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Maafi M. On photokinetics under polychromatic light. Front Chem 2024; 12:1367276. [PMID: 38711947 PMCID: PMC11070525 DOI: 10.3389/fchem.2024.1367276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2024] [Accepted: 03/12/2024] [Indexed: 05/08/2024] Open
Abstract
Since the dawn of photochemistry 150 years ago, photoreactions have been conducted under polychromatic light. However, despite the pivotal role that photokinetics should naturally play for such reactive photosystems, the literature lacks a comprehensive description of that area. Indeed, one fails to identify explicit model integrated rate laws for these reactions, a characteristic type for their kinetic behavior, or their kinetic order. In addition, there is no consensus in the community on standardized investigative tools to evaluate the reactivity of these photosystems, nor are there venues for the discussion of such photokinetic issues. The present work is a contribution addressing some of these knowledge gaps. It proposes an unprecedented general formula capable of mapping out the kinetic traces of photoreactions under polychromatic light irradiation. This article quantitatively discusses several reaction situations, including the effects of initial reactant concentration and the presence of spectator molecules. It also develops a methodology for standardizing actinometers and defines and describes both the spectral range of highest reactivity and the photonic yield. The validity of the model equation has been proven by comparing its results to both theoretical counterparts and those generated by fourth-order Runge-Kutta numerical calculations. For the first time, a confirmation of the Φ -order character of the kinetics under polychromatic light was established.
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Affiliation(s)
- Mounir Maafi
- Leicester School of Pharmacy, De Montfort University, Leicester, United Kingdom
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2
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Wang J, Jiang J, Zhao H, Li Z, Li X, Azam S, Qu B. Phototransformation of halobenzoquinones in aqueous solution under the simulate sunlight: Kinetics, mechanism and products. CHEMOSPHERE 2024; 352:141318. [PMID: 38311038 DOI: 10.1016/j.chemosphere.2024.141318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Revised: 01/26/2024] [Accepted: 01/26/2024] [Indexed: 02/06/2024]
Abstract
Halobenzoquinones (HBQs) are a novel family of unregulated disinfection byproducts (DBPs). Little is known about their phototransformation activities in natural water. Here, five HBQs with various halogenated substituent types, numbers, and structures positions were selected to investigate the kinetics of degradation in aqueous solutions at various concentrations and in the presence of common environmental variables (Cl-, NO2-, and humic acid). The results indicated that dichloride and dibromo-substituted HBQs were photolyzed, whereas tetrachloro-substituted HBQs showed little degradation. The photolysis rate constant (k) of HBQs decreased with increasing initial concentration. The presence of NO2- and Cl- promoted the degradation of HBQs mainly through the formation of hydroxyl radical (•OH), which were confirmed by electron paramagnetic resonance (EPR). In contrast, humic acid played a negative role on HBQs transformation due to the adsorption and quenching reactions. Possible conversion pathways for HBQs were proposed based on the identification of two major photodegradation products, hydroxylated HBQs and halogenated-benzenetriol, as well as reactive free radicals. This study provided meaningful insights into the environmental fates and risk assessments of HBQs in natural aquatic system.
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Affiliation(s)
- Jingyao Wang
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Dalian, 116024, China
| | - Jingqiu Jiang
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, 100012, Beijing, China
| | - Hongxia Zhao
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Dalian, 116024, China.
| | - Zhansheng Li
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Dalian, 116024, China
| | - Xintong Li
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Dalian, 116024, China
| | - Shafiul Azam
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Dalian, 116024, China
| | - Baocheng Qu
- College of Marine Technology and Environment, Dalian Ocean University, Dalian, 116024, China.
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3
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Substituent effects on the activation parameters of the reaction between 1,4-benzoquinones and hydrogen peroxide: A combined experimental and theoretical study. J Mol Struct 2022. [DOI: 10.1016/j.molstruc.2022.132916] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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4
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Maafi M, Al-Qarni MA. Photokinetics of Dacarbazine and Nifedipine under polychromatic light irradiation and their application as new reliable actinometers for the ultraviolet range. Sci Rep 2022; 12:7622. [PMID: 35538090 PMCID: PMC9090909 DOI: 10.1038/s41598-022-11570-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 04/19/2022] [Indexed: 11/30/2022] Open
Abstract
The photokinetic behaviour of drugs driven by polychromatic light is an area of pharmaceutics that has not received a lot of attention. Most often, such photokinetic data is treated by thermal kinetic models (i.e., the classical 0th-, 1st- or 2nd-order equations). Such models were not analytically derived from the rate-laws of the photodegradation reactions. Polychromatic light kinetic modelling is hence of importance, as a means to providing adequate toolkits and metrics. This paper aims at proposing two reliable drug-actinometers useful for polychromatic UVA range. The general actinometric methodology offered here is also useful for any drugs/materials obeying a primary photoprocess where both reactant and photoproduct absorb the incident light, of the \documentclass[12pt]{minimal}
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\begin{document}$$AB{(1\Phi )}_{{\varepsilon }_{B}\ne 0}$$\end{document}AB(1Φ)εB≠0 type. The present method has been consolidated by the η-order kinetics. This framework further demonstrated the lamp-specificity of actinometers. Overall, Dacarbazine and Nifedipine photodegradations obeyed η-order kinetics, and stand as effective actinometers that can be recommended for the ICH Q1b photostability testing.
