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

Resonance Raman spectra, obtained with 5145, 4880 and 3638 Å excitation, are reported for aquo‐, methyl‐, 5′‐deoxyadenosyl‐(coenzyme B 12 ), thiosulfate and cysteinyl cobalamin, of methyl cobinamide, and of Co(II) cobalamin (B 12r ). 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. B 12r 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 B 12r , methyl cobinamide shows Raman intensity behavior typical of the other Co(III) derivatives.