PHOTOCHEMISTRY OF ROUSSINS RED SALT, NA-2[FE2S2(NO)4], AND OF ROUSSINS BLACK SALT, NH4[FE4S3(NO)7] - IN-SITU NITRIC-OXIDE GENERATION TO SENSITIZE GAMMA-RADIATION INDUCED CELL-DEATH
J. Bourassa et al., PHOTOCHEMISTRY OF ROUSSINS RED SALT, NA-2[FE2S2(NO)4], AND OF ROUSSINS BLACK SALT, NH4[FE4S3(NO)7] - IN-SITU NITRIC-OXIDE GENERATION TO SENSITIZE GAMMA-RADIATION INDUCED CELL-DEATH, Journal of the American Chemical Society, 119(12), 1997, pp. 2853-2860
The quantitative photoreactivities in solution of Roussin's red salt (
RRS, Na-2[Fe2S2(NO)(4)]) and of Roussin's black salt (RES, NH4[Fe4S3(N
O)(7)]) are described; Photolysis of the red Roussinate anion Fe2S2(NO
)(4)(2-) in aerobic aqueous solution leads to quantitative formation o
f the black Roussinate anion Fe4S3(NO)(7)(-). The quantum yield for di
sappearance of Fe2S2(NO)(4)(2-) (Phi(I) = 0.14) is independent of exci
tation 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 blac
k Roussinate anion is much less photoactive (Phi(II) = L1 x 10(-3)) bu
t does undergo photodecomposition in aerobic solution to give, eventua
lly, ferric precipitates plus NO. These studies were initiated with th
e goal of developing photochemical strategies for delivering NO to bio
logical targets on demand. In this context, the photolability of Fe2S2
(NO)(4)(2-) was examined as a possible candidate for exploiting the kn
own nitric oxide sensitization of gamma-radiation induced cell killing
in V79 cell cultures (Mitchell, J. B.; et al. Cancer Res. 1993, 53, 5
845-5848). Hypoxic cell cultures treated with RRS solution (1.0 mM) an
d then subjected to gamma-radiation (15 Gy) demonstrated strikingly lo
wer survival rates when simultaneously exposed to white light irradiat
ion than did control systems treated identically but in the dark. The
black salt was similarly probed, but its greater toxicity and lower qu
antum yields for NO release make this a less likely candidate for such
photochemically induced radiation sensitization.