Presentation Relationships between Experimental Radical-Scvenging Rates of Phenolic Antioxidants and Their Thermodynamic Parameters Calculated by Quantum Chemistry Calculations

Nakanishi, Ikuo  ,  Ohkubo, Kei  ,  Uto, Yoshihiro  ,  Matsumoto, Kenichiro

Phenolic antioxidants that exhibit an efficient scavenging activity against reactive oxygen species (ROS), such as hydroxyl and peroxyl radicals, are expected to act as a countermeasure against damages induced by oxidative stresses including ionizing radiation. However, the structure–activity relationship has yet to be fully clarified. In this study, the antioxidative activity of a series of phenolic antioxidants, such as artepillin C, a prenylated phenylpropanoid found specifically in Brazilian propolis, and its analogs, was compared based on experimental kinetic data as well as on quantum chemistry calculations by the density functional theory (DFT).The radical-scavenging activity of the phenolic antioxidants was evaluated experimentally by second-order rate constants (k) of their reaction with 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical used as a reactivity model of ROS in acetonitrile using a stopped-flow technique. The log k values thus obtained were found to be linearly correlated with energy difference values between the phenols and the corresponding phenoxyl radicals calculated by DFT. On the other hand, such a linear correlation cannot be observed between the log k values and calculated ionization potentials of the phenolic antioxidants used in this study. Thus, the quantum chemistry calculation is demonstrated to be a powerful tool to design novel antioxidants.
第1回QST国際シンポジウム「量子生命科学 -Quantum Life Science-」

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