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Medical and biological

Medical and biological applications of EPR also exist. Although radicals are very reactive, so they do not normally occur in high concentrations in biology, special reagents have been developed to attach " spin labels ", also called "spin probes", to molecules of interest. Specially-designed nonreactive radical molecules can attach to specific sites in a biological cell, and EPR spectra then give information on the environment of the spin labels. Spin-labeled fatty acids have been extensively used to study dynamic organisation of lipids in biological membranes, lipid-protein interactions and temperature of transition of gel to liquid crystalline phases. Injection of spin-labeled molecules allows for electron resonance imaging of living organisms.