The antioxidant reactivity of sorbitylfurfural towards potential harmful radicals,studied by radiation chemistry techniques

Ionising radiations, employed in a broad range of dose-rate, together with a complex non-linear computation of reaction mechanisms, allow the determination of boundary values of rate constants concerning sorbitylfurfural (SF) reactivity towards a wide series of oxidant and/or virtually harmful radicals. SF reacts with some radicals (H, SO₄^-˙, CO₃^-˙, Br₂^-˙, CH₃˙), produced with both pulse and stationary radiolysis in neutral aqueous solution, having electrophilic and/or oxidative behaviour. The rate constants range from diffusional (k = (7-9) × 10⁹ M^-1 s^-1) to relatively low values (k = 2 × 10⁵ M^-1 s^-1). The possibility to observe these reactions, by means of radiolytical techniques, is heavily influenced by dose-rate. A relation between the radical E⁰_NHE and their reactivity with SF is hinted.     

Kinetics of one-electron oxidation by the ClO radical

Pulse radiolysis studies were carried out to determine the rate constants for reactions of ClO radicals in aqueous solution. These radicals were produced by the reaction of OH with hypochlorite ions in N₂O saturated solutions. The rate constants for their reactions with several compounds were determined by following the build up of the product radical absorption and in several cases by competition kinetics. ClO was found to be a powerful oxidant which reacts very rapidly with phenoxide ions to form phenoxyl radicals and with dimethoxybenzenes to form the cation radicals (k = 7 × 10⁸ −2 × 10⁹ M^-1 s^-1). ClO also oxidizes ClO^-₂ and N^-₃ ions rapidly (9.4 × 10⁸ and 2.5 × 10⁸ M^-1 s^-1, respectively), but its reactions with formate and benzoate ions were too slow to measure. ClO does not oxidize carbonate but the CO^-₃ radical reacts with ClO^- slowly (k = 5.1 × 10⁵ M^-1 s^-1).     

The antioxidant reactivity of sorbitylfurfural towards potential harmful radicals, studied by radiation chemistry techniques

Ionising radiations, employed in a broad range of dose-rate, together with a complex non-linear computation of reaction mechanisms, allow the determination of boundary values of rate constants concerning sorbitylfurfural (SF) reactivity towards a wide series of oxidant and/or virtually harmful radicals. SF reacts with some radicals (H, SO₄ ^-·, CO₃ ^-·, Br₂ ^-·, CH₃ ^·), produced with both pulse and stationary radiolysis in neutral aqueous solution, having electrophilic and/or oxidative behaviour. The rate constants range from diffusional (k = (7–9 ) × 10⁹ M^-1 s^-1) to relatively low values (k = 2 × 10⁵ M^-1 s^-1). The possibility to observe these reactions, by means of radiolytical techniques, is heavily influenced by dose-rate. A relation between the radical E _NHE ⁰ and their reactivity with SF is hinted.     

Degradation of n-butylparaben and 4-tert-octylphenol in H2O2/UV system

The degradation of two endocrine disrupting compounds: n-butylparaben (BP) and 4-tert-octylphenol (OP) in the H₂O₂/UV system was studied. The effect of operating variables: initial hydrogen peroxide concentration, initial substrate concentration, pH of the reaction solution and photon fluency rate of radiation at 254 nm on reaction rate was investigated. The influence of hydroxyl radical scavengers, humic acid and nitrate anion on reaction course was also studied. A very weak scavenging effect during BP degradation was observed indicating reactions different from hydroxyl radical oxidation. The second-order rate constants of BP and OP with OH radicals were estimated to be 4.8×10⁹ and 4.2×10⁹ M^?1 s^?1, respectively. For BP the rate constant equal to 2.0×10¹⁰ M^?1 s^?1was also determined using water radiolysis as a source of hydroxyl radicals.     

