STUDY OF PHOSPHOLIPID STRUCTURE BY H-1, C-13, P-31 DIPOLAR COUPLINGS FROM 2-DIMENSIONAL NMR

Various motionally averaged P-31-H-1, C-13-H-1, H-1-H-1 and P-31-C-13 dipolar couplings were measured for natural-abundance and unoriented p hosphocholine in the L(alpha) phase. The couplings were obtained and a ssigned by a variety of advanced and partly novel two-dimensional soli d-state NMR experiments. Whereas P-31-H-1 and P-31-C-13 dipolar coupli ngs provide long-range structural constraints, geminal H-1-H-1 couplin gs and the signs of C-13-H-1 couplings are important new elements in a segmental order-tenser analysis of the lipid headgroup and glycerol b ackbone. The implications of these measured dipolar couplings for the conformational exchange of the lipid headgroup and the bending of the headgroup from the glycerol backbone are discussed. These dipolar coup lings are also analyzed semiquantitatively in terms of the segmental o rder tenser.