Dual-Targeting into the Mitochondria of Cancer Cells for Ratiometric Investigation of the Dynamic Fluctuation of Sulfur Dioxide and Formaldehyde with Two-Photon Integrated Semiconducting Polymer Dots

Mitochondrial sulfur dioxide (SO₂) and formaldehyde (FA) in cancer cells serve as important signal molecules in mediating multiple physiological and pathological activities. Accurate monitoring of the dynamic fluctuation of SO₂ and FA in the mitochondria of cancer cells is important for insight into their relationships and functions in cancer, understanding cancer mechanism, and the role of mitochondrial homeostasis in cancer invasion and metastasis. Herein, a novel integrated two-photon semiconducting polymer dot (BF@Pdots) with dual-targeting (cancer cells and mitochondrial) and dual-emission in green and red regions, which is rationally designed through a four-step engineering strategy by using two newly synthesized functionalized polymers PFNA and FD-PSMA as precursors, has been developed for accurate tracking of the dynamic variation of SO₂ and FA in the mitochondria of cancer cells. The sensing mechanism is on the basis of the fluorescence resonance energy transfer (FRET) process in BF@Pdots tuned by the reversible Michael addition reaction between the sensing-groups and SO₂ (or FA). The integrated BF@Pdots nanoprobes display excellent performances in the accurate detection of the dynamic fluctuation of SO₂ and FA such as precise positioning in the mitochondria of cancer cells, self-calibrating ratiometric, two-photon emission with long wavelength excitation, and fast reversible response. The BF@Pdots nanoprobes are also applied to the ratiometric detection of the dynamic fluctuation of exogenous and endogenous SO₂ and FA in the mitochondria of cancer cells for the first time with satisfactory results. Taken together, this work will provide an attractive way to develop versatile integrated Pdots-based fluorescent probes through flexible molecular engineering for applications in accurate imaging of biomolecules in living systems.

Fluorene oxidation by solar-driven photo-Fenton process: toward mild pH conditions

Polycyclic aromatic hydrocarbons (PAHs) are on the list of priority pollutants to be eliminated from the environment due to their carcinogenic and mutagenic action, chemical stability, and resistance to biodegradation. The aim of this study was to evaluate the degradation of fluorene, a well-known PAH, in aqueous solutions (0.03 and 0.08 mg L^-1), by means of a solar-driven conventional (PF) and modified photo-Fenton mediated by ferrioxalate complexes (PFF). Photolysis was also employed for comparison purposes. PF reaction was evaluated at different pH values (2.8, 3.5, and 4.0) and iron concentrations (2, 5, 10, and 20 mg L^-1). On the other hand, PFF studies were conducted at mild pH conditions (4.0, 5.0, and 6.0) and iron content of 2 mg L^-1, keeping initial iron/oxalate molar ratio at 1:3. In both PF and PFF, the initial hydrogen peroxide/iron molar ratio was maintained at 5. In the presence of methanol as cosolvent for fluorene dissolution, the PF reaction was hampered and no consumption of H₂O₂ was observed during the reaction carried out at constant pH (2.8). This led to low degradation rates, similar to those achieved by photolysis. Under the same pH but using acetonitrile as cosolvent for fluorene dissolution, fluorene degradation was found to be proportional to the iron content used in the PF experiments. On the other hand, at an invariable iron concentration of 5 mg Fe²⁺ L^-1, the increase in pH was accompanied by a decrease in the molar fraction of the most photoactive iron complex (FeOH²⁺) and ferric hydroxides precipitation, leading to a reduction in the fluorene degradation rate. With regard to the PFF tests, similar fluorene degradation performance was achieved at pH 4 and 5, while at pH 6 iron precipitation became relevant and the degradation rate was slightly slower. PFF has shown to be more efficient than the PF under the same pH (4) and iron concentration (2 mg L^-1). Moreover, even at near neutral pH (6), fluorine degradation was shown to be feasible by using ferrioxalate complexes.

