Molecular motion at the critical point in lipid membranes.

It is shown that the calculated temperature dependence of the deuterium nuclear magnetic resonance (NMR) of labeled cholesterol-phospholipid bilayers is changed by magic-angle spinning. This makes it possible to distinguish different molecular motions at temperatures near a miscibility critical point, for motions with distinct temperature-dependent correlation times. In this way one finds that NMR line broadening due to critical point composition fluctuations can be distinguished from broadening due to the formation and dissociation of complexes.