tailieunhanh - Báo cáo nghiên cứu khoa học: "ESTIMATION OF SCAVENGING ACTIVITY OF PHENOLIC COMPOUNDS BY CALCULATING SPIN DENSITY DISTRIBUTION"

The geometries and spin density distribution of phenolic radicals are investigated by density functional theory (DFT) at the B3LYP level. Rusults are indicated that spin density distribution of phenolic radicals is high at the O and C (para) positions. | TẠP CHÍ PHÁT TRIỂN KH CN TẬP 10 SỐ 12 - 2007 ESTIMATION OF SCAVENGING ACTIVITY OF PHENOLIC COMPOUNDS BY CALCULATING SPIN DENSITY DISTRIBUTION Pham Thanh Quan Le Thanh Hung Tran Thi Ha Thai University of Technology VNU-HCM Manuscript Received on March 21th 2007 Manuscript Revised October 16th 2007 ABSTRACT The geometries and spin density distribution of phenolic radicals are investigated by density functional theory DFT at the B3LYP level. Rusults are indicated that spin density distribution of phenolic radicals is high at the O and C para positions. The stabilization of the free radical responds to the decrease of the highest spin density HSD at a position of structure radical and enhances antioxidant radical scavenging activity. Calculated Highest Spin Density values HSDs are in good agreement with experimental cites thereby estimating of scavenging activity of neutral molecules can be used especially phenolic antioxidants. Key words antioxidants phenolics flavonoids spin density Phenolic antioxidants form an important class of compounds which serve to inhibit the oxidation of materials of both commercial and biological importance. The function of antioxidants is to intercept and react with the free radicals at a faster rate than the substrate and since free radicals are able to attack a variety of targets including lipids fats and proteins it is believed that they are implicated in a number of important degenerative diseases including aging itself 1 . There are two main mechanisms by which antioxidants can play their protective role. The first is H-atom transfer in which a free radical ROO removes a hydrogen atom from the antioxidant ArOH 1 - 4 ROO ArOH ROOH ArO 1 The efficiency of the antioxidant ArOH depends on the stability of the radical ArO which in turn is determined by the number of hydrogen bonds conjugation and resonance effects. The bond dissociation enthalpy BDE of the O-H bonds is an important parameter to evaluate the antioxidant .