Pulse Radiolysis Study Research Articles

Radiation-Induced Chemical Reactions in Hydrogel of Hydroxypropyl Cellulose (HPC): A Pulse Radiolysis Study.

We performed studies on pulse radiolysis of highly transparent and shape-stable hydrogels of hydroxypropyl cellulose (HPC) that were prepared using a radiation-crosslinking technique. Several fundamental aspects of radiation-induced chemical reactions in the hydrogels were investigated. With radiation doses less than 1 kGy, degradation of the HPC matrix was not observed. The rate constants of the HPC composing the matrix, with two water decomposition radicals [hydroxyl radical (•OH) and hydrated electron ([Formula: see text])] in the gels, were determined to be 4.5 × 109 and 1.8 × 107 M-1 s-1, respectively. Direct ionization of HPC in the matrix slightly increased the initial yield of [Formula: see text], but the additionally produced amount of [Formula: see text] disappeared immediately within 200 ps, indicating fast recombination of [Formula: see text] with hole radicals on HPC or on surrounding hydration water molecules. Reactions of [Formula: see text] with nitrous oxide (N2O) and nitromethane (CH3NO2) were also examined. Decay of [Formula: see text] due to scavenging by N2O and CH3NO2 were both slower in hydrogels than in aqueous solutions, showing slower diffusions of the reactants in the gel matrix. The degree of decrease in the decay rate was more effective for N2O than for CH3NO2, revealing lower solubility of N2O in gel than in water. It is known that in viscous solvents, such as ethylene glycol, CH3NO2 exhibits a transient effect, which is a fast reaction over the contact distance of reactants and occurs without diffusions of reactants. However, such an effect was not observed in the hydrogel used in the current study. In addition, the initial yield of [Formula: see text], which is affected by the amount of the scavenged precursor of [Formula: see text], in hydrogel containing N2O was slightly higher than that in water containing N2O, and the same tendency was found for CH3NO2.

Solvent Radical Anions in Irradiated Aliphatic Ketones and Esters as Observed Using Time-Resolved Magnetic Field Effects in the Recombination Fluorescence

Abstract It has been found that addition of alcohols (~0.1 M) to some liquid ketones and esters results in well-pronounced oscillations in the decay of the delayed fluorescence intensity from irradiated solutions. The analysis of the time-resolved magnetic field effects (TR MFEs) in the recombination fluorescence has shown that these oscillations are a manifestation of singlet-triplet transitions in spin-correlated radical ion pairs (RIPs) created by irradiation. Comparison with literature data indicates that the transitions are due to hyperfine couplings (HFCs) in the solvent radical anion (RA), stabilized due to the presence of alcohol molecules. In acetone, this stabilization effect has been observed for methanol, ethanol, 2- propanol, and, to a smaller extent, for tert-butanol. Similar effects have also been observed in diethyl ketone, ethyl acetate, and methyl propionate but not in methyl tert-butyl ketone and ethyl trimethylacetate. The results obtained indicate that the interaction between the radical anions (RAs) of carbonyl compounds and alcohol molecules is of importance in pulse radiolysis studies of organic liquids and their mixtures.

Direct Evaluation of the Molar Absorption Coefficient of Hydrated Electron by the Isosbestic Point Method.

The knowledge of the absorption spectrum of hydrated electron is of importance in numerous pulse radiolysis studies because it is often used for dosimetry or for second-order rate constant determination. We present a direct method for the evaluation of the molar absorption coefficient of the hydrated electron. It is based on the wavelength measurement of isosbestic points during the reaction of e(-)aq with the methylviologen MV(2+) cations which leads to the formation of MV(+•). The molar absorption coefficient of hydrated electron is obtained using the value of the molar absorption coefficient of MV(+•) at the isosbestic point at 600 nm, i.e., ε600nm,(MV(+•)) = 13500 ± 300 L mol(-1) cm(-1). Therefore, at the maximum of the absorption spectrum of e(-)aq at 715 nm, the value is ε715nm,(e(-)aq) = 19700 ± 400 L mol(-1) cm(-1). The absorption spectrum of the hydrated electron has been re-evaluated and completed from 260 to 850 nm.

