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Sample records for activity hydroxyl radical

  1. Vanadium promotes hydroxyl radical formation by activated human neutrophils.

    PubMed

    Fickl, Heidi; Theron, Annette J; Grimmer, Heidi; Oommen, Joyce; Ramafi, Grace J; Steel, Helen C; Visser, Susanna S; Anderson, Ronald

    2006-01-01

    This study was undertaken to investigate the effects of vanadium in the +2, +3, +4, and +5 valence states on superoxide generation, myeloperoxidase (MPO) activity, and hydroxyl radical formation by activated human neutrophils in vitro, using lucigenin-enhanced chemiluminescence (LECL), autoiodination, and electron spin resonance with 5,5-dimethyl-l-pyrroline N-oxide as the spin trap, respectively. At concentrations of up to 25 microM, vanadium, in the four different valence states used, did not affect the LECL responses of neutrophils activated with either the chemoattractant, N-formyl-l-methionyl-l-leucyl-l-phenylalanine (1 microM), or the phorbol ester, phorbol 12-myristate 12-acetate (25 ng/ml). However, exposure to vanadium in the +2, +3, and +4, but not the +5, valence states was accompanied by significant augmentation of hydroxyl radical formation by activated neutrophils and attenuation of MPO-mediated iodination. With respect to hydroxyl radical formation, similar effects were observed using cell-free systems containing either hydrogen peroxide (100 microM) or xanthine/xanthine oxidase together with vanadium (+2, +3, +4), while the activity of purified MPO was inhibited by the metal in these valence states. These results demonstrate that vanadium in the +2, +3, and +4 valence states interacts prooxidatively with human neutrophils, competing effectively with MPO for hydrogen peroxide to promote formation of the highly toxic hydroxyl radical.

  2. Hydroxyl radicals in indoor environments

    NASA Astrophysics Data System (ADS)

    Sarwar, Golam; Corsi, Richard; Kimura, Yosuke; Allen, David; Weschler, Charles J.

    Indoor hydroxyl radical concentrations were estimated using a new indoor air quality model which employs the SAPRC-99 atmospheric chemistry model to simulate indoor homogenous reactions. Model results indicate that typical indoor hydroxyl radical concentrations are lower than typical outdoor summertime urban hydroxyl radical levels of 5-10×10 6 molecules cm -3; however, indoor levels can be similar to or greater than typical nighttime outdoor hydroxyl radical levels of approximately 5×10 4 molecules cm -3. Effects of selected parameters on indoor hydroxyl radical concentrations are presented herein. Indoor hydroxyl radical concentrations are predicted to increase non-linearly with increasing outdoor ozone concentrations, indoor alkene emission rates, and air exchange rates. Indoor hydroxyl radical concentrations decrease with increasing outdoor nitric oxide concentrations. Indoor temperature and indoor light intensity have moderate impacts on indoor hydroxyl radical concentrations. Outdoor hydroxyl radical concentrations, outdoor nitrate (NO 3rad ) radical concentrations, outdoor hydroperoxy radical concentrations, and hydroxyl radical removal by indoor surfaces are predicted to have no appreciable impact on indoor hydroxyl radical concentrations. Production of hydroxyl radicals in indoor environments appears to be controlled primarily by reactions of alkenes with ozone, and nitric oxide with hydroperoxy radical. Estimated indoor hydroxyl radical levels may potentially affect indoor air quality. Two examples are presented in which reactions of d-limonene and α-pinene with indoor hydroxyl radicals produce aldehydes, which may be of greater concern than the original compounds.

  3. Production of hydroxyl radical by redox active flavonoids

    SciTech Connect

    Kalyanaraman, B.; Hodnick, W.F.; Pardini, R.S.

    1986-05-01

    The authors have previously shown that flavonoids autoxidize and generate superoxide (O/sub 2//sup -/) and hydrogen peroxide (H/sub 2/O/sub 2/), suggesting that hydroxyl radical (OH) could be formed via the metal-ion catalyzed Haber-Weiss reaction. In the presence of ethylenediamine tetraacetic acid (EDTA) and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO), myricetin, quercetagetin and quercetin gave an ESR signal for the DMPO-OH spin adduct, and the DMPO-Eto adduct in the presence of excess ethanol, indicating the production of free OH. The addition of FeCl/sub 3/ to the reaction mixture resulted in a dramatic increase in the DMPO-OH signal. Without chelator (EDTA) there was no signal and the presence of diethylenetriamine-pentaacetic acid (DETAPAC) greatly diminished the signal. The presence of superoxide dismutase (SOD) had no effect on the signal while catalase completely abrogated the signal. The addition of Fe (III)-EDTA to flavonoid solutions under anaerobic conditions produced time dependent auxochromic shifts in their absorption spectra and resulted in the reduction of Fe (III) to Fe (II). These data suggest that the flavonoids autoxidize to produce O/sub 2//sup -/ and H/sub 2/O/sub 2/ by dismutation and in the presence of Fe (III)-EDTA the flavonoid can directly reduce the Fe (III) to Fe (II) resulting in the production of OH through Fenton chemistry.

  4. Reduced serum hydroxyl radical scavenging activity in erythropoietin therapy resistant renal anemia.

    PubMed

    Hirayama, Aki; Nagase, Sohji; Gotoh, Michihiro; Ueda, Atsushi; Ishizu, Takashi; Yoh, Keigyou; Aoyagi, Kazumasa; Terao, Junji; Koyama, Akio

    2002-11-01

    Relation between anemia resistant to recombinant human erythropoietin (rHuEPO) therapy and the oxidative stress in hemodialysis (HD) patients was investigated. Stable HD patients who had consistent hemoglobin concentrations on a constant dose of rHuEPO were studied. Patients were excluded if there were factors that might affect hemopoiesis or administration of antioxidant supplements. Patients were classified into three groups: High (9000 U/week), Low (1500-4500 U/week) and No rHuEPO group. Thiobarbituric acid reactive substances (TBARS) of sera and erythrocyte were examined. Serum superoxide and hydroxyl radical scavenging activities were measured using electron spin resonance. TBARS in the erythrocyte was higher in High rHuEPO group compared with No rHuEPO group, though the serum TBARS were similar. A diminution of serum hydroxyl radical scavenging activity was observed in High rHuEPO group. Hydroxyl radical signal intensity showed a strong correlation with the serum ferritin in High rHuEPO group, although ferritin concentrations were not different among the 3 groups. Superoxide scavenging activity showed no differences. These results indicate that increased lipid peroxidation in erythrocyte, raised by decreased serum hydroxyl radical scavenging activity, is one cause of rHuEPO resistant anemia. Serum ferritin may be involved in this hydroxyl radical production.

  5. The role of hydroxyl radical as a messenger in Cr(VI)-induced p53 activation.

    PubMed

    Wang, S; Leonard, S S; Ye, J; Ding, M; Shi, X

    2000-09-01

    The present study investigates whether reactive oxygen species (ROS) are involved in p53 activation, and if they are, which species is responsible for the activation. Our hypothesis is that hydroxyl radical (.OH) functions as a messenger for the activation of this tumor suppressor protein. Human lung epithelial cells (A549) were used to test this hypothesis. Cr(VI) was employed as the source of ROS due to its ability to generate a whole spectrum of ROS inside the cell. Cr(VI) is able to activate p53 by increasing the protein levels and enhancing both the DNA binding activity and transactivation ability of the protein. Increased cellular levels of superoxide radicals (O(2)(-).), hydrogen peroxide (H(2)O(2)), and.OH radicals were detected on the addition of Cr(VI) to the cells. Superoxide dismutase, by enhancing the production of H(2)O(2) from O(2)(-). radicals, increased p53 activity. Catalase, an H(2)O(2) scavenger, eliminated.OH radical generation and inhibited p53 activation. Sodium formate and aspirin,.OH radical scavengers, also suppressed p53 activation. Deferoxamine, a metal chelator, inhibited p53 activation by chelating Cr(V) to make it incapable of generating radicals from H(2)O(2). NADPH, which accelerated the one-electron reduction of Cr(VI) to Cr(V) and increased.OH radical generation, dramatically enhanced p53 activation. Thus.OH radical generated from Cr(VI) reduction in A549 cells is responsible for Cr(VI)-induced p53 activation.

  6. Novel spectroscopic sensor for the hydroxyl radical scavenging activity measurement of biological samples.

    PubMed

    Bekdeşer, Burcu; Özyürek, Mustafa; Güçlü, Kubilay; Apak, Reşat

    2012-09-15

    A novel spectroscopic sensor was developed and validated for hydroxyl radical scavenging (HRS) activity estimation using terephthalate (TP) as probe. This sensor was designed by electrostatic immobilization of the chromogenic oxidizing agent of the CUPric Reducing Antioxidant Capacity (CUPRAC) method, Cu(II)-Neocuproine (Cu(II)-Nc) complex, on a Nafion cation-exchange membrane, and the spectrophotometric assay developed in aqueous-alcoholic solutions was integrated to the CUPRAC sensor. Hydroxyl radicals ((•)OH) generated from an equivalent mixture of Fe(II)+EDTA with hydrogen peroxide attacked both the probe and the (•)OH scavengers in 37 °C-incubated solutions for 1/2h. The HRS activity was measured using the decrease in CUPRAC absorbance at 450 nm - arising from the reduction of Cu(II)-Nc reagent to the Cu(I)-neocuproine chelate - of the hydroxylated probe (TP) undergoing radical attack in the presence of (•)OH scavengers. The HRS activity was evaluated as the second-order rate constants of biologically active compounds for (•)OH scavenging and also as the percentage scavenging of a measured compound or sample relative to a reference compound. Using this reaction, a kinetic approach was adopted to assess the HRS activity of amino acids, plasma- and thiol-antioxidants. This assay, applicable to small molecule antioxidants and tissue homogenates, proved to be efficient for serine and albumin for which the widely used TBARS (thiobarbituric acid-reactive substances) test is nonresponsive. Under optimal conditions, about half of the probe (TP) was converted into 2-hydroxyterephthalate (hTP), and this monohydroxylated derivative, being the only product of hydroxylation, was a more specific marker of (•)OH than the non-specific malondialdehyde end-product of the TBARS test. The sensor gave a linear response to scavenger concentration in the competition kinetic equation.

  7. Detection of hydroxyl radicals during regeneration of granular activated carbon in dielectric barrier discharge plasma system

    NASA Astrophysics Data System (ADS)

    Tang, Shoufeng; Lu, Na; Shang, Kefeng; Li, Jie; Wu, Yan

    2013-03-01

    To understand the reactions taking place in the dielectric barrier discharge (DBD) plasma system of activated carbon regeneration, the determination of active species is necessary. A method based on High Performance Liquid Chromatography with radical trapping by salicylic acid, has been developed to measure hydroxyl radical (•OH) in the DBD plasma reactor. The effects of applied voltage, treatment time, and gas flow rate and atmosphere were investigated. Experimental results indicated that increasing voltage, treatment time and air flow rate could enhance the formation of •OH. Oxygen atmosphere and a suitable GAC water content were contributed to •OH generation. The results give an insight into plasma chemical processes, and can be helpful to optimize the design and application for the plasma system.

  8. Production of Hydroxyl Radical via the Activation of Hydrogen Peroxide by Hydroxylamine.

    PubMed

    Chen, Liwei; Li, Xuchun; Zhang, Jing; Fang, Jingyun; Huang, Yanmin; Wang, Ping; Ma, Jun

    2015-09-01

    The production of the hydroxyl radical (HO·) is important in environmental chemistry. This study reports a new source of HO· generated solely from hydrogen peroxide (H2O2) activated by hydroxylamine (HA). Electron paramagnetic resonance analysis and the oxidation of a HO· probe, benzoic acid, were used to confirm the production of HO·. The production of HO· increased with increasing concentrations of either HA or H2O2 as well as decreasing pH. The second-order rate constant for the reaction was (2.2 ± 0.2) × 10(-4) M(-1) s(-1). HO· was probably produced in two steps: the activation of H2O2 by protonated HA and then reaction between the H2O2 and the intermediate protonated aminoxyl radical generated in the first step. Such a two-step oxidation can possibly be ascribed to the ionizable hydroxyl moiety in the molecular structure of HA, as is suggested by comparing the reactivity of a series of HA derivatives in HO· production. The results shed light on a previously unknown source of HO· formation, which broadens the understanding of its role in environmental processes.

  9. The Antimicrobial Activity of Gramicidin A Is Associated with Hydroxyl Radical Formation

    PubMed Central

    Liou, Je-Wen; Hung, Yu-Jiun; Yang, Chin-Hao; Chen, Yi-Cheng

    2015-01-01

    Gramicidin A is an antimicrobial peptide that destroys gram-positive bacteria. The bactericidal mechanism of antimicrobial peptides has been linked to membrane permeation and metabolism disruption as well as interruption of DNA and protein functions. However, the exact bacterial killing mechanism of gramicidin A is not clearly understood. In the present study, we examined the antimicrobial activity of gramicidin A on Staphylococcus aureus using biochemical and biophysical methods, including hydroxyl radical and NAD+/NADH cycling assays, atomic force microscopy, and Fourier transform infrared spectroscopy. Gramicidin A induced membrane permeabilization and changed the composition of the membrane. The morphology of Staphylococcus aureus during gramicidin A destruction was divided into four stages: pore formation, water permeability, bacterial flattening, and lysis. Changes in membrane composition included the destruction of membrane lipids, proteins, and carbohydrates. Most interestingly, we demonstrated that gramicidin A not only caused membrane permeabilization but also induced the formation of hydroxyl radicals, which are a possible end product of the transient depletion of NADH from the tricarboxylic acid cycle. The latter may be the main cause of complete Staphylococcus aureus killing. This new finding may provide insight into the underlying bactericidal mechanism of gA. PMID:25622083

  10. The antimicrobial activity of gramicidin A is associated with hydroxyl radical formation.

    PubMed

    Liou, Je-Wen; Hung, Yu-Jiun; Yang, Chin-Hao; Chen, Yi-Cheng

    2015-01-01

    Gramicidin A is an antimicrobial peptide that destroys gram-positive bacteria. The bactericidal mechanism of antimicrobial peptides has been linked to membrane permeation and metabolism disruption as well as interruption of DNA and protein functions. However, the exact bacterial killing mechanism of gramicidin A is not clearly understood. In the present study, we examined the antimicrobial activity of gramicidin A on Staphylococcus aureus using biochemical and biophysical methods, including hydroxyl radical and NAD+/NADH cycling assays, atomic force microscopy, and Fourier transform infrared spectroscopy. Gramicidin A induced membrane permeabilization and changed the composition of the membrane. The morphology of Staphylococcus aureus during gramicidin A destruction was divided into four stages: pore formation, water permeability, bacterial flattening, and lysis. Changes in membrane composition included the destruction of membrane lipids, proteins, and carbohydrates. Most interestingly, we demonstrated that gramicidin A not only caused membrane permeabilization but also induced the formation of hydroxyl radicals, which are a possible end product of the transient depletion of NADH from the tricarboxylic acid cycle. The latter may be the main cause of complete Staphylococcus aureus killing. This new finding may provide insight into the underlying bactericidal mechanism of gA.

  11. Role of allyl group in the hydroxyl and peroxyl radical scavenging activity of S-allylcysteine.

    PubMed

    Maldonado, Perla D; Alvarez-Idaboy, J Raúl; Aguilar-González, Adriana; Lira-Rocha, Alfonso; Jung-Cook, Helgi; Medina-Campos, Omar Noel; Pedraza-Chaverrí, José; Galano, Annia

    2011-11-17

    S-Allylcysteine (SAC) is the most abundant compound in aged garlic extracts, and its antioxidant properties have been demonstrated. It is known that SAC is able to scavenge different reactive species including hydroxyl radical (•OH), although its potential ability to scavenge peroxyl radical (ROO•) has not been explored. In this work the ability of SAC to scavenge ROO• was evaluated, as well as the role of the allyl group (-S-CH(2)-CH═CH(2)) in its free radical scavenging activity. Two derived compounds of SAC were prepared: S-benzylcysteine (SBC) and S-propylcysteine (SPC). Their abilities to scavenge •OH and ROO• were measured. A computational analysis was performed to elucidate the mechanism by which these compounds scavenge •OH and ROO•. SAC was able to scavenge •OH and ROO•, in a concentration-dependent way. Such activity was significantly ameliorated when the allyl group was replaced by benzyl or propyl groups. It was shown for the first time that SAC is able to scavenge ROO•.

  12. Synthesis, photocatalytic activity, and photogenerated hydroxyl radicals of monodisperse colloidal ZnO nanospheres

    NASA Astrophysics Data System (ADS)

    Yang, Chong; Li, Qingsong; Tang, Limei; Xin, Kun; Bai, Ailing; Yu, Yingmin

    2015-12-01

    In the present study, monodisperse colloidal zinc oxide (ZnO) nanospheres were successfully synthesized via a newly developed two-stage solution method followed by facile calcination at various temperatures. The effects of calcination temperature on the structure, morphology, and optical properties as well as the photocatalytic activity of the as-made ZnO samples were investigated systematically by Fourier transform infrared spectrometry, X-ray diffraction, field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, diffuse reflectance UV-visible spectroscopy (DRS), photoluminescence, and related photocatalytic activity tests. The thermal decomposition was analyzed by thermogravimetric analysis. The crystallinity was found to gradually increase with increasing calcination temperature, whereas the decrease in the Brunauer-Emmett-Teller specific surface area of the samples with calcination may be ascribed to the increased particle size. The DRS results provided clear evidence for the decrease in band gap energy of ZnO samples with an increase in calcination temperature. The photoluminescence spectra demonstrated the calcination-dependent emission features, especially the UV emission intensity. In particular, the ZnO product calcined at 400 °C exhibited the highest photocatalytic activity, degrading methylene blue by almost 99.1% in 70 min, which is ascribed to the large specific surface area and pore volume, high electron-hole pair separation efficient, and great redox potential of the obtained ZnO nanoparticles. In addition, the production of photogenerated hydroxyl radicals (•OH) was consistent with the methylene blue degradation efficiency over the as-made ZnO nanoparticles. Using isopropanol as a hydroxyl radical scavenger, •OH was determined to be the main active oxygen species in the photocatalytic process. A possible mechanism of photodegradation under UV light irradiation also is proposed.

  13. Different hydroxyl radical scavenging activity of water-soluble beta-alanine C60 adducts.

    PubMed

    Sun, Tao; Jia, Zhishen; Xu, Zhude

    2004-04-01

    Three C(60) derivatives [C(60) (NHCH(2)CH(2)COONa)(n)(H)(n)], n=1, 5, 9] (A, B, C) with different additional number of beta-alanine were synthesized by the control of relative amount of C(60) and beta-alanine added. Hydroxyl radical scavenging activity of the adducts was evaluated in a copper-catalyzed Haber-Weiss reaction by chemiluminescence technology. The 50% inhibition concentrations (IC(50)'s) of A, B, and C were 147.2 micromol/L, 76.3 micromol/L, and 96.2 micromol/L, respectively. The difference should be closely related to the numbers of residual C=C bonds in C(60), steric effect and electron-withstanding effect of amino group especially.

  14. Stereospecificity in hydroxyl radical scavenging activities of four ginsenosides produced by heat processing.

    PubMed

    Kang, Ki Sung; Kim, Hyun Young; Yamabe, Noriko; Yokozawa, Takako

    2006-10-01

    The activity-guided fractionation of sun ginseng (SG, heat processed Panax ginseng C. A. Meyer at 120 degrees C) was carried out to identify its main active hydroxyl radical (*OH) scavenging components. As a result, the n-BuOH fraction mainly consisting of ginsenosides showed the strongest activity. Of several ginsenosides of SG, the *OH scavenging activities of relatively high contents of 20(S)-Rg(3), 20(R)-Rg(3), Rk(1), and Rg(5) were compared. Rg(5) and 20(S)-Rg(3) showed strong *OH scavenging IC(50) values of 0.15 and 0.44 mM, respectively, and these activities were prominently higher than each of their respective isomers. Therefore, stereospecificity exists in the *OH scavenging activities of ginsenosides produced by heat processing. Especially, the double bond at carbon-20(22) or the OH group at carbon-20 geometrically close to OH at carbon-12 is thought to increase the *OH scavenging activity of ginsenosides.

  15. Hydroxyl radical scavenging activities of isoquinoline alkaloids isolated from Coptis chinensis.

    PubMed

    Jang, Moon Hee; Kim, Hyun Young; Kang, Ki Sung; Yokozawa, Takako; Park, Jeong Hill

    2009-03-01

    The hydroxyl radical (*OH) scavenging and ferrous ion chelating activities of four isoquinoline alkaloids isolated from Coptis chinensis Franch were studied for the identification of their structural characteristics to scavenge *OH. The *OH was generated via Fe(II)-catalazed Fenton reaction in this study and the reliable measurement of *OH scavenging activities of isoquinoline alkaloids were achieved using electron spin resonance (ESR) spectrometry method. At the 1 mM concentration, berberrubine (85%) showed the strongest *OH scavenging activity and the next were in the decreasing order of coptisine (79%), berberine (23%), and palmatine (22%). The ferrous ion chelating effects of the alkaloids showed similar pattern with their *OH scavenging effects. These results suggest that *OH scavenging effects of the alkaloids were closely related to their ferrous ion chelating activities. In addition, metal chelating functional groups such as hydroxy group at C-9 and methylenedioxy group at C-9 and C-10 were thought to contribute to the *OH scavenging activities of the isoquinoline alkaloids.

  16. Vibrational Study of Melatonin and its Radioprotective Activity towards Hydroxyl Radical

    NASA Astrophysics Data System (ADS)

    Singh, Gurpreet; Kaur, Sarvpreet; Saini, G. S. S.

    2011-12-01

    Vibrational study of Melatonin (N-acetyl 5-methoxytrypatamin) was done using FTIR and Raman spectroscopy. DFT calculations were employed to the structural analysis of melatonin and to the end products. The theoretical calculations confirmed the different observed vibrational modes. The optimized structure energy calculations of the different end products confirmed the most probable site of the hydroxyl radical attack is the hydrogen attached to nitrogen present in the indole ring.

  17. Membrane permeability of redox active metal chelators: an important element in reducing hydroxyl radical induced NAD+ depletion in neuronal cells.

    PubMed

    Jayasena, T; Grant, R S; Keerthisinghe, N; Solaja, I; Smythe, G A

    2007-03-01

    There is substantial evidence implicating increased production of the hydroxyl radical and oxidative stress in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). Significant amounts of hydroxyl radicals will be produced in the presence of hydrogen peroxide and redox active iron via Fenton chemistry. Increased iron levels within the cytoplasm of vulnerable neurons suggest that this may also be an important site of oxidative activity. We investigated the likelihood that intracellular, rather than extracellular chelation of ferrous or ferric iron may be more effective in reducing hydroxyl radical induced cell damage and preserving NAD(+) levels and cell viability. Using intracellular NAD(H) measurements as an indicator of cell viability we found that membrane permeable ferrous chelators were most efficient in preserving cellular NAD(+) levels. Hydrophilic, ferrous or ferric chelators and lipophilic ferric chelators were essentially ineffective in preventing cellular NAD(+) depletion when added at physiological concentrations. We propose that lipophilic ferrous chelators, due to their actions inside the cell, are effective agents for moderating neuronal damage in conditions such as AD where intracellular oxidative stress plays a significant role in disease pathology. PMID:17210195

  18. Inhibitory activity of flavonoids from Prunus davidiana and other flavonoids on total ROS and hydroxyl radical generation.

    PubMed

    Jung, Hyun Ah; Jung, Mee Jung; Kim, Ji Young; Chung, Hae Young; Choi, Jae Sue

    2003-10-01

    Since reactive oxygen species (ROS) and hydroxyl radicals (*OH) play an important role in the pathogenesis of many human degenerative diseases, much attention has focused on the development of safe and effective antioxidants. Preliminary experiments have revealed that the methanol (MeOH) extract of the stem of Prunus davidiana exerts inhibitory/scavenging activities on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, total ROS and peroxynitrites (ONOO-). In the present study, the antioxidant activities of this MeOH extract and the organic solvent-soluble fractions, dichloromethane (CH2Cl2), ethyl acetate (EtOAc), and n-butanol (n-BuOH), and the water layer of P. davidiana stem were evaluated for the potential to inhibit *OH and total ROS generation in kidney homogenates using 2',7'-dichlorodihydrofluorescein diacetate (DCHF-DA), and for the potential to scavenge authentic ONOO-. We also evaluated the inhibitory activity of seven flavonoids isolated from P. davidiana stem, kaempferol, kaempferol 7-O-beta-D-glucoside, (+)-catechin, dihydrokaempferol, hesperetin 5-O-beta-D-glucoside, naringenin and its 7-O-beta-D-glucoside, on the total ROS, *OH and ONOO- systems. For the further elucidation of the structure-inhibitory activity relationship of flavonoids on total ROS and *OH generation, we measured the antioxidant activity of sixteen flavonoids available, including three active flavonoids isolated from P. davidiana, on the total ROS and *OH systems. We found that the inhibitory activity on total ROS generation increases in strength with more numerous hydroxyl groups on their structures. Also, the presence of an ortho-hydroxyl group, whether on the A-ring or B-ring, and a 3-hydroxyl group on the C-ring increased the inhibitory activity on both total ROS and *OH generation.

  19. Antioxidant activity of trans-resveratrol toward hydroxyl and hydroperoxyl radicals: a quantum chemical and computational kinetics study.

    PubMed

    Iuga, Cristina; Alvarez-Idaboy, J Raúl; Russo, Nino

    2012-04-20

    In this work, we have carried out a systematic study of the antioxidant activity of trans-resveratrol toward hydroxyl ((•)OH) and hydroperoxyl ((•)OOH) radicals in aqueous simulated media using density functional quantum chemistry and computational kinetics methods. All possible mechanisms have been considered: hydrogen atom transfer (HAT), proton-coupled electron transfer (PCET), sequential electron proton transfer (SEPT), and radical adduct formation (RAF). Rate constants have been calculated using conventional transition state theory in conjunction with the Collins-Kimball theory. Branching ratios for the different paths contributing to the overall reaction, at 298 K, are reported. For the global reactivity of trans-resveratrol toward (•)OH radicals, in water at physiological pH, the main mechanism of reaction is proposed to be the sequential electron proton transfer (SEPT). However, we show that trans-resveratrol always reacts with (•)OH radicals at a rate that is diffusion-controlled, independent of the reaction pathway. This explains why trans-resveratrol is an excellent but very unselective (•)OH radical scavenger that provides antioxidant protection to the cell. Reaction between trans-resveratrol and the hydroperoxyl radical occurs only by phenolic hydrogen abstraction. The total rate coefficient is predicted to be 1.42 × 10(5) M(-1) s(-1), which is much smaller than the ones for reactions of trans-resveratrol with (•)OH radicals, but still important. Since the (•)OOH half-life time is several orders larger than the one of the (•)OH radical, it should contribute significantly to trans-resveratrol oxidation in aqueous biological media. Thus, trans-resveratrol may act as an efficient (•)OOH, and also presumably (•)OOR, radical scavenger. PMID:22475027

  20. Hydroxyl radical oxidation of feruloylated arabinoxylan.

    PubMed

    Bagdi, Attila; Tömösközi, Sándor; Nyström, Laura

    2016-11-01

    Feruloylated arabinoxylan (AX) has a unique capacity to form covalent gels in the presence of certain oxidizing agents. The present study demonstrates that hydroxyl radical oxidation does not provoke ferulic acid dimerization and thus oxidative gelation. We studied the hydroxyl radical mediated oxidation of an alkali-extracted AX preparation (purity: 92g/100g dry matter) that showed gel-forming capability upon peroxidase/hydrogen peroxide treatment. Hydroxyl radicals were produced with ascorbate-driven Fenton reaction and the radical formation was monitored with electron paramagnetic resonance, using a POBN/EtOH spin trapping system. Oxidation was carried out at different catalytic concentrations of iron (50 and 100μM) and at different temperatures (20°C, 50°C, and 80°C). It was demonstrated that hydroxyl radical oxidation does not provoke gel formation, but viscosity decrease in AX solution, which suggests polymer degradation. Furthermore, it was demonstrated that hydroxyl radical formation in AX solution can be initiated merely by increasing temperature. PMID:27516272

  1. Degradation of pentachlorophenol by hydroxyl radicals and sulfate radicals using electrochemical activation of peroxomonosulfate, peroxodisulfate and hydrogen peroxide.

    PubMed

    Govindan, Kadarkarai; Raja, Mohan; Noel, Michael; James, E J

    2014-05-15

    The present study is to investigate the reactivity of free radicals (SO4(-) and HO) generated from common oxidants (peroxomonosulfate (PMS), peroxodisulfate (PDS) and hydrogen peroxide (HP)) activated by electrochemically generated Fe(2+)/Fe(3+) ions which furthermore are evaluated to destroy pentachlorophenol (PCP) in aqueous solution. The effect of solution pH and amount of oxidants (PMS, PDS and HP) in electrocoagulation (EC) on PCP degradation is analyzed in detail. The experimental results reveal that, optimum initial solution pH is 4.5 and PMS is more efficient oxidant addition in EC. 75% PCP degradation is achieved at 60min electrolysis time from PMS assisted EC. According to the first order rate constant, faster PCP degradation rate is obtained by PMS assisted EC. The PCP degradation rate by oxidant assisted EC is observed in the following order: EC/PMS>EC/PDS>EC/HP>EC. Further to identify the influences of experimental factors involved in PCP degradation by oxidant assisted EC, an experimental design based on an orthogonal array (OA) L9 (3(3)) is proposed using Taguchi method. The factors that most significantly affect the process robustness are identified as A (oxidant) and B (pH) which together account for nearly 86% of the variance.

  2. A comparative study of the hydroxyl radical scavenging capacity of activated sludge and membrane bioreactor wastewater effluents.

    PubMed

    Grant, Jacque-Ann; Hofmann, Ron

    2016-01-01

    This study evaluated the hydroxyl radical scavenging characteristics of wastewater from five membrane bioreactor (MBR) and five activated sludge (AS) systems. The average values of the characteristics of both wastewater types was found to be significantly different at a 90% confidence interval in terms UV absorbance at 254 nm, alkalinity, and biopolymer concentration. Effluent organic matter (EfOM), with an average kOH,EfOM of (2.75 ± 1.04) × 10(8) M(-1)s(-1), was identified as the primary hydroxyl scavenger contributing to >70% of the background scavenging in all cases, except when nitrite exceeded 0.3 mg NO(2)(-)-N/L. The average scavenging capacity, EfOM scavenging capacity, and the EfOM reaction rate constant of the AS wastewaters exceeded that of the MBR. However, due to the small sample size (n = 5) and considerable variability in scavenging characteristics among the MBR wastewaters, the difference in EfOM reactivity between the two wastewaters was not statistically significant at a 90% confidence interval. Nevertheless, these preliminary findings suggest the possibility that MBR wastewaters may be more amenable to treatment by advanced oxidation. A plausible explanation is that MBRs were observed to reject biopolymers, and a strong correlation was observed between EfOM scavenging capacity and biopolymer concentration.

  3. A comparative study of the hydroxyl radical scavenging capacity of activated sludge and membrane bioreactor wastewater effluents.

    PubMed

    Grant, Jacque-Ann; Hofmann, Ron

    2016-01-01

    This study evaluated the hydroxyl radical scavenging characteristics of wastewater from five membrane bioreactor (MBR) and five activated sludge (AS) systems. The average values of the characteristics of both wastewater types was found to be significantly different at a 90% confidence interval in terms UV absorbance at 254 nm, alkalinity, and biopolymer concentration. Effluent organic matter (EfOM), with an average kOH,EfOM of (2.75 ± 1.04) × 10(8) M(-1)s(-1), was identified as the primary hydroxyl scavenger contributing to >70% of the background scavenging in all cases, except when nitrite exceeded 0.3 mg NO(2)(-)-N/L. The average scavenging capacity, EfOM scavenging capacity, and the EfOM reaction rate constant of the AS wastewaters exceeded that of the MBR. However, due to the small sample size (n = 5) and considerable variability in scavenging characteristics among the MBR wastewaters, the difference in EfOM reactivity between the two wastewaters was not statistically significant at a 90% confidence interval. Nevertheless, these preliminary findings suggest the possibility that MBR wastewaters may be more amenable to treatment by advanced oxidation. A plausible explanation is that MBRs were observed to reject biopolymers, and a strong correlation was observed between EfOM scavenging capacity and biopolymer concentration. PMID:27148707

  4. Linear free energy relationships between aqueous phase hydroxyl radical reaction rate constants and free energy of activation.

    PubMed

    Minakata, Daisuke; Crittenden, John

    2011-04-15

    The hydroxyl radical (HO(•)) is a strong oxidant that reacts with electron-rich sites on organic compounds and initiates complex radical chain reactions in aqueous phase advanced oxidation processes (AOPs). Computer based kinetic modeling requires a reaction pathway generator and predictions of associated reaction rate constants. Previously, we reported a reaction pathway generator that can enumerate the most important elementary reactions for aliphatic compounds. For the reaction rate constant predictor, we develop linear free energy relationships (LFERs) between aqueous phase literature-reported HO(•) reaction rate constants and theoretically calculated free energies of activation for H-atom abstraction from a C-H bond and HO(•) addition to alkenes. The theoretical method uses ab initio quantum mechanical calculations, Gaussian 1-3, for gas phase reactions and a solvation method, COSMO-RS theory, to estimate the impact of water. Theoretically calculated free energies of activation are found to be within approximately ±3 kcal/mol of experimental values. Considering errors that arise from quantum mechanical calculations and experiments, this should be within the acceptable errors. The established LFERs are used to predict the HO(•) reaction rate constants within a factor of 5 from the experimental values. This approach may be applied to other reaction mechanisms to establish a library of rate constant predictions for kinetic modeling of AOPs. PMID:21410278

  5. Evaluation of free hydroxyl radical scavenging activities of some Chinese herbs by capillary zone electrophoresis with amperometric detection.

    PubMed

    Li, Hui; Wang, Qingjiang

    2004-04-01

    Due to the severe damage caused by free hydroxyl radicals (OH.) to cells and tissues, there is much interest in finding and studying effective and non-toxic OH. scavengers, including traditional Chinese herbs. In this paper, the simple and highly-sensitive technique of capillary zone electrophoresis with amperometric detection (CZE-AD) was used to study the OH. scavenging activities of aqueous extracts from some traditional Chinese herbs. Salicylic acid (SAL) was used as an OH. trap, and the content of OH. could be determined by assaying their products, 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA). The optimum conditions for CZE-AD for the determination of 2,3-DHBA and 2,5-DHBA were explored. The linearity ranges of 2,3-DHBA and 2,5-DHBA were 1.0 x10(-7) approximately 1.0 x10(-4) mol L(-1), and their detection limits were as low as 2 x 10(-8) mol L(-1), which were much better than the CE-UV method often used. The traditional Chinese herbs studied included Radix angelicae sinensis, Rhizoma coptidis, Ligustrum lucidum, Ligusticum wallichii, Radices glycyrrhizae and Semen plantaginis. The experiments showed that the aqueous extracts from all of the above traditional Chinese herds had free OH. scavenging activities, although to different degrees. PMID:14985912

  6. Hydroxyl radical generation by red tide algae.

    PubMed

    Oda, T; Akaike, T; Sato, K; Ishimatsu, A; Takeshita, S; Muramatsu, T; Maeda, H

    1992-04-01

    The unicellular marine phytoplankton Chattonella marina is known to have toxic effects against various living marine organisms, especially fishes. However, details of the mechanism of the toxicity of this plankton remain obscure. Here we demonstrate the generation of superoxide and hydroxyl radicals from a red tide unicellular organism, C. marina, by using ESR spectroscopy with the spin traps 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and N-t-butyl-alpha-phenylnitrone (PBN), and by using the luminol-enhanced chemiluminescence response. The spin-trapping assay revealed productions of spin adduct of superoxide anion (O2-) (DMPO-OOH) and that of hydroxyl radical (.OH) (DMPO-OH) in the algal suspension, which was not observed in the ultrasonic-ruptured suspension. The addition of superoxide dismutase (500 U/ml) almost completely inhibited the formation of both DMPO-OOH and DMPO-OH, and carbon-centered radicals were generated with the disappearance of DMPO-OH after addition of 5% dimethyl sulfoxide (Me2SO) and 5% ethanol. Furthermore, the generation of methyl and methoxyl radicals, which are thought to be produced by the reaction of hydroxyl radical and Me2SO under aerobic condition, was identified using spin trapping with a combination of PBN and Me2SO. Luminol-enhanced chemiluminescence assay also supported the above observations. These results clearly indicate that C. marina generates and releases the superoxide radical followed by the production of hydroxyl radical to the surrounding environment. The velocity of superoxide generation by C. marina was about 100 times faster than that by mammalian phagocytes per cell basis. The generation of oxygen radical is suggested to be a pathogenic principle in the toxication of red tide to susceptible aquaculture fishes and may be directly correlated with the coastal pollution by red tide.

  7. Hydroxyl radical scavenging reactivity of proton pump inhibitors.

    PubMed

    Simon, Wolfgang Alexander; Sturm, Ernst; Hartmann, Hans-Jürgen; Weser, Ulrich

    2006-04-28

    In addition to the established control of acid secretion of the class of proton pump inhibitors (PPI) reactivity from the pyridyl methyl sulphinyl benzimidazole type a second independent anti-inflammatory reactivity was observed in vitro. This inhibitory reactivity was clearly noticed using three different assays where the aggressive hydroxyl radicals were successfully trapped in a concentration dependent manner. There is unequivocal evidence that the proton pump inhibitors having the sulphoxide group are able to scavenge hydroxyl radicals which are generated during a Fenton reaction. By way of contrast, the corresponding thioethers were substantially less active. No detectable effect was seen in the superoxide radical scavenging system. In conclusion, pantoprazole as well as the other proton pump inhibitors have a pronounced inhibitory reactivity towards hydroxyl radicals.

  8. MEASUREMENT OF HYDROXYL RADICAL ACTIVITY IN A SOIL SLURRY USING THE SPIN TRAP A-(4-PYRIDYL-1-OXIDE)-N-TERT-BUTYLNITRONE

    EPA Science Inventory

    The spin trap compound a-(4-pyridyl-1-oxide)N-tert-butylnitrone (4-POBN) served as a probe to estimate the activity of Fenton-derived hydroxyl radicals (.OH) in a batch suspension comprised of silica sand and crushes goethite ore. The rate of probe disappearance was used to anal...

  9. Novel hydroxyl radical scavenging antioxidant activity assay for water-soluble antioxidants using a modified CUPRAC method.

    PubMed

    Bektaşoğlu, Burcu; Esin Celik, Saliha; Ozyürek, Mustafa; Güçlü, Kubilay; Apak, Reşat

    2006-07-01

    Reactive oxygen species (ROS) such as superoxide anion, hydroxyl ((*)OH), peroxyl, and alkoxyl radicals may attack biological macromolecules giving rise to oxidative stress-originated diseases. Since (*)OH is very short-lived, secondary products resulting from (*)OH attack to various probes are measured. Although the measurement of aromatic hydroxylation with HPLC/electrochemical detection is more specific than the low-yield TBARS test, it requires sophisticated instrumentation. As a more convenient and less costly alternative, we used p-aminobenzoate, 2,4- and 3,5-dimethoxybenzoate probes for detecting hydroxyl radicals generated from an equivalent mixture of Fe(II)+EDTA with hydrogen peroxide. The produced hydroxyl radicals attacked both the probe and the water-soluble antioxidants in 37 degrees C-incubated solutions for 2h. The CUPRAC (i.e., our original method for total antioxidant capacity assay) absorbance of the ethylacetate extract due to the reduction of Cu(II)-neocuproine reagent by the hydroxylated probe decreased in the presence of (*)OH scavengers, the difference being proportional to the scavenging ability of the tested compound. A rate constant for the reaction of the scavenger with hydroxyl radical can be deduced from the inhibition of color formation. The second-order rate constants of the scavengers were determined with competition kinetics by means of a linear plot of A(0)/A as a function of C(scavenger)/C(probe), where A(0) and A are the CUPRAC absorbances of the system in the absence and presence of scavenger, respectively, and C is the molar concentration of relevant species. The 2,4- and 3,5-dimethoxybenzoates were the best probes in terms of linearity and sensitivity. Iodide, metabisulfite, hexacyanoferrate(II), thiourea, formate, and dimethyl sulfoxide were shown by the modified CUPRAC assay to be more effective scavengers than mannitol, glucose, lysine, and simple alcohols, as in the TBARS assay. The developed method is less lengthy, more

  10. Rate Constants and Activation Energies for Gas‐Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical

    PubMed Central

    Safron, Andreas; Strandell, Michael; Kierkegaard, Amelie

    2015-01-01

    ABSTRACT Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second‐order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140‐mL gas‐phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D4 and D5 with the OH radical are 1.9 × 10−12 (95% confidence interval (CI): (1.7–2.2) × 10−12) and 2.6 × 10−12 (CI: (2.3–2.9) × 10−12) cm3 molecule−1 s−1, respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D6 is 2.8 × 10−12 (CI: (2.5–3.2) × 10−12) cm3 molecule−1 s−1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D5 were 33% higher than for D4 (CI: 30–37%), whereas the rates for D6 were only 8% higher than for D5 (CI: 5–10%). The activation energies of the reactions of D4, D5, and D6 with OH were not statistically different and had a value of 4300 ± 2800 J/mol.

  11. Hydroxyl radical induced degradation of ibuprofen.

    PubMed

    Illés, Erzsébet; Takács, Erzsébet; Dombi, András; Gajda-Schrantz, Krisztina; Rácz, Gergely; Gonter, Katalin; Wojnárovits, László

    2013-03-01

    Pulse radiolysis experiments were used to characterize the intermediates formed from ibuprofen during electron beam irradiation in a solution of 0.1mmoldm(-3). For end product characterization (60)Co γ-irradiation was used and the samples were evaluated either by taking their UV-vis spectra or by HPLC with UV or MS detection. The reactions of OH resulted in hydroxycyclohexadienyl type radical intermediates. The intermediates produced in further reactions hydroxylated the derivatives of ibuprofen as final products. The hydrated electron attacked the carboxyl group. Ibuprofen degradation is more efficient under oxidative conditions than under reductive conditions. The ecotoxicity of the solution was monitored by Daphnia magna standard microbiotest and Vibrio fischeri luminescent bacteria test. The toxic effect of the aerated ibuprofen solution first increased upon irradiation indicating a higher toxicity of the first degradation products, then decreased with increasing absorbed dose.

  12. Petroleum films exposed to sunlight produce hydroxyl radical.

    PubMed

    Ray, Phoebe Z; Tarr, Matthew A

    2014-05-01

    Sunlight exposed oil films on seawater or pure water produced substantial amounts of hydroxyl radical as a result of irradiation. Oil was collected from the surface of the Gulf of Mexico following the Deepwater Horizon spill and exposed to simulated sunlight in thin films over water. Photochemical production of hydroxyl radical was measured with benzoic acid as a selective chemical probe in the aqueous layer. Total hydroxyl radical formation was studied using high benzoic acid concentrations and varying exposure time. The total amount of hydroxyl radical produced in 24 h irradiations of thin oil films over Gulf of Mexico water and pure water were 3.7×10(-7) and 4.2×10(-7) moles respectively. Steady state concentrations of hydroxyl radical were measured using a competition kinetics approach. Hydroxyl radical concentrations of 1.2×10(-16) to 2.4×10(-16) M were observed for seawater and pure water under oil films. Titanium dioxide (TiO2) nanomaterials were added to the system in an effort to determine if the photocatalyst would enhance oil photodegradation. The addition of TiO2 nanoparticles dramatically changed the observed formation rate of hydroxyl radical in the systems with NP water at pH 3, showing increased formation rate in many cases. With photocatalyst, the steady state concentration of radical decreased, predominantly due to an increase in the hydroxyl radical scavenging rate with oxide present. This study illustrates that oil is a strong and important source of hydroxyl radical when exposed to sunlight. The fate of oil and other dissolved species following oil spills will be heavily dependent on the formation and fate of hydroxyl radical.

  13. Petroleum films exposed to sunlight produce hydroxyl radical.

    PubMed

    Ray, Phoebe Z; Tarr, Matthew A

    2014-05-01

    Sunlight exposed oil films on seawater or pure water produced substantial amounts of hydroxyl radical as a result of irradiation. Oil was collected from the surface of the Gulf of Mexico following the Deepwater Horizon spill and exposed to simulated sunlight in thin films over water. Photochemical production of hydroxyl radical was measured with benzoic acid as a selective chemical probe in the aqueous layer. Total hydroxyl radical formation was studied using high benzoic acid concentrations and varying exposure time. The total amount of hydroxyl radical produced in 24 h irradiations of thin oil films over Gulf of Mexico water and pure water were 3.7×10(-7) and 4.2×10(-7) moles respectively. Steady state concentrations of hydroxyl radical were measured using a competition kinetics approach. Hydroxyl radical concentrations of 1.2×10(-16) to 2.4×10(-16) M were observed for seawater and pure water under oil films. Titanium dioxide (TiO2) nanomaterials were added to the system in an effort to determine if the photocatalyst would enhance oil photodegradation. The addition of TiO2 nanoparticles dramatically changed the observed formation rate of hydroxyl radical in the systems with NP water at pH 3, showing increased formation rate in many cases. With photocatalyst, the steady state concentration of radical decreased, predominantly due to an increase in the hydroxyl radical scavenging rate with oxide present. This study illustrates that oil is a strong and important source of hydroxyl radical when exposed to sunlight. The fate of oil and other dissolved species following oil spills will be heavily dependent on the formation and fate of hydroxyl radical. PMID:24405967

  14. Presence of Hydrogen Peroxide, a Source of Hydroxyl Radicals, in Acid Electrolyzed Water

    PubMed Central

    Mokudai, Takayuki; Nakamura, Keisuke; Kanno, Taro; Niwano, Yoshimi

    2012-01-01

    Background Acid electrolyzed water (AEW), which is produced through the electrolysis of dilute sodium chloride (NaCl) or potassium chloride solution, is used as a disinfectant in various fields because of its potent antimicrobial activity. The hydroxyl radical, an oxygen radical species, is often suggested as a putative active ingredient for AEW antimicrobial activity. Methodology/Principal Findings The aim of the present study is to detect hydroxyl radicals in AEW. The hydroxyl radicals in AEW prepared under different conditions were determined using an electron spin resonance (ESR) technique. A signal from 5,5-dimethyl-1-pyrroline N-oxide (DMPO)-OH, an adduct of DMPO and the hydroxyl radical, was detected in AEW prepared by double or triple electrolyses of 1% NaCl but not of 0.1% NaCl solution. Then the presence of hydrogen peroxide as a proposed source of hydroxyl radicals was examined using a combination of ESR and a Fenton reaction. The DMPO-OH signal was clearly detected, even in AEW prepared by single electrolysis of 0.1% NaCl solution, when ferrous sulfate was added to induce a Fenton reaction, indicating the presence of hydrogen peroxide in the AEW. Since sodium formate, a hydroxyl radical scavenger, did not affect the bactericidal activity of AEW, it is concluded that the radical is unlikely to contribute to the antimicrobial activity of AEW, although a small amount of the radical is produced from hydrogen peroxide. Dimethyl sulfoxide, the other hydroxyl radical scavenger used in the present study, canceled the bactericidal activity of AEW, accompanied by complete depletion of free available chlorine, suggesting that hypochlorous acid is probably a major contributor to the antimicrobial activity. Conclusions It is strongly suggested that although hydrogen peroxide is present in AEW as a source of hydroxyl radicals, the antimicrobial activity of AEW does not depend on these radicals. PMID:23029505

  15. Effects of hydroxyl radical scavengers KCN and CO on ultraviolet light-induced activation of crude soluble guanylate cyclase

    SciTech Connect

    Karlsson, J.O.; Axelsson, K.L.; Andersson, R.G.

    1985-01-01

    The crude soluble guanylate cyclase (GC) from bovine mesenteric artery was stimulated by ultraviolet (UV) light (366 nm). Addition of free radical scavengers, dimethylsulfoxide or superoxide dismutase and/or catalase to the GC assay did not abolish the stimulatory effect of UV light. On the contrary, the UV light-induced activation was enhanced in the presence of these scavengers. KCN (1 mM) did not affect the UV light-induced activation, while 0.1 mM of CO potentiated the activation. These results may indicate that UV light is operating through a direct interaction with the ferrous form of the GC-heme.

  16. Hydroxyl radical mediated DNA base modification by manmade mineral fibres.

    PubMed Central

    Leanderson, P; Söderkvist, P; Tagesson, C

    1989-01-01

    Manmade mineral fibres (MMMFs) were examined for their ability to hydroxylate 2-deoxyguanosine (dG) to 8-hydroxydeoxyguanosine (8-OH-dG), a reaction that is mediated by hydroxyl radicals. It appeared that (1) catalase and the hydroxyl radical scavengers, dimethylsulphoxide and sodium benzoate, inhibited the hydroxylation, whereas Fe2+ and H2O2 potentiated it; (2) pretreatment of MMMFs with the iron chelator, deferoxamine, or with extensive heat (200-400 degrees C), attenuated the hydroxylation; (3) the hydroxylation obtained by various MMMFs varied considerably; (4) there was no apparent correlation between the hydroxylation and the surface area of different MMMFs, although increasing the surface area of a fibre by crushing it increased its hydroxylating capacity; and (5) there was good correlation between the hydroxylation of dG residues in DNA and the hydroxylation of pure dG in solution for the 16 different MMMFs investigated. These findings indicate that MMMFs cause a hydroxyl radical mediated DNA base modification in vitro and that there is considerable variation in the reactivity of different fibre species. The DNA modifying ability seems to depend on physical or chemical characteristics, or both, of the fibre. PMID:2765416

  17. Hydroxyl radical production in plasma electrolysis with KOH electrolyte solution

    NASA Astrophysics Data System (ADS)

    Saksono, Nelson; Febiyanti, Irine Ayu; Utami, Nissa; Ibrahim

    2015-12-01

    Plasma electrolysis is an effective technology for producing hydroxyl radical (•OH). This method can be used for waste degradation process. This study was conducted to obtain the influence of applied voltage, electrolyte concentration, and anode depth in the plasma electrolysis system for producing hydroxyl radical. The materials of anode and cathode, respectively, were made from tungsten and stainless steel. KOH solution was used as the solution. Determination of hydroxyl radical production was done by measuring H2O2 amount formed in plasma system using an iodometric titration method, while the electrical energy consumed was obtained by measuring the electrical current throughout the process. The highest hydroxyl radical production was 3.51 mmol reached with 237 kJ energy consumption in the power supply voltage 600 V, 0.02 M KOH, and 0.5 cm depth of anode.

  18. Hydroxyl radical production in plasma electrolysis with KOH electrolyte solution

    SciTech Connect

    Saksono, Nelson; Febiyanti, Irine Ayu Utami, Nissa; Ibrahim

    2015-12-29

    Plasma electrolysis is an effective technology for producing hydroxyl radical (•OH). This method can be used for waste degradation process. This study was conducted to obtain the influence of applied voltage, electrolyte concentration, and anode depth in the plasma electrolysis system for producing hydroxyl radical. The materials of anode and cathode, respectively, were made from tungsten and stainless steel. KOH solution was used as the solution. Determination of hydroxyl radical production was done by measuring H{sub 2}O{sub 2} amount formed in plasma system using an iodometric titration method, while the electrical energy consumed was obtained by measuring the electrical current throughout the process. The highest hydroxyl radical production was 3.51 mmol reached with 237 kJ energy consumption in the power supply voltage 600 V, 0.02 M KOH, and 0.5 cm depth of anode.

  19. Chemical repair activity of free radical scavenger edaravone: reduction reactions with dGMP hydroxyl radical adducts and suppression of base lesions and AP sites on irradiated plasmid DNA.

    PubMed

    Hata, Kuniki; Urushibara, Ayumi; Yamashita, Shinichi; Lin, Mingzhang; Muroya, Yusa; Shikazono, Naoya; Yokoya, Akinari; Fu, Haiying; Katsumura, Yosuke

    2015-01-01

    Reactions of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) with deoxyguanosine monophosphate (dGMP) hydroxyl radical adducts were investigated by pulse radiolysis technique. Edaravone was found to reduce the dGMP hydroxyl radical adducts through electron transfer reactions. The rate constants of the reactions were greater than 4 × 10(8) dm(3) mol(-1) s(-1) and similar to those of the reactions of ascorbic acid, which is a representative antioxidant. Yields of single-strand breaks, base lesions, and abasic sites produced in pUC18 plasmid DNA by gamma ray irradiation in the presence of low concentrations (10-1000 μmol dm(-3)) of edaravone were also quantified, and the chemical repair activity of edaravone was estimated by a method recently developed by the authors. By comparing suppression efficiencies to the induction of each DNA lesion, it was found that base lesions and abasic sites were suppressed by the chemical repair activity of edaravone, although the suppression of single-strand breaks was not very effective. This phenomenon was attributed to the chemical repair activity of edaravone toward base lesions and abasic sites. However, the chemical repair activity of edaravone for base lesions was lower than that of ascorbic acid.

  20. Environmental Implications of Hydroxyl Radicals ((•)OH).

    PubMed

    Gligorovski, Sasho; Strekowski, Rafal; Barbati, Stephane; Vione, Davide

    2015-12-23

    The hydroxyl radical ((•)OH) is one of the most powerful oxidizing agents, able to react unselectively and instantaneously with the surrounding chemicals, including organic pollutants and inhibitors. The (•)OH radicals are omnipresent in the environment (natural waters, atmosphere, interstellar space, etc.), including biological systems where (•)OH has an important role in immunity metabolism. We provide an extensive view on the role of hydroxyl radical in different environmental compartments and in laboratory systems, with the aim of drawing more attention to this emerging issue. Further research on processes related to the hydroxyl radical chemistry in the environmental compartments is highly demanded. A comprehensive understanding of the sources and sinks of (•)OH radicals including their implications in the natural waters and in the atmosphere is of crucial importance, including the way irradiated chromophoric dissolved organic matter in surface waters yields (•)OH through the H2O2-independent pathway, and the assessment of the relative importance of gas-phase vs aqueous-phase reactions of (•)OH with many atmospheric components. Moreover, considering the fact that people spend so much more time in dwellings than outside, the impact of the reactivity of indoor hydroxyl radicals on health and well-being is another emerging research topic of great concern.

  1. Mapping nucleic acid structure by hydroxyl radical cleavage.

    PubMed

    Tullius, Thomas D; Greenbaum, Jason A

    2005-04-01

    Hydroxyl radical footprinting is a widely used method for following the folding of RNA molecules in solution. This method has the unique ability to provide experimental information on the solvent accessibility of each nucleotide in an RNA molecule, so that the folding of all domains of the RNA species can be followed simultaneously at single-nucleotide resolution. In recent work, hydroxyl radical footprinting has been used, often in combination with other global measures of structure, to work out detailed folding pathways and three-dimensional structures for increasingly large and complicated RNA molecules. These include synthetic ribozymes, and group I and group II ribozymes, from yeast, the Azoarcus cyanobacterium and Tetrahymena thermophila. Advances have been made in methods for analysis of hydroxyl radical data, so that the large datasets that result from kinetic folding experiments can be analyzed in a semi-automated and quantitative manner.

  2. A statistical description of the evolution of cloud condensation nuclei activity during the heterogeneous oxidation of squalane and bis(2-ethylhexyl) sebacate aerosol by hydroxyl radicals.

    PubMed

    Harmon, Christopher W; Ruehl, Christopher R; Cappa, Christopher D; Wilson, Kevin R

    2013-06-28

    The heterogeneous reaction of hydroxyl radicals with chemically reduced organic aerosol comprised of either squalane or bis(2-ethylhexyl) sebacate are used as model systems to examine how cloud condensation nuclei (CCN) activity evolves with photochemical oxidation. Over the course of the reaction, the critical super-saturation evolves both by the formation of new oxygen functional groups and by changes in aerosol size through the formation of gas phase reaction products. A statistical model of the heterogeneous reaction reveals that it is the formation, volatilization, solubility, and surface activity of many generations of oxidation products that together control the average changes in aerosol hygroscopicity. The experimental observations and model demonstrate the importance of considering the underlying population or subpopulation of species within a particle and how they each uniquely contribute to the average hygroscopicity of a multi-component aerosol. To accurately predict changes in CCN activity upon oxidation requires a reduction in the surface tension of the activating droplet by a subpopulation of squalane reaction products. These results provide additional evidence that surface tension-concentration parameterizations based on macroscopic data should be modified for microscopic droplets.

  3. Radiocarbon tracer measurements of atmospheric hydroxyl radical concentrations

    NASA Technical Reports Server (NTRS)

    Campbell, M. J.; Farmer, J. C.; Fitzner, C. A.; Henry, M. N.; Sheppard, J. C.

    1986-01-01

    The usefulness of the C-14 tracer in measurements of atmospheric hydroxyl radical concentration is discussed. The apparatus and the experimental conditions of three variations of a radiochemical method of atmosphere analysis are described and analyzed: the Teflon bag static reactor, the flow reactor (used in the Wallops Island tests), and the aircraft OH titration reactor. The procedure for reduction of the aircraft reactor instrument data is outlined. The problems connected with the measurement of hydroxyl radicals are discussed. It is suggested that the gas-phase radioisotope methods have considerable potential in measuring tropospheric impurities present in very low concentrations.

  4. Accelerated crystallization of zeolites via hydroxyl free radicals.

    PubMed

    Feng, Guodong; Cheng, Peng; Yan, Wenfu; Boronat, Mercedes; Li, Xu; Su, Ji-Hu; Wang, Jianyu; Li, Yi; Corma, Avelino; Xu, Ruren; Yu, Jihong

    2016-03-11

    In the hydrothermal crystallization of zeolites from basic media, hydroxide ions (OH(-)) catalyze the depolymerization of the aluminosilicate gel by breaking the Si,Al-O-Si,Al bonds and catalyze the polymerization of the aluminosilicate anions around the hydrated cation species by remaking the Si,Al-O-Si,Al bonds. We report that hydroxyl free radicals (•OH) are involved in the zeolite crystallization under hydrothermal conditions. The crystallization processes of zeolites-such as Na-A, Na-X, NaZ-21, and silicalite-1-can be accelerated with hydroxyl free radicals generated by ultraviolet irradiation or Fenton's reagent.

  5. Iron-induced hydroxyl radical generation from basaltic volcanic ash

    NASA Astrophysics Data System (ADS)

    Horwell, C. J.; Fenoglio, I.; Fubini, B.

    2007-09-01

    Iron-induced hydroxyl radical generation from the surface of volcanic ash particles is a possible mechanism of respiratory toxicity in addition to crystalline silica induced pathogenicity. Here we show that volcanic ash generates hydroxyl radicals, with greater reactivity in iron-rich, silica-poor samples, such as basaltic ash. Basaltic particles expose at the surface high levels of poorly-coordinated iron ions in both Fe(II) and Fe(III) oxidation states which are likely to be the cause of such reactivity. Hitherto, basaltic ash has been disregarded as a hazard due to the lack of crystalline silica particulate but future hazard assessment should consider its toxic potential.

  6. Visible light activity of pulsed layer deposited BiVO4/MnO2 films decorated with gold nanoparticles: The evidence for hydroxyl radicals formation

    NASA Astrophysics Data System (ADS)

    Trzciński, Konrad; Szkoda, Mariusz; Sawczak, Mirosław; Karczewski, Jakub; Lisowska-Oleksiak, Anna

    2016-11-01

    Thin films containing BiVO4 and MnO2 deposited on FTO and modified by Au nanoparticles were studied towards their photoelectrochemical and photocatalytical activities in an aqueous electrolyte. Electrodes were prepared by the pulsed laser deposition (PLD) method. The surfactant-free ablation process was used for preparation of the gold nanoparticles (GNP) water suspension. Obtained layers of varied thicknesses (27-115 nm) were characterized using Raman spectroscopy, UV-vis spectroscopy and scanning electron microscopy. Electrochemical methods such as electrochemical impedance spectroscopy, linear voltammetry and chronoamperometry under visible light illumination and in the dark were applied to characterize layers as photoanodes. Simple modification of the BiVO4 + MnO2 layer by drop-casting of small amount of colloidal gold (1.5 × 10-14 mol of GNP on 1 cm2) leads to enhancement of the generated photocurrent recorded at E = 0.5 V vs. Ag/AgCl (0.1 M KCl) from 63 μA/cm2 to 280 μA/cm2. Photocatalytical studies were also exploited towards decomposition of methylene blue (MB). A possible mechanism of MB photodegradation was proposed. The formation of hydroxyl radicals was detected by photoluminescence spectra using terephthalic acid as the probe molecule.

  7. Antrodia camphorata Potentiates Neuroprotection against Cerebral Ischemia in Rats via Downregulation of iNOS/HO-1/Bax and Activated Caspase-3 and Inhibition of Hydroxyl Radical Formation.

    PubMed

    Yang, Po-Sheng; Lin, Po-Yen; Chang, Chao-Chien; Yu, Meng-Che; Yen, Ting-Lin; Lan, Chang-Chou; Jayakumar, Thanasekaran; Yang, Chih-Hao

    2015-01-01

    Antrodia camphorata (A. camphorata) is a fungus generally used in Chinese folk medicine for treatment of viral hepatitis and cancer. Our previous study found A. camphorata has neuroprotective properties and could reduce stroke injury in cerebral ischemia animal models. In this study, we sought to investigate the molecular mechanisms of neuroprotective effects of A. camphorata in middle cerebral artery occlusion (MCAO) rats. A selective occlusion of the middle cerebral artery (MCA) with whole blood clots was used to induce ischemic stroke in rats and they were orally treated with A. camphorata (0.25 and 0.75 g/kg/day) alone or combined with aspirin (5 mg/kg/day). To provide insight into the functions of A. camphorata mediated neuroprotection, the expression of Bax, inducible nitric oxide synthase (iNOS), haem oxygenase-1 (HO-1), and activated caspase-3 was determined by Western blot assay. Treatment of aspirin alone significantly reduced the expressions of HO-1 (P < 0.001), iNOS (P < 0.001), and Bax (P < 0.01) in ischemic regions. The reduction of these expressions was more potentiated when rats treated by aspirin combined with A. camphorata (0.75 g/kg/day). Combination treatment also reduced apoptosis as measured by a significant reduction in active caspase-3 expression in the ischemic brain compared to MCAO group (P < 0.01). Moreover, treatment of A. camphorata significantly (P < 0.05) reduced fenton reaction-induced hydroxyl radical (OH(•)) formation at a dose of 40 mg/mL. Taken together, A. camphorata has shown neuroprotective effects in embolic rats, and the molecular mechanisms may correlate with the downregulation of Bax, iNOS, HO-1, and activated caspase-3 and the inhibition of OH(•) signals.

  8. Antrodia camphorata Potentiates Neuroprotection against Cerebral Ischemia in Rats via Downregulation of iNOS/HO-1/Bax and Activated Caspase-3 and Inhibition of Hydroxyl Radical Formation

    PubMed Central

    Yang, Po-Sheng; Lin, Po-Yen; Chang, Chao-Chien; Yu, Meng-Che; Yen, Ting-Lin; Lan, Chang-Chou; Jayakumar, Thanasekaran; Yang, Chih-Hao

    2015-01-01

    Antrodia camphorata (A. camphorata) is a fungus generally used in Chinese folk medicine for treatment of viral hepatitis and cancer. Our previous study found A. camphorata has neuroprotective properties and could reduce stroke injury in cerebral ischemia animal models. In this study, we sought to investigate the molecular mechanisms of neuroprotective effects of A. camphorata in middle cerebral artery occlusion (MCAO) rats. A selective occlusion of the middle cerebral artery (MCA) with whole blood clots was used to induce ischemic stroke in rats and they were orally treated with A. camphorata (0.25 and 0.75 g/kg/day) alone or combined with aspirin (5 mg/kg/day). To provide insight into the functions of A. camphorata mediated neuroprotection, the expression of Bax, inducible nitric oxide synthase (iNOS), haem oxygenase-1 (HO-1), and activated caspase-3 was determined by Western blot assay. Treatment of aspirin alone significantly reduced the expressions of HO-1 (P < 0.001), iNOS (P < 0.001), and Bax (P < 0.01) in ischemic regions. The reduction of these expressions was more potentiated when rats treated by aspirin combined with A. camphorata (0.75 g/kg/day). Combination treatment also reduced apoptosis as measured by a significant reduction in active caspase-3 expression in the ischemic brain compared to MCAO group (P < 0.01). Moreover, treatment of A. camphorata significantly (P < 0.05) reduced fenton reaction-induced hydroxyl radical (OH•) formation at a dose of 40 mg/mL. Taken together, A. camphorata has shown neuroprotective effects in embolic rats, and the molecular mechanisms may correlate with the downregulation of Bax, iNOS, HO-1, and activated caspase-3 and the inhibition of OH• signals. PMID:26379739

  9. Hydroxyl radical induced degradation of salicylates in aerated aqueous solution

    NASA Astrophysics Data System (ADS)

    Szabó, László; Tóth, Tünde; Homlok, Renáta; Rácz, Gergely; Takács, Erzsébet; Wojnárovits, László

    2014-04-01

    Ionizing radiation induced degradation of acetylsalicylic acid, its hydrolysis product salicylic acid and a salicylic acid derivative 5-sulpho-salicylic acid, was investigated in dilute aqueous solutions by UV-vis spectrophotometry, HPLC separation and diode-array or MS/MS detection, chemical oxygen demand, total organic carbon content and by Vibrio fischeri toxicity measurements. Hydroxyl radicals were shown to degrade these molecules readily, and first degradation products were hydroxylated derivatives in all cases. Due to the by-products, among them hydrogen peroxide, the toxicity first increased and then decreased with the absorbed dose. With prolonged irradiation complete mineralization was achieved.

  10. Environmentally persistent free radicals (EPFRs)-2. Are free hydroxyl radicals generated in aqueous solutions?

    PubMed

    Khachatryan, Lavrent; Dellinger, Barry

    2011-11-01

    A chemical spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy was employed to measure the production of hydroxyl radical (·OH) in aqueous suspensions of 5% Cu(II)O/silica (3.9% Cu) particles containing environmentally persistent free radicals (EPFRs) of 2-monochlorophenol (2-MCP). The results indicate: (1) a significant differences in accumulated DMPO-OH adducts between EPFR containing particles and non-EPFR control samples, (2) a strong correlation between the concentration of DMPO-OH adducts and EPFRs per gram of particles, and (3) a slow, constant growth of DMPO-OH concentration over a period of days in solution containing 50 μg/mL EPFRs particles + DMPO (150 mM) + reagent balanced by 200 μL phosphate buffered (pH = 7.4) saline. However, failure to form secondary radicals using standard scavengers, such as ethanol, dimethylsulfoxide, sodium formate, and sodium azide, suggests free hydroxyl radicals may not have been generated in solution. This suggests surface-bound, rather than free, hydroxyl radicals were generated by a surface catalyzed-redox cycle involving both the EPFRs and Cu(II)O. Toxicological studies clearly indicate these bound free radicals promote various types of cardiovascular and pulmonary disease normally attributed to unbound free radicals; however, the exact chemical mechanism deserves further study in light of the implication of formation of bound, rather than free, hydroxyl radicals.

  11. Post-ischaemic mild hypothermia inhibits apoptosis in the penumbral region by reducing neuronal nitric oxide synthase activity and thereby preventing endothelin-1-induced hydroxyl radical formation.

    PubMed

    Van Hemelrijck, An; Hachimi-Idrissi, Said; Sarre, Sophie; Ebinger, Guy; Michotte, Yvette

    2005-09-01

    Previously, we showed that treatment with resuscitative, post-ischaemic mild hypothermia (34 degrees C for 2 h) reduced apoptosis in the penumbra (cortex), but not in the core (striatum) of an endothelin-1 (Et-1)-induced focal cerebral infarct in the anaesthetized rat. Therefore, the purpose of this study was to investigate by which pathways resuscitative mild hypothermia exerts its neuroprotective effect in this model. The amino acids glutamate, serine, glutamine, alanine, taurine, arginine and the NO-related compound citrulline were sampled from the striatum and cortex of the ischaemic hemisphere using in vivo microdialysis. The in vivo salicylate trapping method was applied for monitoring hydroxyl radical formation via 2,3 dihydroxybenzoic acid (2,3 DHBA) detection. Caspase-3, neuronal nitric oxide synthase (nNOS) immunoreactivity and the volume of ischaemic damage were determined 24 h after the insult. In both the striatum and the cortex, Et-1-induced increases in glutamate, taurine and alanine were refractory to mild hypothermia. However, mild hypothermia significantly attenuated the ischaemia-induced 2,3 DHBA levels and the nNOS immunoreactivity in the cortex, but not in the striatum. These observations were associated with a decreased caspase-3 immunoreactivity. These results suggest that mild hypothermia exerts its neuroprotective effect in the penumbra partially by reducing nNOS activity and thereby preventing oxidative stress. Furthermore, we confirm our previous findings that the neuroprotective effect of resuscitative hypothermia is not mediated by changes in ischaemia-induced amino acid release as they could not be associated with the ischaemia-induced damage in the Et-1 rat model.

  12. Treating ballast water with hydroxyl radical on introduced organisms

    NASA Astrophysics Data System (ADS)

    Zhang, Zhitao; Bai, Mindi; Xiao, Yu; Bai, Mindong; Yang, Bo; Bai, Xiyao

    2006-06-01

    With physical method of micro-gap gas discharge, a large amount of hydroxyl radical can be produced in 20t/h pilot-scale system using the ionization of O2 and H2O. In this paper, the effect of biochemistry of hydroxyl radicals on introduced organisms in ballast water was experimentally investigated. The results indicate that the contents of chlorophyl- a, chlorophyl- b, chlorophyl- c and carotenoid are decreased by 35% 64% within 8.0s and further to the lowest limit of test 5 minutes. In addition, the main reasons of cell death are the lipid peroxidation, the strong destruction to the monose, amylose, protein, DNA and RNA of cell, and damage in CAT, POD and SOD of antioxidant enzyme system.

  13. Photochemical formation of hydroxyl radical by constituents of natural waters

    SciTech Connect

    Vaughan, P.P.; Blough, N.V.

    1998-10-01

    A new method is employed to determine the rates of photochemical hydroxyl radical (OH) formation in aqueous solutions and in natural waters under both aerobic and anaerobic conditions. Quantum yields for OH formation from the photolysis of nitrate and nitrite obtained by this method are in good agreement with previous measurements. Photolysis of Suwannee River fulvic acid (SRFA) solutions produced the hydroxyl radical under anaerobic conditions in proportion to the SRFA concentration. Under aerobic conditions, the quantum yields for OH formation were slightly higher and exhibited a different wavelength dependence than those obtained under anaerobic conditions. Experiments employing catalase indicate that Fenton chemistry can account for at most 50% of the total signal under aerobic conditions for SRFA irradiated at 310 and 320 nm. These results indicate the presence of a dioxygen-independent pathway of hydroxyl radical production that cannot be assigned to nitrate/nitrite photolysis or to Fenton chemistry. Results from the preliminary application of this method to natural waters are also presented.

  14. Generation of hydroxyl radicals from metal-loaded humic acids

    SciTech Connect

    Paciolla, M.D.; Jansen, S.A.; Davies, G.

    1999-06-01

    Humic acids (HAs) are naturally occurring biopolymers that are ubiquitous in the environment. They are most commonly found in the soil, drinking water, and a variety of plants. Pharmacological and therapeutic studies involving humic acids have been reported to some extent. However, when certain transition metals are bound to humic acids, e.g., iron and copper, they can be harmful to biological organisms. For this study, humic acids were extracted from German, Irish, and New Hampshire soils that were selectively chosen because of their reich abundance in humic material. Each sample was treated at room temperature with 0.1 M ferric and cupric solutions for 48 h. The amount of iron and copper adsorbed by humic acid was accurately quantitated using atomic absorption spectroscopy. The authors further demonstrate that these metal-loaded humic acids can produce deleterious oxidizing species such as the hydroxyl radical (HO*) through the metal-driven Fenton reaction. Electron paramagnetic resonance (EPR) employing spin trapping techniques with 5,5-dimethylpyrroline N-oxide (DMPO) is used to confirm the generation of hydroxyl radicals. The DMPO-OH adduct with hyperfine splitting constants A{sub N} = A{sub H} = 14.9 G is observed upon the addition of exogenous hydrogen peroxide. The concentration of hydroxyl radical was determined using 4-hydroxytempo (TEMPO-OH) as a spin standard. The presence of another oxidizing species, Fe{double_bond}O{sup 2+}, is also proposed in the absence of hydrogen peroxide.

  15. Methyl-esterified 3-hydroxybutyrate oligomers protect bacteria from hydroxyl radicals.

    PubMed

    Koskimäki, Janne J; Kajula, Marena; Hokkanen, Juho; Ihantola, Emmi-Leena; Kim, Jong H; Hautajärvi, Heidi; Hankala, Elina; Suokas, Marko; Pohjanen, Johanna; Podolich, Olga; Kozyrovska, Natalia; Turpeinen, Ari; Pääkkönen, Mirva; Mattila, Sampo; Campbell, Bruce C; Pirttilä, Anna Maria

    2016-05-01

    Bacteria rely mainly on enzymes, glutathione and other low-molecular weight thiols to overcome oxidative stress. However, hydroxyl radicals are the most cytotoxic reactive oxygen species, and no known enzymatic system exists for their detoxification. We now show that methyl-esterified dimers and trimers of 3-hydroxybutyrate (ME-3HB), produced by bacteria capable of polyhydroxybutyrate biosynthesis, have 3-fold greater hydroxyl radical-scavenging activity than glutathione and 11-fold higher activity than vitamin C or the monomer 3-hydroxybutyric acid. We found that ME-3HB oligomers protect hypersensitive yeast deletion mutants lacking oxidative stress-response genes from hydroxyl radical stress. Our results show that phaC and phaZ, encoding polymerase and depolymerase, respectively, are activated and polyhydroxybutyrate reserves are degraded for production of ME-3HB oligomers in bacteria infecting plant cells and exposed to hydroxyl radical stress. We found that ME-3HB oligomer production is widespread, especially in bacteria adapted to stressful environments. We discuss how ME-3HB oligomers could provide opportunities for numerous applications in human health. PMID:26974813

  16. Effects of iron on Vitamin C/copper-induced hydroxyl radical generation in bicarbonate-rich water.

    PubMed

    Jansson, Patric J; Del Castillo, Urko; Lindqvist, Christer; Nordström, Tommy

    2005-05-01

    The aim of this study was to evaluate whether iron, like copper, could support Vitamin C mediated hydroxyl radical formation in bicarbonate-rich water. By using the hydroxyl radical indicator coumarin-3-carboxylic acid, we found that iron, in contrast to copper, was not capable to support Vitamin C induced hydroxyl radical formation. However, when 0.2 mg/l iron and 0.1 mg/l copper were both added to bicarbonate supplemented Milli-Q water, the Vitamin C induced formation of 7-hydroxycoumarin, as measured by HPLC analysis, was inhibited by 47.5%. The inhibition of hydroxyl radical formation by iron was also evident in the experiments performed on copper contaminated bicarbonate-rich household drinking water samples. In the presence of 0.2 mg/l of ferric iron the ascorbic acid induced hydroxyl radical formation was inhibited by 36.0-44.6%. This inhibition was even more significant, 47.0-59.2%, when 0.8 mg/l of ferric iron was present. None of the other redox-active metals, e.g. manganese, nickel or cobalt, could support ascorbic acid induced hydroxyl radical formation and did not have any impact on the ascorbic acid/copper-induced hydroxyl radical generation. Our results show, that iron cannot by itself produce hydroxyl radicals in bicarbonate rich water but can significantly reduce Vitamin C/copper-induced hydroxyl radical formation. These findings might partly explain the mechanism for the iron-induced protective effect on various copper related degenerative disorders that earlier has been observed in animal model systems. PMID:16036332

  17. Citrulline, a novel compatible solute in drought-tolerant wild watermelon leaves, is an efficient hydroxyl radical scavenger.

    PubMed

    Akashi, K; Miyake, C; Yokota, A

    2001-11-23

    Drought-tolerant wild watermelon accumulates high levels of citrulline in the leaves in response to drought conditions. In this work, the hydroxyl radical-scavenging activity of citrulline was investigated in vitro. The second-order rate constant for the reaction between citrulline and hydroxyl radicals was found to be 3.9x10(9) M(-1) s(-1), demonstrating that citrulline is one of the most efficient scavengers among compatible solutes examined so far. Moreover, citrulline effectively protected DNA and an enzyme from oxidative injuries. Liquid chromatography-mass spectrometry analysis revealed that at least four major products were formed by the reaction between citrulline and hydroxyl radicals. Activities of metabolic enzymes were not inhibited by up to 600 mM citrulline, indicating that citrulline does not interfere with cellular metabolism. We reasoned, from these results, that citrulline contributes to oxidative stress tolerance under drought conditions as a novel hydroxyl radical scavenger. PMID:11728468

  18. Future Directions of Structural Mass Spectrometry using Hydroxyl Radical Footprinting

    SciTech Connect

    J Kiselar; M Chance

    2011-12-31

    Hydroxyl radical protein footprinting coupled to mass spectrometry has been developed over the last decade and has matured to a powerful method for analyzing protein structure and dynamics. It has been successfully applied in the analysis of protein structure, protein folding, protein dynamics, and protein-protein and protein-DNA interactions. Using synchrotron radiolysis, exposure of proteins to a 'white' X-ray beam for milliseconds provides sufficient oxidative modification to surface amino acid side chains, which can be easily detected and quantified by mass spectrometry. Thus, conformational changes in proteins or protein complexes can be examined using a time-resolved approach, which would be a valuable method for the study of macromolecular dynamics. In this review, we describe a new application of hydroxyl radical protein footprinting to probe the time evolution of the calcium-dependent conformational changes of gelsolin on the millisecond timescale. The data suggest a cooperative transition as multiple sites in different molecular subdomains have similar rates of conformational change. These findings demonstrate that time-resolved protein footprinting is suitable for studies of protein dynamics that occur over periods ranging from milliseconds to seconds. In this review, we also show how the structural resolution and sensitivity of the technology can be improved as well. The hydroxyl radical varies in its reactivity to different side chains by over two orders of magnitude, thus oxidation of amino acid side chains of lower reactivity are more rarely observed in such experiments. Here we demonstrate that the selected reaction monitoring (SRM)-based method can be utilized for quantification of oxidized species, improving the signal-to-noise ratio. This expansion of the set of oxidized residues of lower reactivity will improve the overall structural resolution of the technique. This approach is also suggested as a basis for developing hypothesis

  19. Quantum Chemical Study on the Antioxidation Mechanism of Piceatannol and Isorhapontigenin toward Hydroxyl and Hydroperoxyl Radicals.

    PubMed

    Lu, Yang; Wang, AiHua; Shi, Peng; Zhang, Hui; Li, ZeSheng

    2015-01-01

    A systematic study of the antioxidation mechanisms behind hydroxyl (•OH) and hydroperoxyl (•OOH) radical scavenging activity of piceatannol (PIC) and isorhapontigenin (ISO) was carried out using density functional theory (DFT) method. Two reaction mechanisms, abstraction (ABS) and radical adduct formation (RAF), were discussed. A total of 24 reaction pathways of scavenging •OH and •OOH with PIC and ISO were investigated in the gas phase and solution. The thermodynamic and kinetic properties of all pathways were calculated. Based on these results, we evaluated the antioxidant activity of every active site of PIC and ISO and compared the abilities of PIC and ISO to scavenge radicals. According to our results, PIC and ISO may act as effective •OH and •OOH scavengers in organism. A4-hydroxyl group is a very important active site for PIC and ISO to scavenge radicals. The introducing of -OH or -OCH3 group to the ortho-position of A4-hydroxyl group would increase its antioxidant activity. Meanwhile, the conformational effect was researched, the results suggest that the presence and pattern of intramolecular hydrogen bond (IHB) are considerable in determining the antioxidant activity of PIC and ISO.

  20. Quantum Chemical Study on the Antioxidation Mechanism of Piceatannol and Isorhapontigenin toward Hydroxyl and Hydroperoxyl Radicals

    PubMed Central

    Lu, Yang; Wang, AiHua; Shi, Peng; Zhang, Hui; Li, ZeSheng

    2015-01-01

    A systematic study of the antioxidation mechanisms behind hydroxyl (•OH) and hydroperoxyl (•OOH) radical scavenging activity of piceatannol (PIC) and isorhapontigenin (ISO) was carried out using density functional theory (DFT) method. Two reaction mechanisms, abstraction (ABS) and radical adduct formation (RAF), were discussed. A total of 24 reaction pathways of scavenging •OH and •OOH with PIC and ISO were investigated in the gas phase and solution. The thermodynamic and kinetic properties of all pathways were calculated. Based on these results, we evaluated the antioxidant activity of every active site of PIC and ISO and compared the abilities of PIC and ISO to scavenge radicals. According to our results, PIC and ISO may act as effective •OH and •OOH scavengers in organism. A4-hydroxyl group is a very important active site for PIC and ISO to scavenge radicals. The introducing of -OH or -OCH3 group to the ortho-position of A4-hydroxyl group would increase its antioxidant activity. Meanwhile, the conformational effect was researched, the results suggest that the presence and pattern of intramolecular hydrogen bond (IHB) are considerable in determining the antioxidant activity of PIC and ISO. PMID:26176778

  1. Quantum Chemical Study on the Antioxidation Mechanism of Piceatannol and Isorhapontigenin toward Hydroxyl and Hydroperoxyl Radicals.

    PubMed

    Lu, Yang; Wang, AiHua; Shi, Peng; Zhang, Hui; Li, ZeSheng

    2015-01-01

    A systematic study of the antioxidation mechanisms behind hydroxyl (•OH) and hydroperoxyl (•OOH) radical scavenging activity of piceatannol (PIC) and isorhapontigenin (ISO) was carried out using density functional theory (DFT) method. Two reaction mechanisms, abstraction (ABS) and radical adduct formation (RAF), were discussed. A total of 24 reaction pathways of scavenging •OH and •OOH with PIC and ISO were investigated in the gas phase and solution. The thermodynamic and kinetic properties of all pathways were calculated. Based on these results, we evaluated the antioxidant activity of every active site of PIC and ISO and compared the abilities of PIC and ISO to scavenge radicals. According to our results, PIC and ISO may act as effective •OH and •OOH scavengers in organism. A4-hydroxyl group is a very important active site for PIC and ISO to scavenge radicals. The introducing of -OH or -OCH3 group to the ortho-position of A4-hydroxyl group would increase its antioxidant activity. Meanwhile, the conformational effect was researched, the results suggest that the presence and pattern of intramolecular hydrogen bond (IHB) are considerable in determining the antioxidant activity of PIC and ISO. PMID:26176778

  2. Ultraviolet irradiation-induced substitution of fluorine with hydroxyl radical for mass spectrometric analysis of perfluorooctane sulfonyl fluoride.

