Unbiasing the estimate of the role of income in carbon footprint of households: Analysis of the Spanish case as a pilot study.

Although the estimation of the elasticity of the household carbon footprint and income is a frequently analysed fact, unfortunately a fundamental aspect of this relationship has not been considered: it is not a constant factor for the whole population. To make an adequate estimate of this relationship, a Quantile Regression is proposed, obtaining significantly different results to those derived from the usual estimations using ordinary least squares (OLS), which have been carried out up to now. This fact is fundamental for the correct planning and evaluation of fiscal policies based on income taxation to reduce the carbon footprint. Our results confirm that the OLS estimation would overestimate the effects of income on CO2 reduction by 26%.

Attitudes Toward and Susceptibility to Doping in Spanish Elite and National-Standard Track and Field Athletes: An Examination of the Sport Drug Control Model.

The Sport Drug Control Model (SDCM) is likely to be the model which most explicitly represents the theoretical paradigm of the psychological study of the use of doping in sport. This model can be further developed through its analysis in different populations and cultures. The main aim of this study was to empirically test the SDCM while analyzing for the first time the intentions and attitudes toward doping in Spanish track and field athletes. A secondary aim was to assess the extent to which the variables in the model together predict attitude, susceptibility, and behavior toward the use of performance-enhancing substances. Participants were 281 Spanish elite and national-standard track and field athletes from whom 80.1% were 18-28 years old and 49.5% were females. Participants completed the SDCM questionnaire measuring morality, legitimacy, benefits appraisal, threat appraisal, self-efficacy to refrain from doping, reference groups' endorsement of doping methods/substances, use of legal supplements, availability and affordability of doping, attitudes toward doping, susceptibility to doping and, self-reported use of banned performance-enhancing substances or methods. Structural equation modeling supported a good fitness of the SDCM and confirmed that positive attitudes toward doping predicted high susceptibility to doping (ß = 0.55, p < 0.001), which is in turn associated with the use of prohibited substances and methods (ß = 0.12, p < 0.05). The factors that have most influence on attitudes toward doping are morality (ß = 0.46, p < 0.001) and reference group opinion (ß =0.62, p <0.001). Self-reported doping use was 9.6%. These findings confirm SDCM reproducibility and variability (as it accounts for several variables) in Spanish track and field competitive athletes. It is recommended to implement preventive programs which allow athletes to acquire a strong moral stance against doping and coaches to employ the tools required to instill and educate their athletes in rejecting these illegal practices that corrupt the integrity of competitive sport.

Photochemical Relaxation Pathways in Dinitropyrene Isomer Pollutants.

Dinitropyrenes are polycyclic aromatic pollutants prevalent in the environment. While their transformations by sunlight in the environment have been documented, the effect that the nitro-group substitution pattern has on the relaxation pathways has not been extensively studied. In this contribution, the steady-state and femtosecond-to-microsecond excited-state dynamics of 1,3-dinitropyrene and 1,8-dinitropyrene isomers are investigated upon visible light excitation at 425 nm and compared with those recently reported for the 1,6-dinitropyrene isomer. The experimental results are complemented with ground- and excited-state density functional calculations. It is shown that excitation at 425 nm results in the ultrafast branching of the excited-state population in the S1 state to populate the triplet state in ca. 90% yield and to form a nitropyrenoxy radical in less than 10% yield. In addition, the position of the NO2 group does not affect significantly the excited-state relaxation mechanism, while it does influence the absorption and fluorescence spectra, the fluorescence, triplet, singlet oxygen, and photodegradation yields, as well as the relative yield of radical formation. Radical formation is implicated in the photodegradation of these pollutants, while in the presence of hydrogen donors, direct reactions from the triplet state are also observed.

The Photochemical Branching Ratio in 1,6-Dinitropyrene Depends on the Excitation Energy.

