SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS–XII. SPIN TRAPPING STUDY OF THE FREE RADICALS GENERATED DURING THE PHOTOLYSIS OF PHOTO ALLERGENS BITHIONOL and FENTICHLOR

Free radicals were trapped and observed by ESR when photoallergens bithionol and fentichlor were irradiated in the presence of spin traps N- t -butyl-α-phenylnitrone (PBN) and 5,5-dimethyl-pyrroline-N-oxide (DMPO). In the absence of air, both PBN and DMPO trapped a carbon-centered radical. The carbon-centered radical, which was capable of abstracting a hydrogen atom from cysteine, glutathione, ethanol and formate, was identified as an aryl radical derived from the homolytic cleavage of the carbon-chlorine bond. In the presence of air, both carbon-centered radicals and hydroxyl radicals were trapped by DMPO. Under similar conditions, the yield of the hydroxyl radicals was greater from bithionol than from fentichlor. The presence of the hydroxyl radical was confirmed by kinetic experiments employing hydroxyl radical scavengers (ethanol, formate). Superoxide and H₂O₂ were not involved. Experiments with oxygen-¹⁷O indicated that the hydroxyl radicals came exclusively from dissolved oxygen. The precursor of the hydroxyl radical is postulated to be a peroxy intermediate (ArOO*) derived from the reaction of an aryl radical (Ar*) with molecular oxygen. Both bithionol and fentichlor photoionized only when excited in the UVC (<270 nm) region. Free radicals have long been postulated in the photodechlorination of bithionol and fentichlor and the present study provides supporting evidence for such a mechanism. Aryl and hydroxyl radicals are reactive chemical species which may trigger a series of events that culminate in photoallergy.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—X. A SPIN-TRAPPING AND DIRECT ELECTRON SPIN RESONANCE STUDY OF THE PHOTOCHEMICAL PATHWAYS OF DAUNOMYCIN AND ADRIAMYCIN

Abstract— Irradiation of daunomycin (or adriamycin) and the spin trap 5,5-dimethyl-l-pyrroline-1-oxide (DMPO) at 490 nm in the presence or in the absence of air generated the hydroxyl radical adduct (DMPO-OH). The observed DMPO-OH signal was not affected by the addition of hydroxyl radical scavengers (ethanol, formate), suggesting that direct trapping of the hydroxyl radical was not involved. The DMPO-OH signal was insensitive to superoxide dismutase and catalase, which ruled out the possibility of superoxide or H₂O₂ involvement. These findings demonstrate that daunomycin (or adriamycin) does not generate hydroxyl radicals or superoxide radical anions when subjected to 490-nm excitation. However, when daunomycin (or adriamycin) was irradiated at 310 nm DMPO adducts derived from two carbon-centered radicals, superoxide and the hydroxyl radical were detected. The superoxide adduct of DMPO was abolished by the addition of SOD, providing unequivocal evidence for the generation of the superoxide anion radical. The daunomycin semiquinone radical, observed upon 310-nm irradiation of daunomycin in the absence of DMPO, appears to be the precursor of the superoxide radical anion. One of the carbon-centered radicals trapped by DMPO exhibited a unique set of hyperfine parameters and was identified as an acyl radical. This suggests that the known photochemical deacylation of daunomycin occurs via a homolytic cleavage mechanism. The free radicals generated photolytically from adriamycin and daunomycin may be involved in the etiology of the skin ulceration and inflammation caused by these drugs. A knowledge of the dependence of these photogenerated radicals on the wavelength of excitation may be important in the development of adriamycin and daunomycin for photodynamic therapy.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—IX. A SPIN TRAPPING STUDY OF THE PHOTOLYSIS OF AMIODARONE AND DESETHYLAMIODARONE

