A Multinuclear Solid-State NMR Analysis of Vitamin B12 in Its Different Polymorphic Forms

Abstract

Multinuclear solid-state nuclear magnetic resonance methods (59Co, 13C, 15N, and 31P NMR) were applied at natural abundance to the structural and dynamic analysis of cyanocobalamin (vitamin B12) polymorphs. These studies involved recrystallizing a series of samples under different conditions and from various solvents, and subsequently recording their powder NMR spectra at different temperature. Two polymorphs could be identified in these studies, in correspondence with the two structures described by Hodgkin and co-workers in their seminal vitamin B12 crystallographic analyses. Most informative about the molecular differences characterizing these two forms were the 13C NMR data, which showed sharp and well-resolved resonances indicative of high sample crystallinity. Diagnostic differences between these two forms could be observed in the chemical shifts of particular resonances, many of which could be assigned to their molecular sites on the basis of solution-state literature and of solid-state spectral ed...