    PubMed

    Wang, Peng; Tang, Xuemei; Huang, Lulu; Kang, Jie; Zhong, Hongying

    2016-01-28

    A rapid and solvent free substitution reaction of a fluorine atom in perfluorooctane sulfonyl fluoride (PFOSF) with a hydroxyl radical is reported. Under irradiation of ultraviolet laser on semiconductor nanoparticles or metal surfaces, hydroxyl radicals can be generated through hole oxidization. Among all fluorine atoms of PFOSF, highly active hydroxyl radicals specifically substitute the fluorine of sulfonyl fluoride functional group. Resultant perfluorooctane sulfonic acid is further ionized through capture of photo-generated electrons that switch the neutral molecules to negatively charged odd electron hypervalent ions. The unpaired electron subsequently initiates α O-H bond cleavage and produces perfluorooctane sulfonate negative ions. Hydroxyl radical substitution and molecular dissociation of PFOSF have been confirmed by masses with high accuracy and resolution. It has been applied to direct mass spectrometric imaging of PFOSF adsorbed on surfaces of plant leaves.

  3. Ultraviolet irradiation-induced substitution of fluorine with hydroxyl radical for mass spectrometric analysis of perfluorooctane sulfonyl fluoride.

    PubMed

    Wang, Peng; Tang, Xuemei; Huang, Lulu; Kang, Jie; Zhong, Hongying

    2016-01-28

    A rapid and solvent free substitution reaction of a fluorine atom in perfluorooctane sulfonyl fluoride (PFOSF) with a hydroxyl radical is reported. Under irradiation of ultraviolet laser on semiconductor nanoparticles or metal surfaces, hydroxyl radicals can be generated through hole oxidization. Among all fluorine atoms of PFOSF, highly active hydroxyl radicals specifically substitute the fluorine of sulfonyl fluoride functional group. Resultant perfluorooctane sulfonic acid is further ionized through capture of photo-generated electrons that switch the neutral molecules to negatively charged odd electron hypervalent ions. The unpaired electron subsequently initiates α O-H bond cleavage and produces perfluorooctane sulfonate negative ions. Hydroxyl radical substitution and molecular dissociation of PFOSF have been confirmed by masses with high accuracy and resolution. It has been applied to direct mass spectrometric imaging of PFOSF adsorbed on surfaces of plant leaves. PMID:26755143

  4. Environmentally Persistent Free Radicals (EPFRs). 3. Free versus Bound Hydroxyl Radicals in EPFR Aqueous Solutions

    PubMed Central

    2015-01-01

    Additional experimental evidence is presented for in vitro generation of hydroxyl radicals because of redox cycling of environmentally persistent free radicals (EPFRs) produced after adsorption of 2-monochlorophenol at 230 °C (2-MCP-230) on copper oxide supported by silica, 5% Cu(II)O/silica (3.9% Cu). A chemical spin trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy was employed. Experiments in spiked O17 water have shown that ∼15% of hydroxyl radicals formed as a result of redox cycling. This amount of hydroxyl radicals arises from an exogenous Fenton reaction and may stay either partially trapped on the surface of particulate matter (physisorbed or chemisorbed) or transferred into solution as free OH. Computational work confirms the highly stable nature of the DMPO–OH adduct, as an intermediate produced by interaction of DMPO with physisorbed/chemisorbed OH (at the interface of solid catalyst/solution). All reaction pathways have been supported by ab initio calculations. PMID:25036238

  5. Kinetic of benzotriazole oxidation by ozone and hydroxyl radical.

    PubMed

    Vel Leitner, Nathalie Karpel; Roshani, Babak

    2010-03-01

    Ozonation experiments were performed in batch reactors in order to determine the rate constants for the reaction of molecular ozone and OH radicals with benzotriazole (BT) at different pHs. The first group of ozonation experiments was carried out for the determination of the rate constant for the direct reactions between ozone and BT. Two different kinetic models were used for the determination of kinetic rate constants: (i) the log-reduction of BT with ozone in excess, (ii) the competition kinetic model. The second-order rate constants for BT with molecular ozone were determined to be 36.4+/-3.8M(-1) s(-1) and 18.4+/-0.8M(-1) s(-1) at pH 2 from the two methods respectively. With the competition method, the value at pH 5 was found to be 22.0+/-2.0M(-1) s(-1). In a following stage, the reaction of BT with OH radicals was investigated at pH values ranging from 2 to 10.2. Using a method involving two probe compounds during the ozonation, the second-order rate constants of the BT reaction with hydroxyl radicals were determined. The rate constants were found to vary from 6.2x10(9)M(-1) s(-1) at pH 10.2 to 1.7x10(10)M(-1) s(-1) at pH 2.

  6. Spectroscopy and reaction dynamics of collision complexes containing hydroxyl radicals

    SciTech Connect

    Lester, M.I.

    1993-12-01

    The DOE supported work in this laboratory has focused on the spectroscopic characterization of the interaction potential between an argon atom and a hydroxyl radical in the ground X{sup 2}II and excited A {sup 2}{summation}{sup +} electronic states. The OH-Ar system has proven to be a test case for examining the interaction potential in an open-shell system since it is amenable to experimental investigation and theoretically tractable from first principles. Experimental identification of the bound states supported by the Ar + OH (X {sup 2}II) and Ar + OH(A {sup 2}{summation}{sup +}) potentials makes it feasible to derive realistic potential energy surfaces for these systems. The experimentally derived intermolecular potentials provide a rigorous test of ab initio theory and a basis for understanding the dramatically different collision dynamics taking place on the ground and excited electronic state surfaces.

  7. Kinetics of the reaction of hydroxyl radicals with nitric acid

    NASA Technical Reports Server (NTRS)

    Margitan, J. J.; Watson, R. T.

    1982-01-01

    An extensive study was made of the reaction of hydroxyl radicals with nitric acid in a laser photolysis-resonance fluorescence system. A 266 nm laser was used to photolyze HNO3 in the temperature range 225-415 K at pressures of 20-300 torr. A temperature dependence was detected below room temperature, with a leveling off at 298 K and a wide spread in the rate constants. A pressure dependence was observed over the entire range and was more pronounced at lower temperatures. The results are noted to be in agreement with those of previous investigations. However, the wide range of rate constants are suggested to be a problem for stratospheric HO(x) modeling for anthropogenic effects. No explanation could be given of the varying results obtained by other investigators regarding the kinetics of the reactions.

  8. Scavenging effect of melatonin on hydroxyl radicals generated by alloxan.

    PubMed

    Brömme, H J; Mörke, W; Peschke, D; Ebelt, H; Peschke, D

    2000-11-01

    Alloxan can act as a generator of reactive oxygen species (ROS) as long as sufficient suitable reducing agents (e.g. reduced glutathione) and oxygen are available. Using electron spin resonance-spectroscopy and the oxygen-centered spin trap DEPMPO, we demonstrate that hydroxyl radicals (OH.) are formed in vitro by alloxan in the presence of glutathione (GSH) and chelated divalent iron. Furthermore, peroxidation of polyunsaturated fatty acids from phosphatidylcholine-containing liposomes with concomitant formation of malondialdehyde (MDA) was used as a further indicator for a preceding OH. formation. Melatonin, the main secretory product of the pineal gland, is an effective scavenger of OH.. The 50%-inhibitor concentration (IC50-value) for melatonin to scavenge OH. generated from the alloxan/GSH-reaction in the presence of ferrous ions was 23 micromol/L. In contrast to the ability to effectively scavenge OH., the potential of melatonin to prevent lipid peroxidation is considerably less pronounced. PMID:11068942

  9. SERCA overexpression reduces hydroxyl radical injury in murine myocardium.

    PubMed

    Hiranandani, Nitisha; Bupha-Intr, Tepmanas; Janssen, Paul M L

    2006-12-01

    Hydroxyl radicals (*OH) are involved in the pathogenesis of ischemia-reperfusion injury and are observed in clinical situations, including acute heart failure, stroke, and myocardial infarction. Acute transient exposure to *OH causes an intracellular Ca(2+) overload and leads to impaired contractility. We investigated whether upregulation of sarcoplasmic reticulum Ca(2+)-ATPase function (SERCA) can attenuate *OH-induced dysfunction. Small, contracting right ventricular papillary muscles from wild-type (WT) SERCA1a-overexpressing (transgenic, TG) and SERCA2a heterogeneous knockout (HET) mice were directly exposed to *OH. This brief 2-min exposure led to a transient elevation of diastolic force (F(dia)) and depression of developed force (F(dev)). In WT mice, F(dia) increased to 485 +/- 49% and F(dev) decreased to 11 +/- 3%. In sharp contrast, in TG mice F(dia) increased only to 241 +/- 17%, whereas F(dev) decreased only to 51 +/- 5% (P < 0.05 vs. WT). In HET mice, F(dia) rose more than WT (to 597 +/- 20%, P < 0.05), whereas F(dev) was reduced in a similar amount. After approximately 45 min after *OH exposure, a new steady state was reached: F(dev) returned to 37 +/- 6% and 32 +/- 6%, whereas F(dia) came back to 238 +/- 28% and 292 +/- 17% in WT and HET mice, respectively. In contrast, the sustained dysfunction was significantly less in TG mice: F(dia) and F(dev) returned to 144 +/- 20% and 67 +/- 6%, respectively. Before exposure to *OH, there is decrease in phospholamban (PLB) phosphorylation at Ser16 (pPLBSer16) and PLB phosphorylation at Thr17 (pPLBThr17) in TG mice and an increase in pPLBSer16 and pPLBThr17 in HET mice versus WT. After exposure to *OH there is decrease in pPLBSer16 in WT, TG, and HET mice but no significant change in the level of pPLBThr17 in any group. The results indicate that SERCA overexpression can reduce the *OH-induced contractile dysfunction in murine myocardium, whereas a reduced SR Ca(2+)-ATPase activity aggravates this injury. Loss of

  10. Hydroxylated chalcones with dual properties: Xanthine oxidase inhibitors and radical scavengers.

    PubMed

    Hofmann, Emily; Webster, Jonathan; Do, Thuy; Kline, Reid; Snider, Lindsey; Hauser, Quintin; Higginbottom, Grace; Campbell, Austin; Ma, Lili; Paula, Stefan

    2016-02-15

    In this study, we evaluated the abilities of a series of chalcones to inhibit the activity of the enzyme xanthine oxidase (XO) and to scavenge radicals. 20 mono- and polyhydroxylated chalcone derivatives were synthesized by Claisen-Schmidt condensation reactions and then tested for inhibitory potency against XO, a known generator of reactive oxygen species (ROS). In parallel, the ability of the synthesized chalcones to scavenge a stable radical was determined. Structure-activity relationship analysis in conjunction with molecular docking indicated that the most active XO inhibitors carried a minimum of three hydroxyl groups. Moreover, the most effective radical scavengers had two neighboring hydroxyl groups on at least one of the two phenyl rings. Since it has been proposed previously that XO inhibition and radical scavenging could be useful properties for reduction of ROS-levels in tissue, we determined the chalcones' effects to rescue neurons subjected to ROS-induced stress created by the addition of β-amyloid peptide. Best protection was provided by chalcones that combined good inhibitory potency with high radical scavenging ability in a single molecule, an observation that points to a potential therapeutic value of this compound class.

  11. Analysis of Hydroxyl Radical Reactivity in the Sierra Nevada Mountains

    NASA Astrophysics Data System (ADS)

    Carlstad, J. M.; Schroeder, J.; Beyersdorf, A. J.; Blake, D. R.

    2015-12-01

    Using the UC Irvine Whole Air Sampler, volatile organic compounds (VOCs) were measured onboard the NASA DC-8 during the Student Airborne Research Program. High levels of ozone were observed near the surface over the Sierra Nevada mountains, and VOC data was used to investigate factors that contributed to ozone production. This was done by calculating the hydroxyl radical reactivity, which can, in proper conditions, be used to predict ozone formation potential. The region was divided into three boxes from east to west, based on wind direction, and the reactivity was analyzed over each region with respect to methane, non-methane alkanes, alkenes, aromatics, and biogenic compounds. In the westernmost box the reactivity was 1.7 ± 0.5 s-1 (1σ), in the middle section it was 1.4 ± 1 s-1, and in the easternmost region it was 0.8 ± 0.3 s-1. The data were compared with a region known to be heavily polluted, the Los Angeles (LA) basin, and it was observed that the reactivity was 1.1 ± 0.6 s-1, lower than in two of the mountainous regions. In the Sierra Nevada mountains a major percentage of the hydroxyl radical reactivity was the result of biogenic influence, at 24% for the western box, 39% for the middle box, and 31% for the easternmost box, in contrast to only 2% biogenic contribution in LA. This indicates that biogenic factors greatly contributed to overall ozone formation in the Sierra Nevada mountains. These mountains are strategically protected, and high pollution levels could lead to health impacts for visitors, vegetation, and wildlife.

  12. Comparison of fluorescence-based techniques for the quantification of particle-induced hydroxyl radicals

    PubMed Central

    Cohn, Corey A; Simon, Sanford R; Schoonen, Martin AA

    2008-01-01

    Background Reactive oxygen species including hydroxyl radicals can cause oxidative stress and mutations. Inhaled particulate matter can trigger formation of hydroxyl radicals, which have been implicated as one of the causes of particulate-induced lung disease. The extreme reactivity of hydroxyl radicals presents challenges to their detection and quantification. Here, three fluorescein derivatives [aminophenyl fluorescamine (APF), amplex ultrared, and dichlorofluorescein (DCFH)] and two radical species, proxyl fluorescamine and tempo-9-ac have been compared for their usefulness to measure hydroxyl radicals generated in two different systems: a solution containing ferrous iron and a suspension of pyrite particles. Results APF, amplex ultrared, and DCFH react similarly to the presence of hydroxyl radicals. Proxyl fluorescamine and tempo-9-ac do not react with hydroxyl radicals directly, which reduces their sensitivity. Since both DCFH and amplex ultrared will react with reactive oxygen species other than hydroxyl radicals and another highly reactive species, peroxynitite, they lack specificity. Conclusion The most useful probe evaluated here for hydroxyl radicals formed from cell-free particle suspensions is APF due to its sensitivity and selectivity. PMID:18307787

  13. Scavenging of hydroxyl radicals generated in human plasma following X-ray irradiation.

    PubMed

    Hosokawa, Yoichiro; Sano, Tomoaki

    2015-11-01

    There are various antioxidant materials that scavenge free radicals in human plasma. It is possible that the radical-scavenging function causes a radiation protective effect in humans. This study estimated the hydroxyl (OH) radical-scavenging activity induced by X-ray irradiation in human plasma. The test subjects included 111 volunteers (75 males and 36 females) ranging from 22 to 35 years old (average, 24.0). OH radicals generated in irradiated human plasma were measured by electron spin resonance (ESR). The relationships between the amount of the OH radical and chemical and biological parameters [total protein, total cholesterol, triglycerides and hepatitis B surface (HBs) antibodies] were estimated in the plasma of the 111 volunteers by a multivariate analysis. The presence of HBs antibodies had the greatest influence on OH radical-scavenging activity. One volunteer who did not have the HBs antibody was given an inoculation of the hepatitis B vaccine. There was a remarkable decrease in the amount of OH radical generated from plasma after the HBs antibody was produced. The results indicate that the HBs antibody is an important factor for the scavenging of OH radicals initiated by X-ray irradiation in the human body.

  14. A pro-chelator triggered by hydrogen peroxide inhibits iron-promoted hydroxyl radical formation.

    PubMed

    Charkoudian, Louise K; Pham, David M; Franz, Katherine J

    2006-09-27

    The synthesis and structural characterization of a new pro-chelating agent, isonicotinic acid [2-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-benzylidene]-hydrazide (BSIH), are presented. BSIH only weakly interacts with iron unless hydrogen peroxide (H2O2) is present to remove the boronic ester protecting group to reveal a phenol that is a key metal-binding group of tridentate salicylaldehyde isonicotinoyl hydrazone (SIH). BSIH prevents deoxyribose degradation caused by hydroxyl radicals that are generated from H2O2 and redox-active iron by sequestering Fe3+ and preventing iron-promoted hydroxyl radical formation. The rate-determining step for iron sequestration is conversion of BSIH to SIH, followed by rapid Fe3+ complexation. The pro-chelate approach of BSIH represents a promising strategy for chelating a specific pool of detrimental metal ions without disturbing healthy metal ion distribution.

  15. A pro-chelator triggered by hydrogen peroxide inhibits iron-promoted hydroxyl radical formation.

    PubMed

    Charkoudian, Louise K; Pham, David M; Franz, Katherine J

    2006-09-27

    The synthesis and structural characterization of a new pro-chelating agent, isonicotinic acid [2-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-benzylidene]-hydrazide (BSIH), are presented. BSIH only weakly interacts with iron unless hydrogen peroxide (H2O2) is present to remove the boronic ester protecting group to reveal a phenol that is a key metal-binding group of tridentate salicylaldehyde isonicotinoyl hydrazone (SIH). BSIH prevents deoxyribose degradation caused by hydroxyl radicals that are generated from H2O2 and redox-active iron by sequestering Fe3+ and preventing iron-promoted hydroxyl radical formation. The rate-determining step for iron sequestration is conversion of BSIH to SIH, followed by rapid Fe3+ complexation. The pro-chelate approach of BSIH represents a promising strategy for chelating a specific pool of detrimental metal ions without disturbing healthy metal ion distribution. PMID:16984186

  16. Photocatalytic oxidation of arsenic(III): evidence of hydroxyl radicals.

    PubMed

    Dutta, Paritam K; Pehkonen, S O; Sharma, Virender K; Ray, Ajay K

    2005-03-15

    Arsenic contamination has been found in the groundwater of several countries. Photocatalysis can rapidly oxidize arsenite (As(III)) to less labile and less toxic arsenate (As(V)), which then can be removed by adsorption onto photocatalyst surfaces. This study investigates the photocatalytic oxidation of As(III) to As(V) as a function of As(III) concentration, pH, catalyst loading, light intensity, dissolved oxygen concentration, type of TiO2 surfaces, and ferric ions to understand the kinetics and the mechanism of As(III) oxidation in the UV/TiO2 system. Photocatalytic oxidation of As(III) to As(V) takes place in minutes and follows zero-order kinetics. Benzoic acid (BA) was used as a hydroxyl radical (.OH) scavenger to provide evidence for the .OH as the main oxidant for oxidation of As(III). The .OH radical was independently generated by nitrate photolysis, and kinetics of As(III) oxidation by the .OH radical was determined. Formation of salicylic acid (SA) from the oxidation of BA by .OH also demonstrates the involvement of .OH in the mechanism of As(III) oxidation. The effect of Fe(III) on As(III) oxidation at different pH values with and without TiO2 under UV light was examined. The results suggest that .OH is the dominant oxidant for As(III) oxidation. Two commercially available TiO2 suspensions, Degussa P25 and Hombikat UV100, were tested for the removal of arsenic through oxidation of As(III) to As(V) followed by adsorption of As(V) onto TiO2 surfaces. Results showed that complete removal of arsenic below the World Health Organization drinking water limit of 10 microg/L could be achieved.

  17. Spin trapping endogenous radicals in MC-1010 cells: evidence for hydroxyl radical and carbon-centered ascorbyl radical adducts.

    PubMed

    Bernofsky, C; Bandara, B M

    1995-07-19

    Incubation of MC-1010 cells with the spin-trapping agent 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) followed by brief treatment with the solid oxidant lead dioxide (PbO2) yielded, after filtration, a cell-free solution that contained two nitroxyl adducts. The first was the hydroxyl radical adduct, 5,5-dimethyl-2-hydroxypyrrolidine-1-oxyl (DMPO-OH), which formed immediately upon PbO2 oxidation. The second had a 6-line EPR spectrum typical of a carbon-centered radical (AN = 15.9 G; AH = 22.4 G) and formed more slowly. No radical signals were detected in the absence of either cells or PbO2 treatment. The 6-line spectrum could be duplicated in model systems that contained ascorbate, DMPO and DMPO-OH, where the latter was formed from hydroxyl radicals generated by sonolysis or the cleavage of hydrogen peroxide with Fe2+ (Fenton reaction). In addition, enrichment of MC-1010 cells with ascorbate prior to spin trapping yielded the 6-line EPR spectrum as the principal adduct following PbO2 oxidation and filtration. These results suggest that ascorbate reacted with DMPO-OH to form a carbon-centered ascorbyl radical that was subsequently trapped by DMPO. The requirement for mild oxidation to detect the hydroxyl radical adduct suggests that DMPO-OH formed in the cells was reduced to an EPR-silent form (i.e., the hydroxylamine derivative). Alternatively, the hydroxylamine derivative was the species initially formed. The evidence for endogenous hydroxyl radical formation in unstimulated leukocytes may be relevant to the leukemic nature of the MC-1010 cell line. The spin trapping of the ascorbyl radical is the first report of formation of the carbon-centered ascorbyl radical by means other than pulse radiolysis. Unless it is spin trapped, the carbon-centered ascorbyl radical immediately rearranges to the more stable oxygen-centered species that is passive to spin trapping and characterized by the well-known EPR doublet of AH4 = 1.8 G.

  18. The reaction of methyl peroxy and hydroxyl radicals as a major source of atmospheric methanol

    PubMed Central

    Müller, Jean-François; Liu, Zhen; Nguyen, Vinh Son; Stavrakou, Trissevgeni; Harvey, Jeremy N.; Peeters, Jozef

    2016-01-01

    Methyl peroxy, a key radical in tropospheric chemistry, was recently shown to react with the hydroxyl radical at an unexpectedly high rate. Here, the molecular reaction mechanisms are elucidated using high-level quantum chemical methodologies and statistical rate theory. Formation of activated methylhydrotrioxide, followed by dissociation into methoxy and hydroperoxy radicals, is found to be the main reaction pathway, whereas methylhydrotrioxide stabilization and methanol formation (from activated and stabilized methylhydrotrioxide) are viable minor channels. Criegee intermediate formation is found to be negligible. Given the theoretical uncertainties, useful constraints on the yields are provided by atmospheric methanol measurements. Using a global chemistry-transport model, we show that the only explanation for the high observed methanol abundances over remote oceans is the title reaction with an overall methanol yield of ∼30%, consistent with the theoretical estimates given their uncertainties. This makes the title reaction a major methanol source (115 Tg per year), comparable to global terrestrial emissions. PMID:27748363

  19. The reaction of methyl peroxy and hydroxyl radicals as a major source of atmospheric methanol

    NASA Astrophysics Data System (ADS)

    Müller, Jean-François; Liu, Zhen; Nguyen, Vinh Son; Stavrakou, Trissevgeni; Harvey, Jeremy N.; Peeters, Jozef

    2016-10-01

    Methyl peroxy, a key radical in tropospheric chemistry, was recently shown to react with the hydroxyl radical at an unexpectedly high rate. Here, the molecular reaction mechanisms are elucidated using high-level quantum chemical methodologies and statistical rate theory. Formation of activated methylhydrotrioxide, followed by dissociation into methoxy and hydroperoxy radicals, is found to be the main reaction pathway, whereas methylhydrotrioxide stabilization and methanol formation (from activated and stabilized methylhydrotrioxide) are viable minor channels. Criegee intermediate formation is found to be negligible. Given the theoretical uncertainties, useful constraints on the yields are provided by atmospheric methanol measurements. Using a global chemistry-transport model, we show that the only explanation for the high observed methanol abundances over remote oceans is the title reaction with an overall methanol yield of ~30%, consistent with the theoretical estimates given their uncertainties. This makes the title reaction a major methanol source (115 Tg per year), comparable to global terrestrial emissions.

  20. Coumestan inhibits radical-induced oxidation of DNA: is hydroxyl a necessary functional group?

    PubMed

    Xi, Gao-Lei; Liu, Zai-Qun

    2014-06-18

    Coumestan is a natural tetracycle with a C═C bond shared by a coumarin moiety and a benzofuran moiety. In addition to the function of the hydroxyl group on the antioxidant activity of coumestan, it is worth exploring the influence of the oxygen-abundant scaffold on the antioxidant activity as well. In this work, seven coumestans containing electron-withdrawing and electron-donating groups were synthesized to evaluate the abilities to trap 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS(•+)), 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH), and galvinoxyl radical, respectively, and to inhibit the oxidations of DNA mediated by (•)OH, Cu(2+)/glutathione (GSH), and 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), respectively. It was found that all of the coumestans used herein can quench the aforementioned radicals and can inhibit (•)OH-, Cu(2+)/GSH-, and AAPH-induced oxidations of DNA. In particular, substituent-free coumestan exhibits higher ability to quench DPPH and to inhibit AAPH-induced oxidation of DNA than Trolox. In addition, nonsubstituted coumestan shows a similar ability to inhibit (•)OH- and Cu(2+)/GSH-induced oxidations of DNA relative to that of Trolox. The antioxidant effectiveness of the coumestan can be attributed to the lactone in the coumarin moiety and, therefore, a hydroxyl group may not be a necessary functional group for coumestan to be an antioxidant.

  1. Hydroxyl radical oxidation of cylindrospermopsin (cyanobacterial toxin) and its role in the photochemical transformation.

    PubMed

    Song, Weihua; Yan, Shuwen; Cooper, William J; Dionysiou, Dionysios D; O'Shea, Kevin E

    2012-11-20

    Cylindrospermopsin (CYN), an alkaloid guanidinium sulfated toxin, is produced by a number of cyanobacteria regularly found in lakes, rivers, and reservoirs. Steady-state and time-resolved radiolysis methods were used to determine reaction pathways and kinetic parameters for the reactions of hydroxyl radical with CYN. The absolute bimolecular reaction rate constant for the reaction of hydroxyl radical with CYN is (5.08 ± 0.16) × 10(9) M(-1) s(-1). Comparison of the overall reaction rate of CYN with hydroxyl radical with the individual reaction rate for addition to the uracil ring in CYN indicate the majority of the hydroxyl radicals (84%) react at the uracil functionality of CYN. Product analyses using liquid chromatography-mass spectrometry indicate the major products from the reaction of hydroxyl radical with CYN involve attack of hydroxyl radical at the uracil ring and hydrogen abstraction from the hydroxy-methine bridge linking the uracil ring to the tricyclic guanidine functionality. The role of hydroxyl radical initiated pathways in the natural organic matter (NOM) photosensitized transformation of CYN were evaluated. Scavenger and trapping experiments indicate that hydroxyl radical mediated transformations account for approximately ~70% of CYN destruction in surface waters under solar irradiation in the presence of NOM. The absence of solvent isotope effect indicates singlet oxygen does not play a significant role in the NOM sensitized transformation of CYN. The primary degradation pathways for HO• mediated and NOM photosensitized destruction of CYN involve destruction of the uracil ring. The fundamental kinetic parameters determined from these studies are critical for the accurate evaluation of hydroxyl-radical based technologies for the remediation of this problematic cyanotoxin in drinking water and important in the assessment of the environmental oxidative transformation of uracil based compounds. PMID:23082747

  2. Reaction mechanism between carbonyl oxide and hydroxyl radical: a theoretical study.

    PubMed

    Mansergas, Alex; Anglada, Josep M

    2006-03-23

    The reaction mechanism of carbonyl oxide with hydroxyl radical was investigated by using CASSCF, B3LYP, QCISD, CASPT2, and CCSD(T) theoretical approaches with the 6-311+G(d,p), 6-311+G(2df, 2p), and aug-cc-pVTZ basis sets. This reaction involves the formation of H2CO + HO2 radical in a process that is computed to be exothermic by 57 kcal/mol. However, the reaction mechanism is very complex and begins with the formation of a pre-reactive hydrogen-bonded complex and follows by the addition of HO radical to the carbon atom of H2COO, forming the intermediate peroxy-radical H2C(OO)OH before producing formaldehyde and hydroperoxy radical. Our calculations predict that both the pre-reactive hydrogen-bonded complex and the transition state of the addition process lie energetically below the enthalpy of the separate reactants (DeltaH(298K) = -6.1 and -2.5 kcal/mol, respectively) and the formation of the H2C(OO)OH adduct is exothermic by about 74 kcal/mol. Beyond this addition process, further reaction mechanisms have also been investigated, which involve the abstraction of a hydrogen of carbonyl oxide by HO radical, but the computed activation barriers suggest that they will not contribute to the gas-phase reaction of H2COO + HO.

  3. Ginsenoside Rb1 directly scavenges hydroxyl radical and hypochlorous acid.

    PubMed

    Lü, Jian-Ming; Weakley, Sarah M; Yang, Zhen; Hu, Ming; Yao, Qizhi; Chen, Changyi

    2012-01-01

    Reactive oxygen species (ROS) have been implicated in a variety of inflammatory diseases including cardiovascular disease (CVD), cancer, diabetes, Alzheimer's disease, autism, cataracts and aging. When endogenous mechanisms for the maintenance of redox homeostasis are overwhelmed, dietary intake of antioxidants contributes substantially to balancing the body's oxidant/antioxidant status. Ginsenosides are thought to be primarily responsible for the pharmacological effect of P. ginseng root extracts on oxidative stress and inflammation. However, little is known about the underlying antioxidant mechanisms of individual ginsenoside; specifically, the reactivity of ginsenoside Rb1 with ROS has not been well studied. We found that Rb1 can significantly and selectively reduce hydroxyl radical (●OH) and hypochlorous acid (HOCl), two of the strongest ROS, with unique molecular mechanisms in a cell-free system. Rb1 directly scavenges the ●OH and protects plasmid DNA from damage induced by ●OH. ●OH likely attacks the double bond on the side chain of Rb1 as well as hydrogen atoms adjacent to the -OH groups, including those of sugar moieties. Rb1 also shows a high reactivity to HOCl and effectively inhibits HOCl-induced tyrosine chlorination in a cell free system. HOCl is added to the double bond of Rb1; the -Cl group and -OH group of HOCl possibly bond at C-24 and C-25 of Rb1 based on the regioselectivity of Markovnikov's Rule. To our knowledge, this is the first demonstration that ginsenoside Rb1 scavenges HOCl and protects tyrosine from HOCl-induced chlorination. Thus, this study reveals unique antioxidant mechanisms of individual ginsenoside Rb1, which may contribute to the pharmacological effect of P. ginseng and to the development of effective strategies for clinical applications of ginsenosides.

  4. Ratiometric coumarin-neutral red (CONER) nanoprobe for detection of hydroxyl radicals.

    PubMed

    Ganea, Gabriela M; Kolic, Paulina E; El-Zahab, Bilal; Warner, Isiah M

    2011-04-01

    Excessive production of reactive oxygen species can lead to alteration of cellular functions responsible for many diseases including cardiovascular diseases, neurodegenerative diseases, cancer, and aging. Hydroxyl radical is a short-lived radical which is considered very aggressive due to its high reactivity toward biological molecules. In this study, a COumarin-NEutral Red (CONER) nanoprobe was developed for detection of hydroxyl radical based on the ratiometric fluorescence signal between 7-hydroxy coumarin 3-carboxylic acid and neutral red dyes. Biocompatible poly lactide-co-glycolide (PLGA) nanoparticles containing encapsulated neutral red were produced using a coumarin 3-carboxylic acid conjugated poly(sodium N-undecylenyl-Nε-lysinate) (C3C-poly-Nε-SUK) as moiety reactive to hydroxyl radicals. The response of the CONER nanoprobe was dependent on various parameters such as reaction time and nanoparticle concentration. The probe was selective for hydroxyl radicals as compared with other reactive oxygen species including O(2)(•-), H(2)O(2), (1)O(2), and OCl(-). Furthermore, the CONER nanoprobe was used to detect hydroxyl radicals in vitro using viable breast cancer cells exposed to oxidative stress. The results suggest that this nanoprobe represents a promising approach for detection of hydroxyl radicals in biological systems.

  5. Involvement of inducible nitric oxide synthase in hydroxyl radical-mediated lipid peroxidation in streptozotocin-induced diabetes

    PubMed Central

    Stadler, Krisztian; Bonini, Marcelo G.; Dallas, Shannon; Jiang, JinJie; Radi, Rafael; Mason, Ronald P.; Kadiiska, Maria B.

    2008-01-01

    Free radical production is implicated in the pathogenesis of diabetes mellitus, where several pathways and different mechanisms were suggested in the pathophysiology of the complications. In this study, we used electron paramagnetic resonance (EPR) spectroscopy combined with in vivo spin-trapping techniques to investigate the sources and mechanisms of free radical formation in streptozotocin-induced diabetic rats. Free radical production was directly detected in the diabetic bile, which correlated with lipid peroxidation in the liver and kidney. EPR spectra showed the trapping of a lipid-derived radical. Such radicals were demonstrated to be induced by hydroxyl radical through isotope labeling experiments. Multiple enzymes and metabolic pathways were examined as the potential source of the hydroxyl radicals using specific inhibitors. Neither xanthine oxidase, cytochrome P450s, the Fenton reaction, nor macrophage activation were required for the production of radical adducts. Interestingly, inducible nitric oxide synthase (apparently uncoupled) was identified as the major source of radical generation. The specific iNOS inhibitor 1400W as well as l-arginine pretreatment reduced the EPR signals to baseline levels, implicating peroxynitrite as the source of hydroxyl radical production. Applying immunological techniques, we localized iNOS overexpression in the liver and kidney of diabetic animals, which was closely correlated with the lipid radical generation and 4-hydroxynonenal-adducted protein formation, indicating lipid peroxidation. In addition, protein oxidation to protein free radicals occurred in the diabetic target organs. Taken together, our studies support inducible nitric oxide synthase as a significant source of EPR-detectable reactive intermediates, which leads to lipid peroxidation and may contribute to disease progression as well. PMID:18620046

  6. Polar transition states in reactions of aromatic hydrocarbons with hydroxyl radicals

    SciTech Connect

    Vysotskaya, N.A.; Rekasheva, A.F.; Bortun, L.N.

    1986-07-01

    The mechanism of formation of radical adducts in the radical hydroxylation of aromatic hydrocarbons has been investigated. The analysis of correlations between the logarithms of the rate constants of the radical hydroxylation of substituted benzenes, naphthalenes, and condensed hydrocarbons in aqueous solutions and the sigma/sup +/ constants of the substituents, the ionization potentials, the localization energies of the arenes, and also the quantum-chemical calculations of the surfaces of potential energies of the hydroxylation of benzene and naphthalene leads to the conclusion that an ion pair in the excited state, formed by the cation radical of the hydrocarbon and the hydroxyl anion, can serve as the model for the transition states of the above-mentioned reactions. A decrease in the ionization potential of the arene leads to an increase in the coulombic interaction in this pair, to its stabilization, and to an increase in the reaction rate.

  7. Pulsed corona discharge: the role of ozone and hydroxyl radical in aqueous pollutants oxidation.

    PubMed

    Preis, S; Panorel, I C; Kornev, I; Hatakka, H; Kallas, J

    2013-01-01

    Ozone and hydroxyl radical are the most active oxidizing species in water treated with gas-phase pulsed corona discharge (PCD). The ratio of the species dependent on the gas phase composition and treated water contact surface was the objective for the experimental research undertaken for aqueous phenol (fast reaction) and oxalic acid (slow reaction) solutions. The experiments were carried out in the reactor, where aqueous solutions showered between electrodes were treated with 100-ns pulses of 20 kV voltage and 400 A current amplitude. The role of ozone increased with increasing oxygen concentration and the oxidation reaction rate. The PCD treatment showed energy efficiency surpassing that of conventional ozonation.

  8. Measurements of hydroxyl and hydroperoxy radicals during CalNex-LA: Model comparisons and radical budgets

    NASA Astrophysics Data System (ADS)

    Griffith, S. M.; Hansen, R. F.; Dusanter, S.; Michoud, V.; Gilman, J. B.; Kuster, W. C.; Veres, P. R.; Graus, M.; Gouw, J. A.; Roberts, J.; Young, C.; Washenfelder, R.; Brown, S. S.; Thalman, R.; Waxman, E.; Volkamer, R.; Tsai, C.; Stutz, J.; Flynn, J. H.; Grossberg, N.; Lefer, B.; Alvarez, S. L.; Rappenglueck, B.; Mielke, L. H.; Osthoff, H. D.; Stevens, P. S.

    2016-04-01

    Measurements of hydroxyl (OH) and hydroperoxy (HO2*) radical concentrations were made at the Pasadena ground site during the CalNex-LA 2010 campaign using the laser-induced fluorescence-fluorescence assay by gas expansion technique. The measured concentrations of OH and HO2* exhibited a distinct weekend effect, with higher radical concentrations observed on the weekends corresponding to lower levels of nitrogen oxides (NOx). The radical measurements were compared to results from a zero-dimensional model using the Regional Atmospheric Chemical Mechanism-2 constrained by NOx and other measured trace gases. The chemical model overpredicted measured OH concentrations during the weekends by a factor of approximately 1.4 ± 0.3 (1σ), but the agreement was better during the weekdays (ratio of 1.0 ± 0.2). Model predicted HO2* concentrations underpredicted by a factor of 1.3 ± 0.2 on the weekends, while measured weekday concentrations were underpredicted by a factor of 3.0 ± 0.5. However, increasing the modeled OH reactivity to match the measured total OH reactivity improved the overall agreement for both OH and HO2* on all days. A radical budget analysis suggests that photolysis of carbonyls and formaldehyde together accounted for approximately 40% of radical initiation with photolysis of nitrous acid accounting for 30% at the measurement height and ozone photolysis contributing less than 20%. An analysis of the ozone production sensitivity reveals that during the week, ozone production was limited by volatile organic compounds throughout the day during the campaign but NOx limited during the afternoon on the weekends.

  9. Endogenous released ascorbic acid suppresses ethanol-induced hydroxyl radical production in rat striatum.

    PubMed

    Huang, Mei; Liu, Wen; Li, Qiang; Wu, Chun Fu

    2002-07-19

    Previous studies have shown that acute systemic administration of ethanol induced ascorbic acid release in the striatum. However, the pharmacological implications of ethanol-induced striatal ascorbic acid release are unclear. In the present study, ethanol-induced extracellular changes of ascorbic acid and hydroxyl radical levels were detected in rat striatum by using brain microdialysis coupled to high-performance liquid chromatography with electrochemical detection. It was found that both in male and female rats, ethanol (3.0 g/kg, i.p.) increased striatal ascorbic acid release in the first 60 min after ethanol administration. Meanwhile, the extracellular hydroxyl radical levels, detected as 2,3- and 2,5-DHBA, were significantly decreased. However, when the ascorbic acid levels returned to the baseline, hydroxyl radical levels rebounded. Administration of DL-fenfluramine (20 mg/kg, i.p.) had no effect on the basal levels of ascorbic acid and hydroxyl radical, but significantly blocked ethanol-induced ascorbic acid release and increased hydroxyl radical levels significantly. Exogenous administration of ascorbic acid (20 mg/kg, s.c.) increased the extracellular levels of ascorbic acid in the striatum, and inhibited the increase of 2,3- and 2,5-DHBA in DL-fenfluramine plus ethanol group. These results provide first evidence that release of endogenous ascorbic acid in the striatum plays an important role in preventing oxidative stress by trapping hydroxyl radical in the central nervous system.

  10. Inhibitory effect of free radical scavenger, MCI-186, in the increase of hydroxyl radical induced by iminodipropionitrile in rats.

    PubMed

    Nomoto, Nobuatsu

    2004-04-15

    Beta,beta'-Iminodipropionitrile (IDPN) is known to produce permanent motor behavioral abnormalities in rats. This behavior syndrome is also termed as "ECC Syndrome", the animal model for Gilles de la Tourette syndrome in humans. Some reports showed that these behavioral abnormalities are caused by monoamine changes. However, there was little research on the relation between IDPN-induced behavioral abnormalities and free radical. 3-Methyl-1-phenyl-2-pyrazolin-5-one (MCI-186), a newly synthesized free radical scavenger, exerts beneficial free radical scavenging and antioxidant characteristics. We investigated that MCI-186 inhibited the process of hydroxyl radical formation induced by IDPN administration in the rat brain. In the group of IDPN administration, hydroxyl radical levels exhibited predominant increase in most parts of the rat brain. In the group of IDPN and MCI-186 administration, hydroxyl radical levels marked significant decrease compared with those in the group of IDPN administration. Therefore, MCI-186 inhibited production of hydroxyl radical and might prove to be effective against ECC syndrome induced by IDPN.

  11. Hydroxyl-radical-dependent DNA damage by ambient particulate matter from contrasting sampling locations

    SciTech Connect

    Shi Tingming; Duffin, Rodger; Borm, Paul J.A.; Li Hui; Weishaupt, Christel; Schins, Roel P.F. . E-mail: roel.schins@uni-duesseldorf.de

    2006-05-15

    Exposure to ambient particulate matter (PM) has been reported to be associated with increased respiratory, cardiovascular, and malignant lung disease. Previously we have shown that PM can induce oxidative DNA damage in A549 human lung epithelial cells. The aims of the present study were to investigate the variability of the DNA-damaging properties of PM sampled at different locations and times and to relate the observed effects to the hydroxyl-radical ({center_dot}OH)-generating activities of these samples. Weekly samples of coarse (10-2.5 {mu}m) and fine (<2.5 {mu}m) PM from four sites (Nordrheim Westfalen, Germany) were analyzed for hydrogen-peroxide-dependent {center_dot}OH formation using electron paramagnetic resonance and formation of 8-hydroxydeoxyguanosine (8-OHdG) in calf thymus DNA using an immuno-dot-blot assay. DNA strand breakage by fine PM in A549 human lung epithelial cells was quantified using the alkaline comet assay. Both PM size distribution fractions elicited {center_dot}OH generation and 8-OHdG formations in calf thymus DNA. Significantly higher {center_dot}OH generation was observed for PM sampled at urban/industrial locations and for coarse PM. Samples of fine PM also caused DNA strand breakage in A549 cells and this damage could be prevented using the hydroxyl-radical scavengers 5,5-dimethyl-1-pyrroline-N-oxide and dimethyl sulfoxide. The observed DNA strand breakage appeared to correlate with the hydroxyl-radical-generating capacities of the PM samples but with different profiles for rural versus urban/industrial samples. In conclusion, when considered at equal mass, {center_dot}OH formation of PM shows considerable variability with regard to the sampling location and time and is correlated with its ability to cause DNA damage.

  12. Inhibition of hydroxyl radical reaction with aromatics by dissolved natural organic matter

    USGS Publications Warehouse

    Lindsey, M.E.; Tarr, M.A.

    2000-01-01

    Reaction of aromatic compounds with hydroxyl radical is inhibited by dissolved natural organic matter (NOM). The degree of inhibition is significantly greater than that expected based on a simple model in which aromatic compound molecules bound to NOM are considered to be unreactive. In this study, hydroxyl radical was produced at steady-state concentrations using Fenton chemistry (H2O2 + Fe2+ ??? Fe3+ + HO- + HO??). Suwannee River fulvic acid and humic acid were used as NOM. The most likely mechanism for the observed inhibition is that hydroxyl radical formation occurs in microenvironmental sites remote from the aromatic compounds. In addition to changes in kinetics, pyrene hydroxyl radical reaction also exhibited a mechanistic change in the presence of fulvic acid. The mechanism changed from a reaction that was apparently firstorder in pyrene to one that was apparently secondorder in pyrene, indicating that pyrene self-reaction may have become the dominant mechanism in the presence of fulvic acid. Dissolved NOM causes significant changes in the rate and mechanism of hydroxyl radical degradation of aromatic compounds. Consequently, literature rate constants measured in pure water will not be useful for predicting the degradation of pollutants in environmental systems. The kinetic and mechanistic information in this study will be useful for developing improved degradation methods involving Fenton chemistry.Reaction of aromatic compounds with hydroxyl radical is inhibited by dissolved natural organic matter (NOM). The degree of inhibition is significantly greater than that expected based on a simple model in which aromatic compounds molecules bounds to NOM are considered to be unreactive. In this study, hydroxyl radical was produced at steady-state concentrations using Fenton chemistry (H2O2 + Fe2+ ??? Fe3+ + HO- + HO??). Suwannee River fulvic acid and humic acid were used as NOM. The most likely mechanisms for the observed inhibition is that hydroxyl radical

  13. Hydroxyl Radical Generation and DNA Nuclease Activity: A Mechanistic Study Based on a Surface-Immobilized Copper Thioether Clip-Phen Derivative.

    PubMed

    Romo, Adolfo I B; Abreu, Dieric S; de F Paulo, Tércio; Carepo, Marta S P; Sousa, Eduardo H S; Lemus, Luis; Aliaga, Carolina; Batista, Alzir A; Nascimento, Otaciro R; Abruña, Héctor D; Diógenes, Izaura C N

    2016-07-11

    Coordination compounds of copper have been invoked as major actors in processes involving the reduction of molecular oxygen, mostly with the generation of radical species the assignment for which has, so far, not been fully addressed. In the present work, we have carried out studies in solution and on surfaces to gain insights into the nature of the radical oxygen species (ROS) generated by a copper(II) coordination compound containing a thioether clip-phen derivative, 1,3-bis(1,10-phenanthrolin-2-yloxy)-N-(4-(methylthio)benzylidene)propan-2-amine (2CP-Bz-SMe), enabling its adsorption/immobilization to gold surfaces. Whereas surface plasmon resonance (SPR) and electrochemistry of the adsorbed complex indicated the formation of a dimeric Cu(I) intermediate containing molecular oxygen as a bridging ligand, scanning electrochemical microscopy (SECM) and nuclease assays pointed to the generation of a ROS species. Electron paramagnetic resonance (EPR) data reinforced such conclusions, indicating that radical production was dependent on the amount of oxygen and H2 O2 , thus pointing to a mechanism involving a Fenton-like reaction that results in the production of OH(.) .

  14. Hydroxyl Radical Generation and DNA Nuclease Activity: A Mechanistic Study Based on a Surface-Immobilized Copper Thioether Clip-Phen Derivative.

    PubMed

    Romo, Adolfo I B; Abreu, Dieric S; de F Paulo, Tércio; Carepo, Marta S P; Sousa, Eduardo H S; Lemus, Luis; Aliaga, Carolina; Batista, Alzir A; Nascimento, Otaciro R; Abruña, Héctor D; Diógenes, Izaura C N

    2016-07-11

    Coordination compounds of copper have been invoked as major actors in processes involving the reduction of molecular oxygen, mostly with the generation of radical species the assignment for which has, so far, not been fully addressed. In the present work, we have carried out studies in solution and on surfaces to gain insights into the nature of the radical oxygen species (ROS) generated by a copper(II) coordination compound containing a thioether clip-phen derivative, 1,3-bis(1,10-phenanthrolin-2-yloxy)-N-(4-(methylthio)benzylidene)propan-2-amine (2CP-Bz-SMe), enabling its adsorption/immobilization to gold surfaces. Whereas surface plasmon resonance (SPR) and electrochemistry of the adsorbed complex indicated the formation of a dimeric Cu(I) intermediate containing molecular oxygen as a bridging ligand, scanning electrochemical microscopy (SECM) and nuclease assays pointed to the generation of a ROS species. Electron paramagnetic resonance (EPR) data reinforced such conclusions, indicating that radical production was dependent on the amount of oxygen and H2 O2 , thus pointing to a mechanism involving a Fenton-like reaction that results in the production of OH(.) . PMID:27310653

  15. Atmospheric Hydroxyl Radical Production from Electronically Excited NO2 and H2O

    NASA Astrophysics Data System (ADS)

    Li, Shuping; Matthews, Jamie; Sinha, Amitabha

    2008-03-01

    Hydroxyl radicals are often called the “detergent” of the atmosphere because they control the atmosphere’s capacity to cleanse itself of pollutants. Here, we show that the reaction of electronically excited nitrogen dioxide with water can be an important source of tropospheric hydroxyl radicals. Using measured rate data, along with available solar flux and atmospheric mixing ratios, we demonstrate that the tropospheric hydroxyl contribution from this source can be a substantial fraction (50%) of that from the traditional O(1D) + H2O reaction in the boundary-layer region for high solar zenith angles. Inclusion of this chemistry is expected to affect modeling of urban air quality, where the interactions of sunlight with emitted NOx species, volatile organic compounds, and hydroxyl radicals are central in determining the rate of ozone formation.

  16. Atmospheric hydroxyl radical production from electronically excited NO2 and H2O.

    PubMed

    Li, Shuping; Matthews, Jamie; Sinha, Amitabha

    2008-03-21

    Hydroxyl radicals are often called the "detergent" of the atmosphere because they control the atmosphere's capacity to cleanse itself of pollutants. Here, we show that the reaction of electronically excited nitrogen dioxide with water can be an important source of tropospheric hydroxyl radicals. Using measured rate data, along with available solar flux and atmospheric mixing ratios, we demonstrate that the tropospheric hydroxyl contribution from this source can be a substantial fraction (50%) of that from the traditional O(1D) + H2O reaction in the boundary-layer region for high solar zenith angles. Inclusion of this chemistry is expected to affect modeling of urban air quality, where the interactions of sunlight with emitted NOx species, volatile organic compounds, and hydroxyl radicals are central in determining the rate of ozone formation.

  17. Atmospheric hydroxyl radical production from electronically excited NO2 and H2O.

    PubMed

    Li, Shuping; Matthews, Jamie; Sinha, Amitabha

    2008-03-21

    Hydroxyl radicals are often called the "detergent" of the atmosphere because they control the atmosphere's capacity to cleanse itself of pollutants. Here, we show that the reaction of electronically excited nitrogen dioxide with water can be an important source of tropospheric hydroxyl radicals. Using measured rate data, along with available solar flux and atmospheric mixing ratios, we demonstrate that the tropospheric hydroxyl contribution from this source can be a substantial fraction (50%) of that from the traditional O(1D) + H2O reaction in the boundary-layer region for high solar zenith angles. Inclusion of this chemistry is expected to affect modeling of urban air quality, where the interactions of sunlight with emitted NOx species, volatile organic compounds, and hydroxyl radicals are central in determining the rate of ozone formation. PMID:18356524

  18. RAPID MEASUREMENT OF AQUEOUS HYDROXYL RADICAL CONCENTRATIONS IN STEADY-STATE HO· FLUX SYSTEMS

    EPA Science Inventory

    The spin-trap compound a-(4-pyridyl-1-oxide)-N-tert-butyl-nitrone (4-POBN) is utilized for the detection and quantitation of the hydroxyl radical (HO·) in aqueous solution. Capillary electrophoresis enables rapid analysis of the probe compound. The thermally unstable HO· radical ...

  19. Pseudomonas and neutrophil products modify transferrin and lactoferrin to create conditions that favor hydroxyl radical formation.

    PubMed Central

    Britigan, B E; Edeker, B L

    1991-01-01

    In vivo most extracellular iron is bound to transferrin or lactoferrin in such a way as to be unable to catalyze the formation of hydroxyl radical from superoxide (.O2-) and hydrogen peroxide (H2O2). At sites of Pseudomonas aeruginosa infection bacterial and neutrophil products could possibly modify transferrin and/or lactoferrin forming catalytic iron complexes. To examine this possibility, diferrictransferrin and diferriclactoferrin which had been incubated with pseudomonas elastase, pseudomonas alkaline protease, human neutrophil elastase, trypsin, or the myeloperoxidase product HOCl were added to a hypoxanthine/xanthine oxidase .O2-/H2O2 generating system. Hydroxyl radical formation was only detected with pseudomonas elastase treated diferrictransferrin and, to a much lesser extent, diferriclactoferrin. This effect was enhanced by the combination of pseudomonas elastase with other proteases, most prominently neutrophil elastase. Addition of pseudomonas elastase-treated diferrictransferrin to stimulated neutrophils also resulted in hydroxyl radical generation. Incubation of pseudomonas elastase with transferrin which had been selectively iron loaded at either the NH2- or COOH-terminal binding site yielded iron chelates with similar efficacy for hydroxyl radical catalysis. Pseudomonas elastase and HOCl treatment also decreased the ability of apotransferrin to inhibit hydroxyl radical formation by a Fe-NTA supplemented hypoxanthine/xanthine oxidase system. However, apotransferrin could be protected from the effects of HOCl if bicarbonate anion was present during the incubation. Apolactoferrin inhibition of hydroxyl radical generation was unaffected by any of the four proteases or HOCl. Alteration of transferrin by enzymes and oxidants present at sites of pseudomonas and other bacterial infections may increase the potential for local hydroxyl radical generation thereby contributing to tissue injury. Images PMID:1655825

  20. Hydroxyl radical regeneration in isoprene oxidation: upgraded mechanism LIM1

    NASA Astrophysics Data System (ADS)

    Peeters, Jozef; Son Nguyen, Vinh; Nguyen, Thanh Lam; Stravrakou, Trissevgeni; Muller, Jean-Francois

    2013-04-01

    The OH regeneration known to occur in isoprene oxidation at low/moderate NO is attributed in the Leuven Isoprene Mechanism to novel, theoretically characterized chemical pathways (LIM0: Peeters et al. 2009; Peeters and Muller 2010). Its key new features are (i) quasi-equilibration of the thermally labile beta-OH- and delta-OH-isoprenylperoxy isomers; (ii) 1,6-H shift isomerisation of the Z-delta-OH-peroxy isomers to yield hydroperoxy-methyl-butenals (HPALDs); (iii) fast photolysis of the HPALDs resulting overall in several OH radicals per HPALD. The OH-regeneration through photolabile HPALDs has recently found experimental support, but the peroxy isomerisation rate, HPALD yield and extent of OH recycling are still uncertain (Crounse et al. 2011; Wolfe et al. 2012). In this work, the upgraded LIM1 mechanism is presented. Based on much higher levels of theory that fully account for dispersion effects, the crucial equilibrium ratio of the isomerising Z-delta-OH-peroxys over the majority beta-OH-isoprenylperoxys is reduced by a factor ≈5 and the isomerisation rate of the Z-delta-OH-peroxys by a factor ≈1.5 compared to LIM0. The chemistry following the 1,6-H shift of the Z-delta-OH-peroxys is also much expanded and extended. Firstly, LIM1 introduces other pathways beside HPALD formation following the Z-delta-OH-peroxy isomerisation, but resulting likewise in OH recycling. This, together with the revised Z-delta-OH- equilibrium and isomerisation data above, affords a fair model-reproduction of the HPALD and other product yields observed by Crounse et al. (2011). Secondly, LIM1 proposes new fast reactions of HO2 with the alpha-oxoketene products from the peroxy isomerisation routes; these reactions are shown to efficiently convert HO2 into OH and are prime candidates for the unknown X + HO2 → OH + ... hydroxyl-recycling routes invoked in recent studies (Hofzumahaus et al.2009; Whalley et al. 2011). Modeling results using the IMAGES global CTM will be presented on

  1. Geminate recombination of hydroxyl radicals generated in 200 nm photodissociation of aqueous hydrogen peroxide.

    SciTech Connect

    Crowell, R. A.; Lian, R.; Oulianov, D. A.; Shkrob, I. A.; Chemistry

    2004-01-15

    The picosecond dynamics of hydroxyl radicals generated in 200 nm photoinduced dissociation of aqueous hydrogen peroxide have been observed through their transient absorbance at 266 nm. It is shown that these kinetics are nearly exponential, with a decay time of ca. 30 ps. The prompt quantum yield for the decomposition of H2O2 is 0.56, and the fraction of hydroxyl radicals escaping from the solvent cage to the water bulk is 64-68%. These recombination kinetics suggest strong caging of the geminate hydroxyl radicals by water. Phenomenologically, these kinetics may be rationalized in terms of the diffusion of hydroxide radicals out of a shallow potential well (a solvent cage) with an Onsager radius of 0.24 nm.

  2. Hydroxyl radical and hydroxide ion in liquid water: a comparative electron density functional theory study.

    PubMed

    Vassilev, Peter; Louwerse, Manuel J; Baerends, Evert Jan

    2005-12-15

    Ab initio density functional theory molecular dynamics simulations of the solvated states of the hydroxyl radical and hydroxide ion are performed using the Becke-Lee-Yang-Parr (BLYP) exchange-correlation functional (Becke, A. D. Phys. Rev. A 1988, 38, 3098. Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785). The structures of the solvation shells of the two species are examined. It is found that the OH radical forms a relatively well-defined solvation complex with four neighboring water molecules. Three of these molecules are hydrogen bonded to the OH, while the fourth is hemibonded via a three-electron two-centered bond between the oxygen atoms of the OH and water. The activity and the diffusion mechanism of the OH radical in water is discussed in comparison with the OH- ion. Although the results are partially influenced by the tendency of the BLYP density functional to overestimate hemibonded structure, the present simulations suggest that the widely accepted picture of rapid diffusion of OH radical in water through hydrogen exchange reaction may need to be reconsidered. PMID:16375337

  3. The decomposition of protoporphyrin IX by ultrasound is dependent on the generation of hydroxyl radicals.

    PubMed

    Xu, Haobo; Sun, Xin; Yao, Jianting; Zhang, Jian; Zhang, Yun; Chen, Haibo; Dan, Juhua; Tian, Zhen; Tian, Ye

    2015-11-01

    The ultrasound activation of certain drugs, such as porphyrins, could cause synergistic cytotoxic effects on cells. Both sonomechanical and sonochemical effects occur and the latter play a critical role because antioxidant agents could exert significant protective effects against the cytotoxicity. To investigate the reactive oxygen species involved in the sonochemical effects, aqueous protoporphyrin IX (PpIX) solutions were characterized under ultrasound sonication in this study. Inertial cavitation was indirectly evaluated using terephthalic acid dosimetry. The fluorescence intensity of the PpIX was measured using a fluorescence spectrophotometer. The effects of PpIX concentration, ultrasound parameters and free radical scavengers on the PpIX activation by ultrasound were investigated. Our results showed that the increase in PpIX decomposition was significantly correlated with cavitation activities (R=0.9874, p<0.05), and the decomposing effect increases with ultrasound intensity (0.6-1.5 W/cm(2)), initial PpIX concentration (1-5 μM), duty cycle (10-100%) and the sonication duration (2-10 min). The fluorescence and absorption spectra of PpIX showed a decrease in the peak intensity without spectral shifts or new peak build-up after sonication. The PpIX decomposition was significantly inhibited by hydroxyl radical scavengers, histidine, mannitol, acetone, methanol and ethanol, but the decomposition was not inhibited by sodium azide, catalase or superoxide dismutase. These results suggest that the decomposition of protoporphyrin IX by ultrasound is dependent on the generation of hydroxyl radicals, which sheds some light on the sonochemical effects of the interaction between ultrasound and porphyrins.

  4. Hydroxyl radical scavenging effects of guaiacol used in traditional dental pulp sedation: reaction kinetic study.

    PubMed

    Mimurai, Toshio; Yazaki, Kinya; Sawaki, Kohei; Ozawa, Toshihiko; Kawaguchi, Mitsuru

    2005-08-01

    Guaiacol, which is a phenolic compound with a methoxy group and used in traditional dental pulp sedation, has the property of inducing cell proliferation. To clarify these mechanisms of guaiacol, this study examined the hydroxyl radical (*OH) scavenging effects of guaiacol in vitro. Generation of *OH was carried out by the Fenton reaction using mixture of ascorbic acid, H2O2, and Fe(III)-EDTA, and *OH was detected by measuring the *OH-mediated production of degradation products of deoxyribose, which reacts with 2-thiobarbituric acid (TBA) and is relatively stable for a long time. At concentrations of 10(-10) M to 10(-3) M, guaiacol inhibited the TBA reactive substance (TBA-RS) formation in a dose-dependent manner. Phenol and formaldehyde were also found to inhibit the TBA-RS formation, but their inhibitory activities were lower than that of guaiacol. The concentrations of guaiacol, phenol, and formaldehyde needed to cause 50% inhibition of TBA-RS formation were approximately 5 x 10(-6), 5 x 10(-5), and 2 x 10(-3) M, respectively. In this reaction system, guaiacol showed no chelating reaction with ferrous ion and did not directly react with H2O2. Guaiacol also exhibited radical scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPH) stable free radical, but its scavenging activity was lower than that toward *OH. These results suggest that guaiacol is a potent scavenger of reactive oxygen radicals and that its radical scavenging activity may be associated with its effect on cell proliferation.

  5. Aliphatic peptidyl hydroperoxides as a source of secondary oxidation in hydroxyl radical protein footprinting

    PubMed Central

    Saladino, Jessica; Liu, Mian; Live, David; Sharp, Joshua S.

    2009-01-01

    Hydroxyl radical footprinting is a technique for studying protein structure and binding that entails oxidizing a protein system of interest with diffusing hydroxyl radicals, and then measuring the amount of oxidation of each amino acid. One important issue in hydroxyl radical footprinting is limiting amino acid oxidation by secondary oxidants to prevent uncontrolled oxidation which can cause amino acids to appear more solvent accessible than they really are. Previous work suggested that hydrogen peroxide was the major secondary oxidant of concern in hydroxyl radical footprinting experiments; however, even after elimination of all hydrogen peroxide, some secondary oxidation was still detected. Evidence is presented for the formation of peptidyl hydroperoxides as the most abundant product upon oxidation of aliphatic amino acids. Both reverse phase liquid chromatography and catalase treatment were shown to be ineffective at eliminating peptidyl hydroperoxides. The ability of these peptidyl hydroperoxides to directly oxidize methionine is demonstrated, suggesting the value of methionine amide as an in situ protectant. Hydroxyl radical footprinting protocols require the use of an organic sulfide or similar peroxide scavenger in addition to removal of hydrogen peroxide in order to successfully eradicate all secondary oxidizing species and prevent uncontrolled oxidation of sulfur-containing residues. PMID:19278868

  6. Computational observation of enhanced solvation of the hydroxyl radical with increased NaCl concentration

    SciTech Connect

    Wick, Collin D.; Dang, Liem X.

    2006-05-11

    Classical molecular dynamics simulations with many-body potentials were carried out to quantitatively determine the effect of NaCl salt concentration on the aqueous solvation and surface concentration of hydroxyl radicals. The potential of mean force technique was used to track the incremental free energy of the hydroxyl radical from the vapor, crossing the air-water interface into the aqueous bulk. Results showed increased NaCl salt concentration significantly enhanced hydroxyl radical solvation, which should significantly increase its accommodation on water droplets. This has been experimentally observed for ozone aqueous accommodation with increased NaI concentration, but to our knowledge, no experimental study has probed this for hydroxyl radicals. The origin for this effect was found to be very favorable hydroxyl radical-chloride ion interactions, being stronger than for water-chloride. This work was performed at Pacific Northwest National Laboratory (PNNL) under the auspices of the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy. Battelle operates PNNL for the Department of Energy.

  7. An ESR and DFT study of Hydration of the 2′-Deoxyuridine-5-yl Radical: Possible Hydroxyl Radical Intermediate

    PubMed Central

    Chomicz, Lidia; Petrovici, Alex; Archbold, Ian; Adhikary, Amitava; Kumar, Anil

    2014-01-01

    The mechanism of radiation-induced frank strand break formation in irradiated 5-bromo-2′-deoxyuridine (BrdU)-labelled DNA is still unclear, despite the proven radiosensitizing property of BrdU. Combination of ESR spectroscopy and quantum chemical modelling points to a simple reaction between the uridine-5-yl radical and water molecule that produces the genotoxic hydroxyl radical. PMID:25306924

  8. Anticancer system created by acrolein and hydroxyl radical generated in enzymatic oxidation of spermine and other biochemical reactions.

    PubMed

    Alarcon, R A

    2012-10-01

    A hypothesis suggesting the existence of a ubiquitous physiological anticancer system created by two highly reactive oxidative stress inducers with anticancer properties, acrolein and hydroxyl radical, is reported in this communication. Both components can originate separately or together in several biochemical interactions, among them, the enzymatic oxidation of the polyamine spermine, which appear to be their main source. The foundations of this hypothesis encompass our initial search for growth-inhibitors or anticancer compounds in biological material leading to the isolation of spermine, a polyamine that became highly cytotoxic through the generation of acrolein, when enzymatically oxidized. Findings complemented with pertinent literature data by other workers and observed anticancer activities by sources capable of producing acrolein and hydroxyl radical. This hypothesis obvious implication: spermine enzymatic oxidations or other biochemical interactions that would co-generate acrolein and hydroxyl radical, the anticancer system components, should be tried as treatments for any given cancer. The biochemical generation of acrolein observed was totally unexpected, since this aldehyde was known; as a very toxic and highly reactive xenobiotic chemical produced in the pyrolysis of fats and other organic material, found as an atmospheric pollutant, in tobacco smoke and car emissions, and mainly used as a pesticide or aquatic herbicide. Numerous studies on acrolein, considered after our work a biological product, as well, followed. In them, acrolein widespread presence, its effects on diverse cellular proteins, such as, growth factors, and its anticancer activities, were additionally reported. Regarding hydroxyl radical, the second component of the proposed anticancer system, and another cytotoxic product in normal cell metabolism, it co-generates with acrolein in several biochemical interactions, occurrences suggesting that these products might jointly fulfill some

  9. Pulse radiolysis studies on reactions of hydroxyl radicals with selenocystine derivatives.

    PubMed

    Mishra, B; Kumbhare, L B; Jain, V K; Priyadarsini, K I

    2008-04-10

    Reactions of hydroxyl radicals (*OH) with selenocystine (SeCys) and two of its analogues, diselenodipropionic acid (SeP) and selenocystamine (SeA), have been studied in aqueous solutions at pHs of 1, 7, and 10 using the pulse radiolysis technique coupled with absorption detection. All of these diselenides react with *OH radicals with rate constants of approximately 10(10) M(-1) s(-1), producing diselenide radical cations ( approximately 1-5 micros after the pulse), with an absorption maximum at 560 nm, by elimination of H(2)O or OH(-) from hydroxyl radical adducts. Assignment of the 560 nm band to the diselenide radical cation was made by comparing the transient spectra with those produced upon reaction of diselenides with specific one-electron oxidants, Cl(2)(*-) (pH 1) and Br(2)(*-) radicals (pHs of 7 and 10). SeP having a carboxylic acid functionality showed quantitative conversion of hydroxyl radical adducts to radical cations. The compounds SeCys and SeA, having an amino functional group, in addition to the radical cations, produced a new transient with lambda(max) at 460 nm, at later time scales ( approximately 20-40 micros after the pulse). The rate and yield of formation of the 460 nm band increased with increasing concentrations of either SeCys or SeA. In analogy with similar studies reported for analogous disulfides, the 460 nm transient absorption band has been assigned to a triselenide radical adduct. The one-electron reduction potentials of the compounds were estimated to be 0.96, 1.3, and 1.6 V versus NHE, respectively, for SeP, SeCys, and SeA at pH 7. From these studies, it has been concluded that the electron-donating carboxylic acid group decreases the reduction potential and facilitates quantitative conversion of hydroxyl radical adducts to radical cations, while the electron-withdrawing NH(3)(+) group not only increases the reduction potential but also leads to fragmentation of the hydroxyl radical adduct to selenyl radicals, which are converted

  10. Glutathione conjugation of busulfan produces a hydroxyl radical-trapping dehydroalanine metabolite.

    PubMed

    Peer, Cody J; Younis, Islam R; Leonard, Stephen S; Gannett, Peter M; Minarchick, Valerie C; Kenyon, Allison J; Rojanasakul, Yon; Callery, Patrick S

    2012-12-01

    The Phase 2 drug metabolism of busulfan yields a glutathione conjugate that undergoes a β-elimination reaction. The elimination product is an electrophilic metabolite that is a dehydroalanine-containing tripeptide, γ-glutamyldehydroalanylglycine (EdAG). In the process, glutathione lacks thiol-related redox properties and gains a radical scavenging dehydroalanine group. EdAG scavenged hydroxyl radical generated in the Fenton reaction in a concentration-dependent manner was monitored by electron paramagnetic resonance (EPR) spectroscopy. The apparent rate of hydroxyl radical scavenging was in the same range as published values for known antioxidants, including N-acyl dehydroalanines. A captodatively stabilized carbon-centered radical intermediate was spin trapped in the reaction of EdAG with hydroxyl radical. The proposed structure of a stable product in the Fenton reaction with EdAG was consistent with that of a γ-glutamylserylglycyl dimer. Observation of the hydroxyl trapping properties of EdAG suggests that the busulfan metabolite EdAG may contribute to or mitigate redox-related cytotoxicity associated with the therapeutic use of busulfan, and reaffirms indicators that support a role in free radical biology for dehydroalanine-containing peptides and proteins.

  11. Rifampin induces hydroxyl radical formation in Mycobacterium tuberculosis.

    PubMed

    Piccaro, Giovanni; Pietraforte, Donatella; Giannoni, Federico; Mustazzolu, Alessandro; Fattorini, Lanfranco

    2014-12-01

    The antituberculosis (anti-TB) drug rifampin (RIF) binds to the beta subunit of the RNA polymerase (RpoB) of Mycobacterium tuberculosis, but the bactericidal responses triggered after target interaction are not known. To evaluate whether RIF induced an oxidative burst, lysates of RIF-treated M. tuberculosis were tested for determination of reactive oxygen species (ROS) by the electron paramagnetic resonance (EPR) technique using 1-hydroxy-3-carboxy-pyrrolidine (CPH) and 5,5-dimethyl-1-pyrrolidine-N-oxide (DMPO) as spin traps. M. tuberculosis killing by RIF stimulated an increase in the rate of formation of the CPH radical (CP·). Lysate pretreatment with the O2·(-) and ·OH scavengers superoxide dismutase (SOD) and thiourea (THIO), respectively, or with the metal chelator diethylene triamine pentaacetic acid (DTPA) inhibited CP· formation, arguing in favor of a metal-catalyzed ROS response. Formation of CP· did not increase following treatment of RIF-resistant strains with RIF, indicating that the ROS were induced after RpoB binding. To identify the ROS formed, lysates of RIF-treated bacilli were incubated with DMPO, a spin trap specific for ·OH and O2·(-), with or without pretreatment with SOD, catalase, THIO, or DTPA. Superoxide dismutase, catalase, and THIO decreased formation of the DMPO-OH adduct, and SOD plus DTPA completely suppressed it, suggesting that RIF activated metal-dependent O2·(-)-mediated mechanisms producing ·OH inside tubercle bacilli. The finding that the metal chelator DTPA reduced the bactericidal activity of RIF supported the possibility that ·OH was generated through these mechanisms and that it participated at least in part in M. tuberculosis killing by the drug. PMID:25288092

  12. Rifampin Induces Hydroxyl Radical Formation in Mycobacterium tuberculosis

    PubMed Central

    Piccaro, Giovanni; Pietraforte, Donatella; Giannoni, Federico; Mustazzolu, Alessandro

    2014-01-01

    The antituberculosis (anti-TB) drug rifampin (RIF) binds to the beta subunit of the RNA polymerase (RpoB) of Mycobacterium tuberculosis, but the bactericidal responses triggered after target interaction are not known. To evaluate whether RIF induced an oxidative burst, lysates of RIF-treated M. tuberculosis were tested for determination of reactive oxygen species (ROS) by the electron paramagnetic resonance (EPR) technique using 1-hydroxy-3-carboxy-pyrrolidine (CPH) and 5,5-dimethyl-1-pyrrolidine-N-oxide (DMPO) as spin traps. M. tuberculosis killing by RIF stimulated an increase in the rate of formation of the CPH radical (CP·). Lysate pretreatment with the O2·− and ·OH scavengers superoxide dismutase (SOD) and thiourea (THIO), respectively, or with the metal chelator diethylene triamine pentaacetic acid (DTPA) inhibited CP· formation, arguing in favor of a metal-catalyzed ROS response. Formation of CP· did not increase following treatment of RIF-resistant strains with RIF, indicating that the ROS were induced after RpoB binding. To identify the ROS formed, lysates of RIF-treated bacilli were incubated with DMPO, a spin trap specific for ·OH and O2·−, with or without pretreatment with SOD, catalase, THIO, or DTPA. Superoxide dismutase, catalase, and THIO decreased formation of the DMPO-OH adduct, and SOD plus DTPA completely suppressed it, suggesting that RIF activated metal-dependent O2·−-mediated mechanisms producing ·OH inside tubercle bacilli. The finding that the metal chelator DTPA reduced the bactericidal activity of RIF supported the possibility that ·OH was generated through these mechanisms and that it participated at least in part in M. tuberculosis killing by the drug. PMID:25288092

  13. Parallel and Competitive Pathways for Substrate Desaturation, Hydroxylation and Radical Rearrangement by the Non-heme Diiron Hydroxylase AlkB

    PubMed Central

    Cooper, Harriet L. R.; Mishra, Girish; Huang, Xiongyi; Pender-Cudlip, Marilla; Austin, Rachel N.; Shanklin, John; Groves, John T.

    2012-01-01

    A purified and highly active form of the non-heme diiron hydroxylase AlkB was investigated using the diagnostic probe substrate norcarane. The reaction afforded C2 (26%) and C3 (43%) hydroxylation and desaturation products (31%). Initial C-H cleavage at C2 led to 7% C2 hydroxylation and 19% 3-hydroxymethylcyclohexene, a rearrangement product characteristic of a radical rearrangement pathway. A deuterated substrate analog, 3,3,4,4-norcarane-d4, afforded drastically reduced amounts of C3 alcohol (8%) and desaturation products (5%), while the radical rearranged alcohol was now the major product (65%). This change in product ratios indicates a large kinetic hydrogen isotope effect of ~20 for both the C-H hydroxylation at C3 and the desaturation pathway, with all of the desaturation originating via hydrogen abstraction at C3 and not C2. The data indicates that AlkB reacts with norcarane via initial C-H hydrogen abstraction from C2 or C3 and that the three pathways, C3 hydroxylation, C3 desaturation and C2 hydroxylation/radical rearrangement, are parallel and competitive. Thus, the incipient radical at C3 either reacts with the iron-oxo center to form an alcohol or proceeds along the desaturation pathway via a second H-abstraction to afford both 2-norcarene and 3-norcarene. Subsequent reactions of these norcarenes lead to detectable amounts of hydroxylation products and toluene. By contrast, the 2-norcaranyl radical intermediate leads to C2 hydroxylation and the diagnostic radical rearrangement, but this radical apparently does not afford desaturation products. The results indicate that C-H hydroxylation and desaturation follow analogous stepwise reaction channels via carbon radicals that diverge at the product-forming step. PMID:23157204

  14. Formation of hydroxyl radical from the photolysis of frozen hydrogen peroxide.

    PubMed

    Chu, Liang; Anastasio, Cort

    2005-07-21

    Hydrogen peroxide (HOOH) in ice and snow is an important chemical tracer for the oxidative capacities of past atmospheres. However, photolysis in ice and snow will destroy HOOH and form the hydroxyl radical (*OH), which can react with snowpack trace species. Reactions of *OH in snow and ice will affect the composition of both the overlying atmosphere (e.g., by the release of volatile species such as formaldehyde to the boundary layer) and the snow and ice (e.g., by the *OH-mediated destruction of trace organics). To help understand these impacts, we have measured the quantum yield of *OH from the photolysis of HOOH on ice. Our measured quantum yields (Phi(HOOH --> *OH)) are independent of ionic strength, pH, and wavelength, but are dependent upon temperature. This temperature dependence for both solution and ice data is best described by the relationship ln(Phi(HOOH --> *OH)) = -(684 +/- 17)(1/T) + (2.27 +/- 0.064) (where errors represent 1 standard error). The corresponding activation energy (Ea) for HOOH (5.7 kJ mol(-1)) is much smaller than that for nitrate photolysis, indicating that the photochemistry of HOOH is less affected by changes in temperature. Using our measured quantum yields, we calculate that the photolytic lifetimes of HOOH in surface snow grains under midday, summer solstice sunlight are approximately 140 h at representative sites on the Greenland and Antarctic ice sheets. In addition, our calculations reveal that the majority of *OH radicals formed on polar snow grains are from HOOH photolysis, while nitrate photolysis is only a minor contributor. Similarly, HOOH appears to be much more important than nitrate as a photochemical source of *OH on cirrus ice clouds, where reactions of the photochemically formed hydroxyl radical could lead to the release of oxygenated volatile organic compounds to the upper troposphere.

  15. Hydroxyl radical formation in skeletal muscle of rats with glucocorticoid-induced myopathy.

    PubMed

    Konno, Shingo

    2005-05-01

    Steroid myopathy is a well-known adverse effect of glucocorticoids that causes muscle weakness and atrophy; however, its pathogenic mechanism is still unclear. Recently, oxidative stress was reported to contribute to steroid myopathy, but there is no report that actually attempts to measure hydroxyl radical. I developed an animal model of steroid myopathy in rat with dexamethasone (9-Fluoro-11beta,17, 21-trihydroxy-16alpha-methylpregna-1,4-diene-3,20-dione), and measured hydroxyl radical using the salicylate trapping method. There was significant dose-dependent relation between both 2,5- and 2,3-dihydroxybenzoic acids and dexamethasone in the treated group, compared to the control group. These results suggest that hydroxyl radical plays a role in the pathogenesis of steroid myopathy.

  16. Insights into the Solvation and Mobility of the Hydroxyl Radical in Aqueous Solution.

    PubMed

    Codorniu-Hernández, Edelsys; Kusalik, Peter G

    2011-11-01

    A detailed description of the local solvation structure and mobility of hydroxyl radicals (OH*) in aqueous solution near ambient conditions is provided by Car-Parrinello molecular dynamics simulations. Here, we demonstrate that for HCTH/120 and BLYP functionals, smaller systems (i.e., 31·H2O-OH*) are contaminated by system size effects, being biased for the presence of a three-electron two-centered hemibond structure between the oxygen atoms of a water molecule and the radical. Radial and spatial distribution functions of relatively large 63·H2O-OH* systems reveal the existence of a 4-fold coordinated "inactive" OH* structure with three H-bond donating neighbors and a strongly coordinated H-bond accepting neighbor. The local hydration structure around the radical exhibits more H-bond ordering than has been predicted by recent simulations employing classical force fields. Local structural fluctuations can end with spontaneous H-transfer reactions from the nearest H-bond donor water molecule, facilitated by the formation of an "active" OH* state, resembling the proton transfer mechanism of hydrated OH(-) (i.e., slight polarization of the (H3O2)* complex). A comparison of the free energy barriers for the H-transfer reaction obtained by both DFT functionals and for both system sizes is also provided, demonstrating that this can be a very rapid process in water. PMID:26598267

  17. Hydroxyl radical generation and oxidative stress in Carassius auratus liver, exposed to pyrene.

    PubMed

    Sun, Yuanyuan; Yin, Ying; Zhang, Jingfei; Yu, Hongxia; Wang, Xiaorong; Wu, Jichun; Xue, Yuqun

    2008-10-01

    This paper studied the hydroxy radical generation and oxidative stress in the liver of goldfish Carassius auratus under the effect of pyrene. Fish were exposed to different concentrations (0.001, 0.005, 0.01, 0.05 and 0.1 mg/L) of pyrene for 10 days, with one group assigned as control. Based on the hyperfine splitting constants and shape of the electron paramagnetic resonance (EPR) spectrum, the free radical which was generated in fish liver was identified as hydroxyl radical ((*)OH). The (*)OH signal intensity showed a significant increase compared with the control. The changes of the activities of catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST) were detected. The reduced glutathione (GSH) level decreased significantly while oxidized glutathione (GSSG) level was increased at higher concentration (0.005-0.1 mg/L), resulting in a decreased GSH/GSSG ratio, and the malondialdehyde (MDA) content increased significantly at 0.005-0.1 mg/L pyrene. The results clearly showed that C. auratus was subjected to oxidative stress and damage when exposed to pyrene.

  18. Kinetics and mechanism of hydroxyl radical and OH-adduct radical reactions with nitroxides and with their hydroxylamines.

    PubMed

    Samuni, Amram; Goldstein, Sara; Russo, Angelo; Mitchell, James B; Krishna, Murali C; Neta, Pedatsur

    2002-07-24

    Stable nitroxide radicals are potent antioxidants and are among the most effective non-thiol radioprotectants, although they react with hydroxyl radicals more slowly than typical phenolic antioxidants or thiols. Surprisingly, the reduced forms of cyclic nitroxides, cyclic hydroxylamines, are better reductants yet have no radioprotective activity. To clarify the reason for this difference, we studied the kinetics and mechanisms of the reactions of nitroxides and their hydroxylamines with (*)OH radicals and with OH-adducts by using pulse radiolysis, fluorimetric determination of phenolic radiation products, and electron paramagnetic resonance spectrometric determination of nitroxide concentrations following radiolysis. Competition kinetics with phenylalanine as a reference compound in pulse radiolysis experiments yielded rate constants of (4.5 +/- 0.4) x 10(9) M(-1) s(-1) for the reaction of (*)OH radical with 2,2,6,6-tetramethylpiperidine-N-oxyl (TPO), 4-hydroxy-TPO (4-OH-TPO), and 4-oxo-TPO (4-O-TPO), (3.0 +/- 0.3) x 10(9) M(-1) s(-1) for deuterated 4-O-TPO, and (1.0 +/- 0.1) x 10(9) M(-1) s(-1) for the hydroxylamine 4-OH-TPO-H. The kinetic isotope effect suggests the occurrence of both (*)OH addition to the aminoxyl moiety of 4-O-TPO and H-atom abstraction from the 2- or 6-methyl groups or from the 3- and 5-methylene positions. This conclusion was further supported by final product analysis, which demonstrated that (*)OH partially oxidizes 4-O-TPO to the corresponding oxoammonium cation. The rate constants for the reactions of the nitroxides with the OH-adducts of phenylalanine and terephthalate have been determined to be near 4 x 10(6) M(-1) s(-1), whereas the hydroxylamine reacted at least 50 times slower, if at all. These findings indicate that the reactivity toward (*)OH does not explain the differences between the radioprotective activities of nitroxides and hydroxylamines. Instead, the radioprotective activity of nitroxides, but not of hydroxylamines, can be

  19. Lycopene-induced hydroxyl radical causes oxidative DNA damage in Escherichia coli.

    PubMed

    Lee, Wonyoung; Lee, Dong Gun

    2014-09-01

    Lycopene, which is a well-known red carotenoid pigment, has been drawing scientific interest because of its potential biological functions. The current study reports that lycopene acts as a bactericidal agent by inducing reactive oxygen species (ROS)-mediated DNA damage in Escherichia coli. Lycopene treatment elevated the level of ROS-in particular, hydroxyl radicals ((•)OH) -which can damage DNA in E. coli. Lycopene-induced DNA damage in bacteria was confirmed and we also observed cell filamentation caused by cell division arrest, an indirect marker of the DNA damage repair system, in lycopene-treated E. coli. Increased RecA expression was observed, indicating activation of the DNA repair system (SOS response). To summarize, lycopene exerts its antibacterial effects by inducing (•)OH -mediated DNA damage that cannot be ameliorated by the SOS response. Lycopene may be a clinically useful adjuvant for current antimicrobial therapies.

