Antioxidant Free Radical Scavenging Mechanism Of Action And Structure - Activity Relationship Study

In view of the importance of scavenging free radicals, now the search of high efficient, low-toxic and inexpensive antioxidants has been one of the substantial subjects in many fields such as biology, chemistry and medicine. There are two ways to enrich the species of antioxidants, one is to increase the activity of antioxidants by improving the structures of them, and the other is to find efficient natural antioxidants. So, the mechanism of antioxidant scavenging free radicals and a preliminary structure-activity relationship should be studied, this will be helpful in order to further the study in this field and accelerate the selection of antioxidants.In this thesis, a new class of antioxidants was designed, the radical- scavenging mechanism of some natural and synthetic antioxidants was investigated on, and the structure-activity relationship (SAR) of them was summarized by quantum chemical computational method DFT. This provides theoretical basis not only for searching and designing novel antioxidants, but also for increasing the species of antioxidants.The main results achieved1) study on the antioxidation of 4, 5-dihydroxyisoquinoline (DHIQ) and its derivativesTo enhance the gas stability of greatly reactive antioxidants, 4, 5-dihydroxyisoq- uinoline (DHIQ) and its derivatives are rationally designed as a new class of antioxidants. The structure-activity relationships (SAR) of the compounds are evaluated by density functional theory (DFT) method. Calculations show that DHIQs have similar reactivity with peroxyl radicals ROO·to that of equivalently substituted phenols 1, 8-naphthalenediols DIOLs ,but higher stability to air oxidation.As a consequence, DHIQs are good antioxidants and DHIQ can be regarded as a potential lead compound.2)Investigation into the transtion states and mechanism of H-atom abstraction by·OOCH3 from 1, 8-naphthalenediol and 4, 5-dihydroxyisoquinoline In this paper, the transtion states and mechanism of H-atom abstraction by·OOCH3 from1, 8-naphthalenediol and 4, 5-dihydroxyisoquinoline were investigated by B3LYP method in 6-311+G (d, p) level. It was confirmed that the reactivity of 1, 8-naphthalenediol is higher than that of 4, 5-dihydroxyisoquinoline by analyzing the structures and energy of their transtion states and intermediate hydrogen-bonded complexes which were formed in the processing of H-atom abstraction. It was also revealed that the mechanism is a direct H-atom tranferring processing (HAT) by analyzing the spin density of the O₁ ,O₂ and H ,as well the electron density of O₁, H, O₂, O₁–H and O₂–H.3)A study on the structure-activity relationships of a few of antioxidants in natural plant rosemaryA study on the structure-activity relationship of carnosic acid (CSA), carnosol (CS), 12-methoxyl-trans-carnosic acid (12-MO-Trans-CSA) and12- methoxyl-cis-carnosic acid (12-MO-Cis-CSA) as antioxidants was performed. It was indicated that CSA and CS are active antioxidants by investigating the geometry of ground state molecules and their radicals, the electron spin density distribution of the radicals, and the O-H bond dissociation enthalpy (BDE); the antioxidative activity of CSA is higher than that of CS andα-tocopherol (α-TOH), and the activity of CS is nearly indentical to that ofα-TOH by comparing their O-H BDEs; the seven-member ring formed by intramolecular hydrogen-bond leads to the higher activity of CSA than that of CS, as well 12-MO-Trans-CSA and 12-MO-Cis-CSA than that of phenol.