Reactive oxygen and nitrogen species (RONS) scavenging reactions of o-vanillin: Pulse radiolysis and stopped flow studies

Reactions of peroxyl radicals and peroxynitrite with o-vanillin (2-hydroxy 3-methoxy benzaldehyde), a positional isomer of the well-known dietary compound vanillin, were studied to understand the mechanisms of its free radical scavenging action. Trichloromethylperoxyl radicals (CCl₃O ₂ ^· ) were used as model peroxyl radicals and their reactions with o-vanillin were studied using nanosecond pulse radiolysis technique with absorption detection. The reaction produced a transient with a bimolecular rate constant of approx. 10⁵ M⁻¹s⁻¹, having absorption in the 400–500 nm region with a maximum at 450 nm. This spectrum looked significantly different from that of phenoxyl radicals of o-vanillin produced by the one-electron oxidation by azide radicals. The spectra and decay kinetics suggest that peroxyl radical reacts with o-vanillin mainly by forming a radical adduct. Peroxynitrite reactions with o-vanillin at pH 6.8 were studied using a stopped-flow spectrophotometer. o-Vanillin reacts with peroxynitrite with a bimolecular rate constant of 3 × 10³ M⁻¹s⁻¹. The reaction produced an intermediate having absorption in the wavelength region of 300–500 nm with a absorption maximum at 420 nm, that subsequently decayed in 20 s with a first-order decay constant of 0.09 s⁻¹. The studies indicate that o-vanillin is a very efficient scavenger of peroxynitrite, but not a very good scavenger of peroxyl radical. The reactions take place through the aldehyde and the phenolic OH group and are significantly different from other phenolic compounds.     

Laser photolysis studies of quaternary ammonium ionic liquids aqueous solution

The reactions between quaternary ammonium ionic liquids ([Me₃NC₂H₄OH]⁺[Zn₂Cl₅]⁻, abbrev. Ch-Zn₂Cl₅) and one-electron oxidant (SO₄^•−), have been studied by nano-second laser photolysis techniques. The mechanism of monophotonic ionization by 266 nm laser excitation was suggested and the quantum yield was estimated to be 0.04. The second-order decay rate constant of SO₄^•− oxidation reactions at 460 nm, 1.3 × 10⁹ M⁻¹ s⁻¹, was almost equal to the product rate constant of 1.5 × 10⁹ M⁻¹ s⁻¹ at 320 nm in Ch-Zn₂Cl₅ aqueous solution showing that the decay and the product were synchronic. Comparison of Ch-Zn₂Cl₅ with chloride choline and ZnCl₂ showed that the anion Zn₂Cl₅ ⁻ played an important role in photoionization while choline cation had little function on its photolysis and radiolysis. The present study would be helpful for understanding the application of ionic liquids in the field of electrochemical deposition.     

Electron transfer,equilibrium, and protonation in the system of cis- and trans-stilbene in 2-propanol

Spectrophotometric pulse radiolysis experiments with cis- and trans-stilbene (S_c and S_t) in 2-propanol show that both isomers react with the solvated electron with a rate constant of 4.5 × 10⁹ M^?1 s^?1. The absorption spectra of the two anion radicals have maxima at 496 and 486 nm, respectively. The absorbances at 400–550 nm disappear exponentially corresponding to a pseudo first order protonation of the anion radicals. The rate constants for the protonation of the cis isomer is 6.4 × 10⁵ and of the trans isomer 0.7 × 10⁵ s^?1. In mixtures of cis- and trans-stilbene the electron transfer

has a forward rate constant of 9 × 10⁷ M^?1 s^?1 while the back reaction has a rate constant of 2.15 × 10⁷ M^?1 s^?1. An equilibrium constant K = 4.2 is calculated.     

Radiation chemistry of Cu(II) tetrasulfophthalocyanine in water-methanol system

The effect of ionising radiation on copper(II) phthalocyanine 3,4′,4′′,4′′′ tetrasulfonic acid, tetrasodium salt (Cu(II)tspc^4-) in aqueous as well as in water-methanol solutions has been studied. The determined yields of complex decomposition (measured on the basis of absorption decay) depend on the composition of matrices and the dose applied. The rate constant of electron scavenging by Cu(II)tspc^4-, k = (1.3 ± 0.1) × 10¹⁰ M^-1 s^-1 in methanol-water (2:8 v/v) solutions has been determined using the pulse radiolysis technique. The rate constant k = (1.16 ± 0.1) × 10¹⁰ M^-1 s^-1 of scavenging of OH radicals applying the competion method with p-nitrosodimethylaniline (pNDA) has been determined in aqueous solutions.     

