Photochemistry of Roussin's Red Salt, Na2[Fe2S2(NO)4], and of Roussin's Black Salt, NH4[Fe4S3(NO)7]. In Situ Nitric Oxide Generation To Sensitize γ-Radiation Induced Cell Death1

Abstract

The quantitative photoreactivities in solution of Roussin's red salt (RRS, Na2[Fe2S2(NO)4]) and of Roussin's black salt (RBS, NH4[Fe4S3(NO)7]) are described. Photolysis of the red Roussinate anion Fe2S2(NO)42- in aerobic aqueous solution leads to quantitative formation of the black Roussinate anion Fe4S3(NO)7-. The quantum yield for disappearance of Fe2S2(NO)42- (ΦI = 0.14) is independent of excitation wavelength over a broad range (313−546 nm). Real time detection of nitric oxide by electrochemical sensors in the photolysis solution demonstrated the release of NO with a quantum yield of 0.07. The black Roussinate anion is much less photoactive (ΦII = 1.1 × 10-3) but does undergo photodecomposition in aerobic solution to give, eventually, ferric precipitates plus NO. These studies were initiated with the goal of developing photochemical strategies for delivering NO to biological targets on demand. In this context, the photolability of Fe2S2(NO)42- was examined as a possible candidate for exploiting the kn...