Mössbauer Studies of Vitamin B12 and Some Related Cobalamins
The Mössbauer spectra of vitamin B12-Co57 (cyanocobalamin-Co57), dicyanocobalamin, and several aquocobalamin derivatives have been investigated. Sources were prepared as thin poly crystalline solids or frozen aqueous solutions and run, mainly at 77°K, against a Na4Fe(CN)6 • 10H2O absorber. The spectra of these cobalamins consist in general of a fairly strong, broad (~ 1 mm/sec half-width) doublet with evidence in many, but not all, cases of a minor contribution from a second doublet. Quadrupole splittings vary from 1.8 to 3.1 mm/sec; isomer shifts (vs. SNP) are largely in the +0.25–0.55 mm/sec range. Chemical changes in dicyanocobalamin solutions are observable by Mössbauer spectroscopy, although undetected by ultraviolet spectroscopy. The similarity of the Mössbauer spectrum of vitamin B12 to those of certain other biologically active compounds, particularly cytochrome c, is discussed, as is the general problem of interpreting “source” experiments.
KeywordsMossbauer Spectroscopy Isomer Shift Quadrupole Splitting Mossbauer Spectrum Cyanide Anion
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