Photolysis of the pentacyanonitrosylferrate (II) ion in sodium nitroprusside (SNP) solutions involves a competition between photosubstitution and photo-oxidation reactions, where the nitrosyl and cyanide ligands can be released as free nitric oxide (NO) or NO+ and free CN- or CN radical. We have irradiated aqueous SNP solutions at several narrow wavelength ranges in the UV/Vis region (314-576 nm), with the aim of investigating the photolability of the CN and NO ligands. Kinetics of photolysis were used to characterize the photosensitivity of SNP solutions in the range 314-576 nm. Spectral changes in the UV/Vis and IR regions upon irradiation and assays for the detection of free CN- and NO, provided additional evidences for the absence of photoprocesses leading to the release of CN- with λirr > 480 nm. In this condition, the main photoproducts were found to be the [FeIII(CN)5(H2O)]2- ion and NO, formed in a intramolecular photo-oxidative process. Irradiation with unfiltered UV/Vis light and with λirr < 480 nm, lead to the release of both CN- and NO and to a mixture of ferrocyanide and ferricyanide products. These results confirm that the exposure of SNP solutions to UV/Vis light below λirr = 480 nm can lead to cyanide poisoning and further support that above this wavelength limit, a selective NO release from SNP can be achieved, with possible implications for its biochemical action.262-3239261Ignarro, L.J., Buga, G.M., Wood, K.S., Byrns, R.E., Chaudhuri, G., Endothelium-derived relaxing factor produced and released from artery and vein is nitric oxide (1987) Proc. Natl. Acad. Sci. U.S.A., 84 (24), pp. 9265-9269Williams, R.J.P., Nitric oxide in biology: Its role as a ligand (1996) Chem. Soc. Rev., 25 (2), pp. 77-83Stamler, J.S., Singel, D.J., Loscalzo, J., Biochemistry of Nitric Oxide and Its Redox-Activated Forms (1992) Science, 258 (5090), pp. 1898-1902Lipton, S.A., Choi, Y.B., Pan, A.H., Lei, S.Z., Chen, H.S.V., Sucher, N.J., Loscalzo, J., Stamler, J.S., A redox-based mechanism for the neuroprotective and neurodestructive effects of nitric oxide and related nitroso-compounds (1993) Nature, 364 (6438), pp. 626-632Lancaster Jr., J., (1996) Nitric Oxide - Principles and Action, , Academic Press, New YorkBrown, G.C., Nitric oxide inhibition of cytochrome oxidase and mitochondrial respiration: Implications for inflammatory, neurodegenerative and ischaemic pathologies (1997) Mol. Cell. Biochem., 174 (1-2), pp. 189-192Albina, J.E., Reichner, J.S., Role of nitric oxide in mediation of macrophage cytotoxicity and apoptosis (1998) Cancer Metast. Rev., 17 (1), pp. 39-53Tamir, S., Butney, S., Tannenbaum, S.R., DNA damage by nitric oxide (1996) Chem. Res. Toxicol., 9 (5), pp. 821-827Singh, R.J., Hogg, N., Kalyanaraman, B., Photosensitized decomposition of S-nitrosothiols and 2-methyl-2-nitrosopropane. Possible use for side-directed nitric oxide production (1995) FEBS Letters, 360 (1), pp. 47-51Pou, S., Anderson, D.E., Surichamorn, W., Keaton, L.L., Tod, M.L., Biological studies of a nitroso compound that releases nitric oxide upon ilumination (1994) Mol. Pharmacol., 46 (4), pp. 709-715Shishido, S.M., De Oliveira, M.G., Polyethylene glycol matrix reduces the rates of photochemical and thermal release of nitric oxide from S-nitroso-N-acetylcysteine (2000) Photochem. Photobiol., 71 (3), pp. 273-280Butler, A.R., Glidewell, C., Recent chemical studies of sodium nitroprusside relevant to its hypotensive action (1987) Chem. Soc. Rev., 16 (4), pp. 361-380Feelisch, M., Noack, E., Nitric oxide (NO) formation from nitrovasodilators occurs independently of hemoglobin or non-heme iron (1987) Eur. J. Pharmacol., 142 (3), pp. 465-469Bates, J.M., Baker, M.T., Guerra Jr., R., Hanison, D.G., Nitric oxide generation from nitroprusside by vascular tissue (1991) Biochem. Pharmacol., 42 SUPPL, pp. 5157-5165Oszajca, J., Stochel, G., Wasielewska, W., Stasicka, Z., Gryglewski, R.J., Jakobowski, A., Cieslik, K., Cyanonitrosylmetallates as potential NO-donors (1998) J. Inorg. Biochem., 69 (1-2), pp. 121-127Campbell, J.M., McCrae, E., Reglinski, J., Wilson, R., Smith, W.E., Sturrock, R.D., The interaction of sodium-nitroprusside with peripheral white blood-cells in vitro-a rationale for cyanide release in vivo (1993) Biochem. Biophys. Acta, 1156 (3), pp. 327-333Brune, B., Hanstein, K., Rapid reversibility of nitric oxide induced platelet inhibition (1998) Thromb. Res., 90 (2), pp. 83-91Ruan, R.S., Leong, S.K., Yeoh, K.H., Ototoxicity of sodium nitroprusside is not due to nitric oxide (1999) Exp. Neurol., 158 (1), pp. 192-201Boullerne, A.I., Nedelkoska, L., Benjamins, J.A., Synergism of nitric oxide and iron in killing the transformed murine oligodendrocyte cell line N20.1 (1999) J. Neurochem., 72 (3), pp. 1050-1060Rauhala, R., Khaldi, A., Mohanakumar, K.P., Chiueh, C.C., Apparent role of hydroxyl radicals in oxidative brain injury induced by sodium nitroprusside (1998) Free Radical Bio. Med., 24 (7-8), pp. 1065-1073Mitra, R.P., Jain, D.V.S., Barerjee, A.K., Chari, K.V.R., Photolysis of sodium nitroprusside and nitroprussic acid (1963) J. Inorg. Nucl. Chem., 25, pp. 1263-1266Buxton, G.V., Sainton, F.S., Kalecinski, J., The radiation chemistry of aqueous solutions of sodium nitroprusside (1969) Int. J. Radiat. Phys. Chem., 1, pp. 87-98Wolfe, S.K., Swinehart, J.H., Photochemistry of pentacyanonitrosylferrate(2-), nitroprusside (1975) Inorg. Chem., 14 (5), pp. 1049-1053Bisset, W.I.K., Burdon, M.G., Butler, A.R., Glidewell, C., Reglinski, J., Photochemistry of the nitroprusside ion and the consequences for the detection of cyanide in mixtures of nitroprusside and blood: Use of sodium nitroprusside as a hypotensive agent (1981) J. Chem. Research (S), 299 (10), pp. 3501-3509Symons, M.C.R., Wilkinson, J.G., West, D., Low-temperature ultra violet photolysis of various glasses of the pentacyanonitrosylferrate (II) ion, [Fe(CN)5(NO)]2- (1982) J. Chem. Soc. Dalton Trans., (10), pp. 2041-2045Stochel, G., Van Eldik, R., Stasicka, Z., Mechanistic information from medium and high-pressure effects on the photooxidation of nitrosylpentacyanoferrate (II) (1986) Inorg. Chem., 25 (20), pp. 3663-3666De Oliveira, M.G., Langley, G.J., Rest, J., Photolysis of the [Fe(CN)5(NO)]2- ion in water and Poly(vinyl alchohol) films - Evidence for cyano radical, cyanide ion and nitric oxide loss and redox pathways (1995) J. Chem. Soc. Dalton. Trans., (12), pp. 2013-2019Garcia-Pascual, A., Costa, G., Labadia, A., Jimenez, E., Triguero, D., Differential mechanisms of urethral smooth muscle relaxation by several NO donors and nitric oxide (1999) Naunyn-Schmiedebergs Archives of Pharmacology, 360 (1), pp. 80-91Triguero, D., Costa, G., Labadia, A., Jimenez, E., Garcia-Pascual, A., Spontaneous photo-relaxation of urethral smooth muscle from sheep, pig and rat and its relationship with nitrergic neurotransmission (2000) J. Physiol. London, 522 (3), pp. 443-1156Zhelyaskov, V.R., Godwin, D.W., Photolytic generation of nitric oxide through a porous glass partitioning membrane (1998) Nitric Oxide-Biol. and Chem., 2 (6), pp. 