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Sample records for quinhydrone

  1. A quinhydrone biofuel cell based on an enzyme-induced pH gradient

    Energy Technology Data Exchange (ETDEWEB)

    Giroud, Fabien; Gondran, Chantal; Gorgy, Karine; Cosnier, Serge [Departement de Chimie Moleculaire, UMR CNRS 5250 ICMG-FR-2607, Universite Joseph Fourier, BP-53, 38041 Grenoble Cedex 9 (France); Pellissier, Aymeric [Departement de Chimie Moleculaire, UMR CNRS 5250 ICMG-FR-2607, Universite Joseph Fourier, BP-53, 38041 Grenoble Cedex 9 (France); Techniques de l' Ingenierie Medicale et de la Complexite - Informatique, Mathematiques Appliquees Grenoble, UMR CNRS 5525, IFRT-IpV 130, IN3S INstitut de l' INgenierie et de l' INformation de Sante, Faculte de Medecine, Universite Joseph Fourier, 38706 La Tronche cedex (France); Lenouvel, Francois; Cinquin, Philippe [Techniques de l' Ingenierie Medicale et de la Complexite - Informatique, Mathematiques Appliquees Grenoble, UMR CNRS 5525, IFRT-IpV 130, IN3S INstitut de l' INgenierie et de l' INformation de Sante, Faculte de Medecine, Universite Joseph Fourier, 38706 La Tronche cedex (France)

    2011-02-01

    We report on an alternative concept of biofuel cell functioning based on the unconventional use of enzymes to create a pH difference generating a potential difference between electrodes soaked in quinhydrone solutions. The electrode and quinhydrone solution were confined in a dialysis bag placed into a compartment containing either glucose oxidase and catalase for the biocathode or urease for the bioanode. In presence of 0.4 mol L{sup -1} glucose and urea, the enzyme reactions generate a pH difference of 3.55, both compartments being separated by an agar-agar wall. The resulting biofuel cell exhibits an open-circuit voltage and maximum power of 208 mV and 30.6 {mu}W, respectively, without immobilization and electrical connection of the involved enzymes. In addition, this biofuel cell was able to provide continuously10 {mu}A during 23 h, producing 0.133 J and 0.828 C. A similar biofuel cell configuration based only on dialysis bags was also developed. A graphite disk electrode elaborated by mechanical compression of graphite particles and quinhydrone, was placed in a dialysis bag itself confined into another dialysis bag containing enzyme solution. The resulting power and open-circuit voltage at saturating substrate conditions are 7.6 {mu}W and 157 mV, respectively. (author)

  2. A quinhydrone biofuel cell based on an enzyme-induced pH gradient

    Science.gov (United States)

    Giroud, Fabien; Gondran, Chantal; Gorgy, Karine; Pellissier, Aymeric; Lenouvel, François; Cinquin, Philippe; Cosnier, Serge

    We report on an alternative concept of biofuel cell functioning based on the unconventional use of enzymes to create a pH difference generating a potential difference between electrodes soaked in quinhydrone solutions. The electrode and quinhydrone solution were confined in a dialysis bag placed into a compartment containing either glucose oxidase and catalase for the biocathode or urease for the bioanode. In presence of 0.4 mol L -1 glucose and urea, the enzyme reactions generate a pH difference of 3.55, both compartments being separated by an agar-agar wall. The resulting biofuel cell exhibits an open-circuit voltage and maximum power of 208 mV and 30.6 μW, respectively, without immobilization and electrical connection of the involved enzymes. In addition, this biofuel cell was able to provide continuously10 μA during 23 h, producing 0.133 J and 0.828 C. A similar biofuel cell configuration based only on dialysis bags was also developed. A graphite disk electrode elaborated by mechanical compression of graphite particles and quinhydrone, was placed in a dialysis bag itself confined into another dialysis bag containing enzyme solution. The resulting power and open-circuit voltage at saturating substrate conditions are 7.6 μW and 157 mV, respectively.

  3. Resonant interactions between discrete phonons in quinhydrone driven by nonlinear electron-phonon coupling

    Science.gov (United States)

    Rury, Aaron S.

