Major Photoproducts Research Articles

Photodegradation of brominated flame retardants in polystyrene: Quantum yields, products and influencing factors

Brominated flame retardants (BFRs) are widely used as additives in plastics, textiles and electronics materials. Here, we investigated the photodegradation of four BFRs including decabromobiphenylether (BDE-209), tetrabromobipsphenol A (TBBPA), tetrabromobisphenol A-bis(2,3-dibromopropylether) (TBBPA-DBPE) and tetrabromobisphenol A bis (allyl) ether (TBBPA-BAE). Experiments were carried out in polystyrene (PS) films using monochromatic and polychromatic irradiations. For comparison, irradiations were also carried in a solvent (tetrahydrofuran: THF). Monitoring of BFR degradation was performed using bulk and surface infrared (IR) measurements, as well as by extraction and HPLC-UV. Photoproducts were characterized using HPLC-high resolution electrospray ionization mass spectrometry (HPLC-ESI-Orbitrap-MS).All four BFRs underwent photochemical transformation in THF at 290 nm with a quantum yield (Φ) ranging from 0.05 for TBBPA to 0.27 for BDE-209, indicating an increase of photoreactivity with the number of Br atoms in BFRs. On the other hand, no major difference in the Φ values was observed when BFRs were embedded in PS films (Φ: 0.82–0.89). The higher photoreactivity in PS appears to be associated with a fast oxidation of PS as revealed by infrared (IR) analysis and yellowing of the films. Interestingly, the faster the yellowing occurred, the faster the BFR degradation was inhibited due to light screening effect. Several major photoproducts were identified for TBBPA and TBBPA-DBPE. Additional photoproducts possibly arising from PS oxidation and bromination by Br● were observed for the first time. This work provides a better understanding of the reactivity and fate of BFRs in polymers allowing for a better assessment of their environmental impacts.

Photodegradation of ciprofloxacin adsorbed in the intracrystalline space of montmorillonite

Although photolysis of antibiotics in aqueous solution was widely studied for a better understanding of their photolytic behavior in aqueous phase, the knowledge about photodegradation of antibiotics adsorbed on solid surfaces is still very limited. In this study, photodegradation of ciprofloxacin (CIP), a fluoroquinolone antibiotic, adsorbed in the intracrystalline space of montmorillonite (MMT) was examined using a xenon light source (300 W, λ > 320 nm). The gradual decrease of basal spacing of MMT from 1.66 to 1.46 nm with irradiation confirmed CIP decomposition in the intracrystalline space under simulated solar irradiation. Nearly 70 percent of adsorbed CIP was degraded after 5 h irradiation, and the reaction followed the first-order kinetics with a rate constant roughly 3 times than that in aqueous solution, indicating more efficient photodegradation of CIP after being adsorbed in the intracrystalline space of MMT. Spectroscopic analysis revealed that direct photolysis was the main photolytic mechanism. The hydroxyl radical induced by irradiated MMT might play an important role. The major photoproducts were identified with liquid chromatography-tandem mass spectrometry, and the main degradation pathways were proposed. The results demonstrated that the photoproduct distribution and degradation pathways of CIP adsorbed in the intracrystalline space differed from those in aqueous solution.

Microscopic environment and molecular orientation of guest molecules within polyfluorinated surfactant and clay hybrids: Photochemical studies of stilbazolium derivatives