The photolysis of amiodarone (AM) and its major metabolite mono-N-desethylamiodarone (DEA), has been studied by absorption spectroscopy, electron spin resonance spectroscopy (spin trapping) and oxygraph measurements. Changes in the absorption spectrum of both AM and DEA upon UV irradiation indicate that both drugs undergo deiodination. Spin trapping experiments with 2-methyl-2-nitrosopropane (MNP), α-phenyl-N- tert -butyl-nitrone (PBN) and 5.5-dimethyl-1-pyrroline-N-oxide (DMPO) suggest the formation of an aryl radical from AM during UV irradiation. Amiodarone also undergoes photoionization. Under aerobic conditions the photoelectron is scavenged by oxygen to give superoxide, which is trapped by DMPO. Oxygraph measurements further confirmed the consumption of oxygen and the generation of superoxide during the irradiation of aqueous solutions of AM. Deiodination, photoionization and superoxide formation were all observed at wavelengths as low as 335 nm, suggesting that some or all of these processes may be involved in AM-induced photosensitivity. The aryl radical derived from AM during UV irradiation abstracted a hydrogen atom from suitable donors (ethanol, glutathione, cysteine, linoleic acid). Reaction of the dienyl radical derived from linoleic acid would yield the corresponding peroxy radical thereby initiating lipid peroxidation. This would explain the deposition of lipofuscin, a pigment formed from the products of lipid peroxidation, in the skin of patients receiving AM.     

ULTRAVIOLET LIGHT-INDUCED FREE RADICAL FORMATION IN SKIN: AN ELECTRON PARAMAGNETIC RESONANCE STUDY

It has been suggested that ultraviolet light induces free radical formation in skin, leading to photoaging and cancer. We have demonstrated by electron paramagnetic resonance that the ascorbate free radical is naturally present in unexposed skin at a very low steady state level. When a section of SKH-1 hairless mouse skin in an EPR cavity is exposed to UV light (4,500 J m⁻²−1, Xe lamp, 305 nm cutoff and IR filters), the ascorbate free radical signal intensity increases. These results indicate that UV light increases free radical oxidative stress, consistent with ascorbate's role as the terminal, small-molecule antioxidant. The initial radicals produced by UV light would have very short lifetimes at room temperature; thus, we have applied EPR spin trapping techniques to detect these radicals. Using α-[4-pyridyl 1-oxide]-N- tert -butyl nitrone (POBN), we have for the first time spin trapped a UV light-produced carbon-centered free radical from intact skin. The EPR spectra exhibited hyperfine splittings that are characteristic of POBN/alkyl radicals, a^N= 15.56 G and a^H= 2.70 G, possibly generated from membrane lipids as a result of β-scission of lipid alkoxyl radicals. Iron can act as a catalyst for free radical oxidative reactions; chronic exposure of skin to UV radiation causes increased iron deposition. Using our spin trapping system, we have shown that topical application of the iron-chelator, Desferal, to a section of skin reduces the UV light-induced POBN adduct radical signal. These results provide direct evidence for free radical generation and a role for iron in UV light-induced dermatopathology. We suggest that iron chelators can serve as photoprotective agents by preventing these oxidations.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS-XIV. THE SPIN TRAPPING OF FREE RADICALS FORMED DURING THE PHOTOLYSIS OF HALOGENATED SALICYLANILIDE ANTIBACTERIAL AGENTS

Several antibacterial halogenated salicylanilides, including 3,3',4',5-tetrachlorosalicylanilide (TCSA) and 3,4',5-tribromosalicylanilide (TBSA) are known to cause photoallergy. We have carried out photochemical and spin trapping studies to determine whether free radicals may be involved in the photoallergic response. Irradiation (lambda greater than 300 nm) of TCSA in buffered (pH 7.4) 50% ethanol resulted in the rapid loss of the 3-chloro atom, followed by the much slower release of 5- and then the 4'-chloro atoms to give 3'-chlorosalicylanilide as a stable photoproduct. Under the same conditions TBSA successively lost the 3-, 5- and 4'-bromine atoms to give salicylanilide. When TCSA or TBSA were irradiated (lambda = 356 nm) in buffered (pH 7.4) 50% ethanol containing 2-methyl-2-nitrosopropane (MNP) only solvent-derived free radicals were detected. However, irradiation (lambda = 356 nm) of TCSA and MNP in 0.1 N NaOH generated an ESR spectrum consisting of a broad triplet (aN = 15.6 G). This spectrum was attributed to the adduct formed by the reaction of MNP with the aryl radical generated by the loss of a chlorine atom from the sterically hindered 3-(or 4'-)-position. Under the same conditions TBSA initially generated a broad triplet (aN = 15.5 G) similar to that observed for TCSA. However, upon further irradiation a 21-line spectrum (aN = 14.4 G, a2H = 2.0 G and a2H = 0.9 G) appeared.(ABSTRACT TRUNCATED AT 250 WORDS)     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS–VIII. A SPIN-TRAPPING STUDY OF LIGHT INDUCED FREE RADICALS FROM CHLORPROMAZINE and PROMAZINE