    2016-06-01

    This study reports experimental, computational, and theoretical evidence for a previously unobserved coherent phonon-phonon interaction in an organic solid that can be described by the application of Fano's analysis to a case without the presence of a continuum. Using Raman spectroscopy of the hydrogen-bonded charge-transfer material quinhydrone, two peaks appear near 700 cm-1 we assign as phonons whose position and line-shape asymmetry depend on the sample temperature and light scattering excitation energy. Density functional theory calculations find two nearly degenerate phonons possessing frequencies near the values found in experiment that share similar atomic motion out of the aromatic plane of electron donor and acceptor molecules of quinhydrone. Further analytical modeling of the steady-state light scattering process using the Peierls-Hubbard Hamiltonian and time-dependent perturbation theory motivates assignment of the physical origin of the asymmetric features of each peak's line shape to an interaction between two discrete phonons via nonlinear electron-phonon coupling. In the context of analytical model results, characteristics of the experimental spectra upon 2.33 eV excitation of the Raman scattering process are used to qualify the temperature dependence of the magnitude of this coupling in the valence band of quinhydrone. These results broaden the range of phonon-phonon interactions in materials in general while also highlighting the rich physics and fundamental attributes specific to organic solids that may determine their applicability in next generation electronics and photonics technologies.

  4. Coulometric titrations of bases in propylene carbonate and g-butyrolactone using hydroquinone as the depolarizer and a quinhydrone indicator electrode

    Directory of Open Access Journals (Sweden)

    Z. D. STANIC

    2000-08-01

    Full Text Available The application of hydroquinone for the coulometric generation of hydrogen ions in propylene carbonate (PC and g-butyrolactone (GBL is described. The current-potential curves recorded for theid sepolarizer, titrated bases, indicator and the solvents used showed that the investigated depolarizer is oxidized at lower potentials than the oxidation potentials of other components in the solution. the hydrogen ions generated by the oxidation of hydroquinone were used for the titration of organic bases (triethylamine, n-butylamine, pyridine, quinoline, aniline, N,N’-diphenylguanidine, piperidine, and 2,2’-bipiridine in PC and GBL with visual (Crystal Violet as indicator and potentiometric end-point detection using a quinhydrone electrode as the indicator electrode. The quinhydrone added to the to be analyzed solution served both as a source of hydrogen ions and, together with the immersed platinum electrode, as a quinhydrone electrode. The relative error of the determination of the bases was about 1 %.

  5. 2,3-Dichloro-1,4-hydro-quinone 2,3-dichloro-1,4-benzoquinone monohydrate: a quinhydrone-type 1:1 donor-acceptor [D-A] charge-transfer complex.

    Science.gov (United States)

    Guégano, Xavier; Hauser, Jürg; Liu, Shi-Xia; Decurtins, Silvio

    2011-11-01

    IN THE CRYSTAL STRUCTURE OF THE TITLE COMPOUND (SYSTEMATIC NAME: 2,3-dichloro-benzene-1,4-diol 2,3-dichloro-cyclo-hexa-2,5-diene-1,4-dione monohydrate), C(6)H(4)Cl(2)O(2)·C(6)H(2)Cl(2)O(2)·H(2)O, the 2,3-dichloro-1,4-hydro-quinone donor (D) and the 2,3-dichloro-1,4-benzoquinone acceptor (A) mol-ecules form alternating stacks along [100]. Their mol-ecular planes [maximum deviations for non-H atoms: 0.0133 (14) (D) and 0.0763 (14) Å (A)] are inclined to one another by 1.45 (3)° and are thus almost parallel. There are π-π inter-actions involving the D and A mol-ecules, with centroid-centroid distances of 3.5043 (9) and 3.9548 (9) Å. Inter-molecular O-H⋯O hydrogen bonds involving the water mol-ecule and the hy-droxy and ketone groups lead to the formation of two-dimensional networks lying parallel to (001). These networks are linked by C-H⋯O inter-actions, forming a three-dimensional structure.

  6. 2,3-Dichloro-1,4-hydroquinone 2,3-dichloro-1,4-benzoquinone monohydrate: a quinhydrone-type 1:1 donor-acceptor [D—A] charge-transfer complex

    Directory of Open Access Journals (Sweden)

    Xavier Guégano

    2011-11-01

    Full Text Available In the crystal structure of the title compound (systematic name: 2,3-dichlorobenzene-1,4-diol 2,3-dichlorocyclohexa-2,5-diene-1,4-dione monohydrate, C6H4Cl2O2·C6H2Cl2O2·H2O, the 2,3-dichloro-1,4-hydroquinone donor (D and the 2,3-dichloro-1,4-benzoquinone acceptor (A molecules form alternating stacks along [100]. Their molecular planes [maximum deviations for non-H atoms: 0.0133 (14 (D and 0.0763 (14 Å (A] are inclined to one another by 1.45 (3° and are thus almost parallel. There are π–π interactions involving the D and A molecules, with centroid–centroid distances of 3.5043 (9 and 3.9548 (9 Å. Intermolecular O—H...O hydrogen bonds involving the water molecule and the hydroxy and ketone groups lead to the formation of two-dimensional networks lying parallel to (001. These networks are linked by C—H...O interactions, forming a three-dimensional structure.