Three kinds of cationic aromatic alkenes, trans-stilbazolium derivatives: trans-4-[2-[4-phenyl]ethenyl]-1-pyridinium chloride (1a), trans-4-[2-[4-phenyl]ethenyl]-1-methylpyridinium bromide (1b), and trans-4-[2-[4-(4′-hexadecyloxy)phenyl]ethenyl]-1-methylpyridinium bromide (1c), were each cointercalated with a cationic polyfluorinated surfactant (C3F-S) within the interlayer of cation-exchangeable clay (SSA) to form hybrid compounds (C3F-S/SSA hybrids). The molecular orientations of the intercalated cationic molecules within the C3F-S/SSA hybrids were investigated photochemically using the stilbazolium derivatives as probes. Compound 1a exhibited selective excimer emission, indicating that at least two 1a molecules take on proximal orientations. However, the major photoproduct from 1a was the cis-isomer, and photodimer production was negligible. Absorption spectroscopic analysis showed that cointercalated 1a molecules were deprotonated within the C3F-S/SSA hybrid. These results suggested that deprotonated 1a was situated in a hydrophobic environment formed by the alkyl chains of C3F-S molecules. Compound 1b also exhibited selective excimer emission and both syn-head-to-head and syn-head-to-tail cyclodimers were obtained, suggesting that 1b could be competitively coadsorbed with C3F-S up to the amount of 100% vs CEC of SSA to form parallel conformational aggregates on the same side of the SSA surface. The amount of 1b that was directly adsorbed on the SSA surface was proportional to the sum of all cationic molecules present (1b and C3F-S). The remaining 1b molecules were solubilized as aggregates in the long alkyl chain “forest” of C3F-S in an antiparallel manner. Compound 1c exhibited predominantly monomer emission, and the cis-isomer was observed as the major photoproduct. These results indicated that cationic 1c was adsorbed as isolated monomers in the C3F-S/SSA hybrids because of the formation of hydrophobic interactions with the substituted long alkyl chains of 1c and C3F-S molecules. Thus, it was revealed that C3F-S/SSA provides a unique microenvironment for guest molecules, such as cationic stilbazolium derivatives, through a delicate balance among (1) electrostatic interactions exerted by the negatively charged SSA surface, (2) hydrophobic interactions from the long alkyl chain of C3F-S, and (3) both hydrophobic and lipophobic interactions from the perfluoropropyl chains of C3F-S that form a polyfluorinated “wall”.

The sequence specificity of UV-induced DNA damage in a systematically altered DNA sequence

The sequence specificity of UV-induced DNA damage was investigated in a specifically designed DNA plasmid using two procedures: end-labelling and linear amplification. Absorption of UV photons by DNA leads to dimerisation of pyrimidine bases and produces two major photoproducts, cyclobutane pyrimidine dimers (CPDs) and pyrimidine(6-4)pyrimidone photoproducts (6-4PPs). A previous study had determined that two hexanucleotide sequences, 5′-GCTC*AC and 5′-TATT*AA, were high intensity UV-induced DNA damage sites. The UV clone plasmid was constructed by systematically altering each nucleotide of these two hexanucleotide sequences. One of the main goals of this study was to determine the influence of single nucleotide alterations on the intensity of UV-induced DNA damage. The sequence 5′-GCTC*AC was designed to examine the sequence specificity of 6-4PPs and the highest intensity 6-4PP damage sites were found at 5′-GTTC*CC nucleotides. The sequence 5′-TATT*AA was devised to investigate the sequence specificity of CPDs and the highest intensity CPD damage sites were found at 5′-TTTT*CG nucleotides. It was proposed that the tetranucleotide DNA sequence, 5’-YTC*Y (where Y is T or C), was the consensus sequence for the highest intensity UV-induced 6-4PP adduct sites; while it was 5′-YTT*C for the highest intensity UV-induced CPD damage sites. These consensus tetranucleotides are composed entirely of consecutive pyrimidines and must have a DNA conformation that is highly productive for the absorption of UV photons.

The Photochemistry of Unprotected DNA and DNA inside Bacillus subtilis Spores Exposed to Simulated Martian Surface Conditions of Atmospheric Composition, Temperature, Pressure, and Solar Radiation.

