1
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Becker P, Nauser T, Wiggenhauser M, Aeschlimann B, Frossard E, Günther D. In Vitro Fossilization for High Spatial Resolution Quantification of Elements in Plant-Tissue Using LA-ICP-TOFMS. Anal Chem 2024; 96:4952-4959. [PMID: 38482755 DOI: 10.1021/acs.analchem.3c05849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/27/2024]
Abstract
Laser ablation in combination with an inductively coupled plasma time-of-flight mass spectrometer (LA-ICP-TOFMS) is an upcoming method for rapid quantitative element mapping of various samples. While widespread in geological applications, quantification of elements in biotissues remains challenging. In this study, a proof-of-concept sample preparation method is presented in which plant-tissues are fossilized in order to solidify the complex biotissue matrix into a mineral-like matrix. This process enables quantification of elements by using silicone as an internal standard for normalization while also providing consistent ablation processes similar to minerals to reduce image blurring. Furthermore, it allows us to generate a quantitative image of the element composition at high spatial resolution. The feasibility of the approach is demonstrated on leaves of sunflowers (Helianthus annuus), soy beans (Glycine max), and corn (Zea mays) as representatives for common crops, which were grown on both nonspiked and cadmium-spiked agricultural soil. The quantitative results achieved during imaging were validated with digestion of whole leaves followed by ICP-OES analysis. LA-ICP-TOFMS element mapping of conventionally dried samples can provide misleading trends due to the irregular ablation behavior of biotissue because high signals caused by high ablation rates are falsely interpreted as enrichment of elements. Fossilization provides the opportunity to correct such phenomena by standardization with Si as an internal standard. The method demonstrated here allows for quantitative image acquisition without time-consuming sample preparation steps by using comparatively safe chemicals. The diversity of tested samples suggests that this sample preparation method is well-suited to achieve reproducible and quantitative element maps of various plant samples.
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Affiliation(s)
- Pascal Becker
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich 8093, Switzerland
| | - Thomas Nauser
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich 8093, Switzerland
| | - Matthias Wiggenhauser
- Institute of Agricultural Sciences, ETH Zurich, Eschikon 33, Lindau CH-8315, Switzerland
| | - Beat Aeschlimann
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich 8093, Switzerland
| | - Emmanuel Frossard
- Institute of Agricultural Sciences, ETH Zurich, Eschikon 33, Lindau CH-8315, Switzerland
| | - Detlef Günther
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich 8093, Switzerland
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2
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de Wild T, Wurm J, Becker P, Günther D, Nauser T, Schmidt TJ, Gubler L, Nemeth T. A Nature-Inspired Antioxidant Strategy based on Porphyrin for Aromatic Hydrocarbon Containing Fuel Cell Membranes. ChemSusChem 2023; 16:e202300775. [PMID: 37551734 DOI: 10.1002/cssc.202300775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 08/08/2023] [Accepted: 08/08/2023] [Indexed: 08/09/2023]
Abstract
The use of hydrocarbon-based proton conducting membranes in fuel cells is currently hampered by the insufficient durability of the material in the device. Membrane aging is triggered by the presence of reactive intermediates, such as HO⋅, which attack the polymer and eventually lead to chain breakdown and membrane failure. An adequate antioxidant strategy tailored towards hydrocarbon-based ionomers is therefore imperative to improve membrane lifetime. In this work, we perform studies on reaction kinetics using pulse radiolysis and γ-radiolysis as well as fuel cell experiments to demonstrate the feasibility of increasing the stability of hydrocarbon-based membranes against oxidative attack by implementing a Nature-inspired antioxidant strategy. We found that metalated-porphyrins are suitable for damage transfer and can be used in the fuel cell membrane to reduce membrane aging with a low impact on fuel cell performance.
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Affiliation(s)
- Tym de Wild
- Electrochemistry Laboratory, Paul Scherrer Institut, 5232, Villigen PSI, Switzerland
| | - Jan Wurm
- Electrochemistry Laboratory, Paul Scherrer Institut, 5232, Villigen PSI, Switzerland
| | - Pascal Becker
- Laboratory of Inorganic Chemistry, ETH Zurich, 8093, Zurich, Switzerland
| | - Detlef Günther
- Laboratory of Inorganic Chemistry, ETH Zurich, 8093, Zurich, Switzerland
| | - Thomas Nauser
- Laboratory of Inorganic Chemistry, ETH Zurich, 8093, Zurich, Switzerland
| | - Thomas J Schmidt
- Electrochemistry Laboratory, Paul Scherrer Institut, 5232, Villigen PSI, Switzerland
- Laboratory of Physical Chemistry, ETH Zurich, 8093, Zurich, Switzerland
| | - Lorenz Gubler
- Electrochemistry Laboratory, Paul Scherrer Institut, 5232, Villigen PSI, Switzerland
| | - Tamas Nemeth
- Electrochemistry Laboratory, Paul Scherrer Institut, 5232, Villigen PSI, Switzerland
- Laboratory of Inorganic Chemistry, ETH Zurich, 8093, Zurich, Switzerland
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3
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Patra S, Mosiagin I, Giri R, Nauser T, Katayev D. Electron-Driven Nitration of Unsaturated Hydrocarbons. Angew Chem Int Ed Engl 2023:e202300533. [PMID: 37097203 DOI: 10.1002/anie.202300533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Revised: 04/21/2023] [Accepted: 04/24/2023] [Indexed: 04/26/2023]
Abstract
Herein, we introduce an electrochemically assisted paradigm for the generation of nitryl radicals from ferric nitrate under mild reaction conditions using a simple setup with inexpensive graphite and stainless-steel electrodes. Mechanistic evidence of such a unique reaction mode was supported by detailed spectroscopic and experimental studies. Powered by electricity and driven by electrons, the synthetic diversity of this concept has been demonstrated through the development of highly efficient nitration protocols of various unsaturated hydrocarbons. In addition to a broad application area, these protocols are easy of scaling to decagrams, while exhibiting exceptional substrate generality and functional group compatibility.
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Affiliation(s)
- Subrata Patra
- University of Fribourg Faculty of Science: Universite de Fribourg Faculte de sciences et de medecine, Department of Chemistry, Chemin du Musée 9, 1700, Fribourg, SWITZERLAND
| | - Ivan Mosiagin
- University of Fribourg: Universite de Fribourg, Department of Chemistry, Chemin du Musée 9, 1700, Fribourg, SWITZERLAND
| | - Rahul Giri
- University of Fribourg: Universite de Fribourg, Department of Chemistry, Chemin du Musée 9, 1700, Fribourg, SWITZERLAND
| | - Thomas Nauser
- ETH Zurich: Eidgenossische Technische Hochschule Zurich, Inorganic Chemistry, Vladimir-Prelog-Weg 1-5/10, 8093, Zurich, SWITZERLAND
| | - Dmitry Katayev
- University of Fribourg: Universite de Fribourg, Department of Chemistry, Chemin du Musée 9, 1700, Fribourg, SWITZERLAND
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4
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Nemeth T, Nauser T, Gubler L. On the Radical-Induced Degradation of Quaternary Ammonium Cations for Anion-Exchange Membrane Fuel Cells and Electrolyzers. ChemSusChem 2022; 15:e202201571. [PMID: 36131629 PMCID: PMC9828592 DOI: 10.1002/cssc.202201571] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Revised: 09/15/2022] [Indexed: 06/15/2023]
Abstract
Four benzylic-type quaternary ammonium (QA) compounds with different electron density at the phenyl group were evaluated for their susceptibility against degradation by radicals. Time-resolved absorption spectroscopy indicated that radicals with oxidizing and reducing character were formed upon oxidation by HO⋅ and O⋅- (conjugate base of HO⋅). It was estimated that, dependent on the QA, 18-41 % of the formed radicals were oxidizing with standard electrode potentials (E0 ) above 0.276 V and 13-23 % exceeded 0.68 V, while 13-48 % were reducing with E0 <-0.448 V. The stability of these model compounds against oxidation and reductive dealkylation was evaluated at both neutral and strongly alkaline conditions, pH 14. Under both conditions, electron-donating groups promoted radical degradation, while electron-withdrawing ones increased stability. Therefore, durability against radical-induced degradation shows an opposite trend to alkaline stability and needs to be considered during the rational design of novel anion-exchange membranes for fuel cells and electrolyzers.
