The origin of magnetic field dependent recombination in alkylcobalamin radical pairs.
The origin of magnetic field dependent recombination in alkylcobalamin radical pairs.
复制标题
烷基钴胺素自由基对中磁场依赖性重组的起源。
DOI：
10.1111/j.1751-1097.1996.tb02460.x
复制
发表时间：
1996
影响因子：
3.3
通讯作者：
Grissom,CB
中科院分区：
文献类型：
--
作者：
Natarajan,E;Grissom,CB
烷基钴胺素光解的磁场效应研究提供了证据，形成一个反应性的自由基对，出生在单重态自旋。导致连续波（CW）量子产率依赖于磁场的自由基对复合过程仅限于扩散自由基对。尽管腺苷（III）的成对基团也会发生磁场依赖性重组（A。M. Chagaltz和C. B。Grissom，J. Am. Soc.115，12152-12157，1993），该过程不能解释仅在粘性溶剂中观察到的CW量子产率的磁场依赖性。甘油和乙二醇增加溶液的微粘度，从而增加自旋相关扩散自由基对的寿命。这使得溶剂笼中的自旋相关扩散自由基对之间的磁场依赖性复合成为可能。磁场依赖的重组是没有观察到的nonviscosignenic醇，如异丙醇的存在下，从而表明介质的微粘度增加的重要性。捕获逃离溶剂笼的烷基自由基的顺磁性自由基清除剂不会减少磁场对CW量子产率的影响，从而排除随机扩散自由基对之间的自由基对重组，以及排除溶剂衍生的自由基的参与。用自由基对动力学和复合的半经典模型模拟了烷基钴胺素自由基对之间的磁场依赖性复合。这些计算支持存在一个单线态自由基对前体。
Magnetic field effect studies of alkylcobalamin photolysis provide evidence for the formation of a reactive radical pair that is born in the singlet spin state. The radical pair recombination process that is responsible for the magnetic field dependence of the continuous‐wave (CW) quantum yield is limited to the diffusive radical pair. Although the geminate radical pair of adenosylcob(III)alamin also undergoes magnetic field dependent recombination (A. M. Chagovetz and C. B. Grissom,J. Am. Chem. Soc.115, 12152–12157, 1993), this process does not account for the magnetic field dependence of the CW quantum yield that is only observed in viscous solvents. Glycerol and ethylene glycol increase the microviscosity of the solution and thereby increase the lifetime of the spin‐correlated diffusive radical pair. This enables magnetic field dependent recombination among spin‐correlated diffusive radical pairs in the solvent cage. Magnetic field dependent recombination is not observed in the presence of nonviscosigenic alcohols such as isopropanol, thereby indicating the importance of the increased microviscosity of the medium. Paramagnetic radical scavengers that trap alkyl radicals that escape the solvent cage do not diminish the magnetic field effect on the CW quantum yield, thereby ruling out radical pair recombination among randomly diffusing radical pairs, as well as excluding the involvement of solvent‐derived radicals. Magnetic field dependent recombination among alkylcobalamin radical pairs has been simulated by a semiclassical model of radical pair dynamics and recombination. These calculations support the existence of a singlet radical pair precursor.