Photochemical Reaction Products Research Articles

Effects of 1,3-Butadiene, Isoprene, and Their Photochemical Degradation Products on Human Lung Cells

Because of potential exposure both in the workplace and from ambient air, the known carcinogen 1,3-butadiene (BD) is considered a priority hazardous air pollutant. BD and its 2-methyl analog, isoprene (ISO), are chemically similar but have very different toxicities, with ISO showing no significant carcinogenesis. Once released into the atmosphere, reactions with species induced by sunlight and nitrogen oxides convert BD and ISO into several photochemical reaction products. In this study, we determined the relative toxicity and inflammatory gene expression induced by exposure of A549 cells to BD, ISO, and their photochemical degradation products in the presence of nitric oxide. Gas chromatography and mass spectrometry analyses indicate the initial and major photochemical products produced during these experiments for BD are acrolein, acetaldehyde, and formaldehyde, and products for ISO are methacrolein, methyl vinyl ketone, and formaldehyde; both formed < 200 ppb of ozone. After exposure the cells were examined for cytotoxicity and interleukin-8 (IL-8) gene expression, as a marker for inflammation. These results indicate that although BD and ISO alone caused similar cytotoxicity and IL-8 responses compared with the air control, their photochemical products significantly enhanced cytotoxicity and IL-8 gene expression. This suggests that once ISO and BD are released into the environment, reactions occurring in the atmosphere transform these hydrocarbons into products that induce potentially greater adverse health effects than the emitted hydrocarbons by themselves. In addition, the data suggest that based on the carbon concentration or per carbon basis, biogenic ISO transforms into products with proinflammatory potential similar to that of BD products.

Photodecomposition of Pigment Yellow 74, a pigment used in tattoo inks.

Tattooing has become a popular recreational practice among younger adults over the past decade. Although some of the pigments used in tattooing have been described, very little is known concerning the toxicology, phototoxicology or photochemistry of these pigments. Seven yellow tattoo inks were obtained from commercial sources and their pigments extracted, identified and quantitatively analyzed. The monoazo compound Pigment Yellow 74 (PY74; CI 11741) was found to be the major pigment in several of the tattoo inks. Solutions of commercial PY74 in tetrahydrofuran (THF) were deoxygenated using argon gas, and the photochemical reaction products were determined after exposure to simulated solar light generated by a filtered 6.5 kW xenon arc lamp. Spectrophotometric and high-pressure liquid chromatography (HPLC) analyses indicated that PY74 photodecomposed to multiple products that were isolated using a combination of silica chromatography and reversed-phase HPLC. Three of the major photodecomposition products were identified by nuclear magnetic resonance and mass spectrometry as N-(2-methoxyphenyl)-3-oxobutanamide (o-acetoacetanisidide), 2-(hydroxyimine)-N-(2-methoxyphenyl)-3-oxobutanamide and N,N''-bis(2-methoxyphenyl)urea. These results demonstrate that PY74 is not photostable in THF and that photochemical lysis occurs at several sites in PY74 including the hydrazone and amide groups. The data also suggest that the use of PY74 in tattoo inks could potentially result in the formation of photolysis products, resulting in toxicity at the tattoo site after irradiation with sunlight or more intense light sources.

Photodegradation of organic pollutants in aqueous solutions caused by Fe(OH)aq2+ photolysis: Evidence of OH radical formation

Photochemistry of Fe(III) hydroxocomplexes has a great interest because of possibility of hydroxyl radical formation at the primary photochemical step. This mechanism is based mainly on the analysis of the final products of photochemical reactions between light‐excited Fe(III) complexes and organic compounds. However, realization of an alternative mechanism of photolysis, based on the intermolecular electron transfer from organic molecules located in the second coordination sphere to the light‐excited complex could take place. To distinguish these mechanisms, the experiments on the nanosecond laser flash photolysis of Fe(OH)aq2+ in water solutions (pH 3) with organic additives; namely nitrobenzene, N,N‐dimethylformamide, and phenol have been performed. And the formation of the organic radicals Ph(•OH)NO2, HCON(CH2•)(CH3), and Ph(OH)2•, was observed, respectively. The rate constants of the formation and decay of the radicals coincide with those found in literature. The results support the formation of the hydroxyl radical upon the photolysis of Fe(OH)aq2+.

