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Jena S, Tulsiyan KD, Sahoo RR, Rout S, Sahu AK, Biswal HS. Critical assessment of selenourea as an efficient small molecule fluorescence quenching probe to monitor protein dynamics. Chem Sci 2023; 14:14200-14210. [PMID: 38098725 PMCID: PMC10718066 DOI: 10.1039/d3sc04287a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Accepted: 09/26/2023] [Indexed: 12/17/2023] Open
Abstract
Organoselenium compounds have recently been the experimentalists' delight due to their broad applications in organic synthesis, medicinal chemistry, and materials science. Selenium atom replacement of the carbonyl oxygen of the urea moiety dramatically reduces the HOMO-LUMO gap and oxidation potential, which completely changes the physicochemical properties of selenocarbonyl compounds. To our surprise, the photophysics and utility of a simple molecule such as selenourea (SeU) have not been explored in detail, which persuaded us to investigate its role in excited state processes. The steady-state emission, temperature-dependent time-correlated single photon counting, and femtosecond fluorescence upconversion experimental results confirmed that SeU significantly enhances the fluorescence quenching through a photoinduced electron transfer (PET) mechanism with an ∼10 ps ultrafast intrinsic PET lifetime component which is mostly absent in thiourea (TU). A wide range of fluorophores, based on their different redox abilities and fluorescence lifetimes covering a broad spectral window (λex: 390-590 nm and λem: 490-690 nm), were chosen to validate the proof of the concept. It was extended to tetramethylrhodamine (TMR)-5-maleimide labeled lysozyme protein, where we observed significant fluorescence quenching in the presence of SeU. The present work emphasizes that the high quenching efficiency with an ultrafast PET process, reduced orbital energy gap, and higher negative free energy change of the electron transfer reaction are the representative characteristics of selenourea or selenoamides to enable them as potential surrogates of thioamides or oxoamides quenching probes to monitor protein conformational changes and dynamics.
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Affiliation(s)
- Subhrakant Jena
- School of Chemical Sciences, National Institute of Science Education and Research (NISER) PO-Bhimpur-Padanpur, Via-Jatni, District-Khurda, PIN-752050 Bhubaneswar India
- Homi Bhabha National Institute, Training School Complex Anushakti Nagar Mumbai 400094 India
| | - Kiran Devi Tulsiyan
- School of Chemical Sciences, National Institute of Science Education and Research (NISER) PO-Bhimpur-Padanpur, Via-Jatni, District-Khurda, PIN-752050 Bhubaneswar India
- Homi Bhabha National Institute, Training School Complex Anushakti Nagar Mumbai 400094 India
| | - Rudhi Ranjan Sahoo
- School of Chemical Sciences, National Institute of Science Education and Research (NISER) PO-Bhimpur-Padanpur, Via-Jatni, District-Khurda, PIN-752050 Bhubaneswar India
- Homi Bhabha National Institute, Training School Complex Anushakti Nagar Mumbai 400094 India
| | - Saiprakash Rout
- School of Chemical Sciences, National Institute of Science Education and Research (NISER) PO-Bhimpur-Padanpur, Via-Jatni, District-Khurda, PIN-752050 Bhubaneswar India
- Homi Bhabha National Institute, Training School Complex Anushakti Nagar Mumbai 400094 India
| | - Akshay Kumar Sahu
- School of Chemical Sciences, National Institute of Science Education and Research (NISER) PO-Bhimpur-Padanpur, Via-Jatni, District-Khurda, PIN-752050 Bhubaneswar India
- Homi Bhabha National Institute, Training School Complex Anushakti Nagar Mumbai 400094 India
| | - Himansu S Biswal
- School of Chemical Sciences, National Institute of Science Education and Research (NISER) PO-Bhimpur-Padanpur, Via-Jatni, District-Khurda, PIN-752050 Bhubaneswar India
- Homi Bhabha National Institute, Training School Complex Anushakti Nagar Mumbai 400094 India
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2
