Magic Angle Sample Spinning in Inhomogeneously Broadened Spin System—Application to Unsonicated Phospholipid Bilayers

Abstract

Nuclear magnetic resonance has been used extensively in the last decade to study the structure and dynamics of model and biological membranes.1 However, the complexity of these systems, which should manifest itself in a corresponding richness of their NMR spectra, has in most cases not been observed because of the substantial breadth of the NMR lines. It is now understood that this breadth is due primarily to residual chemical shift anisotropy and dipole-dipole interactions. For dilute spins, such as 13C and 31P, the dipolar broadening can be removed by sufficiently intense rf irradiation at the proton resonance frequency.2–4 Nevertheless, a substantial broadening due to the anisotropy of the chemical shift remains. In order to obtain “high resolution” NMR spectra, it has become customary to subject multilamellar dispersions to prolonged ultrasonic irradiation.5 This process, which results in particles of reduced size with reduced reorientational correlation times, does indeed improve the resolution of the NMR spectra; however, its exact physical and chemical consequences are a subject of much debate.6 We describe below a method whereby high resolution spectra can be obtained without resorting to sonication.KeywordsAcyl ChainMagic Angle SpinSample RotationHigh Resolution SpectrumPowder SpectrumThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.