Abstract— The clinically important phenothiazine drugs, particularly chlorpromazine, often elicit phototoxic and photoallergic reactions. We have used the spin traps 2-methyl-2-nitrosopropane (MNP) and 5,5-dimethyl-pyrroline-N-oxide (DMPO) to define the radical photolysis pathways of chlorpromazine and promazine. In the absence of oxygen the dechlorination product of chlorpromazine is trapped by MNP. The reactivity of the dechlorination product is similar to that of the phenyl radical as shown by its ability to extract hydrogen atoms from donors. Our results suggest that the dechlorination product is sufficiently reactive to account for the observation that chlorpromazine is more phototoxic than its parent promazine. In the presence of oxygen both chlorpromazine and promazine form a superoxide-dismutase-insensitive oxygen-centered intermediate which, when trapped by DMPO, rapidly decays to DMPO-OOH and subsequently to DMPO-OH. In addition, chlorpromazine readily undergoes photoelectron ejection only when it is excited into the second excited singlet state (Δ < 280 nra). This previously unknown wavelength dependence of photoionization should be considered in establishing the mechanism of chlorpromazine photosensitization.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—IV. THE PHOTOLYSIS OF BENOXAPROFEN, AN ANTI-INFLAMMATORY DRUG WITH PHOTOTOXIC PROPERTIES

Abstract— Benoxaprofen [2-(4-chlorophenyl)-α-methyl-5-benzoxazole acetic acid] is an anti-inflammatory drug that causes acute phototoxicity in many patients. Photolysis studies in organic solvents (ethanol, benzene, dimethylsulfoxide) showed that benoxaprofen underwent both Type I and Type II reactions. Irradiation of an anerobic solution of benoxaprofen in ethanol resulted in hydrogen abstraction from the solvent to yield hydroxyethyl and ethoxyl radicals. In the presence of oxygen, superoxide, singlet oxygen and hydroxyethyl radicals were detected. Photolysis of benoxaprofen in air-saturated benzene or dimethylsulfoxide gave superoxide. However, under anerobic conditions the drug yielded a carbon-centered radical in benzene that could not be identified. These findings suggest that both oxygen-dependent and oxygen-independent processes may be important in the phototoxic reactions of benoxaprofen.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—XL PHOTOLYSIS OF CHLORPROMAZINE METABOLITES: A SPIN-TRAPPING STUDY

Abstract. The photochemistry of chlorpromazine (CPZ) and its metabolites, 7-hydroxychlorpromazine (7OHCPZ), desmethylchlorpromazine (DCPZ), didesmethylchlorpromazine (DDCPZ) and chlorpromazine sulfoxide (CPZSO) was studied by the spin trapping technique with 2-methyl-2-nitrosopropane and 5,5-dimethyl-l-pyrroline- N -oxide. 7-Hydroxychlorpromazine generated hydroxyl radicals when excited at 330 nm under either anaerobic or aerobic conditions. 7-Hydroxychlorpromazine, DCPZ and DDCPZ all underwent dechlorination upon photoexcitation which was enhanced in the absence of air. Chlorpromazine sulfoxide did not undergo photodechlorination but instead generated a high yield of the hydroxyl radical. A comparison among CPZ and its derivatives shows that the yield of the photodechlorinated product is directly related to the degree of phototoxicity. This suggests photodechlorination is an important factor in the phototoxicity of CPZ and its metabolites.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—VI. IDENTIFICATION OF THE FREE RADICALS GENERATED DURING THE PHOTOLYSIS OF MUSK AMBRETTE, MUSK XYLENE AND MUSK KETONE