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Saab M, Nelson DJ, Leech MC, Lam K, Nolan SP, Nahra F, Van Hecke K. Reactions of N-heterocyclic carbene-based chalcogenoureas with halogens: a diverse range of outcomes. Dalton Trans 2022; 51:3721-3733. [PMID: 35169826 DOI: 10.1039/d2dt00010e] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have investigated the reactions of chalcogenoureas derived from N-heterocyclic carbenes, referred to here as [E(NHC)], with halogens. Depending on the structure of the chalcogenourea and the identity of the halogen, a diverse range of reactivity was observed and a corresponding range of structures was obtained. Cyclic voltammetry was carried out to characterise the oxidation and reduction potentials of these [E(NHC)] species; selenoureas were found to be easier to oxidise than the corresponding thioureas. In some cases, a correlation was found between the oxidation potential of these compounds and the electronic properties of the corresponding NHC. The reactivity of these chalcogenoureas with different halogenating reagents (Br2, SO2Cl2, I2) was then investigated, and products were characterised using NMR spectroscopy and single-crystal X-ray diffraction. X-ray analyses elucidated the solid-state coordination types of the obtained products, showing that a variety of possible adducts can be obtained. In some cases, we were able to extrapolate a structure/activity correlation to explain the observed trends in reactivity and oxidation potentials.
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Affiliation(s)
- Marina Saab
- XStruct, Department of Chemistry, Ghent University, Krijgslaan 281, Building S3, 9000 Ghent, Belgium.
| | - David J Nelson
- WestCHEM Department of Pure & Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, Scotland, UK
| | - Matthew C Leech
- School of Science, University of Greenwich, Chatham Maritime ME4 4TB, UK
| | - Kevin Lam
- School of Science, University of Greenwich, Chatham Maritime ME4 4TB, UK
| | - Steven P Nolan
- Department of Chemistry, Ghent University, Krijgslaan 281, Building S3, 9000 Ghent, Belgium
| | - Fady Nahra
- XStruct, Department of Chemistry, Ghent University, Krijgslaan 281, Building S3, 9000 Ghent, Belgium. .,VITO (Flemish Institute for Technological Research), Boeretang 200, 2400 Mol, Belgium.
| | - Kristof Van Hecke
- XStruct, Department of Chemistry, Ghent University, Krijgslaan 281, Building S3, 9000 Ghent, Belgium.
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3
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Skotnicki K, Janik I, Sadowska K, Leszczynska G, Bobrowski K. Radiation-Induced Oxidation Reactions of 2-Selenouracil in Aqueous Solutions: Comparison with Sulfur Analog of Uracil. Molecules 2021; 27:molecules27010133. [PMID: 35011366 PMCID: PMC8746332 DOI: 10.3390/molecules27010133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2021] [Revised: 12/17/2021] [Accepted: 12/20/2021] [Indexed: 11/29/2022] Open
Abstract
One-electron oxidation of 2-selenouracil (2-SeU) by hydroxyl (●OH) and azide (●N3) radicals leads to various primary reactive intermediates. Their optical absorption spectra and kinetic characteristics were studied by pulse radiolysis with UV-vis spectrophotometric and conductivity detection and by the density functional theory (DFT) method. The transient absorption spectra recorded in the reactions of ●OH with 2-SeU are dominated by an absorption band with an λmax = 440 nm, the intensity of which depends on the concentration of 2-SeU and pH. Based on the combination of conductometric and DFT studies, the transient absorption band observed both at low and high concentrations of 2-SeU was assigned to the dimeric 2c-3e Se-Se-bonded radical in neutral form (2●). The dimeric radical (2●) is formed in the reaction of a selenyl-type radical (6●) with 2-SeU, and both radicals are in equilibrium with Keq = 1.3 × 104 M−1 at pH 4 (below the pKa of 2-SeU). Similar equilibrium with Keq = 4.4 × 103 M−1 was determined for pH 10 (above the pKa of 2-SeU), which admittedly involves the same radical (6●) but with a dimeric 2c-3e Se-Se bonded radical in anionic form (2●−). In turn, at the lowest concentration of 2-SeU (0.05 mM) and pH 10, the transient absorption spectrum is dominated by an absorption band with an λmax = 390 nm, which was assigned to the ●OH adduct to the double bond at C5 carbon atom (3●) based on DFT calculations. Similar spectral and kinetic features were also observed during the ●N3-induced oxidation of 2-SeU. In principle, our results mostly revealed similarities in one-electron oxidation pathways of 2-SeU and 2-thiouracil (2-TU). The major difference concerns the stability of dimeric radicals with a 2c-3e chalcogen-chalcogen bond in favor of 2-SeU.