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Affiliation(s)
- Mounir Maafi
- Leicester School of Pharmacy, De Montfort University, The Gateway, Leicester, LE1 9BH, UK.
| | - Mohammed Ahmed Al-Qarni
- Department of Pharmaceutical Chemistry, College of Pharmacy, Taif University, P.O. Box 11099, Taif, 21944, Saudi Arabia
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5
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Gutenthaler SM, Phi MT, Singer H, Daumann LJ. Activity assays of methanol dehydrogenases. Methods Enzymol 2021; 650:57-79. [PMID: 33867025 DOI: 10.1016/bs.mie.2021.01.045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
The field of methanol dehydrogenases (MDHs) has experienced revival in the recent decade due to the observation of lanthanide-dependent MDH, in addition to widely known calcium-MDH. With the advent of lanthanide-dependent alcohol dehydrogenases, the need for reliable assays to evaluate and compare activities between different MDHs is obvious: from extremophilic to neutrophilic organisms, or with different lanthanide ions in the active site. Here we outline four assays that have been reported for Ln-MDH, discussing the advantages and disadvantages of the assays and their components. It should be noted, in 1990Day and Anthony produced a comprehensive summary in Methods in Enzymology on the available methods for Ca-MDH assays at the time (Day & Anthony, 1990). This chapter is an updated appraisal of the most important developments in the last 30years.
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Affiliation(s)
- Sophie M Gutenthaler
- Department of Chemistry, Ludwig-Maximilians-Universität München, München, Germany
| | - Manh Tri Phi
- Department of Chemistry, Ludwig-Maximilians-Universität München, München, Germany
| | - Helena Singer
- Department of Chemistry, Ludwig-Maximilians-Universität München, München, Germany
| | - Lena J Daumann
- Department of Chemistry, Ludwig-Maximilians-Universität München, München, Germany.
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6
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A kinetic study of the photooxidation of water by aqueous cerium(IV) in sulfuric acid using a diode array spectrophotometer. J Photochem Photobiol A Chem 2021. [DOI: 10.1016/j.jphotochem.2020.113110] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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7
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Hung S, Mohan A, Reckhow DA, Godri Pollitt KJ. Assessment of the in vitro toxicity of the disinfection byproduct 2,6-dichloro-1,4-benzoquinone and its transformed derivatives. CHEMOSPHERE 2019; 234:902-908. [PMID: 31519098 DOI: 10.1016/j.chemosphere.2019.06.086] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Revised: 06/10/2019] [Accepted: 06/11/2019] [Indexed: 06/10/2023]
Abstract
An emerging class of unregulated disinfection byproducts, halobenzoquinones (HBQs), has gained recent interest following suggestions of enhanced toxicity compared to regulated disinfection byproducts. While the kinetics of HBQ hydrolysis in water have been well characterized, the stability of HBQs in cell culture media, a critical parameter when evaluating toxicity in vitro, has been overlooked. The objective of this study was: (1) to contrast the stability of a prevalent HBQ, 2,6-dichloro-1,4-benzoquinone (DCBQ), in cell culture media and water, and (2) to evaluate the cytotoxicity of parent and transformed DCBQ compounds as well as the ability of these compounds to generate intracellular reactive oxygen species (ROS) in normal human colon cells (CCD 841 CoN) and human liver cancer cells (HepG2). The half-life of DCBQ in cell media was found to be less than 40 min, compared to 7.2 h in water at pH 7. DCBQ induced a concentration-dependent decrease in cell viability and increase in ROS production in both cell lines. The parent DCBQ compound was found to induce significantly greater cytotoxicity compared to transformed DCBQ products. We demonstrate that the study design used by most published studies (i.e., extended exposure periods) has led to a potential underestimation of the cytotoxicity of HBQs by evaluating the toxicological profile primarily of transformed HBQs, rather than corresponding parent compounds. Future in vitro toxicological studies should account for HBQ stability in media to evaluate the acute cytotoxicity of parent HBQs.
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Affiliation(s)
- Stephanie Hung
- Environmental Health Sciences, School of Public Health and Health Sciences, University of Massachusetts Amherst, Amherst, MA, 01003, USA
| | - Aarthi Mohan
- Civil and Environmental Engineering, College of Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA
| | - David A Reckhow
- Civil and Environmental Engineering, College of Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA
| | - Krystal J Godri Pollitt
- Environmental Health Sciences, School of Public Health, Yale University, New Haven, CT, 06510, USA.
