NMR detection of lipid domains.

Methods for detection of lateral domains by solid-state 2H nuclear magnetic resonance (NMR) and 1H magic angle spinning (MAS)-NMR in model- and biomembranes are presented. 2H NMR has been used for decades to distinguish between liquid-ordered and solid-ordered lamellar phases of phospholipids with deuterated hydrocarbon chains. More recently, it was shown that superposition of liquid-ordered and -disordered phases is detected as well, taking advantage of the large differences in chain order parameters between them. Experiments require preparation of samples with deuterated lipids. In contrast, 1H MAS-NMR utilizes the natural proton NMR signals of lipids in model- and biomembranes. Very good resolution of resonances according to their chemical shifts is achieved by rapid spinning of samples at the "magic angle" (54.7 degrees) to the main magnetic field. Phase transitions to ordered states are detected as broadening of resonances. The method distinguishes liquid-disordered, liquid-ordered, and solid-ordered phases, has much higher sensitivity than 2H NMR, and does not require labeling. In combination with pulsed magnetic field gradients, 1H MAS-NMR yields diffusion rates that may report confinement of lipids to domains with submicrometer dimensions.