Local density augmentation of supercritical water probed by 4,4′-bpyH[rad] radical: A pulse radiolysis study

Solvatochromic shift of 4,4′-bpyH in aqueous solutions at elevated temperatures up to supercritical conditions and in various organic solvents with different dielectric constants, is investigated by pulse-radiolysis technique. 4,4′-bpyH shows a stronger solvent–solute interaction in water than in organic solvents, perhaps due to the hydrogen bond between 4,4′-bpyH and water. At 380°C, local density augmentation, namely ρlocal–ρbulk, in supercritical water becomes 280kgm−3 (ρbulk=208kgm−3), and the density enhancement factor is 8.9. Density fluctuation maximizes when ρbulk is around 120kgm−3. Density inhomogeneity decreases as temperature rises, but is still remarkable at 400°C.

Electrode Potentials of l-Tryptophan, l-Tyrosine, 3-Nitro-l-tyrosine, 2,3-Difluoro-l-tyrosine, and 2,3,5-Trifluoro-l-tyrosine.

Electrode potentials for aromatic amino acid radical/amino acid couples were deduced from cyclic voltammograms and pulse radiolysis experiments. The amino acids investigated were l-tryptophan, l-tyrosine, N-acetyl-l-tyrosine methyl ester, N-acetyl-3-nitro-l-tyrosine ethyl ester, N-acetyl-2,3-difluoro-l-tyrosine methyl ester, and N-acetyl-2,3,5-trifluoro-l-tyrosine methyl ester. Conditional potentials were determined at pH 7.4 for all compounds listed; furthermore, Pourbaix diagrams for l-tryptophan, l-tyrosine, and N-acetyl-3-nitro-l-tyrosine ethyl ester were obtained. Electron transfer accompanied by proton transfer is reversible, as confirmed by detailed analysis of the current waves, and because the slopes of the Pourbaix diagrams obey Nernst's law. E°'(Trp(•),H(+)/TrpH) and E°'(TyrO(•),H(+)/TyrOH) at pH 7 are 0.99 ± 0.01 and 0.97 ± 0.01 V, respectively. Pulse radiolysis studies of two dipeptides that contain both amino acids indicate a difference in E°' of approximately 0.06 V. Thus, in small peptides, we recommend values of 1.00 and 0.96 V for E°'(Trp(•),H(+)/TrpH) and E°'(TyrO(•),H(+)/TyrOH), respectively. The electrode potential of N-acetyl-3-nitro-l-tyrosine ethyl ester is higher, while because of mesomeric stabilization of the radical, those of N-acetyl-2,3-difluoro-l-tyrosine methyl ester and N-acetyl-2,3,5-trifluoro-l-tyrosine methyl ester are lower than that of tyrosine. Given that the electrode potentials at pH 7 of E°'(Trp(•),H(+)/TrpH) and E°'(TyrO(•),H(+)/TyrOH) are nearly equal, they would be, in principle, interchangeable. Proton-coupled electron transfer pathways in proteins that use TrpH and TyrOH are thus nearly thermoneutral.

Free Radical Scavenging Reactions of Tetrahydroxyquinone: A Pulse Radiolysis Study

AbstractFree radical induced redox reaction kinetics and mechanism of tetrahydroxy‐1,4‐benzoquinone (THQ) has been studied using pulse radiolysis technique. THQ efficiently scavenged hydrated electron, superoxide radical anion, ethanol radical, hydroxyl radical, azidyl radical, thiocyanate radical anion, sulfate radical anion, haloperoxyl radical, lipid peroxyl radical, tryptophanyl radical and tyrosyl radical. Transient absorption spectra of THQ semiquinone radical anion, THQ radical cation and THQ radical produced with these free radicals and rate constants for these reactions have been studied. A probable mechanism of free radical induced redox reactions of THQ has been proposed. Reaction of THQ with free radicals and cyclic voltammetry measurements suggest its oxidation potentials at 0.81 V and 0.94 V vs NHE. To the best of our knowledge, free radical reactions of THQ have been reported for the first time.

