Photolysis Products Research Articles

Electronic and Steric Tuning of Catalytic H2 Evolution by Cobalt Complexes with Pentadentate Polypyridyl-Amine Ligands.

Structural modifications of molecular cobalt catalysts have provided important insights into the structure-function relationship for the hydrogen evolution reaction. We have shown that replacement of equatorial pyridines with more basic and conjugate isoquinoline groups of a pentadentate ligand results in lower overpotential and higher catalytic activity for electro- and photolytic H2 production in aqueous solutions. To fully understand the electronic and steric effects of the axial group that lies trans to the proposed cobalt hydride intermediate, isoquinoline groups were introduced in two new pentadentate ligands, N, N-bis(2-pyridinylmethyl)[3-(2-pyridinyl)isoquinoline)]-1-methanamine (DPA-1-MPI) and N, N-bis(2-pyridinylmethyl)[1-(2-pyridinyl)-isoquinoline)]-3-methanamine (DPA-3-MPI). Despite a slight structural difference of the introduced isoquinoline group, the resulting cobalt complexes display drastic changes in their electro- and photochemical properties. There are positive shifts of 290 and 260 mV, respectively, for the CoII/CoI and CoIII-H/CoII-H couples from [Co(DPA-1-MPI)(H2O)](PF6)3 to [Co(DPA-3-MPI)(H2O)](PF6)3, with the former being ∼32 times as active as the latter in photocatalytic H2 production. Density functional theory (DFT) calculations show that the protonation of CoI to yield the CoIII-H species is energetically more favorable for [Co(DPA-1-MPI)(H2O)](PF6)3 than that of [Co(DPA-3-MPI)(H2O)](PF6)3. Both experimental results and DFT computations suggest that the presence of a planar conjugate bipyridyl unit or its isoquinoline derivative is a key feature for stabilizing low valent CoI species toward proton binding. The incorporation of an electron-donating group trans to the proposed Co-H species also facilitates proton binding and H-H bond formation, which is proposed to occur by the heterolytic coupling of CoII-H species. The overall catalytic H2 evolution is presented as the modified electron transfer (E)-proton transfer (C)-electron transfer (E)-proton transfer (C) (mod-ECEC) pathway. This study provides important new insight into the electronic and steric factors controlling catalytic H2 production by Co complexes with pentadentate ligands.

Wavelength-dependent chlorine photolysis and subsequent radical production using UV-LEDs as light sources

UV-LEDs are considered as the most promising UV light sources, because it has the potential to replace conventional UV lamps in some water treatment applications in the foreseeable future. In this study, UV-LEDs at four wavelengths in the UV-C or near UV-C range (i.e., 257.7, 268, 282.3, and 301.2 nm) were used to investigate the wavelength-dependency on chlorine photolysis and its subsequent radical formation. The fluence-based photodecay rates of hypochlorous acid (HOCl) and hypochlorite (OCl−) were monotonically correlated to their molar absorption coefficients and quantum yields, and the chlorine photodecay rates were much more significantly affected by molar absorption coefficients (β = 0.949) than quantum yields (β = 0.055). An empirical model that incorporated the chlorine photodecay rate constants, quantum yields, and molar absorption coefficients of HOCl and OCl− was established, validated and then used to predict the chlorine photodecay rate at any wavelength (257.7–301.2 nm) and pH (5−10). The modelling results suggested that the maximum fluence-based rate constant (1.46 × 10−4 m2 J−1) was obtained at 289.7 nm and pH 9.95. The wavelength dependency was larger at alkaline pH than at acidic pH, and the pH dependency was the largest at the longest wavelength. The formation of hydroxyl radicals (HO·) and reactive chlorine species (RCS) decreased with increasing wavelength at pH 6, and increased with increasing wavelength at pH 7. More HO· was formed at pH 6 than pH 7, but RCS showed the opposite pH-dependency. The findings in this study provide the fundamental information in selecting UV-LEDs with specific wavelength for enhancing/optimizing chlorine photodecay and/or its radical generation at different pHs in real-world applications.

