Abstract
The homolytic Co-C bond dissociation energy (BDE) is central to the understanding of the function of vitamin B12, an important coenzyme of many proteins. We investigate why earlier density functional (B3LYP) estimations of the BDE in methylcobalamin have given so poor results (91-117 kJ/mol) compared to the experimental estimate (155 ± 13 kJ/mol). Improving the basis set increases the discrepancy, as does a proper treatment of basis set superposition error (~3 kJ/mol) and inclusion of zero-point energy corrections (-21 kJ/mol). On the other hand, relativistic (+6 kJ/mol), solvation (+7 kJ/mol in water), and thermal corrections (+6 kJ/mol) increase the BDE. However, neither of these corrections can explain the discrepancy. Instead, the problem seems to be the B3LYP density functional, which gives a corrected BDE of 78 kJ/mol, whereas the density functional Becke-Perdew-86 method and second-order perturbation theory (MP2) give BDEs of 134-139 kJ/mol. A comparison with other methods indicates that the error comes from the Hartree-Fock exchange (~40 kJ/mol) and the LYP functional (~15 kJ/mol). The problem is not restricted to methylcobalamin but seems to be general for homolytic metal-carbon BDEs of transition metals in tetra-pyrrole-like systems.
Original language | English |
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Pages (from-to) | 7539-7545 |
Journal | The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory |
Volume | 107 |
Issue number | 38 |
DOIs | |
Publication status | Published - 2003 |
Bibliographical note
The information about affiliations in this record was updated in December 2015.The record was previously connected to the following departments: Theoretical Chemistry (S) (011001039)
Subject classification (UKÄ)
- Theoretical Chemistry