Emission mössbauer studies of some cobalamins with with and without coordination linkage to the 5,6-dimethyl-benzimidazole base
✍ Scribed by Kimio Inoue; Amar Nath
- Book ID
- 104105874
- Publisher
- Elsevier Science
- Year
- 1977
- Weight
- 555 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0006-3061
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✦ Synopsis
The emission Mijssbauer spectra of "base on" and '&base off' forms of the cyanocob(III)aIamin (vitamin B1z) and the cob(II)alamin (B1zr) and the cob(I)alamin (B1& are studied. The s-electron density on the daughter iron nl;cIeus as reflected by the isomer shift does not change very much while going from B12 + B1sr + Bls especially for the latter, despite the fact that the increasing population of the d subshell is expected to enhance the shielding of the s-electron cloud resulting in diminution of s-electron density on the iron nucleus. These observations can be rationalized if one invokes considerable delocalization of clip electrons from the daughter iron atom onto the corrin ring and also the appreciable hybrid character of dz2 which permits increase of the 4s-electron density concomitantly with an Increase In the population of dz2 orbital. The quadrupole splitting is perhaps predominantly determined by the anisotropy of covalent bonding to the iron atom by the corrin ring and the axial ligands. In the "base off" forms, a water molecule replaces the coordinated benzimidazole base, whereby the c-bonding of the a..iaI ligand (s) is further diminished. The enhanced anisotropy of covalent bonding results in an increase in the magnitude of the quadrupole splittings for the "base off' forms.
The fmger prints of the "base on" and the "base off' B12 and B1zr and B1gs would be valuable in identifying the intermediates in enzymatic reactions invohing B12_