Transformation Reactions of Radicals from the Oxidation of Diphenhydramine: Pulse Radiolysis and Mass Spectrometric Studies

AbstractMechanistic aspects of diphenhydramine (DPH) oxidation induced by hydroxyl (•OH) and sulfate (SO4•−) radicals have been explored in detail by pulse radiolysis technique and high resolution mass spectrometry (HRMS). The transient absorption spectrum along with HRMS analysis undoubtedly established the non‐position selective hydroxylation of DPH by •OH (a; k2 = (1.08 ± 0.06) × 1010 dm3 mol−1 s−1; λmax: 335 nm) led to various transformation products (i ‐ vii) including isomeric mono (Ia‐d), di (IIa‐c) and tri (VIIa‐e) hydroxylated analogues. On the other hand, SO4•− (specific one electron oxidant) ultimately generates another hydroxylated adduct radical ‘c’ λmax: 330 nm, k2=(5.70 ± 0.03) × 109dm3 mol−1 s−1) which is formed as a result of preferential hydroxylation of initially formed radical cation ‘b’ at ipso position. The mechanism leading to the formation of various transformation products induced by •OH and SO4•− are thoroughly discussed. The mechanistic findings obtained from our studies (especially in the case of less investigated oxidant like SO4•−) are capable to enrich the fundamental understanding on environmentally relevant reactions initiated by •OH and SO4•−.

Mechanism of oxidative conversion of Amplex® Red to resorufin: Pulse radiolysis and enzymatic studies

Amplex® Red (10-acetyl-3,7-dihydroxyphenoxazine) is a fluorogenic probe widely used to detect and quantify hydrogen peroxide in biological systems. Detection of hydrogen peroxide is based on peroxidase-catalyzed oxidation of Amplex® Red to resorufin. In this study we investigated the mechanism of one-electron oxidation of Amplex® Red and we present the spectroscopic characterization of transient species formed upon the oxidation. Oxidation process has been studied by a pulse radiolysis technique with one-electron oxidants (N3•, CO3•–,•NO2 and GS•). The rate constants for the Amplex® Red oxidation by N3• (2k=2.1·109M−1s−1, at pH=7.2) and CO3•– (2k=7.6·108M−1s−1, at pH=10.3) were determined. Two intermediates formed during the conversion of Amplex® Red into resorufin have been characterized. Based on the results obtained, the mechanism of transformation of Amplex® Red into resorufin, involving disproportionation of the Amplex® Red-derived radical species, has been proposed. The results indicate that peroxynitrite-derived radicals, but not peroxynitrite itself, are capable to oxidize Amplex® Red to resorufin. We also demonstrate that horseradish peroxidase can catalyze oxidation of Amplex® Red not only by hydrogen peroxide, but also by peroxynitrite, which needs to be considered when employing the probe for hydrogen peroxide detection.

Comprehensive Assessment of Antioxidant Activities of Apigenin Isomers: Vitexin and Isovitexin

