ABSTRACT
The scope of in vivo electron paramagnetic resonance (EPR) encompasses the detection of molecules with unpaired electrons: naturally occurring paramagnetic species, trapped or transient radical intermediates, and specifically targeted spin-probes or spin-labels. The great versatility of in vivo EPR comes with the use of specifically targeted nitroxide spin-probes and spin-labels that may be "designer synthesized" to bind or covalently react with specific cells, enzymes, tissues, or receptors. However, free aqueous cations, such as iron or copper, might exist in occasional pathological states where the signal amplitude could be within the normal EPR capabilities. The single most important characteristic of spin labels has been the sensitivity of their EPR spectra to macromolecular motion and microviscosity. The EPR lineshape changes dramatically from rotational correlation times in the 10 to 100 nsec range. Suffice it to say, microscopic imaging by EPR has a potential place in diagnostic methodology.