DNA is considered a potential biomarker for life-detection experiments destined for Mars. Experiments were conducted to examine the photochemistry of bacterial DNA, either unprotected or within Bacillus subtilis spores, in response to exposure to simulated martian surface conditions consisting of the following: temperature (-10°C), pressure (0.7 kPa), atmospheric composition [CO2 (95.54%), N2 (2.7%), Ar (1.6%), O2 (0.13%), and H2O (0.03%)], and UV-visible-near IR solar radiation spectrum (200-1100 nm) calibrated to 4 W/m2 of UVC (200-280 nm). While the majority (99.9%) of viable spores deposited in multiple layers on spacecraft-qualified aluminum coupons were inactivated within 5 min, a detectable fraction survived for up to the equivalent of ∼115 martian sols. Spore photoproduct (SP) was the major lesion detected in spore DNA, with minor amounts of cyclobutane pyrimidine dimers (CPD), in the order TT CPD > TC CPD >> CT CPD. In addition, the (6-4)TC, but not the (6-4)TT, photoproduct was detected in spore DNA. When unprotected DNA was exposed to simulated martian conditions, all photoproducts were detected. Surprisingly, the (6-4)TC photoproduct was the major photoproduct, followed by SP ∼ TT CPD > TC CPD > (6-4)TT > CT CPD > CC CPD. Differences in the photochemistry of unprotected DNA and spore DNA in response to simulated martian surface conditions versus laboratory conditions are reviewed and discussed. The results have implications for the planning of future life-detection experiments that use DNA as the target, and for the long-term persistence on Mars of forward contaminants or their DNA. Key Words: Bacillus subtilis-DNA-Mars-Photochemistry-Spore-Ultraviolet. Astrobiology 18, 393-402.

Characterization and Photodegradation of Polybrominated Diphenyl Ethers in Car Seat Fabrics from End-of-Life Vehicles.

In this study, we examined the photodegradation of decabromodiphenyl ether (BDE-209) on the surface of car seat covers from end-of-life vehicles (ELVs). Samples were collected at two car dismantling facilities in Sweden and cover car models from 1989 to 1998. The content of polybrominated diphenyl ethers (PBDEs) in nine real samples (fabric and polyurethane foam) was first characterized. Fabric samples that did not contain BDE-209 were then spiked with BDE-209 and irradiated in the laboratory and under sunlight. Photoproducts were identified using high performance liquid chromatography coupled to electrospray ionization mass spectrometer (HPLC-ESI-Orbitrap-MS), whereas volatile products were analyzed by gas chromatography-mass spectrometry (GC-MS). Similar photodegradation rates and oxidation products were observed in fabric samples irradiated in the laboratory and those collected from ELVs. Estimated half-life of BDE-209 on fabric inside vehicles ranged from 3 to 6 years. Thirteen major photoproducts were identified as lower brominated products, hydroxylated BDEs, brominated and hydroxylated dibenzofurans (PBDFs) and dioxins (PBDDs). Furthermore, several photoproducts were found to be transferable into water, particularly bromophenols and hydroxylated BDEs, and others into gas phase, such as bromomethanol and 1,2-dibromoethane. This should be taken into consideration for better estimating exposure to PBDEs and to develop strategies for ELV recycling.

Photolysis of clethodim herbicide and a formulation in aquatic environments: Fate and ecotoxicity assessment of photoproducts by QSAR models

The photochemical fate of the herbicide clethodim in natural waters was investigated under simulated and natural sunlight radiation. This herbicide exhibited a rapid degradation rate in simulated aquatic environment with half-lives ranged from 27.9min to 4.6h. The commercial formulation of clethodim showed a faster degradation with half-lives from 19.3min to 1.4h. It has also been demonstrated that the photolytic behavior of clethodim was affected by the water composition and the radiation intensity. Nine major photoproducts were identified and their distribution was dependent on the experimental conditions.Photodegraded solutions of clethodim were shown to be more toxic to the bacteria Vibrio fischeri than the herbicide itself, reaching the maximum toxicity when the herbicide is completely degraded. QSAR analysis of the fate, ecotoxicological and physicochemical endpoints of the degradation products provided positive alerts for several identified by-products. Environmental fate and transport estimates showed that all photoproducts, unlike the active substance, are potential leachers. Moreover, predicted vapor pressures suggested that dermal contact and ingestion are the most probable exposure routes for workers and general population to both clethodim and its photoproducts.These results highlight the importance of the degradation products in attaining a complete knowledge of the fate and behavior of an herbicide in the environment. To our knowledge, this is the first study to report a detailed QSAR study on clethodim photoproducts under environmental conditions. These results provide a very valuable information that will guide further experimental studies leading to a better pesticide risk assessment.

Indications of 5' to 3' Interbase Electron Transfer as the First Step of Pyrimidine Dimer Formation Probed by a Dinucleotide Analog.

