Decay Of Radicals Research Articles

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

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

Quality of pilsner malt and roasted malt during storage

Malt is usually expected to be stable during 12 months of storage. However, in practice many brewers notice changes in malt aroma during storage. The oxidative stabilities of pilsner malt and roasted malt were evaluated during a 12 month storage at different temperatures (10 and 20 °C) and water activities (0.231 and 0.432). The radical content in malt kernels was measured by electron spin resonance spectroscopy and the volatile profile of the resulting sweet worts was measured by head-space analysis followed by GC-MS analysis. The storage of malt resulted in oxidative reactions and a large change of the volatile profile of the resulting worts. Roasted malt was much more unstable than pilsner malt, as illustrated by a higher initial radical intensity, larger radical decay during storage and a larger change in the volatile profile of the wort with increased amounts of lipid oxidation products. For both roasted malt and pilsner malt, good correlations were found between radical decay and changes in the volatile profile of the wort, where high temperature and high water activity resulted in the largest changes. During the 12 months of storage, the sugar extract of the wort made from the malts remained constant and was not affected by the chemical changes. This study suggests that chemical changes occurring in malts during less than 12 months of storage may potentially affect the aroma of beer, and that water activity and storage temperature should both be kept low in order to maintain a high malt quality. Copyright © 2014 The Institute of Brewing & Distilling

Mechanistic Aspects of Hydration of Guanine Radical Cations in DNA

The mechanistic aspects of hydration of guanine radical cations, G•+ in double- and single-stranded oligonucleotides were investigated by direct time-resolved spectroscopic monitoring methods. The G•+ radical one-electron oxidation products were generated by SO4•– radical anions derived from the photolysis of S2O82– anions by 308 nm laser pulses. In neutral aqueous solutions (pH 7.0), after the complete decay of SO4•– radicals (∼5 μs after the actinic laser flash) the transient absorbance of neutral guanine radicals, G(-H)• with maximum at 312 nm, is dominant. The kinetics of decay of G(-H)• radicals depend strongly on the DNA secondary structure. In double-stranded DNA, the G(-H)• decay is biphasic with one component decaying with a lifetime of ∼2.2 ms and the other with a lifetime of ∼0.18 s. By contrast, in single-stranded DNA the G(-H)• radicals decay monophasically with a ∼ 0.28 s lifetime. The ms decay component in double-stranded DNA is correlated with the enhancement of 8-oxo-7,8-dihydroguanine (8-oxoG) yields which are ∼7 greater than in single-stranded DNA. In double-stranded DNA, it is proposed that the G(-H)• radicals retain radical cation character by sharing the N1-proton with the N3-site of C in the [G•+:C] base pair. This [G(-H)•:H+C ⇆ G•+:C] equilibrium allows for the hydration of G•+ followed by formation of 8-oxoG. By contrast, in single-stranded DNA, deprotonation of G•+ and the irreversible escape of the proton into the aqueous phase competes more effectively with the hydration mechanism, thus diminishing the yield of 8-oxoG, as observed experimentally.

Resistance to Botrytis cinerea and Quality Characteristics during Storage of Raspberry Genotypes

Raspberries are a delicate, high-value crop with an extremely short shelf life exacerbated by postharvest decay caused by Botrytis cinerea Pers. European red raspberry (Rubus idaeus L.) is the most widely grown variety. Yellow (R. idaeus L.), black (R. occidentalis L.), and purple raspberries (R. ×neglectus Peck. or R. occidentalis ×idaeus hybrids) are available mainly at local markets and U-pick farms. To compare the postharvest quality of the raspberry color groups, pesticide-free fruit from cultivars and breeding selections of red, yellow, purple, and black raspberries were examined for oxygen radical absorbance capacity (ORAC), phenolics, anthocyanins, soluble solids, titratable acids, pH, color, firmness, decay and juice leakage rates, ethylene evolution, and respiration. There were significant correlations between decay rate and physiochemical properties. Both decay and leakage rates were correlated with weather conditions before harvest, but each color group responded differently to different weather factors. There were no correlations among changes in color, firmness, decay, or juice leakage rates. All the other color groups were less acidic than the familiar red raspberry. Yellow raspberries had the worst decay rates but the best leakage rates. Black and purple raspberries, with the highest phenolics and anthocyanins and the lowest ethylene evolution rates, resisted decay the longest but bled soonest.