Comparison Between Cyano and C-18 Columns for Separation of Trandolapril and Verapamil with ESI-Q-ToF-MS Characterization of Acidic and Basic Degradation Products: Stability Indicating Assay Methods

Different stationary phases were compared for their separation efficiency of Trandolapril (TRP) and Verapamil (VRP) in presence of acidic, basic, oxidative, and photolytic degradation products. The separation was applied on two different stationary phases. The first stationary phase was the conventional C18, whereas the second was the more polar cyano stationary phase. However, for the conventional C18 packing, two columns with two different lengths were used, 250 and 150 mm. Optimum performance for C18 columns was obtained using acetonitrile: potassium di-hydrogen ortho-phosphate buffer pH 6 adjusted by 0.1 M NaOH (50:50 v/v) as a mobile phase while for cyano column it was acetonitrile: potassium di-hydrogen ortho-phosphate buffer pH 4.5 (25:75 v/v). For both stationary phases, the flow rate was 1 mL min−1 and the detection wavelength was 215 nm. The validations of all the adopted methods were done as per ICH guidelines. The comparison was accomplished in terms of resolution, tailing factor, column efficiency, and total run time of analysis. Both C-18 columns showed superior results over cyano column. The C-18 column (150 mm) exhibited better results than C-18 (250 mm) column in terms of column efficiency and total run time. The results were compared with the reference method and no significant differences were found. In addition, one-way ANOVA testing was done to compare the three methods.

Photolysis of parabens using medium-pressure mercury lamps: Toxicity effects in MCF7, Balb/c 3T3 cells and Ceriodaphnia dubia

Degradation studies of the propylparaben (PrP), butylparaben (BuP) and of the propylparaben-butylparaben mixture (PrP-BuP) in deionized water and surface river water was investigated as a function of pH and initial concentration of the reactants using a medium-pressure mercury lamp. The photolysis of parabens (concentration ranging from 5 to 30 mg L−1) followed apparent pseudo-first-order kinetics, with rate constants (k) in deionized water and surface river water changed from 1.80 × 10−1 to 3.68 × 10−2 min−1 and 1.43 × 10−1 to 1.45 × 10−2 min−1, respectively. Degradation reaction was faster at pH 5 in comparison with pH 7 or 11. The photolysis of parabens was greater than 91%, with low mineralization (26.15%) observed in acidic medium after 95 min. Analysis by chromatography coupled to mass spectrometry (LC-MS/MS) showed that only one product was generated during the degradation reaction and has UV bands similar to 3,4-dihydroxybenzoic acid. Estrogenic activity tests showed that non-degraded parabens stimulated the growth of breast adenocarcinoma (MCF-7) cells and this effect was evaluated after the photolysis. Cytotoxicity assays using fibroblasts cells (Balb/C 3T3 clone A31) indicated that the parental compounds and degradation products were not cytotoxic. On the contrary, non-degraded parabens were toxic to Ceriodaphnia dubia, but the product of photolysis was not. Overall, the photolytic method presented was able to degrade these parabens providing safe and non-estrogenic reaction product.

UV-C inactivation of foodborne bacterial and viral pathogens and surrogates on fresh and frozen berries