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8
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Jin J, Chen Z, Song X, Wu B, Zhang G, Zhang S. Effects of acetylacetone on the thermal and photochemical conversion of benzoquinone in aqueous solution. CHEMOSPHERE 2019; 223:628-635. [PMID: 30798058 DOI: 10.1016/j.chemosphere.2019.02.080] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2018] [Revised: 01/08/2019] [Accepted: 02/13/2019] [Indexed: 06/09/2023]
Abstract
Quinones are components of electron transport chains in photosynthesis and respiration. Acetylacetone (AA), structurally similar to benzoquinone (BQ) for the presence of two identical carbonyl groups, has been reported as a quinone-like electron shuttle. Both BQ and AA are important chemicals in the aquatic environment. However, little information is known about their interactions if co-existed. We found here that AA significantly enhanced the conversion of BQ. By analyzing the evolution of chemical concentration, solution pH, dissolved oxygen, and the final products, the interactions between AA and BQ were elucidated. The reactions between BQ and AA generated oxygen but ultimately led to the reduction of solution pH and dissolved oxygen. The reactions proceeded faster under indoor lighting condition than in the dark. The formation of semiquinone radicals is believed as the primary step. The secondary AA-derived radicals might be strongly oxidative or reductive, depending on the concentration of dissolved oxygen. Insoluble humus was generated in the mixture of BQ and AA. These results suggest that the presence of AA might interfere with photosynthesis and respiration through the interactions with quinones.
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Affiliation(s)
- Jiyuan Jin
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China
| | - Zhihao Chen
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China
| | - Xiaojie Song
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China
| | - Bingdang Wu
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China
| | - Guoyang Zhang
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China
| | - Shujuan Zhang
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China.
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10
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Weng S, Yang JY, Li YH, Blatchley ER. UV-induced effects on toxicity of model disinfection byproducts. THE SCIENCE OF THE TOTAL ENVIRONMENT 2017; 599-600:94-97. [PMID: 28467913 DOI: 10.1016/j.scitotenv.2017.04.198] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 04/13/2017] [Accepted: 04/26/2017] [Indexed: 06/07/2023]
Abstract
UV (Ultraviolet)-based treatment has been demonstrated to be effective for removal of some disinfection byproducts (DBPs) and to be beneficial for reduction of genotoxicity and cytotoxicity in chlorinated water. However, to a large extent, UV-induced effects on chemistry and toxicology have been treated as a black box, in the sense that little or no UV dose-dependent behavior has been reported. To address this issue, the effects of UV254 irradiation on 1,4-dibenzoquinone (BQ), 2,6-dichloro-1,4-benzoquinone (DCBQ), and chlorocreatinine (Cl-Cre) as model DBPs were examined, both in terms of photodegradation and cytotoxicity. These compounds have been identified as DBPs that are relevant in swimming pool settings; however, these compounds will be relevant in other water treatment settings, including drinking water production and wastewater reuse. UV254 irradiation was shown to promote photodecay of all three compounds. However, for BQ and DCBQ, the corresponding cytotoxicity of the UV-irradiated samples remained essentially unchanged, even when the compound was completely photodegraded. These results indicate that the photodegradation products of BQ and DCBQ carry similar cytotoxicity as their respective parent compounds. On the other hand, UV254-irradiation of Cl-Cre yielded a decrease in cytotoxicity that correlated with photodechlorination of Cl-Cre. These experiments also demonstrated a reduction in cytotoxicity in connection with photodechlorination of an N-chlorinated organic compound. Overall, the results of these experiments indicate the importance of defining products of UV photodecay processes, both in terms of chemistry and toxicity; these attributes are expected to be important in many UV-based applications, including potable water production, water reuse, and recreational water settings.
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Affiliation(s)
- ShihChi Weng
- JHU/MWH Alliance, 615 N. Wolfe St., Johns Hopkins University, Baltimore, MD 21205, USA
| | - Jer-Yen Yang
- Department of Basic Medical Sciences, Purdue University, IN 47907, USA; Center for Cancer Research, Purdue University, IN 47907, USA
| | - Yen-Hsing Li
- Department of Basic Medical Sciences, Purdue University, IN 47907, USA
| | - Ernest R Blatchley
- Lyles School of Civil Engineering, Purdue University, IN 47907, USA; Division of Environmental and Ecological Engineering, Purdue University, IN 47907, USA.
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11
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Günay T, Çimen Y. Degradation of 2,4,6-trichlorophenol with peroxymonosulfate catalyzed by soluble and supported iron porphyrins. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2017; 231:1013-1020. [PMID: 28898954 DOI: 10.1016/j.envpol.2017.08.059] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Revised: 08/09/2017] [Accepted: 08/11/2017] [Indexed: 06/07/2023]
Abstract
Degradation of 2,4,6-trichloropenol (TCP) with peroxymonosulfate (PMS) catalyzed by iron porphyrin tetrasulfonate ([FePTS)] was investigated in an 8-to-1 (v/v) CH3OH-H2O mixture. Typical reaction medium contained a 4.00 mL methanol solution of TCP (0.100 mmol), a 0.50 mL aqueous solution of catalyst (5.0 × 10-4 mmol), and 0.100 mmol PMS (as 0.031 g of Oxone). The reaction was performed at ambient temperature. The conversion of TCP was 74% in 30 min and 80% in 6 h when the catalyst was [FePTS]. Amberlite IRA-900 supported [FePTS] catalyst was also prepared. In the recycling experiments the homogeneous [FePTS] lost its activity after the first cycle, while [FePTS]-Amberlite IRA 900 maintained its activity for the first 2 cycles. After the second cycle, the conversion of TCP dropped to <10% for Amberlite IRA-900 supported [FePTS] catalyst. The degradation of TCP with PMS was also attempted using cobalt, copper, nickel and palladium porphyrin tetrasulfonate catalysts, however, no catalytic activity was observed with these structures.