Nitropolycyclic aromatic hydrocarbons constitute one of the most disconcerting classes of pollutants. Photochemical degradation is thought to be a primary mode of their natural removal from the environment, but the microscopic mechanism leading to product formation as a function of excitation wavelength is poorly understood. In this Letter, it is revealed that excitation of 1,6-dinitropyrene with 425, 415, or 340 nm radiation leads to an increasing amount of radical production through photodissociation at the expense of triplet-state population-the two primary reaction pathways in this class of pollutants. Radical formation requires overcoming an energy barrier in the excited singlet manifold. This activation energy explains the large fraction of the initial singlet-state population that intersystem crosses to a doorway triplet state, instead of leading overwhelmingly to photodissociation. The unforeseen excitation wavelength dependence of this branching process is expected to regulate the photochemistry of 1,6-dinitropyrene and possibly of other nitroaromatic pollutants in the environment.

Phototransformations of dinitropyrene isomers on models of the atmospheric particulate matter.

The 1,6 and 1,8-dinitropyrenes (DNP) isomers are strong mutagens and carcinogens encountered in diesel exhaust and airborne particles. Relative photodegradation rates were determined and some products were characterized when these isomers were irradiated adsorbed onto models of the atmospheric matter. These are compared to their photochemical behavior in a polar nonprotic solvent. The 1,8-DNP isomer is three times more reactive than the 1,6-DNP when irradiated adsorbed onto silica gel surfaces, while the reverse order is observed in solution, demonstrating the influence of structural differences and environmental effects on the photoreactivity. Oxygen is a key factor in the formation of pyrenediones from 1,8-DNP in solution and on silica gel which is not the case for 1,6-DNP. The average pore diameter (2.5 versus 6.0 nm) of the silica surfaces induces a significant change in the product distribution and relative yields of 1,8-DNP because pyrenediones or 8-hydroxy-1-nitropyrene are not produced in the smaller pore silica. A 6-hydroxy-1-nitropyrene product is observed both in acidic alumina and silica (6.0 nm) surfaces. On acidic alumina the rates of phototransformation of the isomers are equal, a significant increase in the relative yield of the hydroxynitropyrene product is observed compared to the silica and unidentified products in which the absence of NO2 and pyrene absorption bands were observed, demonstrating the surface effect on the photodegradation. Overall, the presence of some products indicates the occurrence of a nitro-nitrite rearrangement on the surface with the participation of a pyrenoxy radical as their precursor.

Photodegradation mechanisms of 1-nitropyrene, an environmental pollutant: the effect of organic solvents, water, oxygen, phenols, and polycyclic aromatics on the destruction and product yields.

This work describes studies of the photodegradation mechanism of 1-nitropyrene (1-NO(2)Py) in a chemical model system consisting of an organic solvent and known constituents of an aerosol particle. Photoproducts such as 1-hydroxypyrene (1-OHPy), 1-hydroxy-x-nitropyrenes (1-OH-x-NO(2)Py), 1-nitrosopyrene, and 1,6- and 1,8-pyrenediones were identified by high-performance liquid chromatography (HPLC) and HPLC/mass spectrometry (HPLC/MS) techniques, and their quantum yields show a significant dependence on the type of solvent. The photodegradation quantum yield of 1-NO(2)Py, φ((-1-NO2Py)), was larger in toluene, benzene, and polar protic solvents (10(-3)) in comparison with nonpolar and polar aprotic solvents, where the yield is on the order of 10(-4). In solvents with an abstractable hydrogen atom, the products formed in higher yields were 1-OHPy and 1-OH-x-NO(2)Py. These represent 60-80% of the photodestruction yield and result from abstraction and recombination reactions of the pyrenoxy radical, an intermediate postulated to be formed as a result of a nitro-nitrite rearrangement in nitroaromatics. The small O(2) effect in the photodegradation yield and the quenching experiments with azulene demonstrate the small contribution of the (3)(π,π*) state in the 1-NO(2)Py photoreaction. The nitrosopyrene product was not observed under these conditions, demonstrating the participation of the (3)(π,π*) state in its formation. In the presence various phenol aerosol constituents, the photodegradation yield increased by 10-fold in all solvents. This effect is partly ascribed to the reaction of the (3)(π,π*) state with the phenol. The effect of water resulted in the reduction of the 1-NO(2)Py photodegradation yield and of its photoproducts. The phototodegradation of 1-NO(2)Py was also studied in a viscous solvent, hexadecane, and it was determined that this medium does not inhibit its photodecay.

