HIGH FREQUENCY EPR OF VIABLE BIOLOGICAL SYSTEMS

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Over the past decade it has been shown that very high frequency (VHF) EPR offers great advantages in many types of experiments. However, to date we have seen no documented attempts to apply this technique to viable biological systems. The reasons for this are both technical and psychological: the sample volume at W-band (95 GHz) could be 1000-fold smaller than at conventional X-band, and microwave losses are somewhat higher. In the present work we demonstrate the prospects for VHF EPR in cellular studies. The VHF EPR has a better absolute point sensitivity, which is essentially needed in studies of small objects (like a single cell) or surfaces, including cellular membranes. The better g-value resolution offered by VHF EPR enables one to separate spectroscopically different kinds of nitroxide radicals within the same system, or radicals in different molecular environments (e.g. to distinguish more clearly between nitroxide molecules dissolved in lipids, membranes, and aqueous phase of the cell). Another possible application of VHF EPR spectroscopy and imaging is in cryobiology, where nitroxide spin probes could be used to follow redistribution processes in cells during freezing.