454-459Zhelyaskov, V.R., Godwin, D.W., A nitric oxide concentration clamp (1999) Nitric Oxide-Biol. and Chem., 3 (5), pp. 419-425Davies, D.W., Kadar, W.D., Steward, D.J., Munro, I.R., Sudden-death associated with use of sodium nitroprusside for induction of hypotension during anesthesia (1975) Can. Anesth. Soc. J., 22 (5), pp. 547-552Merrifield, A.J., Blundell, M.D., Toxicity of sodium nitroprusside (1974) British J. Anaesthesia, 46 (4), pp. 324-324Jack, R.D., Toxicity of sodium nitroprusside (1974) British J. Anaesthesia, 46 (12), pp. 952-952Manoharan, P.T., Gray, H.B., Electronic structures of metal pentacyanonitrosyls (1966) Inorg. Chem., 5, pp. 823-839Kudo, S., Bourassa, J.L., Boggs, S.E., Sato, Y., Ford, P., In situ nitric oxide (NO) measurement by modified electrodes: NO labilized by photolysis of metal nitrosyl complexes (1997) Anal. Biochem., 247 (2), pp. 193-202Otha, K., Rosner, G., Graf, R., Nitric oxide generation from sodium nitroprusside and hydroxylamine in brain (1997) Neuroreport., 8 (9-10), pp. 2229-2235Stochel, G., Wanat, A., Kulis, E., Stasika, Z., Light and metal complexes in medicine (1998) Coord. Chem. Rev., 171, pp. 203-220Espenson, J.H., Wolenuk Jr., S.G., Kinetics and mechanisms of some substitution reactions of pentacyanoferrate (III) complexes (1972) Inorg. Chem., 11, pp. 2034-2041Stochel, G., Stasika, Z., Solvent complexes of the type [FeIII(CN)5L]n- (1985) Polyhedron., 4 (3), pp. 481-484Stochel, G., High-pressure mechanistic studies on the thermal and photochemical reactions of pentacyanoferrate complexes (1992) Coord. Chem. Rev., 114 (2), pp. 269-295Stochel, G., Stasicka, Z., Photoredox chemistry of nitrosylpenlacyanoferrate(II) in methanolic medium (1985) Polyhedron, 4 (11), pp. 1887-1890Robin, M.B., The color and electronic configurations of Prussian Blue (1962) Inorg. Chem., 1, pp. 3307-3342Itaya, K., Tatsuaki, A., Toshima, S., Spectroelectrochemistry and electrochemical preparation method of Prussian Blue modified electrodes (1982) J. Am. Chem. Soc., 104 (18), pp. 4767-4772Ellis, D., Eckhoff, M., Neff, V.D., Electrochromism in the mixed-valence hexacyanides. 1. Voltametric and spectral studies of the oxidation and reduction of thin films of Prussian Blue (1981) J. Phys. Chem.-US, 85 (9), pp. 1225-1231Reguera, E., Fernández-Bertran, J., Gómes, A., Synthesis and characterization of ferric nitroprusside (1994) Eur. J. Solid State Inorg. Chem., 31 (11), pp. 979-984Fernández-Bertran, J., Reguera, E., The CN stretch of insoluble metal nitroprussides as a sensor of ligand-outer cation interactions (1995) Spectrosc. Lett., 28 (7), pp. 1015-1020Doyle, M.P., Hoekstra, J.W., Oxidation of nitrogen oxides by bound dioxigen in hemoproteins (1981) J. Inorg. Biochem., 14 (4), pp. 351-358Wink, D.A., Feelisch, N., Fukoto, J., Christodoulou, D., Jord'heuil, D., Grisham, M.B., Vodovotz, Y., Mitchell, J.B., The cytotoxicity of nitroxyl: Possible implications for the patophysiological role of NO (1998) Arch. Biochem. Biophys., 351 (1), pp. 66-74Feelisch, N., Noack, E.A., Correlation between nitric oxide formation during degradation of organic nitrates and activation of guanylate cyclase (1987) Eur. J. Pharmacol., 139 (1), pp. 19-30Watt, D.G., Christensen, J.J., Izatt, R.M., Thermodynamics of metal cyanide coordination. G°, H°, and S° values for ferrocyanide and ferricyanide ion formation in aqueous solution at 25° (1965) Inorg. Chem., 4, pp. 220-222MacDiarmid, A.G., Hall, N.F., Complex cyanide-simple cyanide exchange systems (1954) J. Am. Chem. Soc., 76, pp. 4222-4228