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Affiliation(s)
- Tamas Nemeth
- Electrochemistry LaboratoryPaul Scherrer Institut5232Villigen PSISwitzerland
- Laboratory of Inorganic ChemistryETH ZurichVladimir-Prelog-Weg 18093ZurichSwitzerland
| | - Thomas Nauser
- Laboratory of Inorganic ChemistryETH ZurichVladimir-Prelog-Weg 18093ZurichSwitzerland
| | - Lorenz Gubler
- Electrochemistry LaboratoryPaul Scherrer Institut5232Villigen PSISwitzerland
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5
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Nemeth T, Agrachev M, Jeschke G, Gubler L, Nauser T. EPR Study on the Oxidative Degradation of Phenyl Sulfonates, Constituents of Aromatic Hydrocarbon-Based Proton-Exchange Fuel Cell Membranes. J Phys Chem C Nanomater Interfaces 2022; 126:15606-15616. [PMID: 36176316 PMCID: PMC9512017 DOI: 10.1021/acs.jpcc.2c04566] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 08/11/2022] [Indexed: 06/15/2023]
Abstract
Sulfonated aromatic hydrocarbon-based ionomers are potential constituents of next-generation polymer electrolyte fuel cells (PEFCs). Widespread application is currently limited due to their susceptibility to radical-initiated oxidative degradation that, among other intermediates, involves the formation of highly reactive aromatic cation radicals. The intermediates undergo chain cleavage (dealkylation/dearylation) and the loss of protogenic sulfonate groups, all leading to performance loss and eventual membrane failure. Laser flash photolysis experiments indicated that cation radicals can also be formed via direct electron ejection. We aim to establish the major degradation pathway of proton-exchange membranes (PEMs). To this end, we irradiated aqueous solutions of phenyl sulfonate-type model compounds with a Xe arc lamp, thus generating radicals. The radicals were trapped by 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and the formed adducts were observed by electron paramagnetic resonance (EPR). The formed DMPO spin adducts were assigned and relative adduct concentrations were quantified by simulation of the experimental EPR spectra. Through the formation of the DMPO/•SO3 - adduct, we established that desulfonation dominates for monoaromatic phenyl sulfonates. We observed that diaryl ether sulfonates readily undergo homolytic C-O scission that produces DMPO/•aryl adducts. Our results support the notion that polyphenylene sulfonates are the most stable against oxidative attack and effectively transfer electrons from DMPO, forming DMPO/•OH. Our findings help to identify durable moieties that can be used as building blocks in the development of next-generation PEMs.
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Affiliation(s)
- Tamas Nemeth
- Electrochemistry
Laboratory, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
- Laboratory
of Inorganic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland
| | - Mikhail Agrachev
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland
| | - Gunnar Jeschke
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland
| | - Lorenz Gubler
- Electrochemistry
Laboratory, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - Thomas Nauser
- Laboratory
of Inorganic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland
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6
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Nemeth T, de Wild T, Gubler L, Nauser T. Impact of substitution on reactions and stability of one-electron oxidised phenyl sulfonates in aqueous solution. Phys Chem Chem Phys 2022; 24:895-901. [PMID: 34909811 PMCID: PMC8725611 DOI: 10.1039/d1cp04518k] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Highly reactive aromatic cation radicals have been invoked lately in synthetic routes and in the degradation pathways of hydrocarbon-based polymers. Changes in the electron density of aromatic compounds are expected to alter the reaction pathway following one electron oxidation through altering the pKa of the formed intermediate cation radical. Electron-donating groups increase its stability, however, little experimental data are known. While, in theory, the cation radical can be repaired by simple electron transfer, electron transfer to or from its deprotonated form, the hydroxycyclohexadienyl radical, will cause permanent modification or degradation. Time-resolved absorption spectroscopy indicates a pKa ≈ 2–3 for the 4-(tert-butyl)-2-methoxyphenylsulfonate (BMPS) radical cation, while its parent compound 4-(tert-butyl) phenylsulfonate (BPS) is much more acidic. The stability of both compounds towards oxidation by HO˙ was evaluated under air at pH 5 and pH 0. At pH 5, both BMPS and BPS are unstable, and superstoichiometric degradation was observed. Degradation was slightly reduced for BPS at pH 0. In contrast, the more electron rich BMPS showed 80% lower degradation. We unambigously showed that in the presence of Ce(iii) and H2O2 at pH 0 both BMPS and BPS could be catalytically repaired via one electron reduction, resulting in further damage moderation. Functional groups can be used to modify the equilibrium position and tune the reactivity of one electron oxidised aromatic compounds.![]()
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Affiliation(s)
- Tamas Nemeth
- Electrochemistry Laboratory, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.,Laboratory of Inorganic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland.
| | - Tym de Wild
- Electrochemistry Laboratory, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - Lorenz Gubler
- Electrochemistry Laboratory, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - Thomas Nauser
- Laboratory of Inorganic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland.
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7
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Gebicki JM, Nauser T. Initiation and Prevention of Biological Damage by Radiation-Generated Protein Radicals. Int J Mol Sci 2021; 23:ijms23010396. [PMID: 35008823 PMCID: PMC8745036 DOI: 10.3390/ijms23010396] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2021] [Revised: 12/27/2021] [Accepted: 12/27/2021] [Indexed: 12/23/2022] Open
Abstract
Ionizing radiations cause chemical damage to proteins. In aerobic aqueous solutions, the damage is commonly mediated by the hydroxyl free radicals generated from water, resulting in formation of protein radicals. Protein damage is especially significant in biological systems, because proteins are the most abundant targets of the radiation-generated radicals, the hydroxyl radical-protein reaction is fast, and the damage usually results in loss of their biological function. Under physiological conditions, proteins are initially oxidized to carbon-centered radicals, which can propagate the damage to other molecules. The most effective endogenous antioxidants, ascorbate, GSH, and urate, are unable to prevent all of the damage under the common condition of oxidative stress. In a promising development, recent work demonstrates the potential of polyphenols, their metabolites, and other aromatic compounds to repair protein radicals by the fast formation of less damaging radical adducts, thus potentially preventing the formation of a cascade of new reactive species.
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Affiliation(s)
- Janusz M. Gebicki
- Department of Biological Sciences, Macquarie University, Sydney 2109, Australia
- Correspondence:
| | - Thomas Nauser
- Departement für Chemie und Angewandte Biowissenschaften, Eidgenössische Technische Hochschule, 8093 Zurich, Switzerland;
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8
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Liosi K, Stasyuk AJ, Masero F, Voityuk AA, Nauser T, Mougel V, Solà M, Yamakoshi Y. Unexpected Disparity in Photoinduced Reactions of C 60 and C 70 in Water with the Generation of O 2 •- or 1O 2. JACS Au 2021; 1:1601-1611. [PMID: 34723263 PMCID: PMC8549049 DOI: 10.1021/jacsau.1c00239] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Indexed: 06/01/2023]
Abstract
Well-defined fullerene-PEG conjugates, C60-PEG (1) and two C70-PEG (2 and 3 with the addition sites on ab-[6,6] and cc-[6,6]-junctions), were prepared from their corresponding Prato monoadduct precursors. The resulting highly water-soluble fullerene-PEG conjugates 1-3 were evaluated for their DNA-cleaving activities and reactive oxygen species (ROS) generation under visible light irradiation. Unexpectedly, photoinduced cleavage of DNA by C60-PEG 1 was much higher than that by C70-PEG 2 and 3 with higher absorption intensity, especially in the presence of an electron donor (NADH). The preference of photoinduced ROS generation from fullerene-PEG conjugates 1-3 via the type II (energy transfer) or the type I (electron transfer) photoreaction was found to be dependent on the fullerene core (between C60 and C70) and functionalization pattern of C70 (between 2 and 3). This was clearly supported by the electron transfer rate obtained from cyclic voltammetry data and computationally estimated relative rate of each step of the type II and the type I reactions, with the finding that type II energy transfer reactions occurred in the inverted Marcus regime while type I electron transfer reactions proceeded in the normal Marcus regime. This finding on the disparity in the pathways of photoinduced reactions (type I versus type II) provides insights into the behavior of photosensitizers in water and the design of photodynamic therapy drugs.
