Emission Mössbauer studies of some organocobalamins

Bioanalytical applications of Mössbauer spectroscopy

Data on the applications of Mössbauer spectroscopy in the transmission (mainly on 57Fe nuclei) and emission (on 57Co nuclei) variants for analytical studies at the molecular level of metal-containing components in a wide range of biological objects (from biocomplexes and biomacromolecules to supramolecular structures, cells, tissues and organisms) and of objects that are participants or products of biological processes, published in the last 15 years are discussed and systematized. The prospects of the technique in its biological applications, including the developing fields (emission variant, use of synchrotron radiation), are formulated.

The bibliography includes 248 references.

Cobalt(II) complexation with small biomolecules as studied by 57Co emission Mössbauer spectroscopy

In the emission (⁵⁷Co) variant of Mössbauer spectroscopy (EMS), the ⁵⁷Co radionuclide (with a half-life of 9months) is used that undergoes a nuclear decay ⁵⁷Co→⁵⁷Fe via electron capture followed by the emission of a γ-quantum, the energy of which is modified by the chemical state and the close coordination environment of the parent ⁵⁷Co atom. While EMS has been used largely in materials science and nuclear chemistry, its high sensitivity can also be of great advantage in revealing fine structural features and for speciation analysis of biological complexes, whenever the ⁵⁷Co²⁺ cation can be used directly as the coordinating metal or as a substitute for native cobalt or other metal ions. As such EMS applications are yet rare, in order to reliably interpret emission spectra of sophisticated ⁵⁷Co²⁺-doped biosystems, model EMS studies of simple cobalt biocomplexes are necessary. In this work, EMS spectroscopic data are analysed and discussed for ⁵⁷Co²⁺ complexes with a range of small biomolecules of different structures, including 4-n-hexylresorcinol, homoserine lactone and a few amino acids (spectra measured in rapidly frozen dilute aqueous solutions or in the dried state at T=80K). The EMS data obtained are discussed with regard to the available literature data related to the coordination modes of the biocomplexes under study.

A novel form of vitamin B-12 and its derivatives

A new isomeric form of cobalamins is reported. The conversion of cobalamin to cobalamin (the new form) is achieved by substituting the benzimidazole base by a less bulky group like H2O or CN- and modest thermal treatment. The back conversion of adenosylcobalamin to the corresponding regular form occurs in the "base-off" form at room temperature. It seems that the corrin ring becomes quite flexible in the "base-off" form and the freer axial movement of the cobalt atom flips the corrin ring into a different conformation. The change in conformation is borne out by subtle changes in the proton magnetic resonances on the corrin ring and the base, and very marked variation in the emission Mössbauer spectra. The latter is indicative of appreciable changes in the spatial conformation in the immediate vicinity of the central metal atom. The ultraviolet-visible and infrared spectra of cobalamin are indistinguishable from those of its corresponding regular form. The new conformational isomeric species is present as an impurity in all commercially available cobalamins (including pharmaceutical preparations). It raises the question whether the cobalamins' constitute the real biologically active anti-anemic factor in humans.