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Jingwen Chen - One of the best experts on this subject based on the ideXlab platform.

  • Direct Photolysis of MeO-PBDEs in water and methanol: focusing on cyclization product MeO-PBDFs.
    Chemosphere, 2015
    Co-Authors: Weifeng Xue, Jingwen Chen, Qing Xie, Hongxia Zhao
    Abstract:

    Polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs can transform into polybrominated dibenzofurans (PBDFs) via photocyclization. However, it is unclear whether methoxylated PBDEs (MeO-PBDEs) can photocyclize to form MeO-PBDFs. In this study, 5-MeO-BDE-47, 5'-MeO-BDE-99 and 6-MeO-BDE-85 were selected as models to investigate their Direct Photolysis, especially photocyclization in two solvent environments (water and methanol) using simulated photochemical experiments and density functional theory (DFT) calculations. The experimental results showed that MeO-PBDEs had faster Direct Photolysis reactions and higher quantum yields in methanol, and MeO-PBDFs could only be formed in a methanol solution of 5-MeO-BDE-47. The DFT results indicated that the lowest excited triplet state MeO-PBDEs can form dibenzofurans via Direct cyclization pathways. Intra-annular H-elimination was found to be the rate-determining step for most cyclization pathways with high reaction barriers (⩾19.7kcal/mol), while 5-MeO-BDE-47 was found to have a distinct pathway for which the rate-determining step is ring closure with a low barrier (13.8kcal/mol) in a methanol environment. For this pathway, H-elimination assisted by Br cleaved from an ortho-C-Br bond was observed with a 2.0kcal/mol barrier. Thus, the DFT results reasonably explained the experimental findings, and the photocyclization of MeO-PBDEs depended on the specific Br-substitution patterns and specific effects of the environmental media.

  • Theoretical investigations on Direct Photolysis mechanisms of polychlorinated diphenyl ethers.
    Chemosphere, 2014
    Co-Authors: Wang, Jingwen Chen, Ce Hao, Zhanxian Gao, Jieshan Qiu
    Abstract:

    Polychlorinated diphenyl ethers (PCDEs) are a focus of current environmental concern as a group of ubiquitous potential persistent organic pollutants. There are still significant gaps in our knowledge concerning the Photolysis mechanisms of PCDEs. In this study, the Direct Photolysis mechanisms of PCDEs were investigated by density functional theory. The Direct Photolysis of PCDEs has three potential reaction pathways including photodechlorination, C-O bond photodissociation, and PCDFs formation. Taking a representative PCDE (i.e., CDE8) for example, we found that C-Cl bond dissociation is the rate-determining step for the photodechlorination. Chlorobenzene is predicted to be photoproduct of CDE8 through the photodissociation of the C-O bond. Furthermore, the calculated mean bond dissociation energies of both C-Cl and C-O bonds of 20 PCDEs decrease with the increased degree of chlorination. It is also found that the photoactivity of PCDEs increases with an increase of chlorination degree by evaluating the average charge of Cl atoms and mean bond dissociation energies of C-Cl and C-O bonds from reaction thermodynamics. Our findings provided a new insight into the mechanisms of Direct Photolysis of PCDEs, which may be useful in the future in utilizing quantum chemistry calculation in investigating the behavior and fate of organic pollutants in the environment.

  • Quantitative structure-property relationships for Direct Photolysis of polybrominated diphenyl ethers.
    Ecotoxicology and environmental safety, 2006
    Co-Authors: Jingwen Chen, De-gao Wang, Shuanglin Wang, Xianliang Qiao, Liping Huang
    Abstract:

    Abstract Using semiempirical quantum chemical descriptors, by partial least squares (PLS) regression, quantitative structure–property relationships (QSPRs) were established for Direct Photolysis quantum yields ( Φ ) and rate constants ( k ) of polybrominated diphenyl ether congeners dissolved in water/methanol and methanol solutions, respectively, and irradiated by artificial ultraviolet A light. Q cum 2 , a parameter indicating robustness and predictive abilities of PLS models, for the significant QSPR models is larger than 0.702. The gap of frontier molecular orbital energies ( E LUMO – E HOMO ) and the most positive Mulliken atomic charges on a hydrogen atom ( q H + ) are two main molecular structural factors governing the log  Φ values. log  Φ increases with increasing E LUMO – E HOMO and q H + values. log  k is mainly related to bromination degree and pattern which can be characterized by molecular weight ( Mw ), average molecular polarizability ( α ), and average Mulliken atomic charges on bromine atoms ( q Br ). log  k increases with bromination degree ( Mw , α ) and q Br .