Photomodified fluoranthene exerts more harmful effects as compared to intact fluoranthene by inhibiting growth and photosynthetic processes in wheat

Polycyclic aromatic hydrocarbons (PAHs) are toxic to plants. Exposure of PAHs to sunlight can result in the formation of photomodified PAHs, which are generally more toxic than the parent compounds. In the present study, biochemical and physiological effects of intact fluoranthene (FLT) and photomodified FLT (P.FLT) in wheat were investigated. Our results demonstrated that the treatment of FLT and P.FLT, inhibited germination, seedling growth and pigment content. However, inhibition observed on primary photochemistry and photosystem II heterogeneity was more prominent in P.FLT treated plants. Both FLT and P.FLT affected the levels of antioxidant enzymes such as POD, SOD, CAT and GR to similar extent. Greater inhibitory effects of P.FLT than FLT may be ascribed to its effects on growth parameters and photochemistry rather than on the activities of various antioxidant enzymes.

Energy transfer processes along a supramolecular chain of π-conjugated molecules

We have investigated the energy transfer dynamics in a supramolecular linear polymer chain comprising oligofluorene (OF) energy donor units linked by quadruple hydrogen-bonding groups, and oligophenylene (OPV) chain ends that act as energy acceptors. Using femtosecond spectroscopy, we followed the dynamics of energy transfer from the main chain of OF units to the OPV chain ends and simulated these data taking a Monte Carlo approach that included different extents of electronic wave function delocalization for the energy donor and acceptor. Best correlations between experimental and theoretical results were obtained for the assumption of electronic coupling occurring between a localized donor dipole moment and a delocalized acceptor moment. These findings emphasize that geometric relaxation following initial excitation of the donor needs to be taken into account, as it leads to a localization of the donor's excited state wave function prior to energy transfer. In addition, our simulations show that the energy transfer from the main chain to the ends is dominated by an interplay between slow and spatially limited exciton migration along the OF segments comprising the main chain and the comparatively faster hetero-transfer to the end-cap acceptors from directly adjoining OF segments. These results clearly support the description of host-guest energy transfer in linear polymer chains as a two-step mechanism with exciton diffusion in the host being a prerequisite to energy transfer to the guest.

Photo-controllable aptamer

We have successfully developed a new method for photoregulation of G-quadruplex formation using cis-trans photoisomerization of the photochromic nucleobase (8FV)G. Our photo-controllable quadruplexes can be switched between a very stable quadruplex state and a non-structured state in a straightforward and reversible fashion. We also demonstrated reversibly control binding of a G-quadruplex aptamer to thrombin.

Protective effects of antioxidants on micronuclei induced by irradiated 9-fluorenone/N,N-dimethyl-p-toluidine in CHO cells

9-Fluorenone (9F), the aromatic photosensitizer, is widely used as an initiator in visible-light (VL) cured resin systems. There is growing concern that 9F may produce genetic damage by inducing mutation. In this study, 9F in the presence or absence of reducing agent N,N-dimethyl-p-toluidine (DMT) with or without VL irradiation was analyzed for the induction of chromosomal aberrations indicated by micronuclei (MN) induced in CHO cells. Our data demonstrated that a dose-related increase in the frequency of MN and prolonged cell cycles in 9F with or without DMT in the presence or absence of VL irradiation (p < 0.05). The rank orders with respect to genotoxicity and cytotoxicity were found to be as follows: 9F/DMT +VL > 9F/DMT = 9F + VL > 9F. To determine whether oxidative stress could modulate MN induced by 9F/DMT with or without VL irradiation in CHO cells, cells were pretreated with N-acetyl-L-cysteine (NAC), ascorbic acid, and alpha-tocopherol. The pretreatment with antioxidants could diminish not only the prolonged cell cycle but also the decreased frequency of MN which is induced by 9F with or without DMT in the presence or absence of VL irradiation in CHO cells (p < 0.05). Our findings provide the evidences for the induction of MN by 9F in the presence or absence of DMT with or without VL irradiation in CHO cells, indicating clastogenic activity of 9F/DMT in vitro. These antioxidants act as the antagonists against the genotoxicity and cytotoxicity of 9F/DMT. Thus, leaching photoinitiator and reducing agent might be contributing the sources of oxidative stress.

