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1.
Reactions of ·OH/O .? radicals and H‐atoms as well as specific oxidants such as Cl2.? and N3· radicals have been studied with 2‐ and 3‐hydroxybenzyl alcohols (2‐ and 3‐HBA) at various pH using pulse radiolysis technique. At pH 6.8, ·OH radicals were found to react quite fast with both the HBAs (k = 7.8 × 109 dm3 mol?1 s?1 with 2‐HBA and 2 × 109 dm3 mol?1 s?1 with 3‐HBA) mainly by adduct formation and to a minor extent by H‐abstraction from ? CH2OH groups. ·OH‐(HBA) adduct were found to undergo decay to give phenoxyl type radicals in a pH dependent way and it was also very much dependent on buffer‐ion concentrations. It was seen that ·OH‐(2‐HBA) and ·OH‐(3‐HBA) adducts react with HPO42? ions (k = 2.1 × 107 and 2.8 × 107 dm3 mol?1 s?1 at pH 6.8, respectively) giving the phenoxyl type radicals of HBAs. At the same time, this reaction is very much hindered in the presence of H2PO ions indicating the role of phosphate ion concentration in determining the reaction pathway of ·OH adduct decay to final stable product. In the acidic region adducts were found to react with H+ ions. At pH 1, reaction of ·OH radicals with HBAs gave exclusively phenoxyl type radicals. Proportion of the reducing radicals formed by H‐abstraction pathway in ·OH/O .? reactions with HBAs was determined following electron transfer to methyl viologen. H‐atom abstraction is the major pathway in O .? reaction with HBAs compared to ·OH radical reaction. H‐atom reaction with 2‐ and 3‐HBA gave transient species which were found to transfer electron to methyl viologen quantitatively. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

2.
The paper is a short review of experimental data obtained during the study of reactivity of ions of actinides towards inorganic free radicals in irradiated aqueous solutions by pulse radiolysis method. The values of rate constants of reactions of these ions with primary products of water radiolysis (eaq ?, H, OH, O?) and secondary radicals formed via reactions of these products with solutes and/or as a result of direct action of ionizing radiation on solutes (SO4 ?, NO3, Cl2 ?, CO3 ?, O2 ? etc.) are listed. The peculiarities of the reactivity are discussed. The examples of application of the obtained data for the simulation of radiolytical transformations of ions of actinides are presented.  相似文献   

3.
Acid‐catalyzed disproportionation of cyclic nitroxyl radicals R2NO? includes the half‐reactions of their oxidation to oxoammonium cations R2NO+ and reduction to hydroxylamines R2NOH. For many nitroxyl radicals, this reaction is characterized by its ~100% reversibility. Quantitative characteristics of acid–base and redox properties of the whole redox triad may be obtained from research of kinetics and equilibrium of this reaction. Here, we have examined the kinetics for the disproportionation of twenty piperidine‐, pyrroline‐, pyrrolidine‐, and imidazoline nitroxyl radicals in aqueous H2SO4, and interpreted it in terms of the excess acidity function X. The rate‐limiting step of this reaction is R2NO? oxidation by its protonated counterpart R2NOH+?. Kinetic stability of R2NO? in acidic media depends on the basicity of nitroxyl group. This basicity is influenced predominantly by protonation of another, more basic group in radical structure, and its proximity to nitroxyl group. The discovered estimates of pK values for radical cations R2NOH+? (from ?5.8 to ?12.0) indicate a very low basicity of nitroxyl groups in all commonly used R2NO?. For the first time, a linear correlation is obtained between the one‐electron reduction potentials of oxoammonium cations and the basicity of nitroxyl groups of related radicals. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