Influence of high doses γ-irradiation on oxygen permeability of linear low-density polyethylene and cast polypropylene films

Linear low density polyethylene (PE-LLD) and cast polypropylene (PPcast) films were irradiated in a 60Co γ-source. The total irradiation dose varied from 0kGy (unirradiated samples) to 200kGy. Oxygen transport was investigated by a manometric method and the structural changes were studied by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). Free radicals decay as a function of time was monitored by electron spin resonance (ESR) spectroscopy. The results show that the γ-irradiation reduces oxygen permeability coefficient in both films. The reduction was associated with an increase in crystallinity. DSC thermograms revealed a decrease in PPcast melting point with increasing irradiation dose, indicating higher degradation compared to PE-LLD. The observed peak in FTIR spectra for both samples at 1716cm−1 corresponds to the stretching of the carbonyl and carboxylic groups which arise from the reaction of oxygen with the free radicals produced in the polymer matrix as a result of irradiation.

Oxidative stabilization of mixed mayonnaises made with linseed oil and saturated medium-chain triglyceride oil

Mayonnaises, made with either saturated medium chain triglyceride (MCT) oil or unsaturated purified linseed oil (LSO), were mixed. Raman confocal microspectrometry demonstrated that lipid droplets in mixed mayonnaise remained intact containing either MCT oil or LSO. Peroxide formation during storage was lower in mixed mayonnaise compared to LSO mayonnaise, while in mixed oil mayonnaise the level of peroxides was constantly low. Mixed oil mayonnaise had a lower rate of oxygen consumption than mixed mayonnaise, LSO mayonnaise having the highest rate. The decay of water-soluble nitroxyl radicals showed radicals are formed in the aqueous phase with the same rate independent of the lipids. This was also reflected in decay of α-tocopherol during storage being similar in MCT and LSO mayonnaises, but being stable in mixed oil mayonnaise and mixed mayonnaise. Results suggest that other effects than simply diluting unsaturated triglycerides with saturated triglycerides is causing the oxidative stabilization observed for mixed mayonnaise and mixed oil mayonnaise.

Density Functional Theory Study on the Decay of Fullerenyl Radicals RC60•, ROC60•, and ROOC60• (R = tert-Butyl and Cumyl) and Polarizability of the Formed Fullerene Dimers

Currently, there are no comparative studies on the possible routes of decay of fullerenyl radicals. Such information is required for development of new synthetic approaches to the fullerene derivatives, obtained via radical reactions, and understanding mechanisms of oxidative destruction of fullerene-containing materials. In the present work, we have performed a theoretical study on the possible reactions of the selected fullerenyl radicals, generated in the well-known experimental systems. We consider three main routes for the radical decay: formation of fullerene bisadducts via XC60(•) + X(•) reactions, dimerization of XC60(•), and their interaction with molecular oxygen. The calculated heat effects explain the experimental regularities of fullerene radical reactions (e.g., the reversibility of the dimerization and low reactivity of fullerenyls toward molecular oxygen). We have found that the heat effects are maximal for the dimerization of ROOC60(•), so the interaction of C60 with peroxy radicals may provide more effective synthetic routes to the single-bonded C60 dimers compared to the known ones. Moreover, the exothermicity of ROO(•) addition to C60 is increased during the subsequent addition that allows reconsidering the reasons underlying C60 antioxidant activity. Additionally, polarizability and its nonadditivity of fullerene dimers XC60-C60X have been found. Guided by the calculated polarizabilities, we assume a new bistable system "fullerenyl ↔ dimer" for molecular machinery. Depending on the conditions, such a system can exist in two states differing by their response to external electric fields.