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Affiliation(s)
- Konrad Skotnicki
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland;
- Correspondence: (K.S.); (I.J.); Tel.: +48-22-504-1292 (K.S.)
| | - Ireneusz Janik
- Notre Dame Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Correspondence: (K.S.); (I.J.); Tel.: +48-22-504-1292 (K.S.)
| | - Klaudia Sadowska
- Institute of Organic Chemistry, Faculty of Chemistry, Lodz University of Technology, 90-924 Lodz, Poland; (K.S.); (G.L.)
| | - Grazyna Leszczynska
- Institute of Organic Chemistry, Faculty of Chemistry, Lodz University of Technology, 90-924 Lodz, Poland; (K.S.); (G.L.)
| | - Krzysztof Bobrowski
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland;
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4
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Wojnárovits L, Takács E. Rate constants of dichloride radical anion reactions with molecules of environmental interest in aqueous solution: a review. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2021; 28:41552-41575. [PMID: 34086177 PMCID: PMC8354983 DOI: 10.1007/s11356-021-14453-w] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Accepted: 05/13/2021] [Indexed: 05/14/2023]
Abstract
Natural waters, water droplets in the air at coastal regions and wastewaters usually contain chloride ions (Cl-) in relatively high concentrations in the milimolar range. In the reactions of highly oxidizing radicals (e.g., •OH, •NO3, or SO4•-) in the nature or during wastewater treatment in advanced oxidation processes the chloride ions easily transform to chlorine containing radicals, such as Cl•, Cl2•-, and ClO•. This transformation basically affects the degradation of organic molecules. In this review about 400 rate constants of the dichloride radical anion (Cl2•-) with about 300 organic molecules is discussed together with the reaction mechanisms. The reactions with phenols, anilines, sulfur compounds (with sulfur atom in lower oxidation state), and molecules with conjugated electron systems are suggested to take place with electron transfer mechanism. The rate constant is high (107-109 M-1 s-1) when the reduction potential the one-electron oxidized species/molecule couple is well below that of the Cl2•-/2Cl- couple.
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Affiliation(s)
- László Wojnárovits
- Radiation Chemistry Department, Institute for Energy Security and Environmental Safety, Centre for Energy Research, H-1121 Konkoly-Thege Miklós út, Budapest, 29-33, Hungary
| | - Erzsébet Takács
- Radiation Chemistry Department, Institute for Energy Security and Environmental Safety, Centre for Energy Research, H-1121 Konkoly-Thege Miklós út, Budapest, 29-33, Hungary.
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5
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Bouchet LM, Argüello JE. Photoinduced One-Electron Oxidation of Aromatic Selenides: Effect of the Structure on the Reversible Dimerization Reaction. J Org Chem 2018; 83:5674-5680. [PMID: 29683656 DOI: 10.1021/acs.joc.8b00684] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The photochemical one-electron oxidation of alkyl aryl selenides was studied by means of laser flash photolysis (355 nm). Quenching of the sensitizers in their excited state leads to selenide radical cation in the presence of selenium derivatives. The π-type dimer of methyl phenyl selenide radical cation was detected at 630 nm at expenses of the monomeric radical cation (530 nm). The effect of modification of the aryl and alkyl substituents was also studied, resulting that the formation of dimers depends on both, the electronic properties and steric hindrance of the substituents. Both effects, an increase in steric hindrance in the alkyl moiety or the presence of strongly electron donor groups in the aromatic substituent that stabilizes the radical cation, prevent the dimer formation.