Quenching enhancement of the singlet excited state of pheophorbide-a by DNA in the presence of the quinone carboquone.

Changes in the emission fluorescence intensity of pheophorbide-a (PHEO) in the presence of carboquone (CARBOQ) were used to obtain the association constant, the number of CARBOQ molecules interacting with PHEO, and the fluorescence quantum yield of the complex. Excitation spectra of mixtures of PHEO and CARBOQ in ethanol (EtOH) show an unresolved doublet in the red-most excitation band of PHEO, indicating the formation of a loose ground-state complex. The 1:1 CARBOQ-PHEO complex shows a higher fluorescence quantum yield in EtOH (0.41 ± 0.02) than in buffer solution (0.089 ± 0.002), which is also higher than that of the PHEO monomer (0.28). Quenching of the PHEO fluorescence by DNA nucleosides and double-stranded oligonucleotides was also observed and the bimolecular quenching rate constants were determined. The quenching rate constant increase as the oxidation potential of the DNA nucleoside increases. Larger quenching constants were obtained in the presence of CARBOQ suggesting that CARBOQ enhances DNA photo-oxidation, presumably by inhibiting the back-electron-transfer reaction from the photoreduced PHEO to the oxidized base. Thus, the enhanced DNA-base photosensitized oxidation by PHEO in the presence of CARBOQ may be related to the large extent by which this quinone covalently binds to DNA, as previously reported.

A comparative photophysical and photochemical study of nitropyrene isomers occurring in the environment.

Ground state absorption, first excited-singlet state, and properties of reactive intermediates of mononitropyrene isomers encountered in the atmospheric aerosol have been studied under different conditions that could mimic the environment. The nitro group can present different orientations relative to the pyrene ring depending on its geometric location and could induce differences in the photochemistry of the isomers. The 2-NO(2)Py isomer has the largest red shift and lowest oscillator strength in the UV-visible band associated with the nitro group. The isomers show very low fluorescence yields (10(-3)-10(-4)). Only 1-NO(2)Py and 4-NO(2)Py have phosphorescence emission (Φ(p) ≈ 10(-4)), indicating that the lowest triplet state decays mainly through effective radiationless channels. Laser photolysis produces a low-lying triplet state (τ(T) = 10(-5)-10(-6) s), a long-lived pyrenoxy radical, and a PyNO(2)H radical in solvents in which the triplet can abstract a hydrogen atom. Similar triplet yields were calculated (0.1-0.6) for the isomers, while significant differences in the relative yield of the long-lived species were determined. Differences in the quenching rate constants of the triplet by water and phenols suggest a strong hydrogen-bond interaction with the nitro group in the C-2 position, which provides for radiationless deactivation routes.

Photodegradation of 2-chloro substituted phenothiazines in alcohols.

The mechanisms that trigger the phototoxic response to 2-chlorophenothiazine derivatives are still unknown. To better understand the relationship between the molecular structure of halogenated phenothiazines and their phototoxic activity, their photophysics and photochemistry were studied in several alcohols. The photodestruction quantum yields were determined under anaerobic conditions using monochromatic light (313 nm). Absorption- and emission-spectroscopy, (1)H- and (13)C-NMR and GC-MS were used to characterize the photoproducts and reference compounds. An electron transfer mechanism had been previously proposed by Bunce et al. (J. Med. Chem. 22, 202-204) to explain the large difference between the photodestruction quantum yield of 2-chlorpromazine (phi = 0.46) and 2-chlorphenothiazine (phi = 0.20). According to these authors, the alkylamino chain transfers an electron to the phenothiazine moiety. Our results demonstrate that this mechanism is incorrect, because the photodestruction quantum yields of all chlorinated derivatives of this study are the same under the same conditions of solvent and irradiation wavelength. The quantum yield has no dependence on the 10-substituent, but it depends on the solvent. The percentage of each photoproduct, on the other hand, strongly depends on that substituent, but not very much on the solvent. Finally, it is demonstrated that the phototoxic effect of chlorinated phenothiazines is not related to the photodechlorination, although both processes share the same transient.