Free radicals properties of gamma-irradiated penicillin-derived antibiotics: piperacillin, ampicillin, and crystalline penicillin

The aim of this work was to determine the concentrations and properties of free radicals in piperacillin, ampicillin, and crystalline penicillin after gamma irradiation. The radicals were studied by electron paramagnetic resonance (EPR) spectroscopy using an X-band spectrometer (9.3 GHz). Gamma irradiation was performed at a dose of 25 kGy. One- and two-exponential functions were fitted to the experimental data, in order to assess the influence of the antibiotics’ storage time on the measured EPR lines. After gamma irradiation, complex EPR lines were recorded confirming the presence of a large number of free radicals formed during the irradiation. For all tested antibiotics, concentrations of free radicals and parameters of EPR spectra changed with storage time. The results obtained demonstrate that concentration of free radicals and other spectroscopic parameters can be used to select the optimal parameters of radiation sterilization of β-lactam antibiotics. The most important parameters are the constants τ (τ 1(A),(I) and τ 2(A),(I)) and K (K 0(A),(I), K 1(A),(I), K 2(A),(I)) of the exponential functions that describe free radicals decay during samples storage.

Evolution of the Levels of Free Radicals Generated on Wheat Flour and Wheat Bran by Electron Beam

ABSTRACTThis paper presents the experimental data regarding the levels of free radicals investigated by electron spin resonance (ESR) on wheat flour and wheat bran exposed to an electron beam. Samples were irradiated with an electron linear accelerator of 6 MeV and then stored at room temperature in air. ESR spectra of the samples indicated presence of free radicals induced by electron beam. Three types of free radicals have been detected in wheat flour, and signals typical for cellulose‐like radicals have been noticed for wheat bran, their concentration increasing with the irradiation dose. The postirradiation storage of both sample types caused radical decay with a two‐step pattern associated with fast decay of short‐life radicals followed by slow reduction of long‐life radicals. However, in the first step, the irradiated wheat bran exhibited more rapid decay of radicals than irradiated flour owing to their different complex matrixes, which led to paramagnetic structures of different origin after exposure to an electron beam. The ESR technique allows the detection of free radicals induced in wheat flour and bran by electron beam for a limited period after irradiation that could be shorter than the shelf life of the products.

Radical products of thermal decomposition of polydiphenylenesulfophthalide

The investigation of the vacuum thermal decomposition of polydiphenylenesulfophthalide at 100–530 °C showed that there are at least four main types of paramagnetic species (PMSs). The ESR spectrum of type I PMSs (120–250 °C) has a signal (g = 2.0028; ΔH ∼1 mT) with a poorly resolved hyperfine structure (HFS) and an even number of lines. The electronic spectrum of these particles shows an absorption band at ∼410 nm. These particles were assigned to “low-temperature” triarylmethyl-type radicals (TAMTR), which are apparently generated from dioxothioxanthene defect structures of the polymer. Type II PMSs (250–360 °C) give a smooth symmetrical ESR singlet (g = 2.0028; ΔH ∼1 mT) and two absorption bands in the electronic spectrum at ∼410 nm (strong band) and ∼710 nm (weak band). Based on the results of calculations of electronic spectra for a series of model structures at the TD-DFT B3LYP/6-311G(d,p) level of theory, these PMSs were assigned to “high-temperature” TAMTR, which have a fluorenyl structure and are formed through the opening of the sulfophthalide ring. The maximum concentration of TAMTR II (∼1020 spin g−1) is achieved at 320 °C. At T > 320 °C, type II radicals decay and type III radicals are generated. The latter are condensed aromatic species presumably having a phenalene structure. In the temperature range of 350–450 °C, the ESR line width and shape remain mainly unchanged, which attests to the retention of the dominant structure of the radicals. An increase in the thermal decomposition temperature to ∼450 °C or above leads to a decrease in the ESR line width and a change in its shape from the Gaussian to Lorentzian type. This fact is an evidence of type IV paramagnetic species corresponding to even higher condensed aromatic structures.