Musk ambrette (4-tert-butyl-3-methoxy-2,5-dinitrotoluene), a common component of perfumes, soaps, and some food flavorings, can cause cutaneous photosensitization reactions including photoallergy. These may be mediated through free radicals formed during photolysis. When musk ambrette was photolyzed under nitrogen in basic methanol, two distinct nitro anion radicals were identified by electron spin resonance. One radical was centered on a nitro group in the plane of the aromatic ring, while the other was centered on a nitro group twisted out of the plane of the ring due to steric hindrance by bulky substituents on either side of the group: the two radicals appeared to interconvert and maintain an equilibrium concentration ratio. Two closely related compounds which are also used in perfumes, but have not been reported to cause photosensitizing reactions, also produced free radicals during photolysis. Musk xylene (2,4,6-trinitro-1,3-dimethyl-5-tert-butylbenzene) generated two nitro anion radicals, both of which were centered on twisted nitro groups, while musk ketone (3,5-dinitro-2,6-dimethyl-4-tert-butylacetophenone) produced only one nitro anion radical, which is also twisted. Athough these nitro anion radicals are probably the first step in the photolysis of these nitroarornatic molecules, it seems likely that in vivo they will undergo further reduction to produce more reactive species including the corresponding nitroso and hydroxylamine derivatives. In addition, autoxidation of the nitro anion radical intermediate forms superoxide.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—XL PHOTOLYSIS OF CHLORPROMAZINE METABOLITES: A SPIN-TRAPPING STUDY

Abstract. The photochemistry of chlorpromazine (CPZ) and its metabolites, 7-hydroxychlorpromazine (7OHCPZ), desmethylchlorpromazine (DCPZ), didesmethylchlorpromazine (DDCPZ) and chlorpromazine sulfoxide (CPZSO) was studied by the spin trapping technique with 2-methyl-2-nitrosopropane and 5,5-dimethyl-l-pyrroline-N-oxide. 7-Hydroxychlorpromazine generated hydroxyl radicals when excited at 330 nm under either anaerobic or aerobic conditions. 7-Hydroxychlorpromazine, DCPZ and DDCPZ all underwent dechlorination upon photoexcitation which was enhanced in the absence of air. Chlorpromazine sulfoxide did not undergo photodechlorination but instead generated a high yield of the hydroxyl radical. A comparison among CPZ and its derivatives shows that the yield of the photodechlorinated product is directly related to the degree of phototoxicity. This suggests photodechlorination is an important factor in the phototoxicity of CPZ and its metabolites.     

PHOTOSENSITIZATION OF MELANIN: AN ELECTRON SPIN RESONANCE STUDY OF SENSITIZED RADICAL PRODUCTION AND OXYGEN CONSUMPTION

Abstract Rose Bengal is shown to photosensitize free-radical production and oxygen consumption in solutions of melanin from autooxidation of 3,4-dihydroxyphenylalanine (DOPA). In anaerobic solutions the sensitizer enhances rates of free-radical production by up to a factor of 20. In aerobic solutions, rates of oxygen consumption can be increased by a factor of several hundred. The reactions appear to involve the triplet state of the sensitizer. The effect of the sensitizer in increasing oxygen consumption is quenched by low concentrations of azide and enhanced by D₂O, suggesting that a singlet oxygen mechanism is involved.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—I. SPIN TRAPPING OF PHOTOLYSIS PRODUCTS FROM SULFANILAMIDE, 4-AMINOBENZOIC ACID AND RELATED COMPOUNDS