DNA bulky adducts in a Mediterranean population correlate with environmental ozone concentration, an indicator of photochemical smog.

Ozone (O(3)), the major oxidant component in photochemical smog, mostly derives from photolysis of nitrogen dioxide. O(3) may have biologic effects directly and/or via free radicals reacting with other primary pollutants and has been reported to influence daily mortality and to increase lung cancer risk. Although DNA damage may be caused by ozone itself, only other photochemical reaction products (as oxidised polycyclic aromatic hydrocarbons) may form bulky DNA adducts, a reliable biomarker of genotoxic damage and cancer risk, showing a seasonal trend. In a large series consisting of 320 residents in the metropolitan area of Florence, Italy, enrolled in a prospective study for the period 1993-1998 (206 randomly sampled volunteers, 114 traffic-exposed workers), we investigated the correlation between individual levels of DNA bulky adducts and a cumulative O(3) exposure score. The average O(3) concentrations were calculated for different time windows (0-5 to 0-90 days) prior to blood drawing for each participant, based on daily measurements provided by the local monitoring system. Significant correlations between DNA adduct levels and O3 cumulative exposure scores in the last 2-8 weeks before enrollment emerged in never smokers. Correlations were highest in the subgroup of never smokers residing in the urban area and not occupationally exposed to vehicle traffic pollution, with peak values for average concentrations 4-6 weeks before enrollment (r = 0.34). Our current findings indicate that DNA adduct formation may be modulated by individual characteristics and by the cumulative exposure to environmental levels of ozone in the last 4-6 weeks, possibly through ozone-associated reactive pollutants.

Photoinduced Fragmentation of Multilayer CH3Br on Cu/Ru(001)

The broadband UV (230−420 nm) photoinduced chemistry of CH3Br adsorbed on Cu(2ML)/Ru(001) in the coverage range of 1−50 ML was studied by monitoring the desorption products (Δp-TPD mode) in combination with post irradiation work function change measurements before and during surface heating (Δφ-ΤPD mode). Δφ measurements enabled us to follow multilayer restructure and desorption of parent molecules and photochemical reaction products in the temperature range of 80−700 K. Methyl radicals accumulated on the surface are the precursor for the thermal formation of methane and ethylene at 450 K. Dehydrogenation of the methyl group is the rate-limiting step of the surface reaction resulting in the formation of these molecules. Based on work function change measurements, an estimate of the adsorbed methyl dipole moment is μ0 = 0.48 D. Dissociative electron attachment (DEA) driven CH3Br dissociation produced CH3 and CH2 fragments within the parent molecules multilayer matrix. At the multilayer coverage range, Δφ increases by up to 1.1 eV after 10 min UV irradiation. Model calculations qualitatively describe the post irradiation work function changes induced by the embedded photofragments (mostly Br- ions) inside the CH3Br dielectric film. Comparison of the Δφ-TPD spectra on Cu(2ML)/Ru(001) to those on clean Ru(001) indicates that the nature of the molecule−surface interaction and the structure of the first few layers strongly influence the resulting photochemistry at layer thickness up to at least 20 ML.

Hydrogen transfer in photo-excited phenol/ammonia clusters by UV–IR–UV ion dip spectroscopy and ab initio molecular orbital calculations. II. Vibrational transitions

The vibrational spectra of phenol/ammonia clusters (1:2–5) in S0 and those of their photochemical reaction products, (NH3)n−1NH4 (n=2–5), which are generated by excited-state hydrogen transfer, have been measured by UV–IR–UV ion dip spectroscopy. The geometries, IR spectra and normal modes of phenol-(NH3)n (n=1–5) have been examined by ab initio molecular orbital calculations, at the second-order Møller–Plesset perturbation theory level with large basis sets. For the n=2 and 3 reaction products, similar vibrational analyses have been carried out. From the geometrical information of reactants and products, it has been suggested that the reaction products have memories of the reactant’s structure, which we call “memory effect.”

Enzymology below 200 K: the kinetics and thermodynamics of the photochemistry catalyzed by protochlorophyllide oxidoreductase.

