Time-resolved spectroscopic studies of B12 coenzymes: comparison of the influence of solvent on the primary photolysis mechanism and geminate recombination of methyl-, ethyl-, n-propyl-, and 5'-deoxyadenosylcobalamin.
Time-resolved spectroscopic studies of B12 coenzymes: comparison of the influence of solvent on the primary photolysis mechanism and geminate recombination of methyl-, ethyl-, n-propyl-, and 5'-deoxyadenosylcobalamin.
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B12 辅酶的时间分辨光谱研究：比较溶剂对甲基、乙基、正丙基和 5-脱氧腺苷钴胺素的初级光解机制和成对重组的影响。
DOI：
10.1021/jp053202w
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
Cole,AllwynG
中科院分区：
文献类型：
--
作者：
Sension,RoseanneJ;Harris,DAhmasi;Cole,AllwynG
本文报道了甲基钴胺素（MeCbl）、乙基钴胺素（EtCbl）和n-丙基钴胺素（PrCbl）在乙二醇中光解的瞬态吸收研究，时间跨度为60年，从10 fs到10 ns。这些测量探测溶剂对金属-配体电荷转移（MLCT）中间体的形成和衰减的影响，观察到以下激发MeCbl，在EtCbl和PrCbl的光解机制，和双生重组的烷基自由基与钴（II）丙氨酸和逃逸的烷基自由基从初始溶剂笼的速率常数。早期的研究探索了5 ′-右旋腺苷钴胺素（辅酶B12）在水和乙二醇中的动力学（Yoder，L. M.;科尔，A. G.地;步行者湖一、II; Sension，R. J.J.Phys.Chem.B2001，105，12180 - 12188）和水中的烷基钴（科尔，A. G.地;约德湖M.; Shiang，J. J.;安德森，N. A.的;步行者湖一、II; Banaszak Holl，M. M.;森西翁河杰杰·阿姆2002，124，434 - 441）。这些调查的结果进行了讨论的背景下，溶剂的摩擦对化学反应动力学的影响的文献。的测量允许分离的溶剂上的固有速率常数的双生重组和从初始溶剂笼逃逸的速率常数的影响。的速率常数为固有的双生重组的钴（II）的丙氨酸与烷基自由基是弱依赖于溶剂和烷基自由基（Me，Et，Pr，或Ado）的性质。Et、Pr和Ado自由基表现出预期的从初始溶剂笼扩散控制逃逸的行为。相比之下，笼逃逸的Me自由基的幅度远大于预期的流体动力学参数的基础上。
A transient absorption study of the photolysis of methylcobalamin (MeCbl), ethylcobalamin (EtCbl), andn-propylcobalamin (PrCbl) in ethylene glycol spanning six decades in time, from 10 fs to 10 ns, is reported. These measurements probe the influence of solvent on the formation and decay of the metal-to-ligand charge transfer (MLCT) intermediate observed following excitation of MeCbl, the photolysis mechanism in EtCbl and PrCbl, and the rate constants for geminate recombination of the alkyl radicals with cob(II)alamin and for the escape of the alkyl radicals from the initial solvent cage. Earlier investigations probed the dynamics of 5‘-dexoyadenosylcobalamin (coenzyme B12) in water and ethylene glycol (Yoder, L. M.; Cole, A. G.; Walker, L. A., II; Sension, R. J.J. Phys. Chem. B2001,105, 12180−12188) and alkylcobalamins in water (Cole, A. G.; Yoder, L. M.; Shiang, J. J.; Anderson, N. A.; Walker, L. A., II; Banaszak Holl, M. M.; Sension, R. J.J. Am. Chem. Soc.2002,124, 434−441). The results of these investigations are discussed in the context of the literature on the frictional influence of solvent on chemical reaction dynamics. The measurements allow a separation of the influence of the solvent on the intrinsic rate constant for geminate recombination and the rate constant for escape from the initial solvent cage. The rate constant for the intrinsic geminate recombination of cob(II)alamin with the alkyl radical is weakly dependent on the solvent and on the nature of the alkyl radical (Me, Et, Pr, or Ado). The Et, Pr, and Ado radicals exhibit the behavior expected for diffusion-controlled escape from the initial solvent cage. In contrast, the magnitude of cage escape for the Me radical is much larger than anticipated on the basis of hydrodynamic arguments.