Phosphatidylcholine 'wobble' In Vesicles Assessed By High-resolution ~(13)cfield Cycling Nmr Spectroscopy

摘要

Motions of phospholipids in membranes have been the subject of intensive research for several decades. While chain motions are understood in a quantitative fashion as a result of diverse ~2H and ~(13)C NMR studies, the dynamic behavior of the interfacial region, including the fatty acyl carbonyls and the phosphorus moiety, is much less well characterized. Spin-lattice relaxation rates (R_1) measured over a range of magnetic fields can in principle be very useful for determining time scales for different motions in the lipid bilayer. However, for phospholipid aggregates only a few studies have measured R_1 (~2H and ~(13)C) at three or four fields, and those above 1 T, to try and assess lipid motions. Recent high-resolution ~(31)P field cycling spin-lattice relaxation studies have yielded information on the motions of the phosphorus of different phospholipids in diverse aggregates. In this technique, the magnetic field is cycled by mechanically shuttling the sample from the center of the probe to a substantially lower magnetic field above the probe for the delay times normally used in conventional NMR relaxation sequences and then shuttling the sample back to the probe for readout of the relaxation at the lower field.