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Affiliation(s)
- Korinne Liosi
- Laboratorium
für Organische Chemie, ETH Zürich, Vladimir-Prelog-Weg 3, CH-8093 Zürich, Switzerland
| | - Anton J. Stasyuk
- Institut
de Química Computacional i Catàlisi (IQCC) and Departament
de Química, Universitat de Girona, M. Aurèlia Capmany, 69, 17003 Girona, Catalonia, Spain
| | - Fabio Masero
- Laboratorium
für Anorganische Chemie, ETH Zürich, Vladimir-Prelog-Weg 1, CH-8093 Zürich, Switzerland
| | - Alexander A. Voityuk
- Institut
de Química Computacional i Catàlisi (IQCC) and Departament
de Química, Universitat de Girona, M. Aurèlia Capmany, 69, 17003 Girona, Catalonia, Spain
- Institució
Catalana de Recerca i Estudis Avancats (ICREA), 08010 Barcelona, Catalonia, Spain
| | - Thomas Nauser
- Laboratorium
für Anorganische Chemie, ETH Zürich, Vladimir-Prelog-Weg 1, CH-8093 Zürich, Switzerland
| | - Victor Mougel
- Laboratorium
für Anorganische Chemie, ETH Zürich, Vladimir-Prelog-Weg 1, CH-8093 Zürich, Switzerland
| | - Miquel Solà
- Institut
de Química Computacional i Catàlisi (IQCC) and Departament
de Química, Universitat de Girona, M. Aurèlia Capmany, 69, 17003 Girona, Catalonia, Spain
| | - Yoko Yamakoshi
- Laboratorium
für Organische Chemie, ETH Zürich, Vladimir-Prelog-Weg 3, CH-8093 Zürich, Switzerland
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9
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Abstract
Several recent studies have shown that the rates of formation of adduct radicals between carbon-centred radicals and aromatic molecules are virtually diffusion-controlled and reversible. This contrasts with "radical addition", the well-known multistep reaction in preparative organic chemistry where the rate-determining initial formation of radical adducts is perceived to be several orders of magnitude slower and virtually irreversible. Using pulse radiolysis and spectroscopic analysis, we have now re-examined parts of this complex mechanism. The results have significant implications for biological systems: electron-rich, aromatic structures may act like buffers for radicals, moderating their reactivity resulting in a much slower reaction determining the overall rate of oxidation. In vivo, an organism would gain time for an appropriate antioxidant reaction.
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Affiliation(s)
- Thomas Nauser
- Departement für Chemie und Angewandte Biowissenschaften, ETH Zürich, 8093 Zürich, Switzerland.
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10
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Nolte TM, Nauser T, Gubler L, Hendriks AJ, Peijnenburg WJGM. Thermochemical unification of molecular descriptors to predict radical hydrogen abstraction with low computational cost. Phys Chem Chem Phys 2020; 22:23215-23225. [PMID: 33029596 DOI: 10.1039/d0cp03750h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Chemistry describes transformation of matter with reaction equations and corresponding rate constants. However, accurate rate constants are not always easy to get. Here we focus on radical oxidation reactions. Analysis of over 500 published rate constants of hydroxyl radicals led us to hypothesize that a modified linear free-energy relationship (LFER) could be used to predict rate constants speedily, reliably and accurately. LFERs correlate the Gibbs activation-energy with the Gibbs energy of reaction. We calculated the latter as the sum of one-electron transfer and, if appropriate, proton transfer. We parametrized specific transition state effects to orbital delocalizability and the polarity of the reactant. The calculation time for 500 reactions is less than 8 hours on a standard desktop-PC. Rate constants were also calculated for hydrogen and methyl radicals; these controls show that the predictions are applicable to a broader set of oxidizing radicals. An accuracy of 30-40% (standard deviation) with reference to reported experimental values was found suitable for the screening of complex chemical systems for possibly relevant reactions. In particular, potentially relevant reactions can be singled out and scrutinized in detail when prioritizing chemicals for environmental risk assessment.
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Affiliation(s)
- Tom M Nolte
- Eidgenössische Technische Hochschule (ETH) Zurich, Laboratory of Inorganic Chemistry, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland.
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11
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Calvo R, Le Tellier A, Nauser T, Rombach D, Nater D, Katayev D. Synthesis, Characterization, and Reactivity of a Hypervalent-Iodine-Based Nitrooxylating Reagent. Angew Chem Int Ed Engl 2020; 59:17162-17168. [PMID: 32530081 DOI: 10.1002/anie.202005720] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Indexed: 11/11/2022]
Abstract
Herein, the synthesis and characterization of a hypervalent-iodine-based reagent that enables a direct and selective nitrooxylation of enolizable C-H bonds to access a broad array of organic nitrate esters is reported. This compound is bench stable, easy-to-handle, and delivers the nitrooxy (-ONO2 ) group under mild reaction conditions. Activation of the reagent by Brønsted and Lewis acids was demonstrated in the synthesis of nitrooxylated β-keto esters, 1,3-diketones, and malonates, while its activity under photoredox catalysis was shown in the synthesis of nitrooxylated oxindoles. Detailed mechanistic studies including pulse radiolysis, Stern-Volmer quenching studies, and UV/Vis spectroelectrochemistry reveal a unique single-electron-transfer (SET)-induced concerted mechanistic pathway not reliant upon generation of the nitrate radical.
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Affiliation(s)
- Roxan Calvo
- Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland
| | - Antoine Le Tellier
- Department of Organic Chemistry, University of Geneva, Quai Ernest Ansermet 30, 1211, Geneva 4, Switzerland
| | - Thomas Nauser
- Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland
| | - David Rombach
- Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland
| | - Darryl Nater
- Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland
| | - Dmitry Katayev
- Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland
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12
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Calvo R, Le Tellier A, Nauser T, Rombach D, Nater D, Katayev D. Synthese, Charakterisierung und Reaktivität eines Nitrooxylierungsreagenzes basierend auf einer hypervalenten Iodverbindung. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202005720] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Roxan Calvo
- Department of Chemistry and Applied Biosciences Swiss Federal Institute of Technology ETH Zürich Vladimir-Prelog-Weg 2 8093 Zürich Schweiz
| | - Antoine Le Tellier
- Department of Organic Chemistry University of Geneva Quai Ernest Ansermet 30 1211 Geneva 4 Schweiz
| | - Thomas Nauser
- Department of Chemistry and Applied Biosciences Swiss Federal Institute of Technology ETH Zürich Vladimir-Prelog-Weg 2 8093 Zürich Schweiz
| | - David Rombach
- Department of Chemistry and Applied Biosciences Swiss Federal Institute of Technology ETH Zürich Vladimir-Prelog-Weg 2 8093 Zürich Schweiz
| | - Darryl Nater
- Department of Chemistry and Applied Biosciences Swiss Federal Institute of Technology ETH Zürich Vladimir-Prelog-Weg 2 8093 Zürich Schweiz
| | - Dmitry Katayev
- Department of Chemistry and Applied Biosciences Swiss Federal Institute of Technology ETH Zürich Vladimir-Prelog-Weg 2 8093 Zürich Schweiz
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13
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Koppenol WH, Serrano-Luginbuehl S, Nauser T, Kissner R. Thinking Outside the Cage: A New Hypothesis That Accounts for Variable Yields of Radicals from the Reaction of CO2 with ONOO–. Chem Res Toxicol 2020; 33:1516-1527. [DOI: 10.1021/acs.chemrestox.9b00309] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Willem H. Koppenol
- Emeritus (Swiss Federal Institute of Technology), Schwändibergstrasse 25, CH-8784 Braunwald, Switzerland
| | | | - Thomas Nauser
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, CH-8093 Zürich, Switzerland
| | - Reinhard Kissner
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, CH-8093 Zürich, Switzerland
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14
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Nolte TM, Nauser T, Gubler L. Attack of hydroxyl radicals to α-methyl-styrene sulfonate polymers and cerium-mediated repair via radical cations. Phys Chem Chem Phys 2020; 22:4516-4525. [PMID: 32048646 DOI: 10.1039/c9cp05454e] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Both synthetic polymers (membranes, coatings, packaging) and natural polymers (DNA, proteins) are subject to radical-initiated degradation. In order to mitigate the deterioration of the polymer properties, antioxidant strategies need to be devised. We studied the reactions of poly(α-methylstyrene sulfonate), a model compound for fuel cell membrane materials, with different degrees of polymerization with OH˙ radicals as well as subsequent reactions. We observed the resulting OH˙-adducts to react with oxygen and eliminate H2O, the relative likelihood of which is determined by pH and molecular weight. The resulting radical cations can be reduced back to the parent molecule by cerium(iii). This 'repair' reaction is also dependent on molecular weight likely because of intramolecular stabilization. The results from this study provide a starting point for the development of new hydrocarbon-based ionomer materials for fuel cells that are more resistant to radical induced degradation through the detoxification of intermediates via damage transfer and repair pathways. Furthermore, a more fundamental understanding of the mechanisms behind conventional antioxidants in medicine, such as ceria nanoparticles, is achieved.