A re-examination of the decay kinetics of pulse radiolytically generated Br-2 radicals in aqueous solution

The decay of Br^-₂ in Ar-purged or N₂O-saturated aqueous solutions of KBr (0.01-1.0 M) in the pH range 1–7 has been re-examined using the techniques of pulse radiolysis and computer simulation. The dependence of the rate constant for the intrinsic decay of Br^-₂ on ionic strength (controlled by KBr) has been established; the values of k (Br^-₂ + Br^-₂) are (1.9 ± 0.1) × 10⁹, (2.2 ± 0.3) × 10⁹ and (2.4 ± 0.3) × 10⁹ M^-1 s^-1 in the presence of 0.01, 0.1 and 1.0 M KBr, respectively, independent of pH between 2 and 7. The computer simulation of the decay of Br^-₂ has also generated, for the latter species, ϵ = 10,000 ± 700 M^-1 cm^-1 at λ_max = 360 nm; this value has been calculated without making any assumption concerning G(Br^-₂). For the reduction of Br^-₂ by H atoms, a value of k (H + Br^-₂) = (1.4 ± 0.3) × 10¹⁰ M^-1 s^-1 has been obtained in the presence of 0.01-1.0 M KBr, independent of pH between 1–4. For the reduction of Br^-₂ by e^-_aq at pH 7 (10^-3 M phosphates) and μ = 0.1, a value of k (Br^-₂ + e^-_aq = (1.1 ± 0.2) × 10¹⁰ M^-1 s^-1 has been obtained.     

Free radical inactivation of trypsin

Reactivities of free radical oxidants, ^.OH, Br^-·₂ and Cl₃COO^. and a reductant, CO^-·₂, with trypsin and reactive protein components were determined by pulse radiolysis of aqueous solutions at pH 7, 20°C. Highly reactive free radicals, ^.OH, Br^-·₂ and CO^-·₂, react with trypsin at diffusion controlled rates, k(^.OH + trypsin) = 8.2 × 10¹⁰ M^-1 s^-1, k(Br^-·₂ + trypsin) = 2.55 × 10⁹ M^-1 s^-1 and k(CO^-·₂ + trypsin) = 2.6 × 10⁹ M^-1 s^-1. Moderately reactive trichloroperoxy radical, k(Cl₃COO^. + trypsin) = 3 × 10⁸ M^-1 s^-1, preferentially oxidizes histidine residues. The efficiency of inactivation of trypsin by free radicals is inversely proportional to their reactivity. The yields of inactivation of trypsin by ^.OH, Br^-·₂ and CO^-·₂ are low, G(inactivation) = 0.6-0.8, which corresponds to ∾ 10% of the initially produced radicals. In contrast, Cl₃COO^. inactivates trypsin with ∾ 50% efficiency, i.e. G(inactivation) = 3.2.     

Rate constants for hydrogen abstraction reactions of the sulfate radical,SO4−. Alkanes and ethers

Rate constants have been determined for the reactions of SO₄^? with a series of alkanes and ethers. The SO₄^? radical was produced by the laser-flash photolysis of persulfate, S₂O₈^2?. For methane, only an upper limit of 1 × 10⁶ M^?1 s^?1 could be determined. For ethane, propane, and 2-methylpropane, rate constants of 0.44, 4.0, and 10.5 × 10⁷ M^?1 s^?1 were found. For ethyl and n-propyl ether, rate constants of 1.3 × 10⁸ and 2.2 × 10⁸ M^?1 s^?1 were found and for 1,4-dioxane and tetrahydrofuran, rate constants of 7.2 × 10⁷ and 2.8 × 10⁸ were obtained. The reaction of SO₄^? with allyl alcohol was also studied and found to have a rate constant of 1.4 × 10⁹ M^?1 s^?1.     

[Me3NC2H4OH]Zn2Cl5水溶液的激光光解研究

利用时间分辨激光光解技术研究了季铵盐型离子液体[Me₃NC₂H₄OH]Zn₂Cl₅(简写R-Zn₂Cl₅)的光解行为, 研究发现离子液体能被266 nm激光单光子电离, 生成阳离子自由基、[Zn₂Cl₅]^•中性自由基和水合电子, 观察到胆碱激发三线态的存在, 并测定了离子液体光电离的量子产额为0.04. 利用266 nm激光对离子液体、胆碱、氯化锌、氯化钠的光解行为比较, 发现胆碱阳离子的贡献很小, [Zn₂Cl₅]^－阴离子起主要作用. 采用氧化性自由基SO₄^•－引发离子自由基, 揭示其光电离机理, 测定离子液体的动力学反应速率常数, SO₄^•－ 460 nm的衰减速率常数为1.3×10⁹ L•mol^－1•s^－1, 320 nm离子自由基瞬态产物的生成速率常数为1.5×10⁹ L•mol^－1•s^－1, 两者很接近, 说明SO₄^•－自由基的衰减与瞬态自由基的生成是同步的.     