Pyrimidine dimers are the most common DNA lesions generated under UV radiation. To reveal the molecular mechanisms behind their formation, it is of significance to reveal the roles of each pyrimidine residue. We thus replaced the 5'-pyrimidine residue with a photochemically inert xylene moiety (X). The electron-rich X can be readily oxidized but not reduced, defining the direction of interbase electron transfer (ET). Irradiation of the XpT dinucleotide under 254 nm UV light generates two major photoproducts: a pyrimidine (6-4) pyrimidone analog (6-4PP) and an analog of the so-called spore photoproduct (SP). Both products are formed by reaction at C4=O of the photo-excited 3'-thymidine (T), which indicates that excitation of a single "driver" residue is sufficient to trigger pyrimidine dimerization. Our quantum-chemical calculations demonstrated that photo-excited 3'-T accepts an electron from 5'-X. The resulting charge-separated radical pair lowers its energy upon formation of interbase covalent bonds, eventually yielding 6-4PP and SP.

Phototransformation of 5-nitro-2-furaldehyde in aqueous solution. A laser flash photolysis and product analysis study.

Laser flash photolysis of 5-nitro-2-furaldehyde (NFA) in solution shows a short-lived transient absorption with λmax = 475 ± 5 nm, which is relatively insensitive to solvent polarity and is assigned to the lowest triplet state of NFA (3NFA*). In water, the 3NFA* absorption decays to a long-lived absorption, the study of which, at different times after the end of the laser pulse, reveals it to be due to a furyloxyl radical (λmax ≈ 375 nm) and to the radical anion NFA˙- (λmax ≈ 400 nm). These radicals were produced independently to confirm the assignment. The lifetime of 3NFA* depends both on the solvent and the ground-state concentration of NFA. An (n, π*) nature is attributed to 3NFA* on the basis of the propensity of 3NFA* to abstract a hydrogen-atom from the solvent. Kinetic evidence for triplet excimer formation was obtained from the self-quenching of 3NFA* in solvents where the triplet decay is slower. The effect of acidity on the triplet lifetime is discussed with respect to an electron-transfer self-quenching mechanism, assisted by the triplet excimer which is proposed to dissociate into radical ions. Chromatographic and spectroscopic analysis of the photolysed aqueous solution of NFA enabled the identification of 5-hydroxymethylene-2(5H)-furanone, nitrite ion and an unknown substance as the major photoproducts. Conclusive evidence is presented that the observed 5-hydroxymethylene-2(5H)-furanone is formed from the furyloxyl radical. It is shown that the unknown substance can also be obtained from both the photoreduction of NFA in propan-2-ol and chemical reduction of NFA by Fe(s) in water (along with 5-amino-2-furaldehyde). Based on 1H- and 13C-NMR (with 2-D HMQC) and vibrational absorption spectroscopy, a tentative structure is proposed for the substance of tR 3.69 minutes obtained as a photoreduction product of NFA in water. Inorganic anions are shown to be one-electron oxidised by 3NFA* (as indicated by the observation of both the radical anion of NFA and the inorganic radical) with second-order rate constants being dependent on E of the inorganic radical. The implications of the results from complete quenching of 3NFA* by inorganic anions, and subsequent product analysis, for the phototransformation mechanism of NFA in water are discussed.

Lumisterol to Tachysterol Photoisomerization in EPA Glass at 77 K. A Comparative Study

