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Chemosphere Aug 2020Degradation of benzenesulfonic acid (BSA), the simplest aromatic sulfonic acid with extreme industrial importantance, by sonochemically generated hydroxyl radical (OH)...
Degradation of benzenesulfonic acid (BSA), the simplest aromatic sulfonic acid with extreme industrial importantance, by sonochemically generated hydroxyl radical (OH) have been thoroughly investigated. A reasonable reduction (∼50%) in the total organic carbon (TOC) was achieved only after prolonged irradiation (∼275 min, 350 kHz) of ultrasound, although a short irradiation of less than an hour is enough to degrade significant amount of BSA. The degradation efficiency of ultrasound has been reduced in lower and extremely higher frequencies, and upon increasing the pH. An irregular, but continuous, release of sulfate ions was also observed. Further, the release of protons upon the oxidation of BSA consistently reduces the experimental pH to nearly 2. High resolution mass spectrometric (HRMS) analyses reveals the formation of a number of aromatic intermediates, including three mono (I) and two di (II) hydroxylated BSA derivatives as the key products in the initial stages of the reaction. Pulse radiolysis studies revealed the generation of hydroxycyclohexadienyl-type radicals, characterized by absorption bands at 320 nm (k = (7.16 ± 0.04) × 10 M s) and 380 nm, as the immediate intermediates of the reaction. The mechanism(s) leading to the degradation of BSA under sonolytic irradiation conditions along with the effect of various factors, such as the ultrasound frequency and reaction pH, have been explained in detail. The valuable mechanistic aspects obtained from our pulse radiolysis and HRMS studies are essential for the proper implementation of sonochemical techniques into real water purification process and, thus, receives extreme environmental relevance.
Topics: Benzenesulfonates; Hydroxyl Radical; Ions; Kinetics; Mass Spectrometry; Oxidation-Reduction; Sonication; Water; Water Pollutants, Chemical; Water Purification
PubMed: 32222516
DOI: 10.1016/j.chemosphere.2020.126485 -
International Journal of Molecular... Apr 2021Within the reactive oxygen species (ROS) generated by cellular metabolisms, hydroxyl radicals (HO) play an important role, being the most aggressive towards...
Within the reactive oxygen species (ROS) generated by cellular metabolisms, hydroxyl radicals (HO) play an important role, being the most aggressive towards biomolecules. The reactions of HO with methionine residues (Met) in peptides and proteins have been intensively studied, but some fundamental aspects remain unsolved. In the present study we examined the biomimetic model made of Ac-Met-OMe, as the simplest model peptide backbone, and of HO generated by ionizing radiation in aqueous solutions under anoxic conditions. We performed the identification and quantification of transient species by pulse radiolysis and of final products by LC-MS and high-resolution MS/MS after γ-radiolysis. By parallel photochemical experiments, using 3-carboxybenzophenone (CB) triplet with the model peptide, we compared the outcomes in terms of short-lived intermediates and stable product identification. The result is a detailed mechanistic scheme of Met oxidation by HO, and by CB triplets allowed for assigning transient species to the pathways of products formation.
Topics: Gamma Rays; Hydroxyl Radical; Methionine; Oxidation-Reduction; Peptides; Photolysis; Pulse Radiolysis
PubMed: 33946289
DOI: 10.3390/ijms22094773 -
International Journal of Molecular... Jul 2022The use of spectroscopic techniques has shown that human serum albumin (HSA) undergoes reversible self-aggregation through protein−protein interactions. It ensures the...
The use of spectroscopic techniques has shown that human serum albumin (HSA) undergoes reversible self-aggregation through protein−protein interactions. It ensures the subsequent overlapping of electron clouds along with the stiffening of the conformation of the interpenetrating network of amino acids of adjacent HSA molecules. The HSA oxidation process related to the transfer of one electron was investigated by pulse radiolysis and photochemical methods. It has been shown that the irradiation of HSA solutions under oxidative stress conditions results in the formation of stable protein aggregates. The HSA aggregates induced by ionizing radiation are characterized by specific fluorescence compared to the emission of non-irradiated solutions. We assume that HSA dimers are mainly responsible for the new emission. Dityrosine produced by the intermolecular recombination of protein tyrosine radicals as a result of radiolysis of an aqueous solution of the protein is the main cause of HSA aggregation by cross-linking. Analysis of the oxidation process of HSA confirmed that the reaction of mild oxidants (Br2•−, N3•, SO4•−) with albumin leads to the formation of covalent bonds between tyrosine residues. In the case of •OH radicals and partly, Cl2•−, species other than DT are formed. The light emission of this species is similar to the emission of self-associated HSA.
Topics: Fluorescent Dyes; Humans; Oxidation-Reduction; Radiation, Ionizing; Serum Albumin, Human; Tyrosine
PubMed: 35897662
DOI: 10.3390/ijms23158090 -
Antioxidants (Basel, Switzerland) Jun 2023The successive steps of the oxidation mechanism of crocin, a major compound of saffron, by the free OH radical are investigated by pulse radiolysis, steady-state (gamma)...
