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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Rate Constants of Hydroperoxyl Radical Addition to Cyclic Nitrones:A DFT Study
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Rate Constants of Hydroperoxyl Radical Addition to Cyclic Nitrones:A DFT Study

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Nitrones are potential synthetic antioxidants against the reduction of radical-mediated oxidative damage in cells and as analytical reagents for the identification of HO_2~· and other such transient species.In this work,the PCM/B3LYP/6-31+G(d,p)//B3LYP/6-31G(d)and PCM/mPW1K/6-31+G(d,p)density functional theory(DFT)methods were employed to predict the reactivity of HO_2~· with various functionalized nitrones as spin traps.The calculated second-order rate constants and free energies of reaction at both levels of theory were in the range of 10~0-10~3 M~(-1)s~(-1)and 1 to-12 kcal mol~(-1),respectively,and the rate constants for some nitrones are on the same order of magnitude as those observed experimentally.The trend in HO_2~· reactivity to nitrones could not be explained solely on the basis of the relationship of the theoretical positive charge densities on the nitronyl-C,with their respective ionization potentials,electron affinities,rate constants,or free energies of reaction.However,various modes of intramolecular H-bonding interaction were observed at the transition state(TS)structures of HO_2~· addition to nitrones.The presence of intramolecular H-bonding interactions in the transition states were predicted and may play a significant role toward a facile addition of HO_2~· to nitrones.In general,HO_2~· addition to ethoxycarbonyl-and spirolactam-substituted nitrones,as well as those nitrones without electron-withdrawing substituents,such as 5,5-dimethyl-pyrroline N-oxide(DMPO)and 5-spirocyclopentyl-pyrroline N-oxide(CPPO),are most preferred compared to the methylcarbamoyl-substituted nitrones.This study suggests that the use of specific spin traps for efficient trapping of HO_2~· could pave the way toward improved radical detection and antioxidant protection.

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