Outbreaks of foodborne illness associated with berries often involve contamination with hepatitis A virus (HAV) and norovirus but also bacteria such as Escherichia coli O157:H7 and parasites such as Cyclospora caytanensis. We evaluated the applicability of UV-C to the inactivation of pathogens on strawberries, raspberries and blueberries. Our three-step approach consisted of assessing the chemical safety of UV-C-irradiated berries, evaluating the sensory quality after UV-C treatment and finally studying the inactivation of the target microorganisms. Treatments lasting up to 9 min (4000 mJ cm−2) did not produce detectable levels of furan (<5 μg/kg), a known photolysis product of fructose with genotoxic activity and thus were assessed to be toxicologically safe. No effect on taste or appearance was observed, unless treatment was excessively long. 20 s of treatment (an average fluence of ~ 212 mJ cm−2) reduced active HAV titer by >1 log10 unit in 95% of cases except on frozen raspberries, while 120 s were required to inactivate murine norovirus to this extent on fresh blueberries. The mean inactivation of HAV and MNV was greater on blueberries (2–3 log10) than on strawberries and raspberries (<2 log10). MNV was more sensitive on fresh than on frozen berries, unlike HAV. Inactivation of Salmonella, E. coli O157:H7 and Listeria monocytogenes was poor on all three berries, no treatment reducing viable counts by >1 log10 unit. In most matrices, prolonging the treatment did not improve the result to any significant degree. The effect was near its plateau after 20 s of treatment. These results provide insight into the effectiveness of UV-C irradiation for inactivating bacterial and viral pathogens and surrogates on fresh and frozen berries having different surface types, under different physical conditions and at different levels of contamination. Overall they show that UV-C as single processing step is unsuitable to inactivate significant numbers of foodborne pathogens on berries.

Nitrogen-Containing, Light-Absorbing Oligomers Produced in Aerosol Particles Exposed to Methylglyoxal, Photolysis, and Cloud Cycling.

Aqueous methylglyoxal chemistry has often been implicated as an important source of oligomers in atmospheric aerosol. Here we report on chemical analysis of brown carbon aerosol particles collected from cloud cycling/photolysis chamber experiments, where gaseous methylglyoxal and methylamine interacted with glycine, ammonium, or methylammonium sulfate seed particles. Eighteen N-containing oligomers were identified in the particulate phase by liquid chromatography/diode array detection/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry. Chemical formulas were determined and, for 6 major oligomer products, MS2 fragmentation spectra were used to propose tentative structures and mechanisms. Electronic absorption spectra were calculated for six tentative product structures by an ab initio second order algebraic-diagrammatic-construction/density functional theory approach. For five structures, matching calculated and measured absorption spectra suggest that they are dominant light-absorbing species at their chromatographic retention times. Detected oligomers incorporated methylglyoxal and amines, as expected, but also pyruvic acid, hydroxyacetone, and significant quantities of acetaldehyde. The finding that ∼80% (by mass) of detected oligomers contained acetaldehyde, a methylglyoxal photolysis product, suggests that daytime methylglyoxal oligomer formation is dominated by radical addition mechanisms involving CH3CO*. These mechanisms are evidently responsible for enhanced browning observed during photolytic cloud events.

Proposal of degradation pathway with toxicity prediction for hydrolytic and photolytic degradation products of timolol

Timolol (TIM) is a potent β-adrenergic blocker, useful in treatment of ocular hypertension or open-angle glaucoma. Development and validation of stability indicating LCMS assay method for TIM was accomplished coherent with ICH guideline. Successful chromatographic separation of TIM with its four degradation products was attained by using gradient elution mode on reverse phase column using ammonium acetate buffer, pH 4.6 as mobile phase A and organic solvent as the mobile phase B. Chromatographic conditions were set such as 1.0 mL min−1 flow rate, 20 μL injection volume, 30 °C column temperature and 320 nm detection wavelength. Four major degradation products obtained from hydrolysis and photolysis, were identified and characterized with the combination of liquid chromatography–electrospray ionization mass spectrometry (LC–ESI/MS/MS) and accurate mass measurements. Degradation pathways were identified based on a comparison of the fragmentation pattern of the [M+H]+ ions of TIM and its degradation products. The method validation was performed as per ICH guideline Q2 (R1).