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Affiliation(s)
- Lydia M Bouchet
- INFIQC-CONICET-UNC, Dpto. de Química Orgánica, Facultad de Ciencias Químicas , Universidad Nacional de Córdoba, Ciudad Universitaria , X5000HUA Córdoba , Argentina
| | - Juan E Argüello
- INFIQC-CONICET-UNC, Dpto. de Química Orgánica, Facultad de Ciencias Químicas , Universidad Nacional de Córdoba, Ciudad Universitaria , X5000HUA Córdoba , Argentina
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6
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Kumar PV, Singh BG, Phadnis PP, Jain VK, Priyadarsini KI. Effect of Molecular Interactions on Electron-Transfer and Antioxidant Activity of Bis(alkanol)selenides: A Radiation Chemical Study. Chemistry 2016; 22:12189-98. [DOI: 10.1002/chem.201601918] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Indexed: 12/29/2022]
Affiliation(s)
- Pavitra V. Kumar
- Radiation and Photochemistry Division; Bhabha Atomic Research Centre, Trombay; Mumbai 400085 India
- Homi Bhabha National Institute, Anushaktinagar; Mumbai 400094 India
| | - Beena G. Singh
- Radiation and Photochemistry Division; Bhabha Atomic Research Centre, Trombay; Mumbai 400085 India
| | - Prasad P. Phadnis
- Chemistry Division; Bhabha Atomic Research Centre, Trombay; Mumbai 400085 India
| | - Vimal K. Jain
- Homi Bhabha National Institute, Anushaktinagar; Mumbai 400094 India
- Chemistry Division; Bhabha Atomic Research Centre, Trombay; Mumbai 400085 India
| | - K. Indira Priyadarsini
- Radiation and Photochemistry Division; Bhabha Atomic Research Centre, Trombay; Mumbai 400085 India
- Homi Bhabha National Institute, Anushaktinagar; Mumbai 400094 India
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7
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Prasanthkumar KP, Alvarez-Idaboy JR, Kumar PV, Singh BG, Priyadarsini KI. Contrasting reactions of hydrated electron and formate radical with 2-thio analogues of cytosine and uracil. Phys Chem Chem Phys 2016; 18:28781-28790. [DOI: 10.1039/c6cp04483b] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
2-thiocytosine (TC) and 2-thiouracil (TU) were found to react with formate radical via reductive and oxidative pathways simultaneously.
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Affiliation(s)
| | - Juan R. Alvarez-Idaboy
- Departamento de Física y Química Teórica
- Facultad de Química
- Universidad Nacional Autónoma de México
- México D. F
- Mexico
| | - Pavitra V. Kumar
- Radiation and Photochemistry Division
- Chemistry Group
- Bhabha Atomic Research Centre
- Mumbai 400085
- India
| | - Beena G. Singh
- Radiation and Photochemistry Division
- Chemistry Group
- Bhabha Atomic Research Centre
- Mumbai 400085
- India
| | - K. Indira Priyadarsini
- Radiation and Photochemistry Division
- Chemistry Group
- Bhabha Atomic Research Centre
- Mumbai 400085
- India
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8
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Barik A, Singh BG, Sharma A, Jain VK, Priyadarsini KI. Pulse Radiolysis Studies of 3,5-Dimethyl Pyrazole Derivatives of Selenoethers. J Phys Chem A 2014; 118:10179-87. [DOI: 10.1021/jp507369q] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Atanu Barik
- Radiation & Photochemistry Division and ‡Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
| | - Beena G. Singh
- Radiation & Photochemistry Division and ‡Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
| | - Asmita Sharma
- Radiation & Photochemistry Division and ‡Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
| | - Vimal K. Jain
- Radiation & Photochemistry Division and ‡Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
| | - K. Indira Priyadarsini
- Radiation & Photochemistry Division and ‡Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
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9