4.
Free radical‐induced oxidation reactions of glucosamine naphthalene acetic acid (GNaa) and naphthalene acetic acid (Naa) have been studied using pulse radiolysis. GNaa was synthesized by covalently attaching Naa on glucosamine. Hydroxyl adduct (from the reaction of hydroxyl radicals (OH) at the naphthalene ring) was identified as the major transient intermediate (suggesting that the OH reaction is on the naphthalene ring) and is characterized by its absorption maxima of 340 and 400 nm. Both GNaa and Naa undergo similar reaction pattern. The bimolecular rate constants determined for the reactions are 4.8 × 109 and 8.9 × 109 dm3 mol?1 s?1 for GNaa and Naa respectively. The mechanism of reaction of OH with GNaa was further confirmed using steady‐state method. Radical cation of GNaa was detected as an intermediate during the reaction of sulfate radical (SO4●?) with GNaa (k2 = 4.52 × 109 dm3 mol?1 s?1). This radical cation transforms to a OH adduct at higher pH. The radical cation of GNaa is comparatively long lived, and a cyclic transition state by neighboring group participation accounts for its stability. The oxy radical anion (O●?) reacts with GNaa (k2 = 1.12 × 109 dm3 mol?1 s?1) mainly by one‐electron transfer mechanism. The reduction potential values of Naa and GNaa were determined using cyclic voltammetric technique, and these are 1.39 V versus NHE for Naa and 1.60 V versus NHE for GNaa. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

5.
Absolute rate constants for hydroxyl radical, azide radical, and hydrated electron reactions with a sulfa drug 4,4'‐diamino diphenyl sulfone (dapsone) in water have been evaluated using electron pulse radiolysis technique. Absolute rate constants for hydroxyl radical and azide radical were determined as (8.4 ± 0.3) × 109 and (5.6 ± 0.5) × 109 M?1 s?1, respectively. The reduction of dapsone with the hydrated electron occurred with rate constant of (9.2 ± 0.1) × 109 M?1 s?1. Hydroxyl radical reactions result in the synchronous formation of adduct as well as anilino radical. The interesting observation is that the yield of the anilino radical increases with increase in pH. Contrary to this, the yield of the adduct decreases with pH. We propose that hydroxyl radical adds predominantly to the aniline. In contrast, the reaction of azide radical with the dapsone suggests that the reaction occurs at the –NH2 moiety of the aniline ring. The free radical electron transfer from dapsone to parent radical cation of non‐polar solvent also results in the formation of anilino radical only suggesting that the radical cation of dapsone has a short lifetime. The reaction of hydrated electrons with the dapsone suggests that the reaction occurs at different reaction site. The experimental results supported by theoretical calculations of this study provide fundamental mechanistic parameters that probably decide the fate of the radical cation of aniline derivatives. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

6.
Reactions of . OH/O .? radicals, H‐atoms as well as specific oxidants such as N and Cl radicals with 4‐hydroxybenzyl alcohol (4‐HBA) in aqueous solutions have been investigated at various pH values using the pulse radiolysis technique. At pH 6.8, . OH radicals were found to react with 4‐HBA (k = 6 × 109 dm3 mol?1 s?1) mainly by contributing to the phenyl moiety and to a minor extent by H‐abstraction from the ? CH2OH group. . OH radical adduct species of 4‐HBA, i.e., . OH‐(4‐HBA) formed in the addition reaction were found to undergo dehydration to give phenoxyl radicals of 4‐HBA. Decay rate of the adduct species was found to vary with pH. At pH 6.8, decay was very much dependent on phosphate buffer ion concentrations. Formation rate of phenoxyl radicals was found to increase with phosphate buffer ion concentration and reached a plateau value of 1.6 × 105 s?1 at a concentration of 0.04 mol dm?3 of each buffering ion. It was also seen that . OH‐(4‐HBA) adduct species react with HPO ions with a rate constant of 3.7 × 107 dm3 mol?1 s?1 and there was no such reaction with H2PO ions. However, the rate of reaction of . OH‐(4‐HBA) adduct species with HPO ions decreased on adding KH2PO4 to the solution containing a fixed concentration of Na2HPO4 which indicated an equilibrium in the H+ removal from . OH‐(4‐HBA) adduct species in the presence of phosphate ions. In the acidic region, the . OH‐(4‐HBA) adduct species were found to react with H+ ions with a rate constant of 2.5 × 107 dm3 mol?1 s?1. At pH 1, in the reaction of . OH radicals with 4‐HBA (k = 8.8 × 109 dm3 mol?1 s?1), the spectrum of the transient species formed was similar to that of phenoxyl radicals formed in the reaction of Cl radicals with 4‐HBA at pH 1 (k = 2.3 × 108 dm3 mol?1 s?1) showing that . OH radicals quantitatively bring about one electron oxidation of 4‐HBA. Reaction of . OH/O .? radicals with 4‐HBA by H‐abstraction mechanism at neutral and alkaline pH values gave reducing radicals and the proportion of the same was determined by following the extent of electron transfer to methyl viologen. H‐atom abstraction is the major pathway in the reaction of O .? radicals with 4‐HBA compared to the reaction of . OH radicals with 4‐HBA. At pH 1, transient species formed in the reactions of H‐atoms with 4‐HBA (k = 2.1 × 109 dm3 mol?1 s?1) were found to transfer electrons to methyl viologen quantitatively. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

