Selçuki Cenk, van Eldik Rudi, Clark Timothy
Computer-Chemie-Centrum der Universität Erlangen-Nürnberg, Nägelsbachstrasse 25, 91052 Erlangen, Germany.
Inorg Chem. 2004 May 3;43(9):2828-33. doi: 10.1021/ic0347945.
Density functional and molecular orbital theory calculations on models for cobalamin suggest that NO binds similarly to the Co(II) and Co(III) oxidation states. However, Co(III) can bind water far more strongly than Co(II) as a sixth ligand, so that the competition between water and NO complexation strongly favors water for Co(III) in the gas phase. Although the Co(II) oxidation state is found to bind water slightly more strongly than NO in the gas phase, the inclusion of solvation effects via the polarizeable continuum model makes NO binding more favorable. Thus, the experimentally observed ability of cob(II)alamin to bind NO in aqueous solution is the result of its weak complexation with water and the relatively poor solvation of NO. Calculated vibrational frequencies support the interpretation of the cob(II)alamin-NO complex as being cob(III)alamin-NO-, although the DFT calculations underestimate the degree of charge transfer in comparison to Hartree-Fock calculations.
对钴胺素模型进行的密度泛函和分子轨道理论计算表明，NO与Co(II)和Co(III)氧化态的结合方式相似。然而，作为第六配体，Co(III)结合水的能力比Co(II)强得多，因此在气相中，水与NO络合之间的竞争对Co(III)而言强烈有利于水。尽管在气相中发现Co(II)氧化态结合水的能力比NO略强，但通过可极化连续介质模型考虑溶剂化效应后，NO的结合更有利。因此，实验观察到的钴胺(II)素在水溶液中结合NO的能力是其与水的弱络合以及NO相对较差的溶剂化作用的结果。计算得到的振动频率支持将钴胺(II)素-NO络合物解释为钴胺(III)素-NO-，尽管与哈特里-福克计算相比，密度泛函理论计算低估了电荷转移程度。