Photophysics and photochemistry of 1-nitropyrene.

1-Nitropyrene (1NPy) is the most abundant nitropolycyclic aromatic contaminant encountered in diesel exhausts. Understanding its photochemistry is important because of its carcinogenic and mutagenic properties, and potential phototransformations into biologically active products. We have studied the photophysics and photochemistry of 1NPy in solvents that could mimic the microenvironments in which it can be found in the atmospheric aerosol, using nanosecond laser flash photolysis, and conventional absorption and fluorescence techniques. Significant interactions between 1NPy and solvent molecules are demonstrated from the changes in the magnitude of the molar absorption coefficient, bandwidth at half-peak, oscillator strengths, absorption maxima, Stokes shifts, and fluorescence yield. The latter are very low (10 (-4)), increasing slightly with solvent polarity. Low temperature phosphorescence and room temperature transient absorption spectra demonstrate the presence of a low energy (3)(pi,pi*) triplet state, which decays with rate constants on the order of 10 (4)-10 (5) s (-1). This state is effectively quenched by known triplet quenchers at diffusion control rates. Intersystem crossing yields of 0.40-0.60 were determined. A long-lived absorption, which grows within the laser pulse, and simultaneously with the triplet state, presents a maximum absorption in the wavelength region of 420-440 nm. Its initial yield and lifetime depend on the solvent polarity. This species is assigned to the pyrenoxy radical that decays following a pseudo-first-order process by abstracting a hydrogen atom from the solvent to form one the major photoproducts, 1-hydroxypyrene. The (3)(pi,pi*) state reacts readily ( k approximately 10 (7)-10 (9) M (-1) s (-1)) with substances with hydrogen donor abilities encountered in the aerosol, forming a protonated radical that presents an absorption band with maximum at 420 nm.

Environmental photochemistry of nitro-PAHs: direct observation of ultrafast intersystem crossing in 1-nitropyrene.

Femtosecond broadband transient absorption experiments of 1-nitropyrene, a nitro-polycyclic aromatic hydrocarbon of environmental concern are presented in cyclohexane and hexane solutions. The transient absorption spectra show the presence of three species that are assigned to the Franck-Condon excited lowest singlet (S1) state, the structurally relaxed S1 state, and the lowest excited triplet state. The spectral changes at early times are interpreted in terms of conformational dynamics; primarily due to an ultrafast rotation of the nitro group in the S1 state. This excited state relaxation is followed by intersystem crossing with a time constant of 7 ps. CIS/6-31G(d,p) calculations predict planarization of the nitro-aromatic torsional angle as the major nuclear relaxation coordinate, from 32.8 degrees at the HF/6-31G(d,p) level of theory in the ground state (27.46 degrees at B3LYP/6-31++G(d,p)) to 0.07 degrees in the S1 state. Vertical excitation energies at the TDDFT/6-31++G(d,p) and TDDFT/IEFPCM/6-31++G(d,p) levels of theory predict a small energy gap (<0.12 eV) between the S1(pipi*) state and the third excited triplet state T3(npi*) in the gas phase and in cyclohexane, respectively. The small energy gap suggests a large spin-orbit coupling between the S1(pipi*) and T3(npi*) states, which explains the ultrafast intersystem crossing of 1-nitropyrene in nonpolar solvents.

Photophysics and photochemistry of imipramine, desimipramine, and clomipramine in several solvents: a fluorescence, 266 nm laser flash, and theoretical study.