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Affiliation(s)
- Tom M Nolte
- Electrochemistry Laboratory, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
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Santschi N, Jelier BJ, Stähelin S, Nauser T. Profiling the oxidative activation of DMSO-F 6 by pulse radiolysis and translational potential for radical C-H trifluoromethylation. Org Biomol Chem 2019; 17:9734-9742. [PMID: 31710060 DOI: 10.1039/c9ob02119a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The oxidative activation of the perfluorinated analogue of dimethyl sulfoxide, DMSO-F6, by hydroxyl radicals efficiently produces trifluoromethyl radicals based on pulse radiolysis, laboratory scale experiments, and comparison of rates of reaction for analogous radical systems. In comparison to commercially available precursors, DMSO-F6 proved to be more stable, easier to handle and overall more convenient than leading F3C-reagents and may therefore be an ideal surrogate to study F3C radicals for time-resolved kinetics studies. In addition, we present an improved protocol for the preparation of this largely unexplored reagent.
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Affiliation(s)
- Nico Santschi
- Eidgenössische Technische Hochschule (ETH) Zürich, Department of Chemistry and Applied Biosciences, Vladimir-Prelog-Weg 1/2, 8093 Zürich, Switzerland.
| | - Benson J Jelier
- Eidgenössische Technische Hochschule (ETH) Zürich, Department of Chemistry and Applied Biosciences, Vladimir-Prelog-Weg 1/2, 8093 Zürich, Switzerland.
| | - Samuel Stähelin
- Eidgenössische Technische Hochschule (ETH) Zürich, Department of Chemistry and Applied Biosciences, Vladimir-Prelog-Weg 1/2, 8093 Zürich, Switzerland.
| | - Thomas Nauser
- Eidgenössische Technische Hochschule (ETH) Zürich, Department of Chemistry and Applied Biosciences, Vladimir-Prelog-Weg 1/2, 8093 Zürich, Switzerland.
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Nauser T, Gebicki JM. Fast reaction of carbon free radicals with flavonoids and other aromatic compounds. Arch Biochem Biophys 2019; 674:108107. [DOI: 10.1016/j.abb.2019.108107] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2019] [Revised: 08/27/2019] [Accepted: 09/13/2019] [Indexed: 12/26/2022]
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Erdogan H, Vandemeulebroucke A, Nauser T, Bounds PL, Koppenol WH. Jumpstarting the cytochrome P450 catalytic cycle with a hydrated electron. J Biol Chem 2017; 292:21481-21489. [PMID: 29109145 DOI: 10.1074/jbc.m117.813683] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Revised: 10/25/2017] [Indexed: 01/08/2023] Open
Abstract
Cytochrome P450cam (CYP101Fe3+) regioselectively hydroxylates camphor. Possible hydroxylating intermediates in the catalytic cycle of this well-characterized enzyme have been proposed on the basis of experiments carried out at very low temperatures and shunt reactions, but their presence has not yet been validated at temperatures above 0 °C during a normal catalytic cycle. Here, we demonstrate that it is possible to mimic the natural catalytic cycle of CYP101Fe3+ by using pulse radiolysis to rapidly supply the second electron of the catalytic cycle to camphor-bound CYP101[FeO2]2+ Judging by the appearance of an absorbance maximum at 440 nm, we conclude that CYP101[FeOOH]2+ (compound 0) accumulates within 5 μs and decays rapidly to CYP101Fe3+, with a k440 nm of 9.6 × 104 s-1 All processes are complete within 40 μs at 4 °C. Importantly, no transient absorbance bands could be assigned to CYP101[FeO2+por•+] (compound 1) or CYP101[FeO2+] (compound 2). However, indirect evidence for the involvement of compound 1 was obtained from the kinetics of formation and decay of a tyrosyl radical. 5-Hydroxycamphor was formed quantitatively, and the catalytic activity of the enzyme was not impaired by exposure to radiation during the pulse radiolysis experiment. The rapid decay of compound 0 enabled calculation of the limits for the Gibbs activation energies for the conversions of compound 0 → compound 1 → compound 2 → CYP101Fe3+, yielding a ΔG‡ of 45, 39, and 39 kJ/mol, respectively. At 37 °C, the steps from compound 0 to the iron(III) state would take only 4 μs. Our kinetics studies at 4 °C complement the canonical mechanism by adding the dimension of time.
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Affiliation(s)
| | - An Vandemeulebroucke
- Organic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, CH-8093 Zurich, Switzerland
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Nauser T, Gebicki JM. Reaction rates of glutathione and ascorbate with alkyl radicals are too slow for protection against protein peroxidation in vivo. Arch Biochem Biophys 2017; 633:118-123. [PMID: 28939102 DOI: 10.1016/j.abb.2017.09.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Revised: 09/15/2017] [Accepted: 09/18/2017] [Indexed: 11/19/2022]
Abstract
Reaction kinetics of amino acid and peptide alkyl radicals with GSH and ascorbate, the two most abundant endogenous antioxidants, were investigated by pulse radiolysis. Rate constants in the order of 106 M-1s-1 were found. Alkyl radicals react at almost diffusion controlled rates and irreversibly with oxygen to form peroxyl radicals, and competition with this reaction is the benchmark for efficient repair in vivo. We consider repair of protein radicals and assume comparable rate constants for the reactions of GSH/ascorbate with peptide alkyl radicals and with alkyl radicals on a protein surface. Given physiological concentrations of oxygen, GSH and ascorbate, protein peroxyl radicals will always be a major product of protein alkyl radicals in vivo. Therefore, if they are formed by oxidative stress, protein alkyl radicals are a probable cause for biological damage.