Introduction: Fenugreek is known to possess anti-diabetic as well as antioxidant properties known to increase with germination. Previous study from our laboratory has reported vitexin and isovitexin as major antioxidant compounds from germinated fenugreek seeds. The present study aimed to comprehensively assesses and compare their antioxidant activity. Methods: The antioxidant ability of these compounds against various radicals was checked using standard in vitro radical scavenging assays and pulse radiolysis. Protection conferred to mitochondria against oxidative damage was assessed by measuring the levels of lipid peroxides and protein sulphydryls. Protection from hydrogen peroxide induced cytotoxicity in HepG2 cells was checked by MTT assay and by measuring intracellular ROS. Their ability to modulate intracellular antioxidant status was checked both at activity and RNA level. Result: Vitexin and isovitexin exhibited differential antioxidant activity against various radicals. Vitexin was a better nitric oxide scavenger while isovitexin scavenged superoxide radicals more efficiently. Pulse radiolysis studies revealed good antioxidant activity of both compounds against short-lived radicals and affected the formation and decay of the 2-dG transient species to the same extent. In oxidatively damaged mitochondria, lipid peroxidation was inhibited significantly by isovitexin whereas vitexin prevented decrease in protein sulphydryl content more effectively. These compounds protected HepG2 cells to the same extent against hydrogen peroxide induced oxidative insult by reducing intracellular ROS and modulating the levels of antioxidant enzymes. Conclusion: The present study clearly demonstrates differential antioxidant potential of both vitexin and isovitexin and their role in mitigating oxidative stress induced damage and maintaining cellular redox homeostasis.

Charge transfer reactions from tryptophan and tyrosine to sulfur-centered dimer radical cation in aqueous -sulfuric acid medium: a pulse radiolysis study

Charge transfer reactions from tryptophan and tyrosine to sulfur-centered dimer radical cation in aqueous -sulfuric acid medium: a pulse radiolysis study

Role of surfactant derived intermediates in the efficacy and mechanism for radiation chemical degradation of a hydrophobic azo dye, 1-phenylazo-2-naphthol

A combined methodology involving gamma and pulse radiolysis, product analysis and toxicity studies has been adopted to comprehend the degradation process of a model hydrophobic azo dye, 1-phenylazo-2-naphthol, emphasizing the role of the surfactant, which is an integral part of textile waste. Two new and important findings are underlined in this article. The first is the direct attestation of the hydrazyl radical-parent adduct, formed in the reaction of the dye with e−aq followed by protonation and subsequent addition to the unreacted dye molecule. This has been confirmed from concentration dependent studies. Secondly, we have clearly shown that in the reaction of hydroxyl radical with the dye in Triton X-100 media, the initially produced TX radicals cause reductive degradation of the dye. Identification and detailed analysis of HPLC and GCMS data reveals that similar products are formed in both the reactions of e−aq and OH radicals. Moreover, the cytotoxicity of 10−4moldm−3 dye was found to be reduced significantly after irradiation. Thus, the present study not only depicts new pathways for the degradation of hydrophobic azo dye, but also demonstrates the role of a surfactant in the entire process.

Pulse radiolysis study of polystyrene-based polymers with added photoacid generators: Reaction mechanism of extreme-ultraviolet and electron-beam chemically amplified resist

The reaction mechanism of chemically amplified resist (CAR) after irradiation with ionizing radiation is important for developing extreme-ultraviolet and electron-beam lithography. The acid generation after the ionization is an essential reaction in CAR. In this study, the intermediate of the proton source of acid (a radical cation of the base polymer) in the presence of a photoacid generator (PAG) was investigated by the pulse radiolysis method. The deprotonation kinetics of the radical cation of poly(4-hydroxystyrene) (PHS) in solutions with and without PAG shows only a small difference. However, the yield of radical cations of poly(4-methoxystyrene) (PMOS) as a model of the resist with a protecting (releasing) group increases upon adding PAG. The formation of the ion pair between the PMOS radical cation and the dissociated anion with a lifetime of approximately 30 to 40 µs is suggested. The lower acid yield in PMOS than in PHS film is also discussed in terms of the stability of the radical cation.

