APPLICATION OF DOUBLY DECOUPLED C-13(H-1,N-14) NMR-SPECTROSCOPY TO STUDIES OF THE CONFORMATION AND DYNAMICS OF THE CHOLINE HEADGROUP OF PHOSPHOLIPIDS

The high symmetry about the choline nitrogen atom leads to resolvable scalar 13C-14N coupling in the 13C NMR spectrum of choline. For membranes or model membrane systems containing phosphatidyl choline molecules, this coupling can be partially or completely collapsed due to the slower motion and consequently shorter 14N spin lattice relaxation time of the choline nitrogen. In the present study, this effect has been probed by comparison of the 13C NMR spectra obtained using conventional proton decoupling with spectra obtained using simultaneous 14N and 1H decoupling,i.e., 13C {1H, 14N}nmR spectroscopy. The results indicate a partially collapsed triplet structure for the choline methyl resonances in several sonicated lipid vesicles as well as in whole Chinese Hamster Ovary cells labeled with a 3 : 3 : 1 mixture of [1-13C]-, [2-13C]-, and [13CH3] choline. Further, the sharpening of the choline C-2 resonance resulting from the 14N decoupling makes possible the observation of three bond 13C-31P scalar coupling and, consequently, a conformational analysis of the rotational isomerism about the choline OC-1 bond. © 1979.