Imipramine (IPA) and its derivatives are used widely for the treatment of depression and other mental disorders. Although there are more than 20 FDA-approved antidepressant drugs, the search continues for better compounds with fewer deleterious side effects and higher efficacy. Over the past decade, several classes of antipsychotic drugs have been developed, which-in spite of their structural diversity-share an ability to modulate neurotransmission and to produce undesirable side effects. Phototoxicity is one of the most important side effects noted in treatment with tricyclic antidepressants (TCAs), but its mechanism has not yet been elucidated. To develop new knowledge regarding the relationship between the structure and the photophysics of these TCAs, we measured the photophysical properties of IPA, desimipramine (DIPA), and clomipramine (CIPA) in different solvents. The electronic configurations for the ground and the first excited singlet states were calculated using the AM1/RHF/CI and the AM1/RHF/HE semiempirical quantum theoretical methods, respectively. The ground-state properties are solvent-independent, while the emission maxima are red-shifted with increasing solvent polarity/polarizability. However, the fluorescence quantum yield is relatively low in all of the tested solvents (phif<0.02). The primary transient intermediates produced by 266 nm high-intensity laser photolysis are the solvated electron and the corresponding radical cation, with a negligible contribution of triplet-triplet absorption. The properties determined for the primary transients generated with a 266 nm laser flash are consistent with the photodamaging effects generated through a limited radical mechanism.

MAJOR PRODUCTS IN THE PHOTOCHEMISTRY OF PERYLENE ADSORBED IN MODELS OF ATMOSPHERIC PARTICULATE MATTER.

The photodegradation of adsorbed perylene is strongly influenced by the environment in which it is found as demonstrated by the nature of the photoproducts characterized on the adsorbed state in comparison to its photochemical behavior in solution. The separation, characterization, and identification of the products were carried out using HPLC equipped with UV-Vis diode array and MS detection. Two of the products were identified as 1,12-perylenedione and 3,10-perylenedione. Three additional products were characterized as a perylenedione and two perylenediols based on their m/z ratio. Based on this information, two possible mechanisms of formation were proposed for the identified diones. The experimental data showed that both the radical cation and singlet oxygen participate in the route of photodegradation of perylene which occurs through a mixed Type I and Type II pathway. These results assist in the understanding of complex processes undergone by perylene and other PAHs in the environment.

SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES OF 2-AMINOPHENOTHIAZINE.

Phenothiazines derivatives are versatile compounds that are used in many fields, depending on the type and position of the substitution on the parent molecule. The photochemical, photophysical and electrochemical properties of several phenothiazine derivatives have been previously reported in detail. However, no reports have been presented for 2-aminophenothiazine (APH), a candidate that provides for the further chemical modification and the introduction of specific substituents. In this work, the photophysical and electrochemical properties of APH were measured in acetonitrile. The APH ground state absorption and fluorescence spectrum (phi(f) < 0.01) are similar to the corresponding that of PH parent molecule. A mono exponential decay fluorescence lifetime of 0.65 ns was determined for APH in acetonitrile. Characterization of the 355 nm nanosecond laser flash photolysis transient species reveals the presence of the triplet-triplet transient intermediate with a high intersystem crossing quantum yield (phi(T) = 0.72 +/- 0.07), indicating that the APH main excited state deactivation channel is intersystem crossing. The oxidation potential of APH is lower than phenothiazine parent molecule ((0.38 V vs 0.69 V vs Ag/AgCl(sat)). Altogether, these results show that APH has photochemical and photophysical properties similar to the phenothiazine parent molecule, but with the possibility of providing an amino functionality at 2-position for further chemical modification.

Light-induced transformations of aza-aromatic pollutants adsorbed on models of atmospheric particulate matter: Acridine and 9(10-H) acridone.

The effect of the characteristics of the surface on the phototransformation of acridine, one of the most abundant azapolycyclic compounds encountered in urban atmospheres, and of one of its principal photoproducts, acridone, was studied when adsorbed onto models of the atmospherice particulate matter. For this purpose, relative photodegradation rates were determined from absorption or emission intensities as a function of irradiation times, and some products were isolated and characterized. The relative photodegradation rates of adsorbed acridine show the tendency (NH(4))(2) SO(4) > MgO > Al(2)O(3) >SiO(2). In general, the rates decrease as the fraction of protonated acridine species on the surface increases in MgO, Al(2)O(3), and SiO(2), except for (NH(4))(2) SO(4) where a fast surface reaction occurs. Oxygen reduces the photodestruction rates by as much as 40 to 60% when compared to an inert atmosphere, implying the participation of an acrideine triplet state in the transformation processes on all surfaces except on (NH(4))(2)SO(4). Acridone, a major product, undergoes a photoinduced tautomerization to 9-hydroxy acridine. The formation of a dihydrodiol, another photoproduct of acridine, is suggested by comparison to reported spectral properties of these compounds. This is formed through a singlet oxygen reaction. Photoproducts showing the absence of the narrow absorption band of 250 nm, characteristic of the pi -->pi* transition in tricyclic aromatics, were detected in small yields but not identified. These results suggest possible photochemical transformation pathways that could lead to the ultimate fate of these pollutants in the environment.