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Affiliation(s)
- Thomas Nauser
- Laboratorium für Anorganische Chemie, Departement für Chemie und Angewandte Biowissenschaften, Eidgenössische Technische Hochschule (ETH) Zürich, CH - 8093 Zürich, Switzerland.
| | - Janusz M Gebicki
- Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia
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Affiliation(s)
- Nico Santschi
- Eidgenössische Technische Hochschule (ETH) Zürich; Laboratory of Inorganic Chemistry; Vladimir-Prelog-Weg 1 8093 Zürich Switzerland
| | - Thomas Nauser
- Eidgenössische Technische Hochschule (ETH) Zürich; Laboratory of Inorganic Chemistry; Vladimir-Prelog-Weg 1 8093 Zürich Switzerland
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Nauser T, Gebicki JM. Physiological Concentrations of Ascorbate Cannot Prevent the Potentially Damaging Reactions of Protein Radicals in Humans. Chem Res Toxicol 2017; 30:1702-1710. [PMID: 28745873 DOI: 10.1021/acs.chemrestox.7b00160] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The principal initial biological targets of free radicals formed under conditions of oxidative stress are the proteins. The most common products of the interaction are carbon-centered alkyl radicals which react rapidly with oxygen to form peroxyl radicals and hydroperoxides. All these species are reactive, capable of propagating the free radical damage to enzymes, nucleic acids, lipids, and endogenous antioxidants, leading finally to the pathologies associated with oxidative stress. The best chance of preventing this chain of damage is in early repair of the protein radicals by antioxidants. Estimate of the effectiveness of the physiologically significant antioxidants requires knowledge of the antioxidant tissue concentrations and rate constants of their reaction with protein radicals. Previous studies by pulse radiolysis have shown that only ascorbate can repair the Trp and Tyr protein radicals before they form peroxyl radicals under physiological concentrations of oxygen. We have now extended this work to other protein C-centered radicals generated by hydroxyl radicals because these and many other free radicals formed under oxidative stress can produce secondary radicals on virtually any amino acid residue. Pulse radiolysis identified two classes of rate constants for reactions of protein radicals with ascorbate, a faster one in the range (9-60) × 107 M-1 s-1 and a slow one with a range of (0.5-2) × 107 M-1 s-1. These results show that ascorbate can prevent further reactions of protein radicals only in the few human tissues where its concentration exceeds about 2.5 mM.
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Affiliation(s)
- Thomas Nauser
- Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology , Zurich CH8093, Switzerland
| | - Janusz M Gebicki
- Department of Biological Sciences, Macquarie University , Sydney, New South Wales 2109, Australia
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Santschi N, Jelier BJ, Nauser T. Mechanistic insight into the thermal activation of Togni's trifluoromethylation reagents. Phys Chem Chem Phys 2017; 19:18172-18177. [DOI: 10.1039/c7cp01396e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The thermal activation of Togni's reagent was studied by GC-MS and shown to generate CF3 and, concomitantly, alkyl radicals.
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Affiliation(s)
- Nico Santschi
- Department of Chemistry and Applied Biosciences
- Swiss Federal Institute of Technology (ETH) – Zürich
- CH-8093 Zürich
- Switzerland
| | - Benson J. Jelier
- Department of Chemistry and Applied Biosciences
- Swiss Federal Institute of Technology (ETH) – Zürich
- CH-8093 Zürich
- Switzerland
| | - Thomas Nauser
- Department of Chemistry and Applied Biosciences
- Swiss Federal Institute of Technology (ETH) – Zürich
- CH-8093 Zürich
- Switzerland
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Mahmoudi L, Kissner R, Nauser T, Koppenol WH. Electrode Potentials of l-Tryptophan, l-Tyrosine, 3-Nitro-l-tyrosine, 2,3-Difluoro-l-tyrosine, and 2,3,5-Trifluoro-l-tyrosine. Biochemistry 2016; 55:2849-56. [DOI: 10.1021/acs.biochem.6b00019] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Leila Mahmoudi
- Institute of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland
| | - Reinhard Kissner
- Institute of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland
| | - Thomas Nauser
- Institute of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland
| | - Willem H. Koppenol
- Institute of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland
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Gstrein C, Walde P, Schlüter AD, Nauser T. Shielding effects in spacious macromolecules: a case study with dendronized polymers. Photochem Photobiol Sci 2016; 15:964-8. [DOI: 10.1039/c6pp00191b] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The first experimental evidence is shown for the obvious suggestion that diffusion into the backbone of a dendronized polymer is increasingly hindered with increasing dendron generation, i.e. size.
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Affiliation(s)
- Chiara Gstrein
- Laboratory of Polymer Chemistry
- Department of Materials
- ETH Zürich
- CH-8093 Zürich
- Switzerland
| | - Peter Walde
- Laboratory of Polymer Chemistry
- Department of Materials
- ETH Zürich
- CH-8093 Zürich
- Switzerland
| | - A. Dieter Schlüter
- Laboratory of Polymer Chemistry
- Department of Materials
- ETH Zürich
- CH-8093 Zürich
- Switzerland
| | - Thomas Nauser
- Laboratory of Inorganic Chemistry
- Department of Chemistry and Applied Biosciences
- ETH Zürich
- CH-8093 Zürich
- Switzerland
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Abstract
Carbon-centered radicals of alcohols commonly used as hydroxyl radical scavengers (MeOH, EtOH, i-PrOH and t-BuOH) add reversibly to histidine with equilibrium constants up to 3 × 10(3) M(-1) and rate constants on the order of 10(9) M(-1) s(-1). Similar equilibria may compromise determinations of one-electron (radical) electrode potentials.
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Affiliation(s)
- Thomas Nauser
- Laboratorium für Anorganische Chemie, Departement für Chemie und Angewandte Biowissenschaften, ETH Zürich, Vladimir-Prelog Weg 2, CH-8093 Zürich, Switzerland.
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Linscheid C, Heitmann E, Singh P, Wickstrom E, Qiu L, Hodes H, Nauser T, Petroff MG. Trophoblast expression of the minor histocompatibility antigen HA-1 is regulated by oxygen and is increased in placentas from preeclamptic women. Placenta 2015; 36:832-8. [PMID: 26095815 DOI: 10.1016/j.placenta.2015.05.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 05/25/2015] [Accepted: 05/28/2015] [Indexed: 01/27/2023]
Abstract
INTRODUCTION Maternal T-cells reactive towards paternally inherited fetal minor histocompatibility antigens are expanded during pregnancy. Placental trophoblast cells express at least four fetal antigens, including human minor histocompatibility antigen 1 (HA-1). We investigated oxygen as a potential regulator of HA-1 and whether HA-1 expression is altered in preeclamptic placentas. METHODS Expression and regulation of HA-1 mRNA and protein were examined by qRT-PCR and immunohistochemistry, using first, second, and third trimester placentas, first trimester placental explant cultures, and term purified cytotrophoblast cells. Low oxygen conditions were achieved by varying ambient oxygen, and were mimicked using cobalt chloride. HA-1 mRNA and protein expression levels were evaluated in preeclamptic and control placentas. RESULTS HA-1 protein expression was higher in the syncytiotrophoblast of first trimester as compared to second trimester and term placentas (P<0.01). HA-1 mRNA was increased in cobalt chloride-treated placental explants and purified cytotrophoblast cells (P = 0.04 and P<0.01, respectively) and in purified cytotrophoblast cells cultured under 2% as compared to 8% and 21% oxygen (P<0.01). HA-1 mRNA expression in preeclamptic vs. control placentas was increased 3.3-fold (P = 0.015). HA-1 protein expression was increased in syncytial nuclear aggregates and the syncytiotrophoblast of preeclamptic vs. control placentas (P = 0.02 and 0.03, respectively). DISCUSSION Placental HA-1 expression is regulated by oxygen and is increased in the syncytial nuclear aggregates and syncytiotrophoblast of preeclamptic as compared to control placentas. Increased HA-1 expression, combined with increased preeclamptic syncytiotrophoblast deportation, provides a novel potential mechanism for exposure of the maternal immune system to increased fetal antigenic load during preeclampsia.