Direct Observation of an Imidoylnitrene: Photochemical Formation of PhC(=NMe)−N and Me−N from 1‐Methyl‐5‐phenyltetrazole

AbstractThe imidoylnitrene 8, N‐methyl‐C‐phenylimidoylnitrene, has been generated by laser photolysis of 1‐methyl‐5‐phenyltetrazole 6 at 5 K and characterized by its ESR spectrum (|D/hc|=0.9602, |E/hc|=0.0144 cm−1). In addition, the triplet excited states of 6 and of 2‐methyl‐5‐phenyltetrazole 11 were also observed by ESR spectroscopy in the 5 K matrices (6: |D/hc|=0.123 cm−1, E/hc=0.0065 cm−1, 11: |D/hc|=0.126 cm−1, |E/hc|=0.0056 cm−1). The imidoylnitrene 8 is unstable both thermally (disappearing at 80 K) and photochemically (disappearing on continued irradiation at 266 nm). Methyl(phenyl)carbodiimide is the end product of photolysis.

Direct Observation of an Imidoylnitrene: Photochemical Formation of PhC(=NMe)-N and Me-N from 1-Methyl-5-phenyltetrazole.

The imidoylnitrene 8, N-methyl-C-phenylimidoylnitrene, has been generated by laser photolysis of 1-methyl-5-phenyltetrazole 6 at 5 K and characterized by its ESR spectrum (|D/hc|=0.9602, |E/hc|=0.0144 cm-1 ). In addition, the triplet excited states of 6 and of 2-methyl-5-phenyltetrazole 11 were also observed by ESR spectroscopy in the 5 K matrices (6: |D/hc|=0.123 cm-1 , E/hc=0.0065 cm-1 , 11: |D/hc|=0.126 cm-1 , |E/hc|=0.0056 cm-1 ). The imidoylnitrene 8 is unstable both thermally (disappearing at 80 K) and photochemically (disappearing on continued irradiation at 266 nm). Methyl(phenyl)carbodiimide is the end product of photolysis.

Optical properties and antimicrobial effects of silver nanoparticles synthesized by femtosecond laser photoreduction

Silver nanoparticles exhibit a powerful antimicrobial action showing a pronounced potential to be widely used against drug resistance bacteria. The present work describes the optical properties and antimicrobial effect of silver nanoparticles produced by femtosecond laser photoreduction of AgNO3 in the presence of tryptophan water solution. The advantages of this method are the absence of hazardous chemical reducing agents in the solution, and the versatile dimensional control achieved. The synthesized silver nanoparticles were characterized by absorption and fluorescence spectroscopy and their antibacterial activity were determined by monitoring the cell viability of Escherichia coli. The effects of the silver nanoparticles concentration and laser parameters (exposure time and pulse energy), on the formation of the nanoparticles, and its influence on the bacteria growth inhibition were studied. The prepared silver nanoparticles exhibited suitable antimicrobial properties. The results demonstrated that the nanoparticles concentration plays an important role in their bactericidal efficacy. The increase in the laser energy caused an increase in E. coli growth inhibition. Irradiations with energies around 300 μJ for 60 min presented high antimicrobial activity due to the presence of kynurenine, sub product of tryptophan photolysis. The first-time formation mechanism of tryptophan silver nanoparticles in high optical intensities was also discussed.

Effect of triclosan and its photolysis products on marine bacterium V. fischeri and freshwater alga R. subcapitata

The use of antibacterial agents in consumer products may lead to adverse effects in waters receiving treated wastewater. Triclosan is one of the antibacterial agents used widely in the world and its high usage leads to relatively high concentrations in wastewater effluents. In this study, the probable effect of triclosan in receiving waters was assessed using different organisms. The EC50 values were 668 ± 80 μg/L and 7.8 ± 0.1 μg/L, for Vibrio fischeri and Raphidocelis subcapitata, respectively, indicating the higher sensitivity of the alga. The toxicity of triclosan upon exposure to UV light decreased for both species, as suggested by the increase in EC50 values (1300 ± 50 μg/L and 8.7 ± 0.6 μg/L for V. fischeri and R. subcapitata, respectively). The effect of photolysis on toxicity reduction was higher for V. fischeri and the EC50 values were similar for direct and indirect photolysis. LC-MS/MS analysis of samples with and without UV exposure suggested a decrease in triclosan concentration as well as formation of photolysis byproducts upon photolysis.

