Theoretical and experimental studies of the spin trapping of inorganic radicals by 5,5-dimethyl-1-pyrroline N-oxide (DMPO). 2. Carbonate radical anion
Theoretical and experimental studies of the spin trapping of inorganic radicals by 5,5-dimethyl-1-pyrroline N-oxide (DMPO). 2. Carbonate radical anion
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DOI：
10.1021/jp065692d
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发表时间：
2007-01-18
影响因子：
2.9
通讯作者：
Zweier, Jay L.
中科院分区：
文献类型：
--
作者：
Villamena, Frederick A.;Locigno, Edward J.;Zweier, Jay L.
以往的研究表明，酶介导的碳酸根阴离子（CO 3中心点-）的产生可能在细胞氧化损伤的启动中起重要作用。采用密度泛函理论B3 LYP/6-31+G**//B3 LYP/6 - 31 G * 和B3 LYP/6 -311+G* 方法，采用极化连续模型，模拟水的体介电效应对5，5-二甲基-1-吡咯啉N-氧化物（DMPO）的CO 3中心点加成反应热力学的影响.理论数据表明，CO 3中心点-与DMPO加成生成O-中心自由基加合物（DMPO-OCO 2），这取决于CO 3中心点-上的自旋（密度）布居。本文采用电子顺磁共振自旋捕获技术，结合常用的自旋捕获器DMPO，对CO_3中心点进行了探测。H2 O2和DMPO在碳酸钠（Na 2CO 3）或碳酸氢钠（NaHCO 3）存在下的UV光解产生两种物质（即，DMPO-OCO 2和DMPO-OH），其中前者具有a（N）= 14.32 G、a（β-Eta）= 10.68 G和a（γ-H）= 1.37 G的超精细分裂常数值，并且与DMPO-OH相比具有更短的半衰期。使用同位素富集的（H2 O2）-O-17实验证实了所形成的DMPO-OH的来源，这表明HO中心点直接添加到DMPO。对DMPO-OCO 2在水溶液中和在不存在游离HO中心点的情况下（例如在酶促产生的CO 3中心点-的情况下）形成DMPO-OH的其他可能途径的理论研究表明，优选的途径是通过H2O或HO-对碳酸酯部分的亲核取代。亚硝酸盐的形成是DMPO捕获CO 3中心的最终产物，并且部分取决于溶液的碱度。CO 3中心点-在水相中的热力学行为与过氧氢自由基（HO 2中心点）的热力学行为相似。
Previous studies have shown that the enzyme-mediated generation of carbonate radical anion (CO3 center dot-) may play an important role in the initiation of oxidative damage in cells. This study explored the thermodynamics of CO3 center dot- addition to 5,5-dimethyl-1-pyrroline N-oxide (DMPO) using density functional theory at the B3LYP/6-31+G**//B3LYP/6-31G* and B3LYP/6-311+G* levels with the polarizable continuum model to simulate the effect of the bulk dielectric effect of water on the calculated energetics. Theoretical data reveal that the addition of CO3 center dot- to DMPO yields an O-centered radical adduct (DMPO-OCO2) as governed by the spin (density) population on the CO3 center dot-. Electron paramagnetic resonance spin trapping with the commonly used spin trap, DMPO, has been employed in the detection of CO3 center dot-. UV photolysis of H2O2 and DMPO in the presence of sodium carbonate (Na2CO3) or sodium bicarbonate (NaHCO3) gave two species (i.e., DMPO-OCO2 and DMPO-OH) in which the former has hyperfine splitting constant values of a(N) = 14.32 G, a(beta-Eta) = 10.68 G, and a(gamma-H) = 1.37 G and with a shorter half-life compared to DMPO-OH. The origin of the DMPO-OH formed was experimentally confirmed using isotopically enriched (H2O2)-O-17 that indicates direct addition of HO center dot to DMPO. Theoretical studies on other possible pathways for the formation of DMPO-OH from DMPO-OCO2 in aqueous solution and in the absence of free HO center dot such as in the case of enzymatically generated CO3 center dot-, show that the preferred pathway is via nucleophilc substitution of the carbonate moiety by H2O or HO-. Nitrite formation has been observed as the end product of CO3 center dot- trapping by DMPO and is partly dependent on the basicity of solution. The thermodynamic behavior of CO3 center dot- in the aqueous phase is predicted to be similar to that of the hydroperoxyl (HO2 center dot) radical.