We present a comparative study of the photoisomerizations of lumisterol (Lumi), previtamin (Pre), and provitamin D3 (Pro) to tachysterol (Tachy) at 77 K in EPA (5:5:2 ether, isopentane, and ethanol by volume) glass. Fluorescence, fluorescence excitation, and UV spectra, measured in the course of these reactions, were analyzed using singular value decomposition with self-modeling (SVD-SM). This represents an extension of previous work that led to the conclusion that in the EPA glass Pre exists as an s-cis,s-cis-conformer (cZc-Pre) which gives, exclusively, an unstable s-cis,s-cis-conformer of Tachy (cEc-Tachy) and Pro gives mainly the tEc-Tachy, that corresponds to a stable s-trans,s-cis-conformer. ( Redwood , C. ; et al. J. Phys. Chem. Lett. 2013 , 4 , 716 - 721 . ) The surprising result was that the major Pre photoproduct from Pro also has a tZc-Pre conformation instead of the expected cZc-Pre conformation. Accordingly, the Pre to Tachy cis-trans photoisomerization proceeds via a conformer specific one-bond-twist (OBT) process as proposed by Havinga ( Maessen , P. A. ; et al. Angew. Chem. Int. Ed. Engl. 1983 , 22 , 718 - 719 . Maessen , P. A. ; et al. Angew. Chem. Int. Ed. Engl. 1983 , 22 , 994 - 1004 . Maessen , P. A. Ph.D. Thesis, State University at Leiden, Leiden, The Netherlands, 1983. ). The role of the EPA glass in controlling conformer distributions and reaction outcomes is further explored by the extension of the studies to Lumi, whose structure differs substantially from that of its stereoisomer, Pro. Initially, the light-induced conrotatory ring openings of Pro and Lumi are expected to give cZc-Pre conformers that differ in the relative orientation of the double bond dihedral angles that define the chiral axis of the triene moiety: (-)cZ(-)c-Pre and (+)cZ(+)c-Pre, respectively. In the case of Pro, much of the cZc-Pre proceeds to tZc-Pre, the precursor of tEc-Tachy. In contrast, we show that under the same conditions most cZc-Pre formed from Lumi retains the cZc-conformation and isomerizes to cEc-Tachy. cZc-Pre from Lumi was not detected by fluorescence, but UV absorption measurements establish its formation as an essential intermediate to Tachy. Aided by theoretical calculations of conformer UV and CD spectra, we conclude that fluorescent thermodynamic Pre and nonfluorescent Pre from Lumi are both (+)cZ(+)c-Pre conformers. They differ in the orientation of the OH in the A ring, pseudoequatorial in the former and pseudoaxial in the latter. The most likely major photochemical sequences starting from Pre and Lumi are (+)cZ(+)c-Pre-eq-OH → (+)cE(+)c-Tachy-eq-OH and Lumi → (+)cZ(+)c-Pre-ax-OH → (+)cE(+)c-Tachy-eq-OH.

Synthesis and Characterization of a RuPt‐Based Photo‐Hydrogen‐Evolving Molecular Device Tethered to a Single Viologen Acceptor

A dinuclear RuIIPtII complex tethered to a methyl viologen (MV2+) unit {RuPt‐MV2+; [RuII(bpy)2{phen‐bpy(MV2+)}PtIICl2]4+, bpy = 2,2′‐bipyridine, phen = 5‐amino‐1,10‐phenanthroline} has been synthesized to investigate the effect of tethering a single pendant MV2+ acceptor on its photo‐hydrogen‐evolving (PHE) activity. Upon photoirradiation of RuPt‐MV2+ in the presence of EDTA as a sacrificial electron donor, the one‐electron‐reduced species of RuPt‐MV2+ {i.e., [RuII(bpy)2{phen‐bpy(MV+·)}PtIICl2]3+} is generated as a major photoproduct by intramolecular electron transfer (IET) from the 3MLCT excited state of the [RuII(bpy)2(phen)]2+ unit to the MV2+ unit, followed by subsequent reduction of the [RuIII(bpy)2(phen)]3+ unit by EDTA. Although RuPt‐MV2+ shows PHE activity in the presence of EDTA, the estimated turnover number (0.4) is smaller than that for the parent RuIIPtII system, which has no MV2+ tether. The relatively small driving force (0.08 eV) for the IET from the 3MLCT excited state of the [RuII(bpy)2(phen)]2+ unit to the PtIICl2(bpy) unit, which leads to the H2 formation, has been judged to be the major cause of the exceptionally low PHE activity observed for the present system.