Reactions between Flavonoids and <em>α</em>-Hydroxyl Ethyl Peroxyl Radicals: a Pulse Radiolysis Study

Lipid peroxidation (LPO) plays an important role in many pathological processes (such as hepatitis, hepatic sclerosis, atherosclerosis, cerebral hemorrhage and so on), and flavonoids are considered to be effective LPO-inhibitors. Thus we investigated the relationship between the chemical structure of flavonoids and the LPO activity and the antioxidant mechanism of flavonoids. In this work, α-hydroxyl ethyl peroxyl radicals were produced from radiolysis of aerated ethanol to model lipid peroxyl radicals. By detecting the decay of α-hydroxyl ethyl peroxyl radicals in the presence of different concentrations of flavonoids using pulse radiolysis, the reaction rate constants of α-hydroxyl ethyl peroxyl radicals with quercetin, rutin, catechin, and baicalin are determined for the first time. The antioxidant activity of these flavonoids decreases in the order: rutin>quercetin>baicalin>catechin. Flavone and pyrocatechol were used as model compounds for the different components in flavonoids and their reaction rate constants towards α-hydroxyl ethyl peroxyl radicals were (1.7±0.1)×10 and (2.9±0.1)×10 mol-1·dm3· s, respectively. The effect of chemical structure on the scavenging activity towards α-hydroxyl ethyl peroxyl radicals was investigated. The coexistence of the C5-hydroxyl group in the A ring with the C2=C3 in the C ring or the conjugated double bond of the B-C ring and the catechol group in the B ring provides the 199 Acta Phys. ⁃Chim. Sin. 2013 Vol.29 best antioxidant activity. In addition, the C2=C3 in the C ring or the conjugated double bond of the B-C ring is more effective than the catechol group in the B ring, while the C3-rutinose in the C ring has no obvious effect. Therefore, we conclude that the addition reaction between double bonds with peroxyl radicals plays an important role in the antioxidant activity of flavonoids in LPO.

長期保存中の照射食品に誘導されるラジカルの減衰挙動の解析

長期保存中の照射食品に誘導されるラジカルの減衰挙動の解析

Radiation Sterilization of Anthracycline Antibiotics in Solid State

The impact of ionizing radiation generated by a beam of electrons of 25–400 kGy on the stability of such analogs of anthracycline antibiotics as daunorubicin (DAU), doxorubicin (DOX), and epidoxorubicin (EPI) was studied. Based on EPR results, it was established that unstable free radicals decay exponentially with the half-time of 4 days in DAU and DOX and 7 days in EPI after irradiation. Radiation-induced structural changes were analyzed with the use of spectrophotometric methods (UV-Vis and IR) and electron microscope imaging (SEM). A chromatographic method (HPLC-DAD) was applied to assess changes in the contents of the analogs in the presence of their impurities. The study showed that the structures of the analogs did not demonstrate any significant alterations at the end of the period necessary for the elimination of unstable free radicals. The separation of main substances and related substances (impurities and potential degradation products) allowed determining that no statistically significant changes in the content of particular active substances occurred and that their conversion due to the presence of free radicals resulting from exposure to an irradiation of 25 kGy (prescribed to ensure sterility) was not observed.

Surface characterization and radical decay studies of oxygen plasma‐treated PMMA films

Polymethylmethacrylate (PMMA) films were modified by RF oxygen plasma with various powers applied for different periods, and the effects of these parameters on the surface properties such as hydrophilicity, surface free energy (SFE), chemistry, and topography were investigated by water contact angle, goniometer, X‐ray photoelectron spectroscopy (XPS), and atomic force microscopy, and the types of the created free radicals and their decay were detected by electron spin resonance spectroscopy (ESR). SFE and contact angle results varied depending on the plasma parameters. Oxygen plasma treatment (100 W–30 min) enhanced the hydrophilicity of PMMA surface as shown by decreasing the water contact angle from 70° to 26°. XPS analysis showed the change in the amounts of the present functionalities as well as formation of new groups as free carbonyl and carbonate groups. The roughness of the surface increased considerably from ~2 nm to ~75 nm after 100 W–30 min oxygen plasma treatment. ESR analysis indicated the introduction of peroxy radicals by oxygen plasma treatment, and the intensity of the radicals increased with increasing the applied power. Significant decrease in radical concentration was observed especially for the samples treated with higher powers when the samples were kept under the atmospheric conditions. As a conclusion, RF plasma, causes changes in the chemical and physical properties of the materials depending on the applied parameters, and can be used for the creation of specific groups or radicals to link or immobilize active molecules onto the surface of a material. Copyright © 2012 John Wiley & Sons, Ltd.