  7. 2,3-Dichloro-1,4-hydro­quinone 2,3-dichloro-1,4-benzoquinone monohydrate: a quinhydrone-type 1:1 donor-acceptor [D—A] charge-transfer complex

    Science.gov (United States)

    Guégano, Xavier; Hauser, Jürg; Liu, Shi-Xia; Decurtins, Silvio

    2011-01-01

    In the crystal structure of the title compound (systematic name: 2,3-dichloro­benzene-1,4-diol 2,3-dichloro­cyclo­hexa-2,5-diene-1,4-dione monohydrate), C6H4Cl2O2·C6H2Cl2O2·H2O, the 2,3-dichloro-1,4-hydro­quinone donor (D) and the 2,3-dichloro-1,4-benzoquinone acceptor (A) mol­ecules form alternating stacks along [100]. Their mol­ecular planes [maximum deviations for non-H atoms: 0.0133 (14) (D) and 0.0763 (14) Å (A)] are inclined to one another by 1.45 (3)° and are thus almost parallel. There are π–π inter­actions involving the D and A mol­ecules, with centroid–centroid distances of 3.5043 (9) and 3.9548 (9) Å. Inter­molecular O—H⋯O hydrogen bonds involving the water mol­ecule and the hy­droxy and ketone groups lead to the formation of two-dimensional networks lying parallel to (001). These networks are linked by C—H⋯O inter­actions, forming a three-dimensional structure. PMID:22219991

  8. Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid

    Science.gov (United States)

    Rury, Aaron S.; Sorenson, Shayne; Dawlaty, Jahan M.

    2016-03-01

    Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm-1 oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology.

  9. Fast New Method for Temporary Chemical Passivation

    Directory of Open Access Journals (Sweden)

    Marek Solčanský

    2012-12-01

    Full Text Available The main material parameter of silicon, that influences the effectiveness of photovoltaic cells, is the minority carrier bulk lifetime.It may change in the technological process especially during high temperature operations. Monitoring of the carrier bulk-lifetimeis necessary for modifying the whole technological process of production. For the measurement of the minority carrier bulk-lifetimethe characterization method MW PCD (Microwave Photoconductance Decay is used, where the result of measurement is the effectivecarrier lifetime, which is very dependent on the surface recombination velocity and therefore on the quality of a silicon surfacepassivation.This work deals with an examination of a different solution types for the chemical passivation of a silicon surface. Varioussolutions are tested on silicon wafers for their consequent comparison. The main purpose of this work is to find optimal solution, whichsuits the requirements of a time stability and start-up velocity of passivation, reproducibility of the measurements and a possibilityof a perfect cleaning of a passivating solution remains from a silicon surface. Another purpose of this work is to identify the parametersof other quinhydrone solutions with different concentrations as compared with the quinhydrone solution in methanol witha concentration of 0.07 mol/dm³ marked QM007 (referential solution.The method of an effective chemical passivation with a quinhydrone in methanol solution was suggested. The solution witha concentration of 0.07 mol /dm3 fulfills all required criteria. The work also confirms the influence of increased concentrationquinhydrone on the temporal stability of the passivation layer and the effect for textured silicon wafers. In conclusion, the influenceof an illumination and the temperature on the properties of the passivating solution QM007 is discussed.

  10. Effects of fasting and/or oxidizing and reducing agents on absorption of neptunium from the gastrointestinal tract of mice and adult or neonatal rats.

    Science.gov (United States)

    Sullivan, M F; Ruemmler, P S; Ryan, J L

    1984-12-01

    Neptunium-237(V) nitrate was administered by gavage to groups of fed or fasted adult and 5-day-old rats. Some groups also received the oxidants quinhydrone or ferric iron, and others received the reducing agent ferrous iron. Adult mice received ferric or ferrous iron and 235Np. When the adult rats were killed at 7 days after gavage, measurements showed that, compared with rats that were fed, a 24-hr fast caused a fivefold increase in 237Np absorption and retention. Both quinhydrone and ferric iron caused an even greater increase in absorption in both fed and fasted rats. Ferrous iron, on the other hand, decreased absorption in fasted rats to values lower than those obtained in fed rats. Similar results were obtained in mice treated with 235Np and either ferric or ferrous iron. The highest absorption obtained after gavage of ferric iron to fasted rats and mice was about two orders of magnitude higher than the value obtained in animals that were fed before gavage. The effects of ferric and ferrous iron on neptunium absorption by neonatal rats were similar to their effects on adult animals but of lesser magnitude. These results are consistent with the hypothesis that Np(V), when given in small mass quantities to fed animals, is reduced in the gastrointestinal tract to Np(IV), which is less well absorbed than Np(V).

