Identification of structural markers for vitamin B12 and other corrinoid derivatives in solution using FTIR spectroscopy

The identification of structural markers for B12/protein interactions is crucial to a complete understanding of vitamin B12 transport and metabolic reaction mechanisms of B12 coenzymes. Fourier transform infrared spectroscopy can provide direct measurements of changes in the side chains and corrin ring resulting from B12/protein interactions. Using FTIR spectroscopy in various solvent systems, the authors have identified structural markers for corrinoids in the physiological state. They assign the major band (denoted B), which occurs at ca. 1,630 cm-1 in D2O and ca. 1675 cm-1 in ethanol, to the amide I C double-bond stretching mode of the propionamide side chains of the corrin ring. The lower frequency of band B in D2O versus ethanol is due to the greater hydrogen-bonding properties of D2O that stabilize the charged amide resonance form. Since the propionamides are known to be important in protein binding, band B is a suitable marker for monitoring the interaction of these side chains with proteins. They assign bands at ca. 1,575 and 1,545 cm-1 (denoted C and D) as breathing modes of the corrin ring on the basis of the bands' solvent independence and their sensitivity to changes in axial ligation