Stability Indicating 1st Derivative Synchronous Spectrofluorimetric Method for the Determination of the Newly Approved Antiviral Drug Daclatasvir in Presence of Its Oxidative and Photolytic Degradation Products: Application to Tablet Dosage Form

A highly sensitive, simple and rapid first derivative synchronous spectrofluorimetric method was utilized for the determination of daclatasvir dihydrochloride (DCV) in presence of its oxidative and photolytic degradation products. Where synchronous 1st derivative spectrofluorimetric approach was utilized to quantitatively determine DCV at 373 nm in presence of its oxidative degradation product and at 388 nm in presence of its photolytic degradation product that is obtained by exposing DCV to UV light at 312 nm, these were the zero-crossing wavelengths of degradation products without interference. The synchronous fluorescence was scanned at Δ λ of 80 nm. The method was found to be linear across the concentration range of 0.5-5.0 ng/mL with lower detection limit of 0.090 and lower quantification limit of 0.275 ng/mL (at 373 nm) and 0.268 ng/mL (at 388 nm). The adopted approach was successfully applied to commercial tablet and the results exhibited that the derivative synchronous fluorescence spectroscopy is a stabilityindicating method, suitable for routine use within a short analysis time. The proposed method was carefully validated for linearity, accuracy, precision, specificity and robustness.

Application of the UHPLC method for separation and characterization of major photolytic degradation products of trazodone by LC-MS and NMR

This article is about the characterization of degradation products of trazodone which is used in the treatment of depression.

Photochemistry of uranyl complexes with the salicylidene-α-hydroxy acid chelates, X-Sal-AHA

Two dimeric uranyl complexes, K2[UO2(3,5-diCl-Sal-AHA)]2 (1) and Na2[UO2(3,5-ditbutyl-Sal-AHA)]2 (2), were synthesized from salicylidene-α-hydroxy acid-containing chelates of the X-Sal-AHA series. Both are photochemically reactive upon irradiation with UV light, with quantum yields of 4.2% and 2.9% for 1 and 2, respectively. Irradiation results in similar spectroscopic changes for 1 and 2, which differ for each depending on the presence of air. The photolysis products include an air-sensitive U(IV) species, which can reduce methyl viologen, and an aldehyde resulting from decarboxylation of the chelate. The photochemistry of 1 and 2 is more similar to that of the Fe(III) complexes of the X-Sal-AHA chelates than to the typical photochemical reaction of uranyl nitrate in solution.

Low temperature studies of the removal reactions of 1CH2 with particular relevance to the atmosphere of Titan

Methylene, CH2, is one of the major photolysis products of methane by Lyman-α radiation and is involved in the photochemistry of the atmospheres of Titan and the giant planets. The kinetics of the reactions of the first excited state of methylene, 1CH2, with He, N2, O2, H2 and CH4 have been measured over the temperature range 43–160 K by pulsed laser photolysis, monitoring 1CH2 removal by laser induced fluorescence. Low temperatures were obtained with either a pulsed Laval expansion (43–134 K) or a, slow flow reaction cell (160 K). The rate coefficients for the reactions with N2, O2, H2 and CH4 all showed a strong negative temperature dependence. In combination with other literature data, the rate coefficients can be parameterised as:kHe(43 < T/K < 800) = (1.90 ± 0.23) × 10−12 × (T/298)1.74±0.16 × exp((88±23)/T)kN2(43<T/K<800) = (2.29 ± 1.12) × 10−12 × (T/298)−2.15±1.38 × exp((-74±96)/T) + (3.91 ± 0.78) × 10−11 × exp((-469±114)/T)kO2(43<T/K<300) = (6.16 ± 1.09) × 10−11 × (T/298)−0.65±0.14kH2(43<T/K<800) = (1.10 ± 0.04) × 10−10 × (T/298)−0.40±0.06 × exp((11.1±6.9)/T)kCH4(43<T/K<475) = (8.20 ± 0.46) × 10−11 × (T/298)−0.93±0.10 × exp((-20.5±12.8)/T)For the reactions of 1CH2 with H2 and CH4, the branching ratio for quenching to ground state, 3CH2, vs chemical reaction was also determined at 160 and 73 K. The values measured (H2: 0.39 ± 0.10 at 160 K, 0.78 ± 0.15 at 73 K; CH4: 0.49 ± 0.09 at 160 K, 0.64 ± 0.19 at 73 K) confirm trends of an increased proportion of reactive loss with increasing temperature determined at higher temperatures. The impacts of the new measurements for Titan's atmosphere have been ascertained using a 1D chemistry and transport model. A significant decrease (∼40%) in the mixing ratio of ethane between 800 and 1550 km is calculated due to the decrease contribution of methyl production from the reaction of 1CH2 with CH4, with smaller increases in the concentrations of ethene and acetylene. Ethene production is enhanced by more methylene being converted to methylidene, CH, and the subsequent reaction of CH with CH4 to generate ethene. Photolysis of ethene is the major route to acetylene formation.