7.
Pulse radiolysis with optical absorption detection has been used to study the reactions of hydroxyl radical (OH?) with 4‐thiouracil (4TU) in aqueous medium. The transient absorption spectrum for the reaction of OH? with 4TU is characterized by λmax 460 nm at pH 7. A second‐order rate constant k(4TU+OH) of 1.7 × 1010 M?1 s?1 is determined via competition kinetics method. The transient is envisaged as a dimer radical cation [4TU]2?+, formed via the reaction of an initially formed radical cation [4TU]?+ with another 4TU. The formation constant of [4TU]2?+ is 1.8 × 104 M?1. The reactions of dibromine radical ion (Br2??) at pH 7, dichlorine radical ion (Cl2??) at pH 1, and azide radical (N3?) at pH 7 with 4TU have also produced transient with λmax 460 nm. Density functional theory (DFT) studies at BHandHLYP/6–311 + G(d,p) level in aqueous phase showed that [4TU]2?+ is characterized by a two‐centerthree electron (2c‐3e) [?S∴S?] bond. The interaction energy of [?S∴S?] bond in [4TU]2?+ is ?13.01 kcal mol?1. The predicted λmax 457 nm by using the time‐dependent DFT method for [4TU]2?+ is in agreement with experimental λmax. Theoretical calculations also predicted that compared with [4TU]2?+, 4‐thiouridine dimer is more stable, whereas 4‐thiothymine dimer is less stable. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

8.
The reactions of NO and Br radicals with 5‐hydroxyindole (HIn), 5‐hydroxytryptophol (HTpl), 5‐hydroxytryptophan (HTpn) and 5‐hydroxytryptamine (HTpe) were studied using pulse radiolysis. The rate constants for their reaction with NO radical were found to vary from 105 to 107 dm3 mol?1 s?1 in the pH range 5–9 but a higher value (k = 1.4 ± 0.01 × 108 dm3 mol?1 s?1) was noticed in HTpe at pH 9. The gradual increase in reactivity with pH is due to the decrease in the reduction potentials of indoloxyl radicals with E = 0.55 V at pH 9. In contrast, the rate constants with Br radical were found to be diffusion controlled and remained unaffected by the pH. The transient spectra measured are attributed to the indoloxyl radical formed on oxidation with λmax at 420 nm. The indoloxyl radicals further react with the parent hydroxy indole derivative forming the radical adduct and their decay was found to be pH dependent in derivatives containing an amino group. At pH 5, no decay of the radical adducts was seen in all derivatives up to 5 ms whereas those with the amino group decayed faster at pH 9. The total yields of the oxygen centred and carbon centred radicals formed in the reaction of NO radical with hydroxy indoles were found to be nearly equal to G(NO). Our results suggest that NO radical is inefficient in oxidizing hydroxy indoles under physiological conditions preventing the formation of toxic dimers of indole derivatives. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.

