Heating caused by radiofrequency irradiation and sample rotation in 13C magic angle spinning NMR studies of lipid membranes

Application of rapid sample rotation and radiofrequency irradiation in magic angle spinning (MAS) NMR of lipid bilayers can significantly increase the sample temperature. In this work, we studied the extent of heating during the acquisition of H-1-decoupled C-13 MAS spectra of hydrated dimyristoylphosphatidyl-choline (DMPC) in the L. phase. First, we describe a simple procedure for determining the increase in temperature by observing the shift of the H-1 water signal. The method is then used to identify and assess the various factors that contribute to the sample heating. The important factors discussed in this paper include: (i) the spinning speed, (ii) the variable-temperature gas pressure, (iii) the rotor geometry, (iv) the power, duration and frequency of the radiofrequency irradiation and (v) the hydration level. A comparison of different heteronuclear decoupling schemes in terms of their ability to produce highly resolved C-13 spectra of DMPC is also reported. Copyright (C) 2004 John Wiley Sons, Ltd.