ESR study of vitamin B12r substituted in B12b single crystals: Crystal growth and temperature dependence of the spectra

✍ Scribed by A. Schweiger; E. Jörin; Hs.H. Günthard

• Publisher: Elsevier Science
• Year: 1979
• Tongue: English
• Weight: 407 KB
• Volume: 61
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(79)80631-4

✦ Synopsis

The preparation of vitamin

B12b single crystals doped wtth pammagnetic Bit, is described--rrom preliminary ESR data the orientation of B12T with respect to the crysttilogmphic axes system of Bllb is determined. The linewxdth depending on _-temperature, orientation and tni, wII be discussed. The pararnagnetic species of vitamin BI2 have been extensively studied by ESR. The reported results of the reduced low spin cob(II)alamin (B12r) and of its oxygenated form (BLZr02) originate from powder samples and frozen solutions, where only a restricted resolution is available Ii-41 _ For a more detailed discussion concerning the electronic and geometric structure of the biologically active center, it would be useful to get information about the hfs and quadrupole coupling of the axial [S] and the in-plane nitrogen ligands, the orientation of the tensor axes with respect to the BiZr molecule, the motions of weakly coupled ligands at the sixth coordination position etc. This can be obtained in principle from ESR and ENDOR investigations of B1zr and B,,O, single crystals-In this letter we report the preparation of vitamin B12,, (hydroxocob(III)alamin) single crystals, doped with B,,-Preliminary resuhs obtained from single crystal ESR spectra, including a discussion of their temperature dependence, will be given. The X-ray structure of vitamin B12 (cyanocob(III)alamin) has been studied by Hodgkin et al. [6-8]_ In the case of B12b, only the space group and the unit cell dimensions are known_ in B,, as well as in BIzb, a dry and a wet modification are observed which mainly differ in the amount of crystal water. Solid BLzr was prepared reducing an aqueous solution of commercially available B,,., (Fluka CH) with NaBHq under anaerobic conditions_ The brown BIzr compound was precipitated with acetone and dried under vacuum.