Cobalt–carbon bond cleavage is crucial to most natural and synthetic applications of the cobalamin class of compounds, and here we present the first direct electronic and geometric structural characteristics of intermediates formed following photoexcitation of methylcobalamin (MeCbl) using time-resolved X-ray absorption spectroscopy (XAS). We catch transients corresponding to two intermediates, in the hundreds of picoseconds and a few microseconds. Highlights of the picosecond intermediate, which is reduced in comparison to the ground state, are elongation of the upper axial Co–C bond and relaxation of the corrin ring. This is not so with the recombining photocleaved products captured at a few microseconds, where the Co–C bond almost (yet not entirely) reverts to its ground state configuration and a substantially elongated lower axial Co–N_Im bond is observed. The reduced cobalt site here confirms formation of methyl radical as the photoproduct.

中文翻译：

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使用时间分辨X射线吸收光谱法对甲钴胺的光解中间体进行直接结构和化学表征

钴碳键的裂解对于钴胺素类化合物的大多数天然和合成应用至关重要，在这里，我们展示了使用时间分辨的X射线吸收对甲基钴胺素（MeCbl）进行光激发后形成的中间体的第一个直接电子和几何结构特征光谱学（XAS）。我们在数百皮秒和几微秒的时间内捕捉到与两个中间体相对应的瞬变。与基态相比，皮秒级中间产物的亮点是上轴向Co-C键的伸长和柯林环的松弛。在几微秒内捕获的重组光解产物并非如此，其中Co-C键几乎（但尚未完全）回复到其基态构型，并且显着拉长了较低的轴向Co-N观察到_im键。此处还原的钴位点证实形成了作为光产物的甲基自由基。