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Affiliation(s)
- Tuğçe Günay
- Department of Chemistry, Faculty of Science, Anadolu University, 26470 Eskişehir, Turkey
| | - Yasemin Çimen
- Department of Chemistry, Faculty of Science, Anadolu University, 26470 Eskişehir, Turkey.
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12
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Kiss V, Lehoczki G, Ősz K. Mathematical description of pH-stat kinetic traces measured during photochemical quinone decomposition. Photochem Photobiol Sci 2017; 16:519-526. [PMID: 27942682 DOI: 10.1039/c6pp00333h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Substituted 1,4-benzoquinone (QR) derivatives are photosensitive in aqueous solution and form hydroquinones (QR-H2) and hydroxy-quinones (QR-OH), two weak acids in their photoreaction. For this reason, the kinetics of the photoreaction can be conveniently followed by the pH-stat titration technique. The mathematical description of the kinetic traces measured provides the two main parameters of the photoreaction: the differential quantum yield of the reaction (Φ) and the ratio of the two photo-products, i.e. the fraction of QR that is converted to QR-OH (α). These values are described in this paper for 2,5-dichloro-1,4-benzoquinone at different pH values, together with the detailed mathematical evaluation of the application limits of the pH-stat method for such reactions.
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Affiliation(s)
- Virág Kiss
- Department of Physical Chemistry, University of Debrecen, H-4032 Debrecen, Egyetem tér 1., Hungary.
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13
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Pino-Chamorro JÁ, Ditrói T, Lente G, Fábián I. A detailed kinetic study of the direct photooxidation of 2,4,6-trichlorophenol. J Photochem Photobiol A Chem 2016. [DOI: 10.1016/j.jphotochem.2016.07.025] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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14
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Ditrói T, Kalmár J, Pino-Chamorro JA, Erdei Z, Lente G, Fábián I. Construction of a multipurpose photochemical reactor with on-line spectrophotometric detection. Photochem Photobiol Sci 2016; 15:589-94. [DOI: 10.1039/c5pp00407a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A versatile photoreactor was constructed from commercially available parts, which is capable of recording high quality kinetic traces in homogeneous and heterogeneous photoreactions and also easily adaptable to flow-through operation.
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Affiliation(s)
- Tamás Ditrói
- Department of Inorganic and Analytical Chemistry
- University of Debrecen
- Debrecen
- H-4010 Hungary
| | - József Kalmár
- MTA-DE Homogeneous Catalysis and Reaction Mechanisms Research Group
- Debrecen
- H-4010 Hungary
| | | | - Zsolt Erdei
- Department of Inorganic and Analytical Chemistry
- University of Debrecen
- Debrecen
- H-4010 Hungary
| | - Gábor Lente
- Department of Inorganic and Analytical Chemistry
- University of Debrecen
- Debrecen
- H-4010 Hungary
| | - István Fábián
- Department of Inorganic and Analytical Chemistry
- University of Debrecen
- Debrecen
- H-4010 Hungary
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15
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Procházka E, Escher BI, Plewa MJ, Leusch FDL. In Vitro Cytotoxicity and Adaptive Stress Responses to Selected Haloacetic Acid and Halobenzoquinone Water Disinfection Byproducts. Chem Res Toxicol 2015; 28:2059-68. [DOI: 10.1021/acs.chemrestox.5b00283] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Erik Procházka
- Smart
Water Research Centre, Australian Rivers Institute, School of Environment, Griffith University, Gold Coast, Queensland 4222, Australia
| | - Beate I. Escher
- Smart
Water Research Centre, Australian Rivers Institute, School of Environment, Griffith University, Gold Coast, Queensland 4222, Australia
- Cell
Toxicology, Helmholtz Centre for Environmental Research−UFZ, 04318 Leipzig, Germany
- Environmental
Toxicology, Center for Applied Geosciences, Eberhard Karls University Tübingen, 72074 Tübingen, Germany
| | | | - Frederic D. L. Leusch
- Smart
Water Research Centre, Australian Rivers Institute, School of Environment, Griffith University, Gold Coast, Queensland 4222, Australia
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16
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Józsa É, Purgel M, Bihari M, Fehér PP, Sustyák G, Várnagy B, Kiss V, Ladó E, Ősz K. Kinetic studies of hydroxyquinone formation from water soluble benzoquinones. NEW J CHEM 2014. [DOI: 10.1039/c3nj01274c] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Kalmár J, Dóka É, Lente G, Fábián I. Aqueous photochemical reactions of chloride, bromide, and iodide ions in a diode-array spectrophotometer. Autoinhibition in the photolysis of iodide ions. Dalton Trans 2014; 43:4862-70. [DOI: 10.1039/c3dt53255k] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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18