  11. Ensuring complete absence of Ce(IV) and measurement of the stability constant of the fluoride complex of Ce(III)

    Energy Technology Data Exchange (ETDEWEB)

    Sawant, R.M.; Chaudhuri, N.K.; Ramakumar, K.L. [Fuel Chemistry Division, Bhabha Atomic Research Centre, Trombay, 400 085 Mumbai (India)

    2001-01-05

    Literature survey revealed a wide variation in the measured stability constant values of the aqueous fluoride complexes of trivalent cerium. This could be due to inadequate care for full conversion and maintenance of the oxidation state of cerium to trivalent state. In the present work quinhydrone has been used to ensure complete absence of Ce(IV) and the stability constant of CeF{sup 2+} in 1 M NaClO{sub 4} has been measured potentiometrically using a fluoride ion selective electrode. Log {beta}{sub 1} obtained in this work was 2.936{+-}0.024 and fitted well with the general trend of stability constants of the lanthanide (rare earths) fluorides in aqueous solution.

  12. Ensuring complete absence of Ce(IV) and measurement of the stability constant of the fluoride complex of Ce(III).

    Science.gov (United States)

    Sawant, R M; Chaudhuri, N K; Ramakumar, K L

    2001-01-05

    Literature survey revealed a wide variation in the measured stability constant values of the aqueous fluoride complexes of trivalent cerium. This could be due to inadequate care for full conversion and maintenance of the oxidation state of cerium to trivalent state. In the present work quinhydrone has been used to ensure complete absence of Ce(IV) and the stability constant of CeF(2+) in 1 M NaClO(4) has been measured potentiometrically using a fluoride ion selective electrode. Log beta(1) obtained in this work was 2.936+/-0.024 and fitted well with the general trend of stability constants of the lanthanide (rare earths) fluorides in aqueous solution.

  13. Evidence of Ultrafast Charge Transfer Driven by Coherent Lattice Vibrations.

    Science.gov (United States)

    Rury, Aaron S; Sorenson, Shayne A; Dawlaty, Jahan M

    2017-01-05

    We report evidence that intermolecular vibrations coherently drive charge transfer between the sites of a material on ultrafast time scales. Following a nonresonant stimulated Raman pump pulse that excites the organic material quinhydrone, we observe the initial appearance of oscillations due to intermolecular lattice vibrations and then the delayed appearance of a higher-frequency oscillation that we assign to a totally symmetric intramolecular vibration. We use the coherent dynamics of the transient reflectivity signal to propose that coherence transfer drives excitation of this intramolecular vibration. Furthermore, we conclude that the dynamical frequency shift of the intramolecular vibration reports the formation of a quasi-stable charge-separated state on ultrafast time scales. We calculate model dynamics using the extended Hubbard Hamiltonian to explain coherence transfer due to vibrationally driven charge transfer. These results demonstrate that the coherent excitation of low-frequency vibrations can drive charge transfer in the solid state and control material properties.

  14. Low impedance pH sensitive electrochemical devices that are potentially applicable to transcutaneous PCO2 measurements.

    Science.gov (United States)

    Yeung, H N; Beran, A V; Huxtable, R F

    1978-01-01

    Two cases of low impedance, non-glass membrane electrodes for pH measurement were evaluated: (I) Metal--metal oxide electrodes and (II) Reduction-oxidation electrodes. The fundamental cause of oxygen sensitivity of metal-metal oxide electrodes were examined and three approaches for its suppression were proposed. For the case of Sb--Sb2Ox electordes, oxygen sensitivity can be attenuated partially by cell loading, either directly across the reference electrode or indirectly across a third slave electrode. In a PO2 range of 8--54 kPa, more than 95% of the PO2 response can be suppressed by loading the cell emf to half of tis open-circuit value. The oxygen sensitivity also was observed to diminished by grinding the metal-metal oxide and pressing it under high pressure into a pellet electrode. Other metal-metal oxide electrodes that have promise in transcutaneous measurement are the Pd-PdO2 electrodes. The redox electrodes are typified by the Quinhydrone electrode. A membrane Quinhydrome electrode showed a sensitivity of 56 mV/Decade at 37 degree C and no oxygen sensitivity up to 50 kPa and a drift of 1 mV/h over a 24-h period. However, the stability deteriorated over a long-term period.