  20. Theoretical study on the gas phase reaction of allyl chloride with hydroxyl radical.

    PubMed

    Zhang, Yunju; Chao, Kai; Sun, Jingyu; Zhang, Wanqiao; Shi, Haijie; Yao, Cen; Su, Zhongmin; Pan, Xiumei; Zhang, Jingping; Wang, Rongshun

    2014-02-28

    The reaction of allyl chloride with the hydroxyl radical has been investigated on a sound theoretical basis. This is the first time to gain a conclusive insight into the reaction mechanism and kinetics for important pathways in detail. The reaction mechanism confirms that OH addition to the C=C double bond forms the chemically activated adducts, IM1 (CH2CHOHCH2Cl) and IM2 (CH2OHCHCH2Cl) via low barriers, and direct H-abstraction paths may also occur. Variational transition state model and multichannel RRKM theory are employed to calculate the temperature-, pressure-dependent rate constants. The calculated rate constants are in good agreement with the experimental data. At 100 Torr with He as bath gas, IM6 formed by collisional stabilization is the major products in the temperature range 200-600 K; the production of CH2CHCHCl via hydrogen abstractions becomes dominant at high temperatures (600-3000 K). PMID:24588171

  1. Hydroxyl radicals from secondary organic aerosol decomposition in water

    NASA Astrophysics Data System (ADS)

    Tong, Haijie; Arangio, Andrea M.; Lakey, Pascale S. J.; Berkemeier, Thomas; Liu, Fobang; Kampf, Christopher J.; Brune, William H.; Pöschl, Ulrich; Shiraiwa, Manabu

    2016-02-01

    We found that ambient and laboratory-generated secondary organic aerosols (SOA) form substantial amounts of OH radicals upon interaction with liquid water, which can be explained by the decomposition of organic hydroperoxides. The molar OH yield from SOA formed by ozonolysis of terpenes (α-pinene, β-pinene, limonene) is ˜ 0.1 % upon extraction with pure water and increases to ˜ 1.5 % in the presence of Fe2+ ions due to Fenton-like reactions. Upon extraction of SOA samples from OH photooxidation of isoprene, we also detected OH yields of around ˜ 0.1 %, which increases upon addition of Fe2+. Our findings imply that the chemical reactivity and aging of SOA particles is strongly enhanced upon interaction with water and iron. In cloud droplets under dark conditions, SOA decomposition can compete with the classical H2O2 Fenton reaction as the source of OH radicals. Also in the human respiratory tract, the inhalation and deposition of SOA particles may lead to a substantial release of OH radicals, which may contribute to oxidative stress and play an important role in the adverse health effects of atmospheric aerosols.

  2. Hydroxyl radicals from secondary organic aerosol decomposition in water

    NASA Astrophysics Data System (ADS)

    Tong, H.; Arangio, A. M.; Lakey, P. S. J.; Berkemeier, T.; Liu, F.; Kampf, C. J.; Pöschl, U.; Shiraiwa, M.

    2015-11-01

    We found that ambient and laboratory-generated secondary organic aerosols (SOA) form substantial amounts of OH radicals upon interaction with liquid water, which can be explained by the decomposition of organic hydroperoxides. The molar OH yield from SOA formed by ozonolysis of terpenes (α-pinene, β-pinene, limonene) is ~ 0.1 % upon extraction with pure water and increases to ~ 1.5 % in the presence of Fe2+ ions due to Fenton-like reactions. Our findings imply that the chemical reactivity and aging of SOA particles is strongly enhanced upon interaction with water and iron. In cloud droplets under dark conditions, SOA decomposition can compete with the classical H2O2 Fenton reaction as the source of OH radicals. Also in the human respiratory tract, the inhalation and deposition of SOA particles may lead to a substantial release of OH radicals, which may contribute to oxidative stress and play an important role in the adverse health effects of atmospheric aerosols.

  3. Hydroxyl radicals from secondary organic aerosol decomposition in water

    NASA Astrophysics Data System (ADS)

    Tong, Haijie; Arangio, Andrea M.; Lakey, Pascale S. J.; Berkemeier, Thomas; Liu, Fobang; Kampf, Christopher. J.; Pöschl, Ulrich; Shiraiwa, Manabu

    2016-04-01

    We found that ambient and laboratory-generated secondary organic aerosols (SOA) form substantial amounts of OH radicals upon interaction with liquid water, which can be explained by the decomposition of organic hydroperoxides. The molar OH yield from SOA formed by ozonolysis of terpenes (α-pinene, β-pinene, and limonene) is ~ 0.1% upon extraction with pure water, and which increases to ~ 1.5% in the presence of iron ions due to Fenton-like reactions. Our findings imply that the chemical reactivity and aging of SOA particles is strongly enhanced upon interaction with water and iron. In cloud droplets under dark conditions, SOA decomposition can compete with the classical hydrogen peroxide Fenton reaction as the source of OH radicals. Also in the human respiratory tract, the inhalation and deposition of SOA particles may lead to a substantial release of OH radicals, which may contribute to oxidative stress and play an important role in the adverse health effects of atmospheric aerosols.

  4. Decarboxylation of [1-(13)C]leucine by hydroxyl radicals.

    PubMed

    Guitton, J; Tinardon, F; Lamrini, R; Lacan, P; Desage, M; Francina, A

    1998-08-01

    The decarboxylation of [1-13C]leucine by hydroxyl radicals was studied by using gas chromatography-isotope ratio mass spectrometry (GC-IRMS) to follow the production of 13CO2. A Fenton reaction between a (Fe2+)-porphyrin and hydrogen peroxide under aerobic conditions yielded hydroxyl radicals. The decarboxylation rates (VLeu) measured by GC-IRMS were dependent on [1-13C]leucine, porphyrin and hydrogen peroxide concentrations. The 13CO2 production was also dependent on bicarbonate or carbon dioxide added in the reaction medium. Bicarbonate facilitated 13CO2 production, whereas carbon dioxide decreased 13CO2 production. Proton effects on some decarboxylation intermediates could explain bicarbonate or carbon dioxide effects. No effect on the decarboxylation rates was observed in the presence of the classical hydroxyl radicals scavengers dimethyl sulfoxide, mannitol, and uric acid. By contrast, a competitive effect with a strong decrease of the decarboxylation rates was observed in the presence of various amino acids: unlabeled leucine, valine, phenylalanine, cysteine, lysine, and histidine. Two reaction products, methyl-4 oxo-2 pentanoate and methyl-3 butanoate were identified by gas chromatography-mass spectrometry in comparison with standards. The present results suggest that [1-13C]leucine can participate to the coordination sphere of (Fe2+)-porphyrin, with a caged process of the hydroxyl radicals which cannot get out of the coordination sphere. PMID:9680180

  5. QSPR prediction of the hydroxyl radical rate constant of water contaminants.

    PubMed

    Borhani, Tohid Nejad Ghaffar; Saniedanesh, Mohammadhossein; Bagheri, Mehdi; Lim, Jeng Shiun

    2016-07-01

    In advanced oxidation processes (AOPs), the aqueous hydroxyl radical (HO) acts as a strong oxidant to react with organic contaminants. The hydroxyl radical rate constant (kHO) is important for evaluating and modelling of the AOPs. In this study, quantitative structure-property relationship (QSPR) method is applied to model the hydroxyl radical rate constant for a diverse dataset of 457 water contaminants from 27 various chemical classes. The constricted binary particle swarm optimization and multiple-linear regression (BPSO-MLR) are used to obtain the best model with eight theoretical descriptors. An optimized feed forward neural network (FFNN) is developed to investigate the complex performance of the selected molecular parameters with kHO. Although the FFNN prediction results are more accurate than those obtained using BPSO-MLR, the application of the latter is much more convenient. Various internal and external validation techniques indicate that the obtained models could predict the logarithmic hydroxyl radical rate constants of a large number of water contaminants with less than 4% absolute relative error. Finally, the above-mentioned proposed models are compared to those reported earlier and the structural factors contributing to the AOP degradation efficiency are discussed. PMID:27124124

  6. Evidence suggesting a role for hydroxyl radical in passive Heymann nephritis in rats

    SciTech Connect

    Shah, S.V. )

    1988-03-01

    The authors examined the effect of scavengers of reactive oxygen metabolites on proteinuria in the passive Heymann nephritis model of membranous nephropathy. Passive Heymann nephritis was induced by a single intravenous injection of anti-Fx1A IgG in a dose of 10 mg/100 g body weight. Superoxide dismutase, a scavenger of superoxide or catalase which destroys hydrogen peroxide, did not affect the proteinuria. In contrasts, dimethylthiourea (DMTU), a scavenger of hydroxyl radical, markedly reduced the proteinuria. Experiments with {sup 125}I-labeled anti-Fx1A antibody demonstrated that DMTU did not affect the amount of antibody deposited in the kidney. Semiquantitative estimation of IgG and complement deposition in the kidneys showed no differences between the DMTU-treated and control rats. A second hydroxyl radical scavenger, sodium benzoate also resulted in marked reduction in proteinuria. Because of the participation of iron in biological systems to generate hydroxyl radical, they also examined the effect of deferoxamine (DFO) an iron chelator, on the anti-Fx1A-induced proteinuria. There was a significant reduction in proteinuria in rats treated concurrently with DFO. These results suggest a potential role of the hydroxyl radical in passive Heymann nephritis.

  7. HYDROXYL RADICAL/OZONE RATIOS DURING OZONATION PROCESSES. I. THE RCT CONCEPT

    EPA Science Inventory

    The ozonation of model systems and several natural waters was examined in bench-scale batch experiments. In addition to measuring the concentration of ozone (03), the rate of depletion of an in situ hydroxyl radical probe compound was monitored, thus providing information on the ...

  8. PHOTOCHEICAL PRODUCTION OF HYDROXYL RADICAL IN NATURAL WATER - THE ROLE OF IRON AND DISSOLVED ORGANIC MATTER

    EPA Science Inventory

    Photochemical hydroxyl radical (OH) production was measured in several natural waters to investigate the importance of colored dissolved organic matter (CDOM) and iron-CDOM complexes as sources of OH. High rates of OH photoproduction in highly colored, iron-rich, acidic waters a...

  9. A new mechanism for hydroxyl radical production in irradiated nanoparticle solutions.

    PubMed

    Sicard-Roselli, Cécile; Brun, Emilie; Gilles, Manon; Baldacchino, Gérard; Kelsey, Colin; McQuaid, Harold; Polin, Chris; Wardlow, Nathan; Currell, Frederick

    2014-08-27

    The absolute yield of hydroxyl radicals per unit of deposited X-ray energy is determined for the first time for irradiated aqueous solutions containing metal nanoparticles based on a "reference" protocol. Measurements are made as a function of dose rate and nanoparticle concentration. Possible mechanisms for hydroxyl radical production are considered in turn: energy deposition in the nanoparticles followed by its transport into the surrounding environment is unable to account for observed yield whereas energy deposition in the water followed by a catalytic-like reaction at the water-nanoparticle interface can account for the total yield and its dependence on dose rate and nanoparticle concentration. This finding is important because current models used to account for nanoparticle enhancement to radiobiological damage only consider the primary interaction with the nanoparticle, not with the surrounding media. Nothing about the new mechanism appears to be specific to gold, the main requirements being the formation of a structured water layer in the vicinity of the nanoparticle possibly through the interaction of its charge and the water dipoles. The massive hydroxyl radical production is relevant to a number of application fields, particularly nanomedicine since the hydroxyl radical is responsible for the majority of radiation-induced DNA damage.

  10. Arbutin, an intracellular hydroxyl radical scavenger, protects radiation-induced apoptosis in human lymphoma U937 cells.

    PubMed

    Wu, Li-Hua; Li, Peng; Zhao, Qing-Li; Piao, Jin-Lan; Jiao, Yu-Fei; Kadowaki, Makoto; Kondo, Takashi

    2014-11-01

    Ionizing radiation (IR) can generate reactive oxygen species (ROS). Excessive ROS have the potential to damage cellular macromolecules including DNA, proteins, and lipids and eventually lead to cell death. In this study, we evaluated the potential of arbutin, a drug chosen from a series of traditional herbal medicine by measuring intracellular hydroxyl radical scavenging ability in X-irradiated U937 cells. Arbutin (hydroquinone-β-D-glucopyranoside), a naturally occurring glucoside of hydroquinone, has been traditionally used to treat pigmentary disorders. However, there are no reports describing the effect of arbutin on IR-induced apoptosis. We confirmed that arbutin can protect cells from apoptosis induced by X-irradiation. The combination of arbutin and X-irradiation could reduce intracellular hydroxyl radical production and prevent mitochondrial membrane potential loss. It also could down-regulate the expression of phospho-JNK, phospho-p38 in whole cell lysate and activate Bax in mitochondria. Arbutin also inhibits cytochrome C release from mitochondria to cytosol. To verify the role of JNK in X-irradiation-induced apoptosis, the cells were pretreated with a JNK inhibitor, and found that JNK inhibitor could reduce apoptosis induced by X-irradiation. Taken together, our data indicate that arbutin plays an anti-apoptotic role via decreasing intracellular hydroxyl radical production, inhibition of Bax-mitochondria pathway and activation of the JNK/p38 MAPK pathway.

  11. Tropospheric reactions of the haloalkyl radicals formed from hydroxyl radical reaction with a series of alternative fluorocarbons

    NASA Technical Reports Server (NTRS)

    Atkinson, Roger

    1990-01-01

    In the present assessment, the hydrogen containing halocarbons being considered as alternatives to the the presently used chlorofluorocarbons are the hydrochlorofluorocarbons (HCFCs) 123 (CF3CHCl2), 141b (CFCl2CH3), 142b (CF2ClCH3), 22 (CHF2Cl) and 124 (CF3CHFCl) and the hydrofluorocarbons (HFCs) 134a (CF3CH2F), 152a (CHF2CH3) and 125 (CF3CHF2). All of these HCFCs and HFCs will react with the hydroxyl (OH) radical in the troposphere, giving rise to haloalkyl radicals which then undergo a complex series of reactions in the troposphere. These reactions of the haloalkyl radicals formed from the initial OH radical reactions with the HCFCs and HFCs under tropospheric conditions are the focus here.

  12. New model system for testing effects of flavonoids on doxorubicin-related formation of hydroxyl radicals.

    PubMed

    Soucek, Pavel; Kondrova, Eliska; Hermanek, Josef; Stopka, Pavel; Boumendjel, Ahcene; Ueng, Yune-Fang; Gut, Ivan

    2011-02-01

    Doxorubicin belongs to anthracycline cytotoxic drugs and it is widely used as a major therapeutic agent in the treatment of various types of tumors. However,its therapeutic use is limited by the development of myelosuppression and cardiotoxicity after a specific cumulative dose is reached. The aim of this study was to investigate the effect of flavonoids, either natural or synthetic on doxorubicin-mediated formation of oxidative stress implicated in doxorubicin toxicity. Doxorubicin caused a concentration-dependent increase in the formation of hydroxyl radicals in minipig liver microsomes used as an in-vitro model system. When bacterial membranes heterologously expressing human NADPH cytochrome-P450 oxidoreductase were incubated with doxorubicin, formation of the superoxide radical under aerobic conditions and the doxorubicin–semiquinone radical under anaerobic conditions was detected. Forty different flavonoids were tested for their potency to prevent NADPH-induced or Fe2+-induced peroxidation of lipids in the microsomal system. According to the results, seven flavonoids were selected for evaluation of their potency to inhibit doxorubicin-dependent formation of hydroxyl radicals assessed by electron spin resonance. Myricetin, fisetin, and kaempferol were found to produce a significant protective effect against hydroxyl radicals in the minipig liver microsomal system. In conclusion, this study shows the use of a novel cost-effective in-vitro model system for preselection of antioxidants for testing of their protective effects against toxicity of anthracyclines and potentially other oxidative stress-inducing chemicals.

  13. Ab initio study of guanine damage by hydroxyl radical.

    PubMed

    Chaban, Galina M; Wang, Dunyou; Huo, Winifred M

    2015-01-15

    Multiconfigurational ab initio methods are used in this study to examine two initial reactions that take place during the OH radical attack of the DNA base guanine: a ring opening reaction and a hydrogen transfer reaction. The same reactions are also studied in the presence of a single water molecule. The ring opening reaction has a moderate barrier height of ∼20-25 kcal/mol that is relatively insensitive to the presence of water. The barrier of the H-transfer reaction, on the other hand, is lowered from ∼50 to ∼22 kcal/mol when one water molecule is added, thus becoming comparable to the barrier height of the ring opening reaction. PMID:25517252

  14. Formation of hydroxyl radical from the photolysis of salicylic acid.

    PubMed

    Zhou, Can-Hua; Cheng, Shi-Bo; Yin, Hong-Ming; He, Guo-Zhong

    2011-05-26

    Photodissociation dynamics of salicylic acid (SA) in the gas phase at different photolysis wavelengths (266, 315-317 nm) is investigated by probing the nascent OH photoproduct employing the single-photon laser-induced fluorescence (LIF) technique. At all the photolysis wavelengths it is found that the nascent OH radicals are produced mostly in a vibrationally ground state (υ'' = 0) and have similar rotational state distributions. The two spin-orbit and Λ-doublet states of the OH fragment formed in the dissociation are measured to have a nonstatistical distribution at each photolysis wavelength. The LIF signal of the OH could be observed upon photolysis at 317 nm but not at 317.5 nm. The threshold of OH formation from SA photodissociation is estimated to be 98.2 ± 0.9 kcal/mol. The effect of the phenolic OH group on the dissociation of SA is discussed.

  15. Modeling the mechanism of action of lycopene as a hydroxyl radical scavenger.

    PubMed

    Prasad, Ajit Kumar; Mishra, Phool C

    2014-05-01

    The anti-oxidant action of lycopene as a hydroxyl radical scavenger through hydrogen abstraction and addition reaction mechanisms has been investigated. Geometries of seven different conformations of lycopene were optimized employing density functional theory in gas phase which was followed by treatment of their solvation in aqueous media. Thus the all-trans conformation of lycopene was found to be most stable in both gas phase and aqueous media. Four overlapping fragments of all-trans lycopene were considered for calculations of Gibbs barrier energies and rate constants. It is found that several hydrogen atoms can be abstracted from lycopene by a hydroxyl radical barrierlessly. Further, it is shown that addition of an OH radical can also take place to each of the various carbon atoms of lycopene with fairly low barrier energies. Thus lycopene is shown to be an effective anti-oxidant. PMID:24777316

  16. Effect of pH on the conversion of superoxide to hydroxyl free radicals

    SciTech Connect

    Baker, M.S.; Gebicki, J.M.

    1984-10-01

    The conversion of superoxide (O-.2) to the hydroxyl (HO.) free radical by superoxide-driven Fenton reactions was measured by the formation of hydroxylated derivatives from benzoate. Among a range of catalysts required for the conversion, the Fe3+EDTA complex was the most effective. The effect of superoxide dismutase and catalase indicated that O-.2 and H2O2 were essential reactants, while the formation of authentic HO. was confirmed by the inhibiting capacities of formate, t-butanol, and mannitol. The conversion of O-.2 to HO. was tested over a broad pH range, and was found to be highest at pH 4.8 whether Fe3+EDTA or free Fe3+ were used as the catalysts. When Fe3+EDTA was used at the optimum pH, every HO. produced required 3.7 O-.2 radicals, close to the theoretical limit of one HO. from every three O-.2 radicals generated.

  17. Changes in structural characteristics of antioxidative soy protein hydrolysates resulting from scavenging of hydroxyl radicals.

    PubMed

    Zhao, Jing; Xiong, Youling L; McNear, Dave H

    2013-02-01

    Antioxidant activity of soy protein (SP) and its hydrolyzed peptides has been widely reported. During scavenging of radicals, these antioxidative compounds would be oxidatively modified, but their fate is not understood. The objective of this study was to evaluate the structural characteristics of SP hydrolysates (SPHs), compared to intact SP, when used to neutralize hydroxyl radicals (•OH). SPHs with degree of hydrolysis (DH) 1 to 5 were prepared with Alcalase. Antioxidant activity of SPHs was confirmed by lipid oxidation inhibition measured with thiobarbituric acid-reactive substances, ability to scavenge 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radicals, and ferrous ion chelation capability. Oxidation of SPHs was initiated by reaction with •OH generated from 0.1 mM FeCl(3) , 20 mM H(2) O(2) , and 1.0 mM ascorbate. After oxidative stress, carbonyl content of SPHs increased by 2- to 3-fold and sulfhydryl groups decreased by up to 42% compared to nonoxidized samples (P < 0.05). Methionine, histidine, and lysine residues were significantly reduced as a result of inactivating •OH (P < 0.05). Attenuated total reflectance-Fourier transform infrared and circular dichroism spectroscopy suggested the conversion of helical structure to strands and turns. Oxidatively modified SPHs had a lower intrinsic fluorescence intensity but similar solubility when compared to nonoxidized samples. These structural changes due to •OH stress may impact the ingredient interaction and functionality of SPHs in food products. PMID:23331209

  18. Radiation-induced cell lethality of samonella typhimurium ATCC 14028: Cooperative effect of hydroxyl radical and oxygen

    SciTech Connect

    Kim, Y.A.; Thayer, D.W.

    1995-10-01

    The lethality of {gamma}-radiation doses of 0.2 to 1.0 kGy for Salmonella typhimurium ATCC 14028 was measured in the presence of air, N{sub 2} and N{sub 2}O and with the hydroxyl radical scavengers formate and polyethylene glycol (PEG), M{sub r} 8,000. Saturation of cell suspensions with either N{sub 2}O or N{sub 2}/N{sub 2}/N{sub 2}O (1:1, v/v) gas was expected to double the number of hydroxyl radicals (OH{center_dot}) and to produce an equivalent increase in lethality, but this did not occur. Adding 10% (v/v) O{sub 2} to either N{sub 2}/N{sub 2}O gas produced approximately the same {gamma}-irradiation lethality for S. typhimurium as did air. Addition of hydroxyl radical scavengers, 40 mM formate and 1.5% (w/v) PEG, significantly reduced the lethality of {gamma} radiation for S. typhimurium in the presence of air but not in the presence of N{sub 2} or N{sub 2}O gases. Membrane-permeable formate provided slightly better protection than nonpermeable PEG. Cells of S. typhimurium grown under anaerobic conditions were more sensitive to radiation, and were less protected by hydroxyl radical scavengers, especially formate, than when cells grown under aerobic conditions were irradiated in the presence of oxygen. Hydroxyl radical scavengers provided no further protection during irradiation in the absence of oxygen. These results indicated that the increased radiation sensitivity of cells grown under anaerobic conditions may be related to superoxide radicals which could increase intercellular damage during irradiation in the presence of oxygen. However, endogenous superoxide dismutase and catalase activities did not protect cells from the radiation-induced lethality of S. typhimurium. Cytoplasmic extracts protected bacterial DNA in vitro in either the presence of absence of oxygen, and no radiation-induced lipid peroxidation of the cellular components was identified by measuring the levels of 2-thiobarbituric acid. 38 refs., 4 figs., 2 tabs.

  19. The Collisional and Radiative Processes of the Hydroxyl Radical

    NASA Astrophysics Data System (ADS)

    Steffens, Kristen Lisa

    1995-01-01

    The OH radical is an important species in the chemistry of atmospheric and combustion environments, where an understanding of OH concentration and chemistry is necessary to create and validate chemical models. Laser-induced fluorescence (LIF) is used with great success in OH detection, but OH LIF measurements require a vast knowledge of the collisional and spectroscopic properties of OH. Information is still lacking, especially concerning vibrational levels v^' > 0 of the rm A^2Sigma^+ electronic state. We investigate transition probabilities and collisional processes of these higher vibrational levels. Experimental vibrational band transition probabilities from v^' = 3 and 2 of OH rm A^2Sigma^+ are needed to determine the electronic transition moment for the rm A^2Sigma^+ -rm X^2Pi_{i } system to calculate a consistent set of rotational and vibrational dependent transition probabilities for uses including rm X^2Pi_ {i} temperature determinations and rm A^2Sigma^+ and rm X^2Pi_{i} nascent population determinations. Using LIF in a low -pressure CH_4/O_2 flame, we measured relative emission intensities for vibrational bands (3,0) through (3,5) and (2,0) through (2,6). Our emission intensities have been used in another study to determine the best rm A^2 Sigma^+-rm X^2 Pi_{i} electronic transition moment. For quantitative OH concentration measurements in high pressure flames exciting the predissociative v ^' = 3 level, one must account for vibrational energy transfer (VET). We measure the amounts of VET occurring from v^' = 3 in CH_4/O_2 , CH_4/air, and H _2/O_2 flames at pressures between 14 and 760 Torr. Significant amounts of VET occur in all flames and must be accounted for to get accurate OH concentrations. Stratospheric OH concentration measurement employs OH rm A^2Sigma^+v ^' = 1 excitation, which requires accurate VET and quenching cross sections for major colliders. We use LIF to measure the v^ ' = 1 VET and quenching cross sections for N_2, O_2 and CO_2

  20. Hydroxyl radical production and oxidative damage induced by cadmium and naphthalene in liver of Carassius auratus.

    PubMed

    Shi, Huahong; Sui, Yunxia; Wang, Xiaorong; Luo, Yi; Ji, Liangliang

    2005-01-01

    Freshwater goldfish (Carassius auratus) were exposed to cadmium (Cd) from 0 to 5 mg/L, and naphthalene (NAP) from 0 to 50 mg/L. Twenty-four hours after the exposure, reactive oxygen species (ROS) was trapped by phenyl-tert-butyl nitrone and detected by electron paramagnetic resonance (EPR). Protein carbonyl (PCO) and lipid peroxidation (LPO) content were determined. The activities of superoxide dismutase (SOD) and catalase (CAT) were also measured. The EPR spectra signals were characterized by prominent six-line spectra, which were defined as hydroxyl radical ((.)OH). As compared to the control group, Cd and NAP significantly induced (.)OH production marked by the intensity of the prominent spectra at higher concentrations. Both xenobiotics also increased LPO content and PCO content, depending on the concentrations. Either LPO or PCO content showed significant relation with (.)OH production. Cd increased the activity of SOD and decreased that of CAT at 5 mg/L, and NAP increased the activities of SOD and CAT at 5 mg/L. The results clearly indicated that these two structurally different non-redox cycling xenobiotics could induce (.)OH generation and result in oxidative damage in liver of C. auratus, and these effects were concentration-dependent.

  1. Mechanism of O((3)P) formation from a hydroxyl radical pair in aqueous solution.

    PubMed

    Codorniu-Hernández, Edelsys; Hall, Kyle Wm; Boese, A Daniel; Ziemianowicz, Daniel; Carpendale, Sheelagh; Kusalik, Peter G

    2015-10-13

    The reaction mechanism for the rapid formation of a triplet oxygen atom, O((3)P), from a pair of triplet-state hydroxyl radicals in liquid water is explored utilizing extensive Car-Parrinello MD simulations and advanced visualization techniques. The local solvation structures, the evolution of atomic charges, atomic separations, spin densities, electron localization functions, and frontier molecular orbitals, as well as free energy profiles, evidence that the reaction proceeds through a hybrid (hydrogen atom transfer and electron-proton transfer) and hemibond-assisted reaction mechanism. A benchmarking study utilizing high-level ab initio calculations to examine the interactions of a hydroxyl radical pair in the gas phase and the influence of a hemibonded water is also provided. The results presented here should serve as a foundation for further experimental and theoretical studies aimed at better understanding the role and potential applications of the triplet oxygen atom as a potent reactive oxygen species. PMID:26574263

  2. KINETIC STUDIES OF THE REACTION OF HYDROXYL RADICALS WITH TRICHLOROETHYLENE AND TETRACHLOROETHYLENE. (R826169)

    EPA Science Inventory

    Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C2HCl3 (k1) and C2Cl4 (k2) over an extended temperature range at 740±10 Torr in a He bath gas. These...

  3. New technological developments for the remote detection of atmospheric hydroxyl radicals

    NASA Technical Reports Server (NTRS)

    Mcdermid, I. S.; Laudenslager, J. B.; Pacala, T. J.

    1983-01-01

    New developments in the areas of narrowband tunable excimer lasers, high-resolution high-rejection optical filters, and wavelength measurement devices are considered for application to the remote sensing of atmospheric hydroxyl radicals. The conclusion is that an increase in the SNR of 10,000 could readily be gained through the use of these new devices. Also, considerable reductions in size and electrical energy consumption could be realized.

  4. Rate constants for the reactions of hydroxyl and hydroperoxyl radicals with ozone.

    NASA Technical Reports Server (NTRS)

    Demore, W. B.

    1973-01-01

    Chain decomposition of ozone by hydroxyl and hydroperoxyl radicals has been observed. The rate constant at 300 K for OH + O3 yielding HO2 + O2 is eight times ten to the -14th power cubic centimeters per second. The rate constant for HO2 + O3 yielding OH + 2O2 is three times ten to the -15th power cubic centimeters per second. These results have implications concerning stratospheric ozone.

  5. Hydroxyl-radical-initiated oxidation mechanism of bromopropane.

    PubMed

    Martínez-Avilés, Mónica; Rosado-Reyes, Claudette M; Francisco, Joseph S

    2008-08-28

    Bromopropane has been considered as a replacement for chlorofluorocarbons used as the active component of industrial cleaning solvents, more specifically for HCFC-141b. The proposed mechanism for the atmospheric oxidation of bromopropane is studied via ab initio methodology. Ab initio molecular orbital methods at the CCSD(T)/6-311++G(2df,2p)//MP2/6-31G(d) level of theory have been used to determine the structure and energetics of the 58 species and transition states involved in the atmospheric oxidation of bromopropane. The calculations show that the major oxidation species is bromoacetone. Other brominated species that result from the oxidation are BrCH 2CH 2C(O)H, BrC(O)CH 2CH 3, and BrC(O)H, potential new bromine reservoir species that result from bromopropane in the atmosphere. PMID:18666763

  6. Modelling On Photogeneration Of Hydroxyl Radical In Surface Waters And Its Reactivity Towards Pharmaceutical Wastes

    NASA Astrophysics Data System (ADS)

    Das, Radha; Vione, Davide; Rubertelli, Francesca; Maurino, Valter; Minero, Claudio; Barbati, Stéphane; Chiron, Serge

    2010-10-01

    This paper reports a simple model to describe the formation and reactivity of hydroxyl radicals in the whole column of freshwater lakes. It is based on empirical irradiation data and is a function of the water chemical composition (the photochemically significant parameters NPOC, nitrate, nitrite, carbonate and bicarbonate), the lake conformation best expressed as the average depth, and the water absorption spectrum in a simplified Lambert-Beer approach. The purpose is to derive the lifetime of dissolved molecules, due to reaction with •OH, on the basis of their second-order rate constants with the hydroxyl radical. The model was applied to two compounds of pharmaceutical wastes ibuprofen and carbamazepine, for which the second-order rate constants for reaction with the hydroxyl radical were measured by means of the competition kinetics with 2-propanol. The measured values of the rate constants are 1.0×1010 and 1.6×1010M-1 s-1 for ibuprofen and carbamazepine, respectively. The model suggests that the lifetime of a given compound can be very variable in different lakes, even more than the lifetime of different compounds in the same lake. It can be concluded that as far as the reaction with •OH, is concerned the concepts of photolability and photostability, traditionally attached to definite compounds, are ecosystem-dependent at least as much as they depend on the molecule under consideration.

  7. Role of hydrogen peroxide and hydroxyl radical in pyrite oxidation by molecular oxygen

    NASA Astrophysics Data System (ADS)

    Schoonen, Martin A. A.; Harrington, Andrea D.; Laffers, Richard; Strongin, Daniel R.

    2010-09-01

    Hydrogen peroxide and hydroxyl radical are readily formed during the oxidation of pyrite with molecular oxygen over a wide range of pH conditions. However, pretreatment of the pyrite surface influences how much of the intermediates are formed and their fate. Acid-washed pyrite produces significant amounts of hydrogen peroxide and hydroxyl radical when suspended in air-saturated water. However, the hydrogen peroxide concentration shows an exponential decrease with time. Suspensions made with partially oxidized pyrite yield significantly lower amounts of hydrogen peroxide product. The presence of Fe(III)-oxide or Fe(III)-hydroxide patches facilitates the conversion of hydrogen peroxide to oxygen and water. Hence, the degree to which a pyrite surface is covered with patches of Fe(III)-oxide or Fe(III)-hydroxide patches is an important control on the concentration of hydrogen peroxide in solution. Hydrogen peroxide appears to be an important intermediate in the four-electron transfer from pyrite to molecular oxygen. Addition of catalase, an enzyme that decomposes hydrogen peroxide to water and molecular oxygen, to a pyrite suspension reduces the oxidation rate by 40%. By contrast, hydroxyl radical does not appear to play a significant role in the oxidation mechanism. It is estimated on the basis of a molecular oxygen and sulfate mass balance that 5-6% of the molecular oxygen is consumed without forming sulfate.

  8. Modelling On Photogeneration Of Hydroxyl Radical In Surface Waters And Its Reactivity Towards Pharmaceutical Wastes

    SciTech Connect

    Das, Radha; Vione, Davide; Rubertelli, Francesca; Maurino, Valter; Minero, Claudio; Barbati, Stephane; Chiron, Serge

    2010-10-26

    This paper reports a simple model to describe the formation and reactivity of hydroxyl radicals in the whole column of freshwater lakes. It is based on empirical irradiation data and is a function of the water chemical composition (the photochemically significant parameters NPOC, nitrate, nitrite, carbonate and bicarbonate), the lake conformation best expressed as the average depth, and the water absorption spectrum in a simplified Lambert-Beer approach. The purpose is to derive the lifetime of dissolved molecules, due to reaction with OH, on the basis of their second-order rate constants with the hydroxyl radical. The model was applied to two compounds of pharmaceutical wastes ibuprofen and carbamazepine, for which the second-order rate constants for reaction with the hydroxyl radical were measured by means of the competition kinetics with 2-propanol. The measured values of the rate constants are 1.0x10{sup 10} and 1.6x10{sup 10} M{sup -1} s{sup -1} for ibuprofen and carbamazepine, respectively. The model suggests that the lifetime of a given compound can be very variable in different lakes, even more than the lifetime of different compounds in the same lake. It can be concluded that as far as the reaction with OH, is concerned the concepts of photolability and photostability, traditionally attached to definite compounds, are ecosystem-dependent at least as much as they depend on the molecule under consideration.

  9. Pulsed Electron Beam Water Radiolysis for Sub-Microsecond Hydroxyl Radical Protein Footprinting

    PubMed Central

    Watson, Caroline; Janik, Ireneusz; Zhuang, Tiandi; Charvátová, Olga; Woods, Robert J.; Sharp, Joshua S.

    2009-01-01

    Hydroxyl radical footprinting is a valuable technique for studying protein structure, but care must be taken to ensure that the protein does not unfold during the labeling process due to oxidative damage. Footprinting methods based on sub-microsecond laser photolysis of peroxide that complete the labeling process faster than the protein can unfold have been recently described; however, the mere presence of large amounts of hydrogen peroxide can also cause uncontrolled oxidation and minor conformational changes. We have developed a novel method for sub-microsecond hydroxyl radical protein footprinting using a pulsed electron beam from a 2 MeV Van de Graaff electron accelerator to generate a high concentration of hydroxyl radicals by radiolysis of water. The amount of oxidation can be controlled by buffer composition, pulsewidth, dose, and dissolved nitrous oxide gas in the sample. Our results with ubiquitin and β-lactoglobulin A demonstrate that one sub-microsecond electron beam pulse produces extensive protein surface modifications. Highly reactive residues that are buried within the protein structure are not oxidized, indicating that the protein retains its folded structure during the labeling process. Time-resolved spectroscopy indicates that the major part of protein oxidation is complete in a timescale shorter than that of large scale protein motions. PMID:19265387

  10. High-throughput SHAPE and hydroxyl radical analysis of RNA structure and ribonucleoprotein assembly.

    PubMed

    McGinnis, Jennifer L; Duncan, Caia D S; Weeks, Kevin M

    2009-01-01

    RNA folds to form complex structures vital to many cellular functions. Proteins facilitate RNA folding at both the secondary and tertiary structure levels. An absolute prerequisite for understanding RNA folding and ribonucleoprotein (RNP) assembly reactions is a complete understanding of the RNA structure at each stage of the folding or assembly process. Here we provide a guide for comprehensive and high-throughput analysis of RNA secondary and tertiary structure using SHAPE and hydroxyl radical footprinting. As an example of the strong and sometimes surprising conclusions that can emerge from high-throughput analysis of RNA folding and RNP assembly, we summarize the structure of the bI3 group I intron RNA in four distinct states. Dramatic structural rearrangements occur in both secondary and tertiary structure as the RNA folds from the free state to the active, six-component, RNP complex. As high-throughput and high-resolution approaches are applied broadly to large protein-RNA complexes, other proteins previously viewed as making simple contributions to RNA folding are also likely to be found to exert multifaceted, long-range, cooperative, and nonadditive effects on RNA folding. These protein-induced contributions add another level of control, and potential regulatory function, in RNP complexes.

  11. Environmental contamination and airborne microbial counts: a role for hydroxyl radical disinfection units?

    PubMed

    Wong, V; Staniforth, K; Boswell, T C

    2011-07-01

    Environmental contamination is thought to play a role in the spread of infection in hospitals and there has been increased interest in novel air disinfection systems in preventing infection. In this study the efficacy of a hydroxyl radical air disinfection system (Inov8 unit) in reducing the number of airborne bacteria was assessed in a clinical setting. Environmental contamination was assessed using settle plates and air samples in three settings: (1) non-clinical room; (2) non-clinical room with defined activity; and (3) single intensive care unit cubicle. A comparison of air counts and environmental contamination rates was made with the Inov8 units on and off. The Inov8 unit produced an overall reduction in both air sample and settle plate counts in each setting (P<0.001, Wilcoxon signed-rank test). There was a mean reduction in air sample counts of 26%, 39% and 55% for settings 1, 2 and 3 respectively. The corresponding reductions in settle plate counts were 35%, 62% and 54%. These results suggest that this type of novel air disinfection may have a role in improving air quality and reducing environmental contamination within clinical isolation rooms. Further work is required to assess the effect on specific pathogens, and to establish whether this will reduce the risks of patients and/or healthcare workers acquiring such pathogens from the environment.

  12. Making graphene holey. Gold-nanoparticle-mediated hydroxyl radical attack on reduced graphene oxide.

    PubMed

    Radich, James G; Kamat, Prashant V

    2013-06-25

    Graphene oxide (GO) and reduced graphene oxide (RGO) have important applications in the development of new electrode and photocatalyst architectures. Gold nanoparticles (AuNPs) have now been employed as catalyst to generate OH(•) and oxidize RGO via hydroxyl radical attack. The oxidation of RGO is marked by pores and wrinkles within the 2-D network. Nanosecond laser flash photolysis was used in conjunction with competition kinetics to elucidate the oxidative mechanism and calculate rate constants for the AuNP-catalyzed and direct reaction between RGO and OH(•). The results highlight the use of the AuNP-mediated oxidation reaction to tune the properties of RGO through the degree of oxidation and/or functional group selectivity in addition to the nanoporous and wrinkle facets. The ability of AuNPs to catalyze the photolytic decomposition of H2O2 as well as the hydroxyl radical-induced oxidation of RGO raises new issues concerning graphene stability in energy conversion and storage (photocatalysis, fuel cells, Li-ion batteries, etc.). Understanding RGO oxidation by free radicals will aid in maintaining the long-term stability of RGO-based functional composites where intimate contact with radical species is inevitable.

  13. Making graphene holey. Gold-nanoparticle-mediated hydroxyl radical attack on reduced graphene oxide.

    PubMed

    Radich, James G; Kamat, Prashant V

    2013-06-25

    Graphene oxide (GO) and reduced graphene oxide (RGO) have important applications in the development of new electrode and photocatalyst architectures. Gold nanoparticles (AuNPs) have now been employed as catalyst to generate OH(•) and oxidize RGO via hydroxyl radical attack. The oxidation of RGO is marked by pores and wrinkles within the 2-D network. Nanosecond laser flash photolysis was used in conjunction with competition kinetics to elucidate the oxidative mechanism and calculate rate constants for the AuNP-catalyzed and direct reaction between RGO and OH(•). The results highlight the use of the AuNP-mediated oxidation reaction to tune the properties of RGO through the degree of oxidation and/or functional group selectivity in addition to the nanoporous and wrinkle facets. The ability of AuNPs to catalyze the photolytic decomposition of H2O2 as well as the hydroxyl radical-induced oxidation of RGO raises new issues concerning graphene stability in energy conversion and storage (photocatalysis, fuel cells, Li-ion batteries, etc.). Understanding RGO oxidation by free radicals will aid in maintaining the long-term stability of RGO-based functional composites where intimate contact with radical species is inevitable. PMID:23641756

  14. Protective effects of hydroxybenzoic acids and their esters on cell damage induced by hydroxyl radicals and hydrogen peroxides.

    PubMed

    Masaki, H; Okamoto, N; Sakaki, S; Sakurai, H

    1997-04-01

    The purpose of this study was to evaluate the hydroxyl radical scavenging activities of hydroxybenzoic acids and their esters from both chemical and biological aspects. These activities of hydroxybenzoic acids and their related compounds were estimated by ESR-spin trapping method, in which 3,4,5-trihydroxybenzoic acid and its ethyl and propyl esters showed the highest activities as estimated by IC50 value (50% inhibition concentration of hydroxyl radicals generated in the system): 78.04 +/- 11.23, 95.95 +/- 2.64, and 86.46 +/- 2.31 microM, respectively. In addition, 3,4,5-trihydroxybenzoic acid (gallic acid) at a concentration of 25 microM, protected against dermal fibroblast cell damage induced by H2O2, and enhanced the survival to 83.8 +/- 3.1%, in which the survival of control was 44.2 +/- 1.0%. Based on these results, the pretreatment effects of 3,4,5-trihydroxybenzoic acid n-alkyl esters on cell damage induced by H2O2 were examined. The survival of fibroblasts pretreated with the esters increased depending on the alkyl chain-length. Both C12 and C16 alkyl esters gave almost complete cell survival of 89.5 +/- 2.0% and 91.3 +/- 1.0%, respectively. The order of the protective effects of the compounds was in good agreement with that of their partition coefficients, suggesting that 3,4,5-trihydroxybenzoic acid alkyl esters are incorporated into fibroblasts, and thus prevent the cells from the toxicity caused by H2O2. In addition, an increase of intracellular peroxide formation in fibroblasts induced by UVA-irradiation, was suppressed to 2.27 +/- 0.41 nmol/10(4) cells by pretreatment with C16 alkyl ester at a concentration of 25 microM. Since 3,4,5-trihydroxybenzoic group has been demonstrated to possess a potent scavenging activity of hydroxyl radicals, this moiety was indicated to be important in preventing cell damage induced by UVA or H2O2: in turn, these produce hydroxyl radicals in the presence of trace metal ions such as iron and copper in cells.

  15. Degradation pathways of lamotrigine under advanced treatment by direct UV photolysis, hydroxyl radicals, and ozone.

    PubMed

    Keen, Olya S; Ferrer, Imma; Michael Thurman, E; Linden, Karl G

    2014-12-01

    Lamotrigine is recently recognized as a persistent pharmaceutical in the water environment and wastewater effluents. Its degradation was studied under UV and ozone advanced oxidation treatments with reaction kinetics of lamotrigine with ozone (≈4 M(-1)s(-1)), hydroxyl radical [(2.1 ± 0.3) × 10(9)M(-1)s(-1)] and by UV photolysis with low and medium pressure mercury vapor lamps [quantum yields ≈0 and (2.7 ± 0.4)× 10(-4) respectively] determined. All constants were measured at pH 6 and at temperature ≈20°C. The results indicate that lamotrigine is slow to respond to direct photolysis or oxidation by ozone and no attenuation of the contaminant is expected in UV or ozone disinfection applications. The compound reacts rapidly with hydroxyl radicals indicating that advanced oxidation processes would be effective for its treatment. Degradation products were identified under each treatment process using accurate mass time-of-flight spectrometry and pathways of decay were proposed. The main transformation pathways in each process were: dechlorination of the benzene ring during direct photolysis; hydroxyl group addition to the benzene ring during the reaction with hydroxyl radicals; and triazine ring opening after reaction with ozone. Different products that form in each process may be to a varying degree less environmentally stable than the parent lamotrigine. In addition, a novel method of ozone quenching without addition of salts is presented. The new quenching method would allow subsequent mass spectrometry analysis without a solid phase extraction clean-up step. The method involves raising the pH of the sample to approximately 10 for a few seconds and lowering it back and is therefore limited to applications for which temporary pH change is not expected to affect the outcome of the analysis.

  16. Hydroxyl Radical (OH•) Reaction with Guanine in an Aqueous Environment: A DFT Study

    PubMed Central

    Kumar, Anil; Pottiboyina, Venkata; Sevilla, Michael D.

    2011-01-01

    The reaction of hydroxyl radical (OH•) with DNA accounts for about half of radiation-induced DNA damage in living systems. Previous literature reports point out that the reaction of OH• with DNA proceeds mainly through the addition of OH• to the C=C bond of the DNA bases. However, recently it has been reported that the principal reaction of OH• with dGuo (deoxyguanosine) is the direct hydrogen atom abstraction from its exocyclic amine group rather than addition of OH• to the C=C bond. In the present work, these two reaction pathways of OH• attack on guanine (G) in the presence of water molecules (aqueous environment) are investigated using the density functional theory (DFT) B3LYP method with 6-31G* and 6-31++G** basis sets. The calculations show that the initial addition of the OH• at C4=C5 double bond of guanine is barrier free and the adduct radical (G-OH•) has only a small activation barrier of ca. 1 – 6 kcal/mol leading to the formation of a metastable ion-pair intermediate (G•+---OH−). The formation of ion-pair is a result of the highly oxidizing nature of the OH• in aqueous media. The resulting ion-pair (G•+---OH−) deprotonates to form H2O and neutral G radicals favoring G(N1-H)• with an activation barrier of ca. 5 kcal/mol. The overall process from the G(C4)-OH• (adduct) to G(N1-H)• and water is found to be exothermic in nature by more than 13 kcal/mol. (G-OH•), (G•+---OH−), and G(N1-H)• were further characterized by the CAM-B3LYP calculations of their UV-visible spectra and good agreement between theory and experiment is achieved. Our calculations for the direct hydrogen abstraction pathway from N1 and N2 sites of guanine by the OH• show that this is also a competitive route to produce G(N2-H)•, G(N1-H)• and H2O. PMID:22050033

  17. Hydroxyl radical (OH•) reaction with guanine in an aqueous environment: a DFT study.

    PubMed

    Kumar, Anil; Pottiboyina, Venkata; Sevilla, Michael D

    2011-12-22

    The reaction of hydroxyl radical (OH(•)) with DNA accounts for about half of radiation-induced DNA damage in living systems. Previous literature reports point out that the reaction of OH(•) with DNA proceeds mainly through the addition of OH(•) to the C═C bonds of the DNA bases. However, recently it has been reported that the principal reaction of OH(•) with dGuo (deoxyguanosine) is the direct hydrogen atom abstraction from its exocyclic amine group rather than addition of OH(•) to the C═C bonds. In the present work, these two reaction pathways of OH(•) attack on guanine (G) in the presence of water molecules (aqueous environment) are investigated using the density functional theory (DFT) B3LYP method with 6-31G* and 6-31++G** basis sets. The calculations show that the initial addition of the OH(•) at C(4)═C(5) double bond of guanine is barrier free and the adduct radical (G-OH(•)) has only a small activation barrier of ca. 1-6 kcal/mol leading to the formation of a metastable ion-pair intermediate (G(•+)---OH(-)). The formation of ion-pair is a result of the highly oxidizing nature of the OH(•) in aqueous media. The resulting ion-pair (G(•+)---OH(-)) deprotonates to form H(2)O and neutral G radicals favoring G(N(1)-H)(•) with an activation barrier of ca. 5 kcal/mol. The overall process from the G(C(4))-OH(•) (adduct) to G(N(1)-H)(•) and water is found to be exothermic in nature by more than 13 kcal/mol. (G-OH(•)), (G(•+)---OH(-)), and G(N(1)-H)(•) were further characterized by the CAM-B3LYP calculations of their UV-vis spectra and good agreement between theory and experiment is achieved. Our calculations for the direct hydrogen abstraction pathway from N(1) and N(2) sites of guanine by the OH(•) show that this is also a competitive route to produce G(N(2)-H)(•), G(N(1)-H)(•) and H(2)O.

  18. Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling.

    PubMed

    Shannon, Robin J; Blitz, Mark A; Goddard, Andrew; Heard, Dwayne E

    2013-09-01

    Understanding the abundances of molecules in dense interstellar clouds requires knowledge of the rates of gas-phase reactions between uncharged species. However, because of the low temperatures within these clouds, reactions with an activation barrier were considered too slow to play an important role. Here we show that, despite the presence of a barrier, the rate coefficient for the reaction between the hydroxyl radical (OH) and methanol--one of the most abundant organic molecules in space--is almost two orders of magnitude larger at 63 K than previously measured at ∼200 K. We also observe the formation of the methoxy radical product, which was recently detected in space. These results are interpreted by the formation of a hydrogen-bonded complex that is sufficiently long-lived to undergo quantum-mechanical tunnelling to form products. We postulate that this tunnelling mechanism for the oxidation of organic molecules by OH is widespread in low-temperature interstellar environments.

  19. Catalytic ozonation of oxalate with a cerium supported palladium oxide: an efficient degradation not relying on hydroxyl radical oxidation.

    PubMed

    Zhang, Tao; Li, Weiwei; Croué, Jean-Philippe

    2011-11-01

    The cerium supported palladium oxide (PdO/CeO(2)) at a low palladium loading was found very effective in catalytic ozonation of oxalate, a probe compound that is difficult to be efficiently degraded in water with hydroxyl radical oxidation and one of the major byproducts in ozonation of organic matter. The oxalate was degraded into CO(2) during the catalytic ozonation. The molar ratio of oxalate degraded to ozone consumption increased with increasing catalyst dose and decreasing ozone dosage and pH under the conditions of this study. The maximum molar ratio reached around 1, meaning that the catalyst was highly active and selective for oxalate degradation in water. The catalytic ozonation, which showed relatively stable activity, does not promote hydroxyl radical generation from ozone. Analysis with ATR-FTIR and in situ Raman spectroscopy revealed that 1) oxalate was adsorbed on CeO(2) of the catalyst forming surface complexes, and 2) O(3) was adsorbed on PdO of the catalyst and further decomposed to surface atomic oxygen (*O), surface peroxide (*O(2)), and O(2) gas in sequence. The results indicate that the high activity of the catalyst is related to the synergetic function of PdO and CeO(2) in that the surface atomic oxygen readily reacts with the surface cerium-oxalate complex. This kind of catalytic ozonation would be potentially effective for the degradation of polar refractory organic pollutants and hydrophilic natural organic matter.

  20. Optical measurement of static temperature and hydroxyl radical profiles in a hydrogen-fueled supersonic combustor

    NASA Technical Reports Server (NTRS)

    Gaugler, R. E.

    1974-01-01

    Profiles of static temperature and hydroxyl radical concentration were measured in a two-dimensional supersonic combustor test section 22.8 cm downstream of hydrogen injection. A high-pressure gas generator supplied vitiated air to the test section at Mach 2.44, atmospheric pressure, and a total temperature of about 2240 K. Room-temperature hydrogen was injected through a 0.40-cm step slot at Mach 1 and matched pressure. The measurements utilized a noninterfering spectral line absorption technique in which narrow ultraviolet emission lines of the hydroxyl electronic transition are absorbed by the broader absorption lines in the combustion gas. Comparison of the measured temperature profiles with theoretical calculations showed good agreement.

  1. Oxidation of amylose and amylopectin by hydroxyl radicals assessed by electrospray ionisation mass spectrometry.

    PubMed

    Simões, Joana; Moreira, Ana S P; da Costa, Elisabete; Evtyugin, Dmitry; Domingues, Pedro; Nunes, Fernando M; Coimbra, Manuel A; Domingues, M Rosário M

    2016-09-01

    The hydroxyl radicals (HO) are one of the most reactive oxygen species (ROS) involved in the oxidative damage of biological molecules, including carbohydrates. During the industrial processing of food, ROS can be formed. In order to identify the structural changes induced in starch by oxidation, amylose, amylopectin, and maltotriose, an oligosaccharide structurally related to these polysaccharides, were subjected to oxidation with HO generated under Fenton reaction conditions (Fe(2+)/H2O2). The oxidised polysaccharides were hydrolysed by α-amylase and the obtained oligosaccharides were fractionated by ligand-exchange/size-exclusion chromatography. Both acidic and neutral α-amylase resistant oligosaccharides were characterized by mass spectrometry. In oxidised neutral products, new keto, hydroxyl, and hydroperoxy moieties, and oxidative ring scission were observed at the reducing end of the oligosaccharides. The acid sugar residues occurred at the reducing end and included gluconic and glucuronic acid derivatives, and acids formed by oxidative ring scission, namely, arabinonic, erythronic, glyceric and glycolic acids.

  2. The impact of the hydroxyl radical photochemical sources on the rivastigmine drug transformation in mimic and natural waters.

    PubMed

    Passananti, Monica; Temussi, Fabio; Iesce, Maria Rosaria; Mailhot, Gilles; Brigante, Marcello

    2013-09-15

    In this paper we investigated the degradation of the rivastigmine drug induced by hydroxyl radical in synthetic and natural waters focusing on both reactivity and photoproducts identification. The hydroxyl radical formation rate was quantified by using terephthalic acid as trapping molecule and it was related with the rivastigmine degradation rate. The second order rate constant between hydroxyl radical and rivastigmine was estimated to be ≈ 5.8 × 10(9) M(-1) s(-1). Irradiation of rivastigmine in three natural waters (rain, lake and river) and comparison with degradation rates observed in synthetic solutions using nitrite, nitrate and hydrogen peroxide suggest that, in addition to hydroxyl radical, also nitroderived radicals (NO/NO2) are responsible for the pollutant degradation in natural media. In fact, the evaluated degradation rates in three natural waters are greatly higher than those estimated considering only the reactivity with photogenerated hydroxyl radical. Using nitrites and nitrates as photochemical OH source, the rivastigmine degradation cannot be described considering only the hydroxyl radical reactivity suggesting that NO and NO2 radicals could play a key role during indirect degradation. Moreover main degradation products have been identified by means of HPLC-MS. Hydroxylation of the aromatic ring as well as carbamate and amino chain oxidation were suggested as main reaction mechanisms, but also nitroderived compounds were characterized. Finally polychromatic irradiations of three rivastigmine doped natural waters (rain, river and lake) underlined the role of the indirect degradation that needs to be considered when direct degradation of selected pollutants is negligible under environmental-like conditions.

  3. The impact of the hydroxyl radical photochemical sources on the rivastigmine drug transformation in mimic and natural waters.

    PubMed

    Passananti, Monica; Temussi, Fabio; Iesce, Maria Rosaria; Mailhot, Gilles; Brigante, Marcello

    2013-09-15

    In this paper we investigated the degradation of the rivastigmine drug induced by hydroxyl radical in synthetic and natural waters focusing on both reactivity and photoproducts identification. The hydroxyl radical formation rate was quantified by using terephthalic acid as trapping molecule and it was related with the rivastigmine degradation rate. The second order rate constant between hydroxyl radical and rivastigmine was estimated to be ≈ 5.8 × 10(9) M(-1) s(-1). Irradiation of rivastigmine in three natural waters (rain, lake and river) and comparison with degradation rates observed in synthetic solutions using nitrite, nitrate and hydrogen peroxide suggest that, in addition to hydroxyl radical, also nitroderived radicals (NO/NO2) are responsible for the pollutant degradation in natural media. In fact, the evaluated degradation rates in three natural waters are greatly higher than those estimated considering only the reactivity with photogenerated hydroxyl radical. Using nitrites and nitrates as photochemical OH source, the rivastigmine degradation cannot be described considering only the hydroxyl radical reactivity suggesting that NO and NO2 radicals could play a key role during indirect degradation. Moreover main degradation products have been identified by means of HPLC-MS. Hydroxylation of the aromatic ring as well as carbamate and amino chain oxidation were suggested as main reaction mechanisms, but also nitroderived compounds were characterized. Finally polychromatic irradiations of three rivastigmine doped natural waters (rain, river and lake) underlined the role of the indirect degradation that needs to be considered when direct degradation of selected pollutants is negligible under environmental-like conditions. PMID:23863380

  4. Hydroxyl Radical-Mediated Novel Modification of Peptides: N-Terminal Cyclization through the Formation of α-Ketoamide.

    PubMed

    Lee, Seon Hwa; Kyung, Hyunsook; Yokota, Ryo; Goto, Takaaki; Oe, Tomoyuki

    2015-01-20

    The hydroxyl radical-mediated oxidation of peptides and proteins constitutes a large group of post-translational modifications that can result in structural and functional changes. These oxidations can lead to hydroxylation, sulfoxidation, or carbonylation of certain amino acid residues and cleavage of peptide bonds. In addition, hydroxyl radicals can convert the N-terminus of peptides to an α-ketoamide via abstraction of the N-terminal α-hydrogen and hydrolysis of the ketimine intermediate. In the present study, we identified N-terminal cyclization as a novel modification mediated by a hydroxyl radical. The reaction of angiotensin (Ang) II (DRVYIHPF) and the hydroxyl radical generated by the Cu(II)/ascorbic acid (AA) system or UV/hydrogen peroxide system produced N-terminal cyclized-Ang II (Ang C) and pyruvamide-Ang II (Ang P, CH3COCONH-RVYIHPF). The structure of Ang C was confirmed by mass spectrometry and comparison to an authentic standard. The subsequent incubation of isolated Ang P in the presence of Cu(II)/AA revealed that Ang P was the direct precursor of Ang C. The proposed mechanism involves the formation of a nitrogen-centered (aminyl) radical, which cyclizes to form a five-membered ring containing the alkoxy radical. The subsequent β-scission reaction of the alkoxyl radical results in the cleavage of the terminal CH3CO group. The initial aminyl radical can be stabilized by chelation to the Cu(II) ions. The affinity of Ang C toward the Ang II type 1 receptor was significantly lower than that of Ang II or Ang P. Ang C was not further metabolized by aminopeptidase A, which converts Ang II to Ang III. Hydroxyl radical-mediated N-terminal cyclization was also observed in other Ang peptides containing N-terminal alanine, arginine, valine, and amyloid β 1-11 (DAEFRHDSGYE).

  5. Novel method for in vivo hydroxyl radical measurement by microdialysis in fetal sheep brain in utero.

    PubMed

    Yan, Edwin B; Unthank, Jessica K; Castillo-Melendez, Margie; Miller, Suzanne L; Langford, Steven J; Walker, David W

    2005-06-01

    Hydroxyl radical (.OH) is a reactive oxygen species produced during severe hypoxia, asphyxia, or ischemia that can cause cell death resulting in brain damage. Generation of .OH may occur in the fetal brain during asphyxia in utero. The very short half-life of .OH requires use of trapping agents such as salicylic acid or phenylalanine for detection, but their hydroxylated derivatives are either unstable, produced endogenously, or difficult to measure in the small volume of microdialysis samples. In the present study, we used terephthalic acid (TA), hydroxylation of which yields a stable and highly fluorometric isomer (excitation, 326 nm; emission, 432 nm). In vitro studies using .OH generated by the Fenton reaction showed that hydroxylated TA formed quickly (<10 s), was resistant to bleaching (<5% change in fluorescence), and permitted detection of <0.5 pmol .OH. In vivo studies were performed in fetal sheep using microdialysis probes implanted into the parasagittal cortex. The probe was perfused at 2 mul/min with artificial cerebrospinal fluid containing 5 mM TA, and samples were collected every 30 min. Fluorescence measured in 10 mul of dialysate was significantly greater than in the efflux from probes perfused without TA. High-performance liquid chromotography analysis showed that the fluorescence in dialysis samples was entirely due to hydroxylation of TA. Thus this study shows that it is possible to use TA as a trapping agent for detecting low concentrations of .OH both in vitro and in vivo and that low concentrations of .OH are present in fetal brain tissue and fluctuate with time.

  6. A temperature dependent kinetic study of the reaction of the hydroxyl radical with CH2Br

    NASA Technical Reports Server (NTRS)

    Zhang, Zhengyu; Saini, Rameshwar D.; Kurylo, Michael; Huie, Robert E.

    1992-01-01

    Rate constants have been measured for the gas phase reaction of the hydroxyl radical (OH) with CH3Br over the temperature range 250 to 400 K. The Arrhenius expression k = (5.79 x 10 exp -12) exp(-1560/T) cu cm/molecule per sec was derived from the kinetic data. From the rate constant at 277 K, the tropospheric lifetime of CH3Br with respect to reaction with OH is estimated to be 2.2 years and the overall atmospheric lifetime to be 2.1 years.

  7. [Development of a chemical ionization time-of-flight mass spectrometer for continuous measurements of atmospheric hydroxyl radical].

    PubMed

    Dou, Jian; Hua, Lei; Hou, Ke-Yong; Jiang, Lei; Xie, Yuan-Yuan; Zhao, Wu-Duo; Chen, Ping; Wang, Wei-Guo; Di, Tian; Li, Hai-Yang

    2014-05-01

    A home-made chemical ionization time-of-flight mass spectrometer (TOFMS) has been developed for continuous measurements of atmospheric hydroxyl radical. Based on the atmospheric pressure chemical ionization technique, an ionization source with orthogonal dual tube structure was adopted in the instrument, which minimized the interference between the reagent gas ionization and the titration reaction. A 63Ni radioactive source was fixed inside one of the orthogonal tubes to generate reactant ion of NO(-)(3) from HNO3 vapor. Hydroxyl radical was first titrated by excess SO2 to form equivalent concentrations of H2SO4 in the other orthogonal tube, and then reacted with NO(-)(3) ions in the chemical ionization chamber, leading to HSO(-)(4) formation. The concentration of atmospheric hydroxyl radical can be directly calculated by measuring the intensities of the HSOj product ions and the NO(-)(3) reactant ions. The analytical capability of the instrument was demonstrated by measuring hydroxyl radical in laboratory air, and the concentration of the hydroxyl radical in the investigated air was calculated to be 1.6 x 106 molecules*cm ', based on 5 seconds integration. The results have shown that the instrument is competent for in situ continuous measurements of atmospheric trace radical.

  8. Effect of lu-duo-wei on scavenging superoxide and hydroxyl radicals in vitro.

    PubMed

    Fang, Y Z; Sun, C P; Tian, X H; Cong, J H

    1998-01-01

    Irradiation of a riboflavin-containing system by ultraviolet light was used to produce superoxide radical (.O2-). Hydroxyl radical (.OH) was generated by the system of Fe(II)-H2O2. Using electron spin resonance and spin trapping techniques, the effect of Lu-Duo-Wei, a capsule consisting extracts of green tea, Fructus Lycii and Semen Ziziphi Spinosae, on scavenging .O2- and .OH was observed. The results showed that the efficiency of scavenging .O2- and .OH by Lu-Duo-Wei was much higher than that by tea polyphenol alone. It is suggested that the synergistic action of tea polyphenol and other components are responsible for the scavenging effect of Lu-Duo-Wei on .O2- and .OH. PMID:9799967

  9. Estimates of atmospheric hydroxyl radical concentrations from the observed decay of many reactive hydrocarbons in well-defined urban plumes

    SciTech Connect

    Blake, N.J.; Penkett, S.A.; Clemitshaw, K.C. ); Anwyl, P.; Lightman, P.; Marsh, A.R.W. ); Butcher, G. )

    1993-02-20

    An analytical system has been developed which allows the confident identification and measurement of 35 hydrocarbons of different reactivities in air samples collected in many locations. This paper describes the application of the technique to follow the differential decay of hydrocarbons in urban plumes spreading from London during the summer. The data have been used to determine atmospheric hydroxyl radical concentrations, averaged over several hours, on the assumption that the decay of the hydrocarbons is entirely due to reaction with these radicals. Hydroxyl radical concentrations were derived from the measured decay of several alkenes which agreed with theoretical estimates. There are strong indications, however, that substituted aromatic molecules decay much faster than could be accounted for solely by reaction with hydroxyl radicals; this may indicate the presence of a further chemical removal mechanism. 18 refs., 9 figs., 5 tabs.

  10. Removal of 2-MIB and geosmin using UV/persulfate: contributions of hydroxyl and sulfate radicals.

    PubMed

    Xie, Pengchao; Ma, Jun; Liu, Wei; Zou, Jing; Yue, Siyang; Li, Xuchun; Wiesner, Mark R; Fang, Jingyun

    2015-02-01

    2-methylisoborneol (2-MIB) and geosmin are two odor-causing compounds that are difficult to remove and the cause of many consumer complaints. In this study, we assessed the degradation of 2-MIB and geosmin using a UV/persulfate process for the first time. The results showed that both 2-MIB and geosmin could be degraded effectively using this process. The process was modeled based on steady-state assumption with respect to the odor-causing compounds and either hydroxyl or sulfate radicals. The second order rate constants for 2-MIB and geosmin reacting with the sulfate radical (SO4(-)) were estimated to be (4.2 ± 0.6) × 10(8) M(-1)s(-1) and (7.6 ± 0.6) × 10(8) M(-1)s(-1) respectively at a pH of 7.0. The contributions of the hydroxyl radical (OH) to 2-MIB and geosmin degradation were 3.5 times and 2.0 times higher, respectively, than the contribution from SO4(-) in Milli-Q water with 2 mM phosphate buffer at pH 7.0. The pseudo-first-order rate constants (ko(s)) of both 2-MIB and geosmin increased with increasing dosages of persulfate. Although pH did not affect the degradation of 2-MIB and geosmin directly, different scavenging effects of hydrogen phosphate and dihydrogen phosphate resulted in higher values of ko(s) for both 2-MIB and geosmin in acidic condition. Bicarbonate and natural organic matter (NOM) inhibited the degradation of both 2-MIB and geosmin dramatically through consuming OH and SO4(-) and were likely to be the main radical scavengers in natural waters when using UV/persulfate process to control 2-MIB and geosmin.

  11. Hydroxyl-radical-induced degradative oxidation of beta-lactam antibiotics in water: absolute rate constant measurements.

    PubMed

    Dail, Michelle K; Mezyk, Stephen P

    2010-08-19

    The beta-lactam antibiotics are some of the most prevalent pharmaceutical contaminants currently being detected in aquatic environments. Because the presence of any trace level of antibiotic in water may adversely affect aquatic ecosystems and contribute to the production of antibiotic-resistant bacteria, active removal by additional water treatments, such as using advanced oxidation and reduction processes (AO/RPs), may be required. However, to ensure that any AOP treatment process occurs efficiently and quantitatively, a full understanding of the kinetics and mechanisms of all of the chemical reactions involved under the conditions of use is necessary. In this study, we report on our kinetic measurements for the hydroxyl-radical-induced oxidation of 11 beta-lactam antibiotics obtained using electron pulse radiolysis techniques. For the 5-member ring species, an average reaction rate constant of (7.9 +/- 0.8) x 10(9) M(-1) s(-1) was obtained, slightly faster than for the analogous 6-member ring containing antibiotics, (6.6 +/- 1.2) x 10(9) M(-1) s(-1). The consistency of these rate constants for each group infers a common reaction mechanism, consisting of the partitioning of the hydroxyl radical between addition to peripheral aromatic rings and reaction with the central double-ring core of these antibiotics.

  12. Efficient degradation of atrazine by magnetic porous copper ferrite catalyzed peroxymonosulfate oxidation via the formation of hydroxyl and sulfate radicals.

    PubMed

    Guan, Ying-Hong; Ma, Jun; Ren, Yue-Ming; Liu, Yu-Lei; Xiao, Jia-Yue; Lin, Ling-qiang; Zhang, Chen

    2013-09-15

    Magnetic porous copper ferrite (CuFe2O4) showed a notable catalytic activity to peroxymonosulfate (PMS). More than 98% of atrazine was degraded within 15 min at 1 mM PMS and 0.1 g/L CuFe2O4. In contrast, CuFe2O4 exhibited no obvious catalytic activity to peroxodisulfate or H2O2. Several factors affecting the catalytic performance of PMS/CuFe2O4 were investigated. Results showed that the catalytic degradation efficiency of atrazine increased with PMS and CuFe2O4 doses, but decreased with the increase of natural organic matters concentration. The catalytic oxidation also showed a dependence on initial pH. The presence of bicarbonate stimulated atrazine degradation by PMS/CuFe2O4 at low concentrations but inhibited the degradation at high concentrations. Furthermore, the reactive species for atrazine degradation in PMS/CuFe2O4 system were identified as hydroxyl radical (HO) and sulfate radical (SO4(·-)) through competition reactions of atrazine and nitrobenzene, instead of commonly used alcohol scavenging, which was not a reliable method in metal oxide catalyzed oxidation. Surface hydroxyl groups of CuFe2O4 were a critical part in radical generation and the copper on CuFe2O4 surface was an active site to catalyze PMS. The catalytic degradation of atrazine by PMS/CuFe2O4 was also effective under the background of actual waters.

  13. Sugars as hydroxyl radical scavengers: proof-of-concept by studying the fate of sucralose in Arabidopsis.

    PubMed

    Matros, Andrea; Peshev, Darin; Peukert, Manuela; Mock, Hans-Peter; Van den Ende, Wim

    2015-06-01

    Substantial formation of reactive oxygen species (ROS) is inevitable in aerobic life forms. Due to their extremely high reactivity and short lifetime, hydroxyl radicals are a special case, because cells have not developed enzymes to detoxify these most dangerous ROS. Thus, scavenging of hydroxyl radicals may only occur by accumulation of higher levels of simple organic compounds. Previous studies have demonstrated that plant-derived sugars show hydroxyl radical scavenging capabilities during Fenton reactions with Fe(2+) and hydrogen peroxide in vitro, leading to formation of less detrimental sugar radicals that may be subject of regeneration to non-radical carbohydrates in vivo. Here, we provide further evidence for the occurrence of such radical reactions with sugars in planta, by following the fate of sucralose, an artificial analog of sucrose, in Arabidopsis tissues. The expected sucralose recombination and degradation products were detected in both normal and stressed plant tissues. Oxidation products of endogenous sugars were also assessed in planta for Arabidopsis and barley, and were shown to increase in abundance relative to the non-oxidized precursor during oxidative stress conditions. We concluded that such non-enzymatic reactions with hydroxyl radicals form an integral part of plant antioxidant mechanisms contributing to cellular ROS homeostasis, and may be more important than generally assumed. This is discussed in relation to the recently proposed roles for Fe(2+) and hydrogen peroxide in processes leading to the origin of metabolism and the origin of life.

  14. Sugars as hydroxyl radical scavengers: proof-of-concept by studying the fate of sucralose in Arabidopsis.

    PubMed

    Matros, Andrea; Peshev, Darin; Peukert, Manuela; Mock, Hans-Peter; Van den Ende, Wim

    2015-06-01

    Substantial formation of reactive oxygen species (ROS) is inevitable in aerobic life forms. Due to their extremely high reactivity and short lifetime, hydroxyl radicals are a special case, because cells have not developed enzymes to detoxify these most dangerous ROS. Thus, scavenging of hydroxyl radicals may only occur by accumulation of higher levels of simple organic compounds. Previous studies have demonstrated that plant-derived sugars show hydroxyl radical scavenging capabilities during Fenton reactions with Fe(2+) and hydrogen peroxide in vitro, leading to formation of less detrimental sugar radicals that may be subject of regeneration to non-radical carbohydrates in vivo. Here, we provide further evidence for the occurrence of such radical reactions with sugars in planta, by following the fate of sucralose, an artificial analog of sucrose, in Arabidopsis tissues. The expected sucralose recombination and degradation products were detected in both normal and stressed plant tissues. Oxidation products of endogenous sugars were also assessed in planta for Arabidopsis and barley, and were shown to increase in abundance relative to the non-oxidized precursor during oxidative stress conditions. We concluded that such non-enzymatic reactions with hydroxyl radicals form an integral part of plant antioxidant mechanisms contributing to cellular ROS homeostasis, and may be more important than generally assumed. This is discussed in relation to the recently proposed roles for Fe(2+) and hydrogen peroxide in processes leading to the origin of metabolism and the origin of life. PMID:25891826

  15. Photochemical formation of hydroxyl radical in red-soil-polluted seawater - effects of dissolved organic compounds

    NASA Astrophysics Data System (ADS)

    Uehara, M.; Arakaki, T.

    2006-12-01

    Development of pineapple farmlands and construction of recreational facilities caused runoff of red soil into the coastal ocean (locally termed as red soil pollution) in the north of Okinawa Island, Japan. Red soil is acidic and contains a few percent of iron oxide. We were interested in the formation of hydroxyl radical (·OH), the most potent oxidant in the environment, from the photo-Fenton reaction (reaction between Fe(II) and HOOH) in red-soil-polluted seawater. Various artificial seawater solutions were prepared by adding red soil, HOOH, and/or humic acid to clean seawater, and were used for photochemical experiments. Commercially available humic acid was used to represent natural organic compounds. All the solutions were filtered through 0.45 micron filter before conducting photochemical experiments. Comparisons among the solutions indicated that dissolved chemicals from the red-soil only slightly increased the OH radical photoformation. Photoformation rates of OH radicals of the HOOH + red soil solutions were similar to the calculated rates from direct photolysis of HOOH. Furthermore, addition of humic acid to the HOOH + red soil solutions did not significantly enhance the photo-Fenton reaction, suggesting that Fe(II), even if it had been formed, did not react with HOOH to form OH radicals at detectable level in seawater.

  16. Thalidomide Inhibits Angiogenesis in Embryoid Bodies by the Generation of Hydroxyl Radicals

    PubMed Central

    Sauer, Heinrich; Günther, Julia; Hescheler, Jürgen; Wartenberg, Maria

    2000-01-01

    Thalidomide is a teratogen with anti-angiogenic properties and causes stunted limb growth (dysmelia) during human embryogenesis. The molecular mechanisms of thalidomide action in embryopathy are currently unknown. Using the endothelial-specific antigen platelet endothelial cell adhesion molecule-1 and confocal laser scanning microscopy we have demonstrated that thalidomide exerts anti-angiogenic effects on the development of capillary structures in embryoid bodies differentiated from murine embryonic stem cells. Consequently, in thalidomide-treated embryoid bodies the diffusion properties of the tissue were deteriorated. Thalidomide raised reactive oxygen species (ROS), as revealed using 2′7′-dichlorodihydrofluorescein diacetate (H2DCF-DA) as an indicator. A comparable ROS generation was achieved with the thalidomide hydrolysis product phthaloyl glutamic acid (PGA), but not with phthalimide (PI), the major component of thalidomide. ROS formation by thalidomide was inhibited by the hydroxyl radical scavengers mannitol and 2-mercaptoethanol. After coadministration of either 2-mercaptoethanol or mannitol with thalidomide the anti-angiogenic effects of thalidomide were abolished and the diffusion properties of the tissue were restored to the control values. In summary, our data suggest that thalidomide exerts its anti-angiogenic properties via the generation of toxic hydroxyl radicals, which impair vasculogenesis and angiogenesis during embryoid body development. PMID:10623662

  17. Hydroxyl radical scavenging mechanism of human erythrocytes by quercetin-germanium (IV) complex.

    PubMed

    Li, Sheng-Pu; Xie, Wei-Ling; Cai, Huai-Hong; Cai, Ji-Ye; Yang, Pei-Hui

    2012-08-30

    Quercetin is a popular flavonoid in plant foods, herbs, and dietary supplement. Germanium, a kind of trace elements, can enhance the body immunity. This study investigated the hydroxyl-radical-scavenging mechanism of the quercertin-germanium (IV) (Qu-Ge) complex to human erythrocytes, especially the effects on ultrastructure and mechanical properties of cell membrane, plasma membrane potential and intracellular free Ca(2+) concentration. Results showed that QuGe(2), a kind of the Qu-Ge complex, could reduce the oxidative damage of erythrocytes, change the cell-surface morphology, and partly recover the disruption of plasma membrane potential and intracellular free Ca(2+) level. Atomic force microscopy (AFM) was used to characterize the changes of the cell morphology, cell-membrane ultrastructure and biophysical properties at nanoscalar level. QuGe(2) has triggered the antioxidative factor to inhibit cellular damage. These results can improve the understanding of hydroxyl-radical-scavenging mechanism of human erythrocytes induced by the Qu-Ge complex, which can be potentially developed as a new antioxidant for treatment of oxidative damage.

  18. Isoprenoid Alcohols are Susceptible to Oxidation with Singlet Oxygen and Hydroxyl Radicals.

    PubMed

    Komaszylo Née Siedlecka, Joanna; Kania, Magdalena; Masnyk, Marek; Cmoch, Piotr; Lozinska, Iwona; Czarnocki, Zbigniew; Skorupinska-Tudek, Karolina; Danikiewicz, Witold; Swiezewska, Ewa

    2016-02-01

    Isoprenoids, as common constituents of all living cells, are exposed to oxidative agents--reactive oxygen species, for example, singlet oxygen or hydroxyl radicals. Despite this fact, products of oxidation of polyisoprenoids have never been characterized. In this study, chemical oxidation of isoprenoid alcohols (Prenol-2 and -10) was performed using singlet oxygen (generated in the presence of hydrogen peroxide/molybdate or upon photochemical reaction in the presence of porphyrin), oxygen (formed upon hydrogen peroxide dismutation) or hydroxyl radical (generated by the hydrogen peroxide/sonication, UV/titanium dioxide or UV/hydrogen peroxide) systems. The structure of the obtained products, hydroxy-, peroxy- and heterocyclic derivatives, was studied with the aid of mass spectrometry (MS) and nuclear magnetic resonance (NMR) methods. Furthermore, mass spectrometry with electrospray ionization appeared to be a useful analytical tool to detect the products of oxidation of isoprenoids (ESI-MS analysis), as well as to establish their structure on the basis of the fragmentation spectra of selected ions (ESI-MS/MS analysis). Taken together, susceptibility of polyisoprenoid alcohols to various oxidizing agents was shown for the first time.

  19. Hydroxyl radical mediates cisplatin-induced apoptosis in human hair follicle dermal papilla cells and keratinocytes through Bcl-2-dependent mechanism

    PubMed Central

    Luanpitpong, Sudjit; Chanvorachote, Pithi; Leonard, Stephen S.; Pongrakhananon, Varisa; Wang, Liying

    2016-01-01

    Induction of massive apoptosis of hair follicle cells by chemotherapy has been implicated in the pathogenesis of chemotherapy-induced alopecia (CIA), but the underlying mechanisms of regulation are not well understood. The present study investigated the apoptotic effect of cisplatin in human hair follicle dermal papilla cells and HaCaT keratinocytes, and determined the identity and role of specific reactive oxygen species (ROS) involved in the process. Treatment of the cells with cisplatin induced ROS generation and a parallel increase in caspase activation and apoptotic cell death. Inhibition of ROS generation by antioxidants inhibited the apoptotic effect of cisplatin, indicating the role of ROS in the process. Studies using specific ROS scavengers further showed that hydroxyl radical, but not hydrogen peroxide or superoxide anion, is the primary oxidative species responsible for the apoptotic effect of cisplatin. Electron spin resonance studies confirmed the formation of hydroxyl radicals induced by cisplatin. The mechanism by which hydroxyl radical mediates the apoptotic effect of cisplatin was shown to involve down-regulation of the anti-apoptotic protein Bcl-2 through ubiquitin-proteasomal degradation. Bcl-2 was also shown to have a negative regulatory role on hydroxyl radical. Together, our results indicate an essential role of hydroxyl radical in cisplatin-induced cell death of hair follicle cells through Bcl-2 regulation. Since CIA is a major side effect of cisplatin and many other chemotherapeutic agents with no known effective treatments, the knowledge gained from this study could be useful in the design of preventive treatment strategies for CIA through localized therapy without compromising the chemotherapy efficacy. PMID:21573972

  20. Hydroxyl radical mediates cisplatin-induced apoptosis in human hair follicle dermal papilla cells and keratinocytes through Bcl-2-dependent mechanism.

    PubMed

    Luanpitpong, Sudjit; Nimmannit, Ubonthip; Chanvorachote, Pithi; Leonard, Stephen S; Pongrakhananon, Varisa; Wang, Liying; Rojanasakul, Yon

    2011-08-01

    Induction of massive apoptosis of hair follicle cells by chemotherapy has been implicated in the pathogenesis of chemotherapy-induced alopecia (CIA), but the underlying mechanisms of regulation are not well understood. The present study investigated the apoptotic effect of cisplatin in human hair follicle dermal papilla cells and HaCaT keratinocytes, and determined the identity and role of specific reactive oxygen species (ROS) involved in the process. Treatment of the cells with cisplatin induced ROS generation and a parallel increase in caspase activation and apoptotic cell death. Inhibition of ROS generation by antioxidants inhibited the apoptotic effect of cisplatin, indicating the role of ROS in the process. Studies using specific ROS scavengers further showed that hydroxyl radical, but not hydrogen peroxide or superoxide anion, is the primary oxidative species responsible for the apoptotic effect of cisplatin. Electron spin resonance studies confirmed the formation of hydroxyl radicals induced by cisplatin. The mechanism by which hydroxyl radical mediates the apoptotic effect of cisplatin was shown to involve down-regulation of the anti-apoptotic protein Bcl-2 through ubiquitin-proteasomal degradation. Bcl-2 was also shown to have a negative regulatory role on hydroxyl radical. Together, our results indicate an essential role of hydroxyl radical in cisplatin-induced cell death of hair follicle cells through Bcl-2 regulation. Since CIA is a major side effect of cisplatin and many other chemotherapeutic agents with no known effective treatments, the knowledge gained from this study could be useful in the design of preventive treatment strategies for CIA through localized therapy without compromising the chemotherapy efficacy.

  1. Exploring water catalysis in the reaction of thioformic acid with hydroxyl radical: a global reaction route mapping perspective.

    PubMed

    Kaur, Gurpreet; Vikas

    2014-06-12

    Hydrogen abstraction pathways, in the gas-phase reaction of tautomers of thioformic acid (TFA), TFA(thiol), and TFA(thione), with hydroxyl radical in the presence and absence of single water molecule acting as a catalyst, is investigated with high-level quantum mechanical calculations at CCSD(T)/6-311++G(2d,2p)//MP2/6-311++G(2d,2p), CCSD(T)/6-311++G(d,p)//DFT/BHandHLYP/6-311++G(d,p), and DFT/B3LYP/6-311++G(2df,2p) levels of the theory. A systematic and automated search of the potential energy surface (PES) for the reaction pathways is performed using the global reaction route mapping (GRRM) method that employs an uphill walking technique to search prereaction complexes and transition states. The computations reveal significant lowering of the PES and substantial reduction in the activation energy for the hydrogen abstraction pathway in the presence of water, thereby proving water as an efficient catalyst in the reaction of both the TFA tautomers with OH radical. The hydrogen-bonding interactions are observed to be responsible for the large catalytic effect of water. Notably, in the case of TFA(thiol), formyl hydrogen abstraction is observed to be kinetically more favorable, while acidic hydrogen abstraction is observed to be thermodynamically more feasible. Interestingly, in the case of TFA(thione), reaction pathways involving only formyl hydrogen abstraction were observed to be feasible. The water-catalyzed hydrogen abstraction reaction of TFA with hydroxyl radical, investigated in this work, can provide significant insights into the corresponding reaction in the biological systems.