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Singh BG, Thomas E, Sawant SN, Takahashi K, Dedachi K, Iwaoka M, Priyadarsini KI. Radical Cations of Aromatic Selenium Compounds: Role of Se···X Nonbonding Interactions. J Phys Chem A 2013; 117:9259-65. [DOI: 10.1021/jp405798h] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | | | | | - Kohei Takahashi
- Department
of Chemistry, School of Science, Tokai University, Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan
| | - Kenchi Dedachi
- Department
of Chemistry, School of Science, Tokai University, Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan
| | - Michio Iwaoka
- Department
of Chemistry, School of Science, Tokai University, Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan
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10
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Prasanthkumar KP, Suresh CH, Aravindakumar CT. Dimer radical cation of 4-thiouracil: a pulse radiolysis and theoretical study. J PHYS ORG CHEM 2013. [DOI: 10.1002/poc.3116] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- K. P. Prasanthkumar
- School of Chemical Sciences; Mahatma Gandhi University; Kottayam 686560 Kerala India
| | - Cherumuttathu H. Suresh
- National Institute for Interdisciplinary Science & Technology; Trivandrum 695019 Kerala India
| | - C. T. Aravindakumar
- School of Environmental Sciences; Mahatma Gandhi University; Kottayam 686560 Kerala India
- Inter University Instrumentation Center; Mahatma Gandhi University; Kottayam 686560 Kerala India
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11
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Prasanthkumar KP, Suresh CH, Aravindakumar CT. Oxidation reactions of 2-thiouracil: a theoretical and pulse radiolysis study. J Phys Chem A 2012; 116:10712-20. [PMID: 23061532 DOI: 10.1021/jp303808r] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The reaction of hydroxyl radical ((•)OH) with the nucleic acid base analogue 2-thiouracil (1) has been studied by pulse radiolysis experiments and DFT. The generic intermediate radicals feasible for the (•)OH reactions with 1, namely, one electron oxidation product (1(•+)), (•)OH-adducts (3(•), 4(•), and 5(•)), and H-abstracted radicals (6(•) and 7(•)), were characterized by interpreting their electronic and structural properties along with calculated energetics and UV-vis spectra. Pulse radiolysis experiments showed that the transient formed in the reaction of (•)OH with 1 in water at pH 6.5 has λ(max) at 430 nm. A bimolecular rate constant, k(2) of 9.6 × 10(9) M(-1) s(-1), is determined for this reaction via competition kinetics with 2-propanol. The experiments suggested that the transient species could be a dimer radical cation 2(•+), formed by the reaction of 1 with the radical cation 1(•+). For this reaction, an equilibrium constant of 4.7 × 10(3) M(-1) was determined. The transient formed in the reaction of 1 with pulse radiolytically produced Br(2)(•-) at pH 6.5 as well as Cl(2)(•-) at pH 1 has also produced λ(max) at 430 nm and suggested the formation of 2(•+). The calculated UV-vis spectra of the transient species (1(•+), 3(•), 4(•), 5(•), 6(•), and 7(•)) showed no resemblance to the experimental spectra, while that of 2(•+) (λ(max) = 420 nm) agreed well with the experimental value and thus confirmed the formation of 2(•+). The 420 nm peak was due to σ → σ* electronic excitation centered on a 2-center-3-electron (2c-3e) sulfur-sulfur bond [-S∴S-]. 2(•+) is the first reported example of a dimer radical cation in a pyrimidine heterocyclic system. Further, 5-C and 6-C substituted (substituents are -F, -Cl, -NH(2), -N(CH(3))(2), -OCH(3), -CF(3), -CH(3), -CH(2)CH(3), n-propyl, phenyl, and benzyl) and 5,6-disubstituted 2-thiouracil systems have been characterized by DFT and found that the reaction (1 + 1(•+) → 2(•+)) is exergonic (1.12-13.63 kcal/mol) for many of them.