The successive steps of the oxidation mechanism of crocin, a major compound of saffron, by the free OH radical are investigated by pulse radiolysis, steady-state (gamma) radiolysis methods, and molecular simulations. The optical absorption properties of the transient species and their reaction rate constants are determined. The absorption spectrum of the oxidized radical of crocin resulting from the H-abstraction presents a maximum of 678 nm and a band of 441 nm, almost as intense as that of crocin. The spectrum of the covalent dimer of this radical contains an intense band at 441 nm and a weaker band at 330 nm. The final oxidized crocin, issued from radical disproportionation, absorbs weaker with a maximum of 330 nm. The molecular simulation results suggest that the OH radical is electrostatically attracted by the terminal sugar and is scavenged predominantly by the neighbor methyl site of the polyene chain as in a mechanism. Based on detailed experimental and theoretical investigations, the antioxidant properties of crocin are highlighted.
PubMed: 37371932
DOI: 10.3390/antiox12061202 -
Journal of Biochemistry Sep 2021Tardigrades, a phylum of meiofaunal organisms, exhibit extraordinary tolerance to various environmental conditions, including extreme temperatures (-273 to 151°C) and...
Tardigrades, a phylum of meiofaunal organisms, exhibit extraordinary tolerance to various environmental conditions, including extreme temperatures (-273 to 151°C) and exposure to ionizing radiation. Proteins from anhydrobiotic tardigrades with homology to known proteins from other organisms are new potential targets for structural genomics. Recently, we reported spectroscopic and structural characterization of a hexacoordinated haemoglobin (Kumaglobin [Kgb]) found in an anhydrobiotic tardigrade. In the absence of its exogenous ligand, Kgb displays hexacoordination with distal and proximal histidines. In this work, we analysed binding of the molecular oxygen ligand following reduction of haem in Kgb using a pulse radiolysis technique. Radiolytically generated hydrated electrons (eaq-) reduced the haem iron of Kgb within 20 µs. Subsequently, ferrous haem reacted with O2 to form a ferrous-dioxygen intermediate with a second-order rate constant of 3.0 × 106 M-1 s-1. The intermediate was rapidly (within 0.1 s) autooxidized to the ferric form. Redox potential measurements revealed an E'0 of -400 mV (vs. standard hydrogen electrode) in the ferric/ferrous couple. Our results suggest that Kgb may serve as a physiological generator of O2▪- via redox signalling and/or electron transfer.
Topics: Animals; Electron Transport; Globins; Histidine; Ligands; Oxidation-Reduction; Oxygen; Pulse Radiolysis; Tardigrada; Water
PubMed: 33479760
DOI: 10.1093/jb/mvab003 -
Physical Chemistry Chemical Physics :... Mar 2020Concentrated nitric acid solutions subjected to radiation produce radicals of extreme importance in the reprocessing of spent nuclear fuel. Knowledge of the different...
Concentrated nitric acid solutions subjected to radiation produce radicals of extreme importance in the reprocessing of spent nuclear fuel. Knowledge of the different rate constants of the reactions involved in this chemistry is needed to improve the efficiency of the process and to define safe operating practices. Pulse radiolysis measurements are performed to find the rate constant of the reaction between NO3˙ radicals and U(iv) in highly concentrated nitrate solution. The optimal stabilization conditions toward thermal oxidation are defined for the considered solutions at room temperature and at 45 °C by adding anti-nitrous agents such as hydrazinium nitrate (HN) and hydroxyl ammonium nitrate (HAN). The decay of the NO3˙ radical is monitored and its reaction rates with HN, HAN and U(iv) are found to be 1.3 × 105, 1.5 × 107 and 1.6 × 106 M-1 s-1 at room temperature. The latter value is more than 10 times lower than the one currently used in numerical codes for simulation of the long-term radiolytic degradation associated with the reprocessing and storage of spent nuclear waste. At 45 °C, conditions similar to the reprocessing of spent fuel, the values of the rate constants of NO3˙ radical toward HN, HAN and U(iv) increase and are found to be 2.6 × 105, 2.9 × 107 and 9.3 × 106 M-1 s-1.
PubMed: 32090224
DOI: 10.1039/c9cp07034f -
Physical Chemistry Chemical Physics :... Feb 2021Tetrazolium salts (TZs) are pervasively utilized as precursors in the dye industry, colorimetric probes in enzyme assays and for exploring nanomaterial toxicity, but its...
