Novel Visible and Ultraviolet Light Photogeneration of Hydroxyl Radicals by 2‐Methyl‐4‐nitro‐quinoline‐N‐oxide (MNO) and 4, 4′‐Dinitro‐(2, 2′) bipyridinyl‐N, N′‐dioxide (DBD)

Abstract

Chemicals that upon absorption of light generate hydroxyl radicals (.OH), free of other damaging species under physiological conditions, are useful tools for the study of the biological effects of .OH radical and for its utilization for analytical purposes. We report the novel property of 2-methyl-4-nitro-quinoline-N-oxide (MNO) and 4,4'-dinitro-(2,2')bipyridinyl-N,N'-dioxide (DBD) to act as photogenerators of .OH with UV and visible light. Upon irradiation with 360-400 nm light MNO and DBD generate free radicals that convert coumarin carboxylic acid (CCA) to fluorescent 7-OH-CCA; the .OH radical scavengers dimethylsulfoxide (DMSO) and ethanol eliminate the induction of 7-OH-CCA fluorescence. Upon 400 nm illumination in the presence of MNO, supercoiled plasmid DNA is converted to circular and strand breakage is significantly reduced in the presence of DMSO and completely absent in the absence of MNO. The conversion of CCA to 7-OH-CCA and of supercoiled plasmid to circular DNA are also observed in the absence of oxygen. Taken together, these data indicate that MNO and DBD constitute novel .OH-generating compounds. Because currently known .OH-photogenerating compounds require UV illumination (< 360 nm) that also damages DNA and cells directly, the property of MNO to generate .OH upon 400 nm illumination is advantageous when studies on cells, DNA and other biomolecules are conducted.