Kinetic measurements of the gas phase HO2+CH3O2 cross-disproportionation reaction at 298 K

Flash photolysis kinetic absorption spectroscopy was used to investigate the gas phase reaction between hydroperoxy (HO₂) and methylperoxy (CH₃O₂) radicals at 298 K. Due to the large difference between the self-reactivities of the two radicals, first- or second-order kinetic conditions could not be maintained for either species. Thus, the rate constant for the cross reaction was determined from computer-modeled fits of the radical absorption decay curves, at wavelengths between 215 and 280 nm. This procedure yielded k = 2.9 × 10⁻¹² cm³ molecule⁻¹ s⁻¹ independent of total pressure (using N₂) between 25 and 600 Torr, and of the partial pressure of water vapor (up to 11.6 Torr). There was also no effect of water vapor on the rate constant for the self-reaction of methylperoxy radicals.     

Pulse radiolysis study of the formation and the reactivity of baicalin radical anion,and in comparison with rutin,quercetin and acyrlate ester radical anions in ethanol

The reaction of solvated electrons with baicalin in N₂-saturated ethanol has been studied by pulse radiolysis. The results show that a solvated electron can add to baicalin and generate a baicalin radical anion with a maximum UV absorbance peak at 360 nm. Its molar extinction coefficient at this wavelength is 1.3×10⁴ M⁻¹ cm⁻¹. The rate constant for the build-up of the baicalin radical anion is 1.3(±0.4)×10¹⁰ M⁻¹ s⁻¹. Decay of the radical anion is induced by a proton transfer reaction and a recombination reaction, which involves a pseudo-first-order reaction with rate constant 2.6(±0.4)×10³ s⁻¹ and a second-order reaction with rate constant 1.3(±0.2)×10⁹ M⁻¹ s⁻¹. The effect of acetaldehyde on the decay of the baicalin radical anion was also investigated. Electron transfer between the baicalin radical anion and acetaldehyde was not observed, probably due to the low rate of electron transfer between the baicalin radical anion and acetaldehyde. Reactivity of the rutin, quercetin, baicalin and ethyl acrylate radical anions are also compared.     

266 nm光照下水溶液中氯苯与H2O2的反应机理研究

利用瞬态吸收光谱技术研究了不同条件下C₆H₅Cl与H₂O₂水溶液的激光闪光光解情况, 初步考察了其瞬态物种的生长和衰减等行为. 研究表明, •OH自由基和C₆H₅Cl反应生成C₆H₅Cl-OH adduct, 其反应速率常数在近中性、酸性条件下约为(5.89±0.65)×10⁹和(7.07±0.61)×10⁹ L•mol^－1•s^－1; 其衰减则符合双分子二级反应, 速率常数2k/εl＝1.1×10⁶ s^－1, 而在碱性时则为(4.34±0.51)×10⁹ L•mol^－1•s^－1, 衰减呈准一级反应, 速率常数为2.11×10⁵ s^－1. 在有氧条件下, O₂与C₆H₅Cl-OH adduct反应生成C₆H₅Cl-OHO₂ adduct, 其反应速率常数为6.8×10⁸ L•mol^－1•s^－1.     

Electron transfer. 154. Reaction of the nitrosodisulfonate anion radical with one- and multi-electron inorganic reductants

The nitrosodisulfonate anion radical, NO(SO₃)₂ ^2-, a single electron oxidant, reacts cleanly with an array of metal-center reductants. Rates for substitution-labile species generally fall in the range 10⁴ -10⁵ M^-1 s^-1, both for le^-[Eu^II, Fe^II(EDTA)] and 2e^-(U^IV, In^I, Ge^II and Sn^II) reagents. The more weakly reducing donor VO²⁺ reacts more slowly (3 M^-1 s^-1 at 22°C) and the substitution-inert complex Fe(CN)₆ ^4- still more sluggishly. Reductions with the non-metal related donors, azide, formate, hypophosphite, hyponitrite and H2₂AsO₃ ^-, fall in the range 10^-4 -10^-2 M^-1 s^-1. Reactions yield the product HON(SO₃)₂ ^2-. Kinetic decay curves feature no irregularities reflecting formation or loss of one or more transients on a time scale comparable to that of the main conversion, indicating that the experimental rates pertaining to the 2e reductants and to hydrazine (a 4e reductant) are determined by the initial le transfer and that follow-up steps are rapid. The usual distinction between complementary and noncomplementary redox reactions applies poorly to reductions of NO(SO₃)₂ ^2-. Rapid reductions require (1) an adequate potential difference, (2) the possibility of an inner-sphere path and (3) the availability of one or more nonbonding electrons at the reducing site. Substitution-labile metal-based reducing centers embracing a wide range of formal potentials, both le^- and 2e^- donors, may react speedily, although the latter group must operate in steps.     

