NITRIC-OXIDE FORMATION BY ULTRASOUND IN AQUEOUS-SOLUTIONS

In this study we demonstrate formation of nitric oxide in aqueous nitr ogen-containing solutions exposed to 50 kHz cavitation-producing ultra sound (standard bath sonicator) using electron paramagnetic resonance detection of (NO)-N-. by trapping with the sodium N-methyl-D-glucamine dithiocarbamate iron(II) complex ((MGDFe2+) or by measuring the conve rsion of the nitronyl nitroxide, 4-carboxyphenyl)-4,4,5,5-tetramethyli midazoline-3- oxide-1-oxyl (carboxy-PTIO), to the imino nitroxide, box yphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl. The (MGDFe2+ complex w hich was used in most experiments was suitable for (NO)-N-. detection over a wide pH range (pH 3-7.8: the working range for carboxy-PTIO was pH 6-8.5), and the measured rate constant of (MGDFe2+ reaction with ( NO)-N-. was 2.3 times higher than for carboxy-PTIO. In air-saturated w ater the rate of (NO)-N-. production by ultrasound was similar to 0.5 mu M/min. The presence of dissolved oxygen was not essential for produ ction of (NO)-N-.; the highest yields of (NO)-N-. (similar to 1.2 mu M (NO)-N-./min) were found under an atmosphere of 40% N-2 and 60% argon . The formation of (NO)-N-. by ultrasound in aqueous solutions can be understood in terms of combustion chemistry-type reactions occurring i nside the ''hot'' collapsing cavitation bubbles. We also show that oth er N-containing molecules can serve as a source of nitrogen for (NO)-N -. production. The possibility of ultrasound-mediated (NO)-N-. formati on to alleviate hypoxia of tumors should be explored.