Vivo Structure Determination by CW and Pulsed EPR

EPR has been a useful in-vivo probe of vanadium metabolism. One of the earliest experiments to study biolocalization of V(IV) species was reported in 1980. After i.p. administration of sodium metavanadate for 3 days, V(IV) species were detected by EPR in the subcellular fiaction of rat liver. Using the older structural correlation between Ao and g values, flie detected species was proposed to possess mostly O4 coordination and be present in a protein-bound form [92]. 

Chasteen, Lord, and Thompson used EPR to determine the chemical forms of both absorbed vanadium in tissue and excreted vanadium in the urine and feces of rats given VOSO4 in drinking water over long periods. EPR signals were well defined in the stomach, duodenum, liver, spleen, kidney, lung, and elimination products [78], 

In-Vivo High-Resolution Pulsed EPR for Structure Determination 

The first application of higher-resolution pulsed EPR techniques was reported by Fukui et al. in 1995, who reported insights into the in-vivo coordination structure of vanadyl ions in rat kidney and liver, taken from animals administered a chronic i.v. dose of VOSO4 [69]. ESEEM spectroscopy (2-pulse) was used to detect and quantify small superhyperfine coupling constants of vanadyl compounds in these organs. 

Tissue samples were excised from animals following a four-day program of intravenous VOSO4 injections once per day. CW and 2-pulse ESEEM spectra were measured on the tissue samples directly. Reasonable SIN levels were observed in the CW spectra, allowing for orientation selection of flic paramagnetic species by measuring the ESEEM spectrum at the parallel and perpendicular features of die 

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