The photodecomposition of sulfanilamide, 4-aminobenzoic acid and other related analogs has been studied with the aid of the spin trap 2-methyl-2-nitrosopropane. UV photolysis of an aqueous solution of sulfanilamide yielded the following radicals C˙₆H₄SO₂NH₂, C₆H₅SO_2˙, S˙O₂NH₂ and SO^-_#˙ (or SO^-_2dot;). Under the same conditions 4-aminobenzoic acid gave C˙₆H₄COOH. In addition both sulfanilamide and 4-aminobenzoic acid, but not 4-dimethylaminobenzoic acid, generated e^-_aq or hydrogen atoms during UV irradiation. The C₆H₄SO₂NH₂ radical was also produced by photolysis of 4-iodobenzenesul-fonamide and 4-nitrobenzenesulfonamide. The C₆H₄COOH radical was generated by photolysis of 4-nitrobenzoic acid and 4-iodobenzoic acid. Finally the C₆H₄NO₂ radical was formed during the irradiation of 4-nitroaniline, 1,4-dinitrobenzene and 4-iodonitrobenzene. The free radicals generated by sulfanilamide and 4-aminobenzoic acid may play an important role in the phototoxic and photoallergic responses elicited by these drugs in certain individuals.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—II. SPIN TRAPPING OF PHOTOLYSIS PRODUCTS FROM SULFANILAMIDE AND 4-AMINOBENZOIC ACID USING 5,5-DIMETHYL-1-PYRROLINE-1-OXIDE

Abstract— The photodecomposition of sulfanilamide, 4-aminobenzoic acid and related analogs in aqueous solution has been studied with the aid of spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and CH₃NO₂ as well as by direct electron spin resonance techniques. The NH₂ radical was trapped by DMPO during the photolysis of aqueous solutions of sulfanilamide with a Xe arc lamp. Studies with [¹⁵N¹]-sulfanilamide indicated that the NH₂ radical was generated by homolytic fission of the sulfur-nitrogen bond. Under the same conditions DMPO trapped the H and SO⁻₃ radicals during photolysis of sulfanic acid. Direct photolysis of sulfanilamide, sulfanilic acid and Na₂SO₃ in the absence of any spin trap yielded the SO⁻³ radical. Photolysis of 4-aminobenzoic acid at pH 7 gave the H radical which was trapped by DMPO. At low pH values OH and C₆H₄COOH radicals were generated during the photolysis of 4-aminobenzoic acid. No e⁻_aq were trapped by CH₃NO₂ when acid (pH 4) and neutral aqueous solutions of sulfanilamide or 4-aminobenzoic acid were photoirradiated. The mechanism of formation of known photoproducts from the free radicals generated by sulfanilamide and 4-aminobenzoic acid during irradiation are discussed. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects.     

乙烯系单体自由基聚合的阻聚效应──XIX．取代哌啶羟胺和二叔丁基羟胺及其稳定自由基对苯乙烯－丙烯腈共聚合的影响

研究了二叔丁基羟胺（ＤＴＢＨＡ），二叔丁基氮氧自由基（ＤＴＢＮＯ·），２，２，６，６－四甲基－４－羟基哌啶羟胺（ＴＭＨＰＨＡ）和２，２，６，６－四甲基－４－羟基哌啶－１－氧自由基（ＴＭＨＰＯ·）对过氧化苯甲酰（ＢＰＯ）６０℃引发的苯乙烯（Ｍ１）－丙烯腈（Ｍ２）共聚合的阻聚行为．结果表明，这些阻聚剂对Ｓｔ－ＡＮ共聚均表现良好的阻聚行为，其中氮氧自由基优于相应羟胺．同时观察到Ｓｔ—ＡＮ竞聚率的改变，羟胺使ｒ１有所降低，ｒ２略有增大．但相应的氮氧自由基是相反结果．阻聚剂为２００ｐｐｍ时，共聚物中的恒比共聚点由对照实验的０．６１９变化为０．５３３，０．６４５，０．５８９和０．６９８相对于ＤＴＢＨＡ，ＤＴＢＮＯ·，ＴＭＨＰＨＡ和ＴＭＨＰＯ·．     

乙烯系单体自由基聚合的阻聚效应──XIX．取代哌啶羟胺和二叔丁基羟胺及其稳定自由基对苯乙烯－丙烯腈共聚合的影响

研究了二叔丁基羟胺（ＤＴＢＨＡ），二叔丁基氮氧自由基（ＤＴＢＮＯ），２，２，６，６－四甲基－４－羟基哌啶羟胺（ＴＭＨＰＨＡ）和２，２，６，６－四甲基－４－羟基哌啶－１－氧自由基（ＴＭＨＰＯ）对过氧化苯甲酰（ＢＰＯ）６０℃引发的苯乙烯（Ｍ１）－丙烯腈（Ｍ２）共聚合的阻聚物行为。结果表明，这些阻聚剂对Ｓｔ－ＡＮ共聚均表现良好的阻聚行为，其中氮氧自由基优于相应羟胺。同时观察到Ｓｔ－ＡＮ竞聚率的改变，羟胺     