  2. Moringa oleifera Lam. seed extract prevents fat diet induced oxidative stress in mice and protects liver cell-nuclei from hydroxyl radical mediated damage.

    PubMed

    Das, Nilanjan; Ganguli, Debdutta; Dey, Sanjit

    2015-12-01

    High fat diet (HFD) prompts metabolic pattern inducing reactive oxygen species (ROS) production in mitochondria thereby triggering multitude of chronic disorders in human. Antioxidants from plant sources may be an imperative remedy against this disorder. However, it requires scientific validation. In this study, we explored if (i) Moringa oleifera seed extract (MoSE) can neutralize ROS generated in HFD fed mice; (ii) protect cell-nuclei damage developed by Fenton reaction in vitro. Swiss mice were fed with HFD to develop oxidative stress model (HFD group). Other groups were control, seed extract alone treated, and MoSE simultaneously (HS) treated. Treatment period was of 15 days. Antioxidant enzymes with tissue nitrite content (TNC) and lipid peroxidation (LPO) were estimated from liver homogenate. HS group showed significantly higher (P < 0.05) superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH) activity, and ferric reducing antioxidant power (FRAP) compared to only HFD fed group. Further, TNC and LPO decreased significantly (P < 0.05) in HS group compared to HFD fed group. MoSE also protected hepatocytes nuclei from the hydroxyl radicals generated by Fenton reaction. MoSE was found to be polyphenol rich with potent reducing power, free radicals and hydroxyl radicals scavenging activity. Thus, MoSE exhibited robust antioxidant prospective to neutralize ROS developed in HFD fed mice and also protected the nuclei damage from hydroxyl radicals. Hence, it can be used as herbal medication against HFD induced ROS mediated disorders.

  3. Moringa oleifera Lam. seed extract prevents fat diet induced oxidative stress in mice and protects liver cell-nuclei from hydroxyl radical mediated damage.

    PubMed

    Das, Nilanjan; Ganguli, Debdutta; Dey, Sanjit

    2015-12-01

    High fat diet (HFD) prompts metabolic pattern inducing reactive oxygen species (ROS) production in mitochondria thereby triggering multitude of chronic disorders in human. Antioxidants from plant sources may be an imperative remedy against this disorder. However, it requires scientific validation. In this study, we explored if (i) Moringa oleifera seed extract (MoSE) can neutralize ROS generated in HFD fed mice; (ii) protect cell-nuclei damage developed by Fenton reaction in vitro. Swiss mice were fed with HFD to develop oxidative stress model (HFD group). Other groups were control, seed extract alone treated, and MoSE simultaneously (HS) treated. Treatment period was of 15 days. Antioxidant enzymes with tissue nitrite content (TNC) and lipid peroxidation (LPO) were estimated from liver homogenate. HS group showed significantly higher (P < 0.05) superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH) activity, and ferric reducing antioxidant power (FRAP) compared to only HFD fed group. Further, TNC and LPO decreased significantly (P < 0.05) in HS group compared to HFD fed group. MoSE also protected hepatocytes nuclei from the hydroxyl radicals generated by Fenton reaction. MoSE was found to be polyphenol rich with potent reducing power, free radicals and hydroxyl radicals scavenging activity. Thus, MoSE exhibited robust antioxidant prospective to neutralize ROS developed in HFD fed mice and also protected the nuclei damage from hydroxyl radicals. Hence, it can be used as herbal medication against HFD induced ROS mediated disorders. PMID:26742324

  4. UV + V UV double-resonance studies of autoionizing Rydberg states of the hydroxyl radical

    NASA Astrophysics Data System (ADS)

    Green, Amy M.; Liu, Fang; Lester, Marsha I.

    2016-05-01

    The hydroxyl radical (OH) is a key oxidant in atmospheric and combustion chemistry. Recently, a sensitive and state-selective ionization method has been developed for detection of the OH radical that utilizes UV excitation on the A2Σ+-X2Π transition followed by fixed 118 nm vacuum ultraviolet (VUV) radiation to access autoionizing Rydberg states [J. M. Beames et al., J. Chem. Phys. 134, 241102 (2011)]. The present study uses tunable VUV radiation generated by four-wave mixing to examine the origin of the enhanced ionization efficiency observed for OH radicals prepared in specific A2Σ+ intermediate levels. The enhancement is shown to arise from resonant excitation to distinct rotational and fine structure levels of two newly identified 2Π Rydberg states with an A3Π cationic core and a 3d electron followed by ionization. Spectroscopic constants are derived and effects due to uncoupling of the Rydberg electron are revealed for the OH 2Π Rydberg states. The linewidths indicate a Rydberg state lifetime due to autoionization on the order of a picosecond.

  5. An ab initio investigation of possible intermediates in the reaction of the hydroxyl and hydroperoxyl radicals

    NASA Technical Reports Server (NTRS)

    Jackels, C. F.

    1985-01-01

    Ab initio quantum chemical techniques are used to investigate covalently-bonded and hydrogen-bonded species that may be important intermediates in the reaction of hydroxyl and hydroperoxyl radicals. Stable structures of both types are identified. Basis sets of polarized double zeta quality and large scale configuration interaction wave functions are utilized. Based on electronic energies, the covalently bonded HOOOH species is 26.4 kcal/mol more stable than the OH and HO2 radicals. Similarly, the hydrogen bonded HO---HO2 species has an electronic energy 4.7 kcal/mol below that of the component radicals, after correction is made for the basis set superposition error. The hydrogen bonded form is planar, possesses one relatively normal hydrogen bond, and has the lowest energy 3A' and 1A' states that are essentially degenerate. The 1A" and 3A" excited states produced by rotation of the unpaired OH electron into the molecular plane are very slightly bound.

  6. An ab initio investigation of possible intermediates in the reaction of the hydroxyl and hydroperoxyl radicals

    NASA Technical Reports Server (NTRS)

    Jackels, C. F.; Phillips, D. H.

    1986-01-01

    Ab initio quantum chemical techniques have been used to investigate covalently-bonded and hydrogen-bonded species that may be important intermediates in the reaction of hydroxyl and hydroperoxyl radicals. Stable structures of both types were identified. Basic sets of polarized double-zeta quality and large scale configuration interaction wave functions have been utilized. Based upon electronic energies, the covalently-bonded HOOOH species is found to be 26.4 kcal/mol more stable than the OH and HO2 radicals. Similarly, the hydrogen-bonded HO-HO2 species is found to have an electronic energy 4.7 kcal/mol below that of the component radicals, after correction is made for the basis set superposition error. The hydrogen-bonded form is found to be planar, to possess one relatively 'normal' hydrogen bond, and to have lowest energy 3A-prime and 1A-prime states that are essentially degenerate. The 1A-double prime and 3A-double prime excited states produced by rotation of the unpaired OH electron into the molecular plane are found to be very slightly bound.

  7. UV + V UV double-resonance studies of autoionizing Rydberg states of the hydroxyl radical.

    PubMed

    Green, Amy M; Liu, Fang; Lester, Marsha I

    2016-05-14

    The hydroxyl radical (OH) is a key oxidant in atmospheric and combustion chemistry. Recently, a sensitive and state-selective ionization method has been developed for detection of the OH radical that utilizes UV excitation on the A(2)Σ(+)-X(2)Π transition followed by fixed 118 nm vacuum ultraviolet (VUV) radiation to access autoionizing Rydberg states [J. M. Beames et al., J. Chem. Phys. 134, 241102 (2011)]. The present study uses tunable VUV radiation generated by four-wave mixing to examine the origin of the enhanced ionization efficiency observed for OH radicals prepared in specific A(2)Σ(+) intermediate levels. The enhancement is shown to arise from resonant excitation to distinct rotational and fine structure levels of two newly identified (2)Π Rydberg states with an A(3)Π cationic core and a 3d electron followed by ionization. Spectroscopic constants are derived and effects due to uncoupling of the Rydberg electron are revealed for the OH (2)Π Rydberg states. The linewidths indicate a Rydberg state lifetime due to autoionization on the order of a picosecond. PMID:27179488

  8. Hydroxyl radical in/on illuminated polar snow: formation rates, lifetimes, and steady-state concentrations

    NASA Astrophysics Data System (ADS)

    Chen, Zeyuan; Chu, Liang; Galbavy, Edward S.; Ram, Keren; Anastasio, Cort

    2016-08-01

    While the hydroxyl radical (OH) in the snowpack is likely a dominant oxidant for organic species and bromide, little is known about the kinetics or steady-state concentrations of OH on/in snow and ice. Here we measure the formation rate, lifetime, and concentration of OH for illuminated polar snow samples studied in the laboratory and in the field. Laboratory studies show that OH kinetics and steady-state concentrations are essentially the same for a given sample studied as ice and liquid; this is in contrast to other photooxidants, which show a concentration enhancement in ice relative to solution as a result of kinetic differences in the two phases. The average production rate of OH in samples studied at Summit, Greenland, is 5 times lower than the average measured in the laboratory, while the average OH lifetime determined in the field is 5 times higher than in the laboratory. These differences indicate that the polar snows we studied in the laboratory are affected by contamination, despite significant efforts to prevent this; our results suggest similar contamination may be a widespread problem in laboratory studies of ice chemistry. Steady-state concentrations of OH in clean snow studied in the field at Summit, Greenland, range from (0.8 to 3) × 10-15 M, comparable to values reported for midlatitude cloud and fog drops, rain, and deliquesced marine particles, even though impurity concentrations in the snow samples are much lower. Partitioning of firn air OH to the snow grains will approximately double the steady-state concentration of snow-grain hydroxyl radical, leading to an average [OH] in near-surface, summer Summit snow of approximately 4 × 10-15 M. At this concentration, the OH-mediated lifetimes of organics and bromide in Summit snow grains are approximately 3 days and 7 h, respectively, suggesting that hydroxyl radical is a major

  9. Production of hydroxyl radicals from Fe-containing fine particles in Guangzhou, China

    NASA Astrophysics Data System (ADS)

    Ma, Shexia; Ren, Ke; Liu, Xiaowen; Chen, Laiguo; Li, Mei; Li, Xiaoying; Yang, Jian; Huang, Bo; Zheng, Mei; Xu, Zhencheng

    2015-12-01

    Reactive oxygen species (ROS) production from ambient fine particles has been correlated with the soluble transition metal content of PM2.5, which also has clear association with particle-mediated cardiopulmonary toxicity. Hydroxyl radical (rad OH) is the most harmful ROS species through chemical reactions of redox-active particle components. Atmospheric Fe, as the dominant species of the transition metals in the atmosphere, is associated with rad OH generation in ambient particle extracts. Our results revealed that Fe-containing particles (18,730 in total number) contributed approximately 3.7% on average to all detected particles throughout the summer and winter sampling period in Guangzhou, which was clustered into four distinct particle classes, including Fe-rich, Metal-rich, NaK-rich and Dust-rich. Fe-rich class was the dominant one with a fraction of 61%, followed by Dust-rich (14%), Metal-rich (13%). and NaK-rich (12%). The iron oxide was enriched in the Fe-rich class. rad OH generation induced by Fe-containing fine particles collected in Guangzhou (GZ) was quantified in a surrogate lung fluid (SLF), and it was found that Fe-containing fine particles were generally much reactive in generating rad OH in the presence of four antioxidants (200 μM ascorbate, 300 μM citrate, 100 μM reduced L-glutathione, and 100 μM uric acid). The annual average rad OH amount produced in our samples was 132.98 ± 27.43 nmol rad OH mg-1 PM2.5. rad OH production had a clear seasonal pattern with higher amount in summer and lower in winter. By measuring the amount of total and SLF-soluble metal in our PM2.5 samples using ICP-MS, we found that ROS activities were associated with the ionizable Fe through Fenton type reactions in the Guangzhou PM2.5. Expected burdens of PM2.5 derived rad OH in human lung lining fluid suggests that typical daily particulate matter exposure in Guangzhou is already a concern, and it could produce much higher levels of rad OH, leading to higher

  10. Inhibition of Fe(2+)- and Fe(3+)- induced hydroxyl radical production by the iron-chelating drug deferiprone.

    PubMed

    Timoshnikov, V A; Kobzeva, T V; Polyakov, N E; Kontoghiorghes, G J

    2015-01-01

    Deferiprone (L1) is an effective iron-chelating drug that is widely used for the treatment of iron-overload diseases. It is known that in aqueous solutions Fe(2+) and Fe(3+) ions can produce hydroxyl radicals via Fenton and photo-Fenton reactions. Although previous studies with Fe(2+) have reported ferroxidase activity by L1 followed by the formation of Fe(3+) chelate complexes and potential inhibition of Fenton reaction, no detailed data are available on the molecular antioxidant mechanisms involved. Similarly, in vitro studies have also shown that L1-Fe(3+) complexes exhibit intense absorption bands up to 800nm and might be potential sources of phototoxicity. In this study we have applied an EPR spin trapping technique to answer two questions: (1) does L1 inhibit the Fenton reaction catalyzed by Fe(2+) and Fe(3+) ions and (2) does UV-Vis irradiation of the L1-Fe(3+) complex result in the formation of reactive oxygen species. PBN and TMIO spin traps were used for detection of oxygen free radicals, and TEMP was used to trap singlet oxygen if it was formed via energy transfer from L1 in the triplet excited state. It was demonstrated that irradiation of Fe(3+) aqua complexes by UV and visible light in the presence of spin traps results in the appearance of an EPR signal of the OH spin adduct (TMIO-OH, a(N)=14.15G, a(H)=16.25G; PBN-OH, a(N)=16.0G, a(H)=2.7G). The presence of L1 completely inhibited the OH radical production. The mechanism of OH spin adduct formation was confirmed by the detection of methyl radicals in the presence of dimethyl sulfoxide. No formation of singlet oxygen was detected under irradiation of L1 or its iron complexes. Furthermore, the interaction of L1 with Fe(2+) ions completely inhibited hydroxyl radical production in the presence of hydrogen peroxide. These findings confirm an antioxidant targeting potential of L1 in diseases related to oxidative damage. PMID:25451643

  11. Inhibition of Fe(2+)- and Fe(3+)- induced hydroxyl radical production by the iron-chelating drug deferiprone.

    PubMed

    Timoshnikov, V A; Kobzeva, T V; Polyakov, N E; Kontoghiorghes, G J

    2015-01-01

    Deferiprone (L1) is an effective iron-chelating drug that is widely used for the treatment of iron-overload diseases. It is known that in aqueous solutions Fe(2+) and Fe(3+) ions can produce hydroxyl radicals via Fenton and photo-Fenton reactions. Although previous studies with Fe(2+) have reported ferroxidase activity by L1 followed by the formation of Fe(3+) chelate complexes and potential inhibition of Fenton reaction, no detailed data are available on the molecular antioxidant mechanisms involved. Similarly, in vitro studies have also shown that L1-Fe(3+) complexes exhibit intense absorption bands up to 800nm and might be potential sources of phototoxicity. In this study we have applied an EPR spin trapping technique to answer two questions: (1) does L1 inhibit the Fenton reaction catalyzed by Fe(2+) and Fe(3+) ions and (2) does UV-Vis irradiation of the L1-Fe(3+) complex result in the formation of reactive oxygen species. PBN and TMIO spin traps were used for detection of oxygen free radicals, and TEMP was used to trap singlet oxygen if it was formed via energy transfer from L1 in the triplet excited state. It was demonstrated that irradiation of Fe(3+) aqua complexes by UV and visible light in the presence of spin traps results in the appearance of an EPR signal of the OH spin adduct (TMIO-OH, a(N)=14.15G, a(H)=16.25G; PBN-OH, a(N)=16.0G, a(H)=2.7G). The presence of L1 completely inhibited the OH radical production. The mechanism of OH spin adduct formation was confirmed by the detection of methyl radicals in the presence of dimethyl sulfoxide. No formation of singlet oxygen was detected under irradiation of L1 or its iron complexes. Furthermore, the interaction of L1 with Fe(2+) ions completely inhibited hydroxyl radical production in the presence of hydrogen peroxide. These findings confirm an antioxidant targeting potential of L1 in diseases related to oxidative damage.

  12. Carbon kinetic isotope effect in the oxidation of methane by the hydroxyl radical

    NASA Technical Reports Server (NTRS)

    Cantrell, Christopher A.; Shetter, Richard E.; Mcdaniel, Anthony H.; Calvert, Jack G.; Davidson, James A.

    1990-01-01

    The reaction of the hydroxyl radical (HO) with the stable carbon isotopes of methane has been studied as a function of temperature from 273 to 353 K. The measued ratio of the rate coefficients for reaction with (C-12)H4 relative to (C-13)H4 (k12/k13) was 1.0054 (+ or - 0.0009 at the 95 percent confidence interval), independent of temperature within the precision of the measurement, over the range studied. The precision of the present value is much improved over that of previous studies, and this result provides important constraints on the current understanding of the cycling of methane through the atmosphere through the use of carbon isotope measurements.

  13. Development of a group contribution method to predict aqueous phase hydroxyl radical (HO*) reaction rate constants.

    PubMed

    Minakata, Daisuke; Li, Ke; Westerhoff, Paul; Crittenden, John

    2009-08-15

    The hydroxyl radical (HO*) is a strong oxidant that reacts with electron-rich sites of organic compounds and initiates complex chain mechanisms. In order to help understand the reaction mechanisms, a rule-based model was previously developed to predict the reaction pathways. For a kinetic model, there is a need to develop a rate constant estimator that predicts the rate constants for a variety of organic compounds. In this study, a group contribution method (GCM) is developed to predict the aqueous phase HO* rate constants for the following reaction mechanisms: (1) H-atom abstraction, (2) HO* addition to alkenes, (3) HO* addition to aromatic compounds, and (4) HO* interaction with sulfur (S)-, nitrogen (N)-, or phosphorus (P)-atom-containing compounds. The GCM hypothesizes that an observed experimental rate constant for a given organic compound is the combined rate of all elementary reactions involving HO*, which can be estimated using the Arrhenius activation energy, E(a), and temperature. Each E(a) for those elementary reactions can be comprised of two parts: (1) a base part that includes a reactive bond in each reaction mechanism and (2) contributions from its neighboring functional groups. The GCM includes 66 group rate constants and 80 group contribution factors, which characterize each HO* reaction mechanism with steric effects of the chemical structure groups and impacts of the neighboring functional groups, respectively. Literature-reported experimental HO* rate constants for 310 and 124 compounds were used for calibration and prediction, respectively. The genetic algorithms were used to determine the group rate constants and group contribution factors. The group contribution factors for H-atom abstraction and HO* addition to the aromatic compounds were found to linearly correlate with the Taft constants, sigma*, and electrophilic substituent parameters, sigma+, respectively. The best calibrations for 83% (257 rate constants) and predictions for 62% (77

  14. Hydroxyl radical reactions with adenine: reactant complexes, transition states, and product complexes.

    PubMed

    Cheng, Qianyi; Gu, Jiande; Compaan, Katherine R; Schaefer, Henry F

    2010-10-18

    In order to address problems such as aging, cell death, and cancer, it is important to understand the mechanisms behind reactions causing DNA damage. One specific reaction implicated in DNA oxidative damage is hydroxyl free-radical attack on adenine (A) and other nucleic acid bases. The adenine reaction has been studied experimentally, but there are few theoretical results. In the present study, adenine dehydrogenation at various sites, and the potential-energy surfaces for these reactions, are investigated theoretically. Four reactant complexes [A···OH]* have been found, with binding energies relative to A+OH* of 32.8, 11.4, 10.7, and 10.1 kcal mol(-1). These four reactant complexes lead to six transition states, which in turn lie +4.3, -5.4, (-3.7 and +0.8), and (-2.3 and +0.8) kcal mol(-1) below A+OH*, respectively. Thus the lowest lying [A···OH]* complex faces the highest local barrier to formation of the product (A-H)*+H(2)O. Between the transition states and the products lie six product complexes. Adopting the same order as the reactant complexes, the product complexes [(A-H)···H(2)O]* lie at -10.9, -22.4, (-24.2 and -18.7), and (-20.5 and -17.5) kcal mol(-1), respectively, again relative to separated A+OH*. All six A+OH* → (A-H)*+H(2)O pathways are exothermic, by -0.3, -14.7, (-17.4 and -7.8), and (-13.7 and -7.8) kcal mol(-1), respectively. The transition state for dehydrogenation at N(6) lies at the lowest energy (-5.4 kcal mol(-1) relative to A+OH*), and thus reaction is likely to occur at this site. This theoretical prediction dovetails with the observed high reactivity of OH radicals with the NH(2) group of aromatic amines. However, the high barrier (37.1 kcal mol(-1)) for reaction at the C(8) site makes C(8) dehydrogenation unlikely. This last result is consistent with experimental observation of the imidazole ring opening upon OH radical addition to C(8). In addition, TD-DFT computed electronic transitions of the N(6) product around 420 nm

  15. Electrochemiluminescence of palmatine being oxidized by electrogenerated hydroxyl radical and its analytical application.

    PubMed

    Liang, Yao-Dong; Yu, Chun-Xia; Song, Jun-Feng

    2011-01-01

    A strong electrochemiluminescence (ECL) of palmatine in NaOH medium was observed at a vaseline-impregnated graphite anode. The ECL production could be described as follows: hydroxyl radical (OH(•)) was generated via the oxidation of hydroxyl group (OH(-)) in NaOH medium, and the formed OH(•) subsequently oxidized palmatine base converted from palmatine in NaOH medium to the excited state oxypalmatine (oxypalmatine*). As the oxypalmatine* went back to its ground state, a stronger chemiluminescence was produced. Based on the ECL of palmatine, an ECL method for the determination of palmatine was proposed. An ECL signal of palmatine in NaOH solution was obtained by applying direct current of 15 mA to the vaseline-impregnated graphite anode. The ECL intensity was rectilinear with palmatine concentration in the range of 8.0 × 10(-7) to 2.0 × 10(-5) mol l(-1) and the limit of detection (signal-to-noise = 3) was 3 × 10(-7) mol l(-1) . The proposed method was applied to the determination of palmatine in pharmaceutical preparations.

  16. Degradation mechanism of cyanobacterial toxin cylindrospermopsin by hydroxyl radicals in homogeneous UV/H₂O₂ process.

    PubMed

    He, Xuexiang; Zhang, Geshan; de la Cruz, Armah A; O'Shea, Kevin E; Dionysiou, Dionysios D

    2014-04-15

    The degradation of cylindrospermopsin (CYN), a widely distributed and highly toxic cyanobacterial toxin (cyanotoxin), remains poorly elucidated. In this study, the mechanism of CYN destruction by UV-254 nm/H2O2 advanced oxidation process (AOP) was investigated by mass spectrometry. Various byproducts identified indicated three common reaction pathways: hydroxyl addition (+16 Da), alcoholic oxidation or dehydrogenation (-2 Da), and elimination of sulfate (-80 Da). The initiation of the degradation was observed at the hydroxymethyl uracil and tricyclic guanidine groups; uracil moiety cleavage/fragmentation and further ring-opening of the alkaloid were also noted at an extended reaction time or higher UV fluence. The degradation rates of CYN decreased and less byproducts (species) were detected using natural water matrices; however, CYN was effectively eliminated under extended UV irradiation. This study demonstrates the efficiency of CYN degradation and provides a better understanding of the mechanism of CYN degradation by hydroxyl radical, a reactive oxygen species that can be generated by most AOPs and is present in natural water environment.

  17. In vivo hydroxyl radical formation after quinolinic acid infusion into rat corpus striatum.

    PubMed

    Santamaría, A; Jiménez-Capdeville, M E; Camacho, A; Rodríguez-Martínez, E; Flores, A; Galván-Arzate, S

    2001-08-28

    We studied the effect of an acute infusion of quinolinic acid (QUIN) on in vivo hydroxyl radical (.OH) formation in the striatum of awake rats. Using the microdialysis technique, the generation of.OH was assessed through electrochemical detection of the salicylate hydroxylation product 2,3-dihydroxybenzoic acid (2,3-DHBA). The .OH extracellular levels increased up to 30 times over basal levels after QUIN infusion (240 nmol/microl), returning to the baseline 2 h later. This response was attenuated, but not abolished, by pretreatment with the NMDA receptor antagonist MK-801 (10 mg/kg, i.p.) 60 min before QUIN infusion. The mitochondrial toxin 3-nitropropionic acid (3-NPA, 500 nmol/microl) had stronger effects than QUIN on .OH generation, as well as on other markers of oxidative stress explored as potential consequences of .OH increased levels. These results support the hypothesis that early .OH generation contributes to the pattern of toxicity elicited by QUIN. The partial protection by MK-801 suggests that QUIN neurotoxicity is not completely explained through NMDA receptor overactivation, but it may also involve intrinsic QUIN oxidative properties.

  18. Concentration-dependent photodegradation kinetics and hydroxyl-radical oxidation of phenicol antibiotics.

    PubMed

    Li, Kai; Zhang, Peng; Ge, Linke; Ren, Honglei; Yu, Chunyan; Chen, Xiaoyang; Zhao, Yuanfeng

    2014-09-01

    Thiamphenicol and florfenicol are two phenicol antibiotics widely used in aquaculture and are ubiquitous as micropollutants in surface waters. The present study investigated their photodegradation kinetics, hydroxyl-radical (OH) oxidation reactivities and products. Firstly, the photolytic kinetics of the phenicols in pure water was studied as a function of initial concentrations (C0) under UV-vis irradiation (λ>200nm). It was found that the kinetics was influenced by C0. A linear plot of the pseudo-first-order rate constant vs C0 was observed with a negative slope. Secondly, the reaction between the phenicol antibiotics and OH was examined with a competition kinetic method under simulated solar irradiation (λ>290nm), which quantified their bimolecular reaction rate constants of (2.13±0.02)×10(9)M(-1)s(-1) and (1.82±0.10)×10(9)M(-1)s(-1) for thiamphenicol and florfenicol, respectively. Then the corresponding OH oxidated half-lives in sunlit surface waters were calculated to be 90.5-106.1h. Some main intermediates were formed from the reaction, which suggested that the two phenicols underwent hydroxylation, oxygenation and dehydrogenation when OH existed. These results are of importance to assess the phenicol persistence in wastewater treatment and sunlit surface waters. PMID:24997929

  19. Degradation of artificial sweetener saccharin in aqueous medium by electrochemically generated hydroxyl radicals.

    PubMed

    Lin, Heng; Wu, Jie; Oturan, Nihal; Zhang, Hui; Oturan, Mehmet A

    2016-03-01

    The removal of artificial sweetener saccharin (SAC) in aqueous solution by electrochemical advanced oxidation using electro-Fenton process was performed. Experiments were carried out in an undivided cylindrical glass cell with a carbon-felt cathode and a Pt or boron-doped diamond (BDD) anode. The removal of SAC by electrochemically generated hydroxyl radicals followed pseudo-first-order kinetics with both Pt and BDD anode. The absolute rate constant of the SAC hydroxylation reaction was determined for the first time using the competition kinetic method and found to be (1.85 ± 0.01) × 10(9) M(-1) s(-1). The comparative study of TOC removal efficiency during electro-Fenton treatment indicated a higher mineralization rate with BDD than Pt anode. The identification and evolution of short-chain carboxylic acids and inorganic ions formed during oxidation process were monitored by ion-exchange chromatography and ion chromatography, respectively. The assessment of toxicity of SAC and/or its reaction by-products during treatment was performed using Microtox® method based on the Vibrio fischeri bacteria luminescence inhibition. Results showed that the process was able to efficiently detoxify the treated solution.

  20. Low-temperature chemistry between water and hydroxyl radicals: H/D isotopic effects

    NASA Astrophysics Data System (ADS)

    Lamberts, T.; Fedoseev, G.; Puletti, F.; Ioppolo, S.; Cuppen, H. M.; Linnartz, H.

    2016-01-01

    Sets of systematic laboratory experiments are presented - combining Ultra High Vacuum cryogenic and plasma-line deposition techniques - that allow us to compare H/D isotopic effects in the reaction of H2O (D2O) ice with the hydroxyl radical OD (OH). The latter is known to play a key role as intermediate species in the solid-state formation of water on icy grains in space. The main finding of our work is that the reaction H2O + OD → OH + HDO occurs and that this may affect the HDO/H2O abundances in space. The opposite reaction D2O + OH → OD + HDO is much less effective, and also given the lower D2O abundances in space not expected to be of astronomical relevance. The experimental results are extended to the other four possible reactions between hydroxyl and water isotopes and are subsequently used as input for Kinetic Monte Carlo simulations. This way we interpret our findings in an astronomical context, qualitatively testing the influence of the reaction rates.

  1. Hydroxyl and Hydroperoxy Radical Chemistry during the MCMA-2006 Field Campaign: Measurement and Model Comparison

    NASA Astrophysics Data System (ADS)

    Dusanter, S.; Vimal, D.; Stevens, P. S.; Volkamer, R.; Molina, L. T.

    2007-12-01

    The Mexico City Metropolitan Area (MCMA) field campaign, held in March 2006, was a unique opportunity to collect data in one of the most polluted megacities in the world. Such environments exhibit a complex oxidation chemistry involving a strong coupling between odd hydrogen radicals (HOX=OH+HO2) and nitrogen oxides species (NOX=NO+NO2). High levels of volatile organic compounds (VOCs) and NOX control the HOX budget and lead to elevated tropospheric ozone formation. The HOX-NOX coupling can be investigated by comparing measured and model-predicted HOx concentrations. Atmospheric HOX concentrations were measured by the Indiana University laser-induced fluorescence instrument and data were collected at the Instituto Mexicano del Petroleo between 14 and 31 March. Measured hydroxyl radical (OH) concentrations are comparable to that measured in less polluted urban environments and suggest that the OH concentrations are highly buffered under high NOX conditions. In contrast, hydroperoxy radical (HO2) concentrations are more sensitive to the NOX levels and are highly variable between different urban sites. Enhanced levels of OH and HO2 radicals were observed on several days between 9h30-11h00 AM and suggest an additional HOX source for the morning hours and/or a fast HOX cycling under the high NOX conditions of the MCMA. A preliminary investigation of the HOX chemistry occurring in the MCMA urban atmosphere was performed using a photochemical box model based on the Regional Atmospheric Chemistry Mechanism (RACM). Model comparisons will be presented and the agreement between measured and predicted HOX concentrations will be discussed.

  2. High structural resolution hydroxyl radical protein footprinting reveals an extended Robo1-heparin binding interface.

    PubMed

    Li, Zixuan; Moniz, Heather; Wang, Shuo; Ramiah, Annapoorani; Zhang, Fuming; Moremen, Kelley W; Linhardt, Robert J; Sharp, Joshua S

    2015-04-24

    Interaction of transmembrane receptors of the Robo family and the secreted protein Slit provides important signals in the development of the central nervous system and regulation of axonal midline crossing. Heparan sulfate, a sulfated linear polysaccharide modified in a complex variety of ways, serves as an essential co-receptor in Slit-Robo signaling. Previous studies have shown that closely related heparin octasaccharides bind to Drosophila Robo directly, and surface plasmon resonance analysis revealed that Robo1 binds more tightly to full-length unfractionated heparin. For the first time, we utilized electron transfer dissociation-based high spatial resolution hydroxyl radical protein footprinting to identify two separate binding sites for heparin interaction with Robo1: one binding site at the previously identified site for heparin dp8 and a second binding site at the N terminus of Robo1 that is disordered in the x-ray crystal structure. Mutagenesis of the identified N-terminal binding site exhibited a decrease in binding affinity as measured by surface plasmon resonance and heparin affinity chromatography. Footprinting also indicated that heparin binding induces a minor change in the conformation and/or dynamics of the Ig2 domain, but no major conformational changes were detected. These results indicate a second low affinity binding site in the Robo-Slit complex as well as suggesting the role of the Ig2 domain of Robo1 in heparin-mediated signal transduction. This study also marks the first use of electron transfer dissociation-based high spatial resolution hydroxyl radical protein footprinting, which shows great utility for the characterization of protein-carbohydrate complexes. PMID:25752613

  3. Supercharging by m-NBA Improves ETD-Based Quantification of Hydroxyl Radical Protein Footprinting

    NASA Astrophysics Data System (ADS)

    Li, Xiaoyan; Li, Zixuan; Xie, Boer; Sharp, Joshua S.

    2015-08-01

    Hydroxyl radical protein footprinting (HRPF) is an MS-based technique for analyzing protein structure based on measuring the oxidation of amino acid side chains by hydroxyl radicals diffusing in solution. Spatial resolution of HRPF is limited by the smallest portion of the protein for which oxidation amounts can be accurately quantitated. Previous work has shown electron transfer dissociation (ETD) to be the most reliable method for quantifying the amount of oxidation of each amino acid side chain in a mixture of peptide oxidation isomers, but efficient ETD requires high peptide charge states, which limits its applicability for HRPF. Supercharging reagents have been used to enhance peptide charge state for ETD analysis, but previous work has shown supercharging reagents to enhance charge state differently for different peptides sequences; it is currently unknown if different oxidation isomers will experience different charge enhancement effects. Here, we report the effect of m-nitrobenzyl alcohol ( m-NBA) on the ETD-based quantification of peptide oxidation. The addition of m-NBA to both a defined mixture of synthetic isomeric oxidized peptides and Robo-1 protein subjected to HRPF increased the abundance of higher charge state ions, improving our ability to perform efficient ETD of the mixture. No differences in the reported quantitation by ETD were noted in the presence or absence of m-NBA, indicating that all oxidation isomers were charge-enhanced to a similar extent. These results indicate the utility of m-NBA for residue-level quantification of peptide oxidation in HRPF and other applications.

  4. Source-dependent variation in hydroxyl radical production by airborne particulate matter

    SciTech Connect

    Marjan Alaghmand; Neil V. Blough

    2007-04-01

    Epidemiological studies suggest exposure to airborne particles is responsible for a wide range of adverse health effects, potentially arising from particle-induced oxidative stress. A highly sensitive fluorescence method was employed to measure the production of hydroxyl radical by a broad range of particle types including urban dust, diesel particulate matter, coal fly ash, kaolinite, and silica. Little or no production of OH was observed in the absence of an added electron donor or H{sub 2}O{sub 2}. In the presence of a biological electron donor (NADPH, 3 mM), the rate of OH production (R{sub OH}) for 3 mg/mL of these particles varied from 23 nM s{sup -1} for diesel particulate matter (SRM 2975) to 0.20 nM s{sup -1} for coal fly ash (SRM 2689). No detectable OH was produced by kaolinite or silica. Hydroxyl radical formation was eliminated under anaerobic conditions and in the presence of catalase, indicating that O{sub 2} and H{sub 2}O{sub 2} are required for its generation. Partial inhibition of OH formation by superoxide dismutase (SOD) was also observed in some cases, suggesting that superoxide is also involved. The metal chelator deferoxamine mesylate (DFX) in most cases suppressed OH formation, but diethylenetriaminepentaacetic acid (DTPA) generally enhanced it, implicating metal ion reactions in OH generation as well. The dependence of R{sub OH} on NADPH concentration further implicates particle surface reactions in OH formation. To the authors' knowledge, these measurements provide the first quantitative estimate of ROH for a broad range of particle types. 49 refs., 6 figs., 1 tab.

  5. High Structural Resolution Hydroxyl Radical Protein Footprinting Reveals an Extended Robo1-Heparin Binding Interface*

    PubMed Central

    Li, Zixuan; Moniz, Heather; Wang, Shuo; Ramiah, Annapoorani; Zhang, Fuming; Moremen, Kelley W.; Linhardt, Robert J.; Sharp, Joshua S.

    2015-01-01

    Interaction of transmembrane receptors of the Robo family and the secreted protein Slit provides important signals in the development of the central nervous system and regulation of axonal midline crossing. Heparan sulfate, a sulfated linear polysaccharide modified in a complex variety of ways, serves as an essential co-receptor in Slit-Robo signaling. Previous studies have shown that closely related heparin octasaccharides bind to Drosophila Robo directly, and surface plasmon resonance analysis revealed that Robo1 binds more tightly to full-length unfractionated heparin. For the first time, we utilized electron transfer dissociation-based high spatial resolution hydroxyl radical protein footprinting to identify two separate binding sites for heparin interaction with Robo1: one binding site at the previously identified site for heparin dp8 and a second binding site at the N terminus of Robo1 that is disordered in the x-ray crystal structure. Mutagenesis of the identified N-terminal binding site exhibited a decrease in binding affinity as measured by surface plasmon resonance and heparin affinity chromatography. Footprinting also indicated that heparin binding induces a minor change in the conformation and/or dynamics of the Ig2 domain, but no major conformational changes were detected. These results indicate a second low affinity binding site in the Robo-Slit complex as well as suggesting the role of the Ig2 domain of Robo1 in heparin-mediated signal transduction. This study also marks the first use of electron transfer dissociation-based high spatial resolution hydroxyl radical protein footprinting, which shows great utility for the characterization of protein-carbohydrate complexes. PMID:25752613

  6. High structural resolution hydroxyl radical protein footprinting reveals an extended Robo1-heparin binding interface.

    PubMed

    Li, Zixuan; Moniz, Heather; Wang, Shuo; Ramiah, Annapoorani; Zhang, Fuming; Moremen, Kelley W; Linhardt, Robert J; Sharp, Joshua S

    2015-04-24

    Interaction of transmembrane receptors of the Robo family and the secreted protein Slit provides important signals in the development of the central nervous system and regulation of axonal midline crossing. Heparan sulfate, a sulfated linear polysaccharide modified in a complex variety of ways, serves as an essential co-receptor in Slit-Robo signaling. Previous studies have shown that closely related heparin octasaccharides bind to Drosophila Robo directly, and surface plasmon resonance analysis revealed that Robo1 binds more tightly to full-length unfractionated heparin. For the first time, we utilized electron transfer dissociation-based high spatial resolution hydroxyl radical protein footprinting to identify two separate binding sites for heparin interaction with Robo1: one binding site at the previously identified site for heparin dp8 and a second binding site at the N terminus of Robo1 that is disordered in the x-ray crystal structure. Mutagenesis of the identified N-terminal binding site exhibited a decrease in binding affinity as measured by surface plasmon resonance and heparin affinity chromatography. Footprinting also indicated that heparin binding induces a minor change in the conformation and/or dynamics of the Ig2 domain, but no major conformational changes were detected. These results indicate a second low affinity binding site in the Robo-Slit complex as well as suggesting the role of the Ig2 domain of Robo1 in heparin-mediated signal transduction. This study also marks the first use of electron transfer dissociation-based high spatial resolution hydroxyl radical protein footprinting, which shows great utility for the characterization of protein-carbohydrate complexes.

  7. Inhibition of membrane lipid peroxidation by a radical scavenging mechanism: a novel function for hydroxyl-containing ionophores.

    PubMed

    Grijalba, M T; Andrade, P B; Meinicke, A R; Castilho, R F; Vercesi, A E; Schreier, S

    1998-03-01

    In the present study we show that K+/H+ hydroxyl-containing ionophores lasalocid-A (LAS) and nigericin (NIG) in the nanomolar concentration range, inhibit Fe2+-citrate and 2,2'-azobis(2-amidinopropane) dihydrochloride (ABAP)-induced lipid peroxidation in intact rat liver mitochondria and in egg phosphatidylcholine (PC) liposomes containing negatively charged lipids--dicetyl phosphate (DCP) or cardiolipin (CL)--and KCl as the osmotic support. In addition, monensin (MON), a hydroxyl-containing ionophore with higher affinity for Na+ than for K+, promotes a similar effect when NaCl is the osmotic support. The protective effect of the ionophores is not observed when the osmolyte is sucrose. Lipid peroxidation was evidenced by mitochondrial swelling, antimycin A-insensitive O2 consumption, formation of thiobarbituric acid-reactive substances (TBARS), conjugated dienes, and electron paramagnetic resonance (EPR) spectra of an incorporated lipid spin probe. A time-dependent decay of spin label EPR signal is observed as a consequence of lipid peroxidation induced by both inductor systems in liposomes. Nitroxide destruction is inhibited by butylated hydroxytoluene, a known antioxidant, and by the hydroxyl-containing ionophores. In contrast, valinomycin (VAL), which does not possess alcoholic groups, does not display this protective effect. Effective order parameters (Seff), determined from the spectra of an incorporated spin label are larger in the presence of salt and display a small increase upon addition of the ionophores, as a result of the increase of counter ion concentration at the negatively charged bilayer surface. This condition leads to increased formation of the ion-ionophore complex, the membrane binding (uncharged) species. The membrane-incorporated complex is the active species in the lipid peroxidation inhibiting process. Studies in aqueous solution (in the absence of membranes) showed that NIG and LAS, but not VAL, decrease the Fe2+-citrate-induced production

  8. Hydroxyl radical scavenging assay of phenolics and flavonoids with a modified cupric reducing antioxidant capacity (CUPRAC) method using catalase for hydrogen peroxide degradation.

    PubMed

    Ozyürek, Mustafa; Bektaşoğlu, Burcu; Güçlü, Kubilay; Apak, Reşat

    2008-06-01

    Hydroxyl radicals (OH) generated in the human body may play an important role in tissue injury at sites of inflammation in oxidative stress-originated diseases. As a more convenient, efficient, and less costly alternative to HPLC/electrochemical detection techniques and to the nonspecific, low-yield deoxyribose (TBARS) test, we used a salicylate probe for detecting OH generated by the reaction of iron(II)-EDTA complex with H(2)O(2). The produced hydroxyl radicals attack both the salicylate probe and the hydroxyl radical scavengers that are incubated in solution for 10 min. Added radical scavengers compete with salicylate for the OH produced, and diminish chromophore formation from Cu(II)-neocuproine. At the end of the incubation period, the reaction was stopped by adding catalase. With the aid of this reaction, a kinetic approach was adopted to assess the hydroxyl radical scavenging properties of polyphenolics, flavonoids and other compounds (e.g., ascorbic acid, glucose, mannitol). A second-order rate constant for the reaction of the scavenger with OH could be deduced from the inhibition of colour formation due to the salicylate probe. In addition to phenolics and flavonoids, five kinds of herbs were evaluated for their OH scavenging activity using the developed method. The modified CUPRAC (cupric ion reducing antioxidant capacity) assay proved to be efficient for ascorbic acid, gallic acid and chlorogenic acid, for which the deoxyribose assay test is basically nonresponsive. An important contribution of this developed assay is the inhibition of the Fenton reaction with catalase degradation of hydrogen peroxide so that the remaining H(2)O(2) would neither give a CUPRAC absorbance nor involve in redox cycling of phenolic antioxidants, enabling the rapid assay of polyphenolics.

  9. Studies of hydroxyl radical and hydroperoxyl radical in the region of the arctic winter tropopause

    NASA Astrophysics Data System (ADS)

    Simpas, James Bernard B.

    This study is based on in situ measurements made on the NASA DC-8 during the SAGE III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone (SOLVE/THESEO) campaign which was conducted in the 1999-2000 Arctic winter (November, 1999 to April, 2000). The DC-8’s extensive coverage of the arctic winter tropopause region afforded the opportunity to probe more deeply into the unique chemistry of the upper troposphere/lower stratosphere (UTLS). Central to this analysis are the measurements of OH, HO2⊂ (collectively called HOx⊂), and halogen oxides that play a crucial role in the chemistry of this region. We discuss the modified configuration of the Penn State Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) in order to accommodate the University of Colorado ClO/BrO instrument, the salient points of the measurement profiles that were obtained by this unique instrument, the shifts of these profiles in the presence of cirrus clouds that may indicate heterogeneous processing/activation of halogen reservoir species, and the projected impact of the abundance of these species on the local chemical ozone budget in the region.

  10. Hydroxyl radical induced oxidation of theophylline in water: a kinetic and mechanistic study.

    PubMed

    Sunil Paul, M M; Aravind, U K; Pramod, G; Saha, A; Aravindakumar, C T

    2014-08-14

    Oxidative destruction and mineralization of emerging organic pollutants by hydroxyl radicals (˙OH) is a well established area of research. The possibility of generating hazardous by-products in the case of ˙OH reaction demands extensive investigations on the degradation mechanism. A combination of pulse radiolysis and steady state photolysis (H2O2/UV photolysis) followed by high resolution mass spectrometric (HRMS) analysis have been employed to explicate the kinetic and mechanistic features of the destruction of theophylline, a model pharmaceutical compound and an identified pollutant, by ˙OH in the present study. The oxidative destruction of this molecule, for intermediate product studies, was initially achieved by H2O2/UV photolysis. The transient absorption spectrum corresponding to the reaction of ˙OH with theophylline at pH 6, primarily caused by the generation of (T8-OH)˙, was characterised by an absorption band at 330 nm (k2 = (8.22 ± 0.03) × 10(9) dm(3) mol(-1) s(-1)). A significantly different spectrum (λmax: 340 nm) was observed at highly alkaline pH (10.2) due to the deprotonation of this radical (pKa∼ 10.0). Specific one electron oxidants such as sulphate radical anions (SO4˙(-)) and azide radicals (N3˙) produce the deprotonated form (T(-H)˙) of the radical cation (T˙(+)) of theophylline (pKa 3.1) with k2 values of (7.51 ± 0.04) × 10(9) dm(3) mol(-1) s(-1) and (7.61 ± 0.02) × 10(9) dm(3) mol(-1) s(-1) respectively. Conversely, oxide radicals (O˙(-)) react with theophylline via a hydrogen abstraction protocol with a rather slow k2 value of (1.95 ± 0.02) × 10(9) dm(3) mol(-1) s(-1). The transient spectral studies were complemented by the end product profile acquired by HRMS analysis. Various transformation products of theophylline induced by ˙OH were identified by this technique which include derivatives of uric acids (i, iv & v) and xanthines (ii, iii & vi). Further breakdown of the early formed product due to ˙OH attack leads to

  11. Kinetics of methyl radical-hydroxyl radical collisions and methanol decomposition.

    SciTech Connect

    Jasper, A. W.; Klippenstein, S. J.; Harding, L. B.; Ruscic, B.; Chemistry

    2007-01-01

    The CH{sub 3} + OH bimolecular reaction and the dissociation of methanol are studied theoretically at conditions relevant to combustion chemistry. Kinetics for the CH{sub 3} + OH barrierless association reaction and for the H + CH{sub 2}OH and H + CH{sub 3}O product channels are determined in the high-pressure limit using variable reaction coordinate transition state theory and multireference electronic structure calculations to evaluate the fragment interaction energies. The CH{sub 3} + OH {yields} {sup 3}CH{sub 2} + H{sub 2}O abstraction reaction and the H{sub 2} + HCOH and H{sub 2} + H{sub 2}CO product channels feature localized dynamical bottlenecks and are treated using variational transition state theory and QCISD(T) energies extrapolated to the complete basis set limit. The {sup 1}CH{sub 2} + H{sub 2}O product channel has two dynamical regimes, featuring both an inner saddle point and an outer barrierless region, and it is shown that a microcanonical two-state model is necessary to properly describe the association rate for this reaction over a broad temperature range. Experimental channel energies for the methanol system are reevaluated using the Active Thermochemical Tables (ATcT) approach. Pressure dependent, phenomenological rate coefficients for the CH{sub 3} + OH bimolecular reaction and for methanol decomposition are determined via master equation simulations. The predicted results agree well with experimental results, including those from a companion high-temperature shock tube determination for the decomposition of methanol.

  12. Quantification of photoelectrogenerated hydroxyl radical on TiO2 by surface interrogation scanning electrochemical microscopy.

    PubMed

    Zigah, Dodzi; Rodríguez-López, Joaquín; Bard, Allen J

    2012-10-01

    The surface interrogation mode of scanning electrochemical microscopy (SI-SECM) was used for the detection and quantification of adsorbed hydroxyl radical ˙OH((ads)) generated photoelectrochemically at the surface of a nanostructured TiO(2) substrate electrode. In this transient technique, a SECM tip is used to generate in situ a titrant from a reversible redox pair that reacts with the adsorbed species at the substrate. This reaction produces an SECM feedback response from which the amount of adsorbate and its decay kinetics can be obtained. The redox pair IrCl(6)(2-/3-) offered a reactive, selective and stable surface interrogation agent under the strongly oxidizing conditions of the photoelectrochemical cell. A typical ˙OH((ads)) saturation coverage of 338 μC cm(-2) was found in our nanostructured samples by its reduction with the electrogenerated IrCl(6)(3-). The decay kinetics of ˙OH((ads)) by dimerization to produce H(2)O(2) were studied through the time dependence of the SI-SECM signal and the surface dimerization rate constant was found to be ~k(OH) = 2.2 × 10(3) mol(-1) m(2) s(-1). A radical scavenger, such as methanol, competitively consumes ˙OH((ads)) and yields a shorter SI-SECM transient, where a pseudo-first order rate analysis at 2 M methanol yields a decay constant of k'(MeOH) ~ 1 s(-1).

  13. Superoxide mediated production of hydroxyl radicals by magnetite nanoparticles: demonstration in the degradation of 2-chlorobiphenyl.

    PubMed

    Fang, Guo-Dong; Zhou, Dong-Mei; Dionysiou, Dionysios D

    2013-04-15

    Increasing attention has been paid to magnetite nanoparticles (MNPs) due to their highly reductive reactivity toward environmental contaminants. However, there is little information related to the generation of reactive oxygen species (ROS) by MNPs, which in fact plays a vital role for the transformation of contaminants. In this paper, the degradation of 2-chlorobiphenyl (2-CB) by MNPs was investigated. The role of ROS generated by MNPs in this process was elucidated. The results demonstrated that hydroxyl radicals (OH) generated by MNPs at low pH could efficiently degrade 2-CB. The mechanism of the formation of OH by MNPs was divided into two steps: (i) the superoxide radical anion (O2(-)) mediated production of hydrogen peroxide (H2O2), and (ii) the reaction of formed H2O2 with Fe(II) dissolved from MNPs to produce OH through Fenton reaction. Comparison of the degradation products of 2-CB by MNPs with MNPs/ethanol and Fenton reagents further supported the involvement of OH in the degradation of 2-CB. The degradation efficiency of 2-CB by MNPs under acidic conditions was higher than that in alkaline solution. These findings provide a new insight into the understanding of reactivity of MNPs for the transformation of 2-CB and possibly other relevant environmental contaminants. PMID:23434481

  14. Photochemical Formation of Hydroxyl Radical in Red-Soil-Polluted Seawater in Okinawa, Japan -Potential Impacts on Marine Organisms

    NASA Astrophysics Data System (ADS)

    Arakaki, T.; Hamdun, A. M.; Okada, K.; Kuroki, Y.; Ikota, H.; Fujimura, H.; Oomori, T.

    2004-12-01

    Development of pineapple farmlands and construction of recreational facilities caused runoff of red soil into coastal ocean (locally termed as red-soil-pollution) in the north of Okinawa Island, Japan. In an attempt to understand the impacts of red soil on oxidizing power of the seawater, we studied formation of hydroxyl radical (OH radical), the most potent oxidant in the environment, in red-soil-polluted seawaters, using 313 nm monochromatic light. Photo-formation rates of OH radical showed a good correlation with dissolved iron concentrations (R = 0.98). The major source of OH radical was found to be the Fenton reaction (a reaction between Fe(II) and HOOH). The un-filtered red-soil-polluted seawater samples exhibited faster OH radical formation rates than the filtered samples, suggesting that iron-bearing red soil particles enhanced formation of OH radical.

  15. POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS: GAS-PHASE HYDROXYL RADICAL REACTIONS AND RELATED ATMOSPHERIC REMOVAL. (R825377)

    EPA Science Inventory

    Gas-phase reactions with the hydroxyl radical (OH) are
    expected to be an important removal pathway of polychlorinated dibenzo-p-dioxins and dibenzofurans
    (PCDD/F)
    in the atmosphere. Our laboratory recently developed
    a system to measure the rate constants of ...

  16. Hydroxyl radical generation mechanism during the redox cycling process of 1,4-naphthoquinone.

    PubMed

    Shang, Yu; Chen, Chenyong; Li, Yi; Zhao, Jincai; Zhu, Tong

    2012-03-01

    Airborne quinones contribute to adverse health effects of ambient particles probably because of their ability to generate hydroxyl radicals (·OH) via redox cycling, but the mechanisms remain unclear. We examined the chemical mechanisms through which 1,4-naphthoquinone (1,4-NQ) induced ·OH, and the redox interactions between 1,4-NQ and ascorbate acid (AscH(2)). First, ·OH formation by 1,4-NQ was observed in cellular and acellular systems, and was enhanced by AscH(2). AscH(2) also exacerbated the cytotoxicity of 1,4-NQ in Ana-1 macrophages, at least partially due to enhanced ·OH generation. The detailed mechanism was studied in an AscH(2)/H(2)O(2) physiological system. The existence of a cyclic 1,4-NQ process was shown by detecting the corresponding semiquinone radical (NSQ·-) and hydroquinone (NQH(2)). 1,4-NQ was reduced primarily to NSQ·- by O2·- (which was from AscH(2) reacting with H(2)O(2)), not by AscH(2) as normally thought. At lower doses, 1,4-NQ consumed O2·- to suppress ·OH; however, at higher doses, 1,4-NQ presented a positive association with ·OH. The reaction of NSQ·- with H(2)O(2) to release ·OH was another important channel for OH radical formation except for Haber-Weiss reaction. As a reaction precursor for O2·-, the enhanced ·OH response to 1,4-NQ by AscH(2) was indirect. Reducing substrates were necessary to sustain the redox cycling of 1,4-NQ, leading to more ·OH and a deleterious end point.

  17. Copper, zinc superoxide dismutase catalyzes hydroxyl radical production from hydrogen peroxide.

    PubMed

    Yim, M B; Chock, P B; Stadtman, E R

    1990-07-01

    Cu,Zn superoxide dismutase (Cu,Zn-SOD; EC 1.15.1.1) is known to be inhibited slowly by H2O2. Using EPR and the spin traps 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN), we have shown that Cu,Zn-SOD catalyzes the formation of "free" .OH radicals from H2O2 in pH 7.6 bicarbonate buffer. Supporting evidence includes the following: (i) H2O2 and active Cu,Zn-SOD are required to yield significant signals from spin-trap-OH adducts. (ii) With O2-., Cu,Zn-SOD causes the appearance of intense resonance signals due to DMPO-OH adducts. These signals were inhibited strongly by catalase. (iii) With H2O2, Cu,Zn-SOD, and DMPO, radical scavengers formate and azide, but not ethanol, decrease DMPO-OH signals while causing new intense signals due to their corresponding DMPO-radical adducts. Failure of ethanol to quench DMPO-OH signals is discussed in light of the positively charged active channel of the enzyme. (iv) With PBN as a spin trap, ethanol quenches .OH radical signals and yields PBN-trapped hydroxyethyl radical signals. (v) Mn-SOD does not catalyze "free" .OH radical formation and it also exerts no effect on the signals of DMPO-OH adducts when added together with the Cu,Zn-SOD. The capacity of Cu,Zn-SOD to generate "free" .OH radicals from H2O2 may in part explain the biological damage associated with elevated intracellular SOD activity. PMID:2164216

  18. Lunasin peptide purified from Solanum nigrum L. protects DNA from oxidative damage by suppressing the generation of hydroxyl radical via blocking fenton reaction.

    PubMed

    Jeong, Jin Boo; De Lumen, Ben O; Jeong, Hyung Jin

    2010-07-01

    Oxidative DNA damage is the most critical factor implicated in carcinogenesis and other disorders. However, the protective effects of lunasin against oxidative DNA damage have not yet reported. In this study, we report here the protective effect of lunasin purified from Solanum nigrum L. against oxidative DNA. Lunasin protected DNA from the oxidative damage induced by Fe(2+) ion and hydroxyl radical. To better understand the mechanism for the protective effect of lunasin against DNA damage, the abilities to chelate Fe(2+), scavenge the generated hydroxyl radical and block the generation of hydroxyl radical were evaluated. Although it did not scavenge generated hydroxyl radical, lunasin blocked the generation of hydroxyl radical by chelating Fe(2+) ion. We conclude that lunasin protects DNA from oxidation by blocking fenton reaction between Fe(2+) and H(2)O(2) by chelating Fe(2+) and that consumption of lunasin may play an important role in the chemoprevention for the oxidative carcinogenesis. PMID:20083341

  19. DNA damage produced by exposure of supercoiled plasmid DNA to high- and low-LET ionizing radiation: Effects of hydroxyl radical quenchers. DNA breakage, neutrons, OH radicals

    SciTech Connect

    Peak, J.G.; Ito, T.; Peak, M.J.; Robb, F.T.

    1994-08-01

    A supercoiled plasmid of 7300 base pairs was isolated and exposed in an aqueous environment to {sup 60}Co {gamma} rays and JANUS 0.85 MeV fission-spectrum neutrons. Dose responses for the production of single-strand breaks (SSBs), double-strand breaks (DSBs) and alkali-labile sites (ALSs) were compared with computations made from the conversion of the supercoil to its relaxed and linear forms. The relative biological effectiveness (RBE) for production of SSBs and DSBs was similar to that previously measured in the cellular environment. The RBE for destruction of genetic transforming activity of M13 viral DNA followed that for DNA damage. This is in contrast to the situation for biological effects such as lethality, mutagenesis, and cellular transformation measured in mammalian cells, where the RBE values are reversed. The role of hydroxyl (OH) radical in DNA damage induction by neutrons was investigated by exposure of plasmid in the presence of known quenchers of this species. Of four quenchers tested, all were able to reduce the yields of both SSBs and DSBs. These findings are consistent with a model for SSB and DSB induction by high linear energy transfer that involves OH radical mediation.

  20. Synthesis and antioxidant activity of hydroxylated phenanthrenes as cis-restricted resveratrol analogues.

    PubMed

    Ding, De-Jun; Cao, Xiao-Yan; Dai, Fang; Li, Xiu-Zhuang; Liu, Guo-Yun; Lin, Dong; Fu, Xing; Jin, Xiao-Ling; Zhou, Bo

    2012-12-01

    Five hydroxylated phenanthrenes as "cis-configuration-fixed" resveratrol analogues differing in the number and position of the hydroxyl groups were designed and synthesized. Their antioxidant activity was studied by ferric reducing antioxidant power, 2,2-diphenyl-1-picrylhydrazyl free radical-scavenging, and DNA strand breakage-inhibiting assays, corresponding to their electron-donating, hydrogen-transfer and DNA-protecting abilities, respectively. In the above assays, their activity depends significantly on the number and position of the hydroxyl groups, and most of them are more effective than resveratrol. Noticeably, compound 9b (2,4,6-trihydroxyl phenanthrene) with the same hydroxyl group substitutions as resveratrol, is superior to the reference compound, highlighting the importance of extension of the conjugation over multiple aromatic-rings. Similar activity sequences were obtained in different experimental models, but the appreciable differences could contribute detailed insights into antioxidant mechanisms. Based on these results, the hydroxylated phenanthrenes may be considered as a novel type of resveratrol-directed antioxidants.

  1. Oxidative damage to fibronectin. 2. The effect of H2O2 and the hydroxyl radical

    SciTech Connect

    Vissers, M.C.; Winterbourn, C.C. )

    1991-03-01

    The effect of H2O2 and the hydroxyl radical (.OH) on fibronectin was investigated. .OH was generated in three ways: (1) by radiolysis with 60Co under N2O, or by the Fenton system using either (2) equimolar Fe(2+)-EDTA and H2O2 or (3) H2O2 and catalytic amounts of Fe(2+)-EDTA recycled with ascorbate. Each system had a different effect. H2O2 alone caused no changes, even at an 800-fold molar excess. Radiolytic .OH caused a rapid loss of tryptophan fluorescence, an increase in bityrosine fluorescence, and extensive crosslinking. The Fenton system using Fe-EDTA, H2O2, and ascorbate caused a loss in tryptophan fluorescence, a smaller increase in bityrosine than was seen with radiolytic .OH, and a threefold increase in carbonyl groups. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis fragmentation of fibronectin was seen. In contrast, when .OH was generated with equimolar Fe-EDTA and H2O2, the only change was a small increase in bityrosine fluorescence at the highest dose of oxidant. None of the systems used affected cysteine. All the changes except the loss of tryptophan by radiolytic .OH were completely inhibited with mannitol. The differences seen with radiolytic .OH and the Fe-EDTA, H2O2, ascorbate system were not solely due to O2 in the latter system since similar results were obtained under N2. The differences between radiolytic .OH and the Fenton systems could be partly due to the components of the latter systems reacting with .OH and thus competing with fibronectin. The authors results demonstrate that the extent and type of fibronectin damage by .OH is dependent on the mode of radical generation.

  2. Catechol oxidation by ozone and hydroxyl radicals at the air-water interface.

    PubMed

    Pillar, Elizabeth A; Camm, Robert C; Guzman, Marcelo I

    2014-12-16

    Anthropogenic emissions of aromatic hydrocarbons promptly react with hydroxyl radicals undergoing oxidation to form phenols and polyphenols (e.g., catechol) typically identified in the complex mixture of humic-like substances (HULIS). Because further processing of polyphenols in secondary organic aerosols (SOA) can continue mediated by a mechanism of ozonolysis at interfaces, a better understanding about how these reactions proceed at the air-water interface is needed. This work shows how catechol, a molecular probe of the oxygenated aromatic hydrocarbons present in SOA, can contribute interfacial reactive species that enhance the production of HULIS under atmospheric conditions. Reactive semiquinone radicals are quickly produced upon the encounter of 40 ppbv-6.0 ppmv O3(g) with microdroplets containing [catechol] = 1-150 μM. While the previous pathway results in the instantaneous formation of mono- and polyhydroxylated aromatic rings (PHA) and chromophoric mono- and polyhydroxylated quinones (PHQ), a different channel produces oxo- and dicarboxylic acids of low molecular weight (LMW). The cleavage of catechol occurs at the 1,2 carbon-carbon bond at the air-water interface through the formation of (1) an ozonide intermediate, (2) a hydroperoxide, and (3) cis,cis-muconic acid. However, variable [catechol] and [O3(g)] can affect the ratio of the primary products (cis,cis-muconic acid and trihydroxybenzenes) and higher order products observed (PHA, PHQ, and LMW oxo- and dicarboxylic acids). Secondary processing is confirmed by mass spectrometry, showing the production of crotonic, maleinaldehydic, maleic, glyoxylic, and oxalic acids. The proposed pathway can contribute precursors to aqueous SOA (AqSOA) formation, converting aromatic hydrocarbons into polyfunctional species widely found in tropospheric aerosols with light-absorbing brown carbon.

  3. Catechol oxidation by ozone and hydroxyl radicals at the air-water interface.

    PubMed

    Pillar, Elizabeth A; Camm, Robert C; Guzman, Marcelo I

    2014-12-16

    Anthropogenic emissions of aromatic hydrocarbons promptly react with hydroxyl radicals undergoing oxidation to form phenols and polyphenols (e.g., catechol) typically identified in the complex mixture of humic-like substances (HULIS). Because further processing of polyphenols in secondary organic aerosols (SOA) can continue mediated by a mechanism of ozonolysis at interfaces, a better understanding about how these reactions proceed at the air-water interface is needed. This work shows how catechol, a molecular probe of the oxygenated aromatic hydrocarbons present in SOA, can contribute interfacial reactive species that enhance the production of HULIS under atmospheric conditions. Reactive semiquinone radicals are quickly produced upon the encounter of 40 ppbv-6.0 ppmv O3(g) with microdroplets containing [catechol] = 1-150 μM. While the previous pathway results in the instantaneous formation of mono- and polyhydroxylated aromatic rings (PHA) and chromophoric mono- and polyhydroxylated quinones (PHQ), a different channel produces oxo- and dicarboxylic acids of low molecular weight (LMW). The cleavage of catechol occurs at the 1,2 carbon-carbon bond at the air-water interface through the formation of (1) an ozonide intermediate, (2) a hydroperoxide, and (3) cis,cis-muconic acid. However, variable [catechol] and [O3(g)] can affect the ratio of the primary products (cis,cis-muconic acid and trihydroxybenzenes) and higher order products observed (PHA, PHQ, and LMW oxo- and dicarboxylic acids). Secondary processing is confirmed by mass spectrometry, showing the production of crotonic, maleinaldehydic, maleic, glyoxylic, and oxalic acids. The proposed pathway can contribute precursors to aqueous SOA (AqSOA) formation, converting aromatic hydrocarbons into polyfunctional species widely found in tropospheric aerosols with light-absorbing brown carbon. PMID:25423038

  4. A Novel High-Throughput Approach to Measure Hydroxyl Radicals Induced by Airborne Particulate Matter

    PubMed Central

    Son, Yeongkwon; Mishin, Vladimir; Welsh, William; Lu, Shou-En; Laskin, Jeffrey D.; Kipen, Howard; Meng, Qingyu

    2015-01-01

    Oxidative stress is one of the key mechanisms linking ambient particulate matter (PM) exposure with various adverse health effects. The oxidative potential of PM has been used to characterize the ability of PM induced oxidative stress. Hydroxyl radical (•OH) is the most destructive radical produced by PM. However, there is currently no high-throughput approach which can rapidly measure PM-induced •OH for a large number of samples with an automated system. This study evaluated four existing molecular probes (disodium terephthalate, 3′-p-(aminophenyl)fluorescein, coumarin-3-carboxylic acid, and sodium benzoate) for their applicability to measure •OH induced by PM in a high-throughput cell-free system using fluorescence techniques, based on both our experiments and on an assessment of the physicochemical properties of the probes reported in the literature. Disodium terephthalate (TPT) was the most applicable molecular probe to measure •OH induced by PM, due to its high solubility, high stability of the corresponding fluorescent product (i.e., 2-hydroxyterephthalic acid), high yield compared with the other molecular probes, and stable fluorescence intensity in a wide range of pH environments. TPT was applied in a high-throughput format to measure PM (NIST 1648a)-induced •OH, in phosphate buffered saline. The formed fluorescent product was measured at designated time points up to 2 h. The fluorescent product of TPT had a detection limit of 17.59 nM. The soluble fraction of PM contributed approximately 76.9% of the •OH induced by total PM, and the soluble metal ions of PM contributed 57.4% of the overall •OH formation. This study provides a promising cost-effective high-throughput method to measure •OH induced by PM on a routine basis. PMID:26516887

  5. Potential mechanism for pentachlorophenol-induced carcinogenicity: a novel mechanism for metal-independent production of hydroxyl radicals.

    PubMed

    Zhu, Ben-Zhan; Shan, Guo-Qiang

    2009-06-01

    The hydroxyl radical ((*)OH) has been considered to be one of the most reactive oxygen species produced in biological systems. It has been shown that (*)OH can cause DNA, protein, and lipid oxidation. One of the most widely accepted mechanisms for (*)OH production is through the transition metal-catalyzed Fenton reaction. Pentachlorophenol (PCP) was one of the most widely used biocides, primarily for wood preservation. PCP is now ubiquitously present in our environment and even found in people who are not occupationally exposed to it. PCP has been listed as a priority pollutant by the U.S. Environmental Protection Agency (EPA) and classified as a group 2B environmental carcinogen by the International Association for Research on Cancer (IARC). The genotoxicity of PCP has been attributed to its two major quinoid metabolites: tetrachlorohydroquinone and tetrachloro-1,4-benzoquinone (TCBQ). Although the redox cycling of PCP quinoid metabolites to generate reactive oxygen species is believed to play an important role, the exact molecular mechanism underlying PCP genotoxicity is not clear. Using the salicylate hydroxylation assay and electron spin resonance (ESR) secondary spin-trapping methods, we found that (*)OH can be produced by TCBQ and H(2)O(2) independent of transition metal ions. Further studies showed that TCBQ, but not its corresponding semiquinone radical, the tetrachlorosemiquinone radical (TCSQ(*)), is essential for (*)OH production. The major reaction product between TCBQ and H(2)O(2) was identified to be trichloro-hydroxy-1,4-benzoquinone (TrCBQ-OH), and H(2)O(2) was found to be the source and origin of the oxygen atom inserted into this reaction product. On the basis of these data, we propose that (*)OH production by TCBQ and H(2)O(2) is not through a semiquinone-dependent organic Fenton reaction but rather through the following novel mechanism: a nucleophilic attack of H(2)O(2) to TCBQ, leading to the formation of an unstable trichloro-hydroperoxyl-1

  6. Potential mechanism for pentachlorophenol-induced carcinogenicity: a novel mechanism for metal-independent production of hydroxyl radicals.

    PubMed

    Zhu, Ben-Zhan; Shan, Guo-Qiang

    2009-06-01

    The hydroxyl radical ((*)OH) has been considered to be one of the most reactive oxygen species produced in biological systems. It has been shown that (*)OH can cause DNA, protein, and lipid oxidation. One of the most widely accepted mechanisms for (*)OH production is through the transition metal-catalyzed Fenton reaction. Pentachlorophenol (PCP) was one of the most widely used biocides, primarily for wood preservation. PCP is now ubiquitously present in our environment and even found in people who are not occupationally exposed to it. PCP has been listed as a priority pollutant by the U.S. Environmental Protection Agency (EPA) and classified as a group 2B environmental carcinogen by the International Association for Research on Cancer (IARC). The genotoxicity of PCP has been attributed to its two major quinoid metabolites: tetrachlorohydroquinone and tetrachloro-1,4-benzoquinone (TCBQ). Although the redox cycling of PCP quinoid metabolites to generate reactive oxygen species is believed to play an important role, the exact molecular mechanism underlying PCP genotoxicity is not clear. Using the salicylate hydroxylation assay and electron spin resonance (ESR) secondary spin-trapping methods, we found that (*)OH can be produced by TCBQ and H(2)O(2) independent of transition metal ions. Further studies showed that TCBQ, but not its corresponding semiquinone radical, the tetrachlorosemiquinone radical (TCSQ(*)), is essential for (*)OH production. The major reaction product between TCBQ and H(2)O(2) was identified to be trichloro-hydroxy-1,4-benzoquinone (TrCBQ-OH), and H(2)O(2) was found to be the source and origin of the oxygen atom inserted into this reaction product. On the basis of these data, we propose that (*)OH production by TCBQ and H(2)O(2) is not through a semiquinone-dependent organic Fenton reaction but rather through the following novel mechanism: a nucleophilic attack of H(2)O(2) to TCBQ, leading to the formation of an unstable trichloro-hydroperoxyl-1

  7. Oestradiol protects against the harmful effects of fluoride more by increasing thiol group levels than scavenging hydroxyl radicals.

    PubMed

    Dlugosz, Anna; Roszkowska, Anna; Zimmer, Mariusz

    2009-12-01

    The aim of the study was to investigate the role of oestrogens in free radical detoxication upon exposure to fluoride. Interactions between xenobiotics and oestrogens need to be investigated, especially as many chemicals interact with the oestrogen receptor. It is still unknown whether free radical-generating xenobiotics can influence the antioxidative ability of oestradiol (E(2)). In an in vitro examination of human placental mitochondria, thiobarbituric active reagent species (TBARS), hydroxyl radical ((*)OH) generation and protein thiol (-SH) groups were detected. 17beta-E(2) was examined in physiological (0.15-0.73 nM) and experimental (1-10 microM) concentrations and sodium fluoride (NaF) in concentrations of 6-24 microM. E(2) in all the concentrations significantly decreased lipid peroxidation measured as the TBARS level, in contrast to NaF, which increased lipid peroxidation. Lipid peroxidation induced by NaF was decreased by E(2). The influence of E(2) on (*)OH generation was not very significant and depended on the E(2 )concentration. The main mechanism of E(2) protection in NaF exposure appeared to be connected with the influence of E(2 )on thiol group levels, not (*)OH scavenging ability. The E(2) in concentrations 0.44-0.73 nM and 1-10 microM significantly increased the levels of -SH groups, in contrast to NaF, which significantly decreased them. E(2) at every concentration reversed the harmful effects of NaF on -SH group levels. No unfavourable interactions in the influence of E(2) and NaF on TBARS production, (*)OH generation, or -SH group levels were observed. The results suggest that postmenopausal women could be more sensitive to NaF-initiated oxidative stress.

  8. Using pulsed wave ultrasound to evaluate the suitability of hydroxyl radical scavengers in sonochemical systems.

    PubMed

    Xiao, Ruiyang; Diaz-Rivera, David; He, Ziqi; Weavers, Linda K

    2013-05-01

    Hydroxyl radical (()OH) scavengers are commonly used in sonochemistry to probe the site and nature of reaction in aqueous cavitational systems. Using pulsed wave (PW) ultrasound with comparative sonochemistry we evaluated the performance of ()OH scavengers (i.e., formic acid, carbonic acid, terephthalic acid/terephthalate, iodide, methanesulfonate, benzenesulfonate, and acetic acid/acetate) in a sonochemical system to determine which ()OH scavengers react only in bulk solution and which ()OH scavengers interact with cavitation bubbles. The ability of each scavenger to interact with cavitation bubbles was assessed by comparing the pulse enhancement (PE) of 10μM of a probe compound, carbamazepine (CBZ), in the presence and absence of a scavenger. Based on PE results, acetic acid/acetate appears to scavenge ()OH in bulk solution, and not interact with cavitation bubbles. Methanesulfonate acts as reaction promoter, increasing rather than inhibiting the degradation of CBZ. For formic acid, carbonic acid, terephthalic acid/terephthalate, benzenesulfonate, and iodide, the PE was significantly decreased compared to in the absence of the scavenger. These scavengers not only quench ()OH in bulk solution but also affect the cavity interface. The robustness of acetic acid/acetate as a bulk ()OH scavenger was validated for pH values between 3.5 and 8.9 and acetic acid/acetate concentrations from 0.5 to 0.1M.

  9. Determination of hydroxyl radical production in aqueous solutions irradiated to clinically significant doses

    SciTech Connect

    Sagone, A.L. Jr.; Democko, C.; Clark, L.; Kartha, M.

    1983-02-01

    Decarboxylation of /sup 14/C-carboxylbenzoic acid in aqueous solutions after low-dose irradiation has been used to determine the relative magnitude of oxidation reactions and estimate the hydroxyl radicals produced. The G CO/sub 2/ values determined from these measurements of 0.4 to 1.0 mM solutions of benzoic acid after x-ray doses of 1000 rads ranged from 0.72 to 0.77, in excellent agreement with values reported by authors using much higher doses of radiation. Superoxide dismutase and catalase, known scavengers of superoxide and hydrogen peroxide, respectively, did not show impairment of the oxidation of benzoic acid. On the other hand, biologically significant concentrations of phenol and mannitol appear to impair the radiation-induced oxidation of benzoic acid, indicating that the process is secondary to a reaction with OH . . We found that serum and glucose, common cell media contents, are potent OH . scavengers. These observations indicate that the oxidation of benzoic acid can be as a reliable method to estimate OH . with radiation doses of clinically significant magnitudes. In addition, these results suggest that the radiation induced by OH . in cell systems can be significantly modified by the type of buffer used.

  10. Impact of hydroxyl radical-induced injury on calcium handling and myofilament sensitivity in isolated myocardium

    PubMed Central

    Haizlip, Kaylan M.; Hiranandani, Nitisha; Biesiadecki, Brandon J.

    2012-01-01

    Hydroxyl radicals (OH˙) are involved in the pathogenesis of reperfusion injury and are observed in acute heart failure, stroke, and myocardial infarction. Two different subcellular defects are involved in the pathogenesis of OH˙ injury, deranged calcium handling, and alterations of myofilament responsiveness, but their temporal impact on contractile function is not resolved. Initially, after brief OH˙ exposure, there is a corresponding marked increase in diastolic calcium and diastolic force. We followed these parameters until a new steady-state level was reached at ∼45 min post-OH˙ exposure. At this new baseline, diastolic calcium had returned to near-normal, pre-OH˙ levels, whereas diastolic force remained markedly elevated. An increased calcium sensitivity was observed at the new baseline after OH˙-induced injury compared with the pre-OH˙ state. The acute injury that occurs after OH˙ exposure is mainly due to calcium overload, while the later sustained myocardial dysfunction is mainly due to the altered/increased myofilament responsiveness. PMID:22773772

  11. Mobility mechanism of hydroxyl radicals in aqueous solution via hydrogen transfer.

    PubMed

    Codorniu-Hernández, Edelsys; Kusalik, Peter G

    2012-01-11

    The hydroxyl radical (OH*) is a highly reactive oxygen species that plays a salient role in aqueous solution. The influence of water molecules upon the mobility and reactivity of the OH* constitutes a crucial knowledge gap in our current understanding of many critical reactions that impact a broad range of scientific fields. Specifically, the relevant molecular mechanisms associated with OH* mobility and the possibility of diffusion in water via a H-transfer reaction remain open questions. Here we report insights into the local hydration and electronic structure of the OH* in aqueous solution from Car-Parrinello molecular dynamics and explore the mechanism of H-transfer between OH* and a water molecule. The relatively small free energy barrier observed (~4 kcal/mol) supports a conjecture that the H-transfer can be a very rapid process in water, in accord with very recent experimental results, and that this reaction can contribute significantly to OH* mobility in aqueous solution. Our findings reveal a novel H-transfer mechanism of hydrated OH*, resembling that of hydrated OH(-) and presenting hybrid characteristics of hydrogen-atom and electron-proton transfer processes, where local structural fluctuations play a pivotal role. PMID:22107057

  12. Characterization of hydroxyl radical modified GAD65: a potential autoantigen in type 1 diabetes.

    PubMed

    Khan, Mohd Wajid A; Sherwani, Subuhi; Khan, Wahid A; Ali, Rashid

    2009-02-01

    Glutamic acid decarboxylase-65 (GAD(65)) is an immunological marker of type 1 autoimmune diabetes. High titre of autoantibodies against GAD(65) (GAD(65)Abs) have also been detected in some other autoimmune diseases. In search of a potential immunological marker of type 1 diabetes, in vitro GAD(65) was modified by hydroxyl radical followed by the study of structural and conformational perturbed protein by different spectroscopic techniques (UV, fluorescence and CD) and thermal denaturation profile. Binding studies of circulating autoantibodies from diabetic groups (type 1 and type 2) with native and reactive oxygen species (ROS) modified GAD(65), exhibited high recognition of type 1 diabetic serum autoantibodies with modified antigen (p < 0.001) over unmodified GAD(65). Binding specificity of isolated IgG of patients (n = 17) from each diabetic group and control group (n = 10) was checked by inhibition enzyme linked immunosorbent assay (ELISA) and quantitative precipitin titration assay. Relative affinity of ROS-GAD(65)Abs for modified and native GAD(65) was in the order of 1.56 x 10(- 6) and 2.72 x 10(- 7) M, as calculated by Langmuir plot. In coherence, ROS oxidation of GAD(65) causes conformational perturbation, generating highly immunogenic unique neoepitopes that may be one of the factors in antigen-driven induction of type 1 diabetes autoantibodies that can serve as a potential marker in early diagnosis/prognosis of the disease.

  13. Fingerprinting of hydroxyl radical-attacked polysaccharides by N-isopropyl-2-aminoacridone labelling.

    PubMed

    Vreeburg, Robert A M; Airianah, Othman B; Fry, Stephen C

    2014-10-15

    Hydroxyl radicals (•OH) cause non-enzymic scission of polysaccharides in diverse biological systems. Such reactions can be detrimental (e.g. causing rheumatic and arthritic diseases in mammals) or beneficial (e.g. promoting the softening of ripening fruit, and biomass saccharification). Here we present a method for documenting •OH action, based on fluorescent labelling of the oxo groups that are introduced as glycosulose residues when •OH attacks polysaccharides. The method was tested on several polysaccharides, especially pectin, after treatment with Fenton reagents. 2-Aminoacridone plus cyanoborohydride reductively aminated the oxo groups in treated polysaccharides; the product was then reacted with acetone plus cyanoborohydride, forming a stable tertiary amine with the carbohydrate linked to N-isopropyl-2-aminoacridone (pAMAC). Digestion of labelled pectin with 'Driselase' yielded several fluorescent products which on electrophoresis and HPLC provided a useful 'fingerprint' indicating •OH attack. The most diagnostic product was a disaccharide conjugate of the type pAMAC·UA-GalA (UA=unspecified uronic acid), whose UA-GalA bond was Driselase-resistant (product 2A). 2A was clearly distinguishable from GalA-GalA-pAMAC (disaccharide labelled at its reducing end), which was digestible to GalA-pAMAC. The methodology is applicable, with appropriate enzymes in place of Driselase, for detecting natural and artificial •OH attack in diverse plant, animal and microbial polysaccharides.

  14. Numerical analysis of quantitative measurement of hydroxyl radical concentration using laser-induced fluorescence in flame

    NASA Astrophysics Data System (ADS)

    Shuang, Chen; Tie, Su; Yao-Bang, Zheng; Li, Chen; Ting-Xu, Liu; Ren-Bing, Li; Fu-Rong, Yang

    2016-06-01

    The aim of the present work is to quantitatively measure the hydroxyl radical concentration by using LIF (laser-induced fluorescence) in flame. The detailed physical models of spectral absorption lineshape broadening, collisional transition and quenching at elevated pressure are built. The fine energy level structure of the OH molecule is illustrated to understand the process with laser-induced fluorescence emission and others in the case without radiation, which include collisional quenching, rotational energy transfer (RET), and vibrational energy transfer (VET). Based on these, some numerical results are achieved by simulations in order to evaluate the fluorescence yield at elevated pressure. These results are useful for understanding the real physical processes in OH-LIF technique and finding a way to calibrate the signal for quantitative measurement of OH concentration in a practical combustor. Project supported by the National Natural Science Foundation of China (Grant No. 11272338) and the Fund from the Science and Technology on Scramjet Key Laboratory, China (Grant No. STSKFKT2013004).

  15. Predicting the reaction rate constants of micropollutants with hydroxyl radicals in water using QSPR modeling.

    PubMed

    Jin, Xiaohui; Peldszus, Sigrid; Huck, Peter M

    2015-11-01

    Quantitative structure-property relationship (QSPR) models which predict hydroxyl radical rate constants (kOH) for a wide range of emerging micropollutants are a cost effective approach to assess the susceptibility of these contaminants to advanced oxidation processes (AOPs). A QSPR model for the prediction of kOH of emerging micropollutants from their physico-chemical properties was developed with special attention to model validation, applicability domain and mechanistic interpretation. In this study, 118 emerging micropollutants including those experimentally determined by the author and data collected from the literature, were randomly divided into the training set (n=89) and validation set (n=29). 951 DRAGON molecular descriptors were calculated for model development. The QSPR model was calibrated by applying forward multiple linear regression to the training set. As a result, 7 DRAGON descriptors were found to be important in predicting the kOH values which related to the electronegativity, polarizability, and double bonds, etc. of the compounds. With outliers identified and removed, the final model fits the training set very well and shows good robustness and internal predictivity. The model was then externally validated with the validation set showing good predictive power. The applicability domain of the model was also assessed using the Williams plot approach. Overall, the developed QSPR model provides a valuable tool for an initial assessment of the susceptibility of micropollutants to AOPs.