Role of sequence and conformation on the photochemistry and the photophysics of A-T DNA dimers: an experimental and computational approach.

The role of base sequence and conformation on the photochemistry and photophysics of thymidylyl (3'-5')-2'-deoxyadenosine sodium salt (TpdA) and 2-deoxyadenylyl (3'-5')-thymidine ammonium salt (dApT) was studied. To this end, nanosecond transient absorption at 266 nm, steady-state irradiation at 254 nm, and quantum chemical calculations were used. The transient absorption spectra show the solvated electron broad band in the visible region for each dinucleotide. In addition, low-intensity absorption bands are observed in the UV region, which are attributed to the deprotonated and protonated neutral radicals of adenine and thymine bases. Photoionization (PI) occurs by one- and two-photon pathways; the latter accounting for approximately 70% of the net PI yield. A diffusion-limited rate constant of 2.0 x 10(10) M(-1) s(-1) was obtained for the reaction of the neutral molecule with the photoejected electron in both sequences. The photodestruction yield, measured from the chromophore loss at 260 nm, decreases in the presence of well-known electron scavengers. This suggests the participation of base radical anions as one of the photodegradation pathways, which is higher in TpdA than in dApT. The intermediacy of a radical ion pair (charge separated state) between the adjacent adenine and thymine bases is proposed in the formation of the [2 + 2] cycloadduct intermediate. The [2 + 2] cycloadduct intermediate is known to be the precursor of the thymine-adenine eight-member ring photoproduct (TA*). Conformational constrains in the radical ion pair are suggested to explain the absence of the TA* photoproduct in dApT. This hypothesis is supported by semiempirical calculations performed on all relevant reactive intermediates proposed to participate in the mechanism of formation of TA*. Altogether, the results show that sequence and conformation profoundly influence the photochemistry and the photophysics of these DNA model systems.

Photochemical transformations of benzo[e]pyrene in solution and adsorbed on silica gel and alumina surfaces.

The photodegradation of benzo[e]pyrene (BeP), a ubiquitous polycyclic aromatic hydrocarbon (PAH) contaminant, was investigated in solution and adsorbed on surfaces modeling the atmospheric particulate matter to provide fundamental information that could help to clarify its fate in the atmosphere. Diones, diols, and hydroxy derivatives were identified as the major photoproducts of BeP irradiated under simulated atmospheric conditions. The relative distribution of the products and the photodegradation rates of BeP were affected by the average pore size of the surface. Major photoproducts characterized in samples adsorbed on silica gel and alumina surfaces were not observed in irradiated solutions of BeP in hexane. In acetonitrile, the photodegradation rate was faster than in hexane, and one of the diones was observed. Different photoreaction pathways seem to take place in polar versus nonpolar microenvironments.

Substitution and solvent effects on the photophysical properties of several series of 10-alkylated phenothiazine derivatives.