The structure and properties of the paramagnetic centers formed by γ-irradiation at 77 K in sodium sulfate doped with nitrate ions have been investigated by the EPR method. The NO2? 3, NO2 and SO? 4 radicals have been identified. The orientation of NO2? 3 relation to crystallographic axes is determined. In the 77-400 K temperature range the transformations of observable radicals have been studied. The mechanisms of their formation and thermal annealing have been discussed. The symmetry of nitrate ions in sodium sulfate was investigated by diffuse reflectance infrared Fourier transform spectroscopy. At the concentration of NO? 3 up to 5.5 × 1018 g?1 the nitrate ion was supposed to have a planar or pyramidal configuration of the D3h or C3V symmetries. At the concentration of the dopant higher than 5.5 × 1018 g?1 the nitrate ions with the C2V symmetry were observed.  相似文献   

10.
Abstract

On radiolysis tris(acetylacetonato) cobalt(III) in aqueous solutions is found to get reduced by reaction with (1) hydrated electrons, (2) H atoms, (3) OH radicals and (4) C2H2OH radicals. The bimolecular rate constants for the first three reactions, determined by competition kinetics are: 4 × 1010, 2.3 × 109 and 4.7 × 109 M?1sec?1 respectively. Absorption spectra of the irradiated solutions indicate the formation of bis(acetylacetonato) cobalt(II) from reaction (1), but not from (3). The total cobaltous yield in air-free solutions is given byG(Co++) = 5.6 and 6.5 at pH 6.5 and 1 respectively. It appears that Geaq- ∽ H + GoH ∽ 2.8 in neutral solutions. Considerations of material balance for the primary yields of radiolysis of water suggest the possibility that the so-called independent H-atoms in neutral solutions are probably excited water molecules or ion-pairs.  相似文献   

11.
ABSTRACT

The reaction of formic acid (HCOOH) with chlorine atom and amidogen radical (NH2) have been investigated using high level theoretical methods such BH&HLYP, MP2, QCISD, and CCSD(T) with the 6–311?+?G(2df,2p), aug-cc-pVTZ, aug-cc-pVQZ and extrapolation to CBS basis sets. The abstraction of the acidic and formyl hydrogen atoms of the acid by the two radicals has been considered, and the different reactions proceed either by a proton coupled electron transfer (pcet) and hydrogen atom transfer (hat) mechanisms. Our calculated rate constant at 298?K for the reaction with Cl is 1.14?×?10?13?cm3?molecule?1?s?1 in good agreement with the experimental value 1.8?±?0.12/2.0?×?10?13?cm3?molecule?1?s?1 and the reaction proceeds exclusively by abstraction of the formyl hydrogen atom, via hat mechanism, producing HOCO+ClH. The calculated rate constant, at 298?K, for the reaction with NH2 is 1.71?×?10?15?cm3?molecule?1?s?1, and the reaction goes through the abstraction of the acidic hydrogen atom, via a pcet mechanism, leading to the formation of HCOO+NH3.  相似文献   

12.
H‐bonded complexes of p‐X‐PhOH/p‐X‐PhO? with fluoride and hydrofluoric acid (X = OH, H, NO2) were subject of optimization (by means of B3LYP/6‐311+G**) for gradually changed O···F distance from dO···F = 4.0 Å down to (i) the distance of the proton transfer from the hydroxyl group to fluoride leading to O?···HF interaction and (ii) fully optimized system (O?···HF type). In this way, we simulate gradual changes of H‐bond strength estimating simultaneously the energy of interaction, Eint, energy of deformation, Edef, and the binding energy, Etot. The obtained geometrical parameters allow us to show that H‐bond formation causes substantial changes in geometry, even at so distant parts of the system as the ring and bond length in para‐substituents (OH and NO2). All these changes are monotonically dependent on interaction and deformation energies. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
The generation of radical cations of thiourea [(NH2)2C=S], thiosemicarbazide [(NH2―NH)(NH2)C=S], and diethylthiourea [(C2H5―NH)2C=S] in aqueous sulphuric acid media of low to high acid strengths utilizing the pulse radiolysis technique is reported. In this system, the decay half‐life of radical cations of thiourea and its derivatives observed were longer (ranging from 45 to 100 µs at acid strength pH/H0 = ?4.1), and the formation times could be altered with the change in acid strengths. By doing so, a wide range in half‐life of radical cations of thiosemicarbazide (0.7 to 100 µs) was observed in contrast to thiourea and diethylthiourea with the variation in acid strengths (pH/H0) from 0.7 to ?4.1. This perhaps helps in studying the spectral and kinetic properties of transient radical cations comfortably. The general mechanism for the formation of radical cations of the aforementioned compounds in radiolysis has been revisited in which the electron transfer reactions are active. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

