The nature and origin of the NMR spectrum of unsonicated and sonicated aqueous egg yolk lecithin dispersions

Abstract

Listen

Translate article

1. 1. The proton NMR spectrum of unsonicated egg yolk lecithin dispersions was obtained at frequencies up to 300 MHz. A strong frequency dependence of the width of the hydrocarbon chain proton peak was found above about 60 MHz. 2. 2. The linewidths of CH 2 signals from some rubbers also showed a strong frequency dependence. Since this width originates from incomplete motional averaging of dipolar interactions, it is concluded that the lecithin linewidth frequency dependence is not necessarily indicative of a non-dipolar broadening mechanism ( e.g. due to field gradients). It is postulated that hydrocarbon chain protons undergoing very anisotropic motion may in general give a line with a frequency-dependent width. 3. 3. Calculations of expected line narrowing as a function of the radius of a particle tumbling in water showed that the observation after sonication of a high resolution spectrum, with the different linewidths observed, can be explained simply by the extent to which tumbling of small particles averages out dipolar line broadening. 4. 4. Line broadening in high resolution spectra of sonicated dispersions can be interpreted in terms of a reduction in segmental molecular motion if macroscopic effects, e.g. viscosity, are allowed for.