Roles of singlet oxygen and dissolved organic matter in self-sensitized photo-oxidation of antibiotic norfloxacin under sunlight irradiation

Many fluoroquinolone (FLQ) antibiotics undergo rapid photodegradation in sunlit waters and form multifaceted photo-products. The high photodegradation rate is primarily ascribed to their photosensitizing properties. Though widely studied, the photo-reaction pathways are not completely revealed; photo-products mediated by different reactive oxygen species are not identified. In our study, photo-degradation of fluoroquinolone norfloxacin was investigated. A rapid degradation in buffered water was observed with a first-order rate constant of 2.45/hr and a quantum yield of 0.039. After light screening correction, selected DOMs (5 mg C/L) slightly enhanced the photodegradation rate with the exception of Suwannee river hydrophobic organic matter (SR-HPO). Three major photo-products were identified using high resolution mass spectrometry (HRMS). With 1O2 dark formation and competitor experiments, norfloxacin self-sensitized 1O2 was found to oxidize norfloxacin by inducing its piperazine chain cleavage. DOMs exhibited a dual role by inhibiting the 1O2-mediated reaction while enhancing the heterolytic defluorination pathway. DOMs were proposed to enhance heterolytic defluorination by donating electron to triplet state FLQ, this proposal was supported with specific UV absorbance (SUVA) as an indicator for the abundance of π bonds. Fluoride formation indicated a 79% elimination ratio of fluorine, an important functional group for antimicrobial activity. This work provides important new insights into the photochemical fate of fluoroquinolone antibiotics in natural water.

New aspects of UV photolysis of hydrogen peroxide. Nitrogen matrix isolation FTIR and theoretical studies

Abstract UV photochemistry of H 2 O 2 isolated in solid nitrogen at 15 K has been studied experimentally by FTIR matrix isolation technique and theoretically using DFT and MP2 methods. The major photoproducts were identified as (i) nitrous oxide and N 2 O⋯H 2 O complex and (ii) free and complexed to N 2 O hydroxyl radicals. Except for the OH radicals all observed species are unique and characteristic for H 2 O 2 photolysis in solid nitrogen. The identities of the products have been confirmed by comparison with results of quantum chemical calculations, and reference to the spectral data of related molecules. Differences in the photolysis course upon irradiation at 230 and 212 nm are discussed.

Photocatalytic activity of Cu2O supported on multi layers graphene for CO2 reduction by water under batch and continuous flow

The photocatalytic activity of Cu2O supported on multi-layers graphene for CO2 reduction by water was studied under two hydrodynamic environments, in a slurry batch reactor and in a capillary reactor with the catalyst immobilized on the wall. Under both conditions, the major photoproduct was hydrogen observed in the gas phase, accompanied by lesser amounts of ethanol present in the aqueous solution. The maximum production rates were 2031 and 545μmolg−1h−1 for H2 and CH3CH2OH, respectively, and were found under the hydrodynamic mode attained in the capillary reactor.

Characterization of the ultraviolet–visible photoproducts of thiophanate-methyl using high performance liquid chromatography coupled with high resolution tandem mass spectrometry—Detection in grapes and tomatoes

UV–visible irradiation of thiophanate-methyl (TM) led to the formation of nine photoproducts that were characterized by high performance liquid chromatography coupled with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Although carbendazime has been reported in the literature to be the major metabolite and photoproduct of thiophanate-methyl, it was not detected in this study. However, an isomer of carbendazime referred as PP2, which was unambiguously characterized owing to CID experiments, was found in great abundance. Grape berries and cherry tomatoes treated with aqueous solutions of thiophanate-methyl were submitted to irradiation under laboratory conditions. TM and PP2 were detected in both peel and flesh of berries. The ability of TM and PP2 to pass through the fruit skin has been shown to be highly compound and matrix dependent. In vitro bioassays on Vibrio fischeri bacteria showed that the global ecotoxicity of the TM solution increases significantly with the irradiation time. PP2 should likely contribute to this ecotoxicity enhancement since in silico estimations for Daphnia magna provide a LC50 value seven times lower for PP2 than for the parent molecule.

A Study on the Photoreaction of 2(5H)-Furanones with Substituted Acetylenes: Evidence for a Mechanistic Reformulation.

The photoreaction of 2(5H)-furanones with alkynes has been investigated. The complexity of this process is evidenced by the variety of isolated products, which have allowed disclosing interesting mechanistic aspects. When the reaction is performed in acetonitrile under direct excitation, in addition to the primary [2+2] cycloadducts, products derived from an 1,3-acyl shift rearrangement are also formed. For unsymmetrical alkynes, the rearrangement of the head-to-tail primary adducts produces new regioisomers and, when the starting furanone is chiral, this rearrangement inverts the relative anti/syn geometry of the primary cycloadducts. In the reactions performed in acetone under photosensitized conditions, rearranged products were never detected, supporting that the 1,3-acyl shift takes place from the singlet excited state S1 of the β,γ-unsaturated lactone. When bis(trimethylsilyl)acetylene is used as the alkyne partner, the major photoproducts are monocyclic bis(trimethylsilyl)lactones.