Tetrazolium salts (TZs) are pervasively utilized as precursors in the dye industry, colorimetric probes in enzyme assays and for exploring nanomaterial toxicity, but its own toxicity is not investigated enough so far. Using femtosecond transient absorption spectroscopy, nanosecond pulse radiolysis (ns-PRL), western blotting and UV-vis absorption spectroscopy, here we characterized a neutral tetrazolinyl radical (with the same maximum absorption at 420 nm and different lifetimes of 5.0 and 9.0 μs for two selected TZs), the key intermediate of TZs reduction, and noticed TZs-formazan production under UV light irradiation accompanied by 41% increase in the cross-linking of lysozyme (Lyso, model protein) compared to TZs-free sample, which uncovered the photoenhanced oxidation of TZs towards Lyso. The ns-PRL in a reductive atmosphere simulated the electron/proton donors of amino acid residues in Lyso upon photoexcitation and revealed the reduction mechanism of TZs, as that first followed one-electron-transfer and then probably proton-coupled electron transfer. This is the first time to report on the photoenhanced oxidation mechanism of TZs, which would provide new insights into the applications of TZs in cell biology, "click" chemistry and nanotoxicology.
Topics: Amino Acids; Animals; Chickens; Free Radicals; Muramidase; Oxidation-Reduction; Tetrazolium Salts; Ultraviolet Rays
PubMed: 33538741
DOI: 10.1039/d0cp04887a -
Journal of Photochemistry and... Jan 2022Myeloperoxidase (MPO) is a myeloid-lineage restricted enzyme largely expressed in the azurophilic granules of neutrophils. It catalyses the formation of reactive oxygen...
Myeloperoxidase (MPO) is a myeloid-lineage restricted enzyme largely expressed in the azurophilic granules of neutrophils. It catalyses the formation of reactive oxygen species, mainly hypochlorous acid, contributing to anti-pathogenic defense. Disorders in the production or regulation of MPO may lead to a variety of health conditions, mainly of inflammatory origin, including autoimmune inflammation. We have studied the effect of ionizing radiation on the activity of MPO, as measured by the capacity retained by the enzyme to produce hypochlorous acid as reactive oxygen species after exposure to successive doses of solvated electrons, the strongest possible one-e reducing agent in water. Chlorination activity was still present after a very high irradiation dose, indicating that radiation damage does not take place at the active site, hindered in the core of MPO structure. Decay kinetics show a dependence on the wavelength, supporting that the process must occur at peripheral functional groups situated on external and readily accessible locations of the enzyme. These results are relevant to understand the mechanism of resistance of our innate anti-pathogenic defense system and also to get insight into potential strategies to regulate MPO levels as a therapeutic target in autoimmune diseases.
Topics: Peroxidase
PubMed: 34864529
DOI: 10.1016/j.jphotobiol.2021.112369 -
Journal of Radiation Research May 2020Double-stranded oligonucleotides containing cisplatin adducts, with and without a mismatched region, were exposed to hydrated electrons generated by gamma-rays. Gel...
Double-stranded oligonucleotides containing cisplatin adducts, with and without a mismatched region, were exposed to hydrated electrons generated by gamma-rays. Gel electrophoresis analysis demonstrates the formation of cisplatin-interstrand crosslinks from the cisplatin-intrastrand species. The rate constant per base for the reaction between hydrated electrons and the double-stranded oligonucleotides with and without cisplatin containing a mismatched region was determined by pulse radiolysis to be 7 × 109 and 2 × 109 M-1 s-1, respectively. These results provide a better understanding of the radiosensitizing effect of cisplatin adducts in hypoxic tumors and of the formation of interstrand crosslinks, which are difficult for cells to repair.
Topics: Antineoplastic Agents; Cisplatin; Cross-Linking Reagents; DNA; DNA Adducts; Electrons; Humans; Hypoxia; Neoplasms; Nucleic Acid Conformation; Oligonucleotides; Pulse Radiolysis; Spectrometry, Mass, Electrospray Ionization
PubMed: 32211848
DOI: 10.1093/jrr/rraa014 -
Journal of the American Chemical Society Jun 2021Here we report the use of pulse radiolysis and spectroelectrochemistry to generate low-valent nickel intermediates relevant to synthetically important Ni-catalyzed...
Here we report the use of pulse radiolysis and spectroelectrochemistry to generate low-valent nickel intermediates relevant to synthetically important Ni-catalyzed cross-coupling reactions and interrogate their reactivities toward comproportionation and oxidative addition processes. Pulse radiolysis provided a direct means to generate singly reduced [(dtbbpy)NiBr], enabling the identification of a rapid Ni(0)/Ni(II) comproportionation process taking place under synthetically relevant electrolysis conditions. This approach also permitted the direct measurement of Ni(I) oxidative addition rates with electronically differentiated aryl iodide electrophiles ( = 1.3 × 10-2.4 × 10 M s), an elementary organometallic step often proposed in nickel-catalyzed cross-coupling reactions. Together, these results hold implications for a number of Ni-catalyzed cross-coupling processes.
PubMed: 34128676
DOI: 10.1021/jacs.1c04652