A chloro bridged Cu(II)–Cu(II) complex of a new aminophenol ligand: Magnetostructural, radical decay kinetic studies, highly efficient and aerial alcohol oxidation

A new tripodal aminophenol-based ligand containing a pyridine unit was synthesized and characterized by IR and 1H NMR spectroscopic techniques. A dimeric copper(II) complex of this ligand was prepared and characterized by X-ray crystallography, DFT calculations, spectroscopic techniques and magnetic susceptibility measurements. X-ray analysis revealed a complex in which one phenolate, and amine and imine nitrogens of the ligand are arranged in a distorted square pyramidal geometry (SP) around the copper ions. Two chloride bridges hold both copper atoms together to form the binuclear [LAphCuCl]2 complex. This complex exhibits nearly no superexchange coupling between the copper centers. The phenolate moieties of the copper complex were electrochemically oxidized to phenoxyl radical cations [LAphCuCl]2+. The decay kinetics of the mentioned radical were investigated using a simulation of the voltammogram data. In addition, highly efficient and eco-friendly oxidation of alcohols to aldehydes was achieved with molecular oxygen or air as the oxidant and the [LAphCuCl]2–Cs2CO3 system as a catalyst.

Electron beam irradiated polyamide-6 at different temperatures

Electron beam irradiation of Polyamide-6 (PA-6) films was carried out over a range of irradiation doses (15–1200kGy) in air at different temperatures (from room temperature to 80°C), and at a dose rate of 4.48kGy/min. The effect of temperature on the radiochemical crosslinking, scission yield, and the dose of incipient gel formation of PA-6 were investigated on the basis of solution viscosity, molecular weight and gel content. The crosslinking efficiency increases with increasing irradiation dose and temperature. The crosslinking rates of PA-6 irradiated above the glass transition temperature (Tg), about 50°C, are higher than those samples irradiated at temperatures below Tg. FTIR and electron paramagnetic resonance (EPR) spectroscopy are used to determine modifications in the samples induced by irradiation. EPR was also used to study the decay of the free radicals.

Specific features of reactions of Am(V) with reductants in weakly acidic solutions

In EDTA solutions with pH ∼5 at 25°C, Am(V) in a concentration of 5 × 10−4−3 × 10−3 M slowly transforms into Am(III). The Am(V) reduction and Am(III) accumulation follow the zero-order rate law. In the range 60–80°C, the reaction is faster. In some cases, an induction period is observed, disappearing in acetate buffer solutions. In the range pH 3–7, the rate somewhat increases with pH. In an acetate buffer solution, an increase in [EDTA] accelerates the process. The activation energy is 47 kJ mol−1. Zero reaction order with respect to [Am(V)] is observed in solutions of ascorbic and tartaric acids, of Li2SO3 (pH > 3), and of hydrazine. The process starts with the reaction of Am(V) with the reductant. The Am(III) ion formed in the reaction is in the excited state, *Am(III). On collision of *Am(III) with Am(V), the excitation is transferred to Am(V), and it reacts with the reductant: *Am(V) + reductant → Am(IV) + R1 and then Am(IV) + reductant → *Am(III) + R1, Am(V) + R1 → Am(IV) + R2. A branched chain reaction arises. The decay of radicals in side reactions keeps the system in the steady state; therefore, zero reaction order is observed.

Kinetic (T = 201–298 K) and Equilibrium (T = 320–420 K) Measurements of the C3H5 + O2 ⇆ C3H5O2 Reaction

