Redox Potentials of Cobalt Corrinoids with Axial Ligands Correlate with Heterolytic Co-C Bond Dissociation Energies.
We investigate the correlations between the redox potentials of nonalkylated cobalt corrinoids and the Co-C bond dissociation energies (BDEs) of the methylated species with an aqua or histidine axial ligand. A set of cobalt corrinoids, cobalamin, and its model systems, which include new version of myoglobin reconstituted with cobalt didehydrocorrin, are investigated. The Co(III)/Co(II) and Co(II)/Co(I) redox potentials of myoglobin reconstituted with cobalt tetradehydrocorrin and didehydrocorrin and the bare cofactors were determined. Density functional theory (DFT) calculations were performed to estimate the Co-C BDEs of the methylated species. It is found that the redox potentials correlate well with the heterolytic BDEs, which are dependent on the electronegativity of the corrinoid frameworks. The present study offers two important insights into our understanding of how enzymes promote the reactions: (i) homolysis is promoted by strong axial ligation and (ii) heterolysis is controlled by the redox potentials, which are regulated by the saturated framework and axial ligation in the enzyme.
Department of Applied Chemistry, Graduate School of Engineering, Osaka University , Suita 565-0871, Japan.|Institute for Materials Chemistry and Engineering and IRCCS, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.
Yoshitsugu
Y
Morita
Department of Applied Chemistry, Graduate School of Engineering, Osaka University , Suita 565-0871, Japan.|PRESTO, JST, Kawaguchi 332-0012, Japan.|Frontier Research Base for Global Young Researchers, Graduate School of Engineering, Osaka University , Suita 565-0871, Japan.
Koji
K
Oohora
Institute for Materials Chemistry and Engineering and IRCCS, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.
Akiyoshi
A
Sawada
Institute for Materials Chemistry and Engineering and IRCCS, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.|Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University , Nishikyo-ku, Kyoto 615-8520, Japan.
Takashi
T
Kamachi
Institute for Materials Chemistry and Engineering and IRCCS, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.|Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University , Nishikyo-ku, Kyoto 615-8520, Japan.
Kazunari
K
Yoshizawa
Department of Applied Chemistry, Graduate School of Engineering, Osaka University , Suita 565-0871, Japan.
Takashi
http://orcid.org/0000-0002-2215-935X
T
Hayashi
D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D045728:Corrinoids / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011789:Quantum Theory
D056831:Coordination Complexes; D045728:Corrinoids; D008024:Ligands; D003035:Cobalt