Photocatalysis of fluorene adsorbed onto TiO2

The adsorption of fluorene onto TiO2 has been investigated by conducting equilibrium and kinetic experiments. Adsorption isotherms have been evaluated at two different pHs in the range of temperatures 296-325 K. The type III isotherm shapes obtained were modelled by considering several expressions taken from the literature. Temperature exerted a positive influence in fluorene uptake. Addition of phosphates involved a negative effect when computing the final equilibrium fluorene removal. The kinetic experiments carried out at 296 K corroborated the competitiveness of phosphates to occupy the active sites on the titania surface. Nevertheless, equilibrium conditions are faster achieved at pH 2 than at pH 5. The photocatalysis of fluorene at different initial concentrations of the parent compound revealed a slight improvement of the process at pH 5 if compared to the results obtained at pH 2. A Langmuir-Hinselwood representation of the data confirms the previous statement. Catalyst load shows an optimum, concentration values of the photocatalyst above the optimum provoke a decrease in the fluorene abatement rate. Reutilisation of the catalyst indicates that fluorene is completely eliminated from the solid, i.e. it is suggested that fluorene and intermediates are surface oxidised.

Photoinduced intermolecular electron transfer process of fullerene (C60) and amine-substituted fluorenes studied by laser flash photolysis

Photoinduced intermolecular electron transfer process of fullerene (C60) with 9,9-bis(4-triphenylamino)fluorene (BTAF) and 9,9-dimethoxyethyl-2-diphenylaminofluorene (DAF) in toluene and benzonitrile has been investigated by nanosecond laser photolysis technique in the visible/near-IR regions. By the selective excitation of C60 using 532 laser light, it has been proved that the electron transfer takes place from the ground states BTAF and DAF to the triplet excited state of C60 ((3)C60*) by observing the radical anion of C60 and radical cation of BTAF and DAF. It was observed that the electron transfer of BTAF/(3)C60* is more efficient than DAF/(3)C60* reflecting the effect of amine-substitutents of the fluorene moiety on the efficiency of the electron transfer process. On addition of a viologen dication (OV(2+)), the electron of the anion radical of C60 mediates to OV(2+) yielding the OV(+). These results proved that the photosensitized electron-transfer/electron-mediating processes have been confirmed by the transient absorption spectral method.

Aqueous photodegradation and toxicity of the polycyclic aromatic hydrocarbons fluorene, dibenzofuran, and dibenzothiophene

Decay kinetics resulting from the application of UV and UV/H(2)O(2) to the polycyclic aromatic hydrocarbons (PAHs) fluorene, dibenzofuran and dibenzothiophene was studied. Batch experiments were conducted with both low-pressure monochromatic (253.7nm) and medium pressure polychromatic (200-300nm) UV sources alone or in the presence of up to 25mg/L hydrogen peroxide, in a quasi-collimated beam apparatus. Degradation of all three PAHs, by both UV and UV/H(2)O(2), exhibited pseudo-first-order reaction kinetics and low quantum yields ranging from 1.4x10(-3) to 1.8x10(-2)mol/E using both UV lamps. Toxicity testing using a bioluminesence inhibition bioassay was correlated to the decay in concentration of the PAHs as analyzed analytically using HPLC. Results demonstrated that treatment efficacy of oxidative PAH degradation measured by following the decay of the target compound is best complemented by also evaluating the toxicity of the treated water due to byproduct formation concerns.

Relating daily solar ultraviolet radiation dose in salt marsh-associated estuarine systems to laboratory assessments of photoactivated polycyclic aromatic hydrocarbon toxicity