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Lehóczki T, Józsa É, Ősz K. Ferrioxalate actinometry with online spectrophotometric detection. J Photochem Photobiol A Chem 2013. [DOI: 10.1016/j.jphotochem.2012.10.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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19
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Hu M, Wang Y, Xiong Z, Bi D, Zhang Y, Xu Y. Iodine-sensitized degradation of 2,4,6-trichlorophenol under visible light. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2012; 46:9005-9011. [PMID: 22827582 DOI: 10.1021/es301577p] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Molecular iodine has been studied, for the first time, as a sensitizer for the degradation of 2,4,6-trichlorophenol (TCP) in aqueous solution under visible light (λ ≥ 450 nm). TCP was degraded in the presence of commercial I(2), but the reaction rate decreased significantly after 2 h. When a solution of NaI and H(2)O(2) was used as an iodine source with phosphotungstic acid (PW) as a catalyst, TCP degradation was not only fast but also followed zero-order kinetics. Importantly, the I(2) concentration remained unchanged with time, indicative of I(2) recycling as a kind of photocatalyst. During TCP degradation, 2,6-dichloro-1,4-benzoquinone was produced as the main intermediate (76%), which slowly degraded in the irradiated solution. For every equivalent of TCP consumed at the 2 h time point, approximately 1.7 equivalents of chloride ions were produced. Further study of the effect of variables including the type of polyoxometalates (POM) and the initial concentration of each component revealed that the rate of TCP degradation under visible light was determined by the rate of I(2) production in the dark. The optimum pH and apparent activation energy for TCP disappearance were 4.5 and 42.8 kJ/mol, respectively. It is proposed that TCP degradation is initiated by iodine radicals produced from I(2) photolysis, followed by I(2) regeneration through a POM-catalyzed oxidation of I(3)(-) by H(2)O(2).
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Affiliation(s)
- Meiqin Hu
- Department of Chemistry, Zhejiang University, Hangzhou 310027, China
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20
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Hu X, Ji H, Wu L. Singlet oxygen photogeneration and 2,4,6-TCP photodegradation at Pt/TiO2 under visible light illumination. RSC Adv 2012. [DOI: 10.1039/c2ra21661b] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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21
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Gombár M, Józsa É, Braun M, Ősz K. Construction of a photochemical reactor combining a CCD spectrophotometer and a LED radiation source. Photochem Photobiol Sci 2012; 11:1592-5. [DOI: 10.1039/c2pp25166c] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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22
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D'Antonio J, Ghiladi RA. Reactivity of deoxy- and oxyferrous dehaloperoxidase B from Amphitrite ornata: identification of compound II and its ferrous-hydroperoxide precursor. Biochemistry 2011; 50:5999-6011. [PMID: 21619067 DOI: 10.1021/bi200311u] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Dehaloperoxidase (DHP) from the terebellid polychaete Amphitrite ornata is a bifunctional enzyme that possesses both hemoglobin and peroxidase activities. The bifunctional nature of DHP as a globin peroxidase appears to be at odds with the traditional starting oxidation state for each individual activity. Namely, reversible oxygen binding is only mediated via a ferrous heme in globins, and peroxidase activity is initiated from ferric centers and to the exclusion of the oxyferrous oxidation state from the peroxidase cycle. Thus, to address what appears to be a paradox, herein we report the details of our investigations into the DHP catalytic cycle when initiated from the deoxy- and oxyferrous states using biochemical assays, stopped-flow UV-visible, and rapid-freeze-quench electron paramagnetic resonance spectroscopies, and anaerobic methods. We demonstrate the formation of Compound II directly from deoxyferrous DHP B upon its reaction with hydrogen peroxide and show that this occurs both in the presence and in the absence of trihalophenol. Prior to the formation of Compound II, we have identified a new species that we have preliminarily attributed to a ferrous-hydroperoxide precursor that undergoes heterolysis to generate the aforementioned ferryl intermediate. Taken together, the results demonstrate that the oxyferrous state in DHP is a peroxidase competent starting species, and an updated catalytic cycle for DHP is proposed in which the ferric oxidation state is not an obligatory starting point for the peroxidase catalytic cycle of dehaloperoxidase. The data presented herein provide a link between the peroxidase and oxygen transport activities, which furthers our understanding of how this bifunctional enzyme is able to unite its two inherent functions in one system.