  • Quantitative structure-property relationships (QSPRs) on Direct Photolysis quantum yields of PCDDs.
    Chemosphere, 2001
    Co-Authors: Jingwen Chen, Xie Quan, Willie J.g.m. Peijnenburg, Fenglin Yang
    Abstract:

    Abstract By the use of partial least squares (PLS) method and 16 fundamental quantum chemical descriptors computed by PM3 Hamiltonian, quantitative structure–property relationships (QSPRs) were obtained for Direct Photolysis quantum yields of selected polychlorinated dibenzo- p -dioxins (PCDDs). Direct Photolysis quantum yields for PCDDs without experimental quantum yield values were predicted. The QSPR results showed that it was mainly the number of chlorine atoms bonded to the parent structure, the largest positive atomic charge on a chlorine atom, the dipole moment, and the frontier molecular orbital energies ( E homo and E lumo ) that determine the Direct Photolysis quantum yields of the PCDDs. Increasing the number of chlorine atoms, dipole moment, and the largest positive atomic charge on a chlorine atom, leads to decrease of Photolysis quantum yields. Increasing E lumo , E homo and E lumo  −  E homo values lead to increase of log Y values.

  • Quantitative structure-property relationships (QSPRs) on Direct Photolysis of PCDDs.
    Chemosphere, 2001
    Co-Authors: Jingwen Chen, Xie Quan, Karl-werner Schramm, Antonius Kettrup, Fenglin Yang
    Abstract:

    By the use of partial least squares (PLS) method and 27 quantum chemical descriptors computed by PM3 Hamiltonian, a statistically significant QSPR were obtained for Direct Photolysis quantum yields (Y) of selected Polychlorinated dibenzo-p-dioxins (PCDDs). The QSPR can be used for prediction. The Direct Photolysis quantum yields of the PCDDs are dependent on the number of chlorine atoms bonded with the parent structures, the character of the carbon-oxygen bonds, and molecular polarity. Increasing bulkness and polarity of PCDDs lead to decrease of log Y values. Increasing the frontier molecular orbital energies (E-lumo and E-homo) and heat of formation (HOF) values leads to increase of log Y values. (C) 2001 Elsevier Science Ltd. All rights reserved.

Davide Vione - One of the best experts on this subject based on the ideXlab platform.

  • the role of Direct Photolysis in the photodegradation of the herbicide bentazone in natural surface waters
    Chemosphere, 2020
    Co-Authors: Luca Carena, Debora Fabbri, Monica Passananti, Marco Pazzi, Marco Minella, Davide Vione
    Abstract:

    Abstract The photochemical fate of the herbicide bentazone was assessed by lab experiments and modeling tools. Experimental and modeling results showed that bentazone is mainly photodegraded by Direct Photolysis in natural water samples, even in the presence of dissolved organic matter (DOM) that can act as light-screening agent, photosensitizer and scavenger of reactive species. Even when it was dissolved in natural water samples containing different DOM amounts, the phototransformation kinetics of bentazone was unchanged compared to irradiation runs in ultrapure water. This finding suggests that the DOM and the other components of our samples did not affect the Direct Photolysis of bentazone by light-absorption competition, at least at the experimental optical path lengths, and did not induce significant inDirect photodegradation by producing reactive transient species. Photochemical modeling in a lake-water photoreactivity scenario corroborated the observed experimental results, showing the predominant role of Direct Photolysis in the overall (Direct + inDirect) photodegradation of bentazone at different water depths and DOM contents. However, the model predicted a minor but non-negligible contribution of inDirect photochemistry (i.e., reactions triggered by HO•, CO3•− and 3CDOM*) to the herbicide degradation. This contribution (especially by 3CDOM*) could become crucial in deep and DOM-rich water bodies. Finally, several photoproducts formed by Direct Photolysis and HO•-induced photodegradation were identified, which should not be particularly toxic for aquatic organisms and Vibrio fischeri bacteria.