Estuaries of the southeastern United States not only serve an important nursery function but also are common repositories of polycyclic aromatic hydrocarbons (PAHs) derived from upland activities. Thus, these habitats may be at risk for PAH phototoxicity. To better characterize this risk, a daily survey of ultraviolet-A (UV-A; 320-400 nm) irradiance was performed at Leadenwah Creek (Wadmalaw Island, SC, USA) on June 27 and August 1, 2003. In addition, laboratory assays were completed using two light exposure regimes: One that was typical of historical phototoxicity assessments (continuous light [C-UV]), and a more environmentally realistic regime (ER-UV). On both survey days, irradiance at a depth of 10 cm exhibited a pattern generally similar to that observed at the surface, whereas irradiance at the bottom of the creek was a function of both tidal height and time of day. Total UV-A dose at a 10-cm depth on June 27 and August 1, 2003 was 4.37 and 4.78 J/cm2, respectively. Attenuation coefficients on both days varied as a function of tidal height. In the laboratory, larval grass shrimp (Palaemonetes pugio) exposed to an ER-UV regime for these habitats (photoperiod, 12:12-h light:dark; total daily UV-A dose, 4.40 J/cm2) exhibited a 2.5-fold decrease in toxicity compared with those exposed to the C-UV regime (photoperiod, 24:0-h light:dark; total daily UV dose, 1.50 J/cm2), despite a threefold higher UV dose in the ER-UV regime. The lower potency under the ER-UV regime likely is attributable to the presence of a 12-h dark period allowing for recovery. The consequences of these results are discussed in the context of habitat-specific UV-A dose and its relevance to future laboratory assessments of PAH phototoxicity.

Photoactivated polycyclic aromatic hydrocarbon toxicity in medaka (Oryzias latipes) embryos: relevance to environmental risk in contaminated sites

The hazard for photoactivated toxicity of polycyclic aromatic hydrocarbons (PAHs) has been clearly demonstrated; however, to our knowledge, the risk in contaminated systems has not been characterized. To address this question, a median lethal dose (LD50) for fluoranthene photoactivated toxicity in medaka (Orvzias latipes) embryos was determined experimentally and then compared with ultraviolet-A (UV-A; 320-400 nm) radiation exposures in a PAH-contaminated field site. The dose metric, J/cm2/ microg fluoranthene/g egg wet weight, provided the means to estimate risk as the depth where the LD50 level would be exceeded at realistic field PAH concentrations, based on estimates of UV-A exposure. The estimates were made using 30 years of solar radiation data for Duluth (MN, USA) and measurements of water-column UV-A transmittance in a PAH-contaminated field site. Medaka embryo failure was strongly related to tissue PAH concentration and UV-A exposure. The LD50 was estimated to be 12.64 J/cm2/ microg fluoranthene/g egg wet weight; the 95% confidence interval was 8.46 to 19.7 J/cm2/microg fluoranthene/g egg wet weight. Embryo failures were characterized by undifferentiated cell proliferation that occurred very early in development. No partial effects or embryo/larval malformations were observed. Estimates of the depth at which the LD50 would be exceeded in the contaminated field site ranged from 10.7 cm (clear-sky conditions and lowest attenuation) to 0.0 cm (cloudy conditions and highest attenuation). Similar calculations were done using water-column attenuation estimates from 12 sites across the Great Lakes (USA). For these, the depths at which the LD50 would be exceeded ranged from 0.00 to 271.6 cm under the conditions described above. These results suggest that PAH phototoxicity may be a risk factor in specific contaminated sites, and they provide a framework for assessing that risk.

Photoinduced charge transfer and efficient solar energy conversion in a blend of a red polyfluorene copolymer with CdSe nanoparticles

We present measurements of charge transfer and the photovoltaic effect in a blend of the alternating polyfluorene copolymer poly(2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)) with branched CdSe nanoparticles. Quasi-steady-state photoinduced absorption measurements identified a long-lived charged species that formed after photoexcitation at room temperature. Photovoltaic devices based on this blend system showed a spectral response extending to 650 nm and gave a solar power conversion efficiency of 2.4% under Air Mass 1.5 Global (AM1.5G) conditions.

Photodegradation of Polyfluorene and Fluorene Oligomers with Alkyl and Aromatic Disubstitutions

The stability of fluorene-based compounds and polymers, especially at the bridged C-9 position under photoirradiation and thermal treatment, has claimed wide attention. We report the electronic, vibrational, and MALDI-TOF mass spectral combined studies for the fluorene oligomers with alkyl and aromatic substitutions under UV-light irradiation. The low-energy emission and the formation of ketonic defects after degradation highly depend on the proportion of alkyl substitution. The oligomer with fully aromatic substitution shows good stability, but when the proportion of alkyl substitution increases, their photostability rapidly decreases. The mass spectra show not only the mass of the fluorenone-fluorene trimer but also another new degradation product with a large mass (pristine oligomer plus 14) from alkyl oxidation, which testify to the assistance of alkyl side chain during degradation. We propose that the degradation of fluorene is a radical chain process propagated by alkyl side chains, and then the different stability between alkyl and aromatic substitution can be well explained.