TRAPPING OF NITRIC OXIDE FORMED DURING PHOTOLYSIS OF SODIUM NITROPRUSSIDE IN AQUEOUS AND LIPID PHASES: AN ELECTRON SPIN RESONANCE STUDY

Abstract— Photolytic decomposition of sodium nitroprusside (SNP), a widely used nitrovasodilator, produced nitric oxide (NO), which was continuously monitored by electron spin resonance (ESR) spectroscopy. The NO present in the aqueous or the lipid phase was trapped by either a hydrophilic or a hydrophobic nitronyl nitroxide, respectively, to form the corresponding imino nitroxide. The conversion of nitronyl nitroxide to imino nitroxide was monitored by ESR spectrometry. The quantum yield for the generation of NO from SNP, measured from the rate of decay of nitronyl nitroxide, was 0.201 ± 0.007 and 0.324 ± 0.01 (¯± SD, n = 3) at 420 nm and 320 nm, respectively. The action spectrum for NO generation was found to overlap the optical absorption spectrum of SNP closely. A mechanism for the reaction between SNP and nitronyl nitroxide in the presence of light is proposed and computer-aided simulation of this mechanism using published rate constants agreed well with experimental data. The methodology described here may be used to assay NO production continuously during photoactivation of NO donors in aqueous and lipid environments. Biological implications of this methodology are discussed.     

PHOTOCHEMISTRY OF AQUEOUS ADRIAMYCIN AND DAUNOMYCIN. A SPIN TRAPPING STUDY WITH 17O ENRICHED OXYGEN AND WATER

Abstract— Photolyses at 485 or 490 nm of air saturated, H₂^I7O enriched, aqueous solutions of adriamycin (ADR) in the presence of 5,5-dimethyl-l-pyrroline-l-oxide (DMPO) produce a mixture of hydroxyl radical spin-adducts, i.e. DMPO-¹⁶OH- and DMPO-¹⁷OH-, as detected by electron spin resonance (ESR). DMPO-¹⁷OH- was also observed during the irradiation at these same wavelengths of aqueous solutions of ADR or daunomycin (DA) containing DMPO and ¹⁷O enriched oxygen. Therefore, the observed hydroxyl radical spin-adducts derive from both water and gaseous oxygen. It is concluded from the measured relative spin-adduct concentrations and from the enrichment fractions that most of the DMPO-OH adducts originate from water. However, if anaerobic diluted solutions of ADR (200 μ M ) or DA (600 μM) in the presence of DMPO (13 mM and 27 m M respectively) are irradiated at these same wavelengths no spin adduct is detected, indicating that oxygen is needed for the adduct formation, at these drug and spin trap concentrations. DMPO-OH- is always observed if relatively high concentrations of either the drug (1.1–2.9 mM) or the spin trap(100–150 m M ) are used in argon saturated solutions. A water photooxidation mediated mechanism is proposed in order to account for these results, analogous to previous observations in the photochemistry of other water soluble anthraquinone derivatives.     

PHOTOSENSITIZATION BY ANTITUMORAGENTS–6. PRODUCTION OF SUPEROXIDE RADICAL AND HYDROGEN PEROXIDE DURING ILLUMINATION OF DIAMINOANTHRACENEDIONES IN THE PRESENCE OF NADH IN AQUEOUS SOLUTIONS: AN EPR STUDY

Abstract— Photosensitizing capabilities of anthracenedione anticancer agents to oxidize NADH in aqueous solutions have been studied by EPR and spin trapping techniques. It is demonstrated that 1,4-diamino substituted anthraquinones, like mitoxantrone and ametantrone, do not photosensitize NADH oxidation while 1,5- and l,8-bis[[(diethylamino)ethyl]amino]anthraquinones do, undergoing simultaneous one-electron reduction to their semiquinone radical forms upon illumination with visible light. In aerated aqueous solutions the reaction leads to the production of superoxide ion and hydrogen peroxide.