TRAPPING OF NITRIC-OXIDE FORMED DURING PHOTOLYSIS OF SODIUM-NITROPRUSSIDE IN AQUEOUS AND LIPID PHASES - AN ELECTRON-SPIN-RESONANCE STUDY

Photolytic decomposition of sodium nitroprusside (SNP), a widely used nitrovasodilator, produced nitric oxide ((NO)-N-.), which was continuo usly monitored by electron spin resonance (ESR) spectroscopy. The (NO) -N-. present in the aqueous or the lipid phase was trapped by either a hydrophilic or a hydrophobic nitronyl nitroxide, respectively, to for m the corresponding imino nitroxide. The conversion of nitronyl nitrox ide to imino nitroxide was monitored by ESR spectrometry. The quantum yield for the generation of (NO)-N-. fr-om SNP, measured from the rate of decay of nitronyl nitroxide, was 0.201 +/- 0.007 and 0.324 +/- 0.0 1 (($) over bar x +/- SD, n = 3) at 420 nm and 320 nm, respectively. T he action spectrum for (NO)-N-. generation was found to overlap the op tical absorption spectrum of SNP closely. A mechanism for the reaction between SNP and nitronyl nitroxide in the presence of light is propos ed and computer-aided simulation of this mechanism using published rat e constants agreed well with experimental data. The methodology descri bed here may be used to assay (NO)-N-. production continuously during photoactivation of (NO)-N-. donors in aqueous and lipid environments. Biological implications of this methodology are discussed.