DFT) B3LYP method with 6-311G(d,p) basis set.
The properties of the glycyrrhiza flavonoids have been discussed in detail based on their molecular structures,NBO charges on hydrogen atoms,the dissociation energy of O-H 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 results showed that C_7-OH is likely the most active site to eliminate free radicals in human body by dehydrogenation,while the 4'-OH also is probably an active site to enhance the antioxidant activity of the molecules.Smaller 7-OH bond dissociation energy of hydroxyl,bigger positive charge value on hydrogen atom,relatively higher the HOMO energy,and smaller ΔE_(LUMO-HOMO) are contributive to improve the antioxidant activity of the flavonoids.Isoliquiritigenin and Isoliquiritoside are completely planar due to the presence of the double bond between C_2 and C_3,which can increase the molecular itself antioxidant activity due to the larger conjugate π molecular orbital.The glucoside substitute for the hydrogen of 4'-OH can slightly increase the energy level of the HOMO and LUMO,but,at the same time,the losing 4'-OH decreases the total molecular antioxidant activity since lost one active site.
CONCLUSIONS:
As a result,it was revealed that the antioxidant activity of the compounds goes along with the series Isoliquiritigenin ≧ Isoliquiritoside Liquiritigenin ≧liquiritin. |
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