ONE-ELECTRON REDUCTION OF ARENEDIAZONIUM COMPOUNDS BY PHYSIOLOGICAL ELECTRON-DONORS GENERATES ARYL RADICALS - AN EPR AND SPIN-TRAPPING INVESTIGATION

Arenediazonium compounds (ArN2+) are strong oxidizing agents, which up on one-electron reduction decompose, releasing aryl radicals (Ar-.). T he present studies were undertaken to determine whether reductive frag mentation of ArN2+ can be induced by biologically relevant electron do nors. We found that 4-X-Ph-N-2(+) (where X: -NO2, -Br, -Cl, -OMe and - N(Et)(2)) decomposes to the respective aryl radicals when reduced by a scorbate, NADH, potassium ferrocyanide, catechol or p-hydroquinone in aqueous solutions. Radical identification was based on analysis of the EPR spectra of spin adducts formed by reaction of these radicals with spin traps 2-methyl-2-nitrosopropane (MNP), 3,5-dibromo-4-nitrosobenz ene sulphonate (DBNBS) or 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Thi s study shows that reduction of arenediazonium ions can be a convenien t method for generating aryl radicals in aqueous solutions, In additio n, this investigation confirms that biological reducing agents are cap able of inducing fragmentation of ArN2+ into aryl radicals. This react ion may be pertinent to some biological actions of arenediazonium comp ounds.