  15. Regulation effects on soil urease kinetics as affected by urease inhibitor hydroquinone%脲酶抑制剂氢醌对土壤脲酶动力学行为的调控效应

    Institute of Scientific and Technical Information of China (English)

    隽英华; 陈振华; 张玉兰; 张丽莉; 陈利军

    2015-01-01

    研究了不同温度条件下脲酶抑制剂氢醌( HQ)对东北3种典型土壤(白浆土、棕壤、褐土)脲酶动力学参数的影响。结果表明,土壤类型、培养时间、培养温度及其相互作用均显著影响土壤脲酶动力学参数。与对照相比,加入HQ使土壤脲酶米氏常数(Km)增加,最大反应速率(Vmax)降低,表明HQ对土壤脲酶的作用机理属于混合型抑制。与白浆土相比,棕壤和褐土脲酶动力学参数受HQ的影响程度较大,表明高肥力土壤生物学活性较稳定。随着培养时间延长,土壤脲酶Km降低, Vmax和Vmax/Km增加。随着温度升高,土壤脲酶Km和Vmax增加, Vamx/Km无规律性变化。相关性分析表明,土壤脲酶动力学参数Km、 Vmax和Vmax/Km与pH值、有机质、全氮、碱解氮和质地组成之间存在显著相关关系。%The effect of urease inhibitor quinhydrone ( HQ) on kinetic parameters of urease in three typical soils ( i. e. albic soil, brown soil, cinnamon soil) in Northeast China under different temperature conditions. The results showed that, soil type, incubation time, incubation temperature and their interactions significantly influenced soil urease kinetics. Compared with control, Km increase and Vmax decrease in the soils with HQ and it showed HQ was mixed inhibition to soil urease. Compared with albic soil, in brown soil and cinnamon soil the influence on kinetic parameters of soil urease as affected by HQ was greater, which indicated that high fertility soils could have stable biological characteristics. With incubation time increasing, Km decreased, but Vmax and Vmax/Km increased. With incubation temperature increasing, Km and Vmax in-creased, Vmax/Km changed irregularly. Statistical analysis indicated that, Km, Vmax and Vmax/Km of soil urease had significantly correlations with pH, organic matter, total nitrogen, alkali-hydrolyzed nitrogen and texture structure.

  16. Approaches to improve the Voc of CDTE devices: Device modeling and thinner devices, alternative back contacts

    Science.gov (United States)

    Walkons, Curtis J.

    An existing commercial process to develop thin film CdTe superstrate cells with a lifetime tau=1-3 ns results in Voc= 810-850 mV which is 350 mV lower than expected for CdTe with a bandgap EG = 1.5 eV. Voc is limited by 1.) SRH recombination in the space charge region; and 2.) the Cu2Te back contact to CdTe, which, assuming a 0.3 eV CdTe/Cu2Te barrier, exhibits a work function of phi Cu2Te= 5.5 eV compared to the CdTe valence band of Ev,CdTe=5.8 eV. Proposed solutions to develop CdTe devices with increased Voc are: 1.) reduce SRH recombination by thinning the CdTe layer to ≤ 1 mum; and 2.) develop an ohmic contact back contact using a material with phi BC≥5.8 eV. This is consistent with simulations using 1DSCAPS modeling of CdTe/CdS superstrate cells under AM 1.5 conditions. Two types of CdTe devices are presented. The first type of CdTe device utilizes a window/CdTe stack device with an initial 3-9 mum CdTe layer which is then chemically thinned resulting in regions of the CdTe film with thickness less than 1 mum. The CdTe surface was contacted with a liquid junction quinhydrone-Pt (QH-Pt) probe which enables rapid repeatable Voc measurements on CdTe before and after thinning. In four separate experiments, the window/CdTe stack devices with thinned CdTe exhibited a Voc increase of 30-170 mV, which if implemented using a solid state contact could cut the Voc deficit in half. The second type of CdTe device utilizes C61 PCBM as a back contact to the CdTe, selected since PCBM has a valence band maximum energy (VBM) of 5.8 eV. The PCBM films were grown by two different chemistries and the characterization of the film properties and device results are discussed. The device results show that PCBM exhibits a blocking contact with a 0.6 eV Schottky barrier and possible work function of phiPCBM = 5.2 eV.

  17. 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.

    Science.gov (United States)

    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