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Affiliation(s)
- K P Prasanthkumar
- School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686560, India
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12
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Singh BG, Thomas E, Kumakura F, Dedachi K, Iwaoka M, Priyadarsini KI. One-electron redox processes in a cyclic selenide and a selenoxide: a pulse radiolysis study. J Phys Chem A 2010; 114:8271-7. [PMID: 20666479 DOI: 10.1021/jp103727e] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
One-electron redox reactions of cyclic selenium compounds, DL-trans-3,4-dihydroxy-1-selenolane (DHS(red)), and DL-trans-3,4-dihydroxy-1-selenolane oxide (DHS(ox)) were carried out in aqueous solutions using nanosecond pulse radiolysis, and the resultant transients were detected by absorption spectroscopy. Both *OH radical and specific one-electron oxidant, Br(2)(*-) radical reacted with DHS(red) to form similar transients absorbing at 480 nm, which has been identified as a dimer radical cation (DHS(red))(2)(*+). Secondary electron transfer reactions of the (DHS(red))(2)(*+) were studied with 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS(2-)) and superoxide (O(2)(*-)) radicals. The bimolecular rate constants for the electron transfer reaction between (DHS(red))(2)(*+) with ABTS(2-) was determined as 2.4 +/- 0.4 x 10(9) M(-1) s(-1). From this reaction, the yield of (DHS(red))(2)(*+) formed on reaction with *OH radical was estimated in the presence of varying phosphate concentrations. (DHS(red))(2)(*+) reacted with O(2)(*-) radical with a bimolecular rate constant of 2.7 +/- 0.1 x 10(9) M(-1) s(-1) at pH 7. From the same reaction, the positive charge on (DHS(red))(2)(*+) was confirmed by the kinetic salt effect. HPLC analysis of the products formed in the reaction of (DHS(red))(2)(*+) with O(2)(*-) radicals showed formation of the selenoxide, DHS(ox). In order to know if a similar mechanism operated during the reduction of DHS(ox), its reactions with e(aq)(-) were studied at pH 7. The rate constant for this reaction was determined as 5.6 +/- 0.9 x 10(9) M(-1) s(-1), and no transient absorption could be observed in the wavelength region from 280 to 700 nm. It is proposed that the radical anion (DHS(ox))(*-) formed by a one-electron reduction would get protonated to form a hydroxyl radical adduct, which in presence of proton donors, would undergo dehydration to form DHS(*+). Evidence for this mechanism was obtained by converting DHS(*+) to (DHS(red))(2)(*+) with the addition of DHS(red) to the same system. Quantum chemical calculations provided supporting evidence for some of the redox reactions.
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Affiliation(s)
- Beena G Singh
- Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India.
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López Ó, Maza S, Ulgar V, Maya I, Fernández-Bolaños JG. Synthesis of sugar-derived isoselenocyanates, selenoureas, and selenazoles. Tetrahedron 2009. [DOI: 10.1016/j.tet.2009.01.038] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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14
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Priyadarsini KI, Mishra B. Radical cations of some water-soluble organoselenium compounds: Insights from pulse radiolysis studies. Radiat Phys Chem Oxf Engl 1993 2008. [DOI: 10.1016/j.radphyschem.2008.05.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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15
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Mishra B, Kumar BS, Priyadarsini K. Pulse and γ-radiolysis studies on aqueous solution of 1,1′-dimethyl-2-selenourea. Radiat Phys Chem Oxf Engl 1993 2008. [DOI: 10.1016/j.radphyschem.2007.03.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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16