Response mechanisms to joint exposure of triclosan and its chlorinated derivatives on zebrafish (Danio rerio) behavior

Triclosan (TCS), 2,4,6-trichlorophenol (2,4,6-TCP) and 2,4-dichlorophenol (2,4-DCP) frequently co-exist in real-world aquatic environments; the latter two contaminants contributing to TCS photolytic products or chlorinated derivatives. There is a paucity of information regarding their joint toxicity to aquatic organisms leading us to study their effects on the swimming behavior of zebrafish (Danio rerio). Herein, we reported that 0.28 mg/L TDT exposure (mixtures of TCS, 2,4,6-TCP and 2,4-DCP) enhanced 24-hpf embryonic spontaneous movement frequency, 96-hpf larval activity; however, the 0.56 and 1.12 mg/L TDT treatments decreased all of these behavioral endpoints. All adult behavioral tests demonstrated that chronic TDT exposure (0.14 mg/L) led to hyperactivity and restlessness in adult zebrafish. A 0.14 mg/L TD DATE /@ "M/d/yyyy" 11/21/2017T treatment led to anxiety-like behavior in a bottom dwelling test and excessive panic and low hedging capacity in a conditioned place preference test. Social interaction test demonstrated that zebrafish preferred quiet and isolated space in response to TDT stress. Zebrafish memory was significantly decreased in a T-maze experiment. Whole mount in situ hybridization of pax2a and bcl2l11 genes revealed that their differential expression in the brain and skeleton were related to the corresponding phenotypic behavioral abnormality. A series of biomarker and estrogen receptor assays demonstrated that TDT acute exposure caused abnormal energy metabolism and neurological diseases. AO staining revealed that TDT exposure produced vascular ablation in the head, as well as the occurrence of massive apoptosis in the brain. TEM observation showed pyknosis of nucleus following TDT exposure. These results allow assessment of mechanisms for zebrafish abnormal behavior in response to TDT exposure, and are useful for early intervention and gene therapy of contaminant-induced diseases.

Contrasting Photolytic and Thermal Decomposition of Phenyl Azidoformate: The Curtius Rearrangement Versus Intramolecular C-H Amination.

The decomposition of phenyl azidoformate, PhOC(O)N3, was studied by combining matrix isolation spectroscopy and quantum chemical calculations. Upon UV laser photolysis (193 and 266 nm), the azide isolated in cryogenic noble gas matrices (Ne and Ar, 2.8 K) decomposes into N2 and a novel oxycarbonylnitrene PhOC(O)N, which was identified by matrix-isolation IR spectroscopy (with 15N labeling) and EPR spectroscopy (|D/hc| = 1.620 cm-1 and |E/hc| = 0.024 cm-1). Subsequent visible-light irradiation (532 nm) causes rearrangement of the nitrene into phenoxy isocyanate PhONCO with complex secondary fragmentation (PhO· + ·NCO) and radical recombination species in matrices. The observation of PhONCO provides solid evidence for the Curtius rearrangement of phenyl azidoformate. In sharp contrast, flash vacuum pyrolysis (FVP) of PhOC(O)N3 at 550 K yields N2 and exclusively the intramolecular C-H amination product 3H-benzooxazol-2-one. FVP at higher temperature (700 K) leads to further dissociation into CO2, HNCO, and ring-contraction products. To account for the very different photolytic and thermal decomposition products, the underlying mechanisms for the Curtius rearrangement (concerted and stepwise) of PhOC(O)N3 and the intramolecular C-H amination of the nitrene in both singlet and triplet states are discussed with the aid of quantum chemical calculations using the B3LYP, CBS-QB3, and CASPT2 methods.