The kinetics and equilibrium of the allyl radical reaction with molecular oxygen have been studied in direct measurements using temperature-controlled tubular flow reactor coupled to a laser photolysis/photoionization mass spectrometer. In low-temperature experiments (T = 201-298 K), association kinetics were observed, and the measured time-resolved C(3)H(5) radical signals decayed exponentially to the signal background. In this range, the determined rate coefficients exhibited a negative temperature dependence and were observed to depend on the carrier-gas (He) pressure {p = 0.4-36 Torr, [He] = (1.7-118.0) × 10(16) cm(-3)}. The bimolecular rate coefficients obtained vary in the range (0.88-11.6) × 10(-13) cm(3) s(-1). In higher-temperature experiments (T = 320-420 K), the C(3)H(5) radical signal did not decay to the signal background, indicating equilibration of the reaction. By measuring the radical decay rate under these conditions as a function of temperature and following typical second- and third-law procedures, plotting the resulting ln K(p) values versus 1/T in a modified van't Hoff plot, the thermochemical parameters of the reaction were extracted. The second-law treatment resulted in values of ΔH(298)° = -78.3 ± 1.1 kJ mol(-1) and ΔS(298)° = -129.9 ± 3.1 J mol(-1) K(-1), with the uncertainties given as one standard error. When results from a previous investigation were taken into account and the third-law method was applied, the reaction enthalpy was determined as ΔH(298)° = -75.6 ± 2.3 kJ mol(-1).

ANTIOXIDANT POTENTIAL IN LIPOPHILIC AND HYDROPHILIC EXTRACTS FROM MEDICINAL HERBS (<i>SALVIA OFFICINALIS</i> AND <i>ECHINACEA ANGUSTIFOLIA</i>). A COMPARISON BETWEEN ASSAYS BASED ON ELECTRON PARAMAGNETIC RESONANCE AND SPECTROPHOTOMETRY

Recently, detection of antioxidant activity of plant extracts has caught the attention of researchers. Determination of antioxidant activity is usually performed using stable free radicals. A number of assays is available for screening the antioxidant activity of food constituents, but few of these methods are applicable to lipophilic substances. EPR is the analytical technique that directly measures free radicals making possible the analysis of turbid or highly colored samples. The aim of this study was to determine how the detection technique, plant species and the different growing conditions influenced the antioxidative activity of aqueous and lipid extracts from leaves. Sage (Salvia officinalis L.) and coneflower (Echinacea angustifolia DC.) grown in hydroponics and in soil, were analyzed. Radical decay kinetics, due to plant extracts, were monitored by an EPR spectrometer, equipped with a data acquisition system and a software package designed for analysis and simulation of spectra. Parameters obtained by the fitting of the curves allowed the calculation of the antioxidant potential. The radicals Fremy’s salt (hydrophilic) and 1,1-diphenyl-2-picrylhydrazyl (DPPH, lipophilic) were employed. Comparisons with data obtained by a spectrophotometric detection with the radical cation ABTS+ [2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)] were also made. Fremy’s salt and DPPH gave 1st and 2nd order kinetics, respectively. EPR can give more reliable measurements of the antioxidant potential than spectrophotometric assay. The reduced sensitivity of spectrophotometric detection was showed both for sage and coneflower extracts. Antioxidant potential of sage resulted extraordinary high compared to coneflower and a different ratio of aqueous to lipid antioxidant potential in the two species could be monitored. Antioxidant potentials were also higher for coneflower grown in hydroponics than in soil. In addition to the technique adopted, the detection of antioxidant potential was influenced by the growing conditions of plants and hydroponics showed to be able to increase antioxidant potential of both coneflower lipophilic and hydrophilic extracts. By registration of EPR kinetics we can get reliable measurements of the antioxidant potential of plant extracts, avoiding the artifacts due to the appearance of other radicals resulting from oxidative processes.

The free radical species in polyacrylonitrile fibers induced by γ-radiation and their decay behaviors

Free radicals in vacuum, air and oxygen atmospheres were studied using electron spin resonance (ESR). Mainly two types of radicals, namely alkyl radicals and polyimine radicals, are formed in polyacrylonitrile (PAN) fibers after γ-ray irradiation. The G value of the radical formation was calculated to be 2.1 (number of radicals per 100eV absorbed) in air at room temperature based on the ESR measurements. The radical stability and decay behaviors at room temperature and elevated temperatures were also investigated under different atmospheres. The alkyl radicals were found to be rather stable when stored in vacuum at room temperature, but they decayed via reaction with oxygen when stored in air. The alkyl radicals disappeared completely after a thermal treatment at 110°C in vacuum, but only 15% of the polyimine radicals decayed; this indicates that polyimine radicals are more stable compared to the alkyl radicals due to their lower mobility.