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Affiliation(s)
- C Linscheid
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS, USA
| | - E Heitmann
- Saint Luke's Health System, Department of Maternal and Fetal Medicine, Kansas City, MO, USA
| | - P Singh
- Saint Luke's Health System, Department of Maternal and Fetal Medicine, Kansas City, MO, USA
| | - E Wickstrom
- Saint Luke's Health System, Department of Maternal and Fetal Medicine, Kansas City, MO, USA
| | - L Qiu
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS, USA
| | - H Hodes
- The Center for Women's Health, Overland Park, KS, USA
| | - T Nauser
- The Center for Women's Health, Overland Park, KS, USA
| | - M G Petroff
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS, USA
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Abstract
Protein thiyl radicals are important intermediates generated in redox processes of thiols and disulfides. Thiyl radicals efficiently react with glutathione and ascorbate, and the common notion is that these reactions serve to eliminate thiyl radicals before they can enter potentially hazardous processes. However, over the past years increasing evidence has been provided for rather efficient intramolecular hydrogen transfer processes of thiyl radicals in proteins and peptides. Based on rate constants published for these processes, we have performed kinetic simulations of protein thiyl radical reactivity. Our simulations suggest that protein thiyl radicals enter intramolecular hydrogen transfer reactions to a significant extent even under physiologic conditions, i.e., in the presence of 30 µM oxygen, 1 mM ascorbate, and 10 mM glutathione. At lower concentrations of ascorbate and glutathione, frequently observed when tissue is exposed to oxidative stress, the extent of irreversible protein thiyl radical-dependent protein modification increases.
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Affiliation(s)
- Thomas Nauser
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland.
| | - Willem H Koppenol
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland
| | - Christian Schöneich
- Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, KS 66047, USA.
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Nauser T, Steinmann D, Grassi G, Koppenol WH. Why Selenocysteine Replaces Cysteine in Thioredoxin Reductase: A Radical Hypothesis. Biochemistry 2014; 53:5017-22. [DOI: 10.1021/bi5003376] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Thomas Nauser
- Institute of Inorganic Chemistry and ‡Institute of Physical Chemistry,
Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg
2, CH-8093 Zürich, Switzerland
| | - Daniel Steinmann
- Institute of Inorganic Chemistry and ‡Institute of Physical Chemistry,
Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg
2, CH-8093 Zürich, Switzerland
| | - Guido Grassi
- Institute of Inorganic Chemistry and ‡Institute of Physical Chemistry,
Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg
2, CH-8093 Zürich, Switzerland
| | - Willem H. Koppenol
- Institute of Inorganic Chemistry and ‡Institute of Physical Chemistry,
Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg
2, CH-8093 Zürich, Switzerland
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Das AB, Nauser T, Koppenol WH, Kettle AJ, Winterbourn CC, Nagy P. Rapid reaction of superoxide with insulin-tyrosyl radicals to generate a hydroperoxide with subsequent glutathione addition. Free Radic Biol Med 2014; 70:86-95. [PMID: 24561577 DOI: 10.1016/j.freeradbiomed.2014.02.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Revised: 01/28/2014] [Accepted: 02/05/2014] [Indexed: 10/25/2022]
Abstract
Tyrosine (Tyr) residues are major sites of radical generation during protein oxidation. We used insulin as a model to study the kinetics, mechanisms, and products of the reactions of radiation-induced or enzyme-generated protein-tyrosyl radicals with superoxide to demonstrate the feasibility of these reactions under oxidative stress conditions. We found that insulin-tyrosyl radicals combined to form dimers, mostly via the tyrosine at position 14 on the α chain (Tyr14). However, in the presence of superoxide, dimerization was largely outcompeted by the reaction of superoxide with insulin-tyrosyl radicals. Using pulse radiolysis, we measured a second-order rate constant for the latter reaction of (6±1) × 10(8) M(-1) s(-1) at pH 7.3, representing the first measured rate constant for a protein-tyrosyl radical with superoxide. Mass-spectrometry-based product analyses revealed the addition of superoxide to the insulin-Tyr14 radical to form the hydroperoxide. Glutathione efficiently reduced the hydroperoxide to the corresponding monoxide and also subsequently underwent Michael addition to the monoxide to give a diglutathionylated protein adduct. Although much slower, conjugation of the backbone amide group can form a bicyclic Tyr-monoxide derivative, allowing the addition of only one glutathione molecule. These findings suggest that Tyr-hydroperoxides should readily form on proteins under oxidative stress conditions where protein radicals and superoxide are both generated and that these should form addition products with thiol compounds such as glutathione.
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Affiliation(s)
- Andrew B Das
- Centre for Free Radical Research, Department of Pathology, University of Otago Christchurch, Christchurch 8140, New Zealand
| | - Thomas Nauser
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8092 Zurich, Switzerland
| | - Willem H Koppenol
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8092 Zurich, Switzerland
| | - Anthony J Kettle
- Centre for Free Radical Research, Department of Pathology, University of Otago Christchurch, Christchurch 8140, New Zealand
| | - Christine C Winterbourn
- Centre for Free Radical Research, Department of Pathology, University of Otago Christchurch, Christchurch 8140, New Zealand
| | - Péter Nagy
- Centre for Free Radical Research, Department of Pathology, University of Otago Christchurch, Christchurch 8140, New Zealand.
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Grotzky A, Altamura E, Adamcik J, Carrara P, Stano P, Mavelli F, Nauser T, Mezzenga R, Schlüter AD, Walde P. Structure and enzymatic properties of molecular dendronized polymer-enzyme conjugates and their entrapment inside giant vesicles. Langmuir 2013; 29:10831-10840. [PMID: 23895383 DOI: 10.1021/la401867c] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Macromolecular hybrid structures were prepared in which two types of enzymes, horseradish peroxidase (HRP) and bovine erythrocytes Cu,Zn-superoxide dismutase (SOD), were linked to a fluorescently labeled, polycationic, dendronized polymer (denpol). Two homologous denpols of first and second generation were used and compared, and the activities of HRP and SOD of the conjugates were measured in aqueous solution separately and in combination. In the latter case the efficiency of the two enzymes in catalyzing a two-step cascade reaction was evaluated. Both enzymes in the two types of conjugates were highly active and comparable to free enzymes, although the efficiency of the enzymes bound to the second-generation denpol was significantly lower (up to a factor of 2) than the efficiency of HRP and SOD linked to the first-generation denpol. Both conjugates were analyzed by atomic force microscopy (AFM), confirming the expected increase in object size compared to free denpols and demonstrating the presence of enzyme molecules localized along the denpol chains. Finally, giant phospholipid vesicles with diameters of up to about 20 μm containing in their aqueous interior pool a first-generation denpol-HRP conjugate were prepared. The HRP of the entrapped conjugate was shown to remain active toward externally added, membrane-permeable substrates, an important prerequisite for the development of vesicular multienzyme reaction systems.
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Affiliation(s)
- Andrea Grotzky
- Laboratory of Polymer Chemistry, Department of Materials, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland
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Koppenol WH, Mahmoudi L, Kissner R, Nauser T. Electron transfer without metals. How amino acid radicals (mis)behave. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.999.5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | - Thomas Nauser
- Chemistry and Applied BiosciencesETHZürichSwitzerland
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Kshirsagar S, Alam S, Jasti S, Hodes H, Nauser T, Gilliam M, Billstrand C, Hunt J, Petroff M. Immunomodulatory molecules are released from the first trimester and term placenta via exosomes. Placenta 2012; 33:982-90. [PMID: 23107341 PMCID: PMC3534832 DOI: 10.1016/j.placenta.2012.10.005] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 09/04/2012] [Accepted: 10/08/2012] [Indexed: 12/22/2022]
Abstract
The semiallogenic fetus is tolerated by the maternal immune system through control of innate and adaptive immune responses. Trophoblast cells secrete nanometer scale membranous particles called exosomes, which have been implicated in modulation of the local and systemic maternal immune system. Here we investigate the possibility that exosomes secreted from the first trimester and term placenta carry HLA-G and B7 family immunomodulators. Confocal microscopy of placental sections revealed intracellular co-localization of B7-H1 with CD63, suggesting that B7-H1 associates with subcellular vesicles that give rise to exosomes. First trimester and term placental explants were then cultured for 24 h. B7H-1 (CD274), B7-H3 (CD276) and HLA-G5 were abundant in pelleted supernatants of these cultures that contained microparticles and exosomes; the latter, however, was observed only in first trimester pellets and was nearly undetectable in term explant-derived pellets. Further purification of exosomes by sucrose density fractionation confirmed the association of these proteins specifically with exosomes. Finally, culture of purified trophoblast cells in the presence or absence of EGF suggested that despite the absence of HLA-G5 association with term explant-derived exosomes, it is present in exosomes secreted from mononuclear cytotrophoblast cells. Further, differentiation of cytotrophoblast cells reduced the presence of HLA-G5 in secreted exosomes. Together, the results suggest that the immunomodulatory proteins HLA-G5, B7-H1 and B7-H3, are secreted from early and term placenta, and have important implications in the mechanisms by which trophoblast immunomodulators modify the maternal immunological environment.
