LITHIUM PHTHALOCYANINE - A PROBE FOR ELECTRON-PARAMAGNETIC-RESONANCE OXIMETRY IN VIABLE BIOLOGICAL-SYSTEMS

Lithium phthalocyanine (LiPc) is a prototype of another generation of synthetic, metallic-organic, paramagnetic crystallites that appear ver y useful for in vitro and in vivo electron paramagnetic resonance oxim etry. The peak-to-peak line width of the electron paramagnetic resonan ce spectrum of LiPc is a linear function of the partial pressure of ox ygen (pO2); this linear relation is independent of the medium surround ing the LiPc. It has an extremely exchange-narrowed spectrum (peak-to- peak line width = 14 mG in the absence of O2). Physicochemically LiPc is very stable; its response to pO2 does not change with conditions an d environments (e.g., pH, temperature, redox conditions) likely to occ ur in viable biological systems. These characteristics provide the sen sitivity, accuracy, and range to measure physiologically and pathologi callly pertinent O2 tensions (0.1-50 mmHg; 1 mmHg = 133 Pa). The appli cation of LiPc in biological systems is demonstrated in measurements o f pO2 in vivo in the heart, brain, and kidney of rats.