Photosensitive damage of lysozyme caused by pazufloxacin and the protective effect of ferulic acid

Laser flash photolysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) experiments were carried out to study the photosensitive damage induced by pazufloxacin (PAX) and the protection of lysozyme (Lyso) by ferulic acid (FCA), an active antioxidant. Transient absorption spectra revealed electron transfer from Lyso and FCA to (3)PAX*, with respective bimolecular reaction rate constants of 6.3x10(7) and 1.4x10(10) dm(3)/(mol s). A pulse radiolysis study was also performed to investigate the formation of Lyso radical cations. Results showed that FCA effectively inhibits the cross-linking of protein induced by fluoroquinolones. Finally, a mechanism of the protective effect of FCA on Lyso was proposed.

Correction to “Pulse Radiolysis Studies of 3,5-Dimethyl Pyrazole Derivatives of Selenoethers”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to “Pulse Radiolysis Studies of 3,5-Dimethyl Pyrazole Derivatives of Selenoethers”Atanu Barik*, Beena G. Singh, Asmita Sharma, Vimal K. Jain, and K. Indira PriyadarsiniCite this: J. Phys. Chem. A 2014, 118, 49, 11652Publication Date (Web):November 26, 2014Publication History Published online26 November 2014Published inissue 11 December 2014https://doi.org/10.1021/jp511751dCopyright © 2014 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views137Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (106 KB) Get e-Alerts Get e-Alerts

A pulse radiolysis study of hyperoside isolated from Hypericum mysorense

The recent growth in knowledge of free radicals in biology is producing a medical revolution that promises a new age in health and disease management. In the last two decades there has been an explosive interest in the role of oxygen free radicals, more generally known as “reactive oxygen species” and of “reactive nitrogen species” in experimental and clinical medicine. The flowering top extract of Hypericum mysorense possessing potent anti-oxidant activity was subjected to bio-active guided isolation. Pulse radiolysis technique was used to determine the transient spectrum and rate constant for the one-electron oxidation of hyperoside by OH, N3, NO2, NO, CCl3OO radicals in aqueous solution. Three compounds were isolated and characterized as rutin, quercetin-3-O-galactoside (hyperoside) and quercetin from spectral analysis. The hyperoside radical showed pKa1 and pKa2 at 5.4 and 9.2. Both, Cu(II) and iron(II) ions form chelate with hyperoside. The Cu–hyperoside chelate was able to scavenge O2−, k=7.0(±0.3)×106 dm3 mol−1 s−1 at pH 9. The repair rates for tryptophan and guanosine radicals by hyperoside were also determined. The reduction potential of hyperoside radical was determined by cyclic voltammetric and pulse radiolysis methods.

Pulse radiolysis studies of the reactions of nitrogen dioxide with the vitamin B12 complexes cob(II)alamin and nitrocobalamin

Although now recognized to be an important reactive nitrogen species in biological systems that modifies the structures of proteins, DNA and lipids, there are few studies on the reactivity of NO2, including the reactions between NO2 and transition metal complexes. We report kinetic studies on the reactions of NO2 with two forms of vitamin B12 — cob(II)alamin and nitrocobalamin. UV–visible spectroscopy and HPLC analysis of the product solution show that NO2 cleanly oxidizes the metal center of cob(II)alamin to form nitrocobalamin, with a second-order rate constant of (3.5±0.3)×108M−1s−1 (pH7.0 and 9.0, room temperature, I=0.20M). The stoichiometry of the reaction is 1:1. No reaction is detected by UV–visible spectroscopy and HPLC analysis of the product solution when nitrocobalamin is exposed to up to 2.0molequiv. NO2.

Radiation-induced pink nickel oligomeric clusters in water. Pulse radiolysis study.