The photophysical properties of several 2-substituted, 10-alkylated phenothiazines were measured in several solvents to investigate the relevance of the molecular structure in their photophysics and consequent photochemistry. Because the interaction modes of each drug and its corresponding species strongly depend on the variety of microenvironments in the cells, the properties of each one of these species must also be determined separately to understand fully the mechanism of action of the drug and the mechanism of its side effects. Information on the chemical interactions of the different species at the cellular level can be inferred from the corresponding electronic properties. In this work, we present absorption, steady-state, and time-resolved emission, laser flash photolysis, and quantum theoretical results for the ground state, the first excited singlet and triplet states, and the cation radical of promazine hydrochloride (PZ), 2-chlorpromazine hydrochloride (CPZ), 2-trifluoromethylpromazine hydrochloride (TFMPZ), 2-trifluoromethylperazine dihydrochloride (TFMP), 2-thiomethylpromazine (TMPZ), and thioridazine hydrochloride (TR). The corresponding nonalkylated phenothiazines are included as references. The photophysical properties of this drug family depend more on the solvent and the 2-substituents than on the dialkylaminopropyl chain. The largest effect was found for the triplet state of the 2-halogenated derivatives in phosphate buffer (PBS). Both the quantum yield and the lifetime of this intermediate drop to less than 5% of the corresponding value in organic solvents. The triplet state of halogenated promazines is efficiently quenched by a proton-transfer mechanism, and the rate of this quenching correlates very well with the phototoxicity of the promazine drugs. Therefore, we postulate that this species is directly related to the phototoxic side effect of neuroleptic drugs.

Characterization of acridine species adsorbed on (NH4)2SO4, SiO2, Al2O3, and MgO by steady-state and time-resolved fluorescence and diffuse reflectance techniques.

The ground- and excited-state species of acridine adsorbed on (NH(4))(2)SO(4), SiO(2), Al(2)O(3), and MgO surfaces were investigated in order to determine the precursor species and electronic states responsible for acridine photodegradation on particles serving as models of atmospheric particulate matter. The species present on each solid surface were characterized by comparing the steady-state absorption and fluorescence spectra, time-resolved fluorescence, and absorption measurements on acridine in solution with those corresponding to adsorbed acridine. On silica, the ground-state species present were hydrogen-bonded, neutral, and protonated, while on alumina hydrogen-bonded and neutral species were identified. A comparison of the protonated acridine absorption and emission intensities on silica and alumina with those observed for acridine in acidic water demonstrated that the emission on the surfaces is higher than expected. This was interpreted as resulting from photoprotolytic reactions on silica and alumina. For acridine adsorbed on ammonium sulfate, protonated acridine was the only adsorbed species identified. Since, at a similar ground-state absorbance, the fluorescence intensity of acridine on ammonium sulfate was smaller than for acridine in acidic water, the quenching of the excited state or a rapid photochemical reaction with the surface was proposed. On magnesium oxide, the presence of neutral and hydrogen-bonded acridine species were characterized from the two-component analysis of the fluorescence, the triplet-triplet absorption decay curves, and the time-resolved emission spectra at different time delays. As demonstrated in these studies, acridine adsorbed species and their decay pathways depend on the acidic properties of these models of atmospheric particulate matter. In addition, a comparison of the photodegradation rates of acridine on the different solids tested is presented and discussed in terms of the nature of the species and their decay pathways.

Formamidopyrimidines as major products in the low- and high-intensity UV irradiation of guanine derivatives.

Two major UV-induced transformation products of guanosine (Guo) in oxygen-free aqueous solution were isolated and characterized using reverse-phase HPLC-ESI-MS and UV absorption spectrophotometric techniques. These products were identified as two different sugar isomers of 2,6-diamino-4-hydroxy-5-formamidopyrimidine ribonucleosides, FapyGuo. A formation quantum yield of the order of 10(-3) for these products was obtained at a 75 microM concentration of Guo, while an increase in the ground state concentration of Guo from 10(-5) to 10(-4) M decreased their formation yield by a factor of ten. The formation of FapydGuo was also observed in the 254 nm photolysis of 2'-deoxyguanosine. In addition, the formation FapyGua was identified in the UV photolysis of all the guanine derivatives investigated. A formation quantum yield of the order of 10(-4) was obtained for the latter product, except in the photolysis of Gua in which a higher formation yield (10(-3)) was determined. These results suggest that hydration of the radical cation of guanine, followed by opening of the imidazole ring to form Fapy products, is one of the main low-intensity UV radiation-induced photo-transformation pathway of the guanine derivatives in oxygen-free aqueous solutions. Furthermore, the formation of the Fapy products and base release occurs through a similar photo-transformation pathways using a high-intensity UV radiation source.