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Affiliation(s)
- Jennifer D'Antonio
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA
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Zelenay V, Monge ME, D'Anna B, George C, Styler SA, Huthwelker T, Ammann M. Increased steady state uptake of ozone on soot due to UV/Vis radiation. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010jd015500] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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24
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Simon A, Ballai C, Lente G, Fábián I. Structure–reactivity relationships and substituent effect additivity in the aqueous oxidation of chlorophenols by cerium(iv). NEW J CHEM 2011. [DOI: 10.1039/c0nj00529k] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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25
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Filáry Á, Horváth AK. Photochemically induced catalysis of iodide ion and iodine in the tetrathionate–periodate reaction. Phys Chem Chem Phys 2010; 12:6742-9. [DOI: 10.1039/b921858k] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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26
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Zidki T, Cohen H, Meyerstein D. Photochemical induced growth and aggregation of metal nanoparticles in diode-array spectrophotometer via excited dimethyl-sulfoxide. Phys Chem Chem Phys 2010; 12:12862-7. [DOI: 10.1039/c0cp01037e] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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27
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Lente G, Kalmár J, Baranyai Z, Kun A, Kék I, Bajusz D, Takács M, Veres L, Fábián I. One- Versus Two-Electron Oxidation with Peroxomonosulfate Ion: Reactions with Iron(II), Vanadium(IV), Halide Ions, and Photoreaction with Cerium(III). Inorg Chem 2009; 48:1763-73. [DOI: 10.1021/ic801569k] [Citation(s) in RCA: 159] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Gábor Lente
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, POB 21, Hungary, H-4010
| | - József Kalmár
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, POB 21, Hungary, H-4010
| | - Zsuzsa Baranyai
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, POB 21, Hungary, H-4010
| | - Alíz Kun
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, POB 21, Hungary, H-4010
| | - Ildikó Kék
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, POB 21, Hungary, H-4010
| | - Dávid Bajusz
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, POB 21, Hungary, H-4010
| | - Marcell Takács
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, POB 21, Hungary, H-4010
| | - Lilla Veres
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, POB 21, Hungary, H-4010
| | - István Fábián
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, POB 21, Hungary, H-4010
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Görner H, von Sonntag C. Photoprocesses of Chloro-Substituted p-Benzoquinones. J Phys Chem A 2008; 112:10257-63. [DOI: 10.1021/jp805046p] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Helmut Görner
- Max-Planck-Institut für Bioanorganische Chemie, D-45413 Mülheim an der Ruhr, Germany
| | - Clemens von Sonntag
- Max-Planck-Institut für Bioanorganische Chemie, D-45413 Mülheim an der Ruhr, Germany
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Zhao B, Wang J. Chemical oscillations during the photoreduction of 1,4-benzoquinone in acidic bromate solution. J Photochem Photobiol A Chem 2007. [DOI: 10.1016/j.jphotochem.2007.05.025] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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31
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Galajda M, Lente G, Fábián I. Photochemically Induced Autocatalysis in the Chlorate Ion−Iodine System. J Am Chem Soc 2007; 129:7738-9. [PMID: 17539644 DOI: 10.1021/ja072361l] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Mónika Galajda
- Department of Inorganic and Analytical Chemistry, University of Debrecen, P.O.B. 21 H-4010 Derecen, Hungary
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Görner H. Electron transfer from aromatic amino acids to triplet quinones. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2007; 88:83-9. [PMID: 17604179 DOI: 10.1016/j.jphotobiol.2007.05.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Revised: 05/03/2007] [Accepted: 05/03/2007] [Indexed: 10/23/2022]
Abstract
The photoreduction of 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-anthraquinone (AQ) and several methylated or halogenated derivatives in argon-saturated acetonitrile-water mixtures by indole, N-acetyltryptophan and N-acetyltyrosine was studied by time-resolved UV-vis spectroscopy using 20 ns UV laser pulses. The quinone triplet state is quenched by the aromatic amino acids and the rate constants are (1-5)x10(9)M(-1)s(-1). The semiquinone radical anion Q.(-) is the major observable transient after electron transfer from amino acids to the quinone triplet state. Termination of Q.(-) and amino acid derived radicals takes place in the mus-ms range. The effects of structure and other specific properties of quinones and amino acids are discussed. The radicals are subjects of intercept with oxygen, whereby hydrogen peroxide is eventually formed. The quantum yield of oxygen uptake Phi(-O2) as a measure of formation of hydrogen peroxide increases with increasing amino acid concentration, approaching Phi(-O2) for AQ in air-saturated solution.
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Affiliation(s)
- Helmut Görner
- Max-Planck-Institut für Bioanorganische Chemie, D-45413 Mülheim an der Ruhr, Germany.
