NMR Detection of Lipid Domains

Methods for detection of lateral domains by solid-state ² H nuclear magnetic resonance (NMR) and ¹ H magic angle spinning (MAS)-NMR in model- and biomembranes are presented. ² H 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, ¹ H 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�) 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 ² H NMR, and does not require labeling. In combination with pulsed magnetic field gradients, ¹ H MAS-NMR yields diffusion rates that may report confinement of lipids to domains with submicrometer dimensions.