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Affiliation(s)
- S.K. Kshirsagar
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA
| | - S.M. Alam
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA
| | - S. Jasti
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA
| | - H. Hodes
- The Center for Women’s Health, Overland Park, KS, USA
| | - T. Nauser
- The Center for Women’s Health, Overland Park, KS, USA
| | - M. Gilliam
- Department of Obstetrics and Gynecology, University of Chicago, Chicago, IL
| | - C. Billstrand
- Department of Human Genetics, University of Chicago, Chicago, IL
| | - J.S. Hunt
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA
| | - M.G. Petroff
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA
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35
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Filipovic MR, Miljkovic JL, Nauser T, Royzen M, Klos K, Shubina T, Koppenol WH, Lippard SJ, Ivanović-Burmazović I. Chemical characterization of the smallest S-nitrosothiol, HSNO; cellular cross-talk of H2S and S-nitrosothiols. J Am Chem Soc 2012; 134:12016-27. [PMID: 22741609 PMCID: PMC3408084 DOI: 10.1021/ja3009693] [Citation(s) in RCA: 266] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2012] [Indexed: 01/20/2023]
Abstract
Dihydrogen sulfide recently emerged as a biological signaling molecule with important physiological roles and significant pharmacological potential. Chemically plausible explanations for its mechanisms of action have remained elusive, however. Here, we report that H(2)S reacts with S-nitrosothiols to form thionitrous acid (HSNO), the smallest S-nitrosothiol. These results demonstrate that, at the cellular level, HSNO can be metabolized to afford NO(+), NO, and NO(-) species, all of which have distinct physiological consequences of their own. We further show that HSNO can freely diffuse through membranes, facilitating transnitrosation of proteins such as hemoglobin. The data presented in this study explain some of the physiological effects ascribed to H(2)S, but, more broadly, introduce a new signaling molecule, HSNO, and suggest that it may play a key role in cellular redox regulation.
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Affiliation(s)
- Milos R Filipovic
- Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, 91058 Erlangen, Germany.
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Affiliation(s)
- Dustin Hofstetter
- Department of Chemistry and Applied Biosciences, Institute
of Inorganic Chemistry, ETH Zurich, 8093
Zürich, Switzerland
| | - Basil Thalmann
- Department of Chemistry and Applied Biosciences, Institute
of Inorganic Chemistry, ETH Zurich, 8093
Zürich, Switzerland
| | - Thomas Nauser
- Department of Chemistry and Applied Biosciences, Institute
of Inorganic Chemistry, ETH Zurich, 8093
Zürich, Switzerland
| | - Willem H. Koppenol
- Department of Chemistry and Applied Biosciences, Institute
of Inorganic Chemistry, ETH Zurich, 8093
Zürich, Switzerland
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37
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Grotzky A, Nauser T, Erdogan H, Schlüter AD, Walde P. A Fluorescently Labeled Dendronized Polymer–Enzyme Conjugate Carrying Multiple Copies of Two Different Types of Active Enzymes. J Am Chem Soc 2012; 134:11392-5. [DOI: 10.1021/ja304837f] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Andrea Grotzky
- Laboratory
of Polymer Chemistry, Department of Materials and ‡Laboratory of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093
Zürich, Switzerland
| | - Thomas Nauser
- Laboratory
of Polymer Chemistry, Department of Materials and ‡Laboratory of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093
Zürich, Switzerland
| | - Huriye Erdogan
- Laboratory
of Polymer Chemistry, Department of Materials and ‡Laboratory of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093
Zürich, Switzerland
| | - A. Dieter Schlüter
- Laboratory
of Polymer Chemistry, Department of Materials and ‡Laboratory of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093
Zürich, Switzerland
| | - Peter Walde
- Laboratory
of Polymer Chemistry, Department of Materials and ‡Laboratory of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093
Zürich, Switzerland
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38
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Nauser T, Koppenol WH, Schöneich C. Reversible hydrogen transfer reactions in thiyl radicals from cysteine and related molecules: absolute kinetics and equilibrium constants determined by pulse radiolysis. J Phys Chem B 2012; 116:5329-41. [PMID: 22483034 PMCID: PMC3736814 DOI: 10.1021/jp210954v] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The mercapto group of cysteine (Cys) is a predominant target for oxidative modification, where one-electron oxidation leads to the formation of Cys thiyl radicals, CysS(•). These Cys thiyl radicals enter 1,2- and 1,3-hydrogen transfer reactions, for which rate constants are reported in this paper. The products of these 1,2- and 1,3-hydrogen transfer reactions are carbon-centered radicals at position C(3) (α-mercaptoalkyl radicals) and C(2) ((•)C(α) radicals) of Cys, respectively. Both processes can be monitored separately in Cys analogues such as cysteamine (CyaSH) and penicillamine (PenSH). At acidic pH, thiyl radicals from CyaSH permit only the 1,2-hydrogen transfer according to equilibrium 12, (+)H(3)NCH(2)CH(2)S(• )⇌ (+)H(3)NCH(2)(•)CH-SH, where rate constants for forward and reverse reaction are k(12) ≈ 10(5) s(-1) and k(-12) ≈ 1.5 × 10(5)s(-1), respectively. In contrast, only the 1,3-hydrogen transfer is possible for thiyl radicals from PenSH according to equilibrium 14, ((+)H(3)N/CO(2)H)C(α)-C(CH(3))(2)-S(•) ⇌ ((+)H(3)N/CO(2)H)(•)C(α)-C(CH(3))(2)-SH, where rate constants for the forward and the reverse reaction are k(14) = 8 × 10(4) s(-1) and k(-14) = 1.4 × 10(6) s(-1). The (•)C(α) radicals from PenSH and Cys have the additional opportunity for β-elimination of HS(•)/S(•-), which proceeds with k(39) ≈ (3 ± 1) × 10(4) s(-1) from (•)C(α) radicals from PenSH and k(-34) ≈ 5 × 10(3) s(-1) from (•)C(α) radicals from Cys. The rate constants quantified for the 1,2- and 1,3-hydrogen transfer reactions can be used as a basis to calculate similar processes for Cys thiyl radicals in proteins, where hydrogen transfer reactions, followed by the addition of oxygen, may lead to the irreversible modification of target proteins.
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Affiliation(s)
- Thomas Nauser
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland
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39
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Koppenol WH, Bounds PL, Nauser T, Kissner R, Rüegger H. Peroxynitrous acid: controversy and consensus surrounding an enigmatic oxidant. Dalton Trans 2012; 41:13779-87. [DOI: 10.1039/c2dt31526b] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Wnuk SF, Penjarla JAK, Dang T, Mebel AM, Nauser T, Schöneich C. Modeling of the ribonucleotide reductases substrate reaction. Hydrogen atom abstraction by a thiyl free radical and detection of the ribosyl-based carbon radical by pulse radiolysis. ACTA ACUST UNITED AC 2011. [DOI: 10.1135/cccc2011085] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The 1,4-anhydro-5-deoxy-6-thio-D-ribo-hexofuranitol (1) was prepared from 1,2-O-isopropylidene-α-D-glucose in 10 steps. In a key step treatment of the 1,2-O-isopropylidenehexofuranose derivative with BF3/Et3SiH effected deacetonization and reductive deoxygenation at carbon 1. Pulse radiolysis experiments with 6-thiohexofuranitol 1 and its disulfide derivative demonstrated formation of the ribosyl-based carbon-centered radical upon generation of 6-thiyl radical in basic medium. The proposed [1,5]-hydrogen shift abstraction with generation of the C3 radical mimics the initial substrate reaction of RNRs. The reversible H-atom transfer has been quantified and was correlated with the computed rate constants for the internal H atom abstraction from C1, C2, C3 and C4 by the thiyl radical. The energy barrier for the H3 and H4 abstractions were calculated to be most favorable with the corresponding barriers of 11.1 and 11.2 kcal/mol, respectively.
