Visible and near‐ultraviolet resonance Raman spectra of photolabile vitamin B12 derivatives with a rapid‐flow technique

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Abstract
Resonance Raman spectra, obtained with 5145, 4880 and 3638 Å excitation, are reported for aquo‐, methyl‐, 5′‐deoxyadenosyl‐(coenzyme B12), thiosulfate and cysteinyl cobalamin, of methyl cobinamide, and of Co(II) cobalamin (B12r). Laser‐induced photodecomposition was held to acceptable levels with a rapid‐flow technique. A rich assortment of corrin ring vibrations are observed above 600 cm−1, but the frequencies are constant (within ±3 cm−1) for all the derivatives. Some Raman bands show differential enhancement by the visible and near‐ultraviolet electronic transitions, reflecting their different polarizations. B12r shows large relative intensity changes in bands at 1500 and 1600 cm−1, with respect to the Co(III) derivatives. Despite an absorption spectrum resembling that of B12r, methyl cobinamide shows Raman intensity behavior typical of the other Co(III) derivatives.

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