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Görner H. Photoreactions of 1,4-Naphthoquinones: Effects of Substituents and Water on the Intermediates and Reactivity¶. Photochem Photobiol 2007. [DOI: 10.1111/j.1751-1097.2005.tb00197.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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34
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Kerezsi I, Lente G, Fábián I. Kinetics and Mechanism of the Photoinitiated Autoxidation of Sulfur(IV) in the Presence of Iodide Ion. Inorg Chem 2007; 46:4230-8. [PMID: 17441709 DOI: 10.1021/ic061521b] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The kinetics and mechanism of the photoinitiated and iodide ion-catalyzed aqueous autoxidation of sulfur(IV) has been studied in a diode-array spectrophotometer using the same light beam for excitation and detection. Light absorption of both the iodide ion and sulfur(IV) contribute to the initiation of a highly efficient radical chain reaction, the overall rate of which depends on the reactant and catalyst concentrations, the pH, and the light intensity in a complex manner. To interpret all the experimental findings, an elaborate scheme is proposed, in which the chain carriers are SO3-*, SO4-*, SO5-*, I*, and I2-*. There are three termination steps, each of them is second-order with respect to the chain carriers. Model calculations and nonlinear fitting have been used to show that the proposed scheme gives an excellent quantitative interpretation of the experimental results.
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Affiliation(s)
- Ildikó Kerezsi
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, P.O.B. 21, Hungary H-4010
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Görner H. Oxygen Uptake upon Photolysis of 1,4-Benzoquinones and 1,4-Naphthoquinones in Air-Saturated Aqueous Solution in the Presence of Formate, Amines, Ascorbic Acid, and Alcohols. J Phys Chem A 2007; 111:2814-9. [PMID: 17388578 DOI: 10.1021/jp0683061] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effects of oxygen in the photoreduction of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), and a series of derivatives were studied in aqueous solution in the presence of acetonitrile and formate, aliphatic amines, e.g., EDTA or triethylamine, ascorbic acid, and alcohols, e.g., methanol or 2-propanol. The quinone triplet state is quenched, whereby the semiquinone and donor radicals are formed which react subsequently with oxygen. The overall reaction is oxidation of the donors and conversion of oxygen via the hydroperoxyl/superoxide radical into hydrogen peroxide. The quantum yield (Phi-O2) of this oxygen uptake changes in 2-propanol-water (1:10) from <0.01 for BQ to Phi-O2 = 0.5-0.8 for NQ. Generally Phi-O2 increases with increasing donor concentration. The specific properties of quinone structure, the radical equilibria and reactivity, and the concentration dependences are discussed.
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Affiliation(s)
- Helmut Görner
- Max-Planck-Institut für Bioanorganische Chemie, D-45413 Mülheim an der Ruhr, Germany
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36
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Lente G, Fábián I. Kinetics and mechanism of the oxidation of water soluble porphyrin FeIIITPPS with hydrogen peroxide and the peroxomonosulfate ion. Dalton Trans 2007:4268-75. [PMID: 17893816 DOI: 10.1039/b708961a] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The overall six-electron oxidation of water soluble porphyrin Fe(III)TPPS by hydrogen peroxide and peroxomonosulfate ion was studied by the stopped-flow method with UV-vis detection. A three-step consecutive reaction was observed with two intermediates: Fe(III)TPPS --> Int(1)--> Int(2)--> products. The products were identified as the iron(iii) complex of the biliverdin analog formed from TPPS and 4-sulfobenzoic acid. All the rate constants with both oxidizing agents were determined. Intermediate Int(1) is proposed to be the species (TPPS (+))Fe(IV)=O. Although no unambiguous proposal for the structure of Int(2) can be made, it is most probably the product of the four-electron oxidation of the original Fe(III)TPPS, contains an iron-oxo center and has a dissociable proton with a pK of around 3.1. In spite of the protolytic equilibria occuring in the pH region 2-4, the kinetic observations do not show pH dependence.
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Affiliation(s)
- Gábor Lente
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, P.O.B. 21, Hungary, H-4010.
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Varga D, Horváth AK, Nagypál I. Unexpected Formation of Higher Polythionates in the Oxidation of Thiosulfate by Hypochlorous Acid in a Slightly Acidic Medium. J Phys Chem B 2006; 110:2467-70. [PMID: 16471841 DOI: 10.1021/jp0567873] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It has been clearly shown that not only tetrathionate but also pentathionate or even higher polythionates is formed in the oxidation of thiosulfate by hypochlorous acid in a slightly acidic medium. In thiosulfate excess, the absorbance-time curves registered at 250 nm may go through a maximum followed by a minimum, suggesting the presence of a short-lived absorbing intermediate proposed to be S(2)O(3)OCl(3-). Matrix rank analysis (MRA) studies have revealed that altogether five independent absorbing species are present in the wavelength range 240-400 nm. A kinetic model is suggested to take all of the experimental observations into account.
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Görner H. Photoreactions of p-Quinones with Dimethyl Sulfide and Dimethyl Sulfoxide in Aqueous Acetonitrile†. Photochem Photobiol 2006; 82:71-7. [PMID: 16076243 DOI: 10.1562/2005-05-25-ra-540] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The effects of dimethyl sulfide (DMS) and dimethyl sulfoxide (DMSO) on the photoreactions of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 9,10-anthraquinone (AQ) and several derivatives in acetonitrile/water were studied. The observed triplet state of the quinones is quenched and the rate constant is close to the diffusion-controlled limit for reactions of most quinones with DMS and lower with DMSO. Semiquinone radical anions (Q*-) produced by electron transfer from sulfur to the triplet quinone were detected. For both DMS and DMSO the yield of Q*- is similar, being generally low for BQ and NQ, substantial for AQ and largest for chloranil. The specific quencher concentrations and the effects of quinone structure and redox potentials on the time-resolved photochemical properties are discussed.