  16. Ultrasonic application to boost hydroxyl radical formation during Fenton oxidation and release organic matter from sludge.

    PubMed

    Gong, Changxiu; Jiang, Jianguo; Li, De'an; Tian, Sicong

    2015-06-12

    We examined the effects of ultrasound and Fenton reagent on ultrasonic coupling Fenton oxidation (U+F) pre-treatment processes for the disintegration of wastewater treatment plant sludge. The results demonstrated that U+F treatment could significantly increase soluble chemical oxygen demand (SCOD), total organic carbon (TOC), and extracellular polymeric substances (EPS) concentrations in sludge supernatant. This method was more effective than ultrasonic (U) or Fenton oxidation (F) treatment alone. U+F treatment increased the release of SCOD by 2.1- and 1.4-fold compared with U and F alone, respectively. U+F treatment increased the release of EPS by 1.2-fold compared with U alone. After U+F treatment, sludge showed a considerably finer particle size and looser microstructure based on fluorescence microscopy, and the concentration of hydroxyl radicals (OH•) increased from 0.26 mM by F treatment to 0.43 mM by U+F treatment based on fluorescence spectrophotometer. This demonstrated that U+F treatment improves the release of organic matter from sludge.

  17. Hyperfine structure of the hydroxyl free radical (OH) in electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Maeda, Kenji; Wall, Michael L.; Carr, Lincoln D.

    2015-05-01

    We investigate single-particle energy spectra of the hydroxyl free radical (OH) in the lowest electronic and rovibrational level under combined static electric and magnetic fields, as an example of heteronuclear polar diatomic molecules. In addition to the fine-structure interactions, the hyperfine interactions and centrifugal distortion effects are taken into account to yield the zero-field spectrum of the lowest 2Π3 / 2 manifold to an accuracy of less than 2kHz. We also examine level crossings and repulsions in the hyperfine structure induced by applied electric and magnetic fields. Compared to previous work, we found more than 10 percent reduction of the magnetic fields at level repulsions in the Zeeman spectrum subjected to a perpendicular electric field. In addition, we find new level repulsions, which we call Stark-induced hyperfine level repulsions, that require both an electric field and hyperfine structure. It is important to take into account hyperfine structure when we investigate physics of OH molecules at micro-Kelvin temperatures and below. This research was supported in part by AFOSR Grant No.FA9550-11-1-0224 and by the NSF under Grants PHY-1207881 and NSF PHY-1125915. We appreciate the Aspen Center for Physics, supported in part by the NSF Grant No.1066293, for hospitality.

  18. Numerical analysis of quantitative measurement of hydroxyl radical concentration using laser-induced fluorescence in flame

    NASA Astrophysics Data System (ADS)

    Shuang, Chen; Tie, Su; Yao-Bang, Zheng; Li, Chen; Ting-Xu, Liu; Ren-Bing, Li; Fu-Rong, Yang

    2016-06-01

    The aim of the present work is to quantitatively measure the hydroxyl radical concentration by using LIF (laser-induced fluorescence) in flame. The detailed physical models of spectral absorption lineshape broadening, collisional transition and quenching at elevated pressure are built. The fine energy level structure of the OH molecule is illustrated to understand the process with laser-induced fluorescence emission and others in the case without radiation, which include collisional quenching, rotational energy transfer (RET), and vibrational energy transfer (VET). Based on these, some numerical results are achieved by simulations in order to evaluate the fluorescence yield at elevated pressure. These results are useful for understanding the real physical processes in OH-LIF technique and finding a way to calibrate the signal for quantitative measurement of OH concentration in a practical combustor. Project supported by the National Natural Science Foundation of China (Grant No. 11272338) and the Fund from the Science and Technology on Scramjet Key Laboratory, China (Grant No. STSKFKT2013004).

  19. Theoretical study of adducts of dimethyl sulfide with hydroperoxyl and hydroxyl radicals

    NASA Astrophysics Data System (ADS)

    Aloisio, Simone

    2006-08-01

    Structures and energies of complexes of dimethyl sulfide (DMS) with hydroxyl (OH) and hydroperoxyl (HO 2) radicals have been studied using ab initio and density functional theory. Two isomers of the complex between OH and DMS were found, one dipole-dipole complex and one 3e -/2c complex. The binding energies ( D0) of these two complexes have been found to be consistent with previous studies. This is the first reported study of the complex between DMS and HO 2. One structure was found for this complex, and the binding energy ( D0) has been determined to be 9.0 kcal mol -1 using the fully optimized MP2/6-311++G(3df,3pd) level of theory. Vibrational and rotational constants are also presented for all of complexes calculated. Thermodynamic parameters and equilibrium constants for the formation of these complexes from the monomers have been calculated. The results have been related to laboratory experiments studying these reactions, and some implications to oxidation of DMS in the atmosphere have been discussed.

  20. Theoretical study on the gas phase reaction of allyl alcohol with hydroxyl radical.

    PubMed

    Zhang, Yunju; Chao, Kai; Sun, Jingyu; Su, Zhongmin; Pan, Xiumei; Zhang, Jingping; Wang, Rongshun

    2013-08-01

    The complex potential energy surface of allyl alcohol (CH2CHCH2OH) with hydroxyl radical (OH) has been investigated at the G3(MP2)//MP2/6-311++G(d,p) level. On the surface, two kinds of pathways are revealed, namely, direct hydrogen abstraction and addition/elimination. Rice-Ramsperger-Kassel-Marcus theory and transition state theory are carried out to calculate the total and individual rate constants over a wide temperature and pressure region with tunneling correction. It is predicted that CH2CHOHCH2OH (IM1) formed by collisional stabilization is dominate in the temperature range (200-440 K) at atmospheric pressure with N2 (200-315 K at 10 Torr Ar and 100 Torr He). The production of CH2CHCHOH + H2O via direct hydrogen abstraction becomes dominate at higher temperature. The kinetic isotope effect (KIE) has also been calculated for the title reaction. Moreover, the calculated rate constants and KIE are in good agreement with the experimental data.

  1. Predicting the reaction rate constants of micropollutants with hydroxyl radicals in water using QSPR modeling.

    PubMed

    Jin, Xiaohui; Peldszus, Sigrid; Huck, Peter M

    2015-11-01

    Quantitative structure-property relationship (QSPR) models which predict hydroxyl radical rate constants (kOH) for a wide range of emerging micropollutants are a cost effective approach to assess the susceptibility of these contaminants to advanced oxidation processes (AOPs). A QSPR model for the prediction of kOH of emerging micropollutants from their physico-chemical properties was developed with special attention to model validation, applicability domain and mechanistic interpretation. In this study, 118 emerging micropollutants including those experimentally determined by the author and data collected from the literature, were randomly divided into the training set (n=89) and validation set (n=29). 951 DRAGON molecular descriptors were calculated for model development. The QSPR model was calibrated by applying forward multiple linear regression to the training set. As a result, 7 DRAGON descriptors were found to be important in predicting the kOH values which related to the electronegativity, polarizability, and double bonds, etc. of the compounds. With outliers identified and removed, the final model fits the training set very well and shows good robustness and internal predictivity. The model was then externally validated with the validation set showing good predictive power. The applicability domain of the model was also assessed using the Williams plot approach. Overall, the developed QSPR model provides a valuable tool for an initial assessment of the susceptibility of micropollutants to AOPs. PMID:26005810

  2. Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation.

    PubMed

    Rohrer, Franz; Berresheim, Harald

    2006-07-13

    The most important chemical cleaning agent of the atmosphere is the hydroxyl radical, OH. It determines the oxidizing power of the atmosphere, and thereby controls the removal of nearly all gaseous atmospheric pollutants. The atmospheric supply of OH is limited, however, and could be overcome by consumption due to increasing pollution and climate change, with detrimental feedback effects. To date, the high variability of OH concentrations has prevented the use of local observations to monitor possible trends in the concentration of this species. Here we present and analyse long-term measurements of atmospheric OH concentrations, which were taken between 1999 and 2003 at the Meteorological Observatory Hohenpeissenberg in southern Germany. We find that the concentration of OH can be described by a surprisingly linear dependence on solar ultraviolet radiation throughout the measurement period, despite the fact that OH concentrations are influenced by thousands of reactants. A detailed numerical model of atmospheric reactions and measured trace gas concentrations indicates that the observed correlation results from compensations between individual processes affecting OH, but that a full understanding of these interactions may not be possible on the basis of our current knowledge of atmospheric chemistry. As a consequence of the stable relationship between OH concentrations and ultraviolet radiation that we observe, we infer that there is no long-term trend in the level of OH in the Hohenpeissenberg data set. PMID:16838018

  3. Continuous hydroxyl radical planar laser imaging at 50 kHz repetition rate.

    PubMed

    Hammack, Stephen; Carter, Campbell; Wuensche, Clemens; Lee, Tonghun

    2014-08-10

    This study demonstrates high-repetition-rate planar laser-induced fluorescence (PLIF) imaging of hydroxyl radicals (OH) in flames at a continuous framing rate of 50 kHz. A frequency-doubled dye laser is pumped by the second harmonic of an Nd:YAG laser to generate laser radiation near 283 nm with a pulse width of 8 ns and rate of 50 kHz. Fluorescence is recorded by a two-stage image intensifier and complementary metal-oxide-semiconductor camera. The average power of the 283 nm beam reaches 7 W, yielding a pulse energy of 140 μJ. Both a Hencken burner and a DC transient-arc plasmatron are used to produce premixed CH4/air flames to evaluate the OH PLIF system. The average signal-to-noise ratio for the Hencken burner flame is greater than 20 near the flame front and greater than 10 further downstream in a region of the flame near equilibrium. Image sequences of the DC plasmatron discharge clearly illustrate development and evolution of flow features with signal levels comparable to those in the Hencken burner. The results are a demonstration of the ability to make high-fidelity OH PLIF measurements at 50 kHz using a Nd:YAG-pumped, frequency-doubled dye laser. PMID:25320935

  4. Rate coefficients of hydroxyl radical reactions with pesticide molecules and related compounds: A review

    NASA Astrophysics Data System (ADS)

    Wojnárovits, László; Takács, Erzsébet

    2014-03-01

    Rate coefficients published in the literature on hydroxyl radical reactions with pesticides and related compounds are discussed together with the experimental methods and the basic reaction mechanisms. Recommendations are made for the most probable values. Most of the molecules whose rate coefficients are discussed have aromatic ring: their rate coefficients are in the range of 2×109-1×1010 mol-1 dm3 s-1. The rate coefficients show some variation with the electron withdrawing-donating nature of the substituent on the ring. The rate coefficients for triazine pesticides (simazine, atrazine, prometon) are all around 2.5×109 mol-1 dm3 s-1. The values do not show variation with the substituent on the s-triazine ring. The rate coefficients for the non-aromatic molecules which have C=C double bonds or several C-H bonds may also be above 1×109 mol-1 dm3 s-1. However, the values for molecules without C=C double bonds or several C-H bonds are in the 1×107-1×109 mol-1 dm3 s-1 range.

  5. Hydroxyl radical transfer between interface and bulk from transition path sampling

    SciTech Connect

    Wick, Collin D.; Dang, Liem X.

    2007-08-17

    The transition path sampling technique was used to determine trajectories connecting the interface and bulk for the transfer of a hydroxyl radical from the air-water interface to the water bulk. The trajectories were used to calculate the rate of transfer for the process. In addition, transition state and Grote-Hynes theories were used to calculate the rate of transfer. It was found that transition state theory significantly overestimated the rate of transfer, while the Grote-Hynes theory estimated a transmission coefficient that was fairly close to that from transition path sampling. Analysis of transition states found that a majority of them were not at the free energy barrier from the potential of mean force, but shifted towards the vapor phase. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

  6. Ultrasonic application to boost hydroxyl radical formation during Fenton oxidation and release organic matter from sludge

    PubMed Central

    Gong, Changxiu; Jiang, Jianguo; Li, De’an; Tian, Sicong

    2015-01-01

    We examined the effects of ultrasound and Fenton reagent on ultrasonic coupling Fenton oxidation (U+F) pre-treatment processes for the disintegration of wastewater treatment plant sludge. The results demonstrated that U+F treatment could significantly increase soluble chemical oxygen demand (SCOD), total organic carbon (TOC), and extracellular polymeric substances (EPS) concentrations in sludge supernatant. This method was more effective than ultrasonic (U) or Fenton oxidation (F) treatment alone. U+F treatment increased the release of SCOD by 2.1- and 1.4-fold compared with U and F alone, respectively. U+F treatment increased the release of EPS by 1.2-fold compared with U alone. After U+F treatment, sludge showed a considerably finer particle size and looser microstructure based on fluorescence microscopy, and the concentration of hydroxyl radicals (OH•) increased from 0.26 mM by F treatment to 0.43 mM by U+F treatment based on fluorescence spectrophotometer. This demonstrated that U+F treatment improves the release of organic matter from sludge. PMID:26066562

  7. Fingerprinting of hydroxyl radical-attacked polysaccharides by N-isopropyl-2-aminoacridone labelling

    PubMed Central

    Vreeburg, Robert A. M.; Airianah, Othman B.; Fry, Stephen C.

    2014-01-01

    Hydroxyl radicals (•OH) cause non-enzymic scission of polysaccharides in diverse biological systems. Such reactions can be detrimental (e.g. causing rheumatic and arthritic diseases in mammals) or beneficial (e.g. promoting the softening of ripening fruit, and biomass saccharification). Here we present a method for documenting •OH action, based on fluorescent labelling of the oxo groups that are introduced as glycosulose residues when •OH attacks polysaccharides. The method was tested on several polysaccharides, especially pectin, after treatment with Fenton reagents. 2-Aminoacridone plus cyanoborohydride reductively aminated the oxo groups in treated polysaccharides; the product was then reacted with acetone plus cyanoborohydride, forming a stable tertiary amine with the carbohydrate linked to N-isopropyl-2-aminoacridone (pAMAC). Digestion of labelled pectin with ‘Driselase’ yielded several fluorescent products which on electrophoresis and HPLC provided a useful ‘fingerprint’ indicating •OH attack. The most diagnostic product was a disaccharide conjugate of the type pAMAC·UA-GalA (UA=unspecified uronic acid), whose UA-GalA bond was Driselase-resistant (product 2A). 2A was clearly distinguishable from GalA-GalA–pAMAC (disaccharide labelled at its reducing end), which was digestible to GalA–pAMAC. The methodology is applicable, with appropriate enzymes in place of Driselase, for detecting natural and artificial •OH attack in diverse plant, animal and microbial polysaccharides. PMID:25072268

  8. Photochemical formation of hydroxyl radicals in tissue extracts of the coral Galaxea fascicularis.

    PubMed

    Higuchi, Tomihiko; Fujimura, Hiroyuki; Hitomi, Yuya; Arakaki, Takemitsu; Oomori, Tamotsu; Suzuki, Yoshimi

    2010-01-01

    Various stresses induce the formation of reactive oxygen species (ROS) in biological cells. In addition to stress-induced ROS, we studied the photochemical formation of hydroxyl radicals (˙OH), the most potent ROS, in coral tissues using phosphate buffer-extracted solutions and a simulated sunlight irradiation system. ˙OH formation was seen in extracts of both coral host and endosymbiont zooxanthellae. This study is the first to report quantitative measurements of ˙OH photoformation in coral tissue extracts. Our results indicated that whether or not coral bleaching occurred, coral tissues and symbiotic zooxanthellae have the potential to photochemically produce ˙OH under sunlight. However, no significant difference was found in the protein content-normalized formation rates of ˙OH between corals incubated under different temperatures and irradiance conditions. ˙OH formation rates were reduced by 40% by reducing the UV radiation in the illumination. It was indicated that UV radiation strongly affected ˙OH formation in coral tissue and zooxanthellae, in addition to its formation through photoinhibition processes. PMID:21155074

  9. Ultrasonic application to boost hydroxyl radical formation during Fenton oxidation and release organic matter from sludge

    NASA Astrophysics Data System (ADS)

    Gong, Changxiu; Jiang, Jianguo; Li, De'An; Tian, Sicong

    2015-06-01

    We examined the effects of ultrasound and Fenton reagent on ultrasonic coupling Fenton oxidation (U+F) pre-treatment processes for the disintegration of wastewater treatment plant sludge. The results demonstrated that U+F treatment could significantly increase soluble chemical oxygen demand (SCOD), total organic carbon (TOC), and extracellular polymeric substances (EPS) concentrations in sludge supernatant. This method was more effective than ultrasonic (U) or Fenton oxidation (F) treatment alone. U+F treatment increased the release of SCOD by 2.1- and 1.4-fold compared with U and F alone, respectively. U+F treatment increased the release of EPS by 1.2-fold compared with U alone. After U+F treatment, sludge showed a considerably finer particle size and looser microstructure based on fluorescence microscopy, and the concentration of hydroxyl radicals (OH•) increased from 0.26 mM by F treatment to 0.43 mM by U+F treatment based on fluorescence spectrophotometer. This demonstrated that U+F treatment improves the release of organic matter from sludge.

  10. Production of sulfate radical and hydroxyl radical by reaction of ozone with peroxymonosulfate: a novel advanced oxidation process.

    PubMed

    Yang, Yi; Jiang, Jin; Lu, Xinglin; Ma, Jun; Liu, Yongze

    2015-06-16

    In this work, simultaneous generation of hydroxyl radical (•OH) and sulfate radical (SO4•−) by the reaction of ozone (O3) with peroxymonosulfate (PMS; HSO5−) has been proposed and experimentally verified. We demonstrate that the reaction between the anion of PMS (i.e.,SO52−) and O3 is primarily responsible for driving O3 consumption with a measured second order rate constant of (2.12 ± 0.03) × 10(4) M(-1) s(-1). The formation of both •OH and SO4•− from the reaction between SO52− and O3 is confirmed by chemical probes (i.e., nitrobenzene for •OH and atrazine forb oth •OH and SO4•−). The yields of •OH and SO4•− are determined to be 0.43 ± 0.1 and 0.45 ± 0.1 per mol of O3 consumption, respectively. An adduct,−O3SOO− + O3 → −O3SO5−, is assumed as the first step, which further decomposes into SO5•− and O3•−. The subsequent reaction of SO5•− with O3is proposed to generate SO4•−, while O3•− converts to •OH. A definition of R(ct,•OH) and R(ct,SO4•−) (i.e., respective ratios of •OH and SO4•− exposures to O3 exposure) is adopted to quantify relative contributions of •OH and SO4•−. Increasing pH leads to increases in both values of R(ct,•OH) and R(ct,SO4•−) but does not significantly affect the ratio of R(ct,SO4•−) to R(ct,•OH) (i.e., R(ct,SO4•−)/R(ct,•OH)), which represents the relative formation of SO4•− to •OH. The presence of bicarbonate appreciably inhibits the degradation of probes and fairly decreases the relative contribution of •OH for their degradation, which may be attributed to the conversion of both •OH and SO4•− to the more selective carbonate radical (CO3•−).Humic acid promotes O3 consumption to generate •OH and thus leads to an increase in the R(ct,•OH) value in the O3/PMS process,w hile humic acid has negligible influence on the R(ct,SO4•−) value. This discrepancy is reasonably explained by the negligible effect of humic acid on SO

  11. Pectic polysaccharides are attacked by hydroxyl radicals in ripening fruit: evidence from a fluorescent fingerprinting method

    PubMed Central

    Fry, Stephen C.

    2016-01-01

    Background and aims Many fruits soften during ripening, which is important commercially and in rendering the fruit attractive to seed-dispersing animals. Cell-wall polysaccharide hydrolases may contribute to softening, but sometimes appear to be absent. An alternative hypothesis is that hydroxyl radicals (•OH) non-enzymically cleave wall polysaccharides. We evaluated this hypothesis by using a new fluorescent labelling procedure to ‘fingerprint’ •OH-attacked polysaccharides. Methods We tagged fruit polysaccharides with 2-(isopropylamino)-acridone (pAMAC) groups to detect (a) any mid-chain glycosulose residues formed in vivo during •OH action and (b) the conventional reducing termini. The pAMAC-labelled pectins were digested with Driselase, and the products resolved by high-voltage electrophoresis and high-pressure liquid chromatography. Key Results Strawberry, pear, mango, banana, apple, avocado, Arbutus unedo, plum and nectarine pectins all yielded several pAMAC-labelled products. GalA–pAMAC (monomeric galacturonate, labelled with pAMAC at carbon-1) was produced in all species, usually increasing during fruit softening. The six true fruits also gave pAMAC·UA-GalA disaccharides (where pAMAC·UA is an unspecified uronate, labelled at a position other than carbon-1), with yields increasing during softening. Among false fruits, apple and strawberry gave little pAMAC·UA-GalA; pear produced it transiently. Conclusions GalA–pAMAC arises from pectic reducing termini, formed by any of three proposed chain-cleaving agents (•OH, endopolygalacturonase and pectate lyase), any of which could cause its ripening-related increase. In contrast, pAMAC·UA-GalA conjugates are diagnostic of mid-chain oxidation of pectins by •OH. The evidence shows that •OH radicals do indeed attack fruit cell wall polysaccharides non-enzymically during softening in vivo. This applies much more prominently to drupes and berries (true fruits) than to false fruits (swollen

  12. Mammalian cells are not killed by DNA single-strand breaks caused by hydroxyl radicals from hydrogen peroxide

    SciTech Connect

    Ward, J.F.; Blakely, W.F.; Joner, E.I.

    1985-09-01

    Cell killing by ionizing radiation has been shown to be caused by hydroxyl free radicals formed by water radiolysis. The authors have previously suggested that the killing is not caused by individual OH free radicals but by the interaction of volumes of high radical density with DNA to cause locally multiple damaged sites (LMDS). Here they test this hypothesis using hydrogen dioxide as an alternate source of OH radicals. The route to OH production from H/sub 2/O/sub 2/ is expected to cause singly damaged sites rather than LMDS. Chinese hamster V79-171 cells were treated with H/sub 2/O/sub 2/ at varying concentrations for varying times at 0/sup 0/C. The yield of DNA damage produced increases with increasing concentration of H/sub 2/O/sub 2/ and with time of exposure. H/sub 2/O/sub 2/ is efficient in producing single-strand breaks; treatment with 50 ..mu..M for 30 min produces damage equivalent to that formed by 10 Gy of ..cap alpha.. irradiation. In the presence of a hydroxyl radical scavenger, dimethyl sulfoxide (DMSO), the yield of damage decreases with increasing DMSO concentration consistent with the scavenging of hydroxyl radicals. In contrast to DNA damage production, cell killing by H/sub 2/O/sub 2/ treatment at 0/sup 0/C is inefficient. The conclusion drawn is that individual DNA damage sites are ineffectual in killing cells. Mechanisms are suggested for killing at 0/sup 0/C at high concentrations and for the efficient cell killing by H/sub 2/O/sub 2/ at 37/sup 0/C at much lower concentrations.

  13. Shock tube study of the reactions of the hydroxyl radical with combustion species and pollutants. Final report

    SciTech Connect

    Cohen, N.; Koffend, J.B.

    1998-02-01

    Shock heating t-butyl hydroperoxide behind a reflected shock wave has proved to be as a convenient source of hydroxyl radicals at temperatures near 1000 K. We applied this technique to the measurement of reaction rate coefficients of OH with several species of interest in combustion chemistry, and developed a thermochemical kinetics/transition state theory (TK-TST) model for predicting the temperature dependence of OH rate coefficients.

  14. Effects of tetrathiomolybdate and penicillamine on brain hydroxyl radical and free copper levels: a microdialysis study in vivo.

    PubMed

    Zhang, Ji-Wei; Liu, Jun-Xiu; Hou, Hai-Man; Chen, Ding-Bang; Feng, Li; Wu, Chao; Wei, Li-Ting; Li, Xun-Hua

    2015-02-27

    Wilson disease is an inherited disorder of excessive copper accumulation. The commonly used drug d-penicillamine (PA) or trientine both cause a high incidence (10-50%) of neurological worsening, which rarely occurs with tetrathiomolybdate (TM) treatment. To investigate the mechanisms of neurologic deterioration after the initiation of chelation therapy, brain hydroxyl radical and free copper were assessed in vivo in this study. On days 3, 7, 14, and 21 after PA or TM administration, striatal hydroxyl radical levels of both TX mice and controls were assessed by terephthalic acid (TA) combined with microdialysis and high-performance liquid chromatography (HPLC). Within the same microdialysis samples, free copper was measured by inductively coupled plasma mass spectrometry (ICP-MS). The results showed that both hydroxyl radical and free copper markedly increased in the striatum of TX mice during PA administration but were not elevated when administering TM. These results suggested that the further increased free copper in the brain and oxidative stress caused by some chelators might contribute to the neurological deterioration.

  15. Hydroxyl Radical Regeneration in Isoprene Oxidation: the Upgraded Mechanism LIM1

    NASA Astrophysics Data System (ADS)

    Peeters, J.; Nguyen, S.; Nguyen, T.; Stavrakou, T.; Muller, J. J.

    2012-12-01

    Measured hydroxyl radical concentrations in isoprene-rich areas are much higher than predicted by existing chemical models, to the extent that the global oxidizing capacity of our atmosphere should be significantly revised upwards. The OH regeneration that clearly occurs in isoprene oxidation at low/moderate NO is attributed in the Leuven Isoprene Mechanism to novel, theoretically characterized chemical pathways (LIM0: Peeters et al. 2009; Peeters and Muller 2010). The key new features of LIM0 are (i) thermal equilibration of the labile beta-OH- and delta-OH-isoprenylperoxy isomers; (ii) 1,6-H shift isomerisation of the Z-delta-OH-peroxy isomers to yield hydroperoxy-methyl-butenals (HPALDs); (iii) fast photolysis of the HPALDs resulting overall in several OH radicals per HPALD. The OH-regeneration through photolabile HPALDs has recently found experimental support, but the peroxy isomerisation rate, HPALD yield and the extent of OH recycling are still uncertain (Crounse et al. 2011; Wolfe et al. 2012). In this work, the upgraded LIM1 mechanism is presented. Based on better levels of theory, the crucial equilibrium ratio of the isomerising Z-delta-OH-peroxys over the majority beta-OH-isoprenylperoxys had to be reduced by a factor of about 5 compared to LIM0, while the isomerisation rate of the Z-delta-OH-peroxys adopted from Taraborrelli et al. (2012) is about 3 times lower than in LIM0. The chemistry following the 1,6-H shift of the Z-delta-OH-peroxys is much expanded and extended. Firstly, LIM1 introduces other pathways beside HPALD formation following the Z-delta-OH-peroxy isomerisation, resulting likewise in OH recycling. This, together with the revised Z-delta-OH- equilibrium and isomerisation data above, affords a close model-reproduction of the HPALD and other product yields observed by Crounse et al. (2011). Secondly, LIM1 proposes new fast reactions of HO2 with the alpha-oxoketene products from the peroxy isomerisation routes; these reactions are shown to

  16. Hydroxyl radical measurements and oxidation capacity in a boreal forest environment

    NASA Astrophysics Data System (ADS)

    Hens, K.; Tatum Ernest, C.; Novelli, A.; Paasonen, P.; Sipilä, M.; Petäjä, T.; Nölscher, A.; Taraborrelli, D.; Keronen, P.; Trawny, K.; Kubistin, D.; Oswald, R.; Axinte, R.; Hosaynali Beygi, Z.; Auld, J.; Klüpfel, T.; Mesarchaki, E.; Song, W.; Valverde Canossa, J.; González Orozco, D.; Königstedt, R.; Bohn, B.; Rudolf, M.; Fischer, H.; Williams, J.; Crowley, J.; Martinez, M.; Harder, H. D.; Lelieveld, J.

    2012-12-01

    Forests cover about one third of the earth's total land surface and are known to be an important global source of biogenic volatile organic compounds (BVOCs) that are partly very reactive towards OH. Different types of forests are known to emit various characteristic BVOCs significantly influencing atmospheric oxidation chemistry. Measurements of OH and HO2 radicals in forest environments, however, reveal a serious lack of understanding of the underlying processes. The HUMPPA-COPEC intensive field campaign took place in summer 2010 at the SMEAR II station, located in Hyytiälä, Southern Finland, as collaboration between the Max Planck Institute for Chemistry and the University of Helsinki. The main goal of the campaign was to investigate the summertime emissions and photochemistry in a boreal forest. Comprehensive measurements including observations of many VOCs, HOx, and total OH reactivity were conducted to increase our understanding of atmospheric self-cleaning processes based on detailed analysis of production and loss mechanisms of the hydroxyl radical. Also the HOx budget in a coniferous forest was examined by using direct calculations from measured species as well as an observationally constrained chemical box model in steady state. For HUMPPA-COPEC chemical reaction schemes considering isoprene as the predominant primary BVOC lead to an over prediction of the measured OH concentration by a factor of up to 4. However, only a minor fraction of the measured total OH reactivity can be explained by measured isoprene. A preliminary terpene mechanism, taking the most abundant terpenes measured during HUMPPA-COPEC-2010 and their oxidation products into account, improves the agreement between simulated and measured OH, but is not sufficient to explain the missing OH reactivity in all cases. HO2 is described reasonably well by the model for conditions where the modeled and measured total OH reactivity agree. For lower than measured reactivity, the HO2 mixing ratios

  17. Determination of Atmospheric Hydroxyl Radical by Liquid Phase Scrubbing and High Performance Liquid Chromatography.

    NASA Astrophysics Data System (ADS)

    Chen, Xiaohui

    A new in situ method for determining atmospheric hydroxyl radical (OH) was developed. This method is based on liquid phase scrubbing technique and high performance liquid chromatography (LPS-HPLC). The sampling system employs glass bubblers to trap atmospheric OH into a buffered solution containing the chemical probe, salicylic acid (o-hydroxybenzoic acid, OHBA). The reaction of OHBA with OH produces a stable fluorescent product, 2,5-dihydroxybenzoic acid (2,5-DHBA), which is determined by reverse phase HPLC and fluorescence detection. The atmospheric OH concentration ( (OH)) is inferred from the resulting 2,5-DHBA amount in the aqueous scrubbing solution, fraction of 2,5-DHBA in the products, air sampling flow rate, sampling time, local pressure and temperature, etc. HPLC separation efficiency and fluorescence detection sensitivity for 2,5-DHBA have been studied. The results indicate that: the reagent blank can be controlled by suitable recrystallization; pH affects both separation and detection processes; the fluorometer should be adjusted to reach its highest signal-to-noise ratio by light source selection, flow cell size selection, wavelength selection, etc. Preliminary column switch experiments reveal the possibility to automate the whole sampling and detection system to enhance the temporal resolution. During an intercomparison of tropospheric OH measurement techniques at the Caribou site, CO (relatively unpolluted air) in Fall 1993, overlapping data were obtained with long path absorption and ion-assisted coupled with MS methods. LPS -HPLC day-time (OH) s, which range from {< }10^6 to 6times10 ^6 radicals/cm^3, agree well with those derived from the other two methods, especially the latter. LPS-HPLC (OH) depends linearly on the combined effects of solar flux, ozone and water vapor, however, it has a nonlinear dependence on NO _{x} and hydrocarbons. These results are consistent with that predicted from photochemical models. Experimental results and model

  18. Hydroxyl-radical-induced oxidation of 5-methylcytosine in isolated and cellular DNA

    PubMed Central

    Madugundu, Guru S.; Cadet, Jean; Wagner, J. Richard

    2014-01-01

    The methylation and oxidative demethylation of cytosine in CpG dinucleotides plays a critical role in the regulation of genes during cell differentiation, embryogenesis and carcinogenesis. Despite its low abundance, 5-methylcytosine (5mC) is a hotspot for mutations in mammalian cells. Here, we measured five oxidation products of 5mC together with the analogous products of cytosine and thymine in DNA exposed to ionizing radiation in oxygenated aqueous solution. The products can be divided into those that arise from hydroxyl radical (•OH) addition at the 5,6-double bond of 5mC (glycol, hydantoin and imidazolidine products) and those that arise from H-atom abstraction from the methyl group of 5mC including 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC). Based on the analysis of these products, we show that the total damage at 5mC is about 2-fold greater than that at C in identical sequences. The formation of hydantoin products of 5mC is favored, compared to analogous reactions of thymine and cytosine, which favor the formation of glycol products. The distribution of oxidation products is sequence dependent in specific ODN duplexes. In the case of 5mC, the formation of 5hmC and 5fC represents about half of the total of •OH-induced oxidation products of 5mC. Several products of thymine, cytosine, 5mC, as well as 8-oxo-7,8-dihydroguanine (8oxoG), were also estimated in irradiated cells. PMID:24852253

  19. Photometric hydroxyl radical scavenging analysis of standard natural organic matter isolates.

    PubMed

    Donham, J E; Rosenfeldt, E J; Wigginton, K R

    2014-04-01

    Hydroxyl radical (˙OH) scavenging reaction rate constants of standard natural organic matter (NOM) isolates (k˙OH,NOM) were measured with a rapid background scavenging method, to expand the dataset of published k˙OH,NOM values. The proposed method relies on ˙OH generation with a simple UV/H₂O₂ AOP-based system. The associated decay of a ˙OH probe compound is monitored with a field-deployable spectrophotometer and k˙OH,NOM is determined through competition kinetics. The resulting k˙OH,NOM values for the six NOM standard isolates ranged from 1.02 (±0.10) × 10(8) MC(-1) s(-1) for Suwannee River Fulvic Acid I Standard to 2.03 (±0.12) × 10(8) MC(-1) s(-1) for Pony Lake Fulvic Acid Reference NOM, which is within the range reported with more elaborate and time-consuming k˙OH,NOM methods. A slight correlation between nitrogen content and scavenging rate constant was evident while no significant correlation between k˙OH,NOM and atomic composition, carbon structure, weight-average molecular weight, UV absorbance (SUVA₂₅₄), or fluorescence index (FI) was observed. Overall, the results demonstrate that k˙OH,NOM can be rapidly assessed in NOM isolate samples. The results suggest that this type of rapid field-deployable spectrophotometric method may minimize the need for expensive and time-consuming background scavenging methods, and for models that predict k˙OH,NOM based on other NOM characteristics.

  20. Hydroxyl-radical-induced oxidation of 5-methylcytosine in isolated and cellular DNA.

    PubMed

    Madugundu, Guru S; Cadet, Jean; Wagner, J Richard

    2014-06-01

    The methylation and oxidative demethylation of cytosine in CpG dinucleotides plays a critical role in the regulation of genes during cell differentiation, embryogenesis and carcinogenesis. Despite its low abundance, 5-methylcytosine (5mC) is a hotspot for mutations in mammalian cells. Here, we measured five oxidation products of 5mC together with the analogous products of cytosine and thymine in DNA exposed to ionizing radiation in oxygenated aqueous solution. The products can be divided into those that arise from hydroxyl radical (•OH) addition at the 5,6-double bond of 5mC (glycol, hydantoin and imidazolidine products) and those that arise from H-atom abstraction from the methyl group of 5mC including 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC). Based on the analysis of these products, we show that the total damage at 5mC is about 2-fold greater than that at C in identical sequences. The formation of hydantoin products of 5mC is favored, compared to analogous reactions of thymine and cytosine, which favor the formation of glycol products. The distribution of oxidation products is sequence dependent in specific ODN duplexes. In the case of 5mC, the formation of 5hmC and 5fC represents about half of the total of •OH-induced oxidation products of 5mC. Several products of thymine, cytosine, 5mC, as well as 8-oxo-7,8-dihydroguanine (8oxoG), were also estimated in irradiated cells.

  1. Phytic acid suppresses ischemia-induced hydroxyl radical generation in rat myocardium.

    PubMed

    Obata, Toshio; Nakashima, Michiko

    2016-03-01

    The present study examined whether ischemia-reperfusion-induced hydroxyl radical (·OH) generation was attenuated by myo-inositol hexaphosphoric acid (phytic acid). A flexibly mounted microdialysis technique was used to detect the generation of ·OH in in vivo rat hearts. To measure the level of ·OH, sodium salicylate in Ringer's solution (0.5mM or 0.5 nmol/μl/min) was infused directly through a microdialysis probe to detect the generation of ·OH as reflected by the nonenzymatic formation of 2,3-dihydroxybenzoic acid (2,3-DHBA). To confirm the generation of ·OH by Fenton-type reaction, iron(II) was infused through a microdialysis probe. A positive linear correlation between iron(II) and the formation of 2,3-DHBA (R(2)=0.983) was observed. However, the level of 2,3-DHBA in norepinephrine (100 μM) plus phytic acid (100 μM) treated group were significantly lower than those observed in norepinephrine-only-treated group (n=6, *p<0.05). To examine the effect of phytic acid on ischemia-reperfusion-induced ·OH generation, the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery (LAD). When the heart was reperfused, the normal elevation of 2,3-DHBA in the heart dialysate was not observed in animals pretreated with phytic acid. These results suggest that phytic acid is associated with antioxidant effect due to the suppression of iron-induced ·OH generation.

  2. Mechanisms of Sb(III) oxidation by pyrite-induced hydroxyl radicals and hydrogen peroxide.

    PubMed

    Kong, Linghao; Hu, Xingyun; He, Mengchang

    2015-03-17

    Antimony (Sb) is an element of growing interest, and its toxicity and mobility are strongly influenced by redox processes. Sb(III) oxidation mechanisms in pyrite suspensions were comprehensively investigated by kinetic measurements in oxic and anoxic conditions and simulated sunlight. Sb(III) was oxidized to Sb(V) in both solution and on pyrite surfaces in oxic conditions; the oxidation efficiency of Sb(III) was gradually enhanced with the increase of pH. The pyrite-induced hydroxyl radical (·OH) and hydrogen peroxide (H2O2) are the oxidants for Sb(III) oxidation. ·OH is the oxidant for Sb(III) oxidation in acidic solutions, and H2O2 becomes the main oxidant in neutral and alkaline solutions. ·OH and H2O2 can be generated by the reaction of previously existing FeIII(pyrite) and H2O on pyrite in anoxic conditions. The oxygen molecule is the crucial factor in continuously producing ·OH and H2O2 for Sb(III) oxidation. The efficiency of Sb(III) oxidation was enhanced in surface-oxidized pyrite (SOP) suspension, more ·OH formed through Fenton reaction in acidic solutions, but Fe(IV) and H2O2 were formed in neutral and alkaline solutions. Under the illumination of simulated sunlight, more ·OH and H2O2 were produced in the pyrite suspension, and the oxidation efficiency of Sb(III) was remarkably enhanced. In conclusion, Sb(III) can be oxidized to Sb(V) in the presence of pyrite, which will greatly influence the fate of Sb(III) in the environment.

  3. Ratiometric fluorescence probe for monitoring hydroxyl radical in live cells based on gold nanoclusters.

    PubMed

    Zhuang, Mei; Ding, Changqin; Zhu, Anwei; Tian, Yang

    2014-02-01

    Determination of hydroxyl radical ((•)OH) with high sensitivity and accuracy in live cells is a challenge for evaluating the role that (•)OH plays in the physiological and pathological processes. In this work, a ratiometric fluorescence biosensor for (•)OH was developed, in which gold nanocluster (AuNC) protected by bovine serum albumin was employed as a reference fluorophore and the organic molecule 2-[6-(4'-hydroxy)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid (HPF) acted as both the response signal and specific recognition element for (•)OH. In the absence of (•)OH, only one emission peak at 637 nm ascribed to AuNCs was observed, because HPF was almost nonfluorescent. However, fluorescence emission at 515 nm attributed to the HPF product after reaction with (•)OH--dianionic fluorescein--gradually increased with the continuous addition of (•)OH, while the emission at 637 nm stays constant, resulting in a ratiometric determination of (•)OH. The developed fluorescent sensor exhibited high selectivity for (•)OH over other reactive oxygen species (ROS), reactive nitrogen species (RNS), metal ions, and other biological species, as well as high accuracy and sensitivity with low detection limit to ∼0.68 μM, which fulfills the requirements for detection of (•)OH in a biological system. In addition, the AuNC-based inorganic-organic probe showed long-term stability against light illumination and pH, good cell permeability, and low cytotoxicity. As a result, the present ratiometric sensor was successfully used for bioimaging and monitoring of (•)OH changes in live cells upon oxidative stress.

  4. The antagonistic effect of hydroxyl radical on the development of a hypersensitive response in tobacco.

    PubMed

    Deng, Sheng; Yu, Mina; Wang, Ying; Jia, Qin; Lin, Ling; Dong, Hansong

    2010-12-01

    Reactive oxygen species (ROS) are important signalling molecules in living cells. It is believed that ROS molecules are the main triggers of the hypersensitive response (HR) in plants. In the present study of the effect of riboflavin, which is excited to generate ROS in light, on the development of the HR induced by the elicitin protein ParA1 in tobacco (Nicotiana tabacum), we found that the extent of the ParA1-induced HR was diminished by hydroxyl radical (OH•), a type of ROS. As compared with the zones treated with ParA1 only, the HR symptom in the zones that were infiltrated with ParA1 plus riboflavin was significantly diminished when the treated plants were placed in the light. However, this did not occur when the plants were maintained in the dark. Trypan blue staining and the ion leakage measurements confirmed HR suppression in the light. Further experiments proved that HR suppression is attributed to the involvement of the photoexcited riboflavin, and that the suppression can be eliminated with the addition of hydrogen peroxide scavengers or OH• scavengers. Fenton reagent treatment and EPR measurements demonstrated that it is OH• rather than hydrogen peroxide that contributes to HR suppression. Accompanying the endogenous OH• formation, suppression of the ParA1-induced HR occurred in the tobacco leaves that had been treated with high-level abscisic acid, and that suppression was also removed by OH• scavengers. These results offer evidence that OH•, an understudied and little appreciated ROS, participates in and modulates biologically relevant signalling in plant cells. PMID:21073656

  5. Improved Identification and Relative Quantification of Sites of Peptide and Protein Oxidation for Hydroxyl Radical Footprinting

    NASA Astrophysics Data System (ADS)

    Li, Xiaoyan; Li, Zixuan; Xie, Boer; Sharp, Joshua S.

    2013-11-01

    Protein oxidation is typically associated with oxidative stress and aging and affects protein function in normal and pathological processes. Additionally, deliberate oxidative labeling is used to probe protein structure and protein-ligand interactions in hydroxyl radical protein footprinting (HRPF). Oxidation often occurs at multiple sites, leading to mixtures of oxidation isomers that differ only by the site of modification. We utilized sets of synthetic, isomeric "oxidized" peptides to test and compare the ability of electron-transfer dissociation (ETD) and collision-induced dissociation (CID), as well as nano-ultra high performance liquid chromatography (nanoUPLC) separation, to quantitate oxidation isomers with one oxidation at multiple adjacent sites in mixtures of peptides. Tandem mass spectrometry by ETD generates fragment ion ratios that accurately report on relative oxidative modification extent on specific sites, regardless of the charge state of the precursor ion. Conversely, CID was found to generate quantitative MS/MS product ions only at the higher precursor charge state. Oxidized isomers having multiple sites of oxidation in each of two peptide sequences in HRPF product of protein Robo-1 Ig1-2, a protein involved in nervous system axon guidance, were also identified and the oxidation extent at each residue was quantified by ETD without prior liquid chromatography (LC) separation. ETD has proven to be a reliable technique for simultaneous identification and relative quantification of a variety of functionally different oxidation isomers, and is a valuable tool for the study of oxidative stress, as well as for improving spatial resolution for HRPF studies.

  6. Reaction kinetics and efficiencies for the hydroxyl and sulfate radical based oxidation of artificial sweeteners in water.

    PubMed

    Toth, Janie E; Rickman, Kimberly A; Venter, Andre R; Kiddle, James J; Mezyk, Stephen P

    2012-10-11

    Over the past several decades, the increased use of artificial sweeteners as dietary supplements has resulted in rising concentrations of these contaminants being detected in influent waters entering treatment facilities. As conventional treatments may not quantitatively remove these sweeteners, radical-based advanced oxidation and reduction (AO/RP) treatments could be a viable alternative. In this study, we have established the reaction kinetics for both hydroxyl ((•)OH) and sulfate (SO(4)(•-)) radical reaction with five common artificial sweeteners, as well as their associated reaction efficiencies. Rate constants for acesulfame K, aspartame, rebaudioside A, saccharin, and sucralose were <2 × 10(7), (2.28 ± 0.02) × 10(9), (2.1 ± 0.1) × 10(8), <2 × 10(7), and (1.7 ± 0.1) × 10(8) M(-1) s(-1) for the sulfate radical, and (3.80 ± 0.27) × 10(9), (6.06 ± 0.05) × 10(9), (9.97 ± 0.12) × 10(9), (1.85 ± 0.01) × 10(9), and (1.50 ± 0.01) × 10(9) M(-1) s(-1) for the hydroxyl radical, respectively. These latter values have to be combined with their corresponding reaction efficiencies of 67.9 ± 0.9, 52.2 ± 0.7, 43.0 ± 2.5, 52.7 ± 2.9, and 98.3 ± 3.5% to give effective rate constants for the hydroxyl radical reaction that can be used in the modeling of the AOP based removal of these contaminants.

  7. Hydroxyl radical formation during ozonation of multiwalled carbon nanotubes: performance optimization and demonstration of a reactive CNT filter.

    PubMed

    Oulton, Rebekah; Haase, Jason P; Kaalberg, Sara; Redmond, Connor T; Nalbandian, Michael J; Cwiertny, David M

    2015-03-17

    We explored factors influencing hydroxyl radical (•OH) formation during ozonation of multiwalled carbon nanotubes (MWCNTs) and assessed this system's viability as a next-generation advanced oxidation process (AOP). Using standard reactivity metrics for ozone-based AOPs (RCT values), MWCNTs promoted •OH formation during ozonation to levels exceeding ozone (both alone and with activated carbon) and equivalent to ozone with hydrogen peroxide. MWCNTs oxidized with nitric acid exhibited vastly greater rates of ozone consumption and •OH formation relative to as-received MWCNTs. While some of this enhancement reflects their greater suspension stability, a strong correlation between RCT values and surface oxygen concentrations from X-ray photoelectron spectroscopy suggests that surface sites generated during MWCNT oxidation promote •OH exposure. Removal of several ozone-recalcitrant species [para-chlorobenzoic acid (p-CBA), atrazine, DEET, and ibuprofen] was not significantly inhibited in the presence of radical scavengers (humic acid, carbonate), in complex aquatic matrices (Iowa River water) and after 12 h of continuous exposure of MWCNTs to concentrated ozone solutions. As a proof-of-concept, oxidized MWCNTs deposited on a ceramic membrane chemically oxidized p-CBA in a flow through system, with removal increasing with influent ozone concentration and mass of deposited MWCNTs (in mg/cm2). This hybrid membrane platform, which integrates adsorption, oxidation, and filtration via an immobilized MWCNT layer, may serve as the basis for future novel nanomaterial-enabled technologies, although long-term performance trials under representative treatment scenarios remain necessary. PMID:25730285

  8. Hydroxyl radical formation during ozonation of multiwalled carbon nanotubes: performance optimization and demonstration of a reactive CNT filter.

    PubMed

    Oulton, Rebekah; Haase, Jason P; Kaalberg, Sara; Redmond, Connor T; Nalbandian, Michael J; Cwiertny, David M

    2015-03-17

    We explored factors influencing hydroxyl radical (•OH) formation during ozonation of multiwalled carbon nanotubes (MWCNTs) and assessed this system's viability as a next-generation advanced oxidation process (AOP). Using standard reactivity metrics for ozone-based AOPs (RCT values), MWCNTs promoted •OH formation during ozonation to levels exceeding ozone (both alone and with activated carbon) and equivalent to ozone with hydrogen peroxide. MWCNTs oxidized with nitric acid exhibited vastly greater rates of ozone consumption and •OH formation relative to as-received MWCNTs. While some of this enhancement reflects their greater suspension stability, a strong correlation between RCT values and surface oxygen concentrations from X-ray photoelectron spectroscopy suggests that surface sites generated during MWCNT oxidation promote •OH exposure. Removal of several ozone-recalcitrant species [para-chlorobenzoic acid (p-CBA), atrazine, DEET, and ibuprofen] was not significantly inhibited in the presence of radical scavengers (humic acid, carbonate), in complex aquatic matrices (Iowa River water) and after 12 h of continuous exposure of MWCNTs to concentrated ozone solutions. As a proof-of-concept, oxidized MWCNTs deposited on a ceramic membrane chemically oxidized p-CBA in a flow through system, with removal increasing with influent ozone concentration and mass of deposited MWCNTs (in mg/cm2). This hybrid membrane platform, which integrates adsorption, oxidation, and filtration via an immobilized MWCNT layer, may serve as the basis for future novel nanomaterial-enabled technologies, although long-term performance trials under representative treatment scenarios remain necessary.

  9. Silver coordination polymers for prevention of implant infection: thiol interaction, impact on respiratory chain enzymes, and hydroxyl radical induction.

    PubMed

    Gordon, Oliver; Vig Slenters, Tünde; Brunetto, Priscilla S; Villaruz, Amer E; Sturdevant, Daniel E; Otto, Michael; Landmann, Regine; Fromm, Katharina M

    2010-10-01

    Prosthetic joint replacements are used increasingly to alleviate pain and improve mobility of the progressively older and more obese population. Implant infection occurs in about 5% of patients and entails significant morbidity and high social costs. It is most often caused by staphylococci, which are introduced perioperatively. They are a source of prolonged seeding and difficult to treat due to antibiotic resistance; therefore, infection prevention by prosthesis coating with nonantibiotic-type anti-infective substances is indicated. A renewed interest in topically used silver has fostered development of silver nanoparticles, which, however, present a potential health hazard. Here we present new silver coordination polymer networks with tailored physical and chemical properties as nanostructured coatings on metallic implant substrates. These compounds exhibited strong biofilm sugar-independent bactericidal activity on in vitro-grown biofilms and prevented murine Staphylococcus epidermidis implant infection in vivo with slow release of silver ions and limited transient leukocyte cytotoxicity. Furthermore, we describe the biochemical and molecular mechanisms of silver ion action by gene screening and by targeting cell metabolism of S. epidermidis at different levels. We demonstrate that silver ions inactivate enzymes by binding sulfhydryl (thiol) groups in amino acids and promote the release of iron with subsequent hydroxyl radical formation by an indirect mechanism likely mediated by reactive oxygen species. This is the first report investigating the global metabolic effects of silver in the context of a therapeutic application. We anticipate that the compounds presented here open a new treatment field with a high medical impact.

  10. Nitrate-induced photolysis in natural waters: Controls on concentrations of hydroxyl radical photo-intermediates by natural scavenging agents

    SciTech Connect

    Brezonik, P.L.; Fulkerson-Brekken, J.

    1998-10-01

    The importance of the principal natural scavenging agents for hydroxyl radicals ({sup {sm_bullet}}OH) was evaluated, and a general framework was developed to predict the significance of nitrate-induced, {sup {sm_bullet}}OH-mediated degradation of aquatic contaminants. Rate constants for *OH scavenging by dissolved organic matter (DOM) from five surface water sources were in a narrow range which is similar to previously reported values and suggests that the importance of DOM as a {sup {sm_bullet}}OH sink can be estimated simply from the dissolved organic carbon (DOC) concentration of a water. Scavenging of {sup {sm_bullet}}*OH by carbonate and bicarbonate is generally less important, but these ions can be the major cause of *OH scavenging in low DOC, high alkalinity waters. Use of the framework is illustrated by predicting levels of {sup {sm_bullet}}OH and half-lives of the corn herbicide acetochlor in waters ranging from pristine to highly influenced by agricultural activities.

  11. Protease-cleaved iron-transferrin augments oxidant-mediated endothelial cell injury via hydroxyl radical formation.

    PubMed Central

    Miller, R A; Britigan, B E

    1995-01-01

    Previous work has shown that the Pseudomonas-derived protease, pseudomonas elastase (PAE), can modify transferrin to form iron complexes capable of catalyzing the formation of hydroxyl radical (.OH) from neutrophil (PMN)-derived superoxide (.O2-) and hydrogen peroxide (H2O2). As the lung is a major site of Pseudomonas infection, the ability of these iron chelates to augment oxidant-mediated pulmonary artery endothelial cell injury via release of 51Cr from prelabeled cells was examined. Diferrictransferrin previously cleaved with PAE significantly enhanced porcine pulmonary artery endothelial cell monolayer injury from 2.3-6.3 to 15.8-17.0% of maximum, resulting from exposure to H2O2, products of the xanthine/xanthine oxidase reaction, or PMA-stimulated PMNs. Iron associated with transferrin appeared to be responsible for cell injury. Spin trapping and the formation of thiobarbituric acid-reactive 2-deoxyribose oxidation products demonstrated the production of .OH in this system. The addition of catalase, dimethyl thiourea, and the hydrophobic spin trap, alpha-phenyl-n-terbutyl-nitrone, offered significant protection from injury (27.8-58.2%). Since sites of Pseudomonas infection contain other proteases, the ability of porcine pancreatic elastase and trypsin to substitute for PAE was examined. Results were similar to those observed with PAE. We conclude .OH formation resulting from protease alteration of transferrin may serve as a mechanism of tissue injury at sites of bacterial infection and other processes characterized by increased proteolytic activity. Images PMID:7769095

  12. Enhanced hydroxyl radical generation in the combined ozonation and electrolysis process using carbon nanotubes containing gas diffusion cathode.

    PubMed

    Wu, Donghai; Lu, Guanghua; Zhang, Ran; Lin, Qiuhong; Yan, Zhenhua; Liu, Jianchao; Li, Yi

    2015-10-01

    Combination of ozone together with electrolysis (ozone-electrolysis) is a promising wastewater treatment technology. This work investigated the potential use of carbon nanotube (CNT)-based gas diffusion cathode (GDC) for ozone-electrolysis process employing hydroxyl radicals (·OH) production as an indicator. Compared with conventional active carbon (AC)-polytetrafluoroethylene (PTFE) and carbon black (CB)-PTFE cathodes, the production of ·OH in the coupled process was improved using CNTs-PTFE GDC. Appropriate addition of acetylene black (AB) and pore-forming agent Na2SO4 could enhance the efficiency of CNTs-PTFE GDC. The optimum GDC composition was obtained by response surface methodology (RSM) analysis and was determined as CNTs 31.2 wt%, PTFE 60.6 wt%, AB 3.5 wt%, and Na2SO4 4.7 wt%. Moreover, the optimized CNT-based GDC exhibited much more effective than traditional Ti and graphite cathodes in Acid Orange 7 (AO7) mineralization and possessed the desirable stability without performance decay after ten times reaction. The comparison tests revealed that peroxone reaction was the main pathway of ·OH production in the present system, and cathodic reduction of ozone could significantly promote ·OH generation. These results suggested that application of CNT-based GDC offers considerable advantages in ozone-electrolysis of organic wastewater. PMID:26036588

  13. Development of a model for predicting hydroxyl radical reaction rate constants of organic chemicals at different temperatures.

    PubMed

    Li, Chao; Yang, Xianhai; Li, Xuehua; Chen, Jingwen; Qiao, Xianliang

    2014-01-01

    The reaction rate constants of hydroxyl radicals with organic chemicals (kOH) are of great importance for assessing the persistence and fate of organic pollutants in the atmosphere. However, experimental determination of kOH seems fairly unrealistic, due to the soaring number of the emerging chemicals additional to the large number of existing chemicals. Quantitative structure-activity relationship (QSAR) models are excellent choices for evaluating and predicting kOH values. In this study, a QSAR model that can predict kOH at different temperatures was developed by employing quantum chemical descriptors and DRAGON descriptors. The adjusted determination coefficient Radj(2) of the model is 0.873, and the external validation coefficient Qext(2) is 0.835, implying that the model has satisfactory robustness and good predictability. Additionally, a QSAR model was also built for kOH prediction at room-temperature (298 K). The development of the two models followed the guidelines for development and validation of QSAR models proposed by the Organization for Economic Co-operation and Development (OECD). The applicability domains of the current models were extended to several classes of compounds including long-chain alkenes (C8-C13), organophosphates, dimethylnaphthalenes, organic selenium and organic mercury compounds that have not been covered in the previous studies.

  14. Laboratory investigations of the hydroxyl radical-initiated oxidation of atmospheric volatile organic compounds

    NASA Astrophysics Data System (ADS)

    Vimal, Deepali

    The hydroxyl radical (OH) is one of the most important oxidants in the atmosphere, because reaction with OH is the dominant atmospheric fate of most trace atmospheric species. OH is intimately involved in a complex non-linear photochemical pathway involving anthropogenic and biogenic emissions of volatile organic compounds (VOCs) and nitrogen oxides that are emitted from vehicular exhaust and industrial emissions. This chemistry generates secondary tropospheric ozone which is an important greenhouse gas as well as a component of photochemical smog. In addition, this chemistry leads to the formation of secondary organic aerosols in the atmosphere which have implications for public health and climate change. The focus of this dissertation is to improve our understanding of this complex chemistry by investigating the rate-limiting elementary reactions which are part of the OH-initiated oxidation of important VOCs. Experimental (discharge flow technique coupled with resonance fluorescence and laser induced fluorescence) and theoretical studies (Density Functional Theory computations) of the kinetics of three atmospheric VOCs, acetic acid, 1,3-butadiene and methyl ethyl ketone are discussed. The acetic acid and OH reaction has been thought to undergo a hydrogen-bonded complex mediated pathway instead of a direct one leading to faster rate constants at lower temperature. Our results for the experimental investigation between 263-373 K and pressures of 2-5 Torr for the gas phase reaction of acetic acid with OH confirm the complex mediated reaction mechanism and indicate that acetic acid can play an important role especially in the oxidative chemistry of upper troposphere. The 1,3-butadiene and OH reaction is thought to undergo electrophilicaddition by OH which could display a complex pressure dependence similar to isoprene and 232-butenol as noted earlier in this laboratory. However, our results for the kinetics of the reaction between 273-423 K and a pressure range of 1

  15. The effectiveness of clove extracts in the inhibition of hydroxyl radical oxidation-induced structural and rheological changes in porcine myofibrillar protein.

    PubMed

    Chen, Hongsheng; Diao, Jingjing; Li, Yuanyuan; Chen, Qian; Kong, Baohua

    2016-01-01

    Oxidation is a major cause of protein quality deterioration during the storage and processing of food. This study investigated the effects of clove extract (CE) on structural and rheological changes in porcine longissimus myofibrillar proteins (MP) and the effects of oxidizing radicals produced by a Fenton reaction system (FRS). Increased oxidation time was accompanied by increased carbonyl content, reduced Ca-ATPase activity, decreased enthalpy of denaturation, decreased thermal transition temperatures (P<0.05), and increased protein susceptibility to thermal aggregation. The addition of CE significantly inhibited carbonyl formation (P<0.05), enhanced solubility and thermal stability, and improved the gel formation ability (storage modulus, loss modulus) of MP. The protective effect of CE on protein denaturation was demonstrated by its efficacy in maintaining Ca-ATPase activity and decreasing the degree of protein aggregation. Overall, the hydroxyl radical-induced loss of the structural and functional properties of MP was significantly reduced by the presence of CE.

  16. The effectiveness of clove extracts in the inhibition of hydroxyl radical oxidation-induced structural and rheological changes in porcine myofibrillar protein.

    PubMed

    Chen, Hongsheng; Diao, Jingjing; Li, Yuanyuan; Chen, Qian; Kong, Baohua

    2016-01-01

    Oxidation is a major cause of protein quality deterioration during the storage and processing of food. This study investigated the effects of clove extract (CE) on structural and rheological changes in porcine longissimus myofibrillar proteins (MP) and the effects of oxidizing radicals produced by a Fenton reaction system (FRS). Increased oxidation time was accompanied by increased carbonyl content, reduced Ca-ATPase activity, decreased enthalpy of denaturation, decreased thermal transition temperatures (P<0.05), and increased protein susceptibility to thermal aggregation. The addition of CE significantly inhibited carbonyl formation (P<0.05), enhanced solubility and thermal stability, and improved the gel formation ability (storage modulus, loss modulus) of MP. The protective effect of CE on protein denaturation was demonstrated by its efficacy in maintaining Ca-ATPase activity and decreasing the degree of protein aggregation. Overall, the hydroxyl radical-induced loss of the structural and functional properties of MP was significantly reduced by the presence of CE. PMID:26340742

  17. Secondary Organic Aerosol (SOA) formation from hydroxyl radical oxidation and ozonolysis of monoterpenes

    NASA Astrophysics Data System (ADS)

    Zhao, D. F.; Kaminski, M.; Schlag, P.; Fuchs, H.; Acir, I.-H.; Bohn, B.; Häseler, R.; Kiendler-Scharr, A.; Rohrer, F.; Tillmann, R.; Wang, M. J.; Wegener, R.; Wildt, J.; Wahner, A.; Mentel, T. F.

    2014-05-01

    Oxidation by hydroxyl radical (OH) and ozonolysis are the two major pathways of daytime biogenic volatile organic compounds (VOCs) oxidation and secondary organic aerosol (SOA) formation. In this study, we investigated the particle formation of several common monoterpenes (α-pinene, β-pinene, and limonene) by OH dominated oxidation, which has seldom been investigated. OH oxidation experiments were carried out in the SAPHIR chamber in Jülich, Germany, at low NOx (0.01-1 ppbV) and low ozone (O3) concentration. OH concentration and OH reactivity were measured directly so that the overall reaction rates of organic compounds with OH were quantified. Multi-generation reaction process, particle growth, new particle formation, particle yield, and chemical composition were analyzed and compared with that of monoterpene ozonolysis. Multi-generation products were found to be important in OH dominated SOA formation. The relative role of functionalization and fragmentation in the reaction process of OH oxidation was analyzed by examining the particle mass and the particle size as a function of OH dose. We developed a novel method which quantitatively links particle growth to the reaction of OH with organics in a reaction system. This method was also used to analyze the evolution of functionalization and fragmentation of organics in the particle formation by OH oxidation. It shows that functionalization of organics was dominant in the beginning of the reaction (within two lifetimes of the monoterpene) and fragmentation started to be dominant after that. We compared particle formation from OH oxidation with that from pure ozonolysis. In individual experiments, growth rates of the particle size did not necessarily correlate with the reaction rate of monoterpene with OH and O3. Comparing the size growth rates at the similar reaction rates of monoterpene with OH or O3 indicates that generally, OH oxidation and ozonolysis had similar efficiency in particle growth. The SOA yield of

  18. Secondary organic aerosol formation from hydroxyl radical oxidation and ozonolysis of monoterpenes

    NASA Astrophysics Data System (ADS)

    Zhao, D. F.; Kaminski, M.; Schlag, P.; Fuchs, H.; Acir, I.-H.; Bohn, B.; Häseler, R.; Kiendler-Scharr, A.; Rohrer, F.; Tillmann, R.; Wang, M. J.; Wegener, R.; Wildt, J.; Wahner, A.; Mentel, Th. F.

    2015-01-01

    Oxidation by hydroxyl radical (OH) and ozonolysis are the two major pathways of daytime biogenic volatile organic compound (BVOC) oxidation and secondary organic aerosol (SOA) formation. In this study, we investigated the particle formation of several common monoterpenes (α-pinene, β-pinene and limonene) by OH-dominated oxidation, which has seldom been investigated. OH oxidation experiments were carried out in the SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction) chamber in Jülich, Germany, at low NOx (0.01 ~ 1 ppbV) and low ozone (O3) concentration (< 20 ppbV). OH concentration and total OH reactivity (kOH) were measured directly, and through this the overall reaction rate of total organics with OH in each reaction system was quantified. Multi-generation reaction process, particle growth, new particle formation (NPF), particle yield and chemical composition were analyzed and compared with that of monoterpene ozonolysis. Multi-generation products were found to be important in OH-dominated SOA formation. The relative role of functionalization and fragmentation in the reaction process of OH oxidation was analyzed by examining the particle mass and the particle size as a function of OH dose. We developed a novel method which quantitatively links particle growth to the reaction rate of OH with total organics in a reaction system. This method was also used to analyze the evolution of functionalization and fragmentation of organics in the particle formation by OH oxidation. It shows that functionalization of organics was dominant in the beginning of the reaction (within two lifetimes of the monoterpene) and fragmentation started to play an important role after that. We compared particle formation from OH oxidation with that from pure ozonolysis. In individual experiments, growth rates of the particle size did not necessarily correlate with the reaction rate of monoterpene with OH and O3. Comparing the size growth rates at the similar reaction rates

  19. Secondary Organic Aerosol (SOA) Formation from Hydroxyl Radical Oxidation and Ozonolysis of Monoterpenes

    NASA Astrophysics Data System (ADS)

    Zhao, Defeng; Kaminski, Martin; Schlag, Patrick; Fuchs, Hendrik; Acir, Ismail-Hakki; Bohn, Birger; Haeseler, Rolf; Kiendler-Scharr, Astrid; Rohrer, Franz; Tillmann, Ralf; Wang, Mingjin; Wegner, Robert; Wahner, Andreas; Mentel, Thomas

    2014-05-01

    Hydroxyl radical (OH) oxidation and ozonolysis are the two major pathways of daytime biogenic volatile organic compounds (VOCs) oxidation and secondary organic aerosol (SOA) formation. The pure OH oxidation of monoterpenes, an important biogenic VOC class, has seldom been investigated. In order to elucidate the importance of the reaction pathyways of the OH oxidation and ozonolysis and their roles in particle formation and growth, we investigated the particle formation of several common monoterpenes (alpha-pinene, beta-pinene, and limonene) in the large atmosphere simulation chamber SAPHIR in Juelich, Germany. The experiments were conducted for both OH dominant and pure ozonolysis case (in the presence of CO as OH scavenger) at ambient relevant conditions (low OA, low VOC and low NOx concentration). OH and ozone (O3) concentrations were measured so that the oxidation rates of OH and O3 with precursors were quantified. The particle formation and growth, aerosol yield, multi-generation reaction process and aerosol composition were analyzed. Pure ozonolysis generated a large amount of particles indicating ozonolysis plays an important role in particle formation as well as OH oxidation. In individual experiments, particle growth rates did not necessarily correlate with OH or O3 oxidation rates. However, comparing the growth rates at similar OH or O3 oxidation rates shows that generally, OH oxidation and ozonolysis have similar efficiency in particle growth. Multi-generation products are shown to be important in the OH oxidation experiment based on aerosol yield "growth curve" (Ng et al., 2006). The reaction process of OH oxidation experiments was analyzed as a function of OH dose to elucidate the role of functionalization and fragmentation. A novel analysis was developed to link the particle formation with the reaction with OH, which was also used to examine the role of functionalization and fragmentation in the particle formation by OH oxidation. These analyses show

  20. Quantification of Hydroxyl Radical reactivity in the urban environment using the Comparative Reactivity Method (CRM)

    NASA Astrophysics Data System (ADS)

    Panchal, Rikesh; Monks, Paul

    2015-04-01

    Hydroxyl (OH) radicals play an important role in 'cleansing' the atmosphere of many pollutants such as, NOx, CH4 and various VOCs, through oxidation. To measure the reactivity of OH, both the sinks and sources of OH need to be quantified, and currently the overall sinks of OH seem not to be fully constrained. In order to measure the total rate loss of OH in an ambient air sample, all OH reactive species must be considered and their concentrations and reaction rate coefficients with OH known. Using the method pioneered by Sinha and Williams at the Max Plank Institute Mainz, the Comparative Reactivity Method (CRM) which directly quantifies total OH reactivity in ambient air without the need to consider the concentrations of individual species within the sample that can react with OH, has been developed and applied in a urban setting. The CRM measures the concentration of a reactive species that is present only in low concentrations in ambient air, in this case pyrrole, flowing through a reaction vessel and detected using Proton Transfer Reaction - Mass Spectrometry (PTR-MS). The poster will show a newly developed and tested PTR-TOF-MS system for CRM. The correction regime will be detailed to account for the influence of the varying humidity between ambient air and clean air on the pyrrole signal. Further, examination of the sensitivity dependence of the PTR-MS as a function of relative humidity and H3O+(H2O) (m/z=37) cluster ion allows the correction for the humidity variation, between the clean humid air entering the reaction vessel and ambient air will be shown. NO, present within ambient air, is also a potential interference and can cause recycling of OH, resulting in an overestimation of OH reactivity. Tests have been conducted on the effects of varying NO concentrations on OH reactivity and a correction factor determined for application to data when sampling ambient air. Finally, field tests in the urban environment at the University of Leicester will be shown

  1. Mechanisms of hydroxyl radical production from abiotic oxidation of pyrite under acidic conditions

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Yuan, Songhu; Liao, Peng

    2016-01-01

    Hydroxyl radicals (radOH) produced from pyrite oxidation by O2 have been recognized, but mechanisms regarding the production under anoxic and oxic conditions are not well understood. In this study, the mechanisms of radOH production from pyrite oxidation under anoxic and oxic conditions were explored using benzoic acid (BA) as an radOH probe. Batch experiments were conducted at pH 2.6 to explore radOH production under anoxic and oxic conditions. The cumulative radOH concentrations produced under anoxic and oxic conditions increased linearly to 7.5 and 52.2 μM, respectively within 10 h at 10 g/L pyrite. Under anoxic conditions, radOH was produced from the oxidation of H2O on the sulfur-deficient sites on pyrite surface, showing an increased production with the increase of pyrite surface exposure due to oxidation. Under oxic conditions, the formation of radOH proceeds predominantly via the two-electron reduction of O2 on pyrite surface along with a minor contribution from the oxidation of H2O on surface sulfur-defects and the reactions of Fe2+/sulfur intermediates with O2. For both O2 reduction and H2O oxidation on the surface sulfur-defects, H2O2 was the predominant intermediate, which subsequently transformed to radOH through Fenton mechanism. The radOH produced had a significant impact on the transformation of contaminants in the environment. Anoxic pyrite suspensions oxidized 13.9% As(III) (C0 = 6.67 μM) and 17.6% sulfanilamide (C0 = 2.91 μM) within 10 h at pH 2.6 and 10 g/L pyrite, while oxic pyrite suspensions improved the oxidation percentages to 55.4% for As(III) and 51.9% for sulfanilamide. The ratios of anoxic to oxic oxidation are consistent with the relative contribution of surface sulfur-defects to radOH production. However, Fe2+ produced from pyrite oxidation competed with the contaminants for radOH, which is of particular significance with the increase of time in a static environment. We conclude that radOH can be produced from abiotic oxidation of

  2. Formation of hydroxyl radical from San Joaquin Valley particles extracted in a cell-free solution

    NASA Astrophysics Data System (ADS)

    Shen, H.; Anastasio, C.

    2011-06-01

    Previous studies have suggested that the adverse health effects from ambient particulate matter (PM) are linked to the formation of reactive oxygen species (ROS) by PM. While hydroxyl radical (•OH) is the most reactive of the ROS species, there are few quantitative studies of •OH generation from PM. Here we report on •OH formation from PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California. We quantified •OH in PM extracts using a cell-free, phosphate-buffered saline (PBS) solution with or without 50 μM ascorbate (Asc). The results show that generally the urban Fresno PM generates much more •OH than the rural Westside PM. The presence of Asc at a physiologically relevant concentration in the extraction solution greatly enhances •OH formation from all the samples. Fine PM (PM2.5) generally makes more •OH than the corresponding coarse PM (PMcf, i.e., 2.5 to 10 μm) normalized by air volume collected, while the coarse PM typically generates more •OH normalized by PM mass. •OH production by SJV PM is reduced on average by (97 ± 6) % when the transition metal chelator desferoxamine (DSF) is added to the extraction solution, indicating a dominant role of transition metals. By measuring calibration curves of •OH generation from copper and iron, and quantifying copper and iron concentrations in our particle extracts, we find that PBS-soluble copper is primarily responsible for •OH production by the SJV PM, while iron often makes a significant contribution. Extrapolating our results to expected burdens of PM-derived •OH in human lung lining fluid suggests that typical daily PM exposures in the San Joaquin Valley are unlikely to result in a high amount of pulmonary •OH, although high PM events could produce much higher levels of •OH, which might lead to cytotoxicity.

  3. Reaction between CH3O2 and BrO radicals: a new source of upper troposphere lower stratosphere hydroxyl radicals.

    PubMed

    Shallcross, Dudley E; Leather, Kimberley E; Bacak, Asan; Xiao, Ping; Lee, Edmond P F; Ng, Maggie; Mok, Daniel K W; Dyke, John M; Hossaini, Ryan; Chipperfield, Martyn P; Khan, M Anwar H; Percival, Carl J

    2015-05-14

    Over the last two decades it has emerged that measured hydroxyl radical levels in the upper troposphere are often underestimated by models, leading to the assertion that there are missing sources. Here we report laboratory studies of the kinetics and products of the reaction between CH3O2 and BrO radicals that shows that this could be an important new source of hydroxyl radicals:BrO + CH3O2 → products (1). The temperature dependent value in Arrhenius form of k(T) is k1 = (2.42–0.72+1.02) × 10–14 exp[(1617 ± 94)/T] cm3 molecule–1 s–1. In addition, CH2OO and HOBr are believed to be the major products. Global model results suggest that the decomposition of H2COO to form OH could lead to an enhancement in OH of up to 20% in mid-latitudes in the upper troposphere and in the lower stratosphere enhancements in OH of 2–9% are inferred from model integrations. In addition, reaction 1 aids conversion of BrO to HOBr and slows polar ozone loss in the lower stratosphere. PMID:25768043

  4. Bactericidal Effect of Photolysis of H2O2 in Combination with Sonolysis of Water via Hydroxyl Radical Generation.

    PubMed

    Sheng, Hong; Nakamura, Keisuke; Kanno, Taro; Sasaki, Keiichi; Niwano, Yoshimi

    2015-01-01

    The bactericidal effect of hydroxyl radical (·OH) generated by combination of photolysis of hydrogen peroxide (H2O2) and sonolysis of water was examined under the condition in which the yield of ·OH increased additively when H2O2 aqueous solution was concomitantly irradiated with laser and ultrasound. The suspension of Staphylococcus aureus mixed with the different concentrations of H2O2 was irradiated simultaneously with a laser light (wavelength: 405 nm, irradiance: 46 and 91 mW/cm2) and ultrasound (power: 30 w, frequency: 1.65 MHz) at 20 ± 1°C of the water bulk temperature for 2 min. The combination of laser and ultrasound irradiation significantly reduced the viable bacterial count in comparison with the laser irradiation of H2O2 alone. By contrast, the ultrasound irradiation alone exerted almost no bactericidal effect. These results suggested that the combination effect of photolysis of H2O2 and sonolysis of water on bactericidal activity was synergistic. A multi-way analysis of variance also revealed that the interaction of H2O2 concentration, laser power and ultrasound irradiation significantly affected the bactericidal activity. Since the result of oxidative DNA damage evaluation demonstrated that the combination of laser and ultrasound irradiation significantly induced oxidative damage of bacterial DNA in comparison with the laser irradiation of H2O2 alone, it was suggested that the combination effect of photolysis of H2O2 and sonolysis of water on bactericidal activity would be exerted via oxidative damage of cellular components such as DNA.

  5. Bactericidal Effect of Photolysis of H2O2 in Combination with Sonolysis of Water via Hydroxyl Radical Generation

    PubMed Central

    Sheng, Hong; Nakamura, Keisuke; Kanno, Taro; Sasaki, Keiichi; Niwano, Yoshimi

    2015-01-01

    The bactericidal effect of hydroxyl radical (·OH) generated by combination of photolysis of hydrogen peroxide (H2O2) and sonolysis of water was examined under the condition in which the yield of ·OH increased additively when H2O2 aqueous solution was concomitantly irradiated with laser and ultrasound. The suspension of Staphylococcus aureus mixed with the different concentrations of H2O2 was irradiated simultaneously with a laser light (wavelength: 405 nm, irradiance: 46 and 91 mW/cm2) and ultrasound (power: 30 w, frequency: 1.65 MHz) at 20 ± 1°C of the water bulk temperature for 2 min. The combination of laser and ultrasound irradiation significantly reduced the viable bacterial count in comparison with the laser irradiation of H2O2 alone. By contrast, the ultrasound irradiation alone exerted almost no bactericidal effect. These results suggested that the combination effect of photolysis of H2O2 and sonolysis of water on bactericidal activity was synergistic. A multi-way analysis of variance also revealed that the interaction of H2O2 concentration, laser power and ultrasound irradiation significantly affected the bactericidal activity. Since the result of oxidative DNA damage evaluation demonstrated that the combination of laser and ultrasound irradiation significantly induced oxidative damage of bacterial DNA in comparison with the laser irradiation of H2O2 alone, it was suggested that the combination effect of photolysis of H2O2 and sonolysis of water on bactericidal activity would be exerted via oxidative damage of cellular components such as DNA. PMID:26148024

  6. Theoretical study on the gas phase reaction of acrylonitrile with a hydroxyl radical.

    PubMed

    Sun, Jingyu; Wang, Rongshun; Wang, Baoshan

    2011-10-01

    The mechanism and kinetics of the reaction of acrylonitrile (CH(2)=CHCN) with hydroxyl (OH) has been investigated theoretically. This reaction is revealed to be one of the most significant loss processes of acrylonitrile. BHandHLYP and M05-2X methods are employed to obtain initial geometries. The reaction mechanism conforms that OH addition to C[double bond, length as m-dash]C double bond or C atom of -CN group to form the chemically activated adducts, 1-IM1(HOCH(2)=CHCN), 2-IM1(CH(2)=HOCHCN), and 3-IM1(CH(2)=CHCOHN) via low barriers, and direct hydrogen abstraction paths may also occur. Temperature- and pressure-dependent rate constants have been evaluated using the Rice-Ramsperger-Kassel-Marcus theory. The calculated rate constants are in good agreement with the experimental data. At atmospheric pressure with N(2) as bath gas, 1-IM1(OHCH(2)=CHCN) formed by collisional stabilization is the major product in the temperature range of 200-1200 K. The production of CH(2)CCN and CHCHCN via hydrogen abstractions becomes dominant at high temperatures (1200-3000 K).

  7. Oxidation of alpha-tocopherol in micelles and liposomes by the hydroxyl, perhydroxyl, and superoxide free radicals

    SciTech Connect

    Fukuzawa, K.; Gebicki, J.M.

    1983-10-01

    Rates of oxidation of alpha-tocopherol by the hydroxyl- and superoxide free radicals were measured. The radicals were produced in known yields by radiolysis of aqueous solutions with gamma rays. Two main systems were used to dissolve the tocopherol; micelles, made up from charged and uncharged amphiphiles, and membranes made from dimyristyl phosphatidylcholine which could be charged by addition of stearyl amine or dicetyl phosphate. The HO. radicals were efficient oxidants of alpha-tocopherol in all systems, with up to 83% of radicals generated in micelle and 32% in membrane suspensions initiating the oxidation. The HO/sub 2/ radical was an even more effective oxidant, but when most of it was in the O/sub 2/ form at neutral or alkaline pH, the oxidation rates became low. Tocopherol held in positively charged micelles or membranes was oxidized at a higher rate by the O/sub 2/ than in uncharged or negative particles. Possible biological significance of these results is discussed.

  8. Analytical chemical kinetic investigation of the effects of oxygen, hydrogen, and hydroxyl radicals on hydrogen-air combustion

    NASA Technical Reports Server (NTRS)

    Carson, G. T., Jr.

    1974-01-01

    Quantitative values were computed which show the effects of the presence of small amounts of oxygen, hydrogen, and hydroxyl radicals on the finite-rate chemical kinetics of premixed hydrogen-air mixtures undergoing isobaric autoignition and combustion. The free radicals were considered to be initially present in hydrogen-air mixtures at equivalence ratios of 0.2, 0.6, 1.0, and 1.2. Initial mixture temperatures were 1100 K, 1200 K, and 1500 K, and pressures were 0.5, 1.0, 2.0, and 4.0 atm. Of the radicals investigated, atomic oxygen was found to be the most effective for reducing induction time, defined as the time to 5 percent of the total combustion temperature rise. The reaction time, the time between 5 percent and 95 percent of the temperature rise, is not decreased by the presence of free radicals in the initial hydrogen-air mixture. Fuel additives which yield free radicals might be used to effect a compact supersonic combustor design for efficient operation in an otherwise reaction-limited combustion regime.

  9. Predicting tropospheric ozone and hydroxyl radical in a global, three-dimensional, chemistry, transport, and deposition model

    SciTech Connect

    Atherton, C.S.

    1995-01-05

    Two of the most important chemically reactive tropospheric gases are ozone (O{sub 3}) and the hydroxyl radical (OH). Although ozone in the stratosphere is a necessary protector against the sun`s radiation, tropospheric ozone is actually a pollutant which damages materials and vegetation, acts as a respiratory irritant, and is a greenhouse gas. One of the two main sources of ozone in the troposphere is photochemical production. The photochemistry is initiated when hydrocarbons and carbon monoxide (CO) react with nitrogen oxides (NO{sub x} = NO + NO{sub 2}) in the presence of sunlight. Reaction with the hydroxyl radical, OH, is the main sink for many tropospheric gases. The hydroxyl radical is highly reactive and has a lifetime on the order of seconds. Its formation is initiated by the photolysis of tropospheric ozone. Tropospheric chemistry involves a complex, non-linear set of chemical reactions between atmospheric species that vary substantially in time and space. To model these and other species on a global scale requires the use of a global, three-dimensional chemistry, transport, and deposition (CTD) model. In this work, I developed two such three dimensional CTD models. The first model incorporated the chemistry necessary to model tropospheric ozone production from the reactions of nitrogen oxides with carbon monoxide (CO) and methane (CH{sub 4}). The second also included longer-lived alkane species and the biogenic hydrocarbon isoprene, which is emitted by growing plants and trees. The models` ability to predict a number of key variables (including the concentration of O{sub 3}, OH, and other species) were evaluated. Then, several scenarios were simulated to understand the change in the chemistry of the troposphere since preindustrial times and the role of anthropogenic NO{sub x} on present day conditions.

  10. Determination of Arrhenius and Thermodynamic Parameters for the Aqueous Reaction of the Hydroxyl Radical with Lactic Acid

    SciTech Connect

    Leigh R. Martin; Stephen P. Mezyk; Bruce J. Mincher

    2009-01-01

    Lactic acid is a major component of the TALSPEAK process planned for use in the separation of trivalent lanthanide and actinide elements. This acid acts both as a buffer, and also to protect the actinide complexant from radiolytic damage. However, there is little kinetic information on the reaction of water radiolysis species with lactic acid, particularly under the anticipated process conditions of aerated aqueous solution at pH~3, where oxidizing reactions are expected to dominate. Here we have determined temperature-dependent reaction rate constants for the reactions of the hydroxyl radical with lactic acid and the lactate ion. For lactic acid this rate constant is given by the equation: ln k1 = (23.85 ± 0.19) – (1120 ± 54) / T, corresponding to an activation energy of 9.31 ± 0.45 kJ mol-1 and a room temperature reaction rate constant of (5.24 ± 0.09) x 108 M-1 s-1 (24.0oC). For the lactate ion, the temperature-dependent rate constant is given by: ln k2 = (24.83 ± 0.14) – (1295 ± 42) / T, for an activation energy of 10.76 ± 0.35 kJ mol-1 and a room temperature value of (7.77 ± 0.11) x 108 M-1 s-1 (22.2oC). These kinetic data have been combined with autotitration measurements to determine the temperature-dependent behavior of the lactic acid pKa value, allowing thermodynamic parameters for the acid dissociation to be calculated as ?Hº = -10.75 ± 1.77 kJ mol-1, ?Sº = -103.9 ± 6.0 J K-1 mol-1 and ?Gº = 20.24 ± 2.52 kJ mol-1 at low ionic strength.

