X-ray structural chemistry of cobalamins

In recent years, X-ray structural determinations of cobalamins (Cbl) have become very accurate thanks to the use of new detectors and synchrotron radiation. This has allowed in depth study of the geometrical features of cobalamins, regarding the large equatorial ligand and, more importantly, their axial fragment, which is involved in the binding of Cbl to proteins and in the catalytic mechanisms of Vitamin B12 based enzymes. These structural aspects, together with their particular crystal packing, are the focus of this review. Several chemical properties, derived from their structural chemistry and not reported in other reviews, are underlined. A comparison to the well-known simple Cbl model, the cobaloximes is also presented and discussed, as this furnishes useful insights into cobalamin chemistry.