Photofragmentation of the Fluorene Cation: II. Determination of the H-Loss Energy-Dependent Rate Constant

The hydrogen-loss channel, induced by sequential multiphoton absorption, of the vapor-phase fluorene cation was investigated using a pulsed supersonic molecular beam, a time-of-flight mass spectrometer, and pulsed nanosecond lasers. Our new method leads to the determination of the absolute absorption cross section. Its attenuation with the number of absorbed photons has been approximated by means of statistical models. A model-free determination of the evolution of the dissociation rate constant in a relatively large energy range was obtained by solving the set of coupled differential kinetic equations numerically. Particular attention was focused on the data analysis techniques. The free fit of these rate constants is close to the photothermodissociation statistical model, but shows a discrepancy with the Rice and Ramsperger and Kassel model mainly at high energy. The resulting activation energy is in agreement with both that deduced from the ab initio calculations and that from the tight-binding energy potential surface model.

Photofragmentation of the Fluorene Cation: I. New Experimental Procedure Using Sequential Multiphoton Absorption

The hydrogen-loss channel, induced by sequential multiphoton absorption, of the vapor-phase fluorene cation was investigated using a supersonic molecular beam and a time-of-flight mass spectrometer. The fluorene cation was prepared by resonantly enhanced multiphoton ionization. The ultimate goal of this experiment is the determination of the evolution of the dissociation rate constant in a wide energy range. In this paper, we give a description of the original experimental procedure, show that the absorption process is non-Poissonian, and determine the absolute photon absorption cross section.

The effect of camphorquinone (CQ) and CQ-related photosensitizers on the generation of reactive oxygen species and the production of oxidative DNA damage

Recent evidence suggests that following visible-light (VL) irradiation, CQ and the CQ-related photosensitizers benzil (BZ), benzophenone (BP), and 9-fluorenone (9-F) generate initiating radicals that may indiscriminately react with molecular oxygen forming reactive oxygen species (ROS). The purpose of this investigation was to determine whether VL-irradiated CQ, BZ, BP, and 9-F cause DNA damage due to the generation of ROS in vitro. ROS formation by CQ and CQ-related photosensitizers+/-dimethyl-p-toluidine (DMT) was investigated in a cell-free system with VL irradiation. DNA damage was determined using PhiX-174 RF I supercoiled double-stranded plasmid DNA and ROS quantified with 4-((9-acridinecarbonyl)amino)-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-9-AC), a fluorogenic ROS-sensitive probe. VL-irradiated CQ, BZ, BP, and 9-F (+/-DMT) produced significant DNA damage at 0.1, 0.5, and 1.0 mM and in a concentration-dependent manner (p<0.05). TEMPO-9-AC revealed that all investigated VL-irradiated photosensitizers produced significant amounts of ROS with BZ in the presence of DMT generating the most ROS after 30, 60, and 90 min. VL-irradiated CQ, BZ, BP, and 9-F +/-DMT continued to generate significant amounts of ROS 90 min after VL irradiation. As a result, future investigations should evaluate the effect of VL-irradiated photosensitizers in cells and possible protective effects provided by antioxidants.

Three- and four-photon absorption of a multiphoton absorbing fluorescent probe

High-order multiphoton excitation processes are becoming a reality for fluorescence imaging and phototherapy treatment because they afford minimization of scattered light losses and a reduction of unwanted linear absorption in the living organism transparency window, making them less susceptible to photodamage, while improving the irradiation penetration depth and spatial resolution. We report the four-photon-excited fluorescence emission of (7-benzothiazol-2-yl-9,-didecylfluoren-2-yl)diphenylamine in hexane and its four-photon absorption cross section sigma4' = 8.1 x 10(-109) cm8 s3 photon(-3) for the transition S0 --> S1 when excited at 1600 nm with a tunable optical parametric generator (OPG) pumped by picosecond laser pulses. When pumped at 1200 nm, three-photon absorption was observed, corresponding to the same transition.

