Heteronuclear NMR studies of Cobalamins. 10. Nitrogen-15 NMR studies of [15N]cyanocobalt corrins

Abstract

15 N NMR chemical shifts and 13 N- 13 C coupling constants have been determined for cyanocobalamin (CNCbl) and several other monocyano and dicyanocobalt corrins enriched in 15 N or in 15 N and 13 C in the axial cyanide ligand(s). The 15 N chemical shift is found to be nearly as sensitive (ca. 75%) to changes in trans axial ligation as the 13 C chemical shift of 13 CN cyanocobalt corrins. All alterations in the cobalt coordination sphere have opposite effects on the 13 C and 15 N chemical shifts; i.e. there is a strictly inverse relationship between δ 15N and δ 13C