The chlorophyll biosynthesis enzyme protochlorophyllide reductase (POR) catalyzes the light-dependent reduction of protochlorophyllide (Pchlide) into chlorophyllide in the presence of NADPH. As POR is light-dependent, catalysis can be initiated by illumination of the enzyme-substrate complex at low temperatures, making it an attractive model for studying aspects of biological proton and hydride transfers. The early stages in the photoreduction, involving Pchlide binding and an initial photochemical reaction, have been studied in vitro by using low-temperature fluorescence and absorbance measurements. Formation of the ternary POR-NADPH-Pchlide complex produces red shifts in the fluorescence and absorbance maxima of Pchlide, allowing the dissociation constant for Pchlide binding to be measured. We demonstrate that the product of an initial photochemical reaction, which can occur below 200 K, is a nonfluorescent intermediate with a broad absorbance band at 696 nm (A696) that is suggested to represent an ion radical complex. The temperature dependence of the rate of A696 formation has allowed the activation energy for the photochemical step to be calculated and has shown that POR catalysis can proceed at much lower temperatures than previously thought. Calculations of differences in free energy between various reaction intermediates have been calculated; these, together with the quantum efficiency for Pchlide conversion, suggest a quantitative model for the thermodynamics of the light-driven step of Pchlide reduction.

Photochemical Reactions in Gaseous Mixtures of C 2 F 4 and CF 3 I

Products of photochemical reactions occurring in gaseous mixtures of C2F4 and CF3I under vacuum-UV irradiation were studied. The major photolysis products are linear perfluoroparaffins CnF2n+2 and linear perfluoroalkyl iodides CnF2n+2I. The product ratio is consistent with the suggested kinetic scheme of chain reactions of telomers.

Electrophoretic characterization of transient photochemical reaction products.

Electrophoretic characterization of transient photochemical reaction products.

Spatial Separation of Photochemical Oxidation and Reduction Reactions on the Surface of Ferroelectric BaTiO3

When BaTiO3 is illuminated by ultraviolet light in aqueous solutions containing dissolved Pb2+ or Ag+ cations, photochemical reaction products are deposited on the surface in patterns that correspond to the underlying ferroelectric domain structure. On the basis of an analysis of the domain polarization, oxidized Pb and reduced Ag accumulate on the surfaces of domains with opposite polarization. When the domain dipole has its negative end directed toward the surface, Pb is oxidized, and when the dipole is reversed, Ag is reduced. On the basis of these observations, we propose that the static dipolar fields in the different domains separate photogenerated charge carries. In those domains where photogenerated holes are driven to the solid−liquid interface, oxidation is preferred. In oppositely oriented domains, where the field drives photogenerated electrons to the surface, the reduction reaction is preferred. Thus, the separation of charge carriers in the ferroelectric domains creates patterns of oxidized ...

Infrared spectra, photochemistry, and ab initio calculations of matrix isolated methanethiol/sulfur dioxide complex

Intermolecular complexes of methanethiol with sulfur dioxide have been prepared by condensing the reagents diluted in argon and in nitrogen at 12–14K. The 1:1 CH3SH/SO2 complexes were identified from the infrared spectra of the mixtures of methanethiol with sulfur dioxide in argon and nitrogen matrices. Perturbations to the vibrational energy spaces of some vibrational modes were identified and assigned. Ab initio calculations with the 6-311G∗∗ basis set have been performed to get some information about the structure, binding energy, dipole moment, and potential function governing the internal rotation of SO2 for the complex. The calculated results have suggested that the dipole/dipole interaction held the constituent species together to form the complex. Photochemical reactions were performed by exposing the matrix mixtures to UV irradiation. The appearance of new bands indicated the presence of more than one photochemical reaction product.

Enantioselective magnetochiral photochemistry

Many chemical and physical systems can occur in two forms distinguished solely by being mirror images of each other. This phenomenon, known as chirality, is important in biochemistry, where reactions involving chiral molecules often require the participation of one specific enantiomer (mirror image) of the two possible ones. In fact, terrestrial life utilizes only the L enantiomers of amino acids, a pattern that is known as the 'homochirality of life' and which has stimulated long-standing efforts to understand its origin. Reactions can proceed enantioselectively if chiral reactants or catalysts are involved, or if some external chiral influence is present. But because chiral reactants and catalysts themselves require an enantioselective production process, efforts to understand the homochirality of life have focused on external chiral influences. One such external influence is circularly polarized light, which can influence the chirality of photochemical reaction products. Because natural optical activity, which occurs exclusively in media lacking mirror symmetry, and magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic fields, both cause polarization rotation of light, the potential for magnetically induced enantioselectivity in chemical reactions has been investigated, but no convincing demonstrations of such an effect have been found. Here we show experimentally that magnetochiral anisotropy--an effect linking chirality and magnetism--can give rise to an enantiomeric excess in a photochemical reaction driven by unpolarized light in a parallel magnetic field, which suggests that this effect may have played a role in the origin of the homochirality of life.

