The interpretation of proton magnetic resonance linewidths for lecithin dispersions. Effect of particle size and chain packing

Two previously reported theoretical treatments of the effect of sonication on the PMR spectrum of phospholipid bilayer membranes have led to divergent conclusions regarding the effects of sonication on the structure of the bilayer membrane. In this report these two theoretical treatments will be critically reviewed, and it will be shown that only the theory of Seiter and Chan (Seiter, C.H.A. and Chan, S.I. (1973) J. Am. Chem Soc. 95, 7541-7553) yields predictions which are in agreement with experiment. Analysis of available and newly acquired NMR results for sonicated bilayer vesicles of different sizes, both above and below the thermal phase transition, indicates that sonication does disrupt the regular molecular packing of the phospholipid molecules in these systems.