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Glass RS, Schöneich C, Wilson GS, Nauser T, Yamamoto T, Lorance E, Nichol GS, Ammam M. Neighboring pyrrolidine amide participation in thioether oxidation. Methionine as a "hopping" site. Org Lett 2011; 13:2837-9. [PMID: 21563771 DOI: 10.1021/ol200793z] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Methionine residues have been shown to function as efficient "hopping" sites in long-range electron transfer in model polyprolyl peptides. We suggest that a key to this ability of methionine is stabilization of the transient sulfur radical cation by neighboring proline amide participation. That is, in a model system a neighboring pyrrolidine amide lowers the oxidation potential of the thioether by over 0.5 V by formation of a two-center three-electron SO bond.
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Affiliation(s)
- Richard S Glass
- Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721, United States.
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Botti H, Möller MN, Steinmann D, Nauser T, Koppenol WH, Denicola A, Radi R. Distance-dependent diffusion-controlled reaction of •NO and O2•- at chemical equilibrium with ONOO-. J Phys Chem B 2010; 114:16584-93. [PMID: 21067212 DOI: 10.1021/jp105606b] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The fast reaction of (•)NO and O(2)(•-) to give ONOO(-) has been extensively studied at irreversible conditions, but the reasons for the wide variations in observed forward rate constants (3.8 ≤ k(f) ≤ 20 × 10(9) M(-1) s(-1)) remain unexplained. We characterized the diffusion-dependent aqueous (pH > 12) chemical equilibrium of the form (•)NO + O(2)(•-) = ONOO(-) with respect to its dependence on temperature, viscosity, and [ONOO(-)](eq) by determining [ONOO(-)](eq) and [(•)NO](eq). The equilibrium forward reaction rate constant (k(f)(eq)) has negative activation energy, in contrast to that found under irreversible conditions. In contradiction to the law of mass action, we demonstrate that the equilibrium constant depends on ONOO(-) concentration. Therefore, a wide range of k(f)(eq) values could be derived (7.5-21 × 10(9) M(-1) s(-1)). Of general interest, the variations in k(f) can thus be explained by its dependence on the distance between ONOO(-) particles (sites of generation of (•)NO and O(2)(•-)).
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Affiliation(s)
- Horacio Botti
- Unidad de Cristalografía de Proteínas, Instituto Pasteur de Montevideo, Montevideo, 11400, Uruguay.
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Abstract
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The reduction of oxidized glutathione GSSG by hydrated electrons and hydrogen atoms to form GSSG•− is quantitative. The radical anion dissociates into GS• and GS−, and the S-centered radical subsequently abstracts a hydrogen intramolecularly. We observe sequential development of UV absorbance signatures that indicate the formation of both α- and β-carbon-centered radicals. From experiments performed at pH 2 and pH 11.8, we determined forward and reverse rate constants for the overall equilibrium between sulfur-centered and carbon-centered radicals: kforward = 3·105 s−1, kreverse = 7·105 s−1, and K = 0.4. Furthermore, on the basis of the differences between the kinetics traces at 240 and 280 nm, we estimate that α- and β-carbon-centered radicals are formed at a surprising ratio of 1:3. The ratios found at pH 2 also apply to pH 7, with the conclusion that the equilibrium ratio of S-centered:β-centered:α-centered radicals is, very approximately, 8:3:1. The formation of carbon-centered radicals could lead to irreversible damage in proteins via the formation of carbon−carbon bonds or backbone fragmentation.
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Affiliation(s)
- Dustin Hofstetter
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zürich, Switzerland
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45
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Affiliation(s)
- Daniel Steinmann
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zürich, Switzerland
| | - Thomas Nauser
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zürich, Switzerland
| | - Willem H. Koppenol
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zürich, Switzerland
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46
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Nauser T, Steinmann D, Koppenol WH. Why do proteins use selenocysteine instead of cysteine? Amino Acids 2010; 42:39-44. [DOI: 10.1007/s00726-010-0602-7] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Accepted: 04/16/2010] [Indexed: 11/24/2022]
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47
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Piechowski MV, Nauser T, Hoignè J, Bühler RE. O−2 Decay Catalyzed by Cu2+ and Cu+ Ions in Aqueous Solutions: A Pulse Radiolysis Study for Atmospheric Chemistry. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/bbpc.19930970604] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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48
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Glass RS, Hug GL, Schöneich C, Wilson GS, Kuznetsova L, Lee TM, Ammam M, Lorance E, Nauser T, Nichol GS, Yamamoto T. Neighboring amide participation in thioether oxidation: relevance to biological oxidation. J Am Chem Soc 2009; 131:13791-805. [PMID: 19772365 DOI: 10.1021/ja904895u] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
To investigate neighboring amide participation in thioether oxidation, which may be relevant to brain oxidative stress accompanying beta-amyloid peptide aggregation, conformationally constrained methylthionorbornyl derivatives with amido moieties were synthesized and characterized, including an X-ray crystallographic study of one of them. Electrochemical oxidation of these compounds, studied by cyclic voltammetry, revealed that their oxidation peak potentials were less positive for those compounds in which neighboring group participation was geometrically possible. Pulse radiolysis studies provided evidence for bond formation between the amide moiety and sulfur on one-electron oxidation in cases where the moieties are juxtaposed. Furthermore, molecular constraints in spiro analogues revealed that S-O bonds are formed on one-electron oxidation. DFT calculations suggest that isomeric sigma*(SO) radicals are formed in these systems.
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Affiliation(s)
- Richard S Glass
- Department of Chemistry, The University of Arizona, Tucson, Arizona 85721, USA.
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49
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Abstract
We have identified two intermediates in the autoxidation of NO*: ONOO*, which was detected by EPR spectroscopy at 295 K and atmospheric pressure in the gas phase, and ONOONO, a red substance produced at 113 K in 2-methylbutane. The red compound is diamagnetic and absorbs maximally at 500 nm. The ONOONO intermediate is unstable above the melting point of 2-methylbutane and rapidly converts to O2NNO2. From the semiquantitative determination of mole fractions present in the gas phase by EPR spectroscopy, we estimated the rate constants for the steps that lead to ONOO* and ONOONO, from the known overall rate constant of the autoxidation reaction, by assuming that a quasi-stationary mechanism applies. The rate constant for the rate-determining formation of ONOO* is about 3.1 x 10(-18) cm3 molecule(-1) s(-1) (or 80 s(-1) in mole fractions), the dissociation rate constant of ONOO* is about 6.5 x 10(3) s(-1), and ONOONO is formed with a rate constant of k=7.7 x 10(-14) cm3 molecule(-1) s(-1) (1.9 x 10(6) s(-1) in mole fractions). From these constants, we estimate that the equilibrium constant for the formation of ONOO* from NO* and O2 (K(ONOO*)) is 4.8 x 10(-22) cm3 molecule(-1) (1.2 x 10(-2)), and, therefore, DeltaG=+11.0 kJ mol(-1). In water, the Gibbs energy change is close to zero. The presence of ONOO* at steady-state concentrations under dioxygen excess may be important not only for reactions in the atmosphere, but especially for reactions in aerosols and biological environments, because the rate constant for formation in solution is higher than that in the gas phase, and, therefore, the half-life of ONOO* is longer.
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Affiliation(s)
- Benedikt Galliker
- Department of Chemistry and Applied Biosciences, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland
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50
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Affiliation(s)
- Manuel Sturzbecher-Höhne
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
| | - Thomas Nauser
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
| | - Reinhard Kissner
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
| | - Willem H. Koppenol
- Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
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