Set-up combining synchrotron radiation-induced photochemistry with IR probing: (HCl) n in Kr matrix

An FTIR spectrometer samples with an optimized beam guiding optics the volume irradiated with VUV radiation from a high flux beamline and monitors photochemical reaction products. Additionally UV and visible fluorescence spectra are recorded. Dissociation efficiencies for HCl monomers and multimers in Kr matrix are rather similar. The increase in absorption cross-section with multimer size is compensated by a decreasing dissociation quantum efficiency. The H atom cage exit probability of monomers is only some percent in contrast to previous results, and the discrepancy is attributed to saturation effects in fluorescence spectroscopy of electronic transitions in the Cl products. Build-up and decay of Cl–HCl and H–HCl intermediates are monitored and simulated.

Infrared dip spectra of photochemical reaction products in a phenol/ammonia cluster: examination of intracluster hydrogen transfer

The vibrational transitions of the photochemical reaction products in phenol-(NH 3) 3 have been measured by infrared (IR) dip spectroscopy. Two sharp bands at ∼3200 cm −1 and a broad band in the region 2700∼3100 cm −1 are observed. The spectrum is clearly different from that of the cluster in S 0, and also largely different from the IR spectrum of NH 4 +(NH 3) 2. This suggests that hydrogen transfer occurs in electronically excited phenol-(NH 3) 3. Evidence of hydrogen transfer has also been found in phenol-(NH 3) 4 based on the mass spectrum and the IR dip spectrum of the cluster.

Nuclear magnetic resonance spectra and structure of fluorinated oxetanes

Fluorine, hydrogen, and carbon-13 nuclear magnetic resonance spectral data are reported for a variety of oxetane compounds containing fluorine on or near the ring. Effects of substituents on the spectra are analyzed and correlations of chemical shifts and coupling constants in terms of molecular structure are presented. Application of NMR permits the assignment of the regiochemistry and stereochemistry of the products of photochemical reactions between carbonyl compounds and olefins. Steric interactions and possible deviations from ring planarity are discussed in relation to the pathways of nuclear spin–spin interaction and to the trends observed in NMR parameters.

Implication of azelaic acid in a Greenland Ice Core for oceanic and atmospheric changes in high latitudes

A Greenland ice core (450 years) has been studied for low molecular weight dicarboxylic acids (C2‐C10) using a capillary gas chromatography and mass spectrometer. Their molecular distribution generally showed a predominance of succinic acid (C4) followed by oxalic (C2), malonic (C3), glutaric (C5), adipic (C6), and azelaic (C9) acids. Azelaic acid, that is a specific photochemical reaction product of biogenic unsaturated fatty acids, gave a characteristic historical trend in the ice core; i.e., the concentrations are relatively low during late 16th to 19th century (Little Ice Age) but become very high in late 19th to 20th century (warmer periods) with a large peak in 1940s AD. Lower concentrations of azelaic acid may have been caused by a depressed emission of unsaturated fatty acids from seawater microlayers due to enhanced sea ice coverage during Little Ice Age. Inversely, increased concentrations of azelaic acid in late 19th to 20th century are likely interpreted by an enhanced sea‐to‐air emission of the precursor unsaturated fatty acids due to a retreat of sea ice and/or by the enhanced production due to a potentially increased oxidizing capability of the atmosphere.

