Assignments in the carbon-13 nuclear magnetic resonance spectra of vitamin B12' coenzyme B12' and other corrinoids: application of partially-relaxed fourier transform spectroscopy.

High-resolution Fourier transform NMR at 15.08 MHz was used to observe the proton-decoupled natural-abundance (13)C spectra of aqueous solutions of cobinamide dicyanide (0.067 M), cyanocobalamin (0.024 M), dicyanocobalamin (0.14 M), and coenzyme B(12) (0.038 M). Assignments were made with the aid of chemical shift comparisons, off-resonance single-frequency proton decoupling, partially-relaxed Fourier transform spectra, and splittings arising from (13)C-(31)P coupling. As expected, the (13)C spectra of the coronoids were appreciably more informative than the corresponding proton spectra. Nearly all the lines in the (13)C spectra of the corrinoids were well-resolved single-carbon resonances, in spite of the structural complexity. Partially relaxed (13)C Fourier transform NMR spectra, which yield spin-lattice relaxation times of each resolved resonance, were found to be a very useful addition to the arsenal of NMR techniques.