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

Abstract

Multinuclear solid-state nuclear magnetic resonance methods ( 59 Co, 13 C, 15 N, and 31 P NMR) were applied at natural abundance to the structural and dynamic analysis of cyanocobalamin (vitamin B 12 ) 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 B 12 crystallographic analyses. Most informative about the molecular differences characterizing these two forms were the 13 C 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 editing procedures. These shifts indicated a conformational variability that involved a few specific sites in the corrinoid ring and which was not entirely evident from differences among the X-ray structures previously reported for the forms. Further evidence about the conformational flexibility of these sites in the solid is furnished by 13 C spectral shifts observed upon changing temperatures. The relevance of these observations within the context of the extensive structure/ activity relation studies that have been carried out on this class of systems is briefly addressed.

Solid-State Nuclear Magnetic Resonance Spectroscopy-Pharmaceutical Applications

“…Medek and Frydman analyzed vitamin B 12 polymorphs with solid‐state 13 C, 15 N, 31 P, and 59 Co NMR spectroscopy 143. The 13 C NMR data were the most informative because the highly crystalline material produced sharp resonances for most of the carbons in this rather complex organic molecule.…”

High‐Resolution NMR Spectroscopy in Solids by Truly Magic‐Angle Spinning

“…The observed line widths Dn = 1/(pT * 2 ) can be compared with the limiting homogeneous line widths Dn' = 1/ (pT 0 2 ). [7,19,20] The limiting homogeneous line widths provide a good criterion to evaluate the performance of proton decoupling. [7] The T 0 2 values reported in Table 1 were determined from the mono-exponential decays of spin echoes.…”

Rapid determination of vitamin B2 and B12 in human urine by isocratic liquid chromatography

“…Various analytical methods including radioisotope dilution assay [8], spectrophotometry [9], chemiluminescence [10], electrochemical [11], atomic absorption spectrometry [12], plasma desorption mass spectrometry [13], multinuclear solid-state NMR * Corresponding author. Tel.…”