  • the role of Direct Photolysis and inDirect photochemistry in the environmental fate of ethylhexyl methoxy cinnamate ehmc in surface waters
    Science of The Total Environment, 2015
    Co-Authors: Davide Vione, Debora Fabbri, Paola Calza, F Galli, Valentina Santoro, Claudio Medana
    Abstract:

    The aquatic environmental fate of ethylhexyl methoxy cinnamate (EHMC), one of the most used UVB filters worldwide, was studied by assessing its environmental persistence and photoinduced transformations. The role of Direct and inDirect Photolysis was evaluated. Direct Photolysis was shown to play a key role, and this process is expected to be the main attenuation route of EHMC in sunlit surface waters. In contrast, the reaction with OH radicals would be negligible and that with 3CDOM* would at most be a secondary process. The measurement of the quantum yield of Direct Photolysis and of the rate constants of reaction with photogenerated transient species (or, sometimes, the use of reasonable values for the latter) allowed the prediction of the EHMC half-life time in surface waters, by means of a validated photochemical model. The predicted EHMC lifetime is of the order of hours to a few days in fair-weather summertime, and the main factors controlling the EHMC phototransformation in sunlit surface waters would be the water depth and the dissolved organic carbon (DOC) content. The formation of transformation products (TPs) was followed as well via HPLC/HRMS. Three TPs were detected in the samples exposed to UVA radiation, while one additional TP was detected in the samples exposed to UVB radiation. The detected TPs comprised 4-methoxybenzaldehyde, a hydroxylated derivative and dimeric species. Through the use of heterogeneous photocatalysis with TiO2, seven additional TPs were identified, most of them resulting from the further degradation of primary TPs formed through Direct Photolysis and that might be detected in aquatic systems as well. The photodegradation of EHMC in the presence of TiO2 yielded more toxic TPs than the parent compound (as determined with the Vibrio fischeri Microtox assay). The increased toxicity is partially accounted for by the formation of 4-methoxybenzaldehyde.

  • a model assessment of the importance of Direct Photolysis in the photo fate of cephalosporins in surface waters possible formation of toxic intermediates
    Chemosphere, 2015
    Co-Authors: Debora Fabbri, Marco Minella, Valter Maurino, Claudio Minero, Davide Vione
    Abstract:

    The Direct and inDirect photodegradation of six cephalosporins was predicted using a photochemical model, on the basis of literature values of photochemical reactivity. Environmental photodegradation would be important in surface water bodies with depth ⩽2–3 m, and/or in deeper waters with low values of the dissolved organic carbon (DOC ⩽ 1 mg C L−1). The half-life times would range from a few days to a couple of weeks in summertime. In deeper and higher-DOC waters and/or in different seasons, hydrolysis could prevail over photodegradation. The Direct Photolysis of cephalosporins is environmentally concerning because it is known to produce toxic intermediates. It would be a major pathway for cefazolin, an important one for amoxicillin and cefotaxime and, at pH < 6.5, for cefapirin as well. In contrast, Direct Photolysis would be negligible for cefradine and cefalexin. The DOC values would influence the fraction of photodegradation accounted for by Direct Photolysis in shallow water, to a different extent depending on the role of sensitisation by the triplet states of chromophoric dissolved organic matter.

  • A model assessment of the importance of Direct Photolysis in the photo-fate of cephalosporins in surface waters: Possible formation of toxic intermediates
    Chemosphere, 2015
    Co-Authors: Debora Fabbri, Marco Minella, Valter Maurino, Claudio Minero, Davide Vione
    Abstract:

    The Direct and inDirect photodegradation of six cephalosporins was predicted using a photochemical model, on the basis of literature values of photochemical reactivity. Environmental photodegradation would be important in surface water bodies with depth ⩽2–3 m, and/or in deeper waters with low values of the dissolved organic carbon (DOC ⩽ 1 mg C L−1). The half-life times would range from a few days to a couple of weeks in summertime. In deeper and higher-DOC waters and/or in different seasons, hydrolysis could prevail over photodegradation. The Direct Photolysis of cephalosporins is environmentally concerning because it is known to produce toxic intermediates. It would be a major pathway for cefazolin, an important one for amoxicillin and cefotaxime and, at pH 

  • Carbon Stable Isotope Fractionation of Sulfamethoxazole during Biodegradation by Microbacterium sp. Strain BR1 and upon Direct Photolysis.
    Environmental science & technology, 2015
    Co-Authors: Jan Birkigt, Davide Vione, Tetyana Gilevska, Benjamin Ricken, Hans-hermann Richnow, Philippe F.-x. Corvini, Ivonne Nijenhuis, Danuta Cichocka
    Abstract:

    Carbon isotope fractionation of sulfamethoxazole (SMX) during biodegradation by Microbacterium sp. strain BR1 (ipso-hydroxylation) and upon Direct Photolysis was investigated. Carbon isotope signatures (δ13C) of SMX were measured by LC-IRMS (liquid chromatography coupled to isotope ratio mass spectrometry). A new LC-IRMS method for the SMX metabolite, 3-amino-5-methylisoxazole (3A5MI), was established. Carbon isotope enrichment factors for SMX (eC) were −0.6 ± 0.1‰ for biodegradation and −2.0 ± 0.1‰ and −3.0 ± 0.2‰ for Direct Photolysis, at pH 7.4 and pH 5, respectively. The corresponding apparent kinetic isotope effects (AKIE) for ipso-hydroxylation were 1.006 ± 0.001; these fall in the same range as AKIE in previously studied hydroxylation reactions. The differences in SMX and 3A5MI fractionation upon biotic and abiotic degradation suggest that compound specific stable isotope analysis (CSIA) is a suitable method to distinguish SMX reaction pathways. In addition, the study revealed that the extent of is...