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Mishra B, Priyadarsini KI, Mohan H. Effect of pH on One-Electron Oxidation Chemistry of Organoselenium Compounds in Aqueous Solutions. J Phys Chem A 2006; 110:1894-900. [PMID: 16451022 DOI: 10.1021/jp055784n] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Pulse radiolysis coupled with absorption detection has been employed to study one-electron oxidation of selenomethionine (SeM), selenocystine (SeCys), methyl selenocysteine (MeSeCys), and selenourea (SeU) in aqueous solutions. Hydroxyl radicals (*OH) in the pH range from 1 to 7 and specific one-electron oxidants Cl2*- (pH 1) and Br2*- (pH 7) have been used to carry out the oxidation reactions. The bimolecular rate constants for these reactions were reported to be in the range of 2 x 10(9) to 10 x 10(9) M(-1) s(-1). Reactions of oxidizing radicals with all these compounds produced selenium-centered radical cations. The structure and stability of the radical cation were found to depend mainly on the substituent and pH. SeM, at pH 7, produced a monomer radical cation (lambdamax approximately 380 nm), while at pH 1, a dimer radical cation was formed by the interaction between oxidized and parent SeM (lambdamax approximately 480 nm). Similarly, SeCys, at pH 7, on one-electron oxidation, produced a monomer radical cation (lambdamax approximately 460 nm), while at pH 1, the reaction produced a transient species with (lambdamax approximately 560 nm), which is also a monomer radical cation. MeSeCys on one-electron oxidation in the pH range from 1 to 7 produced monomer radical cations (lambdamax approximately 350 nm), while at pH < 0, the reaction produced dimer radical cations (lambdamax approximately 460 nm). SeU at all the pH ranges produced dimer radical cations (lambdamax approximately 410 nm). The association constants of the dimer radical cations of SeM, MeSeCys, and SeU were determined by following absorption changes at lambdamax as a function of concentration. From these studies it is concluded that formation of monomer and dimer radical cations mainly depends on the substitution, pH, and the heteroatoms like N and O. The availability of a lone pair on an N or O atom at the beta or gamma position results in monomer radical cations having intramolecular stabilization. When such a lone pair is not available, the monomer radical cation is converted into a dimer radical cation which acquires intermolecular stabilization by the other selenium atom. The pH dependency confirms the role of protonation on stabilization. The oxidation chemistry of these selenium compounds is compared with that of their sulfur analogues.
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Affiliation(s)
- B Mishra
- Radiation & Photo Chemistry Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085, India
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Mishra B, Hassan PA, Priyadarsini KI, Mohan H. Reactions of Biological Oxidants with Selenourea: Formation of Redox Active Nanoselenium. J Phys Chem B 2005; 109:12718-23. [PMID: 16852575 DOI: 10.1021/jp051328n] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Reactions of biological oxidizing agents, such as hydroxyl radicals ((*)OH), singlet oxygen ((1)O(2)), hydrogen peroxide (H(2)O(2)), and peroxynitrite (ONOO(-)) with selenourea were studied. The kinetics of the reactions was followed using time-resolved techniques, and the bimolecular rate constants were determined. In all these reactions, under aerated conditions, elemental red selenium was produced as one of the reaction products. The average size of the selenium particles could be controlled and stabilized in the range of 20-100 nm with the addition of bovine serum albumin (BSA) or sodium dodecyl sulfate (SDS). The particles were characterized by dynamic light scattering studies (DLS), which revealed that the size and distribution of the particles depended mainly on the amount of selenourea undergoing oxidation. Other factors such as the nature of the oxidant and the concentration of the stabilizer also are important in stabilizing the particles. Nanoselenium-reduced ABTS(*-) to colorless ABTS(2-) (ABTS = 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) and oxidized dichlorodihydrofluoresecein diacetate (DCFA) to fluorescent dichlorofluorescein (DCF) indicating its ability to participate in redox and free radical reactions. The reactivity of selenium nanoparticles with these systems varied linearly with the surface area of the particles. The studies demonstrate that selenourea undergoes oxidation with both one-electron and two-electron oxidants to produce elemental selenium, which, on stabilization to nanometer size, exhibits size-dependent redox activity.
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Affiliation(s)
- B Mishra
- Radiation Chemistry and Chemical Dynamics Division and Novel Materials and Structural Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
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