Treatment system for solid matrix contaminated with fluoranthene. II--Recirculating photodegradation technique

A laboratory-scale solar reactor and photodegradation technique were developed to enhance the degradation process of fluoranthene. Fluoranthene was used in this study to represent toxic polycyclic aromatic hydrocarbons (PAHs) that are persistent in the environment. The extracted fluoranthene from soil in organic solvent (EFOS) and hydrogen peroxide (H2O2) were pumped from a 100 ml vessel into a solar glass cell coated with titanium dioxide (TiO2) at 80 microl min(-1). This work compares the efficiency of the developed photocatalytic degradation technique with the conventional batch process. The degradation efficiency of the developed technique was assessed at different initial concentrations of fluoranthene and percentages of H2O2 in the extract using different flow rates. Preliminary results indicated that the developed technique degraded 99% of fluoranthene from EFOS in the presence of H2O2 and 83% without H2O2. There was no significant difference between fluoranthene degradation rates by the developed technique and the batch method. The developed technique however, treated double the volume of solution that was treated by the batch reactor method which was time consuming and required continuous attention.

Effects of different protective agents on the phototoxicity of fluoranthene to Daphnia magna

Some compounds, accumulated by organisms, are transformed into toxic forms when irradiated with UV light. The polycyclic aromatic hydrocarbon (PAH) fluoranthene is one such compound of environmental importance. In this study on Daphnia magna, fluoranthene toxicity increased significantly after a 2 h exposure to solar-simulating UV light, if organisms were allowed to accumulate the substance for 24 h prior to irradiation. Since no enhanced toxicity was observed if the solutions were irradiated before the daphnids were added and only a slight decrease in toxicity was observed if the daphnids were transferred to pure dilution water prior to exposure, it was concluded that the acute phototoxicity of fluoranthene was predominantly due to photoactivation of accumulated or adsorbed molecules. Thus, the enhanced toxicity of fluoranthene by UV light is thought to act through the production of either singlet oxygen or free radicals. Possible effects of different protective agents (antioxidants, free radical scavengers and UV-screening compounds) were examined in two cultured populations of Daphnia magna. One population received a synthetic diet and the other dried baker's yeast. The yeast-fed population became progressively more sensitive to the photoinduced toxicity of fluoranthene, and after 14 days it was significantly more sensitive than the population that received the synthetic feed. It was not obvious whether any of the additives influenced the UV-induced toxicity significantly, although, alpha-tocopherol, a known antioxidant, was the best candidate.

Increased polycyclic aromatic hydrocarbon toxicity following their photomodification in natural sunlight: impacts on the duckweed Lemna gibba L. G-3

The authors previously demonstrated that simulated solar radiation (SSR), with a fluence rate of only 40 mumol m-2 sec-1, increased polycyclic aromatic hydrocarbon (PAH) toxicity to the duckweed Lemna gibba and that PAHs photomodified in SSR (generally oxygenation of the ring system) are more toxic than the parent compounds (Huang et al., Environ. Toxicol. Chem., 1993, 12, 1067-1077). It is not known, however, to what extent toxicity of PAHs can increase due to photomodification. Thus, natural sunlight, which has a high fluence rate (approximately 2000 mumol m-2 sec-1), was used to photomodify anthracene, benzo[a]pyrene, fluoranthene, phenanthrene, and pyrene. Toxicity was based on growth inhibition of L. gibba, measured as the rate of production of new leaves over an 8-day period. Initially, the toxicity of the PAHs applied in intact form was probed, with the compounds demonstrating greater toxicity in sunlight than in SSR. Next the PAHs were photomodified in sunlight prior to incubation with the plants. The half-lives of the PAHs in sunlight ranged from 12 min to 30 hr. Although most of the products of PAH photomodification are not yet identified, the degree that PAH toxicity increased following photomodification in sunlight could still be probed. The mixtures of photomodified chemicals that were derived from each PAH in sunlight were applied of L. gibba and growth inhibition under 100 mumol m-2 sec-1 of SSR was determined. The LC50s for the PAH photoproducts generated in sunlight were an order of magnitude lower than the LC50s for the PAHs applied in intact form.