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Affiliation(s)
- Helmut Görner
- Max-Planck-Institut für Bioanorganische Chemie, D-45413 Mülheim an der Ruhr, Germany
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Kerezsi I, Lente G, Fábián I. Kinetics of the light-driven aqueous autoxidation of sulfur(iv) in the absence and presence of iron(ii). Dalton Trans 2006:955-60. [PMID: 16462956 DOI: 10.1039/b511363f] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The photochemical autoxidation of aqueous, acidic sulfur(IV) solutions was studied in the absence and presence of iron(II) by a newly introduced technique using a diode-array spectrophotometer, in which the same light source is used to drive and detect the reaction. Based on detailed kinetic and stoichiometric data sets, a non-chain mechanism is proposed for the autoxidation of sulfur(IV). In this mechanism, excited hydrated sulfur dioxide, *H2O.SO2, first reacts with O2 to form peroxomonosulfate ion, HSO5-, which rapidly oxidizes another H2O.SO2 to give hydrogensulfate ion as a final product. In the presence of iron(II), the formation of iron(III) was detected, which can be interpreted through the simultaneous contribution of two additional pathways: some of the HSO5- formed oxidizes iron(II) instead of sulfur(iv), and *H2O.SO2 also reacts directly with iron(II) to yield iron(III). This mechanism provides a sufficient quantitative interpretation of all experimental observations.
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Affiliation(s)
- Ildikó Kerezsi
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, P.O.B. 21, Hungary H-4010
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Kerezsi I, Lente G, Fábián I. Highly Efficient Photoinitiation in the Cerium(III)-Catalyzed Aqueous Autoxidation of Sulfur(IV). An Example of Comprehensive Evaluation of Photoinduced Chain Reacions. J Am Chem Soc 2005; 127:4785-93. [PMID: 15796544 DOI: 10.1021/ja0439120] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photoinitiated and cerium(III)-catalyzed aqueous reaction between sulfite ion and oxygen has been studied in a diode-array spectrophotometer using the same light beam for excitation and detection. Cerium(III) is identified as the photoactive absorbing species, and the production of cerium(IV) initiates a radical chain reaction. To interpret all the experimental findings, a simple scheme is proposed, in which the additional chain carriers are sulfite ion radical (SO3(-.)), sulfate ion radical (SO4(-.), and peroxomonosulfate ion radical (SO5(-.). The overall rate of oxidation is proportional to the square root of the light intensity per unit volume, which is readily interpreted by the second-order termination reaction of the proposed scheme. It is also shown that the reaction proceeds for an extended period of time in the dark following illumination, and a quantitative analysis is presented for this phase as well. The postulated model predicts that cerium(III) should have a cocatalytic or synergistic effect on the autoxidation of sulfite ion in the presence of other catalysts. This prediction was confirmed in the iron(III)-sulfite ion-oxygen system. The experimental method and the mathematical treatment used might be applicable to a wide range of photoinduced chain reactions.
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Affiliation(s)
- Ildikó Kerezsi
- University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, P.O.B. 21, H-4010 Hungary
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Görner H. Photoreactions of 1,4-Naphthoquinones: Effects of Substituents and Water on the Intermediates and Reactivity¶. Photochem Photobiol 2005. [DOI: 10.1562/2004-08-11-ra-270.1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Görner H. Photoreactions of p-benzo-, p-naphtho- and p-anthraquinones with ascorbic acid. Photochem Photobiol Sci 2004; 3:933-8. [PMID: 15480484 DOI: 10.1039/b410386f] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The photoreduction of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 9,10-anthraquinone (AQ) and several derivatives, e.g. dimethylBQ, trimethylBQ, duroquinone, bromoNQ, methoxyNQ, methylAQ and dimethylAQ in acetonitrile-water by ascorbate was studied by time-resolved UV-vis spectroscopy using 20 ns laser pulses at 308 nm and continuous 254 nm irradiation. The semiquinone radical (*QH/Q*(-)) is formed after H-atom transfer from ascorbate to the quinone triplet state. The rate constant for quenching is k(q)=(2-9) x 10(9) M(-1) s(-1). Termination of the radicals takes place in the micros-ms range. The results are compared with those initiated by electron transfer from DABCO under similar conditions, where the k(q) values are similar, but the termination of Q*(-) takes place by electron back transfer not yielding hydroquinones. Specific properties of the quinone triplet state, e.g. self-quenching, nucleophilic water addition and the effects of structure are discussed.
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Affiliation(s)
- Helmut Görner
- Max-Planck-Institut für Bioanorganische Chemie, D-45413 Mülheim an der Ruhr, Germany
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