γ-rays and pulse radiolysis of aqueous solutions of Ni(2+) ions in the presence of polyacrylate (PA(-)) and 2-propanol leads to the formation of metastable species absorbing at 540 nm that are ascribed to "pink" oligomeric clusters of a few nickel atoms only. The molar absorption coefficient is evaluated as ε540 nm = 3300 ± 300 L mol(-1) cm(-1) per Ni(0) atom. The successive steps from the reduction of Ni(2+) into Ni(+) ions to the formation of the pink clusters at 540 nm under conditions of complexation by PA(-) are investigated by pulse radiolysis. The yield of the formation of pink clusters increases markedly with the irradiation dose rate, demonstrating the occurrence of the disproportionation of the [Ni(+), PA(-)] complex after a single electron pulse. The reduction and nucleation mechanisms, including rate constants, in competition with the back oxidation by protons, particularly at low dose rate, are discussed.

Formation of semiquinone radical anion and free radical scavenging reactions of plumbagin: a pulse radiolysis study

Kinetics and mechanism of scavenging of reducing free radicals by plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) are studied using pulse radiolysis technique. It scavenged superoxide radical, hydroxyethyl radical and hydrated electron with bimolecular rate constants of 8.9 × 107, 2.3 × 109 and 1.6 × 1010 M−1 s−1, respectively in aqueous-alcohol medium. Plumbagin also scavenged linoleic acid peroxyl radical and tyrosyl radical with bimolecular rate constants of 1.0 × 108 and 7.0 × 106 M−1 s−1, respectively. Further, redox properties of plumbagin and its transients are studied using standard redox couples and cyclic voltammetry.

Reactivity of hypotaurine and cysteine sulfinic acid toward carbonate radical anion and nitrogen dioxide as explored by the peroxidase activity of Cu,Zn superoxide dismutase and by pulse radiolysis

Hypotaurine and cysteine sulfinic acid are known to be readily oxidized to the respective sulfonates, taurine and cysteic acid, by several oxidative agents that may be present in biological systems. In this work, the relevance of both the carbonate anion and nitrogen dioxide radicals in the oxidation of hypotaurine and cysteine sulfinic acid has been explored by the peroxidase activity of Cu,Zn superoxide dismutase (SOD) and by pulse radiolysis. The extent of sulfinate oxidation induced by the system SOD/H2O2 in the presence of bicarbonate (CO3•– generation), or nitrite (•NO2 generation) has been evaluated. Hypotaurine is efficiently oxidized by the carbonate radical anion generated by the peroxidase activity of Cu,Zn SOD. Pulse radiolysis studies have shown that the carbonate radical anion reacts with hypotaurine more rapidly (k = 1.1 × 109 M−1s−1) than nitrogen dioxide (k = 1.6 × 107 M−1s−1). Regarding cysteine sulfinic acid, it is less reactive with the carbonate radical anion (k = 5.5 × 107 M−1s−1) than hypotaurine. It has also been observed that the one-electron transfer oxidation of both sulfinates by the radicals is accompanied by the generation of transient sulfonyl radicals (RSO2•). Considering that the carbonate radical anion could be formed in vivo at high level from bicarbonate, this radical can be included in the oxidants capable of performing the last metabolic step of taurine biosynthesis. Moreover, the protective effect exerted by hypotaurine and cysteine sulfinate on the carbonate radical anion-mediated tyrosine dimerization indicates that both sulfinates have scavenging activity towards the carbonate radical anion. However, the formation of transient reactive intermediates during sulfinate oxidation by carbonate anion and nitrogen dioxide radical may at the same time promote oxidative reactions.

A pulse radiolysis study of the dynamics of ascorbic acid free radicals within a liposomal environment.

The dynamics of free-radical species in a model cellular system are examined by measuring the formation and decay of ascorbate radicals within a liposome with pulse radiolysis techniques. Upon pulse radiolysis of an N2O-saturated aqueous solution containing ascorbate-loaded liposome vesicles, ascorbate radicals are formed by the reaction of OH(·) radicals with ascorbate in unilamellar vesicles exclusively, irrespective of the presence of vesicle lipids. The radicals are found to decay rapidly compared with the decay kinetics in an aqueous solution. The distinct radical reaction kinetics in the vesicles and in bulk solution are characterized, and the kinetic data are analyzed.