Photochemical instability of 1-nitropyrene, 3-nitrofluoranthene, 1,8-dinitropyrene and their parent polycyclic aromatic hydrocarbons

The environmental contaminants pyrene, 1-nitropyrene, 1,8-dinitropyrene, fluoranthene, and 3-nitrofluoranthene were exposed to light (greater than or equal to 310 nm) either in DMSO, or following coating onto silica. Under all conditions tested the pyrenyl were less stable than the fluoranthenyl compounds. During irradiation in DMSO or on silica, 1-nitropyrene had half-lives of 1.2 and 6 days, while those of 3-nitrofluoranthene were 12.5 and greater than 20 days, respectively. The photodecomposition of 1,8-dinitropyrene resembled that of 1-nitropyrene with half-lives of 0.7 and 5.7 days. A principle photodecomposition product of 1,8-dinitropyrene was identified as 1-nitropyren-8-ol. It was also found that when the nitroarenes were exposed to light, the loss of compound was associated with a concomitant loss of mutagenicity in Salmonella typhimurium strain TA98. The mechanism of nitrated polycyclic aromatic hydrocarbon decomposition and 1-nitropyren-8-ol formation, and the relevance to the atmospheric disposition of these compounds are discussed.

2-Nitrofluoren-9-one: a unique mutagen formed in the photo-oxidation of 2-aminofluorene

Exposure of solutions of 2-aminofluorene (2-AF, dissolved in dimethylsulfoxide) to near ultraviolet light (u.v.a. wavelengths of 320-400 nm) results in the formation of a variety of photo-products, several of which are direct-acting mutagens in the Ames/Salmonella standard-plate assay. Previously published results from our laboratory have described the chemical identification and kinetics of formation of two of these photo-induced mutagens, 2-nitrosofluorene and 2-nitrofluorene. In this report we present recent data concerning the isolation and chemical identification of another mutagenic photoproduct of u.v.a.-irradiated 2-AF, 2-nitrofluoren-9-one (2-NO2F-9-one). Data are also presented concerning the kinetics of phototransformation of 2-aminofluoren-9-one, an early-appearing and predominant photoproduct in u.v.a.-irradiated solutions of 2-AF, into 2-NO2F-9-one. It is well established that N-oxidation is a critical step in the biotransformations (i.e. enzymatic metabolism) of primary aromatic amines into proximate mutagens/carcinogens. In addition to u.v.a.-mediated N-oxidation of aromatic amines, selective ring photo-oxidation can also occur, resulting in, for example, the production of a carbonyl group at the 9-position of the fluorene molecule. The formation of mutagenic 2-NO2F-9-one in the photochemical oxidation of 2-AF appears to be unique to this process.

Photochemical oxidation of 2-aminofluorene: correlation between the induction of direct-acting mutagenicity and the formation of nitro and nitroso aromatics

The kinetics of near ultraviolet light-mediated phototransformation of 2-aminofluorene (2-AF) was studied using high performance liquid chromatography (HPLC) and the Ames/Salmonella mutagenicity bioassay. Employing tester strains TA98, TA1538, and the nitroreductase-deficient TA98NR without the addition of exogenous metabolic enzymes, we were able to detect and discriminate between the UVA exposure-dependent formation of two stable photoproducts, 2-nitrosofluorene (2-NOF) and 2-nitrofluorene (2-NO2F). Mutagenicity of irradiated 2-AF solutions (using dimethyl sulfoxide as a solvent) in the various tester strains indicates the rapid formation of the photo-labile 2-NOF, after which 2-NO2F accounts for the preponderance of mutagenic activity. Continued UVA irradiation (greater than 72 h at 6.8 J/m2/s) of 2-AF results in the formation of greater than 30 photoproducts resolvable on HPLC, several of which, in addition to 2-NOF and 2-NO2F, are mutagenic on Salmonella but are chemically undefined to date. Prolonged irradiation ultimately destroys the photo-induced mutagenicity of 2-AF. However, UVA-induced 2-AF photoproducts are stable for several weeks when stored in sealed vials in the dark. Light potentiated oxidation of aromatic amines constitutes an alternative mechanism for the transformation of aromatic amines into proximate mutagens/carcinogens.

