High-resolution magic-angle spinning H nuclear magnetic resonance studies of lipid dispersions using spherical glass ampoules

A very useful high-resolution magic-angle spinning (MAS) ¹H NMR method for studying lipid dispersions is presented. The sample can be loaded into the spherical glass ampoule very easily, and a spinning speed of more than 10 kHz can be achieved without the problems of sample leakage or water loss. The line width at half height for the HDO peak is less than 1.5 Hz, and the method can be implemented by anyone who has access to a solid-state MAS NMR spectrometer. By using the spherical glass ampoule method we found two water peaks, which could be ascribed to bulk water outside of the multilamellar liposome (peak at high frequency) and interlamellar water (peak at low frequency), in both POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) liposomes. These are the first two examples of lipids without exchangeable protons that exhibit two distinct water resonances. The respective ¹H spin-lattice relaxation times (T₁) were measured, yielding values twice as long for bulk water as compared with interlamellar water. Both the chemical shift and spin relaxation results demonstrate the ability of MAS ¹H NMR to rapidly monitor changes in physical properties that accompany water interactions with zwitterionic phosphatidylcholines.