A high-resolution NMR study (1H, 13C, 31P) of the interaction of paramagnetic ions with phospholipids in aqueous dispersions.

1H-, 13C- and 31P-NMR spectra of egg-yolk phosphatidylcholine (PC), phosphatidylserine (PS) and phosphatidic acid (PA) and cosonicated mixtures of these phospholipids were obtained from ultrasonicated dispersions containing Pr3+, Eu3+, Gd3+ and Mn2+ ions. The differences in chemical shift values, deltaN, between the "inner" and "outer" resonance signals for the different nuclei of the polar head group of egg-yolk phosphatidyl choline provide information about the average distances of the paramagnetic ion within the polar groups of the phospholipid molecules. In the Pr(2H2O)3+n/egg-yolk phosphatidylcholine system the ions are nearest to the phosphate and -CH2CH2 group, respectively but relatively far from the N(CH3)3 group of the polar head group of the lipid. The integral analysis of the 1H-NMR spectra obtained from dispersions containing Pr3+ and Mn2+ ions enables us to calculate the number of the polar groups in both sides of the egg-yolk phosphatidylcholine bilayer, the size of lipid vesicle and to give some features of the arrangement of the phospholipid molecules in cosonicated egg-yolk phosphatidylcholine/phosphatidylserine vesicles. At p2H 8.3 in PC/PS mixtures an extreme asymmetry is observed with PS preferentially in the outer side of the membrane. This side contains approximately three times more PS than PC molecules. Some comments are made concerning the quantitative integral analysis of proton-noise decoupled 31P-NMR spectra as obtained from similar phospholipid mixtures by Michaelson et al. and Berden et al.