Wiley Theodore E, Miller Nicholas A, Miller William R, Sofferman Danielle L, Lodowski Piotr, Toda Megan J, Jaworska Maria, Kozlowski Pawel M, Sension Roseanne J
Department of Chemistry , University of Michigan , 930 North University Avenue , Ann Arbor , Michigan 48109-1055 , United States.
Applied Physics , University of Michigan , 450 Church Street , Ann Arbor , Michigan 48109-1040 , United States.
J Phys Chem A. 2018 Aug 23;122(33):6693-6703. doi: 10.1021/acs.jpca.8b06103. Epub 2018 Aug 14.
Ultrafast time-resolved spectroscopy was used to study the photochemistry of hydroxocobalamin (HOCbl) and aquocobalamin (HOCbl) in solution. Spectroscopic measurements and TD-DFT simulations provide a consistent picture of the spectroscopy and photochemistry. Excitation of HOCbl results in formation of an excited state followed by rapid internal conversion to the ground state (0.35 ± 0.15 ps) through an S/S seam at a slightly elongated Co-O bond length and a significantly elongated Co-N bond length. In contrast, the initial elongation of the axial bonds in HOCbl is followed by contraction to an excited state minimum with bonds slightly shorter than those in the ground state. Internal conversion to the ground state follows on a picosecond time scale (5.3 ± 0.4 ps). For both compounds, photodissociation forming cob(II)alamin and hydroxyl radicals (∼1.5% yield) requires excitation to highly excited states. Dissociation is mediated by competition between internal conversion to the S surface and prompt bond cleavage.
采用超快时间分辨光谱研究了溶液中羟基钴胺素（HOCbl）和水合钴胺素（HOCbl）的光化学。光谱测量和TD-DFT模拟为光谱学和光化学提供了一致的图景。HOCbl的激发导致形成一个激发态，随后通过S/S接缝在钴-氧键长度略有伸长和钴-氮键长度显著伸长的情况下快速内转换回基态（0.35±0.15皮秒）。相比之下，HOCbl中轴向键的初始伸长之后是收缩至激发态最小值，此时键长略短于基态。在皮秒时间尺度（5.3±0.4皮秒）上随后发生内转换回基态。对于这两种化合物，光解离形成钴胺素（II）和羟基自由基（产率约1.5%）需要激发到高激发态。解离是由内转换到S表面和快速键断裂之间的竞争介导的。
