Biologically active forms of cobalamins are crucial cofactors in biochemical reactions and these metabolites can be inhibited by their structurally similar analogues known as antivitamins B₁₂. Phenylethynylcobalamin (PhEtyCbl) or 4-ethylphenylcobalamin (EtPhCbl) exemplify recently synthesized and structurally characterized antivitamins B₁₂. Herein, DFT and TD-DFT studies of EtPhCbl are provided to explore its photochemical behavior, which may lead to design of arylcobalamins that can be used as therapeutic agents in light activated drug applications. To understand the photolability of EtPhCbl, a potential energy surface (PES) for the photodissociation of the Co–C bond was constructed. The S₁ PES contains two energy minima, one being metal-to-ligand charge transfer (MLCT) and another the ligand-field (LF) state. There are two possible pathways for photodissociation: the first pathway (path A) involves initially lengthening the Co–C bond from the MLCT minimum and then elongation of Co–N_Im while the second pathway (path B) involves the lengthening of the Co–N_Im bond through the MLCT region followed by the lengthening of the Co–C bond through the LF region. It is shown that photodissociation involving path A is not energetically favorable whereas preferable photodissociation of the Co–C bond involves path B.

中文翻译：

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乙基苯基钴胺素抗维生素B _12的光解离

钴胺素的生物活性形式是生化反应中至关重要的辅因子，这些代谢物可以通过其结构相似的类似物（称为抗维生素B _12）来抑制。苯乙炔基钴胺素（PhEtyCbl）或4-乙基苯基钴胺素（EtPhCbl）代表了最近合成和结构表征的抗维生素B ₁₂。本文中，提供了对EtPhCbl的DFT和TD-DFT研究，以探索其光化学行为，这可能导致设计可用作光活化药物应用中治疗剂的芳基钴胺素。为了了解EtPhCbl的可光化性，构建了用于Co-C键光解的势能面（PES）。S ₁PES包含两个能量极小值，一个是金属到配体的电荷转移（MLCT），另一个是配体场（LF）状态。光解离有两种可能的途径：第一种途径（路径A）首先从MLCT最小值开始延长Co-C键，然后延长Co-N _Im，而第二种途径（路径B）涉及Co-N延长。 N _ML键穿过MLCT区，然后Co-C键穿过LF区。结果表明，涉及路径A的光解离在能量上是不利的，而Co-C键的优选光解离涉及路径B。