Intramolecular CH Activation and Metallacycle Aromaticity in the Photochemistry of [FeFe]-Hydrogenase Model Compounds in Low-Temperature Frozen Matrices.

The [FeFe]-hydrogenase model complexes [(μ-pdt){Fe(CO)3 }2 ], [(μ-edt){Fe(CO)3 }2 ], and [(μ-mdt){Fe(CO)3 }2 ], where pdt=1,3-propanedithiolate, edt=1,2-ethanedithiolate, and mdt=methanedithiolate, undergo wavelength dependent photodecarbonylation in hydrocarbon matrices at 85 K resulting in multiple decarbonylation isomers. As previously reported in time-resolved solution photolysis experiments, the major photoproduct is attributed to a basal carbonyl-loss species. Apical carbonyl-loss isomers are also generated and may undergo secondary photolysis, resulting in β-hydride activation of the alkyldithiolate bridge, as well as formation of bridging carbonyl isomers. For [(μ-bdt){Fe(CO)3 }2 ], (bdt=1,2-benzenedithiolate), apical photodecarbonylation results in generation of a 10 π-electron aromatic FeS2 C6 H4 metallacycle that coordinates the remaining iron through an η(5) mode.

Structural elucidation of metolachlor photoproducts by liquid chromatography/high-resolution tandem mass spectrometry.

Metolachlor is one of the most intensively used chloroacetanilide herbicides in agriculture. It has been detected in water; consequently, under UV-visible irradiation, it can be transformed in degradation products (TPs). The structures of TPs were elucidated by liquid chromatography/high-resolution tandem mass spectrometry (LC/HR-MS/MS). The potential toxicities of these TPs were estimated by in silico tests. Aqueous solutions of metolachlor were irradiated in a self-made reactor equipped with a mercury vapor lamp. Analyses were carried out using high-performance liquid chromatography coupled to quadrupole time-of-flight (QTOF) mass spectrometer. High-resolution m/z measurements, MS/MS and isotopic labeling experiments allowed structural elucidation of metolachlor TPs. Their toxicities were estimated in silico, using the T.E.S.T. Ten major metolachlor photoproducts were characterized by LC/MS/MS after irradiation of metolachlor in aqueous solution. Elucidation of their chemical structures was identified using high-resolution measurements and MS/MS experiments. They resulted from the combination of dehalogenation, hydroxylation and cyclisation processes. The potential oral rat lethal dose (LD50) was assessed with QSAR tests for metolachlor and each photoproduct. Results indicate that most of the TPs are much more toxic than metolachlor. UV-vis irradiation of metolachlor in aqueous solution leads to the formation of ten photoproducts. QSAR estimations show that the location of added hydroxyl group(s) is of key relevance as regards to biological activity and that routine water analysis should take into account the TPs are more toxic than the parent molecule.

Commentary: Chemiexcitation of melanin derivatives induces DNA photoproducts long after UV exposure.

Commentary: Chemiexcitation of melanin derivatives induces DNA photoproducts long after UV exposure.

Photo-degradation study of dacarbazine by spectrophotometric–chemometrics and HPLC methods

DTIC or dacarbazine is a photosensitive drug which is analyzed by chromatography methods. In this study, chemometric methods were applied to resolve the UV–Vis absorbance spectra recorded during irradiation of DTIC by an artificial lighting source. The photo-degradation reaction was monitored at different pH media (between 2 and 12). Multivariate curve resolution-alternative least square was then employed to simultaneously analyze the absorbance data matrices obtained at various pH media. Factor analysis revealed the presence of five chemical species co-existing in the reaction media. Regarding the analysis of concentration profiles of the detected species at different pH values, three species were attributed to the different acid–base states of DTIC, while the remaining components were considered as acid–base states of the photoproduct. Eventually, the presence of major photoproduct (2-azahypoxanthine) was confirmed by the HPLC method.