14.
The electronic (UV‐vis) and resonance Raman (RR) spectra of a series of para‐substituted trans‐β‐nitrostyrenes were investigated to determine the influence of the electron donating properties of the substituent (X = H, NO2, COOH, Cl, OCH3, OH, N(CH3)2, and O) on the extent of the charge transfer to the electron‐withdrawing NO2 group directly linked to the ethylenic (C = C) unit. The Raman spectra and quantum chemical calculations show clearly the correlation of the electron donating power of the X group with the wavenumbers of the νs(NO2) and ν (C = C)sty normal modes. In conditions of resonance with the lowest excited electronic state, one observes for X = OH and N(CH3)2 that the symmetric stretching of the NO2, νs(NO2), is the most substantially enhanced mode, whereas for X = O, the chromophore is extended over the whole molecule, with substantial enhancement of several carbon backbone modes. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

15.
Relative kinetics of the reactions of OH radicals and Cl atoms with 3‐chloro‐2‐methyl‐1‐propene has been studied for the first time at 298 K and 1 atm by GC‐FID. Rate coefficients are found to be (in cm3 molecule?1 s?1): k1 (OH + CH2 = C(CH3)CH2Cl) = (3.23 ± 0.35) × 10?11, k2 (Cl + CH2 = C(CH3)CH2Cl) = (2.10 ± 0.78) × 10?10 with uncertainties representing ± 2σ. Product identification under atmospheric conditions was performed by solid phase microextraction/GC‐MS for OH reaction. Chloropropanone was identified as the main degradation product in accordance with the decomposition of the 1,2‐hydroxy alcoxy radical formed. Additionally, reactivity trends and atmospheric implications are discussed. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

16.
Kinetics and equilibrium of the acid‐catalyzed disproportionation of cyclic nitroxyl radicals R2NO? to oxoammonium cations R2NO+ and hydroxylamines R2NOH is defined by redox and acid–base properties of these compounds. In a recent work (J. Phys. Org. Chem. 2014, 27, 114‐120), we showed that the kinetic stability of R2NO? in acidic media depends on the basicity of the nitroxyl group. Here, we examined the kinetics of the reverse comproportionation reaction of R2NO+ and R2NOH to R2NO? and found that increasing in –I‐effects of substituents greatly reduces the overall equilibrium constant of the reaction K4. This occurs because of both the increase of acidity constants of hydroxyammonium cations K3H+ and the difference between the reduction potentials of oxoammonium cations ER2NO+/R2NO? and nitroxyl radicals ER2NO?/R2NOH. pH dependences of reduction potentials of nitroxyl radicals to hydroxylamines E1/3Σ and bond dissociation energies D(O–H) for hydroxylamines R2NOH in water were determined. For a wide variety of piperidine‐ and pyrrolidine‐1‐oxyls values of pK3H+ and ER2NO+/R2NO? correlate with each other, as well as with the equilibrium constants K4 and the inductive substituent constants σI. The correlations obtained allow prediction of the acid–base and redox characteristics of redox triads R2NO?–R2NO+–R2NOH. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