  11. Evidence for the involvement of cell wall peroxidase in the generation of hydroxyl radicals mediating extension growth.

    PubMed

    Liszkay, Anja; Kenk, Barbara; Schopfer, Peter

    2003-08-01

    Hydroxyl radicals (*OH), produced in the cell wall, are capable of cleaving wall polymers and can thus mediate cell wall loosening and extension growth. It has recently been proposed that the biochemical mechanism responsible for *OH generation in the cell walls of growing plant organs represents an enzymatic reaction catalyzed by apoplastic peroxidase (POD). This hypothesis was investigated by supplying cell walls of maize ( Zea mays L.) coleoptiles and sunflower ( Helianthus annuus L.) hypocotyls with external NADH, an artificial substrate known to cause *OH generation by POD in vitro. The effects of NADH on wall loosening, growth, and *OH production in vivo were determined. NADH mediates cell wall extension in vitro and in vivo in an H2O2-dependent reaction that shows the characteristic features of POD. NADH-mediated production of *OH in vivo was demonstrated in maize coleoptiles using electron paramagnetic resonance spectroscopy in combination with a specific spin-trapping reaction. Kinetic properties and inhibitor/activator sensitivities of the *OH-producing reaction in the cell walls of coleoptiles resembled the properties of horseradish POD. Apoplastic consumption of external NADH by living coleoptiles can be traced back to the superimposed action of two enzymatic reactions, a KCN-sensitive reaction mediated by POD operating in the *OH-forming mode, and a KCN-insensitive reaction with the kinetic properties of a superoxide-producing plasma-membrane NADH oxidase the activity of which can be promoted by auxin. Under natural conditions, i.e. in the absence of external NADH, this enzyme may provide superoxide (O2*-) (and H2O2 utilized by POD for) *OH production in the cell wall.

  12. Cisplatin enhances the formation of DNA single- and double-strand breaks by hydrated electrons and hydroxyl radicals.

    PubMed

    Rezaee, Mohammad; Sanche, Léon; Hunting, Darel J

    2013-03-01

    The synergistic interaction of cisplatin with ionizing radiation is the clinical rationale for the treatment of several cancers including head and neck, cervical and lung cancer. The underlying molecular mechanism of the synergy has not yet been identified, although both DNA damage and repair processes are likely involved. Here, we investigate the indirect effect of γ rays on strand break formation in a supercoiled plasmid DNA (pGEM-3Zf-) covalently modified by cisplatin. The yields of single- and double-strand breaks were determined by irradiation of DNA and cisplatin/DNA samples with (60)Co γ rays under four different scavenging conditions to examine the involvement of hydrated electrons and hydroxyl radicals in inducing the DNA damage. At 5 mM tris in an N2 atmosphere, the presence of an average of two cisplatins per plasmid increased the yields of single- and double-strand breaks by factors of 1.9 and 2.2, respectively, relative to the irradiated unmodified DNA samples. Given that each plasmid of 3,200 base pairs contained an average of two cisplatins, this represents an increase in radiosensitivity of 3,200-fold on a per base pair basis. When hydrated electrons were scavenged by saturating the samples with N2O, these enhancement factors decreased to 1.5 and 1.2, respectively, for single- and double-strand breaks. When hydroxyl radicals were scavenged using 200 mM tris, the respective enhancement factors were 1.2 and 1.6 for single- and double-strand breaks, respectively. Furthermore, no enhancement in DNA damage by cisplatin was observed after scavenging both hydroxyl radicals and hydrated electrons. These findings show that hydrated electrons can induce both single- and double-strand breaks in the platinated DNA, but not in unmodified DNA. In addition, cisplatin modification is clearly an extremely efficient means of increasing the formation of both single- and double-strand breaks by the hydrated electrons and hydroxyl radicals created by ionizing

  13. Theoretical and kinetic study of the hydrogen atom abstraction reactions of unsaturated C6 methyl esters with hydroxyl radical

    NASA Astrophysics Data System (ADS)

    Wang, Quan-De; Ni, Zhong-Hai

    2016-04-01

    This work reports a systematic ab initio and chemical kinetic study of the rate constants for hydrogen atom abstraction reactions by hydroxyl radical (OH) on typical isomers of unsaturated C6 methyl esters at the CBS/QB3 level of theory. The high-pressure limit rate constants at different reaction sites for all the methyl esters in the temperature range from 500 to 2000 K are calculated via transition-state theory with the Wigner method for quantum tunneling effect and fitted to the modified three parameters Arrhenius expression using least-squares regression. Further, a branching ratio analysis for each reaction site has been performed.

  14. Investigation of the loss mechanisms of hydroxyl radicals in the decomposition of organic compounds using plasma generated over water

    NASA Astrophysics Data System (ADS)

    Takeuchi, Nozomi; Ando, Mizuki; Yasuoka, Koichi

    2015-11-01

    Many types of plasma processes have been investigated as potential agents for decomposing persistent organic compounds in water using hydroxyl radicals (•OH), and a wide range of energy efficiency in the reduction of total organic carbon (TOC) has been observed. In this study, loss mechanisms of •OH that limit the energy efficiency were investigated using a plasma generated over an acetic acid solution. Various experiments, including the analysis of the decomposition process, a parametric study, and a numerical simulation, revealed that there are two main loss mechanisms: (i) a self-quenching reaction that generates hydrogen peroxide (H2O2) and (ii) a reaction of •OH with H2O2 and hydroperoxyl radicals (HO2•). In the solution, •OH reacts with these scavengers rather than target compounds. A pulsed plasma with a low current density, low repetition rate, and short pulse duration can be utilized to achieve high efficiency.

  15. Risk assessment of marine environments from ballast water discharges with laboratory-scale hydroxyl radicals treatment in Tianjin Harbor, China.

    PubMed

    Zhang, Nahui; Zhang, Yubo; Bai, Mindong; Zhang, Zhitao; Chen, Cao; Meng, Xiangying

    2014-12-01

    For the majority of ballast water treatment system (BWTS) that employ active substances (e.g., oxidative compounds), relevant chemicals (RCs) formation is an issue owing to their potential adverse effects on aquatic organisms. Accordingly, BWTS must be approved by the International Maritime Organization (IMO), and the approval procedure requires environmental risk assessment. The most commonly employed harbor used to calculate predicted environmental concentrations (PECs) for RCs in treated ballast water is the GESAMP-BWWG (Group of Experts on Scientific Aspects of Marine Environmental Protection-Ballast Water Working Group) model harbor. However, there is very little assessment data available regarding the associated environmental impacts in ports and harbors of China. Therefore, in this study the concentration of fifteen RCs from the existing laboratory-scale BWTS using hydroxyl radicals was obtained and input into the MAMPEC (Marine Antifoulant Model to Predict Environmental Concentrations) model to compute PECs in Tianjin Harbor, China. The potential risks to the aquatic environment posed by treated ballast water in Tianjin Harbor were further assessed based on the calculated ratio of PECs and predicted no effect concentrations (PNECs). Only monochloroacetic acid and dichloroacetic acid were found to have potential risks, and the ratios of PECs and PNECs to the other measured RCs were less than 1, indicating that the environmental risk posed by treated ballast water discharged into Tianjin Harbor is of little concern. The concentration of total residual oxidant recommended by the IMO (<0.2 mg/L) in treated ballast water at discharge was found to be at levels that may pose a risk to the aquatic environment in Tianjin Harbor.

  16. Attacking mechanism of hydroxyl radical to DNA base-pair: density functional study in vacuum and in water.

    PubMed

    Shimizu, Eisuke; Tokuyama, Yuki; Okutsu, Naoko; Nomura, Kazuya; Danilov, Victor I; Kurita, Noriyuki

    2015-01-01

    Recently, the influence of radiation on human body has been recognized as a serious problem. In particular, highly reactive hydroxyl radicals *OH produced by the radiation react with DNA, resulting in a great damage on its structure and electronic properties. It is thus important to investigate the reaction mechanism of *OH to DNA for elucidating the initial damage in DNA induced by the radiation. In the present study, we search for transition states (TS) of the reaction between G-C/A-T base-pair and [Formula: see text] in vacuum and in water, by the density functional theory (DFT) calculations. At first, we obtain the stable structures for the dehydrogenated G-C and A-T, in which the hydrogen atom of NH2 group of G or A base is abstracted by [Formula: see text]. From the structures of the dehydrogenated as well as the natural base-pairs, the TS between these structures is searched for and the activation free energy (AFE) is estimated for the reaction. In vacuum, AFEs for the G-C and A-T are almost the same each other, while the stabilization energy by the reaction for G-C is about 4.9 kcal/mol larger than that for A-T, indicating that the population of the dehydrogenated G-C is remarkably larger than that of the dehydrogenated A-T in vacuum. On the other hand, in water approximated by the continuum solvation model, the AFE for A-T is 2.6 kcal/mol smaller than that for G-C, indicating that the reaction dehydrogenated by [Formula: see text] occurs more frequently for the solvated A-T base-pair than G-C.

  17. Aqueous oxidation of green leaf volatiles by hydroxyl radical as a source of SOA: Kinetics and SOA yields

    NASA Astrophysics Data System (ADS)

    Richards-Henderson, Nicole K.; Hansel, Amie K.; Valsaraj, Kalliat T.; Anastasio, Cort

    2014-10-01

    Green leaf volatiles (GLVs) are a class of oxygenated hydrocarbons released from vegetation, especially during mechanical stress or damage. The potential for GLVs to form secondary organic aerosol (SOA) via aqueous-phase reactions is not known. Fog events over vegetation will lead to the uptake of GLVs into water droplets, followed by aqueous-phase reactions with photooxidants such as the hydroxyl radical (OH). In order to determine if the aqueous oxidation of GLVs by OH can be a significant source of secondary organic aerosol, we studied the partitioning and reaction of five GLVs: cis-3-hexen-1-ol, cis-3-hexenyl acetate, methyl salicylate, methyl jasmonate, and 2-methyl-3-butene-2-ol. For each GLV we measured the kinetics of aqueous oxidation by OH, and the corresponding SOA mass yield. The second-order rate constants for GLVs with OH were all near diffusion controlled, (5.4-8.6) × 109 M-1 s-1 at 298 K, and showed a small temperature dependence, with an average activation energy of 9.3 kJ mol-1 Aqueous-phase SOA mass yields ranged from 10 to 88%, although some of the smaller values were not statistically different from zero. Methyl jasmonate was the most effective aqueous-phase SOA precursor due to its larger Henry's law constant and high SOA mass yield (68 ± 8%). While we calculate that the aqueous-phase SOA formation from the five GLVs is a minor source of aqueous-phase SOA, the availability of other GLVs, other oxidants, and interfacial reactions suggest that GLVs overall might be a significant source of SOA via aqueous reactions.

  18. Sequestering ability of butylated hydroxytoluene, propyl gallate, resveratrol, and vitamins C and E against ABTS, DPPH, and hydroxyl free radicals in chemical and biological systems.

    PubMed

    Soares, Daniele G; Andreazza, Ana C; Salvador, Mirian

    2003-02-12

    The antioxidant capacity of butylated hydroxytoluene (BHT; 2,6-di-tert-butyl-p-cresol), propyl gallate (3,4,5-trihydroxybenzoic acid n-propyl ester), resveratrol (trans-3,4',5-trihydroxystilbene), and vitamins C (l-ascorbic acid) and E [(+)-alpha-tocopherol] was studied in chemical and biological systems. The chemical assays evaluated the capacity of these antioxidants to sequester 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS.) and 1,1 diphenyl-2-picrylhydrazyl (DPPH.). A new colorimetric method to determine hydroxyl radical scavenging is also described. The biological tests use the eucaryotic cells of Saccharomyces cerevisiae treated with the antioxidants in the presence of the stressing agents apomorphine, hydrogen peroxide, and paraquat dichloride (methylviologen; 1,1'-dimethyl-4,4'-bipyridinium dichloride). The results in chemical systems showed that all of the antioxidants were able to significantly inhibit the oxidation of beta-carotene by hydroxyl free radicals. The assays in yeast showed that the antioxidant activity of the tested compounds depended on the stressing agent used and the mechanism of action of the antioxidant.

  19. Identification of hydroxyl radical oxidation products of N-hexanoyl-homoserine lactone by reversed-phase high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

    PubMed

    Cui, Yiling; Frey, Rebecca L; Ferry, John L; Ferguson, P Lee

    2009-04-01

    A reversed-phase high-performance liquid chromatography/electrospray tandem mass spectrometry method was developed for the characterization of hydroxyl radical oxidation products of N-hexanoyl-homoserine lactone (C6-HSL), a member of the N-acylhomoserine lactone (AHL) class of microbial quorum-sensing signaling molecules identified in many Gram-negative strains of bacteria. Six products were identified: four with molecular weight (MW) of 213 and two with MW of 260. The characteristic product ions formed through collision-induced dissociation (CID) provided diagnostic structural information. One of the photolysis products was determined to be N-(3-oxohexanoyl)homoserine lactone (3OC6-HSL), a highly active quorum-sensing signal, by comparison with a reference standard. Three structural isomers with the same mass as 3OC6-HSL were identified as acyl side chain oxidized C6-HSL (keto/enol functionalized) by accurate mass measurement and the structures of these products were proposed from CID spectral interpretation. Two structural isomers formed from concurrent oxidation and nitration of C6-HSL were also observed and their structures were postulated based on CID spectra. In addition to the six hydroxyl radical oxidation products formed from the C6-HSL precursor, five additional compounds generated from combined oxidation and lactonolysis of C6-HSL were identified and structures were postulated.

  20. The three nitric-oxide synthases differ in their kinetics of tetrahydrobiopterin radical formation, heme-dioxy reduction, and arginine hydroxylation.

    PubMed

    Wei, Chin-Chuan; Wang, Zhi-Qiang; Durra, Deborah; Hemann, Craig; Hille, Russ; Garcin, Elsa D; Getzoff, Elizabeth D; Stuehr, Dennis J

    2005-03-11

    The nitric-oxide synthases (NOSs) make nitric oxide and citrulline from l-arginine. How the bound cofactor (6R)-tetrahydrobiopterin (H4B) participates in Arg hydroxylation is a topic of interest. We demonstrated previously that H4B radical formation in the inducible NOS oxygenase domain (iNOSoxy) is kinetically coupled to the disappearance of a heme-dioxy intermediate and to Arg hydroxylation. Here we report single turnover studies that determine and compare the kinetics of these transitions in Arg hydroxylation reactions catalyzed by the oxygenase domains of endothelial and neuronal NOSs (eNOSoxy and nNOSoxy). There was a buildup of a heme-dioxy intermediate in eNOSoxy and nNOSoxy followed by a monophasic transition to ferric enzyme during the reaction. The rate of heme-dioxy decay matched the rates of H4B radical formation and Arg hydroxylation in both enzymes. The rates of H4B radical formation differed such that nNOSoxy (18 s(-1)) > iNOSoxy (11 s(-1)) > eNOSoxy (6 s(-1)), whereas the lifetimes of the resulting H4B radical followed an opposite rank order. 5MeH4B supported a three-fold faster radical formation and greater radical stability relative to H4B in both eNOSoxy and nNOSoxy. Our results indicate the following: (i) the three NOSs share a common mechanism, whereby H4B transfers an electron to the heme-dioxy intermediate. This step enables Arg hydroxylation and is rate-limiting for all subsequent steps in the hydroxylation reaction. (ii) A direct correlation exists between pterin radical stability and the speed of its formation in the three NOSs. (iii) Uncoupled NO synthesis often seen for eNOS at low H4B concentrations may be caused by the slow formation and poor stability of its H4B radical. PMID:15632185

  1. Oh where OH where is Oh? Measuring the Elusive Hydroxyl Radical in the Atmosphere Using Laser-Induced Fluorescence

    NASA Astrophysics Data System (ADS)

    Stevens, Philip S.

    2016-06-01

    The hydroxyl radical (OH) plays a central role in the chemistry of the atmosphere. In addition to controlling the lifetimes of many trace gases important to issues of global climate change and stratospheric ozone depletion, the OH radical initiates the oxidation of carbon monoxide and volatile organic compounds which in the presence of nitrogen oxides can lead to the production of ground-level ozone and secondary organic aerosols, the primary components of photochemical smog. Accurate measurements of OH radical concentrations in the atmosphere can provide critical tests of our understanding of atmospheric chemistry and ground-level ozone production in urban and rural areas. Because of its high reactivity, mixing ratios of OH in the atmosphere are extremely low (typically less than 0.1 parts per trillion) and its chemical lifetime very short (less than 1 second). As a result, measurements of OH present a serious analytical challenge, especially on the timescale necessary to test our understanding of the fast photochemistry of the atmosphere. This presentation will describe the Indiana University laser-induced fluorescence instrument for the sensitive detection of OH radicals in the atmosphere, including recent results from several measurement campaigns in both urban and rural environments.

  2. Measurement of Hydroxyl-Radical Formation in the Rat Striatum by In Vivo Microdialysis and GC-MS.

    PubMed

    Nguyen, V; Bonds, D V; Prokai, L

    2008-10-01

    A GC-MS method was developed for measuring hydroxyl-radical capture products of salicylic acid, a common trapping agent for this reactive oxygen species, in samples obtained by in vivo cerebral microdialysis experiments. The assay employed liquid-liquid extraction followed by derivatization of 2,3- and 2,5-dihydroxybenzoic acid, along with 3,5-dihydroxybenzoic acid added as an internal standard. Due to their simple electron ionization mass spectra featuring [M - 57](+) ions through the loss of tertiary alkyl group from the corresponding molecular ions, tert-butyldimethylsilyl (TBDMS) derivatives afforded straightforward method development based on selected-ion monitoring. In addition, tandem mass spectrometry probing collision-induced dissociation of [M - 57](+) ions obtained from the isomeric tert-butyldimethylsilyl derivatives revealed characteristic differences in the resultant product-ion spectra. Our work has demonstrated the applicability of GC-MS for the assay of microdialysates for 2,3- and 2,5-dihydroxybenzoic acid by confirming that local administration of the excitotoxic glutamate into the rat striatum significantly increased in vivo hydroxyl-radical production in this brain region and that subsequent systemic administration of α-phenyl-tert-butylnitrone reversed glutamate-induced oxidative stress.

  3. Study on the free radical scavenging activity of sea cucumber (Paracaudina chinens var.) gelatin hydrolysate

    NASA Astrophysics Data System (ADS)

    Zeng, Mingyong; Xiao, Feng; Zhao, Yuanhui; Liu, Zunying; Li, Bafang; Dong, Shiyuan

    2007-07-01

    Gelatin from the sea cucumber (Paracaudina chinens var.) was hydrolyzed by bromelain and the hydrolysate was found to have a high free radical scavenging activity. The hydrolysate was fractionated through an ultrafiltration membrane with 5 kDa molecular weight cutoff (MWCO). The portion (less than 5 kDa) was further separated by Sephadex G-25. The active peak was collected and assayed for free radical scavenging activity. The scavenging rates for superoxide anion radicals (O2·-) and hydroxyl radicals (·OH) of the fraction with the highest activity were 29.02% and 75.41%, respectively. A rabbit liver mitochondrial free radical damage model was adopted to study the free radical scavenging activity of the fraction. The results showed that the sea cucumber gelatin hydrolysate can prevent the damage of rabbit liver and mitochondria.

  4. Stability and properties of the two-dimensional hexagonal boron nitride monolayer functionalized by hydroxyl (OH) radicals: a theoretical study.

    PubMed

    Wang, Hong-mei; Liu, Yue-jie; Wang, Hong-xia; Zhao, Jing-xiang; Cai, Qing-hai; Wang, Xuan-zhang

    2013-12-01

    Motivated by the great advance in graphene hydroxide--a versatile material with various applications--we performed density functional theory (DFT) calculations to study the functionalization of the two-dimensional hexagonal boron nitride (h-BN) sheet with hydroxyl (OH) radicals, which has been achieved experimentally recently. Particular attention was paid to searching for the most favorable site(s) for the adsorbed OH radicals on a h-BN sheet and addressing the roles of OH radical coverage on the stability and properties of functionalized h-BN sheet. The results indicate that, for an individual OH radica, the most stable configuration is that it is adsorbed on the B site of the h-BN surface with an adsorption energy of -0.88 eV and a magnetic moment of 1.00 μ(B). Upon adsorption of more than one OH radical on a h-BN sheet, however, these adsorbates prefer to adsorb in pairs on the B and its nearest N atoms from both sides of h-BN sheet without magnetic moment. An energy diagram of the average adsorption energy of OH radicals on h-BN sheet as a function of its coverage indicates that when the OH radical coverage reaches to 60 %, the functionalized h-BN sheet is the most stable among all studied configurations. More importantly, this configuration exhibits good thermal and dynamical stability at room temperature. Owing to the introduction of certain impurity levels, the band gap of h-BN sheet gradually decreases with increasing OH coverage, thereby enhancing its electrical conductivity. PMID:24092267

  5. Stability and properties of the two-dimensional hexagonal boron nitride monolayer functionalized by hydroxyl (OH) radicals: a theoretical study.

    PubMed

    Wang, Hong-mei; Liu, Yue-jie; Wang, Hong-xia; Zhao, Jing-xiang; Cai, Qing-hai; Wang, Xuan-zhang

    2013-12-01

    Motivated by the great advance in graphene hydroxide--a versatile material with various applications--we performed density functional theory (DFT) calculations to study the functionalization of the two-dimensional hexagonal boron nitride (h-BN) sheet with hydroxyl (OH) radicals, which has been achieved experimentally recently. Particular attention was paid to searching for the most favorable site(s) for the adsorbed OH radicals on a h-BN sheet and addressing the roles of OH radical coverage on the stability and properties of functionalized h-BN sheet. The results indicate that, for an individual OH radica, the most stable configuration is that it is adsorbed on the B site of the h-BN surface with an adsorption energy of -0.88 eV and a magnetic moment of 1.00 μ(B). Upon adsorption of more than one OH radical on a h-BN sheet, however, these adsorbates prefer to adsorb in pairs on the B and its nearest N atoms from both sides of h-BN sheet without magnetic moment. An energy diagram of the average adsorption energy of OH radicals on h-BN sheet as a function of its coverage indicates that when the OH radical coverage reaches to 60 %, the functionalized h-BN sheet is the most stable among all studied configurations. More importantly, this configuration exhibits good thermal and dynamical stability at room temperature. Owing to the introduction of certain impurity levels, the band gap of h-BN sheet gradually decreases with increasing OH coverage, thereby enhancing its electrical conductivity.

  6. The active titration method for measuring local hydroxyl radical concentration

    NASA Technical Reports Server (NTRS)

    Sprengnether, Michele; Prinn, Ronald G.

    1994-01-01

    We are developing a method for measuring ambient OH by monitoring its rate of reaction with a chemical species. Our technique involves the local, instantaneous release of a mixture of saturated cyclic hydrocarbons (titrants) and perfluorocarbons (dispersants). These species must not normally be present in ambient air above the part per trillion concentration. We then track the mixture downwind using a real-time portable ECD tracer instrument. We collect air samples in canisters every few minutes for roughly one hour. We then return to the laboratory and analyze our air samples to determine the ratios of the titrant to dispersant concentrations. The trends in these ratios give us the ambient OH concentration from the relation: dlnR/dt = -k(OH). A successful measurement of OH requires that the trends in these ratios be measureable. We must not perturb ambient OH concentrations. The titrant to dispersant ratio must be spatially invariant. Finally, heterogeneous reactions of our titrant and dispersant species must be negligible relative to the titrant reaction with OH. We have conducted laboratory studies of our ability to measure the titrant to dispersant ratios as a function of concentration down to the few part per trillion concentration. We have subsequently used these results in a gaussian puff model to estimate our expected uncertainty in a field measurement of OH. Our results indicate that under a range of atmospheric conditions we expect to be able to measure OH with a sensitivity of 3x10(exp 5) cm(exp -3). In our most optimistic scenarios, we obtain a sensitivity of 1x10(exp 5) cm(exp -3). These sensitivity values reflect our anticipated ability to measure the ratio trends. However, because we are also using a rate constant to obtain our (OH) from this ratio trend, our accuracy cannot be better than that of the rate constant, which we expect to be about 20 percent.

  7. Reaction of diethyl maleate and diethyl fumarate with hydrated electrons and hydroxyl radicals

    NASA Astrophysics Data System (ADS)

    Bíró, Á.; Wojnárovits, L.

    1996-03-01

    In dilute aqueous solution diethyl maleate (DEM) and diethyl fumarate (DEF) scavenge hydrated electrons with a rate constant of 2.2·10 10 mol -1 dm 3 s -1. DEM - reversibly protonates with pK a = 5.2. The pK a of DEF - is below 4. The electron adducts decay in second order reactions. The OH radicals add to the double bonds with 5.9·10 9 mol -1 dm 3 s -1. In the reaction α-carboxyalkyl radicals are produced. In disproportionation of radicals oxalacetic acid ethylester forms that in alkaline solution leads to strong permanent absorbency in the UV.

  8. Characterisation of an inlet pre-injector laser-induced fluorescence instrument for the measurement of atmospheric hydroxyl radicals

    NASA Astrophysics Data System (ADS)

    Novelli, A.; Hens, K.; Tatum Ernest, C.; Kubistin, D.; Regelin, E.; Elste, T.; Plass-Dülmer, C.; Martinez, M.; Lelieveld, J.; Harder, H.

    2014-10-01

    Atmospheric measurements of hydroxyl radicals (OH) are challenging due to a high reactivity and consequently low concentration. The importance of OH as an atmospheric oxidant has motivated a sustained effort leading to the development of a number of highly sensitive analytical techniques. Recent work has indicated that the laser-induced fluorescence of the OH molecules method based on the fluorescence assay by gas expansion technique (LIF-FAGE) for the measurement of atmospheric OH in some environments may be influenced by artificial OH generated within the instrument, and a chemical method to remove this interference was implemented in a LIF-FAGE system by Mao et al. (2012). While it is not clear whether other LIF-FAGE instruments suffer from the same interference, we have applied this method to our LIF-FAGE HORUS (Hydroxyl Radical Measurement Unit based on fluorescence Spectroscopy) system, and developed and deployed an inlet pre-injector (IPI) to determine the chemical zero level in the instrument via scavenging the ambient OH radical. We describe and characterise this technique in addition to its application at field sites in forested locations in Finland, Spain and Germany. Ambient measurements show that OH generated within the HORUS instrument is a non-negligible fraction of the total OH signal, which can comprise 30 to 80% during daytime and 60 to 100% during the night. The contribution of the background OH varied greatly between measurement sites and was likely related to the type and concentration of volatile organic compounds (VOCs) present at each particular location. Two inter-comparisons in contrasting environments between the HORUS instrument and two different chemical ionisation mass spectrometers (CIMS) are described to demonstrate the efficacy of IPI and the necessity of the chemical zeroing method for our LIF-FAGE instrument in such environments.

  9. DNA-templated Ag nanoclusters as fluorescent probes for sensing and intracellular imaging of hydroxyl radicals.

    PubMed

    Zhang, Li; Liang, Ru-Ping; Xiao, Sai-Jin; Bai, Jian-Mei; Zheng, Lin-Ling; Zhan, Lei; Zhao, Xi-Juan; Qiu, Jian-Ding; Huang, Cheng-Zhi

    2014-01-01

    We have developed a simple, rapid and label-free sensor for the essential biological OH radicals based on the fluorescence quenching of DNA-templated Ag nanoclusters (DNA-Ag NCs). The OH radicals generated from the Fenton reagent attack and cleave the DNA template, which disturbs the microenvironments around Ag NCs, resulting in spontaneous aggregation due to the lack of stabilization and further the quenching of the Ag NCs fluorescence. These changes in fluorescence intensity allow sensing of OH radicals with good sensitivity and selectivity under optimal conditions. The sensor can be also applied for quantifying the radical scavenging action of antioxidants. Various characterizations including absorption spectra, fluorescence lifetimes, light scattering (LS) spectra, transmission electron microscopy (TEM), dark field light scattering imaging, and circular dichroism (CD) spectrometry have been employed to illustrate the proposed sensing mechanism. Further investigations demonstrate that the fluorescent probe could penetrate into intact cell membranes to selectively detect intracellular OH radicals induced by the phorbol myristate acetate (PMA) stimulation. These advantageous characteristics make the fluorescent DNA-Ag NCs potentially useful as a new candidate to monitor OH in broad biosystems. PMID:24274306

  10. Confirmation of hydroxyl radicals (•OH) generated in the presence of TiO2 supported on AC under microwave irradiation.

    PubMed

    Zhang, Zhaohong; Yu, Fengyang; Huang, Lirong; Jiatieli, Jianaerguli; Li, Yuanyuan; Song, Lijun; Yu, Ning; Dionysiou, Dionysios D

    2014-08-15

    In order to study the degradation mechanism of technology of microwave (MW) combined with TiO2 supported on activated carbon (TiO2/AC), the reactive oxygen species (ROS) was explored through oxidation of 1,5-diphenyl carbazide (DPCI) to 1,5-diphenyl carbazone (DPCO). Furthermore, 2,6-di-tert-butyl-4-methylphenol (BHT), Mannitol (MT) and Vitamin C (VC) were used as radical scavengers to confirm the generation of the hydroxyl radicals ((•)OH). In addition, the influence of some parameters such as TiO2 mass ratio content, irradiation time, material dose, DPCI concentration and MW power on the determination of (•)OH were examined. The results showed that the (•)OH could be generated under MW combined with loaded TiO2/AC. Also, anatase TiO2/AC can generate more (•)OH radicals than rutile TiO2/AC under MW irradiation. This work would provide new mechanistic insights on the enhanced degradation effect of organic pollutants in water using the supported TiO2/AC coupled with MW technology.

  11. QSAR models for oxidation of organic micropollutants in water based on ozone and hydroxyl radical rate constants and their chemical classification.

    PubMed

    Sudhakaran, Sairam; Amy, Gary L

    2013-03-01

    Ozonation is an oxidation process for the removal of organic micropollutants (OMPs) from water and the chemical reaction is governed by second-order kinetics. An advanced oxidation process (AOP), wherein the hydroxyl radicals (OH radicals) are generated, is more effective in removing a wider range of OMPs from water than direct ozonation. Second-order rate constants (k(OH) and k(O3) are good indices to estimate the oxidation efficiency, where higher rate constants indicate more rapid oxidation. In this study, quantitative structure activity relationships (QSAR) models for O(3) and AOP processes were developed, and rate constants, k(OH) and [Formula: see text] , were predicted based on target compound properties. The k(O3) and k(OH) values ranged from 5 * 10(-4) to 10(5) M(-1)s(-1) and 0.04 to 18 * (10(9)) M(-1) s(-1), respectively. Several molecular descriptors which potentially influence O(3) and OH radical oxidation were identified and studied. The QSAR-defining descriptors were double bond equivalence (DBE), ionisation potential (IP), electron-affinity (EA) and weakly-polar component of solvent accessible surface area (WPSA), and the chemical and statistical significance of these descriptors was discussed. Multiple linear regression was used to build the QSAR models, resulting in high goodness-of-fit, r(2) (>0.75). The models were validated by internal and external validation along with residual plots. PMID:23260175

  12. Kinetics and products of the reactions of hydroxyl radicals with selected volatile organic compounds, including oxygenated compounds

    NASA Astrophysics Data System (ADS)

    Bethel, Heidi Lynn

    Kinetics, products and reaction mechanisms of the OH radical-initiated reactions of selected volatile organic compounds (VOCs) and oxygenated compounds were examined. These compounds are important smog forming chemicals that are found in gasoline and many consumer products. Smog is created by the interaction of these VOCs with oxides of nitrogen in the presence of sunlight. The hydroxyl (OH) radical is a daytime species and a key initiator of the VOC reactions which lead to photochemical smog formation. Chapter II investigates the OH radical-initiated reactions of p-xylene, 1,2,3-, and 1,2,4-trimethylbenzene which are components of gasoline fuels, vehicle exhaust and ambient air in urban areas. Experiments were conducted at varying NO2 concentrations in indoor environmental chambers in order to determine the dependence of the product yields as a function of NO2 concentrations. From these experiments and previous literature yields, a majority of the products from these reactions under atmospheric conditions have now been elucidated. Chapter III examines the OH radical-initiated reaction of 3-hexene-2,5-dione which is formed from the reactions of p-xylene and 1,2,4-trimethylbenzene (Chapter II). Due to its polar nature, 3-hexene-2,5-dione and its reaction products are difficult to handle experimentally. Products identified from this reaction through the use of in situ atmospheric pressure ionization tandem mass spectrometry were CH3C(O)CH(OH)CHO and CH 3C(O)CH(OH)CH(ONO2)C(O)CH3. Chapters IV, V, and VI examine the OH radical-initiated reactions of 6 different alcohols, including diols. The products examined in Chapters IV and V are those from 2-methyl-2,4-pentanediol and 1,2-, 1,3-, and 2,3-butanediol, which are found in various solvents. Reaction rates were determined using a relative rate method. Hydroxyaldehyde and hydroxyketone products from these reactions were also quantified. Chapter VI examined the reaction rates and products formed from the OH radical

  13. In situ radiolysis time-resolved ESR studies of spin trapping by DMPO: Re-evalution of hydroxyl radical and hydrated electron trapping rates and spin adduct yields

    SciTech Connect

    Madden, K.P.; Taniguchi, Hitoshi

    1996-05-02

    The second-order rate constants for the reaction of 5, 5-dimethyl-1-pyrroline N-oxide (DMPO) with radiolytically produced hydroxyl radicals and hydrated electrons have been measured in aqueous solution by direct observation of spin adduct initial yield using time-resolved electron spin resonance. The rate constants are 2.8 x 10{sup 9} mol{sup -1} dm{sup 3} S{sup -1} for the DMPO-hydroxyl radical reaction and 3.2 x 10{sup 9} mol{sup -1} dm{sup 3} s{sup -1} for the reaction of DMPO and hydrated electron, using sodium formate and chloroacetic acid as competitive scavengers of the hydroxyl radical and hydrated electron, respectively. The hydrated electron-DMPO competition study determined the fraction of DMPO-H produced directly from radiolytically produced hydrogen atoms as 0.082 of the total DMPO-H yield, indicating that approximately half of the hydrogen atoms react with DMPO to produce non-aminoxyl products. The fraction of the total hydroxyl radical yield leading to DMPO-OH spin adduct was determined to be 0.94, using the bleach of 2,2,6,6-tetramethylpiperidone-N-oxyl by carbon dioxide radical anion as a reference standard. 36 refs., 8 figs., 1 tab.

  14. Molecular dynamics study of the hydration of the hydroxyl radical at body temperature.

    PubMed

    Pabis, Anna; Szala-Bilnik, Joanna; Swiatla-Wojcik, Dorota

    2011-05-28

    Classical molecular dynamics (MD) simulation of ˙OH in liquid water at 37 °C has been performed using flexible models of the solute and solvent molecules. We derived the Morse function describing the bond stretching of the radical and the potential for ˙OH-H(2)O interactions, including short-range interactions of hydrogen atoms. Scans of the potential energy surface of the ˙OH-H(2)O complex have been performed using the DFT method with the B3LYP functional and the 6-311G(d,p) basis set. The DFT-derived partial charges, ±0.375e, and the equilibrium bond-length, 0.975 Å, of ˙OH resulted in the dipole moment of 1.76 D. The radical-water radial distribution functions revealed that ˙OH is not built into the solvent structure but it rather occupies distortions or cavities in the hydrogen-bonded network. The solvent structure at 37 °C has been found to be the same as that of pure water. The hydration cage of the radical comprises 13-14 water molecules. The estimated hydration enthalpy -42 ± 5 kJ mol(-1) is comparable with the experimental value -39 ± 6 kJ mol(-1) for 25 °C. Inspection of hydrogen bonds showed the importance of short-range interaction of hydrogen atoms and indicated that neglect of the angular condition greatly overestimates the number of the H-acceptor radical-water bonds. The mean number ̅n = 0.85 of radical-water H-bonds has been calculated using geometric definition of H-bond and ̅n = 0.62 has been obtained when the energetic condition, E(da)≤-8 kJ mol(-1), was additionally considered. The continuous lifetimes of 0.033 ps and 0.024 ps have been estimated for the radical H-donor and the H-acceptor bonds, respectively. Within statistical uncertainty the radical self-diffusion coefficient, (2.9 ± 0.6) × 10(-9) m(2) s(-1), is the same as (3.1 ± 0.5) × 10(-9) m(2) s(-1) calculated for water in solution and in pure solvent. To the best of our knowledge, this is the first study of the ˙OH(aq) properties at a biologically relevant body

  15. Role of hydroxyl radical in modification of cell wall polysaccharides and aril breakdown during senescence of harvested longan fruit.

    PubMed

    Duan, Xuewu; Zhang, Haiyan; Zhang, Dandan; Sheng, Jiangfeng; Lin, Hetong; Jiang, Yueming

    2011-09-01

    The effects of reactive oxygen species (ROS), especially hydroxyl radical (OH), on cellular wall disassembly in vitro and in vivo, and aril breakdown in longan fruit, were investigated. OH caused the disassembly of cell wall material (CWM) in vitro, demonstrated by the increases of total sugars and uronic acid released, and the downshift in molecular mass of CDTA soluble pectin (CSP) and Na2CO3 soluble pectin (CO3-SP). In addition, OH resulted in decreased CO3-SP content and increased CSP content in CWM suspension, suggesting the conversion of CO3-SP to CSP. Application of exogenous OH accelerated aril breakdown in longan fruit while the process was delayed by l-cysteine·HCl, a ROS scavenger. Furthermore, lower CWM content and decreased molecular mass of pectins were observed in OH-treated fruit. These results indicated that OH contributed to the degradation of cell wall polysaccharides, resulting in aril breakdown in longan fruit.

  16. Generation mechanism of hydroxyl radical species and its lifetime prediction during the plasma-initiated ultraviolet (UV) photolysis

    PubMed Central

    Attri, Pankaj; Kim, Yong Hee; Park, Dae Hoon; Park, Ji Hoon; Hong, Young J.; Uhm, Han Sup; Kim, Kyoung-Nam; Fridman, Alexander; Choi, Eun Ha

    2015-01-01

    Through this work, we have elucidated the mechanism of hydroxyl radicals (OH•) generation and its life time measurements in biosolution. We observed that plasma-initiated ultraviolet (UV) photolysis were responsible for the continues generation of OH• species, that resulted in OH• to be major reactive species (RS) in the solution. The density and lifetime of OH• species acted inversely proportional to each other with increasing depth inside the solution. The cause of increased lifetime of OH• inside the solution is predicted using theoretical and semiempirical calculations. Further, to predict the mechanism of conversion of hydroxide ion (OH−) to OH• or H2O2 (hydrogen peroxide) and electron, we determined the current inside the solution of different pH. Additionally, we have investigated the critical criterion for OH• interaction on cancer cell inducing apoptosis under effective OH• exposure time. These studies are innovative in the field of plasma chemistry and medicine. PMID:25790968

  17. Combustion Processes as a Source of High Levels of Indoor Hydroxyl Radicals through the Photolysis of Nitrous Acid.

    PubMed

    Bartolomei, V; Gomez Alvarez, E; Wittmer, J; Tlili, S; Strekowski, R; Temime-Roussel, B; Quivet, E; Wortham, H; Zetzsch, C; Kleffmann, J; Gligorovski, S

    2015-06-01

    Hydroxyl radicals (OH) are known to control the oxidative capacity of the atmosphere but their influence on reactivity within indoor environments is believed to be of little importance. Atmospheric direct sources of OH include the photolysis of ozone and nitrous acid (HONO) and the ozonolysis of alkenes. It has been argued that the ultraviolet light fraction of the solar spectrum is largely attenuated within indoor environments, thus, limiting the extent of photolytic OH sources. Conversely, the ozonolysis of alkenes has been suggested as the main pathway of OH formation within indoor settings. According to this hypothesis the indoor OH radical concentrations span in the range of only 10(4) to 10(5) cm(-3). However, recent direct OH radical measurements within a school classroom yielded OH radical peak values at moderate light intensity measured at evenings of 1.8 × 10(6) cm(-3) that were attributed to the photolysis of HONO. In this work, we report results from chamber experiments irradiated with varying light intensities in order to mimic realistic indoor lighting conditions. The exhaust of a burning candle was introduced in the chamber as a typical indoor source causing a sharp peak of HONO, but also of nitrogen oxides (NOx). The photolysis of HONO yields peak OH concentration values, that for the range of indoors lightning conditions were estimated in the range 5.7 ×· 10(6) to 1.6 × 10(7) cm(-3). Excellent agreement exists between OH levels determined by a chemical clock and those calculated by a simple PSS model. These findings suggest that significant OH reactivity takes place at our dwellings and the consequences of this reactivity-that is, formation of secondary oxidants-ought to be studied hereafter. PMID:25942056

  18. Relationships between the structure of natural organic matter and its reactivity towards molecular ozone and hydroxyl radicals

    USGS Publications Warehouse

    Westerhoff, P.; Aiken, G.; Amy, G.; Debroux, J.

    1999-01-01

    Oxidation reaction rate parameters for molecular ozone (O3) and hydroxyl (HO) radicals with a variety of hydrophobic organic acids (HOAs) isolated from different geographic locations were determined from batch ozonation studies. Rate parameter values, obtained under equivalent dissolved organic carbon concentrations in both the presence and absence of non-NOM HO radical scavengers, varied as a function of NOM structure. First-order rate constants for O3 consumption (k(O3)) averaged 8.8 x 10-3 s-1, ranging from 3.9 x 10-3 s-1 for a groundwater HOA to > 16 x 10-3 s-1 for river HOAs with large terrestrial carbon inputs. The average second-order rate constant (k(HO,DOC) between HO radicals and NOM was 3.6 x 108 l (mol C)-1 s-1; a mass of 12 g C per mole C was used in all calculations. Specific ultraviolet absorbance (SUVA) at 254 or 280 nm of the HOAs correlated well (r > 0.9) with O3 consumption rate parameters, implying that organic ??-electrons strongly and selectively influence oxidative reactivity. HO radical reactions with NOM were less selective, although correlation between k(HO,DOC) and SUVA existed. Other physical-chemical properties of NOM, such as aromatic and aliphatic carbon content from 13C-NMR spectroscopy, proved less sensitive for predicting oxidation reactivity than SUVA. The implication of this study is that the structural nature of NOM varies temporally and spatially in a water source, and both the nature and amount of NOM will influence oxidation rates.

  19. Calculation of the relative geometry of tRNAs in the ribosome from directed hydroxyl-radical probing data.

    PubMed Central

    Joseph, S; Whirl, M L; Kondo, D; Noller, H F; Altman, R B

    2000-01-01

    The many interactions of tRNA with the ribosome are fundamental to protein synthesis. During the peptidyl transferase reaction, the acceptor ends of the aminoacyl and peptidyl tRNAs must be in close proximity to allow peptide bond formation, and their respective anticodons must base pair simultaneously with adjacent trinucleotide codons on the mRNA. The two tRNAs in this state can be arranged in two nonequivalent general configurations called the R and S orientations, many versions of which have been proposed for the geometry of tRNAs in the ribosome. Here, we report the combined use of computational analysis and tethered hydroxyl-radical probing to constrain their arrangement. We used Fe(II) tethered to the 5' end of anticodon stem-loop analogs (ASLs) of tRNA and to the 5' end of deacylated tRNA(Phe) to generate hydroxyl radicals that probe proximal positions in the backbone of adjacent tRNAs in the 70S ribosome. We inferred probe-target distances from the resulting RNA strand cleavage intensities and used these to calculate the mutual arrangement of A-site and P-site tRNAs in the ribosome, using three different structure estimation algorithms. The two tRNAs are constrained to the S configuration with an angle of about 45 degrees between the respective planes of the molecules. The terminal phosphates of 3'CCA are separated by 23 A when using the tRNA crystal conformations, and the anticodon arms of the two tRNAs are sufficiently close to interact with adjacent codons in mRNA. PMID:10688361

  20. Endogenous 3, 4- Dihydroxyphenylalanine and Dopaquinone Modifications on Protein Tyrosine: links to mitochondrially derived oxidative stress via hydroxyl radical

    SciTech Connect

    Zhang, Xu; Monroe, Matthew E.; Chen, Baowei; Chin, Mark H.; Heibeck, Tyler H.; Schepmoes, Athena A.; Yang, Feng; Petritis, Brianne O.; Camp, David G.; Pounds, Joel G.; Jacobs, Jon M.; Smith, Desmond J.; Bigelow, Diana J.; Smith, Richard D.; Qian, Weijun

    2010-06-02

    Oxidative modifications of protein tyrosines have been implicated in multiple human diseases. Among these modifications, elevations in levels of 3, 4-dihydroxyphenylalanine (DOPA), a major product of hydroxyl radical addition to tyrosine, has been observed in a number of pathologies. Here we report the first global proteome survey of endogenous site-specific modifications, i.e, DOPA and its further oxidation product dopaquinone (DQ) in mouse brain and heart tissues. Results from LC-MS/MS analyses included 203 and 71 DOPA-modified tyrosine sites identified from brain and heart, respectively, with a false discovery rate of ~1%; while only a few nitrotyrosine containing peptides, a more commonly studied marker of oxidative stress, were detectable, suggesting the much higher abundance for DOPA modification as compared with tyrosine nitration. Moreover, 57 and 29 DQ modified peptides were observed from brain and heart, respectively; nearly half of these peptides were also observed with DOPA modification on the same sites. For both tissues, these modifications are preferentially found in mitochondrial proteins with metal-binding properties, consistent with metal catalyzed hydroxyl radical formation from mitochondrial superoxide and hydrogen peroxide. These modifications also link to a number of mitochondria-associated and other signaling pathways. Furthermore, many of the modification sites were common sites of previously reported tyrosine phosphorylation suggesting potential disruption of signaling pathways. Structural aspects of DOPA-modified tyrosine sequences are distinct from those of nitrotyrosines suggesting that each type of modifications provides a marker for different in vivo reactive chemistries and can be used to predict sensitive protein targets. Collectively, the results suggest that these modifications are linked with mitochondrially-derived oxidative stress, and may serve as sensitive markers for disease pathologies.

  1. A Synchrotron-Based Hydroxyl Radical Footprinting Analysis of Amyloid Fibrils and Prefibrillar Intermediates with Residue-Specific Resolution

    PubMed Central

    2015-01-01

    Structural models of the fibrils formed by the 40-residue amyloid-β (Aβ40) peptide in Alzheimer’s disease typically consist of linear polypeptide segments, oriented approximately perpendicular to the long axis of the fibril, and joined together as parallel in-register β-sheets to form filaments. However, various models differ in the number of filaments that run the length of a fibril, and in the topological arrangement of these filaments. In addition to questions about the structure of Aβ40 monomers in fibrils, there are important unanswered questions about their structure in prefibrillar intermediates, which are of interest because they may represent the most neurotoxic form of Aβ40. To assess different models of fibril structure and to gain insight into the structure of prefibrillar intermediates, the relative solvent accessibility of amino acid residue side chains in fibrillar and prefibrillar Aβ40 preparations was characterized in solution by hydroxyl radical footprinting and structural mass spectrometry. A key to the application of this technology was the development of hydroxyl radical reactivity measures for individual side chains of Aβ40. Combined with mass-per-length measurements performed by dark-field electron microscopy, the results of this study are consistent with the core filament structure represented by two- and three-filament solid state nuclear magnetic resonance-based models of the Aβ40 fibril (such as 2LMN, 2LMO, 2LMP, and 2LMQ), with minor refinements, but they are inconsistent with the more recently proposed 2M4J model. The results also demonstrate that individual Aβ40 fibrils exhibit structural heterogeneity or polymorphism, where regions of two-filament structure alternate with regions of three-filament structure. The footprinting approach utilized in this study will be valuable for characterizing various fibrillar and nonfibrillar forms of the Aβ peptide. PMID:25382225

  2. A Synchrotron-Based Hydroxyl Radical Footprinting Analysis of Amyloid Fibrils and Prefibrillar Intermediates with Residue-Specific Resolution

    SciTech Connect

    Klinger, Alexandra L.; Kiselar, Janna; Ilchenko, Serguei; Komatsu, Hiroaki; Chance, Mark R.; Axelsen, Paul H.

    2014-11-09

    The structural models of the fibrils formed by the 40-residue amyloid-β (Aβ40) peptide in Alzheimer’s disease typically consist of linear polypeptide segments, oriented approximately perpendicular to the long axis of the fibril, and joined together as parallel in-register β-sheets to form filaments. However, various models differ in the number of filaments that run the length of a fibril, and in the topological arrangement of these filaments. In addition to questions about the structure of Aβ40 monomers in fibrils, there are important unanswered questions about their structure in prefibrillar intermediates, which are of interest because they may represent the most neurotoxic form of Aβ40. To assess different models of fibril structure and to gain insight into the structure of prefibrillar intermediates, the relative solvent accessibility of amino acid residue side chains in fibrillar and prefibrillar Aβ40 preparations was characterized in solution by hydroxyl radical footprinting and structural mass spectrometry. A key to the application of this technology was the development of hydroxyl radical reactivity measures for individual side chains of Aβ40. When we combined mass-per-length measurements performed by dark-field electron microscopy, we determined that the results of our study were consistent with the core filament structure represented by two- and three-filament solid state nuclear magnetic resonance-based models of the Aβ40 fibril (such as 2LMN, 2LMO, 2LMP, and 2LMQ), with minor refinements, but they are inconsistent with the more recently proposed 2M4J model. Our results also demonstrate that individual Aβ40 fibrils exhibit structural heterogeneity or polymorphism, where regions of two-filament structure alternate with regions of three-filament structure. The footprinting approach utilized in this study will be valuable for characterizing various fibrillar and nonfibrillar forms of the Aβ peptide.

  3. Inhibition of the iron-catalysed formation of hydroxyl radicals by nitrosouracil derivatives: protection of mitochondrial membranes against lipid peroxidation.

    PubMed

    Rabion, A; Verlhac, J B; Fraisse, L; Roche, B; Seris, J L

    1993-01-01

    A new series of metal ligands containing the 1,3-dimethyl-6-amino-5- nitrosouracil moiety has been synthesized and they have been studied as potential inhibitors of iron-dependent lipid peroxidation. For this purpose, these new derivatives have been tested in the Fenton induced deoxyribose degradation assay, which allows a quantitative measurement of their inhibitory effect towards hydroxyl radical generation. When iron(II) is complexed by these ligands, a strong inhibition of deoxyribose degradation is observed, especially in the case of tris-[2-(1,3-dimethyl-5-nitrosouracil-6-yl)aminoethyl] amine (5). This inhibitory effect is clearly related to a specific complexation of iron(II) and is not due to the direct scavenging of hydroxyl radical by the ligand. Inhibition of the iron mediated Fenton reaction presumably results from inactivation of the reactivity of the metal center towards hydrogen peroxide. These derivatives, as well as long alkyl chain substituted nitrosouracils were evaluated in the protection of biological membranes against lipid peroxidation (induced by iron(II)/dihydroxyfumaric acid and determined with the 2-thiobarbituric acid test). Ligand 5 inhibited lipid peroxidation at a rate similar to Desferal (desferrioxamine B) and slightly higher than bathophenanthroline sulphonate (BPS), which are respectively good iron(III) and iron(II) chelators. When covalently bound with a long alkyl chain, the increase of lipophilic character of the ligand allows its location near the mitochondrial membrane, where lipid peroxidation occurs. Lower concentrations (IC50 = 4 microM) are then necessary to inhibit lipid peroxidation. This IC50 concentration should be compared to those obtained for Trolox (IC50 = 3 microM) or the 21-aminosteroid U74500A (IC50 = 1 microM) described previously.

  4. Hydroxyl radical scavenger ameliorates cisplatin-induced nephrotoxicity by preventing oxidative stress, redox state unbalance, impairment of energetic metabolism and apoptosis in rat kidney mitochondria.

    PubMed

    Santos, N A G; Bezerra, C S Catão; Martins, N M; Curti, C; Bianchi, M L P; Santos, A C

    2008-01-01

    Nephrotoxicity is the major dose-limiting factor of cisplatin chemotherapy. Reactive oxygen species generated in mitochondria are thought to be the main cause of cellular damage in such injury. The present study examined, in vivo, the protective potential of the hydroxyl radical scavenger dimethylthiourea (DMTU) against cisplatin-induced effects on renal mitochondrial bioenergetics, redox state and oxidative stress. Adult male Wistar rats (200 to 220 g) were divided into four groups of eight animals each. The control group was treated only with an intraperitoneal (i.p.) injection of saline solution (1 ml/100 g body weight). The second group was given only DMTU (500 mg/kg body weight, i.p, followed by 125 mg/Kg, i.p., twice a day until they were killed). The third group was given a single injection of cisplatin (10 mg/kg body weight, i.p.). The fourth group was given DMTU (500 mg/kg body weight, i.p.), just before the cisplatin injection (10 mg/kg body weight, i.p.), followed by injections of DMTU (125 mg/kg body weight, i.p.) twice a day until they were killed. Animals were killed 72 h after the treatment. Besides not presenting any direct effect on mitochondria, DMTU substantially inhibited cisplatin-induced mitochondrial injury and cellular death by apoptosis, suppressing the occurrence of acute renal failure. All the following cisplatin-induced effects were prevented by DMTU: (1) increased plasmatic levels of creatinine and blood urea nitrogen (BUN); (2) decreased ATP content, calcium uptake and electrochemical potential; (3) oxidation of lipids, including cardiolipin; and oxidation of proteins, including sulfhydryl, and aconitase enzyme, as well as accumulation of carbonyl proteins; (4) depletion of the antioxidant defense (NADPH and GSH) and (5) increased activity of the apoptosis executioner caspase-3. Our findings show the important role played by mitochondria and hydroxyl radicals in cisplatin-induced nephrotoxicity, as well as the effectiveness of DMTU in

  5. Hydroxyl radical scavenger ameliorates cisplatin-induced nephrotoxicity by preventing oxidative stress, redox state unbalance, impairment of energetic metabolism and apoptosis in rat kidney mitochondria.

    PubMed

    Santos, N A G; Bezerra, C S Catão; Martins, N M; Curti, C; Bianchi, M L P; Santos, A C

    2008-01-01

    Nephrotoxicity is the major dose-limiting factor of cisplatin chemotherapy. Reactive oxygen species generated in mitochondria are thought to be the main cause of cellular damage in such injury. The present study examined, in vivo, the protective potential of the hydroxyl radical scavenger dimethylthiourea (DMTU) against cisplatin-induced effects on renal mitochondrial bioenergetics, redox state and oxidative stress. Adult male Wistar rats (200 to 220 g) were divided into four groups of eight animals each. The control group was treated only with an intraperitoneal (i.p.) injection of saline solution (1 ml/100 g body weight). The second group was given only DMTU (500 mg/kg body weight, i.p, followed by 125 mg/Kg, i.p., twice a day until they were killed). The third group was given a single injection of cisplatin (10 mg/kg body weight, i.p.). The fourth group was given DMTU (500 mg/kg body weight, i.p.), just before the cisplatin injection (10 mg/kg body weight, i.p.), followed by injections of DMTU (125 mg/kg body weight, i.p.) twice a day until they were killed. Animals were killed 72 h after the treatment. Besides not presenting any direct effect on mitochondria, DMTU substantially inhibited cisplatin-induced mitochondrial injury and cellular death by apoptosis, suppressing the occurrence of acute renal failure. All the following cisplatin-induced effects were prevented by DMTU: (1) increased plasmatic levels of creatinine and blood urea nitrogen (BUN); (2) decreased ATP content, calcium uptake and electrochemical potential; (3) oxidation of lipids, including cardiolipin; and oxidation of proteins, including sulfhydryl, and aconitase enzyme, as well as accumulation of carbonyl proteins; (4) depletion of the antioxidant defense (NADPH and GSH) and (5) increased activity of the apoptosis executioner caspase-3. Our findings show the important role played by mitochondria and hydroxyl radicals in cisplatin-induced nephrotoxicity, as well as the effectiveness of DMTU in

  6. A shock tube study of the reactions of the hydroxyl radical with combustion species

    SciTech Connect

    Cohen, N.; Koffend, J.B.

    1993-12-01

    To extend the semi-empirical techniques of Benson and coworkers, and to extend the database of reliable high temperature measurements of OH radicals with hydrocarbons and other fuels and their decomposition products, the authors undertook a research program with both experimental and computational tasks. The experimental goal was to design a procedure for measuring, at combustion temperatures, the reaction rate coefficients of OH radicals with fuels and other species of importance in combustion or propulsion systems. The computational effort was intended to refine the semi-empirical transition-state-theory procedures for extrapolating rate coefficients of reactions of OH with combustion species of interest, for predicting rate coefficients for species not studied in the laboratory, and to examine the ability of the theory to predict rate coefficients for different pathways in the case the reagent possessed more than one nonequivalent H atoms.

  7. Complexes pairing aliphatic amines with hydroxyl and hydroperoxyl radicals: A computational study

    NASA Astrophysics Data System (ADS)

    Solimannejad, Mohammad; Nielsen, Claus J.; Scheiner, Steve

    2008-12-01

    Quantum calculations are used to analyze the nature and strength of binding of complexes pairing aliphatic amines with the HO and HOO radicals, with particular emphasis on the comparison of HO with HOO. Complexes are stabilized by N⋯HO(O) H-bonds involving the N lone pair. The OOH radical binds more strongly in all cases than does OH, and shows a longer stretch of its OH bond, as well as a greater red shift of this bond's stretching frequency. MP2/6-311++G(3df, 3pd) binding energies vary from 28 kJ/mol for CH 3NH 2⋯HO to a maximum of 56 kJ/mol for (CH 3) 2NH⋯HOO. The reliability of a new hybrid meta exchange-correlation functional, M05-2X, compares favorably with MP2, generally better than B3LYP.

  8. LIF diagnostics of hydroxyl radical in a methanol containing atmospheric-pressure plasma jet

    NASA Astrophysics Data System (ADS)

    Qian, Mu-Yang; Liu, San-Qiu; Pei, Xue-Kai; Lu, Xin-Pei; Zhang, Jia-Liang; Wang, De-Zhen

    2016-10-01

    In this paper, a pulsed-dc CH3OH/Ar plasma jet generated at atmospheric pressure is studied by laser-induced fluorescence (LIF) and optical emission spectroscopy (OES). A gas-liquid bubbler system is proposed to introduce the methanol vapor into the argon gas, and the CH3OH/Ar volume ratio is kept constant at about 0.1%. Discharge occurs in a 6-mm needle-to-ring gap in an atmospheric-pressure CH3OH/Ar mixture. The space-resolved distributions of OH LIF inside and outside the nozzle exhibit distinctly different behaviors. And, different production mechanisms of OH radicals in the needle-to-ring discharge gap and afterglow of plasma jet are discussed. Besides, the optical emission lines of carbonaceous species, such as CH, CN, and C2 radicals, are identified in the CH3OH/Ar plasma jet. Finally, the influences of operating parameters (applied voltage magnitude, pulse frequency, pulsewidth) on the OH radical density are also presented and analyzed. Project supported by the National Natural Science Foundation of China (Grant Nos. 11465013 and 11375041), the Natural Science Foundation of Jiangxi Province, China (Grant Nos. 20151BAB212012 and 20161BAB201013), and the International Science and Technology Cooperation Program of China (Grant No. 2015DFA61800).

  9. Volatile organic compound conversion by ozone, hydroxyl radicals, and nitrate radicals in residential indoor air: Magnitudes and impacts of oxidant sources

    PubMed Central

    Waring, Michael S.; Wells, J. Raymond

    2016-01-01

    Indoor chemistry may be initiated by reactions of ozone (O3), the hydroxyl radical (OH), or the nitrate radical (NO3) with volatile organic compounds (VOC). The principal indoor source of O3 is air exchange, while OH and NO3 formation are considered as primarily from O3 reactions with alkenes and nitrogen dioxide (NO2), respectively. Herein, we used time-averaged models for residences to predict O3, OH, and NO3 concentrations and their impacts on conversion of typical residential VOC profiles, within a Monte Carlo framework that varied inputs probabilistically. We accounted for established oxidant sources, as well as explored the importance of two newly realized indoor sources: (i) the photolysis of nitrous acid (HONO) indoors to generate OH and (ii) the reaction of stabilized Criegee intermediates (SCI) with NO2 to generate NO3. We found total VOC conversion to be dominated by reactions both with O3, which almost solely reacted with d-limonene, and also with OH, which reacted with d-limonene, other terpenes, alcohols, aldehydes, and aromatics. VOC oxidation rates increased with air exchange, outdoor O3, NO2 and d-limonene sources, and indoor photolysis rates; and they decreased with O3 deposition and nitric oxide (NO) sources. Photolysis was a strong OH formation mechanism for high NO, NO2, and HONO settings, but SCI/NO2 reactions weakly generated NO3 except for only a few cases. PMID:26855604

  10. Volatile organic compound conversion by ozone, hydroxyl radicals, and nitrate radicals in residential indoor air: Magnitudes and impacts of oxidant sources

    NASA Astrophysics Data System (ADS)

    Waring, Michael S.; Wells, J. Raymond

    2015-04-01

    Indoor chemistry may be initiated by reactions of ozone (O3), the hydroxyl radical (OH), or the nitrate radical (NO3) with volatile organic compounds (VOC). The principal indoor source of O3 is air exchange, while OH and NO3 formation are considered as primarily from O3 reactions with alkenes and nitrogen dioxide (NO2), respectively. Herein, we used time-averaged models for residences to predict O3, OH, and NO3 concentrations and their impacts on conversion of typical residential VOC profiles, within a Monte Carlo framework that varied inputs probabilistically. We accounted for established oxidant sources, as well as explored the importance of two newly realized indoor sources: (i) the photolysis of nitrous acid (HONO) indoors to generate OH and (ii) the reaction of stabilized Criegee intermediates (SCI) with NO2 to generate NO3. We found total VOC conversion to be dominated by reactions both with O3, which almost solely reacted with D-limonene, and also with OH, which reacted with D-limonene, other terpenes, alcohols, aldehydes, and aromatics. VOC oxidation rates increased with air exchange, outdoor O3, NO2 and D-limonene sources, and indoor photolysis rates; and they decreased with O3 deposition and nitric oxide (NO) sources. Photolysis was a strong OH formation mechanism for high NO, NO2, and HONO settings, but SCI/NO2 reactions weakly generated NO3 except for only a few cases.

  11. Photocatalytic activity of Pt-TiO2 films supported on hydroxylated fly ash cenospheres under visible light

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Yang, Zewei; An, Hao; Zhai, Jianping; Li, Qin; Cui, Hao

    2015-01-01

    TiO2 was coated on the surface of hydroxylated fly ash cenospheres (FACs) by the sol-gel method. Platinum (Pt) was then deposited on these TiO2/FAC particles by a photoreduction method to form PTF photocatalyst. The photocatalytic activity of PTF for the degradation of methylene blue (MB) under visible-light irradiation was determined. The PTF sample that was calcined at 450 °C and had a Pt/TiO2 mass ratio of 1.5% exhibited the optimal photocatalytic activity for degradation of MB with a catalyst concentration of 3 g L-1. MB was photodecomposed by PTF in aqueous solution more effectively at alkali pH than at acidic pH, because more MB molecules were adsorbed on the surface of PTF under alkaline conditions than that under acidic. The effect of various inorganic anions (HCO3-, F-, SO42-, NO3-, and Cl-) on the photodegradation of MB by PTF was also investigated. Addition of anions with a concentration of 5 mM enhanced the photocatalytic efficiency of PTF because of the improved adsorption of MB. This effect weakened as the anion concentration was increased, which was attributed to the ability of the anions to scavenge hydroxyl radicals and holes. Our results indicated that the photodegradation of MB took place mainly on the catalyst surface. The generation of hydroxyl radicals in the photocatalytic reaction was measured by the fluorescence method. KI was used to determine the participation of holes in the photocatalytic reaction. Both hydroxyl radicals and valence-band holes were detected in the PTF system. Recycling tests revealed that calcination of the used PTF helped to regain its photocatalytic activity.

  12. Electron spin resonance studies on photosensitized formation of hydroxyl radical by C-phycocyanin from Spirulina platensis.

    PubMed

    Zhang, S; Xie, J; Zhang, J; Zhao, J; Jiang, L

    1999-01-01

    Visible light (>470 nm) irradiation of an oxygen-saturated solution of C-phycocyanin (C-PC) in the presence of the spin trap 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) gave an ESR spectrum characteristic of the DMPO-hydroxyl radical spin adduct DMPO-OH. The signal intensities of DMPO-OH adduct were enhanced by superoxide dismutase (SOD) and partly inhibited by catalase. It was partly responsible for the production of DMPO-OH that superoxide anion radical (O.-2) dismutated to generate hydrogen peroxide (H2O2) which decomposed ultimately to generate the highly reactive .OH. In addition, it can be concluded that singlet oxygen (1O2) was an important intermediate according to the strong inhibitory action of 1,4-diazabicyclo[2.2.2]octane (DABCO) and histidine on DMPO-OH formation. The experimental results suggest that photodynamic action of C-PC proceed via both type I and type II mechanisms. Furthermore, the decay kinetics of DMPO-OH adduct, the effects of DMPO and C-PC concentrations as well as irradiation time on DMPO-OH adduct formation were also discussed. Concentration of C-PC should be an important factor to influence the ESR signal intensities of DMPO-OH. Therefore, it may be concluded that reasonably lower concentration of C-PC might prolong the duration of photosensitized formation of .OH and might strengthen the photodynamic action.

  13. Aircraft-borne, laser-induced fluorescence instrument for the in situ detection of hydroxyl and hydroperoxyl radicals

    NASA Technical Reports Server (NTRS)

    Wennberg, P. O.; Cohen, R. C.; Hazen, N. L.; Lapson, L. B.; Allen, N. T.; Hanisco, T. F.; Oliver, J. F.; Lanham, N. W.; Demusz, J. N.; Anderson, J. G.

    1994-01-01

    The odd-hydrogen radicals OH and HO2 are central to most of the gas-phase chemical transformations that occur in the atmosphere. Of particular interest is the role that these species play in controlling the concentration of stratospheric ozone. This paper describes an instrument that measures both of these species at volume mixing ratios below one part in 10(exp 14) in the upper troposphere and lower stratosphere. The hydroxyl radical (OH) is measured by laser induced fluorescence at 309 nm. Tunable UV light is used to pump OH to the first electric state near 282 nm. the laser light is produced by a high-repetition rate pulsed dye-laser powered with all solid-state pump lasers. HO2 is measured as OH after gas-phase titration with nitric oxide. Measurements aboard a NASA ER-2 aircraft demonstrate the capability of this instrument to perform reliably with very high signal-to-noise ratios (greater than 30) achieved in short integration times (less than 20 sec).

  14. Gas-phase reaction of methyl isothiocyanate and methyl isocyanate with hydroxyl radicals under static relative rate conditions.

    PubMed

    Lu, Zhou; Hebert, Vincent R; Miller, Glenn C

    2014-02-26

    Gaseous methyl isothiocyanate (MITC), the principal breakdown product of the soil fumigant metam sodium (sodium N-methyldithiocarbamate), is an inhalation exposure concern to persons living near treated areas. Inhalation exposure also involves gaseous methyl isocyanate (MIC), a highly reactive and toxic transformation product of MITC. In this work, gas-phase hydroxyl (OH) radical reaction rate constants of MITC and MIC have been determined using a static relative rate technique under controlled laboratory conditions. The rate constants obtained are 15.36 × 10(-12) cm(3) molecule(-1) s(-1) for MITC and 3.62 × 10(-12) cm(3) molecule(-1) s(-1) for MIC. The average half-lives of MITC and MIC in the atmosphere are estimated to be 15.7 and 66.5 h, respectively. The molar conversion of MITC to MIC for OH radical reactions is 67% ± 8%, which indicates that MIC is the primary product of the MITC-OH reaction in the gas phase.

  15. Fingerprinting of polysaccharides attacked by hydroxyl radicals in vitro and in the cell walls of ripening pear fruit.

    PubMed Central

    Fry, S C; Dumville, J C; Miller, J G

    2001-01-01

    Hydroxyl radicals (*OH) may cause non-enzymic scission of polysaccharides in vivo, e.g. in plant cell walls and mammalian connective tissues. To provide a method for detecting the action of endogenous *OH in vivo, we investigated the products formed when polysaccharides were treated with *OH (generated in situ by ascorbate-H(2)O(2)-Cu(2+) mixtures) followed by NaB(3)H(4). Treatment with *OH increased the number of NaB(3)H(4)-reacting groups present in citrus pectin, homogalacturonan and tamarind xyloglucan. This increase is attributed partly to the formation of glycosulose and glycosulosuronic acid residues, which are then reduced back to the original (but radioactive) sugar residues and their epimers by NaB(3)H(4). The glycosulose and glycosulosuronic acid residues were stable for >16 h at 20 degrees C in ethanol or buffer (pH 4.7), but were destroyed in alkali. Driselase-digestion of the radiolabelled polysaccharides yielded characteristic patterns of (3)H-products, which included galactose and galacturonate from pectin, and isoprimeverose, galactose, glucose and arabinose from xyloglucan. Pectin yielded at least eight (3)H-labelled anionic products, separable by electrophoresis at pH 3.5. The patterns of radioactive products form useful 'fingerprints' by which *OH-attacked polysaccharides may be recognized. Applied to the cell walls of ripening pear (Pyrus communis) fruit, the method gave evidence for progressive *OH radical attack on polysaccharides during the softening process. PMID:11463343

  16. Neutral and acidic products derived from hydroxyl radical-induced oxidation of arabinotriose assessed by electrospray ionisation mass spectrometry.

    PubMed

    Moreira, Ana S P; da Costa, Elisabete V; Evtuguin, Dmitry V; Coimbra, Manuel A; Nunes, Fernando M; Domingues, M Rosário M

    2014-04-01

    The oxidation of α-(1 → 5)-L-arabinotriose (Ara3), an oligosaccharide structurally related to side chains of coffee arabinogalactans, was studied in reaction with hydroxyl radicals generated under conditions of Fenton reaction (Fe(2+)/H2O2). The acidic and neutral oxidation products were separated by ligand exchange/size-exclusion chromatography, subsequently identified by electrospray ionisation mass spectrometry (ESI-MS) and structurally characterised by tandem MS (ESI-MS/MS). In acidic fraction were identified several oxidation products containing an acidic residue at the corresponding reducing end of Ara3, namely arabinonic acid, and erythronic, glyceric and glycolic acids formed by oxidative scission of the furanose ring. In neutral fractions were identified derivatives containing keto, hydroxy and hydroperoxy moieties, as well as derivatives resulting from the ring scission at the reducing end of Ara3. In both acidic and neutral fractions, beyond the trisaccharide derivatives, the corresponding di- and monosaccharide derivatives were identified indicating the occurrence of oxidative depolymerisation. The structural characterisation of these oxidation products by ESI-MS/MS allowed the differentiation of isobaric and isomeric species of acidic and neutral character. The species identified in this study may help in detection of roasting products associated with the free radical-mediated oxidation of coffee arabinogalactans.

  17. CHEMISTRY OF FOG WATERS IN CALIFORNIA'S CENTRAL VALLEY: 1. IN SITU PHOTOFORMATION OF HYDROXYL RADICAL AND SINGLET MOLECULAR OXYGEN. (R825433)

    EPA Science Inventory

    The aqueous-phase photoformation of hydroxyl radical (characterOH) and singlet molecular oxygen (O2(1Δg) or 1O*

  18. Method of making a membrane having hydrophilic and hydrophobic surfaces for adhering cells or antibodies by using atomic oxygen or hydroxyl radicals

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L. (Inventor); Spaulding, Glenn F. (Inventor)

    1994-01-01

    A portion of an organic polymer article such as a membrane is made hydrophilic by exposing a hydrophobic surface of the article to a depth of about 50 to about 5000 angstroms to atomic oxygen or hydroxyl radicals at a temperature below 100C., preferably below 40 C, to form a hydrophilic uniform surface layer of hydrophilic hydroxyl groups. The atomic oxygen and hydroxyl radicals are generated by a flowing afterglow microwave discharge, and the surface is outside of a plasma produced by the discharge. A membrane having both hydrophilic and hydrophobic surfaces can be used in an immunoassay by adhering antibodies to the hydrophobic surface. In another embodiment, the membrane is used in cell culturing where cells adhere to the hydrophilic surface. Prior to adhering cells, the hydrophilic surface may be grafted with a compatibilizing compound. A plurality of hydrophilic regions bounded by adjacent hydrophobic regions can be produced such that a maximum of one cell per each hydrophilic region adheres.

  19. Nitrones are able to release nitric oxide in aqueous environment under hydroxyl free radical attack.

    PubMed

    Croitoru, Mircea Dumitru; Ibolya, Fülöp; Pop, Maria Cristiana; Dergez, Timea; Mitroi, Brânduşa; Dogaru, Maria Titica; Tokés, Béla

    2011-10-30

    Importance of a nitric oxide donor that can act as a spin trap might bring some new therapeutic possibilities regarding the treatment of ischemic diseases by reducing the intensity of free radical produced reperfusion lesions. These substances might be also used as a new type of photo protectors since they can absorb UV radiation, capture free radicals formed by interaction of UV radiation with tissue constituents, and tanning of the skin will be permitted due to nitric oxide release. The purpose of this work was to measure the ability of nitrones to release nitric oxide and how different factors (temperature, nitrone concentration, and free radicals) influence the releasing ability. Mostly, indirect determination of nitric oxide was carried out, by measuring nitrite and nitrate amounts (as decomposition products of nitric oxide), all nitrones proved to release significant amounts of nitric oxide. Nitrite measurements were made based on an HPLC-VIS method that uses pre-column derivatization of nitrite by forming an azo dye (limit of quantification: 5ng/ml). No good correlation was found between the amount of nitric oxide and temperature for most studied nitrones but between the formation of nitric oxide and nitrone concentration an asymptotic correlation was found. Fenton reagent also yielded formation of nitric oxide from nitrones and formed amounts were not different from those recorded for UV irradiation. Most of the nitrones effectively released about 0.5% of the maximum amount of nitric oxide that is chemically possible and estimated concentrations of 0.1μM were present in the solutions during decomposition.

  20. Nitrones are able to release nitric oxide in aqueous environment under hydroxyl free radical attack.

    PubMed

    Croitoru, Mircea Dumitru; Ibolya, Fülöp; Pop, Maria Cristiana; Dergez, Timea; Mitroi, Brânduşa; Dogaru, Maria Titica; Tokés, Béla

    2011-10-30

    Importance of a nitric oxide donor that can act as a spin trap might bring some new therapeutic possibilities regarding the treatment of ischemic diseases by reducing the intensity of free radical produced reperfusion lesions. These substances might be also used as a new type of photo protectors since they can absorb UV radiation, capture free radicals formed by interaction of UV radiation with tissue constituents, and tanning of the skin will be permitted due to nitric oxide release. The purpose of this work was to measure the ability of nitrones to release nitric oxide and how different factors (temperature, nitrone concentration, and free radicals) influence the releasing ability. Mostly, indirect determination of nitric oxide was carried out, by measuring nitrite and nitrate amounts (as decomposition products of nitric oxide), all nitrones proved to release significant amounts of nitric oxide. Nitrite measurements were made based on an HPLC-VIS method that uses pre-column derivatization of nitrite by forming an azo dye (limit of quantification: 5ng/ml). No good correlation was found between the amount of nitric oxide and temperature for most studied nitrones but between the formation of nitric oxide and nitrone concentration an asymptotic correlation was found. Fenton reagent also yielded formation of nitric oxide from nitrones and formed amounts were not different from those recorded for UV irradiation. Most of the nitrones effectively released about 0.5% of the maximum amount of nitric oxide that is chemically possible and estimated concentrations of 0.1μM were present in the solutions during decomposition. PMID:21645628

  1. Gas-Phase Reaction of Hydroxyl Radical with p-Cymene over an Extended Temperature Range.

    PubMed

    Bedjanian, Yuri; Morin, Julien; Romanias, Manolis N

    2015-11-12

    The kinetics of the reaction of OH radicals with p-cymene has been studied in the temperature range of 243-898 K using a flow reactor combined with a quadrupole mass spectrometer: OH + p-cymene → products. The reaction rate constant was determined as a result of absolute measurements, from OH decay kinetics in excess of p-cymene and employing the relative rate method with OH reactions with n-pentane, n-heptane,1,3-dioxane, HBr, and Br2 as the reference ones. For the rate coefficient of the H atom abstraction channel, the expression k1b = (3.70 ± 0.42) × 10(-11) exp[-(772 ± 72)/T] was obtained over the temperature range of 381-898 K. The total rate constant (addition + abstraction) determined at T = 243-320 K was k1 = (1.82 ± 0.48) × 10(-12) exp[(607 ± 70)/T] or, in a biexponential form, k1 = k1a + k1b = 3.7 × 10(-11) exp(-772/T) + 6.3 × 10(-13) exp(856/T), independent of the pressure between 1 and 5 Torr of helium. In addition, our results indicate that the reaction pathway involving alkyl radical elimination upon initial addition of OH to p-cymene is most probably unimportant. PMID:26473634

  2. Gas-Phase Reaction of Hydroxyl Radical with p-Cymene over an Extended Temperature Range.

    PubMed

    Bedjanian, Yuri; Morin, Julien; Romanias, Manolis N

    2015-11-12

    The kinetics of the reaction of OH radicals with p-cymene has been studied in the temperature range of 243-898 K using a flow reactor combined with a quadrupole mass spectrometer: OH + p-cymene → products. The reaction rate constant was determined as a result of absolute measurements, from OH decay kinetics in excess of p-cymene and employing the relative rate method with OH reactions with n-pentane, n-heptane,1,3-dioxane, HBr, and Br2 as the reference ones. For the rate coefficient of the H atom abstraction channel, the expression k1b = (3.70 ± 0.42) × 10(-11) exp[-(772 ± 72)/T] was obtained over the temperature range of 381-898 K. The total rate constant (addition + abstraction) determined at T = 243-320 K was k1 = (1.82 ± 0.48) × 10(-12) exp[(607 ± 70)/T] or, in a biexponential form, k1 = k1a + k1b = 3.7 × 10(-11) exp(-772/T) + 6.3 × 10(-13) exp(856/T), independent of the pressure between 1 and 5 Torr of helium. In addition, our results indicate that the reaction pathway involving alkyl radical elimination upon initial addition of OH to p-cymene is most probably unimportant.

  3. Manganese Catalysts for C–H activation: An Experimental/Theoretical Study Identifies the Stereoelectronic Factor that Controls the Switch between Hydroxylation and Desaturation Pathways

    PubMed Central

    Hull, Jonathan F.; Balcells, David; Sauer, Effiette L. O.; Raynaud, Christophe; Brudvig, Gary W.; Crabtree, Robert H.; Eisenstein, Odile

    2010-01-01

    We describe competitive C–H activation chemistry of two types, desaturation and hydroxylation, using synthetic manganese catalysts with several substrates. 9,10-dihydrophenanthrene (DHP) gives the highest desaturation activity, the final products being phenanthrene (P1) and phenanthrene-9,10-oxide (P3), the latter being thought to arise from epoxidation of some of the phenanthrene. The hydroxylase pathway also occurs as suggested by the presence of the dione product, phenanthrene-9,10-dione (P2), thought to arise from further oxidation of hydroxylation intermediate 9-hydroxy-9,10-dihydrophenanthrene. The experimental work together with the DFT calculations shows that the postulated Mn oxo active species, [Mn(O)(tpp)(Cl)] (tpp = tetraphenyl porphyrin), can promote the oxidation of dihydrophenanthrene by either desaturation or hydroxylation pathways. The calculations show that these two competing reactions have a common initial step – radical H abstraction from one of the DHP sp3 C–H bonds. The resulting Mn hydroxo intermediate is capable of promoting not only OH rebound (hydroxylation) but also a second H abstraction adjacent to the first (desaturation). Like the active MnV=O species, this MnIV-OH species also has radical character on oxygen and can thus give H abstraction. Both steps have very low and therefore very similar energy barriers, leading to a product mixture. Since the radical character of the catalyst is located on the oxygen p orbital perpendicular to the MnIV-OH plane, the orientation of the organic radical with respect to this plane determines which reaction, desaturation or hydroxylation, will occur. Stereoelectronic factors such as the rotational orientation of the OH in the enzyme active site is thus likely to constitute the switch between hydroxylation and desaturation behavior. PMID:20481432

  4. Quantitative analysis of the kinetic constant of the reaction of N,N'-propylenedinicotinamide with the hydroxyl radical using dimethyl sulfoxide and deduction of its structure in chloroform.

    PubMed

    Akimoto, T

    2000-04-01

    N,N'-Propylenedinicotinamide (Nicaraven) is presently being developed for the treatment of cerebral stroke including subarachnoid hemorrhage. This drug is promising because some data suggest it to have an ability to scavenge the hydroxyl radical under physiological conditions in vivo, while it also has a high permeability through the blood brain barrier. Using the kinetic constant of the reaction between the hydroxyl radical and dimethyl sulfoxide, the formula derived by Babbs and Griffin (Free Rad. Biol. Med., 6 1989) was applied to obtain the kinetic constant of Nicaraven with the hydroxyl radical using a dimethyl sulfoxide-xanthine oxidase-hypoxanthine-Fe system, and this yielded the kinetic constant 3.4x10(9) M(-1) s(-1) (1 M=1 mol dm(-3)) for Nicaraven. Structurally related compounds were also investigated. The amide group of Nicaraven was thus found to play an important part in the reaction with the hydroxyl radical. Methanesulfinic acid, which was obtained from the reaction between dimethyl sulfoxide and the hydroxyl radical, was found to be stable under this adopted experimental condition and therefore was used to quantify the kinetic constant of Nicaraven. The structure of Nicaraven has also been investigated in CDCl3 using IR spectra, computer calculations and 1H-NMR analysis, and Nicaraven was thus shown to have an intramolecular hydrogen bond which forms a 7-membered ring that resembles a part of the 1H-1,4-benzodiazepines. This structure may play an important role in the penetration through the blood brain barrier.

  5. Effect of adenosine A(2A) receptor antagonists and L-DOPA on hydroxyl radical, glutamate and dopamine in the striatum of 6-OHDA-treated rats.