One-electron oxidation of glutathione by azide radicals in neutral medium: A gamma and pulse radiolysis study

The selective interactions of azide radicals with glutathione (GSH) have been quantitatively studied in buffered neutral aqueous solutions using γ and pulse radiolysis. The sulfur centered GS̽ and GSSG⨪ radicals are produced in pulse and γ radiolysis. Kinetic experiments and simulation allowed to estimate the rate constant of N̽₃ with GSH which has been found to be equal to (9.5 ± 0.5) × 10⁶M⁻¹ s⁻¹ at pH 7. In steady state radiolysis, we have found GSSG as the final product formed with an initial G value of 2.9 × 10⁻⁷ mol J⁻¹.     

Absolute rate constants for hydrogen abstraction from hydrocarbons by the trichloromethylperoxyl radical

Absolute rate constants have been measured for the reactions of trichloromethylperoxyl radicals with cyclohexane, cyclohexene, and hexamethylbenzene. The CCl₃O₂ radicals were produced by pulse radiolysis of air-saturated CCl₄ solutions containing various amounts of the hydrocarbons. The rate constants were determined by competition with the one-electron oxidation of metalloporphyrins, using the rate of formation of the metalloporphyrin radical cation absorption to monitor the reaction by kinetic spectrophotometry. The rate constants for hydrogen abstraction from cyclohexane, cyclohexene, and hexamethylbenzene were found to be 1 × 10³, 1.0 × 10⁵, and 7.5 × 10⁴ M^?1 s^?1, respectively.     

Flash photolysis study for reactions of NO3· with sulfur compounds in acetonitrile solution

The rate constants for the reaction of NO₃· with sulfur compounds in acetonitrile have been determined by the flash photolysis method. The rate constant for dimethyl sulfone (2.7 × 10⁴ M^?1s^?1 at ?10°C) is larger than that of the deuterium derivative, indicating that NO₃· abstracts the hydrogen atom from dimethyl sulfone. In the case of dimethyl sulfide, the rate constant was evaluated to be 1.5 × 10⁹ M^?1 s^?1 at ?10°C; the transient absorption band attributable to the cation radical was observed after the decay of NO₃·, suggesting the electron transfer reaction from the sulfide to NO₃·. For diphenyl sulfide and dimethyl disulfide, the electron transfer reactions were also confirmed. For dimethyl sulfoxide, the reaction rate constant of 1.2 × 10⁹ M^?1 s^?1 (at ?10°C) was not practically affected by the deuterium substitution, suggesting that NO₃· adds to sulfur atom forming (CH₃)₂?(O)-ONO₂. On the other hand, for diphenyl sulfoxide, the electron transfer reaction occurs. By the comparison of these rate constants in acetonitrile solution with the reported rate constants in the gas phase, the change of the reaction paths was revealed.     

Laser-flash photolysis study of dithiobis (tetrazole); reactivities of tetrazole-thio radical

The photo-cleavage of S S bond of 5,5′-dithiobis (1-phenyl-1H-tetrazole) has been studied by the nanosecond-laser flash photolysis method. The transient absorption band at ca. 430 nm was attributed to 1-phenyl-1H-tetrazole-5-thio radical forming by the S S bond fission. For the reaction with conjugated dienes, an addition reaction takes place forming the S C bond, suggesting that unpaired electron of the radical localizes mainly on the S-atom. From the decay rates of the radical, the addition reaction rate constant for 2-methyl-1,3-butadiene is evaluated to be 5.5 × 10⁹ M⁻¹ s⁻¹ in THF at 23°C, which is as fast as diffusion controlled limit. The reactivity of the radical is ca. 100 times higher than that of the PhS˙. The reactivity of the thio radical to O₂ was too low to evaluate, which is one of the characteristics of a S-centered radical. The rate constant for 1,4-cyclohexadienene (1.4 × 10⁸ M⁻¹ s⁻¹) is larger than that of cyclohexene (2.8 × 10⁷ M⁻¹ s⁻¹) suggesting the hydrogen abstraction is a main reaction. The MO calculations have been performed for these radicals to reveal the reason of the high reactivity of the radical. © 1996 John Wiley & Sons, Inc.