Is Photolytic Production a Viable Source of HCN and HNC in Astrophysical Environments? A Laboratory-based Feasibility Study of Methyl Cyanoformate

Motivated by the possibility that cyano-containing hydrocarbons may act as photolytic sources for HCN and HNC in astrophysical environments, we conducted a combined experimental and theoretical investigation of the 193 nm photolysis of the cyano-ester, methyl cyanoformate (MCF). Experimentally, nanosecond time-resolved infrared emission spectroscopy was used to detect the emission from nascent products generated in the photolysis reaction. The time-resolved spectra were analyzed using a recently developed spectral reconstruction analysis, which revealed spectral bands assignable to HCN and HNC. Fitting of the emission band shape and intensity allowed determination of the photolysis quantum yields of HCN, HNC, and CN (A22 Π1)and an HNC/HCN ratio of ∼0.076 ± 0.059. Additionally, multiconfiguration self-consistent field calculations were used to characterize photoexcitation-induced reactions in the ground and four lowest singlet excited states of MCF. At 193 nm excitation, dissociation is predicted to occur predominantly on the repulsive S 2 state, with minor pathways via internal conversion from S 2 to highly excited ground state. An automated transition-state search algorithm was employed to identify the corresponding ground-state dissociation channels, and Rice-Ramsperger-Kassel-Marcus and Kinetic Monte Carlo simulations were used to calculate the associated branching ratios. The proposed mechanisms were validated using the experimentally measured and quasi-classical trajectory-deduced nascent internal energy distributions of HCN and HNC. This work, along with previous studies, illustrates the propensity for cyano-containing hydrocarbons to act as photolytic sources for astrophysical HCN and HNC and may help explain the observed overabundance of HNC in astrophysical environments.

Photolysis- and Dissolved Organic Matter-Induced Toxicity of Triclocarban to Daphnia magna

Triclocarban (TCC) is a common antimicrobial compound used in soaps and other household products and is found globally in many surface waters. This study investigated the acute toxicity of TCC and its photolyzed products to Daphnia magna using 50% 96-h lethal concentration (LC50) tests. The effects of dissolved organic matter (DOM) on the toxicity of TCC photoproducts to D. magna were also studied. Direct photolysis of TCC formed photoproducts that were significantly less toxic (LC50 value of 2.67 ± 0.6 μM) than the parent TCC compound (LC50 value of 0.087 ± 0.3 μM). In contrast, the indirect photolysis of TCC in the presence of DOM produced photoproducts that were significantly more toxic (LC50 value of 0.032 ± 0.015 μM). Chlorinated anilines and isocyanates, identified by mass spectrometry, were formed in the presence of DOM as indirect photolysis products of TCC and were shown to be partially responsible for the observed toxicity.

Photochemical transformations of sphingosine and serinol in aqueous and ethanol solutions

It has been established that the main products of the direct photolysis of C15-sphingosine and serinol are 2-tridecenal and glycolaldehyde, which are formed as a result of C–C bond cleavage in the parent compounds. It has been shown that the addition of hydrogen peroxide and acetone to the test solutions extended the range of the photolysis products due to the occurrence of deamination processes. The set of the experimental data has made it possible to propose mechanisms for the photochemical reactions of C15- sphingosine and serinol fragmentation, which occur through the steps of the formation of N- and C-centered radicals.