    PubMed

    Gołembiowska, Krystyna; Dziubina, Anna

    2012-02-01

    A(2A) adenosine receptor antagonists have been proposed as a new therapy of PD. Since oxidative stress plays an important role in the pathogenesis of PD, we studied the effect of the selective A(2A) adenosine receptor antagonists 8-(-3-chlorostyryl)caffeine (CSC) and 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385) on hydroxyl radical generation, and glutamate (GLU) and dopamine (DA) extracellular level using a microdialysis in the striatum of 6-OHDA-treated rats. CSC (1 mg/kg) and ZM 241385 (3 mg/kg) given repeatedly for 14 days decreased the production of hydroxyl radical and extracellular GLU level, both enhanced by prior 6-OHDA treatment in dialysates from the rat striatum. CSC and ZM 241385 did not affect DA and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA) extracellular levels in the striatum of 6-OHDA-treated rats. L-DOPA (6 mg/kg) given twice daily for two weeks in the presence of benserazide (3 mg/kg) decreased striatal hydroxyl radical and glutamate extracellular level in 6-OHDA-treated rats. At the same time, L-DOPA slightly but significantly increased the extracellular levels of DOPAC and HVA. A combined repeated administration of L-DOPA and CSC or ZM 241385 did not change the effect of L-DOPA on hydroxyl radical production and glutamate extracellular level in spite of an enhancement of extracellular DA level by CSC and elevation of extracellular level of DOPAC and HVA by ZM 241385. The data suggest that the 6-OHDA-induced damage of nigrostriatal DA-terminals is related to oxidative stress and excessive release of glutamate. Administration of L-DOPA in combination with CSC or ZM 241385, by restoring striatal DA-glutamate balance, suppressed 6-OHDA-induced overproduction of hydroxyl radical.

  6. Interaction of the Pseudomonas aeruginosa secretory products pyocyanin and pyochelin generates hydroxyl radical and causes synergistic damage to endothelial cells. Implications for Pseudomonas-associated tissue injury.

    PubMed Central

    Britigan, B E; Roeder, T L; Rasmussen, G T; Shasby, D M; McCormick, M L; Cox, C D

    1992-01-01

    Pyocyanin, a secretory product of Pseudomonas aeruginosa, has the capacity to undergo redox cycling under aerobic conditions with resulting generation of superoxide and hydrogen peroxide. By using spin trapping techniques in conjunction with electron paramagnetic resonance spectrometry (EPR), superoxide was detected during the aerobic reduction of pyocyanin by NADH or porcine endothelial cells. No evidence of hydroxyl radical formation was detected. Chromium oxalate eliminated the EPR spectrum of the superoxide-derived spin adduct resulting from endothelial cell exposure to pyocyanin, suggesting superoxide formation close to the endothelial cell plasma membrane. We have previously reported that iron bound to the P. aeruginosa siderophore pyochelin (ferripyochelin) catalyzes the formation of hydroxyl free radical from superoxide and hydrogen peroxide via the Haber-Weiss reaction. In the present study, spin trap evidence of hydroxyl radical formation was detected when NADH and pyocyanin were allowed to react in the presence of ferripyochelin. Similarly, endothelial cell exposure to pyocyanin and ferripyochelin also resulted in hydroxyl radical production which appeared to occur in close proximity to the cell surface. As assessed by 51Cr release, endothelial cells which were treated with pyocyanin or ferripyochelin alone demonstrated minimal injury. However, endothelial cell exposure to the combination of pyochelin and pyocyanin resulted in 55% specific 51Cr release. Injury was not observed with the substitution of iron-free pyochelin and was diminished by the presence of catalase or dimethyl thiourea. These data suggest the possibility that the P. aeruginosa secretory products pyocyanin and pyochelin may act synergistically via the generation of hydroxyl radical to damage local tissues at sites of pseudomonas infection. PMID:1469082

  7. The kinetics and mechanism of an aqueous phase isoprene reaction with hydroxyl radical

    NASA Astrophysics Data System (ADS)

    Huang, D.; Zhang, X.; Chen, Z. M.; Zhao, Y.; Shen, X. L.

    2011-08-01

    Aqueous phase chemical processes of organic compounds in the atmosphere have received increasing attention, partly due to their potential contribution to the formation of secondary organic aerosol (SOA). Here, we analyzed the aqueous OH-initiated oxidation of isoprene and its reaction products including carbonyl compounds and organic acids, regarding the acidity and temperature as in-cloudy conditions. We also performed a laboratory simulation to improve our understanding of the kinetics and mechanisms for the products of aqueous isoprene oxidation that are significant precursors of SOA; these included methacrolein (MACR), methyl vinyl ketone (MVK), methyl glyoxal (MG), and glyoxal (GL). We used a novel chemical titration method to monitor the concentration of isoprene in the aqueous phase. We used a box model to interpret the mechanistic differences between aqueous and gas phase OH radical-initiated isoprene oxidations. Our results were the first demonstration of the rate constant for the reaction between isoprene and OH radical in water, 1.2 ± 0.4) × 1010 M-1 s-1 at 283 K. Molar yields were determined based on consumed isoprene. Of note, the ratio of the yields of MVK (24.1 ± 0.8 %) to MACR (10.9 ± 1.1%) in the aqueous phase isoprene oxidation was approximately double that observed for the corresponding gas phase reaction. We hypothesized that this might be explained by a water-induced enhancement in the self-reaction of a hydroxy isoprene peroxyl radical (HOCH2C(CH3)(O2)CH = CH2) produced in the aqueous reaction. The observed yields for MG and GL were 11.4 ± 0.3 % and 3.8 ± 0.1 %, respectively. Model simulations indicated that several potential pathways may contribute to the formation of MG and GL. Finally, oxalic acid increased steadily throughout the course of the study, even after isoprene was consumed completely. The observed yield of oxalic acid was 26.2 ± 0.8 % at 6 h. The observed carbon balance accounted for ~50 % of the consumed isoprene. The

  8. A DFT Study Toward the Reaction Mechanisms of TNT With Hydroxyl Radicals for Advanced Oxidation Processes.

    PubMed

    He, Xi; Zeng, Qun; Zhou, Yang; Zeng, Qingxuan; Wei, Xianfeng; Zhang, Chaoyang

    2016-05-26

    The degradation pathway of environmental contaminant 2,4,6-trinitrotoluene (TNT) was investigated computationally at the SMD(Pauling)/M06-2X/6-311+G(d,p) level of theory. The dominant decomposition pathway of TNT → 4,6-dinitro-o-cresol → 4,6-dinitro-2-hydroxybenzylalcohol → 4,6-dinitro-2-hydroxybenzaldehyde was provided, and the corresponding predicted products and their distributions are in a good agreement with available experimental data on TNT degradation by Fenton reaction. It was shown that the mechanism of addition-elimination is crucial for this stage of the reaction. The reaction of H atom abstraction is a minor competing pathway. The details on transition states, intermediate radicals, and free energy surfaces for all proposed reactions are given and make up for a lack of experimental knowledge. PMID:27135259

  9. Formation of hydroxyl radicals from photolysis of secondary organic aerosol material

    NASA Astrophysics Data System (ADS)

    Badali, K. M.; Zhou, S.; Aljawhary, D.; Antiñolo, M.; Chen, W. J.; Lok, A.; Mungall, E.; Wong, J. P. S.; Zhao, R.; Abbatt, J. P. D.

    2015-02-01

    This paper demonstrates that OH radicals are formed by photolysis of secondary organic aerosol (SOA) material formed by terpene ozonolysis. The SOA aerosol is collected on filters, dissolved in water containing a radical trap (benzoic acid), and then exposed to ultraviolet light in a photochemical reactor. The OH formation rates, which are similar for both α-pinene and limonene SOA, are measured from the formation rate of p-hydroxybenzoic acid as measured using offline HPLC analysis. To evaluate whether the OH is formed by photolysis of H2O2 or organic hydroperoxides (ROOH), the peroxide content of the SOA was measured using the horseradish peroxidase-dichlorofluorescein (HRP-DCF) assay, which was calibrated using H2O2. The OH formation rates from SOA are five times faster than from the photolysis of H2O2 solutions whose concentrations correspond to the peroxide content of the SOA solutions assuming that the HRP-DCF signal arises from H2O2 alone. The higher rates of OH formation from SOA are likely due to ROOH photolysis. This result is substantiated by photolysis experiments conducted with t-butyl hydroperoxide and cumene hydroperoxide which produce over three times more OH than photolysis of equivalent concentrations of H2O2. Relative to the peroxide level in the SOA, the quantum yield for OH generation from α-pinene SOA is 0.8 ± 0.4. This is the first demonstration of an efficient photolytic source of OH in SOA, one that may affect both cloudwater and aerosol chemistry.

  10. Formation of hydroxyl radicals from photolysis of secondary organic aerosol material

    NASA Astrophysics Data System (ADS)

    Badali, K. M.; Zhou, S.; Aljawhary, D.; Antiñolo, M.; Chen, W. J.; Lok, A.; Mungall, E.; Wong, J. P. S.; Zhao, R.; Abbatt, J. P. D.

    2015-07-01

    This paper demonstrates that OH radicals are formed by photolysis of secondary organic aerosol (SOA) material formed by terpene ozonolysis. The SOA is collected on filters, dissolved in water containing a radical trap (benzoic acid), and then exposed to ultraviolet light in a photochemical reactor. The OH formation rates, which are similar for both α-pinene and limonene SOA, are measured from the formation rate of p-hydroxybenzoic acid as measured using offline HPLC analysis. To evaluate whether the OH is formed by photolysis of H2O2 or organic hydroperoxides (ROOH), the peroxide content of the SOA was measured using the horseradish peroxidase-dichlorofluorescein (HRP-DCF) assay, which was calibrated using H2O2. The OH formation rates from SOA are 5 times faster than from the photolysis of H2O2 solutions whose concentrations correspond to the peroxide content of the SOA solutions, assuming that the HRP-DCF signal arises from H2O2 alone. The higher rates of OH formation from SOA are likely due to ROOH photolysis, but we cannot rule out a contribution from secondary processes as well. This result is substantiated by photolysis experiments conducted with t-butyl hydroperoxide and cumene hydroperoxide which produce over 3 times more OH than photolysis of equivalent concentrations of H2O2. Relative to the peroxide level in the SOA and assuming that the peroxides drive most of the ultraviolet absorption, the quantum yield for OH generation from α-pinene SOA is 0.8 ± 0.4. This is the first demonstration of an efficient photolytic source of OH in SOA, one that may affect both cloud water and aerosol chemistry.

  11. Evaluation of hydroxyl radical-scavenging abilities of silica hydride, an antioxidant compound, by a Fe2+-EDTA-induced 2-hydroxyterephthalate fluorometric analysis.

    PubMed

    Stephanson, Cory J; Stephanson, Anne M; Flanagan, G Patrick

    2003-01-01

    The hydroxyl radical scavenging capacity and efficacy of a novel organosiliceous anionic hydride compound, silica hydride, were quantified by a recently developed method. The method measures a direct relationship between the hydroxyl radical scavenging capability of the antioxidant compound and the linear decrease in signal from a fluorescent 2-hydroxyterephthalate product created by reacting an Fe(2+)-EDTA complex in the presence of a potential radical scavenger. A fluorescence signal half-inhibition, IC(50), value of 1.4 +/- 0.1 muM was obtained for silica hydride compounds. The validity of the analysis was verified by electron spin resonance spectroscopy, spectrophotometric analysis of NAD(+)/NADH ratios, mitochondrial membrane potential measurements, and assays of both cytochrome c (Fe(3+)) to cytochrome c (Fe(2+)) and epinephrine to adenochrome reductions.

  12. Stimulatory effects of hydroxyl radical generation by Ga-Al-As laser irradiation on mineralization ability of human dental pulp cells.

    PubMed

    Matsui, Satoshi; Tsujimoto, Yasuhisa; Matsushima, Kiyoshi

    2007-01-01

    The present study was conducted to investigate the effects of Ga-Al-As laser irradiation on the mineralization ability of human dental pulp (HDP) cells. HDP cells in vitro were irradiated once with a Ga-AL-As laser at 0.5 W for 500 s and at 1.0 W for 500 s in order to investigate free radicals as one mechanism for transmission of laser photochemical energy to cells. Production of the hydroxyl radical (*OH) was measured using the ESR spin-trapping method and was found to be increased by laser irradiation. The DMPO-OH was not detected in the presence of dimethyl sulfoxide (DMSO), a *OH scavenger. The formation of calcification nodule was also investigated by von Kossa staining. The number of calcified nodules was increased by 1.0 W-laser irradiation. Alkaline phosphatase (ALP) activity was higher in the 1.0 W-laser irradiation group. Expression of mRNAs for heat shock protein 27, bone morphogenetic proteins (BMPs) and ALP were greater in the 1.0 W-laser irradiation group. Expression of BMPs in the conditioned medium was also higher in the 1.0 W-laser irradiation group. In particular, DMSO decreased the number of calcified nodule produced by 1.0 W-laser irradiation. These results supposed that the mineralization of HDP cells is stimulated by laser irradiation, and that *OH generated by laser irradiation is a trigger for promotion of HDP cell mineralization.

  13. Thermochemistry of Aqueous Hydroxyl Radical from Advances in Photoacoustic Calorimetry and ab Initio Continum Solvation Theory

    SciTech Connect

    Autrey, Thomas; Brown, Aaron K.; Camaioni, Donald M.; Dupuis, Michel; Foster, Nancy S.; Getty, April D.

    2004-03-31

    Photoacoustic signals from dilute ({approx}30 mM) solutions of H{sub 2}O{sub 2} were measured over the temperature range from 10-45 C to obtain the reaction enthalpy and volume change for H{sub 2}O{sub 2}(aq) {yields} 2 OH(aq) from which we ultimately determined {Delta}{sub f}G{sup o}, {Delta}{sub f}H{sup o} and partial molal volume, v{sup o}, of OH (aq). We find {Delta}{sub r}H = 46.8 {+-} 1.4 kcal/mol, which is 4 kcal/mol smaller than the gas phase bond energy, and {Delta}V{sub r} = 6.5 {+-} 0.4 mL/mol. The v{sup o} for OH in water is 14.4 {+-} 0.4 mL/ml: smaller than the v{sup o} of water. Using ab initio continuum theory, the hydration free energy is calculated to be -3.9 {+-} 0.3 kcal/mol (for standard states in number density concentration units) by a novel approach devised to capture in the definition of the solute cavity the strength and specific interactions of the solute with a water solvent molecule. The shape of the cavity is defined by ''rolling'' a 3 dimensional electron density isocontour of water on the ab initio water-OH minimum interaction surface. The value of the contour is selected to reproduce the volume of OH in water. We obtain for OH(aq): {Delta}{sub f}H{sup o} = -0.2 {+-} 1.4 and {Delta}{sub f}G{sup o} = 5.8 {+-} 0.4 kcal/mol that are in agreement with literature values. The results provide confidence in the pulsed PAC technique for measuring aqueous thermochemistry of radicals and open the way to obtaining thermochemistry for most radicals that can be formed by reaction of OH with aqueous substrates while advancing the field of continuum solvation theory towards ab initio-defined solute cavities.

  14. Saturated fluorescence measurements of the hydroxyl radical in laminar high-pressure flames

    NASA Technical Reports Server (NTRS)

    Carter, Campbell D.; King, Galen B.; Laurendeau, Normand M.

    1990-01-01

    The efficacy of laser saturated fluorescence (LSF) for OH concentration measurements in high pressure flames was studied theoretically and experimentally. Using a numerical model describing the interaction of hydroxyl with nonuniform laser excitation, the effect of pressure on the validity of the balanced cross-rate model was studied along with the sensitivity of the depopulation of the laser-coupled levels to the ratio of rate coefficients describing: (1) electronic quenching to (sup 2) Sigma (+) (v double prime greater than 0), and (2) vibrational relaxation from v double prime greater than 0 to v double prime = 0. At sufficiently high pressures and near-saturated conditions, the total population of the laser-coupled levels reaches an asymptotic value, which is insensitive to the degree of saturation. When the ratio of electronic quenching to vibrational relaxation is small and the rate of coefficients for rotational transfer in the ground and excited electronic states are nearly the same, the balanced cross-rate model remains a good approximation for all pressures. When the above ratio is large, depopulation of the laser-coupled levels becomes significant at high pressures, and thus the balanced cross-rate model no longer holds. Under these conditions, however, knowledge of the depletion of the laser-coupled levels can be used to correct the model. A combustion facility for operation up to 20 atm was developed to allow LSF measurements of OH in high pressure flames. Using this facility, partial saturation in laminar high pressure (less than or equal to 12.3 atm) C2H6/O2/N2 flames was achieved. To evaluate the limits of the balanced cross-rate model, absorption and calibrated LSF measurements at 3.1 and 6.1 atm were compared. The fluorescence voltages were calibrated with absorption measurements in an atmospheric flame and corrected for their finite sensitivity to quenching with: (1) estimated quenching rate coefficients, and (2) an in situ measurement from a

  15. Hydroxyl radical recycling in isoprene oxidation driven by hydrogen bonding and hydrogen tunneling: the upgraded LIM1 mechanism.

    PubMed

    Peeters, Jozef; Müller, Jean-François; Stavrakou, Trissevgeni; Nguyen, Vinh Son

    2014-09-25

    The Leuven isoprene mechanism, proposed earlier to aid in rationalizing the unexpectedly high hydroxyl radical (OH) concentrations in isoprene-rich, low-nitric-oxide (NO) regions ( Peeters ; et al. Phys. Chem. Chem. Phys . 2009 , 11 , 5935 ), is presented in an upgraded and extended version, LIM1. The kinetics of the crucial reactions in the proposed isoprene-peroxy radical interconversion and isomerization pathways are re-evaluated theoretically, on the basis of energy barriers computed at the much higher CCSD(T)/aug-cc-pVTZ//QCISD/6-311G(d,p) level of theory, and using multiconformer partition functions obtained at the M06-2X/6-311++G(3df,2p) level that, different from the B3LYP level used in our earlier work, accounts for the crucial London dispersion effects in the H-bonded systems involved. The steady-state fraction of the specific Z-δ-OH-peroxy radical isomers/conformers that can isomerize by a 1,6-H shift is shown to be largely governed by hydrogen-bond strengths, whereas their isomerization itself is found to occur quasi-exclusively by hydrogen atom tunneling. The isomer-specific Z-δ-OH-peroxy 1,6-H-shift rate coefficients are predicted to be of the order of 1 s(-1) at 298 K, but the experimentally accessible bulk rate coefficients, which have to be clearly distinguished from the former, are 2 orders of magnitude lower due to the very low Z-δ-OH-peroxy steady-state fractions that are only around or below 0.01 at low to moderate NO and depend on the peroxy lifetime. Two pathways subsequent to the peroxy radical 1,6-H shift are identified, the earlier predicted route yielding the photolabile hydroperoxy-methylbutenals (HPALDs), and a second, about equally important path, to dihydroperoxy-carbonyl peroxy radicals (di-HPCARP). Taking this into account, our predicted bulk peroxy isomerization rate coefficients are about a factor 1.8 higher than the available experimental results for HPALD production ( Crounse ; et al. Phys. Chem. Chem. Phys. 2011 , 13 , 13607

  16. Velocity distributions of hydrogen atoms and hydroxyl radicals produced through solar photodissociation of water

    NASA Technical Reports Server (NTRS)

    Wu, C. Y. R.; Chen, F. Z.

    1993-01-01

    The velocity distributions of H and OH fragments produced through solar photodissociation of gaseous H2O molecules under collisionless conditions are presented. The calculations are carried out using: the most recently available absolute partial cross sections for the production of H and OH through photodissociation of H2O from its absorption onset at 1860 A down to 500 A; the newly available vibrational and rotational energy distributions of both the excited and ground state OH photofragments; the calculated cross sections for the total dissociation processes; and the integrated solar flux in 10 A increments from 500 to 1860 A in the continuum regions and the specific wavelength and flux at the bright solar lines. The calculated results show that the H atoms and the OH radicals produced exhibit multiple velocity groups. Since most current cometary modeling uses a single velocity of 20 km/sec associated with the photodissociation of H2O, the present results may be useful in interpreting the many peaks observed in the velocity distributions of the H Lyman alpha and H alpha of comets.

  17. Hydroxyl radical and thermal annealing on amorphous InGaZnO4 films for DNA immobilizations.

    PubMed

    Sun, Dali; Yamahara, Hiroyasu; Nakane, Ryosho; Matsui, Hiroaki; Tabata, Hitoshi

    2015-06-01

    The effect of hydroxyl radicals (OH) and thermal annealing on an amorphous InGaZnO4 (aIGZO) film surface was investigated for manipulation of DNA immobilization. X-ray photoemission and fluorescence measurements were conducted to reveal the status of surface OH coverage and DNA immobilization, respectively. Systematic examinations concerning OH termination on the film surface suggested that the surface coverage of OH leveling DNA immobilization was related to the local surface potential. Furthermore, OH affinity on the aIGZO film surface was sensitive to thermal annealing. A remarkable change in surface OH coverage was observed for the film surface annealed at high temperature. This behavior was framed by a structural change from amorphous to crystalline state, which regulated DNA immobilization. These results indicate that the OH affinity on aIGZO films is dependent on structural properties such as defects. This study suggests that an amorphous structure is critical for obtaining a high OH surface coverage governing DNA immobilization, and is hence more suitable for biosensing. PMID:25935561

  18. Oxidative damage of U937 human leukemic cells caused by hydroxyl radical results in singlet oxygen formation.

    PubMed

    Rác, Marek; Křupka, Michal; Binder, Svatopluk; Sedlářová, Michaela; Matušková, Zuzana; Raška, Milan; Pospíšil, Pavel

    2015-01-01

    The exposure of human cells to oxidative stress leads to the oxidation of biomolecules such as lipids, proteins and nuclei acids. In this study, the oxidation of lipids, proteins and DNA was studied after the addition of hydrogen peroxide and Fenton reagent to cell suspension containing human leukemic monocyte lymphoma cell line U937. EPR spin-trapping data showed that the addition of hydrogen peroxide to the cell suspension formed hydroxyl radical via Fenton reaction mediated by endogenous metals. The malondialdehyde HPLC analysis showed no lipid peroxidation after the addition of hydrogen peroxide, whereas the Fenton reagent caused significant lipid peroxidation. The formation of protein carbonyls monitored by dot blot immunoassay and the DNA fragmentation measured by comet assay occurred after the addition of both hydrogen peroxide and Fenton reagent. Oxidative damage of biomolecules leads to the formation of singlet oxygen as conformed by EPR spin-trapping spectroscopy and the green fluorescence of singlet oxygen sensor green detected by confocal laser scanning microscopy. It is proposed here that singlet oxygen is formed by the decomposition of high-energy intermediates such as dioxetane or tetroxide formed by oxidative damage of biomolecules.

  19. Hydroxyl radical and thermal annealing on amorphous InGaZnO4 films for DNA immobilizations.

    PubMed

    Sun, Dali; Yamahara, Hiroyasu; Nakane, Ryosho; Matsui, Hiroaki; Tabata, Hitoshi

    2015-06-01

    The effect of hydroxyl radicals (OH) and thermal annealing on an amorphous InGaZnO4 (aIGZO) film surface was investigated for manipulation of DNA immobilization. X-ray photoemission and fluorescence measurements were conducted to reveal the status of surface OH coverage and DNA immobilization, respectively. Systematic examinations concerning OH termination on the film surface suggested that the surface coverage of OH leveling DNA immobilization was related to the local surface potential. Furthermore, OH affinity on the aIGZO film surface was sensitive to thermal annealing. A remarkable change in surface OH coverage was observed for the film surface annealed at high temperature. This behavior was framed by a structural change from amorphous to crystalline state, which regulated DNA immobilization. These results indicate that the OH affinity on aIGZO films is dependent on structural properties such as defects. This study suggests that an amorphous structure is critical for obtaining a high OH surface coverage governing DNA immobilization, and is hence more suitable for biosensing.

  20. Opening of ATP-sensitive K(+) (KATP) channels enhance hydroxyl radical generation induced by MPP(+) in rat striatum.

    PubMed

    Obata, Toshio; Nakashima, Michiko

    2016-07-15

    The present study examined whether opening of adenosine triphosphate (ATP) sensitive K(+) (KATP) channels can enhance 1-methyl-4-phenylpyridinium (MPP(+))-induced hydroxyl radical (OH) generation in rat striatum. Rats were anesthetized, and sodium salicylate in Ringer's solution (0.5nmol/ml per min) was infused through a microdialysis probe to detect the generation of OH as reflected by the non-enzymatic formation of 2.3-dihydroxybenzoic acid (DHBA) in the striatum. MPP(+) (5mM) enhanced generation of OH with concomitant increased efflux of dopamine (DA). Cromakalim (100μM), a KATP channel opener, through the microdialysis probe significantly increased both DA efflux and OH formation induced by MPP(+). Another KATP channel opener, nicorandil (1mM), also increased the level DA or DHBA, but these changes were not significant. However, in the presence of glibenclamide (10μM), a KATP channel antagonist, and the increase of MPP(+)-induced DA or DHBA were not observed. Cromakalim (10, 50 and 100μM) increased MPP(+)-induced DHBA formation in a concentration-dependent manner. However, the effects of cromakalim in the presence of glibenclamide were abolished. These results suggest that opening of KATP channels may cause OH generation by MPP(+). PMID:27288802

  1. Comparison of Measurements of Hydroxyl Radicals in the Tropical Troposphere during GABRIEL with the Box Model MECCA

    NASA Astrophysics Data System (ADS)

    Kubistin, D.; Harder, H.; Martinez, M.; Rudolf, M.; Sander, R.; Bartenbach, S.; Bozem, H.; Colomb, A.; Eerdekens, G.; Fischer, H.; Ganzeveld, L.; Gebhardt, S.; Gurk, C.; Hofmann, R.; Kluepfel, T.; Koenigstedt, R.; Parchatka, U.; Schiller, C.; Stickler, A.; Williams, J.; Yassaa, N.; Lelieveld, J.

    2006-12-01

    Hydroxyl radicals play a major role in the chemistry of the troposphere and dominate its oxidation capacity during daytime. Their main source in the unpolluted troposphere is the photolysis of O3 and following reactions with water vapour. The largest contribution to the global oxidation capacity occurs in the tropical region. The GABRIEL campaign, Oct 2005, took place in equatorial South America (Suriname) to gain basic understanding of the dominant processes over the tropical rainforest and their influence on the HOx budget. Global models predict that the emissions of hydrocarbons from the rainforest reduce the amount of HOx and therefore the selfcleaning capacity significantly. The poster concentrates on understanding the HOx budget and its interdependence with other species measured during the campaign. Since OH and HO2 have very short lifetimes, MECCA, a box model, is applied in steady state mode and used for detailed analysis. Hereby all measured species like radiation, O3, isoprene, NO, HCHO, CO, hydrocarbons are used as constraint parameters to model OH and HO2.

  2. Effect of prenatal lead exposure on nigrostriatal neurotransmission and hydroxyl radical formation in rat neostriatum: dopaminergic-nitrergic interaction.

    PubMed

    Nowak, Przemysław; Szczerbak, Grazyna; Nitka, Dariusz; Kostrzewa, Richard M; Sitkiewicz, Tomasz; Brus, Ryszard

    2008-04-01

    The present study was designed to explore the role of ontogenetic lead (Pb(2+)) exposure on a putative dopaminergic-nitrergic interaction in the nigrostriatal pathway. Pregnant Wistar rats were given tap water containing 250-ppm lead acetate, for the duration of pregnancy, with regular tap water (without Pb(2+)) being substituted at birth. Control rats were derived from dams that consumed tap water throughout pregnancy, and had no exposure to Pb(2+) afterwards. At 12 weeks after birth in vivo microdialysis of the neostriatum was employed to demonstrate that maternal Pb(2+) exposure was without effect on the baseline dopamine (DA) microdialysate concentration as well as amphetamine (AMPH, 1.0mg/kg i.p.)-evoked release of striatal DA. Also, prenatal Pb(2+) exposure did not enhance AMPH- and 7-nitroindazole (neuronal nitric oxide synthase inhibitor) (7-NI, 20mg/kg i.p.)-induced hydroxyl radical (HO) formation in the striatum, as indicated by analysis of the salicylate spin-trap product 2,5-dihydroxybenzoic acid. However, in rats exposed prenatally to Pb(2+), the facilitatory effect of 7-NI on DA exocytosis was attenuated. On the basis of the current study we conclude that maternal Pb(2+) exposure distorts the dopaminergic-nitrergic interaction in the nigrostriatal pathway, but without involvement of reactive oxygen species (ROS).

  3. Oxidative and nitrosative stress induced in myofibrillar proteins by a hydroxyl-radical-generating system: impact of nitrite and ascorbate.

    PubMed

    Villaverde, Adriana; Parra, Vita; Estévez, Mario

    2014-03-12

    Understanding the chemistry behind the redox properties of nitrite and ascorbate is essential to identify the impact of curing agents on food quality and optimize the formulation of cured meat products. This study was designed to gain insight into the interactions between curing agents and myofibrillar proteins (MPs) during in vitro oxidation by a hydroxyl-radical-generating system. MPs (4 mg/mL) were oxidized for 4 days at 37 °C under constant stirring with 25 μM iron(III) and 2.5 mM hydrogen peroxide. Dependent upon the addition of nitrite (0, 75, and 150 mg/L) and ascorbate (0, 250, and 500 mg/L), nine different reaction units were prepared in triplicate (n = 3) according to a total factorial design. Upon completion of the oxidation assay, samples were analyzed for the concentration of tryptophan (TRP), α-aminoadipic semialdehyde (AAS), Schiff bases (SBs), and 3-nitrotyrosine (3NT). Ascorbate at 250 mg/L significantly inhibited the depletion of TRP (∼20% inhibition) and the formation of AAS and SBs (>90% inhibition) in MP suspensions. Nitrite, alone, had a negligible effect on protein oxidation but induced the formation of a specific marker of nitrosative stress, namely, 3NT. Ascorbate was also efficient at inhibiting the formation of 3NT by a dose-dependent anti-nitrosative effect and enabled the antioxidant action of nitrite.

  4. Radiation protection of in vitro mammalian cells: effects of hydroxyl radical scavengers on the slopes and shoulders of survival curves

    SciTech Connect

    Ewing, D.; Walton, H.L. )

    1991-05-01

    We have tested several chemical compounds, characterized and widely used as hydroxyl radical (.OH) scavengers, for their effects on the radiation sensitivity of Chinese hamster V79 cells irradiated in air or nitrogen. Our purpose is to reexamine the proposed relationship between the level of protection and the rates at which the scavengers react with .OH. We found that the additives can have two apparently independent effects on the shape of survival curves: a reduction in sensitivity (i.e., 'protection,' a decrease in the value of k) and an increase in the size of the shoulder of the survival curve (an increase in the value of Dq). We measured intracellular scavenger concentrations, and, using these values in our analysis, we found that neither of the two effects is correlated with the rates at which the scavengers react with .OH. Although these results could mean that .OH do not cause lethal damage, the interpretation we believe most probably correct is that these scavengers protect in multiple ways. The protection would occur in addition to or instead of simple .OH removal.

  5. [Detection of hydroxyl radical in heterogeneous photo-Fenton system using the fluorescence technique and influencing factor study].

    PubMed

    Liu, Ting; You, Hong; Chen, Qi-Wei; Wang, Zhi-Chao

    2009-09-15

    The Fe2O3/TiO2/Al2O3 catalyst was prepared by using TiO2/Al2O3 as carrier and the heterogeneous photo-Fenton system was established in the three-phase fluidized bed. A fluorescence technique was developed for the determination of the hydroxyl radicals (*OH) from the heterogeneous photo-Fenton system, using coumarin as the fluorescence probe. In addition, four main factors, namely pH, H2O2 concentration, catalyst loading and UV light intensity, which could influence the concentration of OH produced during the reaction process, was also discussed. The fluorescence method using coumarin as the fluorescence probe was demonstrated to be capable of detecting *OH generated in heterogeneous photo-Fenton system with veracity and high reproducibility. It was also found that the *OH generated in heterogeneous photo-Fenton system conformed to the zero reaction dynamics in 30 min. Moreover, the pH, H2O2 concentration, catalyst loading and UV light intensity influenced the *OH generated during the reaction process.

  6. Development of UV Optical Measurements of Nitric Oxide and Hydroxyl Radical at the Exit of High Pressure Gas Turbine Combustors

    NASA Technical Reports Server (NTRS)

    Liscinsky, D. S.; Knight, B. A.; Shirley, J. A.

    1998-01-01

    Measurements of nitric oxide (NO) and hydroxyl radical (OR) have been made in a laboratory flat flame at pressures up to 30 atm using line-of-sight resonant absorption. Data are reported at equivalence ratios of 0.98 and 1.3 and pressures of 1, 5, 10, 20 and 30 atm. The performance of the in-situ LTV absorption technique with assessed at these elevated pressures by comparing the measured absorption with those predicted by detailed theoretical spectroscopic models for NO and OH. Previous to this experiment the resonant models had not been verified at pressures greater than two atmospheres. Agreement within 25% was found between the measurements and predictions with only slight modification of the existing models for both NO and OH to account for line center shifting and pressure broadening. Continuum interference of hot oxygen (O2) on the NO absorption spectra was not significant in the interpretation of the data. The optical methods used in this study are distinct from laser-based diagnostics such as laser induced fluorescence and, hence, have the potential to provide independent verification of the laser-based measurements. The methodology is also of sufficient simplicity to be hardened into a portable optical measurement system that can be deployed in gas turbine engine test cells. A miniature fiber optic couple portable instrument is described.

  7. Antioxidant Activity of Caffeic Acid against Iron-Induced Free Radical Generation—A Chemical Approach

    PubMed Central

    Genaro-Mattos, Thiago C.; Maurício, Ângelo Q.; Rettori, Daniel; Alonso, Antonio; Hermes-Lima, Marcelo

    2015-01-01

    Caffeic acid (CA) is a phenolic compound widely found in coffee beans with known beneficial effects in vivo. Many studies showed that CA has anti-inflammatory, anti-mutagenic, antibacterial and anti-carcinogenic properties, which could be linked to its antioxidant activity. Taking in consideration the reported in vitro antioxidant mechanism of other polyphenols, our working hypothesis was that the CA antioxidant activity could be related to its metal-chelating property. With that in mind, we sought to investigate the chemical antioxidant mechanism of CA against in vitro iron-induced oxidative damage under different assay conditions. CA was able to prevent hydroxyl radical formation promoted by the classical Fenton reaction, as determined by 2-deoxyribose (2-DR) oxidative degradation and DMPO hydroxylation. In addition to its ability to prevent hydroxyl radical formation, CA had a great inhibition of membrane lipid peroxidation. In the lipid peroxidation assays CA acted as both metal-chelator and as hydrogen donor, preventing the deleterious action promoted by lipid-derived peroxyl and alkoxyl radicals. Our results indicate that the observed antioxidant effects were mostly due to the formation of iron-CA complexes, which are able to prevent 2-DR oxidation and DMPO hydroxylation. Noteworthy, the formation of iron-CA complexes and prevention of oxidative damage was directly related to the pH of the medium, showing better antioxidant activity at higher pH values. Moreover, in the presence of lipid membranes the antioxidant potency of CA was much higher, indicating its enhanced effectiveness in a hydrophobic environment. Overall, our results show that CA acts as an antioxidant through an iron chelating mechanism, preventing the formation of free hydroxyl radicals and, therefore, inhibiting Fenton-induced oxidative damage. The chemical properties of CA described here—in association with its reported signaling effects—could be an explanation to its beneficial effects

  8. Antioxidant Activity of Caffeic Acid against Iron-Induced Free Radical Generation--A Chemical Approach.

    PubMed

    Genaro-Mattos, Thiago C; Maurício, Ângelo Q; Rettori, Daniel; Alonso, Antonio; Hermes-Lima, Marcelo

    2015-01-01

    Caffeic acid (CA) is a phenolic compound widely found in coffee beans with known beneficial effects in vivo. Many studies showed that CA has anti-inflammatory, anti-mutagenic, antibacterial and anti-carcinogenic properties, which could be linked to its antioxidant activity. Taking in consideration the reported in vitro antioxidant mechanism of other polyphenols, our working hypothesis was that the CA antioxidant activity could be related to its metal-chelating property. With that in mind, we sought to investigate the chemical antioxidant mechanism of CA against in vitro iron-induced oxidative damage under different assay conditions. CA was able to prevent hydroxyl radical formation promoted by the classical Fenton reaction, as determined by 2-deoxyribose (2-DR) oxidative degradation and DMPO hydroxylation. In addition to its ability to prevent hydroxyl radical formation, CA had a great inhibition of membrane lipid peroxidation. In the lipid peroxidation assays CA acted as both metal-chelator and as hydrogen donor, preventing the deleterious action promoted by lipid-derived peroxyl and alkoxyl radicals. Our results indicate that the observed antioxidant effects were mostly due to the formation of iron-CA complexes, which are able to prevent 2-DR oxidation and DMPO hydroxylation. Noteworthy, the formation of iron-CA complexes and prevention of oxidative damage was directly related to the pH of the medium, showing better antioxidant activity at higher pH values. Moreover, in the presence of lipid membranes the antioxidant potency of CA was much higher, indicating its enhanced effectiveness in a hydrophobic environment. Overall, our results show that CA acts as an antioxidant through an iron chelating mechanism, preventing the formation of free hydroxyl radicals and, therefore, inhibiting Fenton-induced oxidative damage. The chemical properties of CA described here--in association with its reported signaling effects--could be an explanation to its beneficial effects

  9. Antioxidant Activity of Caffeic Acid against Iron-Induced Free Radical Generation--A Chemical Approach.

    PubMed

    Genaro-Mattos, Thiago C; Maurício, Ângelo Q; Rettori, Daniel; Alonso, Antonio; Hermes-Lima, Marcelo

    2015-01-01

    Caffeic acid (CA) is a phenolic compound widely found in coffee beans with known beneficial effects in vivo. Many studies showed that CA has anti-inflammatory, anti-mutagenic, antibacterial and anti-carcinogenic properties, which could be linked to its antioxidant activity. Taking in consideration the reported in vitro antioxidant mechanism of other polyphenols, our working hypothesis was that the CA antioxidant activity could be related to its metal-chelating property. With that in mind, we sought to investigate the chemical antioxidant mechanism of CA against in vitro iron-induced oxidative damage under different assay conditions. CA was able to prevent hydroxyl radical formation promoted by the classical Fenton reaction, as determined by 2-deoxyribose (2-DR) oxidative degradation and DMPO hydroxylation. In addition to its ability to prevent hydroxyl radical formation, CA had a great inhibition of membrane lipid peroxidation. In the lipid peroxidation assays CA acted as both metal-chelator and as hydrogen donor, preventing the deleterious action promoted by lipid-derived peroxyl and alkoxyl radicals. Our results indicate that the observed antioxidant effects were mostly due to the formation of iron-CA complexes, which are able to prevent 2-DR oxidation and DMPO hydroxylation. Noteworthy, the formation of iron-CA complexes and prevention of oxidative damage was directly related to the pH of the medium, showing better antioxidant activity at higher pH values. Moreover, in the presence of lipid membranes the antioxidant potency of CA was much higher, indicating its enhanced effectiveness in a hydrophobic environment. Overall, our results show that CA acts as an antioxidant through an iron chelating mechanism, preventing the formation of free hydroxyl radicals and, therefore, inhibiting Fenton-induced oxidative damage. The chemical properties of CA described here--in association with its reported signaling effects--could be an explanation to its beneficial effects

  10. In vitro effects of coal fly ashes: hydroxyl radical generation, iron release, and DNA damage and toxicity in rat lung epithelial cells

    SciTech Connect

    van Maanen, J.M.; Borm, P.J.; Knaapen, A; van Herwijnen, M.; Schilderman, P.A.; Smith, K.R.; Aust, A.E.; Tomatis, M.; Fubini, B.

    1999-12-15

    The authors measured iron release, acellular generation of hydroxyl radicals, and oxidative DNA damage and cytotoxicity in rat lung epithelial (RLE) cells by different coal fly ashes (CFA) that contain both quartz and iron. Seven samples of CFA with different particle size and quartz content (up to 14.1%) were tested along with silica (alpha-quartz), ground coal, and coal mine dust (respirable) as positive control particles, and fine TiO{sub 2} (anatase) as a negative control. Five test samples were pulverized fuel ashes (PFA), two samples were coal gasification (SCG) ashes (quartz content {lt} 0.1%), and one sample was a ground coal. No marked differences between SCG and PFA fly ashes were observed, and toxicity did not correlate with physicochemical characteristics or effect parameters. Stable surface radicals were only detected in the reference particles silica and coal mine dust, but not in CFA. On the other hand, hydroxyl radical generation by all fly ashes was observed in the presence of hydrogen peroxide. Also a relationship between acellular hydroxyl radical generation and oxidative DNA damage in RLE cells by CFA was observed. The respirable ashes (MAT023, 38, and 41) showed an extensive level of hydroxyl radical generation in comparison to nonrespirable fly ashes and respirable references. This was related to the iron mobilization from these particles. Themechanisms by which CFA and the positive references (silica, coal mine dust) affect rat lung epithelial cells seem to be different, and the data suggest that quartz in CFA does not act the same as quartz in silica or coal mine dust. However, the results indicate an important role for size and iron release in generation and subsequent effects of reactive oxygen species caused by CFA.

  11. The metabolites of glutamine prevent hydroxyl radical-induced apoptosis through inhibiting mitochondria and calcium ion involved pathways in fish erythrocytes.

    PubMed

    Li, Huatao; Jiang, Weidan; Liu, Yang; Jiang, Jun; Zhang, Yongan; Wu, Pei; Zhao, Juan; Duan, Xudong; Zhou, Xiaoqiu; Feng, Lin

    2016-03-01

    The present study explored the apoptosis pathways in hydroxyl radicals ((∙)OH)-induced carp erythrocytes. Carp erythrocytes were treated with the caspase inhibitors in physiological carp saline (PCS) or Ca(2+)-free PCS in the presence of 40μM FeSO4/20μM H2O2. The results showed that the generation of reactive oxygen species (ROS), the release of cytochrome c and DNA fragmentation were caspase-dependent, and Ca(2+) was involved in calpain activation and phosphatidylserine (PS) exposure in (∙)OH-induced carp erythrocytes. Moreover, the results suggested that caspases were involved in PS exposure, and Ca(2+) was involved in DNA fragmentation in (∙)OH-induced fish erythrocytes. These results demonstrated that there might be two apoptosis pathways in fish erythrocytes, one is the caspase and cytochrome c-dependent apoptosis that is similar to that in mammal nucleated cells, the other is the Ca(2+)-involved apoptosis that was similar to that in mammal non-nucleated erythrocytes. So, fish erythrocytes may be used as a model for studying oxidative stress and apoptosis in mammal cells. Furthermore, the present study investigated the effects of glutamine (Gln)'s metabolites [alanine (Ala), citrulline (Cit), proline (Pro) and their combination (Ala10Pro4Cit1)] on the pathways of apoptosis in fish erythrocytes. The results displayed that Ala, Cit, Pro and Ala10Pro4Cit1 effectively suppressed ROS generation, cytochrome c release, activation of caspase-3, caspase-8 and caspase-9 at the physiological concentrations, prevented Ca(2+) influx, calpain activation, PS exposure, DNA fragmentation and the degradation of the cytoskeleton and oxidation of membrane and hemoglobin (Hb) and increased activity of anti-hydroxyl radical (AHR) in (∙)OH-induced carp erythrocytes. Ala10Pro4Cit1 produced a synergistic effect of inhibited oxidative stress and apoptosis in fish erythrocytes. These results demonstrated that Ala, Cit, Pro and their combination can protect mammal erythrocytes

  12. Antinephritis and radical scavenging activity of prenylflavonoids.

    PubMed

    Fukai, Toshio; Satoh, Kazue; Nomura, Taro; Sakagami, Hiroshi

    2003-12-01

    Antinephritis activity of 5 prenylflavonoids similar to glabridin (1-5), isolated from Morus alba, Artocarpus communis, Glycyrrhiza uralensis and G. inflata, was evaluated in mice with glomerular disease (Masugi-nephritis). Oral administrations of artonin E (2) or licochalcone A (4) for 10 days (30 mg kg(-1) day(-1)) reduced the amount of urinary protein excretion compared to nephritic mice. ESR spectroscopy demonstrated that morusin (1) and licorisoflavan A (5) increased the radical intensity of sodium ascorbate by about two times. Morusin, licoricidin (3), licochalcone A and licorisoflavan A showed weak scavenging activity against superoxide anion radical.

  13. Boron-doped bismuth oxybromide microspheres with enhanced surface hydroxyl groups: Synthesis, characterization and dramatic photocatalytic activity.

    PubMed

    Liu, ZhangSheng; Liu, JinLong; Wang, HaiYang; Cao, Gang; Niu, JiNan

    2016-02-01

    B-doped BiOBr photocatalysts were successfully synthesized via a facile solvothermal method with boric acid used as boron source. As-obtained products consist of novel hierarchical microspheres, whose nanosheet building units were formed by nanoparticles splicing. They showed dramatic photocatalytic efficiency toward the degradation of Rhodamine B (RhB) and phenol under the visible-light irradiation and the highest activity was achieved by 0.075B-BiOBr. The enhanced photocatalytic activity could be attributed to the enriched surface hydroxyl groups on B-doped BiOBr samples, which not only improved the adsorption of pollutant on the photocatalyst but also promoted the separation of photogenerated electron-hole pairs. In addition, it was found that the main reactive species responsible for the degradation of organic pollutant were h(+) and O2(-) radicals, instead of OH radicals. PMID:26590875

  14. Boron-doped bismuth oxybromide microspheres with enhanced surface hydroxyl groups: Synthesis, characterization and dramatic photocatalytic activity.

    PubMed

    Liu, ZhangSheng; Liu, JinLong; Wang, HaiYang; Cao, Gang; Niu, JiNan

    2016-02-01

    B-doped BiOBr photocatalysts were successfully synthesized via a facile solvothermal method with boric acid used as boron source. As-obtained products consist of novel hierarchical microspheres, whose nanosheet building units were formed by nanoparticles splicing. They showed dramatic photocatalytic efficiency toward the degradation of Rhodamine B (RhB) and phenol under the visible-light irradiation and the highest activity was achieved by 0.075B-BiOBr. The enhanced photocatalytic activity could be attributed to the enriched surface hydroxyl groups on B-doped BiOBr samples, which not only improved the adsorption of pollutant on the photocatalyst but also promoted the separation of photogenerated electron-hole pairs. In addition, it was found that the main reactive species responsible for the degradation of organic pollutant were h(+) and O2(-) radicals, instead of OH radicals.

  15. Comparison of Diffusion Coefficients of Aryl Carbonyls and Aryl Alcohols in Hydroxylic Solvents. Evidence that the Diffusion of Ketyl Radicals in Hydrogen-Bonding Solvents is Not Anomalous?

    SciTech Connect

    Autrey, S Thomas ); Camaioni, Donald M. ); Kandanarachchi, Pramod H.; Franz, James A. )

    2000-12-01

    The diffusion coefficients of a benzyl-, sec-phenethyl-, and diphenylmethyl alcohol and the corresponding aryl carbonyls (benzaldehyde, acetophenone and benzophenone) were measured by Taylor's dispersion method in both ethyl and isopropyl alcohol. The experimental values are compared to published transient grating measurements of the corresponding aryl ketyl radicals (benzyl-, sec-phenethyl-, and diphenylmethyl-ketyl radical). In general, the diffusion coefficient of the aryl alcohols and the corresponding aryl ketyl radicals are equivalent within experimental error. This work shows that the diffusion of ketyl radicals is not anomalously slow and that aryl alcohols are significantly better models than the corresponding aryl ketones for analyzing the diffusion of aryl ketyl radicals in both ethyl and isopropyl alcohol. Empirical estimates of the diffusion coefficients of aryl alcohols using the Spernol-Wirtz and Wilke-Chang modifications to the Stokes-Einstein diffusion equation do not adequately account for the interactions between the aryl ketyl radicals or aryl alcohols with the hydroxylic solvents ethyl and isopropyl alcohol. The excellent agreement between the experimental diffusion coefficients of the aryl alcohols and the corresponding ketyl radicals show that the transient grating method can provide accurate estimates for the diffusion coefficients of transient species. This is especially important when a stable model is not available, for example the pyranyl radical.

  16. Comparative study on DBPs formation profiles of intermediate organics from hydroxyl radicals oxidation of microbial cells.

    PubMed

    Ou, Tai-You; Wang, Gen-Shuh

    2016-05-01

    This study assessed the characteristics of disinfection byproducts (DBPs) formation from intermediate organics during UV/H2O2 treatment of activated sludge and algae cells under various reaction conditions. The DBPs including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs) and haloacetonitriles (HANs) in UV/H2O2-treated and chlorinated water were measured. The results showed that both dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) increased during the initial stage of UV/H2O2 treatment due to the lysis of sludge and algae cells, which enhanced the formation of both C- and N-DBPs; however, both DOC and DON decreased after longer reaction times. During the UV/H2O2 treatments, THMs formation potential (THMFP) peaked earlier than did HAAs formation potential (HAAFP). This shows that the dissolved organics released from lysis of microbial cells in the early stages of oxidation favor the production of THMs over HAAs; however, HAAs precursors increased with the oxidation time. Chlorination with bromide increased the formation of THMs and HAAs but less HKs and HANs were produced. Comparisons of normalized DBP formation potential (DBPFP) of samples collected during UV/H2O2 treatments of four different types of organic matter showed that the highest DBPFP occurred in filtered treated wastewater effluent, followed by samples of activated sludge, filtered eutrophicated pond water, and samples of algae cells. With increasing oxidation time, the dominant DBP species shifted from THMs to HAAs in the samples of activated sludge and algae cells. The DBPFP tests also showed that more HAAs were formed in biologically treated wastewater effluent, while the eutrophicated source water produced more THMs.

  17. Comparative study on DBPs formation profiles of intermediate organics from hydroxyl radicals oxidation of microbial cells.

    PubMed

    Ou, Tai-You; Wang, Gen-Shuh

    2016-05-01

    This study assessed the characteristics of disinfection byproducts (DBPs) formation from intermediate organics during UV/H2O2 treatment of activated sludge and algae cells under various reaction conditions. The DBPs including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs) and haloacetonitriles (HANs) in UV/H2O2-treated and chlorinated water were measured. The results showed that both dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) increased during the initial stage of UV/H2O2 treatment due to the lysis of sludge and algae cells, which enhanced the formation of both C- and N-DBPs; however, both DOC and DON decreased after longer reaction times. During the UV/H2O2 treatments, THMs formation potential (THMFP) peaked earlier than did HAAs formation potential (HAAFP). This shows that the dissolved organics released from lysis of microbial cells in the early stages of oxidation favor the production of THMs over HAAs; however, HAAs precursors increased with the oxidation time. Chlorination with bromide increased the formation of THMs and HAAs but less HKs and HANs were produced. Comparisons of normalized DBP formation potential (DBPFP) of samples collected during UV/H2O2 treatments of four different types of organic matter showed that the highest DBPFP occurred in filtered treated wastewater effluent, followed by samples of activated sludge, filtered eutrophicated pond water, and samples of algae cells. With increasing oxidation time, the dominant DBP species shifted from THMs to HAAs in the samples of activated sludge and algae cells. The DBPFP tests also showed that more HAAs were formed in biologically treated wastewater effluent, while the eutrophicated source water produced more THMs. PMID:26894677

  18. Evaluation of a technique to measure tropospheric hydroxyl radicals using an aqueous phase salicylic acid scrubbing solution, HPLCseparation and fluorescence detection

    NASA Astrophysics Data System (ADS)

    Salmon, R. A.; Schiller, C. L.; Harris, G. W.

    2003-04-01

    A novel method for monitoring gas phase hydroxyl radicals was examined using a liquid-phase salicylic acid solution to trap tropospheric OH. Quantification occurred following HPLC seperaration and fluorescence detection of one of the products, 2,5-dihydroxy benzoic acid. Although the sensitivity was sufficient to measure typical daytime OH concentrations, the method was hindered by a number of interferences. While most of these were identified and eliminated, an interference from methylperoxy radicals was discovered that could not be removed. The validity of previous reports of OH detection using this method is therefore brought into question.

  19. Quantification of hydroxyl radical-derived oxidation products in peptides containing glycine, alanine, valine, and proline.

    PubMed

    Morgan, Philip E; Pattison, David I; Davies, Michael J

    2012-01-15

    Proteins are a major target for oxidation due to their abundance and high reactivity. Despite extensive investigation over many years, only limited quantitative data exist on the contributions of different pathways to the oxidation of peptides and proteins. This study was designed to obtain quantitative data on the nature and yields of oxidation products (alcohols, carbonyls, hydroperoxides, fragment species) formed by a prototypic oxidant system (HO(•)/O(2)) on small peptides of limited, but known, amino acid composition. Peptides composed of Gly, Ala, Val, and Pro were examined with particular emphasis on the peptide Val-Gly-Val-Ala-Pro-Gly, a repeat motif in elastin with chemotactic activity and metalloproteinase regulation properties. The data obtained indicate that hydroperoxide formation occurs nonrandomly (Pro > Val > Ala > Gly) with this inversely related to carbonyl yields (both peptide-bound and released). Multiple alcohols are generated at both side-chain and backbone sites. Backbone fragmentation has been characterized at multiple positions, with sites adjacent to Pro residues being of major importance. Summation of the product concentrations provides clear evidence for the occurrence of chain reactions in peptides exposed to HO(•)/O(2), with the overall product yields exceeding that of the initial HO(•) generated.

  20. Kinetics of the Hydrogen Atom Abstraction Reactions from 1-Butanol by Hydroxyl Radical: Theory Matches Experiment and More

    SciTech Connect

    Seal, Prasenjit; Oyedepo, Gbenga; Truhlar, Donald G.

    2013-01-17

    In the present work, we study the H atom abstraction reactions by hydroxyl radical at all five sites of 1-butanol. Multistructural variational transition state theory (MS-VTST) was employed to estimate the five thermal rate constants. MS-VTST utilizes a multifaceted dividing surface that accounts for the multiple conformational structures of the transition state, and we also include all the structures of the reactant molecule. The vibrational frequencies and minimum energy paths (MEPs) were computed using the M08-HX/MG3S electronic structure method. The required potential energy surfaces were obtained implicitly by direct dynamics employing interpolated variational transition state theory with mapping (IVTST-M) using a variational reaction path algorithm. The M08-HX/MG3S electronic model chemistry was then used to calculate multistructural torsional anharmonicity factors to complete the MS-VTST rate constant calculations. The results indicate that torsional anharmonicity is very important at higher temperatures, and neglecting it would lead to errors of 26 and 32 at 1000 and 1500 K, respectively. Our results for the sums of the site-specific rate constants agree very well with the experimental values of Hanson and co-workers at 896–1269 K and with the experimental results of Campbell et al. at 292 K, but slightly less well with the experiments of Wallington et al., Nelson et al., and Yujing and Mellouki at 253–372 K; nevertheless, the calculated rates are within a factor of 1.61 of all experimental values at all temperatures. Finally, this gives us confidence in the site-specific values, which are currently inaccessible to experiment.

  1. The role of boundary layer dynamics on the diurnal evolution of isoprene and the hydroxyl radical over tropical forests

    NASA Astrophysics Data System (ADS)

    Vilã-Guerau de Arellano, Jordi; Patton, Edward G.; Karl, Thomas; van den Dries, Kees; Barth, Mary C.; Orlando, John J.

    2011-04-01

    We investigate diurnal variability of isoprene and related chemical species in the Amazonian region. The dynamics and chemistry of an atmospheric boundary layer are studied with a large-eddy simulation code and a mixed-layer model which are guided by observations available for the same area. The main features of isoprene and related species are reproduced well, but their evolution raises questions regarding the physical and chemical processes responsible for the observed diurnal behaviors. To address these questions, we systematically examine the role of (1) the exchange of chemical species between the free troposphere and the atmospheric boundary layer (entrainment), (2) surface isoprene and nitric oxide emissions, and (3) new chemical pathways to recycle the hydroxyl radical. The entrainment flux of isoprene is shown to be equally important as surface isoprene emissions in determining the isoprene temporal evolution. Varying the relationship between the initial isoprene mixing ratio in the boundary layer and that in the overlying free troposphere in the early morning results in an 50% increase/decrease in isoprene mixing ratio or more within the atmospheric boundary layer at noon. Entrainment of free tropospheric nitrogen oxides creates changes of similar magnitude to the boundary layer isoprene mixing ratio. These effects of entrainment and surface emissions on isoprene are found for two different chemical regimes. The introduction of an OH recycling pathway in the chemical mechanism increases midday OH. Our findings show that atmospheric dynamics and chemistry are equally important for interpreting the diurnal observation of reactants and for including in regional-scale modeling efforts where turbulence is parameterized.

  2. Rate constants for aqueous-phase reactions of hydroxyl radical ({center_dot}OH) with aldehydes and ketones

    SciTech Connect

    Allen, J.M.; Allen, S.K.

    1995-12-31

    A wide variety of aldehydes and ketones are formed in the troposphere by the gas-phase oxidation of hydrocarbons. These compounds are expected to readily partition into cloud, fog, and aquated aerosol drops where they can participate in a variety of aqueous-phase reactions. It has been previously demonstrated by other researchers that aqueous-phase photochemical reactions involving aromatic aldehydes and ketones may lead to the formation of hydrogen peroxide. Hydrogen peroxide is an important oxidant for S(IV) and is also an {center_dot}OH precursor. Aldehydes and ketones may also participate in other aqueous-phase reactions within atmospheric water drops including reactions with {center_dot}OH. Rate constants for reactions involving {center_dot}OH in aqueous solutions have been reported for only a limited number of tropospheric aldehydes and ketones. The authors have measured the rate constants for aqueous-phase reactions of {center_dot}OH with several tropospheric aldehydes and ketones by the technique of competition kinetics. Hydroxyl radicals were generated by continuous illumination at 313 nm of an aqueous acidified solution containing Fe(ClO{sub 4}){sub 3}, an {center_dot}OH scavenger, the aldehyde or ketone whose rate constant was to be measured, and a standard for which the rate constant for reaction with {center_dot}OH is well known. Nitrobenzene was used as the standard in all experiments. Loss of the aldehyde or ketone and the standard were monitored by HPLC. Losses attributable to direct photolysis and dark reactions were minimal.

  3. Theoretical study of the hydroxyl radical addition to uracil and photochemistry of the formed U6OH• adduct.

    PubMed

    Francés-Monerris, Antonio; Merchán, Manuela; Roca-Sanjuán, Daniel

    2014-03-20

    Hydroxyl radical ((•)OH) is produced in biological systems by external or endogenous agents. It can damage DNA/RNA by attacking pyrimidine nucleobases through the addition to the C5═C6 double bond. The adduct resulting from the attachment at the C5 position prevails in the experimental measurements, although the reasons for this preference remain unclear. The first aim of this work is therefore to shed light on the comprehension of this important process. Thus, the thermal (•)OH addition to the C5═C6 double bond of uracil has been studied theoretically by using DFT, MP2, and the multiconfigurational CASPT2//CASSCF methodologies. The in-vacuo results obtained with the latter protocol plus the analysis of solvent effects support the experimental observation. A significant lower barrier height is predicted for the C5 pathway with respect to that of the C6 route. In contrast to the C5 adduct, the C6 adduct is able to absorb visible light. Hence, the second aim of the work is to study the photochemistry of this species using the CASPT2//CASSCF methodology within the framework of the photochemical reaction path approach (PRPA). The nonradiative decay to the ground state of this compound has been characterized. A photoreactive character is predicted for the C6 adduct in the excited states according to the presence of excited-state minima along the main decay channel. Finally, a new mechanism of photodissociation has been explored, which implies the photoinduced regeneration of the canonical nucleobase by irradiating with visible light, being therefore relevant in RNA protection against damage by reactive oxygen species.

  4. Observations of hydroxyl and peroxy radicals and the impact of BrO at Summit, Greenland in 2007 and 2008

    NASA Astrophysics Data System (ADS)

    Liao, J.; Huey, L. G.; Tanner, D. J.; Brooks, S.; Dibb, J. E.; Stutz, J.; Thomas, J. L.; Lefer, B.; Haman, C.; Gorham, K.

    2011-04-01

    The Greenland Summit Halogen-HOx (GSHOX) Campaign was performed in spring~2007 and summer~2008 to investigate the impact of halogens on HOx (=OH + HO2) cycling above the Greenland Ice Sheet. Chemical species including hydroxyl and peroxy radicals (OH and HO2 + ROx), ozone (O3), nitrogen oxide (NO), nitric acid (HNO2), nitrous acid (HONO), reactive gaseous mercury (RGM), and bromine oxide (BrO) were measured during the campaign. The median midday values of HO2 + RO2 and OH concentrations observed by chemical ionization mass spectrometry (CIMS) were 2.7 × 108 molec cm-3 and 3.0 × 106 molec cm-3 in spring 2007, and 4.2 × 108 molec cm-3 and 4.1 × 106 molec cm-3 in summer~2008. A basic photochemical 0-D box model highly constrained by observations of H2O, O3, CO, CH4, NO, and J values predicted HO2 + RO2 (R = 0.90, slope = 0.87 in 2007; R = 0.79, slope = 0.96 in 2008) reasonably well and under predicted OH (R = 0.83, slope = 0.72 in 2007; R = 0.76, slope = 0.54 in 2008). Constraining the model to HONO observations did not significantly change the predictions. Including bromine chemistry in the model constrained by observations of BrO improved the correlation between observed and predicted HO2 + RO2 and OH, and brought the average hourly OH and HO2+RO2 predictions closer to the observations. These model comparisons confirmed our understanding of the dominant HOx sources and sinks in this environment and indicated that BrO impacted the OH levels at Summit. Although, significant discrepancies between observed and predicted OH could not be explained by the measured BrO. Finally, observations of enhanced RGM were found to be coincident with under prediction of OH.

  5. Towards reducing DBP formation potential of drinking water by favouring direct ozone over hydroxyl radical reactions during ozonation.

    PubMed

    De Vera, Glen Andrew; Stalter, Daniel; Gernjak, Wolfgang; Weinberg, Howard S; Keller, Jurg; Farré, Maria José

    2015-12-15

    When ozonation is employed in advanced water treatment plants to produce drinking water, dissolved organic matter reacts with ozone (O3) and/or hydroxyl radicals (OH) affecting disinfection byproduct (DBP) formation with subsequently used chlorine-based disinfectants. This study presents the effects of varying exposures of O3 and •OH on DBP concentrations and their associated toxicity generated after subsequent chlorination. DBP formation potential tests and in vitro bioassays were conducted after batch ozonation experiments of coagulated surface water with and without addition of tertiary butanol (t-BuOH, 10 mM) and hydrogen peroxide (H2O2, 1 mg/mg O3), and at different pH (6-8) and transferred ozone doses (0-1 mg/mg TOC). Although ozonation led to a 24-37% decrease in formation of total trihalomethanes, haloacetic acids, haloacetonitriles, and trihaloacetamides, an increase in formation of total trihalonitromethanes, chloral hydrate, and haloketones was observed. This effect however was less pronounced for samples ozonated at conditions favoring molecular ozone (e.g., pH 6 and in the presence of t-BuOH) over •OH reactions (e.g., pH 8 and in the presence of H2O2). Compared to ozonation only, addition of H2O2 consistently enhanced formation of all DBP groups (20-61%) except trihalonitromethanes. This proves that •OH-transformed organic matter is more susceptible to halogen incorporation. Analogously, adsorbable organic halogen (AOX) concentrations increased under conditions that favor •OH reactions. The ratio of unknown to known AOX, however, was greater at conditions that promote direct O3 reactions. Although significant correlation was found between AOX and genotoxicity with the p53 bioassay, toxicity tests using 4 in vitro bioassays showed relatively low absolute differences between various ozonation conditions.

  6. Protease cleavage of iron-transferrin augments pyocyanin-mediated endothelial cell injury via promotion of hydroxyl radical formation.

    PubMed Central

    Miller, R A; Rasmussen, G T; Cox, C D; Britigan, B E

    1996-01-01

    Although a number of bacterium- and host-derived factors have been suggested to contribute to the pathogenesis of Pseudomonas aeruginosa-associated tissue injury, the mechanism remains unclear. We have previously shown that protease modification of iron (Fe)-transferrin generates new iron chelates capable of catalyzing hydroxyl radical (.OH) formation from superoxide and hydrogen peroxide. The latter two oxidants are generated during redox cycling of another P. aeruginosa secretory product, pyocyanin. The lung is a major site of P. aeruginosa infection, with damage to local endothelial cells contributing to the pathogenesis of such infections. Endothelial cells are highly susceptible to oxidant-mediated injury. Therefore, we examined whether pseudomonas elastase-cleaved Fe-transferrin and pyocyanin synergistically enhance pulmonary artery endothelial cell injury via .OH formation. By measuring 51Cr release from cultured endothelial cell monolayers, pseudomonas elastase-cleaved Fe-transferrin significantly augmented cell injury resulting from cellular exposure to sublethal concentrations of pyocyanin. This enhancement in injury was not protease specific, as similar results were obtained with pyocyanin in combination with trypsin- or porcine pancreatic elastase-cleaved Fe-transferrin. The association of iron with the transferrin appeared to be necessary in this process. Supporting the involvement of .OH generation via the Haber-Weiss reaction in augmenting cell injury, catalase, dimethyl thiourea, superoxide dismutase, deferoxamine, and dimethyl sulfoxide significantly inhibited cell injury resulting from exposure to pyocyanin and protease-cleaved Fe-transferrin. Furthermore, spin trapping demonstrated the production of .OH in this cellular system. We conclude that .OH formation resulting from the interaction of protease-cleaved Fe-transferrin and endothelial cell redox cycling of pyocyanin may contribute to P. aeruginosa-associated tissue injury via endothelial cell

  7. Aqueous benzene-diols react with an organic triplet excited state and hydroxyl radical to form secondary organic aerosol.

    PubMed

    Smith, Jeremy D; Kinney, Haley; Anastasio, Cort

    2015-04-21

    Chemical processing in atmospheric aqueous phases, such as cloud and fog drops, can play a significant role in the production and evolution of secondary organic aerosol (SOA). In this work we examine aqueous SOA production via the oxidation of benzene-diols (dihydroxy-benzenes) by the triplet excited state of 3,4-dimethoxybenzaldehyde, (3)DMB*, and by hydroxyl radical, ˙OH. Reactions of the three benzene-diols (catechol (CAT), resorcinol (RES) and hydroquinone (HQ)) with (3)DMB* or ˙OH proceed rapidly, with rate constants near diffusion-controlled values. The two oxidants exhibit different behaviors with pH, with rate constants for (3)DMB* increasing as pH decreases from pH 5 to 2, while rate constants with ˙OH decrease in more acidic solutions. Mass yields of SOA were near 100% for all three benzene-diols with both oxidants. We also examined the reactivity of atmospherically relevant mixtures of phenols and benzene-diols in the presence of (3)DMB*. We find that the kinetics of phenol and benzene-diol loss, and the production of SOA mass, in mixtures are generally consistent with rate constants determined in experiments containing a single phenol or benzene-diol. Combining our aqueous kinetic and SOA mass yield data with previously published gas-phase data, we estimate a total SOA production rate from benzene-diol oxidation in a foggy area with significant wood combustion to be nearly 0.6 μg mair(-3) h(-1), with approximately half from the aqueous oxidation of resorcinol and hydroquinone, and half from the gas-phase oxidation of catechol.

  8. A comparison of hydroxyl radical and hydrogen peroxide generation in ambient particle extracts and laboratory metal solutions

    NASA Astrophysics Data System (ADS)

    Shen, Huiyun; Anastasio, Cort

    2012-01-01

    Generation of reactive oxygen species (ROS) - including superoxide ( rad O 2-), hydrogen peroxide (HOOH), and hydroxyl radical ( rad OH) - has been suggested as one mechanism underlying the adverse health effects caused by ambient particulate matter (PM). In this study we compare HOOH and rad OH production from fine and coarse PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California, as well as from laboratory solutions containing dissolved copper or iron. Samples were extracted in a cell-free, phosphate-buffered saline (PBS) solution containing 50 μM ascorbate (Asc). In our laboratory solutions we find that Cu is a potent source of both HOOH and rad OH, with approximately 90% of the electrons that can be donated from Asc ending up in HOOH and rad OH after 4 h. In contrast, in Fe solutions there is no measurable HOOH and only a modest production of rad OH. Soluble Cu in the SJV PM samples is also a dominant source of HOOH and rad OH. In both laboratory copper solutions and extracts of ambient particles we find much more production of HOOH compared to rad OH: e.g., HOOH generation is approximately 30-60 times faster than rad OH generation. The formation of HOOH and rad OH are positively correlated, with roughly 3% and 8% of HOOH converted to rad OH after 4 and 24 h of extraction, respectively. Although the SJV PM produce much more HOOH than rad OH, since rad OH is a much stronger oxidant it is unclear which species might be more important for oxidant-mediated toxicity from PM inhalation.

  9. A Comparison of Hydroxyl Radical and Hydrogen Peroxide Generation in Ambient Particle Extracts and Laboratory Metal Solutions

    PubMed Central

    Shen, Huiyun; Anastasio, Cort

    2011-01-01

    Generation of reactive oxygen species (ROS) – including superoxide (•O2−), hydrogen peroxide (HOOH), and hydroxyl radical (•OH) – has been suggested as one mechanism underlying the adverse health effects caused by ambient particulate matter (PM). In this study we compare HOOH and •OH production from fine and coarse PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California, as well as from laboratory solutions containing dissolved copper or iron. Samples were extracted in a cell-free, phosphate-buffered saline (PBS) solution containing 50 μM ascorbate (Asc). In our laboratory solutions we find that Cu is a potent source of both HOOH and •OH, with approximately 90% of the electrons that can be donated from Asc ending up in HOOH and •OH after 4 h. In contrast, in Fe solutions there is no measurable HOOH and only a modest production of •OH. Soluble Cu in the SJV PM samples is also a dominant source of HOOH and •OH. In both laboratory copper solutions and extracts of ambient particles we find much more production of HOOH compared to •OH: e.g., HOOH generation is approximately 30 – 60 times faster than •OH generation. The formation of HOOH and •OH are positively correlated, with roughly 3 % and 8 % of HOOH converted to •OH after 4 and 24 hr of extraction, respectively. Although the SJV PM produce much more HOOH than •OH, since •OH is a much stronger oxidant it is unclear which species might be more important for oxidant-mediated toxicity from PM inhalation. PMID:22267949

  10. A Comparison of Hydroxyl Radical and Hydrogen Peroxide Generation in Ambient Particle Extracts and Laboratory Metal Solutions.

    PubMed

    Shen, Huiyun; Anastasio, Cort

    2012-01-01

    Generation of reactive oxygen species (ROS) - including superoxide ((•)O(2) (-)), hydrogen peroxide (HOOH), and hydroxyl radical ((•)OH) - has been suggested as one mechanism underlying the adverse health effects caused by ambient particulate matter (PM). In this study we compare HOOH and (•)OH production from fine and coarse PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California, as well as from laboratory solutions containing dissolved copper or iron. Samples were extracted in a cell-free, phosphate-buffered saline (PBS) solution containing 50 μM ascorbate (Asc). In our laboratory solutions we find that Cu is a potent source of both HOOH and (•)OH, with approximately 90% of the electrons that can be donated from Asc ending up in HOOH and (•)OH after 4 h. In contrast, in Fe solutions there is no measurable HOOH and only a modest production of (•)OH. Soluble Cu in the SJV PM samples is also a dominant source of HOOH and (•)OH. In both laboratory copper solutions and extracts of ambient particles we find much more production of HOOH compared to (•)OH: e.g., HOOH generation is approximately 30 - 60 times faster than (•)OH generation. The formation of HOOH and (•)OH are positively correlated, with roughly 3 % and 8 % of HOOH converted to (•)OH after 4 and 24 hr of extraction, respectively. Although the SJV PM produce much more HOOH than (•)OH, since (•)OH is a much stronger oxidant it is unclear which species might be more important for oxidant-mediated toxicity from PM inhalation. PMID:22267949

  11. EPR detection of hydroxyl radical generation and oxidative perturbations in lead-exposed earthworms (Eisenia fetida) in the presence of decabromodiphenyl ether.

    PubMed

    Liu, Kou; Chen, Lin; Zhang, Wei; Lin, Kuangfei; Zhao, Li

    2015-03-01

    Lead (Pb) and decabromodiphenyl ether (BDE209) are the main contaminants at e-waste recycling sites, and their potential toxicological effects on terrestrial organisms have received extensive attention. However, the impacts on the oxidative perturbations and hydroxyl radical (·OH) generation in earthworms of exposure to the two chemicals remain almost unknown. Therefore, indoor incubation tests were performed on control and contaminated soil samples to determine the effects of Pb in earthworms Eisenia fetida in the presence of BDE209 through the use of several biomarkers in microcosms. The results have demonstrated that the addition of BDE209 (1 or 10 mg kg(-1)) decreased the enzymatic activities [superoxide dismutase, catalase (CAT), peroxidase] and total antioxidant capacity (T-AOC) compared with exposure to BDE209 alone (50, 250 or 500 mg kg(-1)). Electron paramagnetic resonance spectra indicated that ·OH radicals in earthworms were significantly induced by Pb in the presence of BDE209. The changing pattern of malondialdehyde (MDA) contents was accordant with that of ·OH intensity suggested that reactive oxygen species might lead to cellular lipid peroxidation. Furthermore, CAT exhibited more sensitive response to single Pb exposure than the other biomarkers, while T-AOC, ·OH and MDA might be three most sensitive biomarkers in earthworms after simultaneous exposure to Pb and BDE209. The results of these observations suggested that oxidative stress appeared in E. fetida, and it may play an important role in inducing the Pb and BDE209 toxicity to earthworms.

  12. Theoretical study of the oxidation mechanisms of naphthalene initiated by hydroxyl radicals: the OH-addition pathway.

    PubMed

    Shiroudi, Abolfazl; Deleuze, Michael S; Canneaux, Sébastien

    2014-07-01

    The oxidation mechanisms of naphthalene by OH radicals under inert (He) conditions have been studied using density functional theory along with various exchange-correlation functionals. Comparison has been made with benchmark CBS-QB3 theoretical results. Kinetic rate constants were correspondingly estimated by means of transition state theory and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Comparison with experiment confirms that, on the OH-addition reaction pathway leading to 1-naphthol, the first bimolecular reaction step has an effective negative activation energy around -1.5 kcal mol(-1), whereas this step is characterized by an activation energy around 1 kcal mol(-1) on the OH-addition reaction pathway leading to 2-naphthol. Effective rate constants have been calculated according to a steady state analysis upon a two-step model reaction mechanism. In line with experiment, the correspondingly obtained branching ratios indicate that, at temperatures lower than 410 K, the most abundant product resulting from the oxidation of naphthalene by OH radicals must be 1-naphthol. The regioselectivity of the OH(•)-addition onto naphthalene decreases with increasing temperatures and decreasing pressures. Because of slightly positive or even negative activation energies, the RRKM calculations demonstrate that the transition state approximation breaks down at ambient pressure (1 bar) for the first bimolecular reaction steps. Overwhelmingly high pressures, larger than 10(5) bar, would be required for restoring to some extent (within ∼5% accuracy) the validity of this approximation for all the reaction channels that are involved in the OH-addition pathway. Analysis of the computed structures, bond orders, and free energy profiles demonstrate that all reaction steps involved in the oxidation of naphthalene by OH radicals satisfy Leffler-Hammond's principle. Nucleus independent chemical shift indices and natural bond orbital analysis also show that the computed

  13. Novel relationship between hydroxyl radical initiation and surface group of ceramic honeycomb supported metals for the catalytic ozonation of nitrobenzene in aqueous solution.

    PubMed

    Zhao, Lei; Sun, Zhizhong; Ma, Jun

    2009-06-01

    Comparative experiments have been performed to investigate the degradation efficiency of nitrobenzene and the removal efficiency of TOC in aqueous solution bythe processes of ceramic honeycomb supported different metals (Fe, Ni, and Zn) catalytic ozonation, indicating that the modification with metals can enhance the activity of ceramic honeycomb for the catalytic ozonation of nitrobenzene, and the loading percentage of metal and the metallicity respectively presents a positive influence on the degradation of nitrobenzene. The degradation efficiency of nitrobenzene is determined by the initiation of hydroxyl radical (*OH) according to a good linear correlation in all the processes of modified ceramic honeycomb catalytic ozonation at the different loading percentages of metals. The modification of ceramic honeycomb with metals results in the conversion of the pH at the point of zero charge (pHpzc) and the evolution of surface groups. Divergence from the conventional phenomenon, the enhancement mechanism of ozone decomposition on the modified ceramic honeycomb with metals is proposed due to the basic attractive forces of electrostatic forces or/and hydrogen bonding. Consequently, a novel relationship between the initiation of *OH and the surface-OH2+ group on the modified catalyst is established based on the synergetic effect between homogeneous and heterogeneous reaction systems.

  14. Radical Scavenging Activities of Undaria pinnatifida Extracts Fermented with Cordyceps militaris Mycelia.

    PubMed

    Kim, Yon-Suk; Kim, Eun-Kyung; Hwang, Jin-Woo; Han, Young-Ki; Kim, Seong-Eun; Jeong, Jae-Hyun; Moon, Sang-Ho; Jeon, Byong-Tae; Park, Pyo-Jam

    2015-06-01

    The present study was performed to investigate the various radical scavenging activities of fermented Undaria pinnatifida by the mycelia fermentation method. U. pinnatifida was fermented with Cordyceps militaris (C. militaris) mycelia using solid culture and compared with unfermentated U. pinnatifida and C. militaris mycelia for antioxidant activities. The various radical scavenging activities of extracts from U. pinnatifida fermented with C. militaris mycelia (FUCM) were evaluated by electron spin resonance. The antioxidant activities of the FUCM extracts were assayed for ferric reducing antioxidant power, 2,2'-azinobis-(3- ethybenzothiazoline-6-sulfonic acid) radical scavenging activity, and oxygen radical absorption capacity. The free radical scavenging activity of FUCM extracts was higher than that of C. militaris mycelia or U. pinnatifida alone. FUCM extracts were significantly (p < 0.05) increased up to 35 times, 10 times, and 16 times that of U. pinnatifida extracts on DPPH, alkyl, and hydroxyl radical scavenging activities, respectively. These results indicate that FUCM extracts have different chemical ingredients from U. pinnatifida and could provide beneficial antioxidant activity.

  15. Intensification of volatile organic compounds mass transfer in a compact scrubber using the O3/H2O2 advanced oxidation process: kinetic study and hydroxyl radical tracking.

    PubMed

    Biard, Pierre-François; Couvert, Annabelle; Renner, Christophe; Levasseur, Jean-Pierre

    2011-11-01

    This study assesses the potential of ozonation and advanced oxidation process O(3)/H(2)O(2) to enhance the dimethyldisulfide (DMDS) mass transfer in a compact chemical scrubber developed for air treatment applications. Theoretical calculations, through Hatta number and enhancement factor evaluations for two parallel irreversible reactions, were compared to experimental data and enabled the description of the mass transfer mechanisms. These calculations required the determination of the kinetic constant of the DMDS oxidation by molecular ozone ( [Formula: see text] ) and the measurement of the hydroxyl radical concentration within the scrubber. The competitive kinetic method using the 1,2-dihydroxybenzene (resorcinol) enabled to determine a value of the kinetic constant [Formula: see text] of 1.1×10(6)M(-1)s(-1) at 293K. Then, experiments using para-chlorobenzoic acid in solution allowed measuring the average hydroxyl concentration in the scrubber between the inlet and the outlet depending on the chemical conditions (pH and inlet O(3) and H(2)O(2) concentrations). High hydroxyl radical concentrations (10(-8)M) and ratio of the HO°-to-O(3) exposure (R(ct)≈10(-4)) were put in evidence.

  16. Observations of hydroxyl and peroxy radicals and the impact of BrO at Summit, Greenland in 2007 and 2008

    NASA Astrophysics Data System (ADS)

    Liao, J.; Huey, L. G.; Tanner, D. J.; Brough, N.; Brooks, S.; Dibb, J. E.; Stutz, J.; Thomas, J. L.; Lefer, B.; Haman, C.; Gorham, K.

    2011-08-01

    The Greenland Summit Halogen-HOx (GSHOX) Campaign was performed in spring 2007 and summer 2008 to investigate the impact of halogens on HOx (= OH + HO2) cycling above the Greenland Ice Sheet. Chemical species including hydroxyl and peroxy radicals (OH and HO2 + RO2), ozone (O3), nitrogen oxide (NO), nitric acid (HNO3), nitrous acid (HONO), reactive gaseous mercury (RGM), and bromine oxide (BrO) were measured during the campaign. The median midday values of HO2 + RO2 and OH concentrations observed by chemical ionization mass spectrometry (CIMS) were 2.7 × 108 molec cm-3 and 3.0 × 106 molec cm-3 in spring 2007, and 4.2 × 108 molec cm-3 and 4.1 × 106 molec cm-3 in summer 2008. A basic photochemical 0-D box model highly constrained by observations of H2O, O3, CO, CH4, NO, and J values predicted HO2 + RO2 (R = 0.90, slope = 0.87 in 2007; R = 0.79, slope = 0.96 in 2008) reasonably well and under predicted OH (R = 0.83, slope = 0.72 in 2007; R = 0.76, slope = 0.54 in 2008). Constraining the model to HONO observations did not significantly improve the ratio of OH to HO2 + RO2 and the correlation between predictions and observations. Including bromine chemistry in the model constrained by observations of BrO improved the correlation between observed and predicted HO2 + RO2 and OH, and brought the average hourly OH and HO2 + RO2 predictions closer to the observations. These model comparisons confirmed our understanding of the dominant HOx sources and sinks in this environment and indicated that BrO impacted the OH levels at Summit. Although, significant discrepancies between observed and predicted OH could not be explained by the measured BrO. Finally, observations of enhanced RGM were found to be coincident with under prediction of OH.

  17. On the use of hydroxyl radical kinetics to assess the number-average molecular weight of dissolved organic matter.

    PubMed

    Appiani, Elena; Page, Sarah E; McNeill, Kristopher

    2014-10-21

    Dissolved organic matter (DOM) is involved in numerous environmental processes, and its molecular size is important in many of these processes, such as DOM bioavailability, DOM sorptive capacity, and the formation of disinfection byproducts during water treatment. The size and size distribution of the molecules composing DOM remains an open question. In this contribution, an indirect method to assess the average size of DOM is described, which is based on the reaction of hydroxyl radical (HO(•)) quenching by DOM. HO(•) is often assumed to be relatively unselective, reacting with nearly all organic molecules with similar rate constants. Literature values for HO(•) reaction with organic molecules were surveyed to assess the unselectivity of DOM and to determine a representative quenching rate constant (k(rep) = 5.6 × 10(9) M(-1) s(-1)). This value was used to assess the average molecular weight of various humic and fulvic acid isolates as model DOM, using literature HO(•) quenching constants, kC,DOM. The results obtained by this method were compared with previous estimates of average molecular weight. The average molecular weight (Mn) values obtained with this approach are lower than the Mn measured by other techniques such as size exclusion chromatography (SEC), vapor pressure osmometry (VPO), and flow field fractionation (FFF). This suggests that DOM is an especially good quencher for HO(•), reacting at rates close to the diffusion-control limit. It was further observed that humic acids generally react faster than fulvic acids. The high reactivity of humic acids toward HO(•) is in line with the antioxidant properties of DOM. The benefit of this method is that it provides a firm upper bound on the average molecular weight of DOM, based on the kinetic limits of the HO(•) reaction. The results indicate low average molecular weight values, which is most consistent with the recent understanding of DOM. A possible DOM size distribution is discussed to

  18. Formation of hydroxyl radical from San Joaquin Valley particles extracted in a cell-free surrogate lung fluid

    NASA Astrophysics Data System (ADS)

    Shen, H.; Anastasio, C.