17.
The formation and decay kinetics of chain linked triplet radical pairs derived from photo-induced electron transfer reactions in a series of 21 zinc porphyrin-flexible spacer-viologen (ZnP-Sp n -Vi2+) dyads containing 2–138 atoms (n) in the spacer, have been examined by nanosecond laser flash photolysis techniques in an external magnetic field. In non-viscous polar solvents (acetone and CHCl3 plus CH3OH = 1:1 v/v), the effect of the spacer length on the rate constant of forward electron transfer can be described by the equation: k et = k 0 et(n + 6)?1.5, with k 0 et = 3 × 1010 s?1 and 1.2 × 1010 s?1 for electron transfer from the singlet and triplet states of ZnP, respectively. In zero magnetic field, the value of the triplet radical pair recombination rate constant, k r(0) = 0.7 × 106-8 × 106 s?1, is significantly smaller than k et. The dependence of k r(0) on n has an extremum with the maximum near n = 20. In a strong magnetic field (B = 0.21 T), significant retardation of triplet radical pair recombination is observed. In strong magnetic fields the effect of the chain length on triplet radical pair recombination rates is rather small and k r(B) may vary in the range 0.3 × 106-1 × 107 s?1. The phenomena observed are discussed in terms of the interplay of molecular and spin dynamics in the limits of slow and fast encounters, taking into account the exchange-interaction.  相似文献   

18.
Free radicals are observed in γ-irradiated single crystals of 5-nitrouracil with the unpaired electron showing hyperfine interaction with one nitrogen atom. The principal values of hyperfine coupling are Ax = 22·5 g, Ay = 25·2 g, and Az = 40·0 g, and the principal values of the spectroscopic splitting factor are gu = 2·0117, gv = 2·0064 and gw = 2·0027. The relationship of the directions of the corresponding principal axes to the molecular orientations show that the unpaired electron must be located in an sp 2 orbital on either N(1) or N(5). Considerations of the mechanism of radical formation and comparison to radiation damage in other molecules make the N(1) location seem more probable. The π interaction of the nitro group on C(5) evidently prevents the formulation of free radicals with the unpaired electron on C(5). That carbon atom is the most common location of unpaired electron density in other pyrimidine free radicals.  相似文献   

19.
The kinetics of the O3, OH and NO3 radical reactions with diazomethane were studied in smog chamber experiments employing long-path FTIR and PTR-ToF-MS detection. The rate coefficients were determined to be k CH2NN+O3?=?(3.2?±?0.4)?×?10?17 and k CH2NN+OH?=?(1.68?±?0.12)?×?10?10 cm3 molecule?1 s?1 at 295?±?3?K and 1013?±?30 hPa, whereas the CH2NN?+?NO3 reaction was too fast to be determined in the static smog chamber experiments. Formaldehyde was the sole product observed in all the reactions. The experimental results are supported by CCSD(T*)-F12a/aug-cc-pVTZ//M062X/aug-cc-pVTZ calculations showing the reactions to proceed exclusively via addition to the carbon atom. The atmospheric fate of diazomethane is discussed.  相似文献   

20.
The density functional and the transition state theories were used to estimate detailed thermochemical and kinetic data for the oxidative damage to cholesterol induced by peroxyl radicals (ROO?) in lipid media. Two mechanisms of reactions were considered, the hydrogen transfer and the radical adduct formation, and it was found that hydrogen transfer is the only important route in this case, particularly at allylic sites. 7α products are predicted to represent more than 90% of the total initial damage, albeit 7β products are expected to be found in small but not negligible proportion. The chlorination degree was found to play an important role in the extent of the oxidative damage to cholesterol inflicted by the ROO? family. The estimated rate constants are 2.74 × 105, 1.32 × 105, 3.09 × 102, 6.07 × 101, and 8.75 × 10?1 M?1 s?1 for the reactions with ?OOCHCl2, ?OOCCl3, ?OOCH2Cl, ?OOH, and ?OOCH3, respectively. These values indicate that only chlorinated peroxyl radicals represent a significant hazard to the chemical integrity of cholesterol. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

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