This chapter describes the general features of the absorption spectra of vitamin B12 derivatives. The spectroscopic properties of these compounds can then be monitored to deduce structural and environmental perturbations on the corrinoid coenzyme structure and function. Both circular dichroism (CD) and fluorescence polarization spectroscopy are useful for the assignment of various absorption bands of B12 derivatives. To characterize room temperature spectra, recording of low temperature spectra in optical dewars is particularly useful for vitamin B12 derivatives, because of markedly enhanced spectral resolution. Although rectangular cuvettes present minimum optical artifacts, such as reflection compared to cylindrical cells, the former tend to crack owing to strains from freezing at low temperatures. It should be noted that the spectral shift and “enhanced” extinction coefficient are often due to the increased refractive index of the medium at the lower temperature. In this study, the so-called normal spectrum is displayed by dicyanocobalamin and descobalt B12, with well-resolved visible (α, β) and near-UV bands. The CD spectra of pentacoordinate B12 Co3+ derivatives and hexacoordinate B12 Co2+ derivatives are quite alike, and neither of them strongly resembles the spectra of hexacoordinate B12 Co3+ derivatives. © 1980, Elsevier Inc. All rights reserved.
Song, P. S. (1980).  Spectroscopic Analysis of Vitamin B12 Derivatives. Methods in Enzymology, 67(C), 5–11. https://doi.org/10.1016/S0076-6879(80)67004-9