MOTIONAL PROPERTIES OF HYDROCARBON NITROXIDES IN PHOSPHOLIPID BILAYERS

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Partitioning of small piperidine-based nitroxides (2,2,6,6-tetramethyl-piperidine-N-oxyl-4-R) into lipid bilayers followed by examination of these systems through electron paramagnetic resonance (EPR) spectroscopy has provided useful information concerning the structure and function of the cell membrane. However, there are classes of membranes which do not readily lend themselves to partitioning studies by these nitroxides (for example, the red blood cell membrane). Additionally, piperidine-based nitroxides are typically spherically symmetric and do not provide much information about directional anisotropy in the lipid regions of membranes. Therefore we have developed a panel of oxazolidine-derived nitroxides of increasing chain length to both permit partitioning studies in formerly inaccessable membrane systems and to provide structural and hence motional anisotropy. We describe the synthesis, derived from the method of Keana et al, of this series of nitroxide spin label probes and t heir characterization by IR, NMR, and mass spectrometry. Experimental results on partitioning and motion by X- and W-band EPR of these nitroxides in lipid bilayers (liposomes) of dipalmitoylphosphatidylcholine and phospholipid mixtures have also been obtained and analyzed. This is a continuing project.