Fenglin Yang - One of the best experts on this subject based on the ideXlab platform.

Jeyong Yoon - One of the best experts on this subject based on the ideXlab platform.

  • uv Direct Photolysis of 2 2 azino bis 3 ethylbenzothiazoline 6 sulfonate abts in aqueous solution kinetics and mechanism
    Journal of Photochemistry and Photobiology A-chemistry, 2008
    Co-Authors: Changha Lee, Jeyong Yoon
    Abstract:

    Abstract The Direct Photolysis of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) in aqueous solution was investigated under monochromatic ultraviolet (UV) irradiation at 254 nm. ABTS was found to be Directly photolyzed by UV irradiation to yield the one-electron oxidized radical, ABTS + , which is a blue-green colored persistent radical species that has strong visible absorption bands. The photochemical production of ABTS + was strongly dependent on the solution pH and the presence of dissolved oxygen. The presence of dissolved oxygen increased the quantum yields at pH 3, whereas it inhibited the production of ABTS + at pH 6.5. Spectrophotometric and spectrofluorometric data indicated that ABTS Photolysis may occur as a result of the transfer of one-electron between the singlet excited state and the ground state of ABTS. Observations made during UV/H 2 O 2 experiments with ABTS suggested that the dependence of the photoloysis of ABTS on the solution pH and the presence of dissolved oxygen is related to the role of the hydroperoxyl/superoxide radical (HO 2 /O 2 − ), which appears to be formed via a secondary reaction of the reduced intermediate of ABTS with dissolved oxygen. The proposed photolytic reactions were supported by the observed stoichiometry between the amount of ABTS + radicals produced and the amount of ABTS molecules decomposed.

  • UV Direct Photolysis of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) in aqueous solution: Kinetics and mechanism
    Journal of Photochemistry and Photobiology A-chemistry, 2008
    Co-Authors: Changha Lee, Jeyong Yoon
    Abstract:

    Abstract The Direct Photolysis of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) in aqueous solution was investigated under monochromatic ultraviolet (UV) irradiation at 254 nm. ABTS was found to be Directly photolyzed by UV irradiation to yield the one-electron oxidized radical, ABTS + , which is a blue-green colored persistent radical species that has strong visible absorption bands. The photochemical production of ABTS + was strongly dependent on the solution pH and the presence of dissolved oxygen. The presence of dissolved oxygen increased the quantum yields at pH 3, whereas it inhibited the production of ABTS + at pH 6.5. Spectrophotometric and spectrofluorometric data indicated that ABTS Photolysis may occur as a result of the transfer of one-electron between the singlet excited state and the ground state of ABTS. Observations made during UV/H 2 O 2 experiments with ABTS suggested that the dependence of the photoloysis of ABTS on the solution pH and the presence of dissolved oxygen is related to the role of the hydroperoxyl/superoxide radical (HO 2 /O 2 − ), which appears to be formed via a secondary reaction of the reduced intermediate of ABTS with dissolved oxygen. The proposed photolytic reactions were supported by the observed stoichiometry between the amount of ABTS + radicals produced and the amount of ABTS molecules decomposed.

  • UV Direct Photolysis of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) in aqueous solution: Kinetics and mechanism
    Journal of Photochemistry and Photobiology A: Chemistry, 2008
    Co-Authors: Changha Lee, Jeyong Yoon
    Abstract:

    The Direct Photolysis of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) in aqueous solution was investigated under monochromatic ultraviolet (UV) irradiation at 254 nm. ABTS was found to be Directly photolyzed by UV irradiation to yield the one-electron oxidized radical, ABTS{radical dot}+, which is a blue-green colored persistent radical species that has strong visible absorption bands. The photochemical production of ABTS{radical dot}+ was strongly dependent on the solution pH and the presence of dissolved oxygen. The presence of dissolved oxygen increased the quantum yields at pH 3, whereas it inhibited the production of ABTS{radical dot}+ at pH 6.5. Spectrophotometric and spectrofluorometric data indicated that ABTS Photolysis may occur as a result of the transfer of one-electron between the singlet excited state and the ground state of ABTS. Observations made during UV/H2O2 experiments with ABTS suggested that the dependence of the photoloysis of ABTS on the solution pH and the presence of dissolved oxygen is related to the role of the hydroperoxyl/superoxide radical (HO2{radical dot}/O2{radical dot}-), which appears to be formed via a secondary reaction of the reduced intermediate of ABTS with dissolved oxygen. The proposed photolytic reactions were supported by the observed stoichiometry between the amount of ABTS{radical dot}+ radicals produced and the amount of ABTS molecules decomposed.close4

Jeanmarc Chovelon - One of the best experts on this subject based on the ideXlab platform.

