41 research outputs found
Electronic Structure of One-Electron-Oxidized Form of the Methylcobalamin Cofactor: Spin Density Distribution and Pseudo-Jahn–Teller Effect
The electronic and structural properties of the one-electron-oxidized
form of methylcobalamin (MeCbl) cofactor have been investigated using
density functional theory (DFT) and CASSCF/MC-XQDPT2 calculations.
We applied two types of functionals (hybrid and GGA) which produced
quite different results in terms of spin density profiles: the B3LYP
description was consistent with CoÂ(III) and the Ï€-cation corrin
radical while the BP86 result was more in line with the CoÂ(IV) oxidation
state. A closer inspection of both outcomes indicates that the oxidized
species have a mixed Ï€-cation corrin radical and CoÂ(III)/CoÂ(IV)
character. This mixed character was further supported by high-level <i>ab initio</i> CASSCF/MC-XQDPT2 calculations, which reveal the
strong mixing of the electronic states due to nondynamical correlation
effects. The near degeneracy, which takes place between the ground
and first excited state, was consistent with the presence of a pseudo-Jahn–Teller
(pJT) effect in the oxidized form of MeCbl. In addition, the DFT-based
investigation of the structurally related porphyrin complexes gives
a description consistent with corrin-based analogues and reveals that
the corrin species have more CoÂ(IV) character. The most important
finding of the present study, regardless of the type of functional
used, was the significant lowering of dissociation energy (∼35%),
which might be due to the partial depopulation of the Co–C
σ orbital upon removal of an electron