Mutagenic activation of 2-aminofluorene by fluorescent light

To determine the effect of artificially produced light on the direct mutagenicity of 2-aminofluorene, that arylamine was irradiated with either sun, cool-white, black, blue, or yellow fluorescent light or held in the dark prior to assaying for mutagenicity using Salmonella typhimurium strain TA98. The effectiveness of these exposures in potentiating the mutagenicity of 2-aminofluorene was sun greater than black greater than cool-white greater than blue greater than yellow approximately equal to dark. By varying the radiant flux densities produced by the lamps and using optical filters, wavelengths of light up to approximately 450 nm were found to be effective in the mutagenic potentiation. Studies using radical scavengers and oxygen modifiers indicated that the light-induced mutagenicity was dependent on oxygen and that singlet oxygen may be an effective activator of 2-aminofluorene. The mutagenicity of fluorene was not increased by exposure to light, while only sunlight potentiated the mutagenicity of 2-acetylaminofluorene. This result suggested the importance of the primary amine in the mutagenic activation of 2-aminofluorene by light. Light-activated 2-aminofluorene was less mutagenic in strains TA98NR and TA98/1,8-DNP6 than in TA98. This observation, combined with the dependence of the photoactivation on oxygen and amino-substitution, indicated that the light-enhanced mutagenicity was at least partially due to N-oxidized photoproducts. These studies indicate that the effect of light on environmental contaminants must be considered in assessing their genotoxic potential.

Mutagenicity of photochemical reaction products of polycyclic aromatic hydrocarbons with nitrite

Six kinds of polycyclic aromatic hydrocarbons (PAHs) were subjected to ultraviolet light irradiation with nitrite for 1, 4, 8 and 24 h, and the irradiated samples were tested for mutagenicity towards Salmonella typhimurium TA 98, TA 100 and TA 1538. Irradiated samples of pyrene, fluoranthene and benzo[a]pyrene showed marked mutagen responses towards TA 98 and TA 1538, especially in the absence of S9 mix. The direct-acting mutagenic activity of these samples, showing high activities at 1-8 h, decreased greatly with the development of irradiation. Further, these direct-acting mutagens were mostly present in the neutral fraction. On the other hand, the mutagenicity of the irradiated sample of 5,6-benzoquinoline was high both with and without S9 mix, and was mostly present in the basic fraction because of its authentic characteristic. There was no correlation between the yield of 1-nitropyrene and the mutagenic activity of the photochemical reaction product of pyrene with nitrite. Further studies by TLC separation suggested that a considerable number of direct-acting mutagens formed in this experiment were more polar than nitrated PAH such as 1-nitropyrene.

Irradiation-induced adduct formation of RNA with carcinogenic arylamine derivatives

Radiolysis of N2O-saturated solutions of transfer RNA (tRNA) and the arylacethydroxamic acids, N-hydroxy-N-2-acetylaminofluorene and N-hydroxy-N-4-acetylaminobiphenyl; their corresponding acetamides, 2-acetylaminofluorene and 4-acetylaminofluorene; or the O-glucuronide of N-hydroxy-N-2-acetylaminofluorene resulted in adduct formation of the nucleic acid with these carcinogenic arylamine derivatives. The yield of adducts on irradiation of the arylacethdroxamic acids with tRNA was greater than that for their corresponding acetamides or the O-glucuronide. The fluorenylacethydroxamic acid and acetamide were also more reactive than the biphenyl analogs. Adduct formation resulting from radiolysis of tRNA and the arylacethydroxamic acids or the O-glucuronide proceeded with retention of both the aromatic nucleus and the N-acetyl group. The yields of adducts were much greater for irradiated mixtures than for irradiation of either component alone followed by mixing. Evaluation of the data shows that initial modification of the tRNA or the carcinogen can lead to adduct formation. In the case of primary radical attack of the nucleic acid, it has been shown that short-lived reactive RNA intermediates are responsible for a major fraction of the observed yield of adducts in the irradiated mixtures. Comparative studies showed that irradiation under conditions that favor reaction of oxidizing radicals enhanced formation of the adducts. Oxygen was shown to protect RNA from irradiation-induced binding of the arylacethydroxamine acids due to competition of O2 with the carcinogen for the reactive RNA intermediates.