    2011-09-01

    Previous studies have suggested that the adverse health effects from ambient particulate matter (PM) are linked to the formation of reactive oxygen species (ROS) by PM in cardiopulmonary tissues. While hydroxyl radical (•OH) is the most reactive of the ROS species, there are few quantitative studies of •OH generation from PM. Here we report on •OH formation from PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California. We quantified •OH in PM extracts using a cell-free, phosphate-buffered saline (PBS) solution with or without 50 μM ascorbate (Asc). The results show that generally the urban Fresno PM generates much more •OH than the rural Westside PM. The presence of Asc at a physiologically relevant concentration in the extraction solution greatly enhances •OH formation from all the samples. Fine PM (PM2.5) generally makes more •OH than the corresponding coarse PM (PMcf, i.e. with diameters of 2.5 to 10 μm) normalized by air volume collected, while the coarse PM typically generates more •OH normalized by PM mass. •OH production by SJV PM is reduced on average by (97 ± 6) % when the transition metal chelator desferoxamine (DSF) is added to the extraction solution, indicating a dominant role of transition metals. By measuring calibration curves of •OH generation from copper and iron, and quantifying copper and iron concentrations in our particle extracts, we find that PBS-soluble copper is primarily responsible for •OH production by the SJV PM, while iron often makes a significant contribution. Extrapolating our results to expected burdens of PM-derived •OH in human lung lining fluid suggests that typical daily PM exposures in the San Joaquin Valley are unlikely to result in a high amount of pulmonary •OH, although high PM events could produce much higher levels of •OH, which might lead to cytotoxicity.

  19. Formation of hydroxyl radical from San Joaquin Valley particles extracted in a cell-free surrogate lung fluid.

    PubMed

    Shen, H; Anastasio, C

    2011-09-16

    Previous studies have suggested that the adverse health effects from ambient particulate matter (PM) are linked to the formation of reactive oxygen species (ROS) by PM in cardiopulmonary tissues. While hydroxyl radical ((•)OH) is the most reactive of the ROS species, there are few quantitative studies of (•)OH generation from PM. Here we report on (•)OH formation from PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California. We quantified (•)OH in PM extracts using a cell-free, phosphate-buffered saline (PBS) solution with or without 50μM ascorbate (Asc). The results show that generally the urban Fresno PM generates much more (•)OH than the rural Westside PM. The presence of Asc at a physiologically relevant concentration in the extraction solution greatly enhances (•)OH formation from all the samples. Fine PM (PM(2.5)) generally makes more (•)OH than the corresponding coarse PM (PM(cf), i.e. with diameters of 2.5 to 10 μm) normalized by air volume collected, while the coarse PM typically generates more (•)OH normalized by PM mass. (•)OH production by SJV PM is reduced on average by (97±6)% when the transition metal chelator desferoxamine (DSF) is added to the extraction solution, indicating a dominant role of transition metals. By measuring calibration curves of (•)OH generation from copper and iron, and quantifying copper and iron concentrations in our particle extracts, we find that PBS-soluble copper is primarily responsible for (•)OH production by the SJV PM, while iron often makes a significant contribution. Extrapolating our results to expected burdens of PM-derived (•)OH in human lung lining fluid suggests that typical daily PM exposures in the San Joaquin Valley are unlikely to result in a high amount of pulmonary (•)OH, although high PM events could produce much higher levels of (•)OH, which might lead to cytotoxicity. PMID:22121357

  20. Formation of hydroxyl radical from San Joaquin Valley particles extracted in a cell-free surrogate lung fluid

    PubMed Central

    Shen, H.; Anastasio, C.

    2011-01-01

    Previous studies have suggested that the adverse health effects from ambient particulate matter (PM) are linked to the formation of reactive oxygen species (ROS) by PM in cardiopulmonary tissues. While hydroxyl radical (•OH) is the most reactive of the ROS species, there are few quantitative studies of •OH generation from PM. Here we report on •OH formation from PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California. We quantified •OH in PM extracts using a cell-free, phosphate-buffered saline (PBS) solution with or without 50μM ascorbate (Asc). The results show that generally the urban Fresno PM generates much more •OH than the rural Westside PM. The presence of Asc at a physiologically relevant concentration in the extraction solution greatly enhances •OH formation from all the samples. Fine PM (PM2.5) generally makes more •OH than the corresponding coarse PM (PMcf, i.e. with diameters of 2.5 to 10 μm) normalized by air volume collected, while the coarse PM typically generates more •OH normalized by PM mass. •OH production by SJV PM is reduced on average by (97±6)% when the transition metal chelator desferoxamine (DSF) is added to the extraction solution, indicating a dominant role of transition metals. By measuring calibration curves of •OH generation from copper and iron, and quantifying copper and iron concentrations in our particle extracts, we find that PBS-soluble copper is primarily responsible for •OH production by the SJV PM, while iron often makes a significant contribution. Extrapolating our results to expected burdens of PM-derived •OH in human lung lining fluid suggests that typical daily PM exposures in the San Joaquin Valley are unlikely to result in a high amount of pulmonary •OH, although high PM events could produce much higher levels of •OH, which might lead to cytotoxicity. PMID:22121357

  1. Extraction and free radical scavenging activity of polysaccharide from 'Anji Baicha' (Camellia sinensis (L.) O. Kuntze).

    PubMed

    Zhang, Zhongshan; Wang, Xiaomei; Li, Jingfen; Wang, Guozhi; Mao, Genxiang

    2016-03-01

    In this study, the optimization of the extraction conditions of polysaccharide from 'Anji Baicha' (Camellia sinensis (L.) O. Kuntze) (AP) was investigated by response surface methodology (RSM). Three main independent variables (extraction temperature, time, ratio of water to raw material) were taken into consideration. And then the free radical scavenging activities of the sample were investigated including scavenging effects of superoxide and hydroxyl radicals. The RSM analysis showed good correspondence between experimental and predicted values.. The optimal condition to obtain the highest yield of AP was determined as follows: temperature 76.79 °C, time 2.48 h, ratio of water to material 22.53 mL/g. For the free radical scavenging activity, the IC50 values of Vc and AP were 7.78 and 83.25 μg/mL. And for the scavenging effect on hydroxyl radical, that of AP and Vc were 1.80 and 1.69 mg/mL. AP showed excellent antioxidant activity. This exhibited AP had a good potential for antioxidant. The purification and structure needs to be study in further.

  2. Regioselective and stereospecific hydroxylation of GR24 by Sorghum bicolor and evaluation of germination inducing activities of hydroxylated GR24 stereoisomers toward seeds of Striga species.

    PubMed

    Ueno, Kotomi; Ishiwa, Shunsuke; Nakashima, Hitomi; Mizutani, Masaharu; Takikawa, Hirosato; Sugimoto, Yukihiro

    2015-09-15

    Bioconversion of GR24, the most widely used synthetic strigolactone (SL), by hydroponically grown sorghum (Sorghum bicolor) and biological activities of hydroxylated GR24 stereoisomers were studied. Analysis of extracts and exudates of sorghum roots previously fed with a racemic and diastereomeric mixture of GR24, using liquid chromatography-tandem mass spectrometry with multiple reaction monitoring (MRM), confirmed uptake of GR24 and suggested its conversion to mono-hydroxylated products. Two major GR24 metabolites, 7-hydroxy-GR24 and 8-hydroxy-GR24, were identified in the root extracts and exudates by direct comparison of chromatographic behavior with a series of synthetic mono-hydroxylated GR24 analogues. Separate feeding experiments with each of the GR24 stereoisomers revealed that the hydroxylated products were derived from 2'-epi-GR24, an evidence of sterical recognition of the GR24 molecule by sorghum. Trans-4-hydroxy-GR24 isomers derived from all GR24 stereoisomers were detected in the exudates as minor metabolites. The synthetic hydroxy-GR24 isomers induced germination of Striga hermonthica in decreasing order of C-8>C-7>C-6>C-5>C-4. In contrast the stereoisomers having the same configuration of orobanchol, irrespective of position of hydroxylation, induced germination of Striga gesnerioides. The results confirm previous reports on structural requirements of SLs and ascribe a critical role to hydroxylation, but not to the position of the hydroxyl group in the AB part of the molecule, in induction of S. gesnerioides seed germination.

  3. Stability of 5,5-dimethyl-1-pyrroline-N-oxide as a spin-trap for quantification of hydroxyl radicals in processes based on Fenton reaction.

    PubMed

    Fontmorin, J M; Burgos Castillo, R C; Tang, W Z; Sillanpää, M

    2016-08-01

    Fenton reaction was used to produce hydroxyl radicals under conditions similar to AOPs with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap agent in electron paramagnetic resonance (EPR) analysis. A theoretical kinetics model was developed to determine conditions under which the spin-adduct DMPO-OH is not further oxidized by Fe(3+) and excessive radicals, so that hydroxyl radicals concentration could be accurately inferred. Experiments were designed based upon the model and H2O2 and Fe(2+) concentrations were varied from 1 to 100 mM and from 0.1 to 10 mM, respectively, with a constant H2O2: Fe(2+) ratio of 10:1. Results confirmed that DMPO concentration should be at least 20 times higher than the concentration of H2O2 and 200 times higher than iron concentration to produce stable DMPO-OH EPR signal. When DMPO: H2O2 ratio varied from 1 to 10, DMPO-OH could generate intermediates and be further oxidized leading to the apparition of an additional triplet. This signal was attributed to a paramagnetic dimer: its structure and a formation mechanism were proposed. Finally, the utilization of sodium sulfite and catalase to terminate Fenton reaction was discussed. Catalase appeared to be compatible with DMPO. However, sodium sulfite should be avoided since it reacted with DMPO-OH to form DMPO-SO3. PMID:27132196

  4. Inhibition of peroxynitrite-mediated DNA strand cleavage and hydroxyl radical formation by aspirin at pharmacologically relevant concentrations: Implications for cancer intervention

    SciTech Connect

    Chen, Wei; Zhu, Hong; Jia, Zhenquan; Li, Jianrong; Misra, Hara P.; Zhou, Kequan; Li, Yunbo

    2009-12-04

    Epidemiological studies have suggested that the long-term use of aspirin is associated with a decreased incidence of human malignancies, especially colorectal cancer. Since accumulating evidence indicates that peroxynitrite is critically involved in multistage carcinogenesis, this study was undertaken to investigate the ability of aspirin to inhibit peroxynitrite-mediated DNA damage. Peroxynitrite and its generator 3-morpholinosydnonimine (SIN-1) were used to cause DNA strand breaks in {phi}X-174 plasmid DNA. We demonstrated that the presence of aspirin at concentrations (0.25-2 mM) compatible with amounts in plasma during chronic anti-inflammatory therapy resulted in a significant inhibition of DNA cleavage induced by both peroxynitrite and SIN-1. Moreover, the consumption of oxygen caused by 250 {mu}M SIN-1 was found to be decreased in the presence of aspirin, indicating that aspirin might affect the auto-oxidation of SIN-1. Furthermore, EPR spectroscopy using 5,5-dimethylpyrroline-N-oxide (DMPO) as a spin trap demonstrated the formation of DMPO-hydroxyl radical adduct (DMPO-OH) from authentic peroxynitrite, and that aspirin at 0.25-2 mM potently diminished the radical adduct formation in a concentration-dependent manner. Taken together, these results demonstrate for the first time that aspirin at pharmacologically relevant concentrations can inhibit peroxynitrite-mediated DNA strand breakage and hydroxyl radical formation. These results may have implications for cancer intervention by aspirin.

  5. Identification of a mechanism of iron uptake by cells which is stimulated by hydroxyl radicals generated via the iron-catalysed Haber-Weiss reaction.

    PubMed

    Richardson, D R; Ponka, P

    1995-11-01

    Recent studies have demonstrated that preincubation of SK-Mel-28 melanoma cells with ferric ammonium citrate (FAC) resulted in marked stimulation of 59Fe uptake from 59Fe-125I-transferrin (Tf), but only at Tf concentrations above that required for saturation of the Tf receptor (Richardson and Baker (1992) J. Biol. Chem. 267, 13972-13979). The mechanism responsible for this stimulation was unknown and is the subject of the present report. Preincubation of cells with FAC (25 micrograms/ml), followed by a 2 h incubation with 59Fe-125I-Tf (0.1 mg/ml; 1.25 microM), resulted in temperature-dependent 59Fe uptake to approx. 200% of the control value. Furthermore, the effect was not specific for melanoma cells and was also observed in other normal and neoplastic cells. Preincubation of melanoma cells with FAC also stimulated 59Fe uptake from 59Fe-citrate, but to a far greater extent than that observed with 59Fe-125I-Tf (viz., > 20-fold that seen for the control). Interestingly, neither receptor-mediated endocytosis nor the postulated diferric Tf reductase were involved in the FAC-activated Fe uptake process from Tf. However, the addition of free radical scavengers to FAC such as catalase, superoxide dismutase, ceruloplasmin, Hepes, mannitol and high concentrations of BSA or ascorbate, markedly depressed FAC-activated 59Fe uptake from 59Fe-125I-Tf and 59Fe-citrate. These agents when added to control cells had no effect on 59Fe uptake. The addition of superoxide generating agents and hydrogen peroxide to minimum essential medium (MEM) containing FAC but not to MEM alone, also stimulated 59Fe uptake. These data suggest that the initial activation of the FAC-stimulated Fe uptake system was caused by the production of hydroxyl radicals via the Fe-catalysed Haber-Weiss reaction. We propose that this Fe uptake process represents an important cellular defense mechanism against oxidant stress generated in the presence of low-molecular-weight Fe complexes.

  6. In vivo monitoring of hydroxyl radical generation caused by x-ray irradiation of rats using the spin trapping/EPR technique.

    PubMed

    Takeshita, Keizo; Fujii, Kaori; Anzai, Kazunori; Ozawa, Toshihiko

    2004-05-01

    Measurement of hydroxyl radical (*OH) in living animals irradiated with ionizing radiation should be required to clarify the mechanisms of radiation injury and the in vivo assessment of radiation protectors, because generation of *OH is believed to be one of the major triggers of radiation injury. In this study, *OH generation was monitored by spin trapping the secondary methyl radical formed by the reaction of *OH with dimethyl sulfoxide (DMSO). Rats were injected intraperitoneally with a DMSO solution of alpha-phenyl-N-tert-butylnitrone (PBN). X-irradiation of the rats remarkedly increased the six-line EPR signal in the bile. The strengthened signal was detectable above 40 Gy. Use of 13C-substituted DMSO revealed that the signal included the methyl radical adduct of PBN as a major component. The EPR signal of the PBN-methyl radical adduct was completely suppressed by preadministration of methyl gallate, a scavenger of *OH but not of methyl radical. Methyl gallate did not reduce the spin adducts to EPR-silent forms. These observations indicate that what we were measuring was *OH generated in vivo by x-irradiation. This is the first report of the in vivo monitoring of *OH generation at a radiation dose close to what people might receive in the case of radiological accident or radiation therapy.

  7. Atomic-scale insight into the interactions between hydroxyl radicals and DNA in solution using the ReaxFF reactive force field

    NASA Astrophysics Data System (ADS)

    Verlackt, C. C. W.; Neyts, E. C.; Jacob, T.; Fantauzzi, D.; Golkaram, M.; Shin, Y.-K.; van Duin, A. C. T.; Bogaerts, A.

    2015-10-01

    Cold atmospheric pressure plasmas have proven to provide an alternative treatment of cancer by targeting tumorous cells while leaving their healthy counterparts unharmed. However, the underlying mechanisms of the plasma-cell interactions are not yet fully understood. Reactive oxygen species, and in particular hydroxyl radicals (OH), are known to play a crucial role in plasma driven apoptosis of malignant cells. In this paper we investigate the interaction of OH radicals, as well as H2O2 molecules and HO2 radicals, with DNA by means of reactive molecular dynamics simulations using the ReaxFF force field. Our results provide atomic-scale insight into the dynamics of oxidative stress on DNA caused by the OH radicals, while H2O2 molecules appear not reactive within the considered time-scale. Among the observed processes are the formation of 8-OH-adduct radicals, forming the first stages towards the formation of 8-oxoGua and 8-oxoAde, H-abstraction reactions of the amines, and the partial opening of loose DNA ends in aqueous solution.

  8. Reactive carbonyls and polyunsaturated fatty acids produce a hydroxyl radical-like species: a potential pathway for oxidative damage of retinal proteins in diabetes.

    PubMed

    Pennathur, Subramaniam; Ido, Yasuo; Heller, Jozsef I; Byun, Jaeman; Danda, Ratna; Pergola, Pablo; Williamson, Joseph R; Heinecke, Jay W

    2005-06-17

    The pattern of oxidized amino acids in aortic proteins of nonhuman primates suggests that a species resembling hydroxyl radical damages proteins when blood glucose levels are high. However, recent studies argue strongly against a generalized increase in diabetic oxidative stress, which might instead be confined to the vascular wall. Here, we describe a pathway for glucose-stimulated protein oxidation and provide evidence of its complicity in diabetic microvascular disease. Low density lipoprotein incubated with pathophysiological concentrations of glucose became selectively enriched in ortho-tyrosine and meta-tyrosine, implicating a hydroxyl radical-like species in protein damage. Model system studies demonstrated that the reaction pathway requires both a reactive carbonyl group and a polyunsaturated fatty acid, involves lipid peroxidation, and is blocked by the carbonyl scavenger aminoguanidine. To explore the physiological relevance of the pathway, we used mass spectrometry and high pressure liquid chromatography to quantify oxidation products in control and hyperglycemic rats. Hyperglycemia raised levels of ortho-tyrosine, meta-tyrosine, and oxygenated lipids in the retina, a tissue rich in polyunsaturated fatty acids. Rats that received aminoguanidine did not show this increase in protein and lipid oxidation. In contrast, rats with diet-induced hyperlipidemia in the absence of hyperglycemia failed to exhibit increased protein and lipid oxidation products in the retina. Our observations suggest that generation of a hydroxyl radical-like species by a carbonyl/polyunsaturated fatty acid pathway might promote localized oxidative stress in tissues vulnerable to diabetic damage. This raises the possibility that antioxidant therapies that specifically inhibit the pathway might delay the vascular complications of diabetes.

  9. Kinetics and Mechanism of the Oxidation of Cyclic Methylsiloxanes by Hydroxyl Radical in the Gas Phase: An Experimental and Theoretical Study.

    PubMed

    Xiao, Ruiyang; Zammit, Ian; Wei, Zongsu; Hu, Wei-Ping; MacLeod, Matthew; Spinney, Richard

    2015-11-17

    The ubiquitous presence of cyclic volatile methylsiloxanes (cVMS) in the global atmosphere has recently raised environmental concern. In order to assess the persistence and long-range transport potential of cVMS, their second-order rate constants (k) for reactions with hydroxyl radical ((•)OH) in the gas phase are needed. We experimentally and theoretically investigated the kinetics and mechanism of (•)OH oxidation of a series of cVMS, hexamethylcyclotrisiloxane (D3), octamethycyclotetrasiloxane (D4), and decamethycyclopentasiloxane (D5). Experimentally, we measured k values for D3, D4, and D5 with (•)OH in a gas-phase reaction chamber. The Arrhenius activation energies for these reactions in the temperature range from 313 to 353 K were small (-2.92 to 0.79 kcal·mol(-1)), indicating a weak temperature dependence. We also calculated the thermodynamic and kinetic behaviors for reactions at the M06-2X/6-311++G**//M06-2X/6-31+G** level of theory over a wider temperature range of 238-358 K that encompasses temperatures in the troposphere. The calculated Arrhenius activation energies range from -2.71 to -1.64 kcal·mol(-1), also exhibiting weak temperature dependence. The measured k values were approximately an order of magnitude higher than the theoretical values but have the same trend with increasing size of the siloxane ring. The calculated energy barriers for H-atom abstraction at different positions were similar, which provides theoretical support for extrapolating k for other cyclic siloxanes from the number of abstractable hydrogens.

  10. Radical-scavenging activity, protective effect against lipid peroxidation and mineral contents of monofloral Cuban honeys.

    PubMed

    Alvarez-Suarez, José M; Giampieri, Francesca; Damiani, Elisabetta; Astolfi, Paola; Fattorini, Daniele; Regoli, Francesco; Quiles, José L; Battino, Maurizio

    2012-03-01

    Several monofloral Cuban honeys were analyzed to determine their free radical-scavenging activity and from this the total antioxidant content was estimated. The protective effect against lipid peroxidation in an in vitro model of rat liver homogenates was evaluated and, lastly, the mineral content of the honeys, which can be related to the maintenance of intracellular oxidative balance, was determined. The scavenging capacities against hydroxyl and superoxide radicals were determined using the spin-trapping technique and the hypoxanthine/xanthine oxidase assay, respectively. Lipid peroxidation was evaluated through the production of TBARS and hydroperoxides. All honeys tested showed potential antioxidant activity with Linen vine displaying the highest scavenging capacity towards the DPPH, hydroxyl and superoxide radicals, while the least efficient was Christmas vine honey. Honeys also inhibited, in a concentration-dependent mode, lipid peroxidation in rat liver homogenates, with Linen vine resulting the best while the least effective was Christmas vine honey. The ability to scavenge free radicals and protect against lipid peroxidation may contribute to the ability of certain Cuban honeys to help in preventing/reducing some inflammatory diseases in which oxidative stress is involved. A total of eight minerals were identified and quantified as follows: cadmium, chromium, copper, nickel, iron, manganese, lead, and zinc. Minerals found in higher concentrations were iron, zinc and manganese.

  11. Transport and Distribution of Hydroxyl Radicals and Oxygen Atoms from H2O Photodissociation in the Inner Coma of Comet 67P/Churyumov-Gerasimenko

    NASA Astrophysics Data System (ADS)

    Lai, Ian-Lin; Su, Cheng-Chin; Ip, Wing-Huen; Wei, Chen-En; Wu, Jong-Shinn; Lo, Ming-Chung; Liao, Ying; Thomas, Nicolas

    2016-03-01

    With a combination of the Direct Simulation Monte Carlo (DSMC) calculation and test particle computation, the ballistic transport process of the hydroxyl radicals and oxygen atoms produced by photodissociation of water molecules in the coma of comet 67P/Churyumov-Gerasimenko is modelled. We discuss the key elements and essential features of such simulations which results can be compared with the remote-sensing and in situ measurements of cometary gas coma from the Rosetta mission at different orbital phases of this comet.

  12. Rate constants of hydroxyl radical oxidation of polychlorinated biphenyls in the gas phase: A single-descriptor based QSAR and DFT study.

    PubMed

    Yang, Zhihui; Luo, Shuang; Wei, Zongsu; Ye, Tiantian; Spinney, Richard; Chen, Dong; Xiao, Ruiyang

    2016-04-01

    The second-order rate constants (k) of hydroxyl radical (·OH) with polychlorinated biphenyls (PCBs) in the gas phase are of scientific and regulatory importance for assessing their global distribution and fate in the atmosphere. Due to the limited number of measured k values, there is a need to model the k values for unknown PCBs congeners. In the present study, we developed a quantitative structure-activity relationship (QSAR) model with quantum chemical descriptors using a sequential approach, including correlation analysis, principal component analysis, multi-linear regression, validation, and estimation of applicability domain. The result indicates that the single descriptor, polarizability (α), plays an important role in determining the reactivity with a global standardized function of lnk = -0.054 × α ‒ 19.49 at 298 K. In order to validate the QSAR predicted k values and expand the current k value database for PCBs congeners, an independent method, density functional theory (DFT), was employed to calculate the kinetics and thermodynamics of the gas-phase ·OH oxidation of 2,4',5-trichlorobiphenyl (PCB31), 2,2',4,4'-tetrachlorobiphenyl (PCB47), 2,3,4,5,6-pentachlorobiphenyl (PCB116), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB169), and 2,3,3',4,5,5',6-heptachlorobiphenyl (PCB192) at 298 K at B3LYP/6-311++G**//B3LYP/6-31 + G** level of theory. The QSAR predicted and DFT calculated k values for ·OH oxidation of these PCB congeners exhibit excellent agreement with the experimental k values, indicating the robustness and predictive power of the single-descriptor based QSAR model we developed.

  13. Rate constants of hydroxyl radical oxidation of polychlorinated biphenyls in the gas phase: A single-descriptor based QSAR and DFT study.

    PubMed

    Yang, Zhihui; Luo, Shuang; Wei, Zongsu; Ye, Tiantian; Spinney, Richard; Chen, Dong; Xiao, Ruiyang

    2016-04-01

    The second-order rate constants (k) of hydroxyl radical (·OH) with polychlorinated biphenyls (PCBs) in the gas phase are of scientific and regulatory importance for assessing their global distribution and fate in the atmosphere. Due to the limited number of measured k values, there is a need to model the k values for unknown PCBs congeners. In the present study, we developed a quantitative structure-activity relationship (QSAR) model with quantum chemical descriptors using a sequential approach, including correlation analysis, principal component analysis, multi-linear regression, validation, and estimation of applicability domain. The result indicates that the single descriptor, polarizability (α), plays an important role in determining the reactivity with a global standardized function of lnk = -0.054 × α ‒ 19.49 at 298 K. In order to validate the QSAR predicted k values and expand the current k value database for PCBs congeners, an independent method, density functional theory (DFT), was employed to calculate the kinetics and thermodynamics of the gas-phase ·OH oxidation of 2,4',5-trichlorobiphenyl (PCB31), 2,2',4,4'-tetrachlorobiphenyl (PCB47), 2,3,4,5,6-pentachlorobiphenyl (PCB116), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB169), and 2,3,3',4,5,5',6-heptachlorobiphenyl (PCB192) at 298 K at B3LYP/6-311++G**//B3LYP/6-31 + G** level of theory. The QSAR predicted and DFT calculated k values for ·OH oxidation of these PCB congeners exhibit excellent agreement with the experimental k values, indicating the robustness and predictive power of the single-descriptor based QSAR model we developed. PMID:26748251

  14. Generation of hydroxyl radical in isolated pea root cell wall, and the role of cell wall-bound peroxidase, Mn-SOD and phenolics in their production.

    PubMed

    Kukavica, Biljana; Mojovic, Milos; Vuccinic, Zeljko; Maksimovic, Vuk; Takahama, Umeo; Jovanovic, Sonja Veljovic

    2009-02-01

    The hydroxyl radical produced in the apoplast has been demonstrated to facilitate cell wall loosening during cell elongation. Cell wall-bound peroxidases (PODs) have been implicated in hydroxyl radical formation. For this mechanism, the apoplast or cell walls should contain the electron donors for (i) H(2)O(2) formation from dioxygen; and (ii) the POD-catalyzed reduction of H(2)O(2) to the hydroxyl radical. The aim of the work was to identify the electron donors in these reactions. In this report, hydroxyl radical (.OH) generation in the cell wall isolated from pea roots was detected in the absence of any exogenous reductants, suggesting that the plant cell wall possesses the capacity to generate .OH in situ. Distinct POD and Mn-superoxide dismutase (Mn-SOD) isoforms different from other cellular isoforms were shown by native gel electropho-resis to be preferably bound to the cell walls. Electron paramagnetic resonance (EPR) spectroscopy of cell wall isolates containing the spin-trapping reagent, 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO), was used for detection of and differentiation between .OH and the superoxide radical (O(2)(-).). The data obtained using POD inhibitors confirmed that tightly bound cell wall PODs are involved in DEPMPO/OH adduct formation. A decrease in DEPMPO/OH adduct formation in the presence of H(2)O(2) scavengers demonstrated that this hydroxyl radical was derived from H(2)O(2). During the generation of .OH, the concentration of quinhydrone structures (as detected by EPR spectroscopy) increased, suggesting that the H(2)O(2) required for the formation of .OH in isolated cell walls is produced during the reduction of O(2) by hydroxycinnamic acids. Cell wall isolates in which the proteins have been denaturated (including the endogenous POD and SOD) did not produce .OH. Addition of exogenous H(2)O(2) again induced the production of .OH, and these were shown to originate from the Fenton reaction with tightly bound metal ions

  15. Chemical modification and structure-activity relationships of pyripyropenes. 1. Modification at the four hydroxyl groups.

    PubMed

    Obata, R; Sunazuka, T; Li, Z; Tian, Z; Harigaya, Y; Tabata, N; Tomoda, H; Omura, S

    1996-11-01

    Four hydroxyl groups of pyripyropenes have been modified and evaluated for their ability to inhibit microsomal acyl-CoA:cholesterol acyltransferase (ACAT) activity in vitro and to lower cholesterol absorption in vivo in a cholesterol-fed hamster. 7-O-n-Valeryl derivative (8c) improved the in vitro ACAT inhibitory activity (IC50 = 13 nM) about 7 times better than pyripyropene A. Introduction of methanesulfonyl group at 11-hydroxyl group (17a) increased both in vitro activity (IC50 = 19 nM) and in vivo efficacy (ED50 = 10 mg/kg). PMID:8982343

  16. Isomeric product detection in the heterogeneous reaction of hydroxyl radicals with aerosol composed of branched and linear unsaturated organic molecules.

    PubMed

    Nah, Theodora; Zhang, Haofei; Worton, David R; Ruehl, Christopher R; Kirk, Benjamin B; Goldstein, Allen H; Leone, Stephen R; Wilson, Kevin R

    2014-12-11

    The influence of molecular structure (branched vs linear) on product formation in the heterogeneous oxidation of unsaturated organic aerosol is investigated. Particle phase product isomers formed from the reaction of squalene (C30H50, a branched alkene with six C═C double bonds) and linolenic acid (C18H30O2, a linear carboxylic acid with three C═C double bonds) with OH radicals are identified and quantified using two-dimensional gas chromatography-mass spectrometry. The reactions are measured at low and high [O2] (∼1% vs 10% [O2]) to understand the roles of hydroxyalkyl and hydroxyperoxy radical intermediates in product formation. A key reaction step is OH addition to a C═C double bond to form a hydroxyalkyl radical. In addition, allylic alkyl radicals, formed from H atom abstraction reactions by hydroxyalkyl or OH radicals play important roles in the chemistry of product formation. Functionalization products dominate the squalene reaction at ∼1% [O2], with the total abundance of observed functionalization products being approximately equal to the fragmentation products at 10% [O2]. The large abundance of squalene fragmentation products at 10% [O2] is attributed to the formation and dissociation of tertiary hydroxyalkoxy radical intermediates. For linolenic acid aerosol, the formation of functionalization products dominates the reaction at both ∼1% and 10% [O2], suggesting that the formation and dissociation of secondary hydroxyalkoxy radicals are minor reaction channels for linear molecules. The distribution of linolenic acid functionalization products depends upon [O2], indicating that O2 controls the reaction pathways of the secondary hydroxyalkyl radical. For both reactions, alcohols are formed in favor of carbonyl functional groups, suggesting that there are some key differences between heterogeneous reactions involving allylic radical intermediates and those reactions of OH radicals with simple saturated hydrocarbons.

  17. Catalytic activity of unsaturated coordinated Cu-MOF to the hydroxylation of phenol

    NASA Astrophysics Data System (ADS)

    Jian, Lijuan; Chen, Chao; Lan, Fan; Deng, Shengjun; Xiao, Weiming; Zhang, Ning

    2011-05-01

    A 2D metal-organic framework [Cu 2 (BPTC) (Im) 4(H 2O) (DMF)] n ( 1) with unsaturated coordinated Cu(II) sites has been prepared under solvothermal condition, and applied to the hydroxylation of phenol after activating. The catalytic results indicate that 1a (the activated 1) exhibits an obvious activity for phenol hydroxylation at 40 °C for 4 h. Compared to the control experiments where the free Cu(II) (from Cu(OAc) 2 salt) has been utilized as the catalysts, 1a shows the higher selectivity to diphenols. This suggests that the coordinated environment of unsaturated coordinated Cu(II) sites in the 2D layer play the key role in the phenol hydroxylation.

  18. Quantitative protein topography analysis and high-resolution structure prediction using hydroxyl radical labeling and tandem-ion mass spectrometry (MS).

    PubMed

    Kaur, Parminder; Kiselar, Janna; Yang, Sichun; Chance, Mark R

    2015-04-01

    Hydroxyl radical footprinting based MS for protein structure assessment has the goal of understanding ligand induced conformational changes and macromolecular interactions, for example, protein tertiary and quaternary structure, but the structural resolution provided by typical peptide-level quantification is limiting. In this work, we present experimental strategies using tandem-MS fragmentation to increase the spatial resolution of the technique to the single residue level to provide a high precision tool for molecular biophysics research. Overall, in this study we demonstrated an eightfold increase in structural resolution compared with peptide level assessments. In addition, to provide a quantitative analysis of residue based solvent accessibility and protein topography as a basis for high-resolution structure prediction; we illustrate strategies of data transformation using the relative reactivity of side chains as a normalization strategy and predict side-chain surface area from the footprinting data. We tested the methods by examination of Ca(+2)-calmodulin showing highly significant correlations between surface area and side-chain contact predictions for individual side chains and the crystal structure. Tandem ion based hydroxyl radical footprinting-MS provides quantitative high-resolution protein topology information in solution that can fill existing gaps in structure determination for large proteins and macromolecular complexes.

  19. Label-Free Fluorescence Assay of S1 Nuclease and Hydroxyl Radicals Based on Water-Soluble Conjugated Polymers and WS2 Nanosheets

    PubMed Central

    Li, Junting; Zhao, Qi; Tang, Yanli

    2016-01-01

    We developed a new method for detecting S1 nuclease and hydroxyl radicals based on the use of water-soluble conjugated poly[9,9-bis(6,6-(N,N,N-trimethylammonium)-fluorene)-2,7-ylenevinylene-co-alt-2,5-dicyano-1,4-phenylene)] (PFVCN) and tungsten disulfide (WS2) nanosheets. Cationic PFVCN is used as a signal reporter, and single-layer WS2 is used as a quencher with a negatively charged surface. The ssDNA forms complexes with PFVCN due to much stronger electrostatic interactions between cationic PFVCN and anionic ssDNA, whereas PFVCN emits yellow fluorescence. When ssDNA is hydrolyzed by S1 nuclease or hydroxyl radicals into small fragments, the interactions between the fragmented DNA and PFVCN become weaker, resulting in PFVCN being adsorbed on the surface of WS2 and the fluorescence being quenched through fluorescence resonance energy transfer. The new method based on PFVCN and WS2 can sense S1 nuclease with a low detection limit of 5 × 10−6 U/mL. Additionally, this method is cost-effective by using affordable WS2 as an energy acceptor without the need for dye-labeled ssDNA. Furthermore, the method provides a new platform for the nuclease assay and reactive oxygen species, and provides promising applications for drug screening. PMID:27304956

  20. Label-Free Fluorescence Assay of S1 Nuclease and Hydroxyl Radicals Based on Water-Soluble Conjugated Polymers and WS₂ Nanosheets.

    PubMed

    Li, Junting; Zhao, Qi; Tang, Yanli

    2016-06-13

    We developed a new method for detecting S1 nuclease and hydroxyl radicals based on the use of water-soluble conjugated poly[9,9-bis(6,6-(N,N,N-trimethylammonium)-fluorene)-2,7-ylenevinylene-co-alt-2,5-dicyano-1,4-phenylene)] (PFVCN) and tungsten disulfide (WS₂) nanosheets. Cationic PFVCN is used as a signal reporter, and single-layer WS₂ is used as a quencher with a negatively charged surface. The ssDNA forms complexes with PFVCN due to much stronger electrostatic interactions between cationic PFVCN and anionic ssDNA, whereas PFVCN emits yellow fluorescence. When ssDNA is hydrolyzed by S1 nuclease or hydroxyl radicals into small fragments, the interactions between the fragmented DNA and PFVCN become weaker, resulting in PFVCN being adsorbed on the surface of WS₂ and the fluorescence being quenched through fluorescence resonance energy transfer. The new method based on PFVCN and WS₂ can sense S1 nuclease with a low detection limit of 5 × 10(-6) U/mL. Additionally, this method is cost-effective by using affordable WS₂ as an energy acceptor without the need for dye-labeled ssDNA. Furthermore, the method provides a new platform for the nuclease assay and reactive oxygen species, and provides promising applications for drug screening.

  1. Quantitative Protein Topography Analysis and High-Resolution Structure Prediction Using Hydroxyl Radical Labeling and Tandem-Ion Mass Spectrometry (MS)*

    PubMed Central

    Kaur, Parminder; Kiselar, Janna; Yang, Sichun; Chance, Mark R.

    2015-01-01

    Hydroxyl radical footprinting based MS for protein structure assessment has the goal of understanding ligand induced conformational changes and macromolecular interactions, for example, protein tertiary and quaternary structure, but the structural resolution provided by typical peptide-level quantification is limiting. In this work, we present experimental strategies using tandem-MS fragmentation to increase the spatial resolution of the technique to the single residue level to provide a high precision tool for molecular biophysics research. Overall, in this study we demonstrated an eightfold increase in structural resolution compared with peptide level assessments. In addition, to provide a quantitative analysis of residue based solvent accessibility and protein topography as a basis for high-resolution structure prediction; we illustrate strategies of data transformation using the relative reactivity of side chains as a normalization strategy and predict side-chain surface area from the footprinting data. We tested the methods by examination of Ca+2-calmodulin showing highly significant correlations between surface area and side-chain contact predictions for individual side chains and the crystal structure. Tandem ion based hydroxyl radical footprinting-MS provides quantitative high-resolution protein topology information in solution that can fill existing gaps in structure determination for large proteins and macromolecular complexes. PMID:25687570

  2. Light Absorption by Secondary Organic Aerosol Produced from Aqueous Reaction of Phenols with an Organic Excited Triplet State and Hydroxyl Radical

    NASA Astrophysics Data System (ADS)

    Smith, J.; Yu, L.; George, K.; Ruthenburg, T. C.; Dillner, A. M.; Zhang, Q.; Anastasio, C.

    2012-12-01

    Although reactions in atmospheric condensed phases can form and transform secondary organic aerosol (SOA), these reactions are not well represented in many air quality models. Previous experiments have focused on hydroxyl radical-mediated oxidation of low molecular weight precursors such as gyloxal and methylglyoxal. In our work we are examining aqueous SOA formed from phenols, which are emitted from biomass burning and formed from the oxidation of anthropogenic aromatics such as benzene and toluene. In this work we examine aqueous SOA production from oxidation of three phenols (phenol, guaiacol, syringol) and three benzene-diols (catechol, resorcinol, 1,4-hydroquinone) by hydroxyl radical (OH) and the triplet excited state of 3,4-dimethoxybenzaldehyde (DMB). Our focus is on light absorption by the reaction products, which we characterized by measuring UV-Vis spectra and calculating mass absorption coefficients. To understand the elemental and molecular composition of the SOA, we also analyzed the samples with high resolution mass spectrometry and infrared spectroscopy. Our results indicate that aqueous oxidation of phenols and benzene-diols via OH and triplet excited states efficiently produce SOA that is highly absorbing in the UV-A wavelengths, consists of both small and large molecular weight products, and is highly oxidized.

  3. A rapid and sensitive method for hydroxyl radical detection on a microfluidic chip using an N-doped porous carbon nanofiber modified pencil graphite electrode.

    PubMed

    Ouyang, Jun; Li, Zhong-Qiu; Zhang, Jing; Wang, Chen; Wang, Jiong; Xia, Xing-Hua; Zhou, Guo-Jun

    2014-07-01

    Hydroxyl radicals (˙OH) play an important role in human diseases. Traditional detection methods are time consuming and require expensive instruments. Here, we present a simple and sensitive method for the detection of hydroxyl radicals on a microfluidic chip using an electrochemical technique. Aniline monomer is electrochemically polymerized on the surface of a pencil graphite electrode and carbonized at 800 °C. The resulting N-doped porous carbon nanofiber-modified pencil graphite electrode is embedded into a microfluidic chip directly as a working electrode. 4-Hydroxybenzoic acid (4-HBA) is selected as the trapping agent owing to its unique 3,4-DHBA product and high trapping efficiency. A low detection limit of 1.0 × 10(-6) M is achieved on the microfluidic chip. As a demonstration, the microfluidic chip is successfully utilized for the detection of ˙OH in cigarette smoke. The strong π-π stacking and hydrophobic interactions between the nitrogen-doped carbon materials and the pencil graphite make the modified electrode well-suited for the microfluidic chip.

  4. Impact of nitrous acid photolysis on the total hydroxyl radical budget during the Limitation of Oxidant Production/Pianura Padana Produzione di Ozono study in Milan

    NASA Astrophysics Data System (ADS)

    Alicke, B.; Platt, U.; Stutz, J.

    2002-11-01

    The photolysis of nitrous acid (HONO) in the early morning hours is believed to be a significant source of hydroxyl radicals (OH), the most important daytime oxidizing species. Although the importance of this mechanism has been recognized for many years, no accurate experimental quantification is available. Here we present measurements of HONO, NO2, SO2, O3 and HCHO by Differential Optical Absorption Spectroscopy (DOAS) during the Limitation of Oxidant Production/Pianura Padana Produzione di Ozono (LOOP/PIPAPO) study in May-June 1998 in Milan, Italy. The concentration of NO and J(NO2)/J(HONO) were simultaneously monitored by in situ monitors. The photolysis frequencies of HCHO and O3 were determined with a radiative transfer model. High nocturnal HONO mixing ratios of up to 4.4 ppb were regularly observed. Elevated daytime HONO levels during cloudy periods show that the formation of HONO proceeds after sunrise and therefore also represents a source of hydroxyl radicals throughout the day. Averaged over 24 hours, HCHO photolysis is the most important source of OH in Milan, followed by either ozone or HONO photolysis. Our observations indicate that on certain days the OH production from HONO can be even more important than that from ozone photolysis. The diurnal variation of the different OH formation mechanisms shows that HONO photolysis is by far the most important source in the early hours of the morning, and can be as large as and even surpass the total OH production at noon.

  5. Free-radical scavenging activity and antibacterial impact of Greek oregano isolates obtained by SFE.

    PubMed

    Stamenic, Marko; Vulic, Jelena; Djilas, Sonja; Misic, Dusan; Tadic, Vanja; Petrovic, Slobodan; Zizovic, Irena

    2014-12-15

    The antioxidant and antibacterial properties of Greek oregano extracts obtained by fractional supercritical fluid extraction (SFE) with carbon dioxide were investigated and compared with the properties of essential oil obtained by hydrodistillation. According to DPPH, hydroxyl radical and superoxide anion radical scavenging activity assays, the supercritical extracts expressed stronger antioxidant activity comparing to the essential oil. The most effective was the supercritical extract obtained by fractional extraction at 30 MPa and 100°C after the volatile fraction had been extracted at lower pressure. At the same time this extract showed strong antibacterial activity against staphylococci, including MRSA strain, but did not affect Escherichia coli of normal intestinal flora. The essential oil obtained by hydrodistillation showed stronger antibacterial activity against E. coli, Salmonella and Klebsiella pneumoniae, comparing to the supercritical extracts but at the same affected the normal gut flora.

  6. A bryozoan species may offer novel antioxidants with anti-carbon-dioxide anion radical activity.

    PubMed

    Pejin, Boris; Savic, Aleksandar G; Hegedis, Aleksandar; Karaman, Ivo; Horvatovic, Mladen; Mojovic, Milos

    2014-01-01

    The antiradical activity of the freshwater bryozoan Hyalinella punctata water extracts (two samples, seasonal collection) was evaluated by using electron paramagnetic resonance spectroscopy against hydroxyl (√OH), superoxide anion (√O2(- )), methoxy (√CH2OH), carbon-dioxide anion (√CO2(- )), nitric-oxide (√NO) and 2,2-diphenyl-1-picrylhydrazyl (√DPPH) radicals. The extracts reduced the production of all tested radicals but to a varying degree. The better activity was observed against √CO2(- ) and √CH2OH radicals (54 ± 5% and 44 ± 4%, and 58 ± 6% and 22 ± 2%, respectively) than towards √DPPH, √NO, √OH and √O2(- ) radicals (59 ± 6% and 1.0 ± 0.1%, 46 ± 5% and 14 ± 1%, 7.0 ± 0.5% and 34 ± 3%, and 33 ± 3% and 0%, respectively). FTIR spectra of the both extracts indicate the presence of cyclic peptides and polypeptides which might be responsible for the observed activity. According to the experimental data obtained, H. punctata water extract may be considered as a novel promising resource of natural products with anti √CO2(- ) radical activity.

  7. A bryozoan species may offer novel antioxidants with anti-carbon-dioxide anion radical activity.

    PubMed

    Pejin, Boris; Savic, Aleksandar G; Hegedis, Aleksandar; Karaman, Ivo; Horvatovic, Mladen; Mojovic, Milos

    2014-01-01

    The antiradical activity of the freshwater bryozoan Hyalinella punctata water extracts (two samples, seasonal collection) was evaluated by using electron paramagnetic resonance spectroscopy against hydroxyl (√OH), superoxide anion (√O2(- )), methoxy (√CH2OH), carbon-dioxide anion (√CO2(- )), nitric-oxide (√NO) and 2,2-diphenyl-1-picrylhydrazyl (√DPPH) radicals. The extracts reduced the production of all tested radicals but to a varying degree. The better activity was observed against √CO2(- ) and √CH2OH radicals (54 ± 5% and 44 ± 4%, and 58 ± 6% and 22 ± 2%, respectively) than towards √DPPH, √NO, √OH and √O2(- ) radicals (59 ± 6% and 1.0 ± 0.1%, 46 ± 5% and 14 ± 1%, 7.0 ± 0.5% and 34 ± 3%, and 33 ± 3% and 0%, respectively). FTIR spectra of the both extracts indicate the presence of cyclic peptides and polypeptides which might be responsible for the observed activity. According to the experimental data obtained, H. punctata water extract may be considered as a novel promising resource of natural products with anti √CO2(- ) radical activity. PMID:24897340

  8. Black Hydroxylated Titanium Dioxide Prepared via Ultrasonication with Enhanced Photocatalytic Activity

    PubMed Central

    Fan, Chenyao; Chen, Chao; Wang, Jia; Fu, Xinxin; Ren, Zhimin; Qian, Guodong; Wang, Zhiyu

    2015-01-01

    The amorphous TiO2 derived from hydroxylation has become an effective approach for the enhancement of photocatalytic activity of TiO2 since a kind of special black TiO2 was prepared by engineering disordered layers on TiO2 nanocrystals via hydrogenation. In this contribution, we prepared totally amorphous TiO2 with various degrees of blackness by introducing hydroxyls via ultrasonic irradiation, through which can we remarkably enhance the photocatalytic activity of TiO2 with improved light harvesting and narrowed band gap. PMID:26133789

  9. Large enhancement in the heterogeneous oxidation rate of organic aerosols by hydroxyl radicals in the presence of nitric oxide

    SciTech Connect

    Richards-Henderson, Nicole K.; Goldstein, Allen H.; Wilson, Kevin R.

    2015-10-27

    In this paper we report an unexpectedly large acceleration in the effective heterogeneous OH reaction rate in the presence of NO. This 10–50 fold acceleration originates from free radical chain reactions, propagated by alkoxy radicals that form inside the aerosol by the reaction of NO with peroxy radicals, which do not appear to produce chain terminating products (e.g., alkyl nitrates), unlike gas phase mechanisms. Lastly, a kinetic model, constrained by experiments, suggests that in polluted regions heterogeneous oxidation plays a much more prominent role in the daily chemical evolution of organic aerosol than previously believed.

  10. A theoretical study of O2 activation by the Au7-cluster on Mg(OH)2: roles of surface hydroxyls and hydroxyl defects.

    PubMed

    Jia, Chuanyi; Fan, Weiliu

    2015-11-11

    Using density functional theory (DFT) calculations, we investigated O2 activation by the Au7-cluster supported on the perfect and hydroxyl defective Mg(OH)2(0001) surface. It is revealed that hydroxyl groups on the perfect Mg(OH)2(0001) surface can not only enhance the stability of the Au7-cluster, but also help the adsorption of the O2 molecule through hydrogen-bonding interactions with the 2nd-layered interfacial Au sites. Density of states (DOS) analysis shows that the d-band centers of the 2nd-layered interfacial Au atoms are very close to the Fermi level, which thereby reduce the Pauli repulsion and promote the O2 adsorption. These two responses make the 2nd-layered interfacial Au atoms favor O2 activation. Interestingly, the surface hydrogen atoms activated by the 1st-layered Au atoms can facilitate the O2 dissociation process as well. Such a process is dynamically favorable and more inclined to occur at low temperatures compared to the direct dissociation process. Meanwhile, the hydroxyl defects of Mg(OH)2(0001) located right under the Au7-cluster can also up-shift the d-band centers of the surrounding Au atoms toward the Fermi level, enhancing its catalytic activity for O2 dissociation. In contrast, the d-band center of Au atoms surrounding the hydroxyl defect near the Au7-cluster exhibits an effective down-shift to lower energies, and therefore holds low activity. These results unveiled the roles of surface hydroxyls and hydroxyl defects on the Au/Mg(OH)2 catalyst in O2 activation and could provide a theoretical guidance for chemists to efficiently synthesize Au/hydroxide catalysts. PMID:26529519

  11. Role of hydroxyl groups on the stability and catalytic activity of Au clusters on rutile surface

    SciTech Connect

    Kent, Paul R

    2011-01-01

    Hydroxyls are present as surface terminations of transition metal oxides under ambient conditions and may modify the properties of supported catalysts. We perform first-principles density functional theory calculations to investigate the role of hydroxyls on the catalytic activity of supported gold clusters on TiO{sub 2} (rutile). We find that they have a long-range effect increasing the adhesion of gold clusters on rutile. While hydroxyls make one gold atom more electronegative, a more complex charge-transfer scenario is observed on larger clusters which are important for catalytic applications. This enhances the molecular adsorption and coadsorption energies of CO and O{sub 2}, thereby increasing the catalytic activity of gold clusters for CO oxidation, consistent with reported experiments. Hydroxyls at the interface between gold and rutile surface are most important to this process, even when not directly bound to gold. As such, accurate models of catalytic processes on gold and other catalysts should include the effect of surface hydroxyls.

  12. Glycyl radical activating enzymes: structure, mechanism, and substrate interactions.

    PubMed

    Shisler, Krista A; Broderick, Joan B

    2014-03-15

    The glycyl radical enzyme activating enzymes (GRE-AEs) are a group of enzymes that belong to the radical S-adenosylmethionine (SAM) superfamily and utilize a [4Fe-4S] cluster and SAM to catalyze H-atom abstraction from their substrate proteins. GRE-AEs activate homodimeric proteins known as glycyl radical enzymes (GREs) through the production of a glycyl radical. After activation, these GREs catalyze diverse reactions through the production of their own substrate radicals. The GRE-AE pyruvate formate lyase activating enzyme (PFL-AE) is extensively characterized and has provided insights into the active site structure of radical SAM enzymes including GRE-AEs, illustrating the nature of the interactions with their corresponding substrate GREs and external electron donors. This review will highlight research on PFL-AE and will also discuss a few GREs and their respective activating enzymes.

  13. Calmodulin Methionine Residues are Targets For One-Electron Oxidation by Hydroxyl Radicals: Formation of S therefore N three-electron bonded Radical Complexes

    SciTech Connect

    Nauser, Thomas; Jacoby, Michael E.; Koppenol, Willem H.; Squier, Thomas C.; Schoneich, Christian

    2005-02-01

    The one-electron (1e) oxidation of organic sulfides and methionine (Met) constitutes an important reaction mechanism in vivo.1,2 Evidence for a Cu(II)-catalyzed oxidation of Met35 in the Alzheimer's disease -amyloid peptide was obtained,3 and, based on theoretical studies, Met radical cations were proposed as intermediates.4 In the structure of -amyloid peptide, the formation of Met radical cations appears to be facilitated by a preexisting close sulfur-oxygen (S-O) interaction between the Met35 sulfur and the carbonyl oxygen of the peptide bond C-terminal to Ile31.5 Substitution of Ile31 with Pro31 abolishes this S-O interaction,5 significantly reducing the ability of -amyloid to reduce Cu(II), and converts the neurotoxic wild-type -amyloid into a non-toxic peptide.6 The preexisting S-O bond characterized for wild-type -amyloid suggests that electron transfer from Met35 to Cu(II) is supported through stabilization of the Met radical cation by the electron-rich carbonyl oxygen, generating an SO-bonded7 sulfide radical cation (Scheme 1, reaction 1).5

  14. Structure-guided unravelling: Phenolic hydroxyls contribute to reduction of acrylamide using multiplex quantitative structure-activity relationship modelling.

    PubMed

    Zhang, Yu; Huang, Mengmeng; Wang, Qiao; Cheng, Jun

    2016-05-15

    We reported a structure-activity relationship study on unravelling phenolic hydroxyls instead of alcoholic hydroxyls contribute to the reduction of acrylamide formation by flavonoids. The dose-dependent study shows a close correlation between the number of phenolic hydroxyls of flavonoids and their reduction effects. In view of positions of hydroxyls, the 3',4'(ortho)-dihydroxyls in B cycle, 3-hydroxyl or hydroxyls of 3-gallate in C cycle, and 5,7(meta)-dihydroxyls in A cycle of flavonoid structures play an important role in the reduction of acrylamide. Flavone C-glycosides are more effective at reducing the formation of acrylamide than flavone O-glycosides when sharing the same aglycone. The current multiplex quantitative structure-activity relationship (QSAR) equations effectively predict the inhibitory rates of acrylamide using selected chemometric parameters (R(2): 0.835-0.938). This pioneer study opens a broad understanding on the chemoprevention of acrylamide contaminants on a structural basis.

  15. Antioxidant and radical scavenging activities of chamazulene.

    PubMed

    Capuzzo, Andrea; Occhipinti, Andrea; Maffei, Massimo E

    2014-01-01

    Essential oils (EOs) of chamomile contain several bioactive compounds, including monoterpenes, sesquiterpenes, triterpenes and fatty acids. Hydrodistillation of chamomile EO induces the formation of chamazulene, a bioactive compound. Chamazulene was isolated from the EO by column chromatography. The total antioxidant capacity confirmed a higher antioxidant activity of chamazulene (IC50 = 6.4 μg mL(- 1)) than of ascorbic acid (IC50 = 12.8 μg mL(- 1)), α-tocopherol (IC50 = 20.5 μg mL(- 1)) and of butylated hydroxytoluene (BHT) (IC50 = 30.8 μg mL(- 1)). Chamazulene was unable to react with DPPH√. However, when chamazulene was assayed with ABTS√, a strong and significantly (P < 0.05) higher free radical scavenging activity was observed (IC50 = 3.7 μg mL(- 1)), with respect to BHT (IC50 = 6.2 μg mL(- 1)) and α-tocopherol (IC50 = 11.5 μg mL(- 1)). The results of this work show that chamazulene is an important factor for the antioxidant power of chamomile oil. PMID:24980540

  16. Proposed chemical mechanisms leading to secondary organic aerosol in the reactions of aliphatic amines with hydroxyl and nitrate radicals

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The presence and importance of amines in the atmosphere continues to gain more attention including aliphatic amines commonly associated with agricultural facilities. The atmospheric reaction mechanisms of these amines with key atmospheric radicals are important to predict both daytime and nighttime...

  17. Activity of key enzymes in microsomal and mitochondrial membranes depends on the redox reactions involving lipid radicals.

    PubMed

    Dmitriev, L F

    2001-07-01

    The work reviews membrane processes, such as monooxygenase reaction and oxidative phosphorylation with special reference to hydroxylation of a xenobiotic benzo(a)pyrene and the effects of the radical scavenger propyl gallate and radical generator Fe2+ ions on the reaction kinetics. A possibility is discussed that tocopherol provides for the activity of the lipid-radical cycles involving cytochrome b5. The lipid-radical cycles protect membrane lipids from oxidation and control the kinetics of membrane processes. The NADPH oxidation energy is transformed into the energy of lipid pulsations and this energy is used for activation of membrane enzymes. To account for the role of lipid pulsations in membrane processes, a new parameter is introduced - the internal temperature. It is supposed that there should be the equilibrium between the pro- and antioxidant factors in the membranes, and the presence of exogenous antioxidants (propyl gallate etc.) should be considered as a negative factor. PMID:11699868

  18. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    DOE PAGES

    Yu, L.; Smith, J.; Laskin, A.; Anastasio, C.; Laskin, J.; Zhang, Q.

    2014-12-23

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol (compound with formula C6H5OH)), guaiacol (2-methoxyphenol), and syringol (2,6-dimethoxyphenol) with two major aqueous-phase oxidants – the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (· OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenatedmore » molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85–1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than · OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenolic compound has reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV–visible region, suggesting that aqueous-phase reactions of phenols may contribute to formation of secondary brown carbon in the atmosphere, especially in regions influenced by biomass burning.« less

  19. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    DOE PAGES

    Yu, L.; Smith, J.; Laskin, A.; Anastasio, C.; Laskin, J.; Zhang, Q.

    2014-08-19

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants – the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (·OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified,more » including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85–1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than ·OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.« less

  20. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    SciTech Connect

    Yu, Lu; Smith, Jeremy; Laskin, Alexander; Anastasio, Cort N.; Laskin, Julia; Zhang, Qi

    2014-01-01

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants – the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (•OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), desorption electrospray ionization mass spectrometry (DESIMS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O/C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than •OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O/C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.

  1. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    NASA Astrophysics Data System (ADS)

    Yu, L.; Smith, J.; Laskin, A.; Anastasio, C.; Laskin, J.; Zhang, Q.

    2014-08-01

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants - the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (\\centerdot OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than \\centerdot OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.

  2. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    NASA Astrophysics Data System (ADS)

    Yu, L.; Smith, J.; Laskin, A.; Anastasio, C.; Laskin, J.; Zhang, Q.

    2014-12-01

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol (compound with formula C6H5OH)), guaiacol (2-methoxyphenol), and syringol (2,6-dimethoxyphenol) with two major aqueous-phase oxidants - the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (· OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than · OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenolic compound has reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-visible region, suggesting that aqueous-phase reactions of phenols may contribute to formation of secondary brown carbon in the atmosphere, especially in regions influenced by biomass burning.

  3. Metallophthalocyanines photosensitize the breakdown of (hydro)peroxides in solution to yield hydroxyl or alkoxyl and peroxyl free radicals via different interaction pathways.

    PubMed

    Gantchev, Tsvetan G; Sharman, Wesley M; van Lier, Johan E

    2003-05-01

    Interactions of organic peroxides (R'OOR) and hydroperoxides (R'OOH), including H2O2, with excited triplet and singlet state metallophthalocyanines (MPc, M = Zn, Al) have been studied by T-T absorption decay and fluorescence quenching. The ensuing photochemical processes result in decomposition of (hydro)peroxides as assessed by photo-EPR (electron paramagnetic resonance) and spin trapping. In argon-saturated apolar solutions and low MPc concentrations, alkoxyl free radicals (*OR) were identified as the primary products of (hydro)peroxide breakdown. Similarly, photosensitized decomposition of symmetric disulfides results in the formation of sulfur-centered radicals. In air-free aqueous solutions, ROOH photosensitization always gave rise to a mixture of hydroxyl and peroxyl radical (*OOR) adducts in varying molar ratios. At high MPc concentrations, both in polar and in apolar solutions, the most abundant products of ROOH decomposition were identified as *OOR. This indicates a change in the predominant interaction pathway, most likely mediated by MPc exciplexes and involving H-atom abstraction from ROOH by MPc-cation radicals. The prevalence of MPc singlet vs. triplet state interactions was confirmed by the much higher singlet quenching rate constants (log kq up to 9.5; vs. log kT < or = 4.5). In contrast to the triplet quenching, singlet quenching rates were found to depend on the (hydro)peroxide structure, following closely the trend of varying *OR yields for different substrates. Thermodynamic calculations were performed to correlate experimental results with models for electronic energy and charge transfer processes in agreement with the Marcus theory (Rhem and Weller approximation) and Savéant's model for a concerted dissociative electron transfer mechanism.

  4. Effect of halide ions and carbonates on organic contaminant degradation by hydroxyl radical-based advanced oxidation processes in saline waters.

    PubMed

    Grebel, Janel E; Pignatello, Joseph J; Mitch, William A

    2010-09-01

    Advanced oxidation processes (AOPs) generating nonselective hydroxyl radicals (HO*) provide a broad-spectrum contaminant destruction option for the decontamination of waters. Halide ions are scavengers of HO* during AOP treatment, such that treatment of saline waters would be anticipated to be ineffective. However, HO* scavenging by halides converts HO* to radical reactive halogen species (RHS) that participate in contaminant destruction but react more selectively with electron-rich organic compounds. The effects of Cl-, Br-, and carbonates (H2CO3+HCO3-+CO3(2-)) on the UV/H2O2 treatment of model compounds in saline waters were evaluated. For single target organic contaminants, the impact of these constituents on contaminant destruction rate suppression at circumneutral pH followed the order Br->carbonates>Cl-. Traces of Br- in the NaCl stock had a greater effect than Cl- itself. Kinetic modeling of phenol destruction demonstrated that RHS contributed significantly to phenol destruction, mitigating the impact of HO* scavenging. The extent of treatment efficiency reduction in the presence of halides varied dramatically among different target organic compounds. Destruction of contaminants containing electron-poor reaction centers in seawater was nearly halted, while 17beta-estradiol removal declined by only 3%. Treatment of mixtures of contaminants with each other and with natural organic matter (NOM) was evaluated. Although NOM served as an oxidant scavenger, conversion of nonselective HO* to selective radicals due to the presence of anions enhanced the efficiency of electron-rich contaminant removal in saline waters by focusing the oxidizing power of the system away from the NOM toward the target contaminant. Despite the importance of contaminant oxidation by halogen radicals, the formation of halogenated byproducts was minimal. PMID:20681567

  5. Reply to the comment of S. Rayne on "QSAR model reproducibility and applicability: A case study of rate constants of hydroxyl radical reaction models applied to polybrominated diphenyl ethers and (benzo-)triazoles".

    PubMed

    Gramatica, Paola; Kovarich, Simona; Roy, Partha Pratim

    2013-07-30

    We appreciate the interest of Dr. Rayne on our article and we completely agree that the dataset of (benzo-)triazoles, which were screened by the hydroxyl radical reaction quantitative structure-activity relationship (QSAR) model, was not only composed of benzo-triazoles but also included some simpler triazoles (without the condensed benzene ring), such as the chemicals listed by Dr. Rayne, as well as some related heterocycles (also few not aromatic). We want to clarify that in this article (as well as in other articles in which the same dataset was screened), for conciseness, the abbreviations (B)TAZs and BTAZs were used as general (and certainly too simplified) notations meaning an extended dataset of benzo-triazoles, triazoles, and related compounds.

  6. Insulin Therapy of Nondiabetic Septic Patients Is Predicted by para-Tyrosine/Phenylalanine Ratio and by Hydroxyl Radical-Derived Products of Phenylalanine.

    PubMed

    Kun, Szilárd; Molnár, Gergő A; Sélley, Eszter; Szélig, Lívia; Bogár, Lajos; Csontos, Csaba; Miseta, Attila; Wittmann, István

    2015-01-01

    Hydroxyl radical converts Phe to para-, meta-, and ortho-Tyr (p-Tyr, m-Tyr, o-Tyr), while Phe is converted enzymatically to p-Tyr in the kidney and could serve as substrate for gluconeogenesis. Pathological isoforms m- and o-Tyr are supposed to be involved in development of hormone resistances. Role of Phe and the three Tyr isoforms in influencing insulin need was examined in 25 nondiabetic septic patients. Daily insulin dose (DID) and insulin-glucose product (IGP) were calculated. Serum and urinary levels of Phe and Tyr isoforms were determined using a rpHPLC-method. Urinary m-Tyr/p-Tyr ratio was higher in patients with DID and IGP over median compared to those below median (P = 0.005 and P = 0.01, resp.). Urinary m-Tyr and m-Tyr/p-Tyr ratio showed positive correlation with DID (P = 0.009 and P = 0.023, resp.) and with IGP (P = 0.004 and P = 0.008, resp.). Serum Phe was a negative predictor, while serum p-Tyr/Phe ratio was positive predictor of both DID and IGP. Urinary m-Tyr and urinary m-Tyr/p-Tyr, o-Tyr/p-Tyr, and (m-Tyr+o-Tyr)/p-Tyr ratios were positive predictors of both DID and IGP. Phe and Tyr isoforms have a predictive role in carbohydrate metabolism of nondiabetic septic patients. Phe may serve as substrate for renal gluconeogenesis via enzymatically produced p-Tyr, while hydroxyl radical derived Phe products may interfere with insulin action.

  7. Antidiabetic drug miglitol inhibits myocardial apoptosis involving decreased hydroxyl radical production and Bax expression in an ischaemia/reperfusion rabbit heart.

    PubMed

    Wang, Ningyuan; Minatoguchi, Shinya; Chen, Xuehai; Uno, Yoshihiro; Arai, Masazumi; Lu, ChuanJiang; Takemura, Genzou; Fujiwara, Takako; Fujiwara, Hisayoshi

    2004-07-01

    1 We examined whether antidiabetic drug miglitol could reduce ischaemia/reperfusion-induced myocardial apoptosis by attenuating production. 2 Japanese white rabbits were subjected to 30-min coronary occlusion followed by 4-h reperfusion with miglitol (10 mg kg(-1), i.v., n=20) or saline (n=20). The infarct area was determined by myoglobin staining, and the infarct size (IS) was expressed as a percentage of the area at risk. DNA fragmentation was assessed by TUNEL method and DNA ladder formation. The expression of Bcl-XL and Bax was detected by immunohistochemical analysis and Western blot analysis. Myocardial interstitial 2,5-DHBA levels, an indicator of hydroxyl radicals, were measured during 30-min ischaemia and 30-min reperfusion in the absence (n=10) or presence of miglitol (10 mg kg(-1), i.v., n=10) using a microdialysis technique. 3 The IS was significantly reduced in the miglitol group (22.4+/-3.4%, n=10) compared to the control group (52.8+/-3.5%, n=10). Miglitol significantly decreased the 2,5-DHBA level during ischaemia and reperfusion and suppressed the incidence of TUNEL-positive myocytes in the ischaemic region (from 10.7+/-3.4 to 4.1+/-3.0%) and the intensity of DNA ladder formation. Miglitol significantly decreased the incidence of Bax-positive myocytes in the ischaemic region (7.4+/-1.7 vs 13.7+/-1.9% of the control) and significantly attenuated the upregulation of Bax protein in the ischaemic regions (from 179+/-17 to 90+/-12% of sham). There was no difference in the expression of Bcl-XL between the two groups. 4 These data suggest that miglitol reduces myocardial apoptosis by attenuating production of hydroxyl radicals and suppressing the upregulation of the expression of Bax protein.

  8. Radical scavenging activity of antioxidants evaluated by means of electrogenerated HO radical.

    PubMed

    Oliveira, Raquel; Geraldo, Dulce; Bento, Fátima

    2014-11-01

    A method is proposed and tested concerning the characterization of antioxidants by means of their reaction with electrogenerated HO radicals in galvanostatic assays with simultaneous O2 evolution, using a Pt anode fairly oxidized. The consumption of a set of species with antioxidant activity, ascorbic acid (AA), caffeic acid (CA), gallic acid (GA) and trolox (T), is described by a first order kinetics. The rate of the processes is limited by the kinetics of reaction with HO radicals and by the kinetics of charge transfer. Information regarding the scavenger activity of antioxidants is obtained by the relative value of the rate constant of the reaction between antioxidants and HO radicals, k(AO,HO)/k(O2). The number of HO radicals scavenged per molecule of antioxidant is also estimated and ranged from 260 (ascorbic acid) to 500 (gallic acid). The method is applied successfully in the characterization of the scavenger activity of ascorbic acid in a green-tea based beverage.

  9. Spectral Response and Diagnostics of Biological Activity of Hydroxyl-Containing Aromatic Compounds

    NASA Astrophysics Data System (ADS)

    Tolstorozhev, G. B.; Mayer, G. V.; Bel'kov, M. V.; Shadyro, O. I.

    2016-08-01

    Using IR Fourier spectra and employing quantum-chemical calculations of electronic structure, spectra, and proton-acceptor properties, synthetic derivatives of aminophenol exhibiting biological activity in the suppression of herpes, influenza, and HIV viruses have been investigated from a new perspective, with the aim of establishing the spectral response of biological activity of the molecules. It has been experimentally established that the participation of the aminophenol hydroxyl group in intramolecular hydrogen bonds is characteristic of structures with antiviral properties. A quantum-chemical calculation of the proton-acceptor ability of the investigated aminophenol derivatives has shown that biologically active structures are characterized by a high proton-acceptor ability of oxygen of the hydroxyl group. A correlation that has been obtained among the formation of an intramolecular hydrogen bond, high proton-acceptor ability, and antiviral activity of substituted aminophenols enables us to predict the pharmacological properties of new medical preparations of the given class of compounds.

  10. Antioxidant and free radical scavenging activities of some fruits.

    PubMed

    Prakash, Dhan; Upadhyay, Garima; Pushpangadan, P; Gupta, Charu

    2011-01-01

    Phenols, a major group of antioxidant phytochemicals, have profound importance due to their biological and free radical scavenging activities. To identify their potential sources extracts of some fruits and their different parts were studied for total phenolic contents (TPC), antioxidant (AOA) and free radical scavenging activities (FRSA). The amount of TPC varied from 10.5 (Carissa carandus, fruit peel) to 343.2 mg/g (Caesalpinia Mexicana, fruits) and AOA from 20.3% (Musa paradisiacal, fruits) to 96.7% (Caesalpinia Mexicana, fruits). Fruits of Caesalpinia Mexicana, Acacia auriculiformis, fruit pericarp green fibres of Cocus nucifera, and fruits of Emblica officinalis were found to have high TPC (73.1-343.2 mg/g) and high AOA (68.5-96.7%). Promising fruits were studied for their FRSA and reducing power (RP) measured by DPPH assay where the fruits of Caesalpinia mexicana, fruit pericarp fibres of Cocus nucifera, fruits of Emblica officinalis showed very low IC50 ranging from 0.009 to 0.016 mg/ml, EC50 from 0.39 to 0.70 mg/mg DPPH and reasonably high values (142.1-256.3) of anti radical power (ARP), indicating their strong FRSA and reducing power (RP) as evident by their low ASE/ml values (0.42-1.08). They also showed better inhibition of lipid peroxidation measured by using ferric thiocyanate assay and by using egg yolk compared to the reference standard quercetin. The ferrous and ferric ion chelating capacity of the promising fruits and their underutilized parts in terms of IC50 varied from 0.12 (Emblica officinalis, fruits) to 2.44 mg/ml (Mangifera indica, Seed kernel) and 0.22 (Caesalpinia Mexicana, fruits) to 2.59 mg/ml (Litchi chinensis, fruit peel) respectively. Fruit pulp, peel and seeds of Litchi chinensis with reasonable amount of phenols (48.3, 43.9, 50.1 mg/ml) showed low ARP (23.5, 38.3, 33.8) and ASE/ml (3.13, 2.18, 2.62) respectively in contrast to Aegle marmelos with comparatively lower phenols (35.1 mg/g) exhibited good ARP (57.4) and RP (1.67 ASE

  11. Free-Radical Triggered Ordered Domino Reaction: An Approach to C-C Bond Formation via Selective Functionalization of α-Hydroxyl-(sp(3))C-H in Fluorinated Alcohols.

    PubMed

    Xu, Zhengbao; Hang, Zhaojia; Liu, Zhong-Quan

    2016-09-16

    A free-radical mediated highly ordered radical addition/cyclization/(sp(3))C-C(sp(3)) formation domino reaction is developed. Three new C-C bonds are formed one by one in a mixed system. Furthermore, it represents the first example of cascade C-C bond formation via selective functionalization of α-hydroxyl-C(sp(3))-H in fluorinated alcohols.

  12. Phytochemical Analysis and Free Radical Scavenging Activity of Medicinal Plants Gnidia glauca and Dioscorea bulbifera

    PubMed Central

    Ghosh, Sougata; Derle, Abhishek; Ahire, Mehul; More, Piyush; Jagtap, Soham; Phadatare, Suvarna D.; Patil, Ajay B.; Jabgunde, Amit M.; Sharma, Geeta K.; Shinde, Vaishali S.; Pardesi, Karishma; Dhavale, Dilip D.; Chopade, Balu A.

    2013-01-01

    Gnidia glauca and Dioscorea bulbifera are traditional medicinal plants that can be considered as sources of natural antioxidants. Herein we report the phytochemical analysis and free radical scavenging activity of their sequential extracts. Phenolic and flavonoid content were determined. Scavenging activity was checked against pulse radiolysis generated ABTS•+ and OH radical, in addition to DPPH, superoxide and hydroxyl radicals by biochemical methods followed by principal component analysis. G. glauca leaf extracts were rich in phenolic and flavonoid content. Ethyl acetate extract of D. bulbifera bulbs and methanol extract of G. glauca stem exhibited excellent scavenging of pulse radiolysis generated ABTS•+ radical with a second order rate constant of 2.33×106 and 1.72×106, respectively. Similarly, methanol extract of G. glauca flower and ethyl acetate extract of D. bulbifera bulb with second order rate constants of 4.48×106 and 4.46×106 were found to be potent scavengers of pulse radiolysis generated OH radical. G. glauca leaf and stem showed excellent reducing activity and free radical scavenging activity. HPTLC fingerprinting, carried out in mobile phase, chloroform: toluene: ethanol (4: 4: 1, v/v) showed presence of florescent compound at 366 nm as well as UV active compound at 254 nm. GC-TOF-MS analysis revealed the predominance of diphenyl sulfone as major compound in G. glauca. Significant levels of n-hexadecanoic acid and octadecanoic acid were also present. Diosgenin (C27H42O3) and diosgenin (3á,25R) acetate were present as major phytoconstituents in the extracts of D. bulbifera. G. glauca and D. bulbifera contain significant amounts of phytochemicals with antioxidative properties that can be exploited as a potential source for herbal remedy for oxidative stress induced diseases. These results rationalize further investigation in the potential discovery of new natural bioactive principles from these two important medicinal plants. PMID:24367520

  13. Scavenging mechanism of curcumin toward the hydroxyl radical: a theoretical study of reactions producing ferulic acid and vanillin.

    PubMed

    Agnihotri, Neha; Mishra, P C

    2011-12-15

    Curcumin is known to be an antioxidant, as it can scavenge free radicals from biological media. A sequence of H-abstraction and addition reactions involving up to eight OH radicals and curcumin or its degradation products leading to the formation of two other antioxidants, namely, ferulic acid and vanillin, was studied. Single electron transfer from curcumin to an OH radical was also studied. All relevant extrema on the potential energy surfaces were located by optimizing geometries of the reactant and product complexes, as well as those of the transition states, at the BHandHLYP/6-31G(d,p) level of density functional theory in the gas phase. Single-point energy calculations were also performed in the gas phase at the BHandHLYP/aug-cc-pVDZ and B3LYP/aug-cc-pVDZ levels of theory. Solvent effects in aqueous media were treated by performing single-point energy calculations at all of the above-mentioned levels of theory employing the polarizable continuum model and the geometries optimized at the BHandHLYP/6-31G(d,p) level in the gas phase. A few reaction steps were also studied by geometry optimization in aqueous media, and the thus-obtained Gibbs free energy barriers were similar to those obtained by corresponding single-point energy calculations. Our calculations show that the hydrogen atom of the OH group attached to the phenol moiety of curcumin would be most efficiently abstracted by an OH radical, in agreement with experimental observations. Further, our study shows that OH addition would be most favored at the C10 site of the heptadiene chain. It was found that curcumin can serve as an effective antioxidant.

  14. Protective Effect of Sinapine against Hydroxyl Radical-Induced Damage to Mesenchymal Stem Cells and Possible Mechanisms.

    PubMed

    Li, Xican; Han, Lu; Li, Yunrong; Zhang, Jing; Chen, Jiemin; Lu, Wenbiao; Zhao, Xiaojun; Lai, Yingtao; Chen, Dongfeng; Wei, Gang

    2016-01-01

    As a phenolic alkaloid occurring in Cruciferous plants, sinapine was observed to protect mesenchymal stem cells (MSCs) against ·OH-induced damage in this study. It was also found to prevent DNA from damage, to scavenge various free radicals (·OH, ·O2(-), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid diammonium salt) (ABTS)(+·), and 1,1-diphenyl-2-picrylhydrazyl radical (DPPH·)), and to reduce Cu(2+) to Cu(+). To further explore the mechanism, the end-product of sinapine reaction with DPPH· was determined using HPLC-electrospray ionization (ESI)-MS/MS and HPLC-diode array detector (DAD). Four molecular ion peaks (m/z 701, 702, 703, and 351) in HPLC-ESI-MS/MS analysis indicated a radical adduct formation (RAF) pathway; while a bathochromic shift (λ(max) 334→475 nm) in HPLC-DAD indicated the formation of quinone as the oxidized product of the phenolic -OH group. Based on these results, it may be concluded that, (i) sinapine can effectively protect against ·OH-induced damage to DNA and MSCs; such protective effect may provide evidence for a potential role for sinapine in MSC transplantation therapy, and be responsible for the beneficial effects of Cruciferous plants. (ii) The possible mechanism for sinapine to protect against ·OH-induced oxidative damage is radical-scavenging, which is thought to be via hydrogen atom (H·) transfer (HAT) (or sequential electron (e) proton transfer (SEPT))→RAF pathways.

  15. Ab Initio Kinetics of Hydrogen Abstraction from Methyl Acetate by Hydrogen, Methyl, Oxygen, Hydroxyl, and Hydroperoxy Radicals.

    PubMed

    Tan, Ting; Yang, Xueliang; Krauter, Caroline M; Ju, Yiguang; Carter, Emily A

    2015-06-18

    The kinetics of hydrogen abstraction by five radicals (H, O((3)P), OH, CH3, and HO2) from methyl acetate (MA) is investigated theoretically in order to gain further understanding of certain aspects of the combustion chemistry of biodiesels, such as the effect of the ester moiety. We employ ab initio quantum chemistry methods, coupled cluster singles and doubles with perturbative triples correction (CCSD(T)) and multireference averaged coupled pair functional theory (MRACPF2), to predict chemically accurate reaction energetics. Overall, MRACPF2 predicts slightly higher barrier heights than CCSD(T) for MA + H/CH3/O/OH, but slightly lower barrier heights for hydrogen abstraction by HO2. Based on the obtained reaction energies, we also report high-pressure-limit rate constants using transition state theory (TST) in conjunction with the separable-hindered-rotor approximation, the variable reaction coordinate TST, and the multi-structure all-structure approach. The fitted modified Arrhenius expressions are provided over a temperature range of 250 to 2000 K. The predictions are in good agreement with available experimental results. Abstractions from both of the methyl groups in MA are expected to contribute to consumption of the fuel as they exhibit similar rate coefficients. The reactions involving the OH radical are predicted to have the highest rates among the five abstracting radicals, while those initiated by HO2 are expected to be the lowest. PMID:25974050

  16. Determination of Bimolecular Rate Constants for Reactions of Hydroxyl Radical with Pharmaceutical and Cosmetics Chemicals - Implications to the Fate in the Aquatic Environment

    NASA Astrophysics Data System (ADS)

    Nakajima, H.; Arakaki, T.; Anastasio, C.

    2008-12-01

    Large organic compounds such as hyaluronic acid and chondroitin sulfate are often used in pharmaceutical and cosmetics products, but their chemical degradation pathways are not well understood. To better elucidate their fate in the aquatic environment, we initiated a study to determine bimolecular rate constants between these organic compounds and hydroxyl radical (OH), which is a potent oxidant in the environment. The lifetimes of many organic compounds are determined by reactions with OH radicals, and the lifetime of OH is often controlled by reactions with organic compounds. To determine these bimolecular rate constants we used a competition kinetics technique with either hydrogen peroxide or nitrate as a source of OH and benzoate as the competing sink. Since the molecular weights of some of the large organic compounds we studied were not known, we used dissolved organic carbon (DOC) concentrations to determine mole-carbon based bimolecular rate constants, instead of the commonly used molar-based bimolecular rate constants. We will report the mole-carbon based bimolecular rate constants of OH, determined at room temperature, with hyaluronic acid, chondroitin sulfate and some other large organic compounds.

  17. Natural montmorillonite induced photooxidation of As(III) in aqueous suspensions: roles and sources of hydroxyl and hydroperoxyl/superoxide radicals.

    PubMed

    Wang, Yajie; Xu, Jing; Li, Jinjun; Wu, Feng

    2013-09-15

    Photooxidation of arsenite(As(III)) in a suspension of natural montmorillonite under the irradiation of metal halide lamp (λ ≥ 313 nm)has been investigated. The results showed that the natural montmorillonite induced the photooxidation of As(III) by generating hydroxyl radicals (HO·) and hydroperoxyl/superoxide radicals (HO₂·/O₂⁻·). HO· which was responsible for the As(III) photooxidation. Approximately 38% of HO· was generated by the photolysis of ferric ions, and the formation of the remaining 62% was strongly dependent on the HO₂·/O₂⁻·. The presence of free ironions (Fe(2+) and Fe(3+)), made significant contributions to the photogeneration of these reactive oxygen species (ROS). The photooxidation of As(III) in natural montmorillonite suspensions was greatly influenced by the pH values. The photooxidation of As(III) by natural montmorillonite followed the Langmuir-Hinshelwood equation. In addition, the photooxidation of As(III) could be enhanced by the addition of humic acid. This work demonstrates that photooxidation may be an important environmental process for the oxidation of As(III) and may be a way to remove As(III) from acidic surface water containing iron-bearing clay minerals. PMID:23770489

  18. ROLE OF THE PHOTO-FENTON REACTION IN THE PRODUCTION OF HYDROXYL RADICALS AND PHOTOBLEACHING OF COLORED DISSOLVED ORGANIC MATTER IN A COASTAL RIVER OF THE SOUTHEASTERN UNITED STATES

    EPA Science Inventory

    Photochemical reactions involving colored dissolved organic matter (CDOM) in natural waters are important determinants of nutrient cycling, trace gas production and control of light penetration into the water column. In this study the role of the hydroxyl radical ((OH)-O-.) in CD...

  19. Kinetics study of reactions of α-pinene and β-pinene with