Photochemistry of Os(dmpe)2H2: Matrix, Transient Solution, and NMR Studies of 16-Electron Os(dmpe)2(dmpe = Me2PCH2CH2PMe2)

The complex Os(dmpe)2H2 (dmpe = Me2PCH2CH2PMe2) was synthesized by reaction of trans-Os(dmpe)2Cl2 with sodium under hydrogen and was shown to consist of cis and trans isomers in a ratio of ca. 60:1. UV irradiation in argon and methane matrices yielded Os(dmpe)2 with a characteristic multiband UV−vis spectrum; the lowest energy transition occurs close to 800 nm. In CO-doped matrices, Os(dmpe)2(CO) was generated. Laser flash photolysis experiments (266 nm excitation) demonstrated that the same species was produced in cyclohexane solutions of Os(dmpe)2H2 at room temperature. The initial photoproduct, Os(dmpe)2, is formed within 60 ns of the laser flash. This species reacts with hydrogen and with CO with rate constants exceeding 109 dm3 mol-1 s-1, indicating that there is essentially no barrier to its reaction with these substrates. Rate constants for reaction with ethene, triethylsilane, and nitrogen are all close to 108 dm3 mol-1 s-1. Comparison of the UV−vis spectrum of Os(dmpe)2 with Ru0, Rh+, and Ir+ analogues indicates that Os(dmpe)2 has a structure close to square planar (local D2h symmetry). The products of photochemical reaction of Os(dmpe)2H2 in solution were also studied by NMR spectroscopy. Reaction with benzene yields cis-Os(dmpe)2(Ph)H, while reaction with ethene yields cis- and trans-Os(dmpe)2(CHCH2)H.

Spatial and temporal variations of particulate precursor gases and photochemical reaction products during SJVAQS/AUSPEX ozone episodes

SJVAQS/AUSPEX acquired PM 2.5, PM 10, and gas samples at ten sites in central California during five ozone episodes over a period of 14 intensive sampling days. Four sample sets per day were collected for 5-and 7-hour durations during this period and analyzed for particulate mass, elements, ions, and organic and elemental carbon (OC and EC). Gaseous ammonia, nitric acid, and sulfur dioxide were collected with absorbing filters. Ozone (O 3), nitrogen oxides (NO x ), and peroxyacetyl nitrate (PAN) were measured continuously. Concentrations varied by sampling site, time of the day, and ozone episode. The highest concentrations of most chemical species were found at sites in the southern San Joaquin Valley. Nitrate occurred mainly in the gas phase during the daytime when temperatures exceeded 25°C, and in the particulate phase during the nighttime when temperatures decreased to less than 10°C. Significant amounts of nitrate volatilized from particles collected on quartz-fiber filters. Diurnal patterns of ozone, nitrogen oxides, PAN, nitric acid, and total particle nitrate were similar at most of the sites, which were separated by hundreds of kilometers, showing evidence of both photochemical conversion and transport of polluted air masses.

Quantitative Measurements of CpRh(CO)2 (Cp = η5-C5H5) Photochemistry in Various Hydrocarbon Solutions: Mechanisms for Ligand Photosubstitution and Intermolecular C−H and Si−H Bond Activation Reactions

The quantitative solution photochemistry of CpRh(CO)2 (Cp = η5-C5H5) involving ligand substitution and intermolecular C−H and Si−H bond activation processes has been investigated in several hydrocarbon solvents at room temperature following excitation in the region 313−458 nm. These photoreactions have been monitored by UV−vis and FTIR spectroscopy, and the absolute quantum efficiencies (φcr), determined to be in the 0.0007−0.31 range, are dependent on the entering ligand concentration, excitation wavelength, and solvent. The observed wavelength dependence is consistent with distinct reaction pathways occurring from two rapidly dissociating ligand-field (LF) excited states. Analysis of the quantitative photochemical results has led to a comprehensive mechanistic description for all of the various competing reaction pathways in the photochemistry of CpRh(CO)2. In the absence of an entering ligand, a carbonyl-bridged trans-Cp2Rh2(CO)3 complex is identified as the major photochemical reaction product; this s...

Translational diffusion of intermediate species in solutions

In this article, applications of the TG method to measurements of the translational diffusion of photochemically created intermediate species are reviewed. The intermediate species include unstable isomers, photochromic charged molecules, transient radicals created by photochemical reactions, and the electronically photoexcited species. Diffusional behaviors of these intermediates are different from those of stable molecules, which have been investigated extensively so far. The investigations of the diffusion of these species will provide opportunity to reveal the unique intermolecular interaction between the intermediates and matrix. Furthermore, by using products of photochemical reactions as probe molecules, the molecular dynamics of the system can be studied. This information will be valuable for understanding photochemistry in solution.