  • photochemical degradation of sunscreen agent 2 phenylbenzimidazole 5 sulfonic acid in different water matrices
    Water Research, 2013
    Co-Authors: Lei Zhou, Marcello Brigante, Gilles Mailhot, Ya Zhang, Corinne Ferronato, Xi Yang, Jeanmarc Chovelon
    Abstract:

    Abstract The occurrence of sunscreen agents in natural environment is of scientific concern recently due to their potential risk to ecology system and human beings as endocrine disrupting chemicals (EDCs). In this work the photodegradation mechanism and pathways of sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid (PBSA) were investigated under artificial solar irradiation with the goal of assessing the potential of Photolysis as a transformation mechanism in aquatic environments. The quantum yield of PBSA Direct Photolysis in pH 6.8 buffer solution under filtered mercury lamp irradiation was determined as 2.70 × 10−4. Laser flash Photolysis (LFP) experiments confirmed the involvement of PBSA radical cation (PBSA +) during Direct Photolysis. Acidic or basic condition facilitated PBSA Direct Photolysis in aqueous solution. InDirect Photolysis out-competes Direct Photolysis as a major process for PBSA attenuation only at higher level of photosensitizers (e.g., NO 3 −  > 2 mM). Thus, Direct Photolysis is likely to be the major loss pathway responsible for the elimination of PBSA in natural sunlit surface waters, while inDirect Photolysis (e.g., mediated by HO ) appeared to be less important due to a general low level of steady-state concentration of HO ([HO ]ss) in natural surface waters. Direct Photolysis pathways of PBSA includes desulfonation and benzimidazole ring cleavage, which are probably initiated by the excited triplet state (3PBSA∗) and radical cation (PBSA +). Conversely, hydroxylation products of PBSA and 2-phenyl-1H-benzimidazole as well as their ring opening intermediates were found in nitrate-induced PBSA Photolysis, suggesting the inDirect photodegradation was primarily mediated by HO and followed a different mechanism.

  • Photochemical degradation of sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid in different water matrices
    Water Research, 2013
    Co-Authors: Y. F. Ji, Gilles Mailhot, Lei Zhou, Ya Zhang, Corinne Ferronato, Xi Yang, M. Brigante, Jeanmarc Chovelon
    Abstract:

    The occurrence of sunscreen agents in natural environment is of scientific concern recently due to their potential risk to ecology system and human beings as endocrine disrupting chemicals (EDCs). In this work the photodegradation mechanism and pathways of sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid (PBSA) were investigated under artificial solar irradiation with the goal of assessing the potential of Photolysis as a transformation mechanism in aquatic environments. The quantum yield of PBSA Direct Photolysis in pH 6.8 buffer solution under filtered mercury lamp irradiation was determined as 2.70 x 10(-4). Laser flash Photolysis (LFP) experiments confirmed the involvement of PBSA radical cation (PBSA(center dot+)) during Direct Photolysis. Acidic or basic condition facilitated PBSA Direct Photolysis in aqueous solution. InDirect Photolysis out-competes Direct Photolysis as a major process for PBSA attenuation only at higher level of photosensitizers (e.g., NO3- > 2 mM). Thus, Direct Photolysis is likely to be the major loss pathway responsible for the elimination of PBSA in natural sunlit surface waters, while inDirect Photolysis (e.g., mediated by HO center dot.) appeared to be less important due to a general low level of steady-state concentration of HO center dot ([HO center dot](ss)) in natural surface waters. Direct Photolysis pathways of PBSA includes desulfonation and benzimidazole ring cleavage, which are probably initiated by the excited triplet state ((3)PBSA*) and radical cation (PBSA(center dot+)). Conversely, hydroxylation products of PBSA and 2-phenyl-1H-benzimidazole as well as their ring opening intermediates were found in nitrate-induced PBSA Photolysis, suggesting the inDirect photodegradation was primarily mediated by HO center dot and followed a different mechanism. (C) 2013 Elsevier Ltd. All rights reserved.