Zinc Substitution of Cobalt in Vitamin B-12: Zincobyric acid and Zincobalamin as Luminescent Structural B-12-Mimics

摘要

Replacing the central cobalt ion of vitamin B-12 by other metals has been a long-held aspiration within the B-12-field. Herein, we describe the synthesis from hydrogenobyric acid of zincobyric acid (Znby) and zincobalamin (Znbl), the Zn-analogues of the natural cobalt-corrins cobyric acid and vitamin B-12, respectively. The solution structures of Znby and Znbl were studied by NMR-spectroscopy. Single crystals of Znby were produced, providing the first X-ray crystallographic structure of a zinc corrin. The structures of Znby and of computationally generated Znbl were found to resemble the corresponding Co-II-corrins, making such Zn-corrins potentially useful for investigations of B-12-dependent processes. The singlet excited state of Znby had a short life-time, limited by rapid intersystem crossing to the triplet state. Znby allowed the unprecedented observation of a corrin triplet (E-T=190 kJ mol(-1)) and was found to be an excellent photo-sensitizer for O-1(2) (phi(Delta)=0.70).