Formation Of Peroxide Radicals Research Articles

Radioprotective Effects of Vitamin C, Cimetidine, and Famotidine on Lipid Peroxidase and Hepatic Glutathione Levels in Mouse Liver.

Radiation therapy is one of the most effective treatments for approximately 60% of patients with cancer. During radiation exposure, the overproduction of reactive oxygen species (ROS) disrupts the lipid layer of the membrane, leading to subsequent peroxide radical formation. Cimetidine (Cim) and famotidine (Fam) are histamine H2 receptor antagonists (H2 blocker), also known as peptic ulcer drugs, that exert radioprotective effects. Vitamin C (Vit.C) is an effective free radical and ROS scavenger with significant radioprotective effects. In this experimental study, male mice (6-8 weeks and 28 ± 3 g) were used in five groups. To evaluate ionizing radiation, gamma rays were used at two doses of 2 and 4 Gy and different doses of Cim, Fam, and Vit.C administered as the protectives. Finally, the livers of the mice were isolated and homogenized. The levels of lipid peroxidase and reduced and oxidized glutathione were measured using standard methods. With increasing radiation dose, lipid peroxidase activity, GSSG level, and glutathione content increased. The findings showed that in the drug-only group, Vit.C had better protection than the other two drugs, and the combination of the three drugs had excellent radiation protection. Radiation protection of normal cells in radiotherapy is a valuable necessity. A number of drugs can protect cells against ionizing radiation through different mechanisms. The results suggest that Fam, Cim, and Vit.C can be radioprotective individually or in combination.

Sexual dimorphisms in renal mitochondrial bioenergetics

BackgroundStudies have shown that men have higher incidences of end‐stage renal disease than women at every point across the lifespan. Animal models for various renal diseases have similar occurrence with males being affected more frequently. Recent efforts have been heavily focused on delineating the mechanisms behind these sex‐based differences from various angles, with the mitochondria being highlighted as a target for sex difference‐related renal pathologies. The goal of this study is to investigate the sexual dimorphisms of renal mitochondria and their dependency on renal hemodynamics before disease onset.MethodsMitochondria were isolated from PBS‐flushed kidneys of Sprague Dawley male (SDM) and female (SDF) rats at 11 weeks of age using differential centrifugation. Renal cortex (SDMC vs SDFC) and medulla (SDMMvs SDFM) were separated for individual measurements. Mitochondrial membrane potential and hydrogen peroxide production were measured in spectrofluorimetry using the fluorescent dyes TMRM and Amplex Red, respectively. A portion of mitochondria were submitted to a histology core for electron microscopy. Additionally, mitochondrial oxygen consumption rate (OCR) was also assessed using Seahorse assay. Lipid peroxide radical formation was detected using electron paramagnetic resonance (EPR) with in vivo spin trapping. As a measure of renal function, GFR was assessed using FITC‐Inulin in conscious animals.ResultsElectron microscopy revealed similar yield of mainly round‐shaped isolated mitochondria with retained cristae and membrane structures in all groups. SDFM showed a higher membrane potential than SDMM (238.1±12.4 vs 162.0±8.8 au, p<0.001; respectively). Both SDFC and SDFM had higher hydrogen peroxide production in comparison to their male counterparts (cortex: 99443.7±3061.7 vs 69943.4±1708.6 au/protein, p<0.001; respectively. medulla: 113366.7±5430.7 vs 60613±2297.1 au/protein, p<0.001; respectively). Overall female mitochondria exhibited decreases in their basal, ATP‐linked, leaked OCRs as well as spare capacity compared to males (spare capacity: cortex: 5.9±0.6 vs 14.3±1.3, p<0.001; respectively. medulla: 4.9±0.6 vs 11.6±0.7 pmol/min/protein, p<0.001; respectively). EPR showed similar lipid peroxide radical levels in both sexes and sections of kidney. In the next part of the study, we explored if renal mitochondrial bioenergetics correlated with the GFR of the animal. Our data show the following GFR values for male and female rats as normalized to two kidney weights (2KW) and 2KW/ total body weight (2KW/TBW), respectively: 1.4±0.2 vs 0.8±0.1 mL/min/2KW, p=0.1416 and 0.5±0.1 vs 0.2±0.02 mL/min/2KW/TBW, p=0.0143. We did not observe any correlation between mitochondrial membrane potential and ROS production (measured in the isolated renal cortical mitochondria) with GFR in male or female rats (n= 5 in each group).ConclusionsOverall, we show here that female renal mitochondria exhibit lower oxygen consumption, higher ROS emission, and membrane potential vs males; however, lipid peroxidation is similar. Currently, we do not see a correlation between mitochondrial bioenergetics and GFR. More studies designed with higher statistical power are required to further elucidate the relationship between renal blood flow and mitochondrial bioenergetics.

Ozonation of Decalin as a Model Saturated Cyclic Molecule: A Spectroscopic Study.

Ozonolysis is used for oxidation of a model cyclic molecule-decalin, which may be considered as an analog of saturated cyclic molecules present in heavy oil. The conversion of decalin exceeds 50% with the highest yield of formation of acids about 15–17%. Carboxylic acids, ketones/aldehydes, and alcohols are produced as intermediate products. The methods of UV-visible, transmission IR, attenuated total reflection IR-spectroscopy, NMR and mass-spectrometry were used to identify reaction products and unravel a possible reaction mechanism. The key stage of the process is undoubtedly the activation of the first C-H bond and the formation of peroxide radicals.

ON THE KINETICS OF ANODIC PROCESSES AT OXIDATION OF AQUEOUS SOLUTIONS OF DIMETHYL SULFOXIDE

Dimethyl sulfoxide is a feedstock for a large number of organic substances syntheses. Nowadays research is considerably focused on the production of general products of dimethyl sulfoxide oxidation – dimethyl sulfone and methane sulfonic acid. Dimethyl sulfone is well–known as a food supplement for the treating and strengthening of human joints and ligaments. dimethyl sulfone is basically synthesized by oxidation of dimethyl sulfoxide in hot 30 % hydrogen peroxide in glacial acetic acid. Synthesis is accompanied by significant losses of hydrogen peroxide, the target product has to be significantly purified. It becomes possible to control the synthesis of pure dimethyl sulfone and methane sulfonic acid when using the electrochemical method of oxidation of dimethyl sulfoxide in its aqueous solution with chemically resistant anode and high overvoltage of oxygen reaction Controlled synthesis is relevant because sulfur tends to change the oxidation rate. Study of kinetics of anodic processes at platinum electrode was performed in the dimethyl sulfoxide concentration range about 1.0…4.0 mol∙dm–3. Current raise was observed at potentials that are more positive than 1.3…1.4 V. This potential range corresponds to oxygen release. Dissolved sulfuric acid (0.2 mol∙dm–3) was added in order to inhibit the oxygen release and achieve the potential for the formation of peroxide radicals in aqueous solutions of dimethyl sulfoxide. It is known that sulfate ions are adsorbed on the surface of the platinum anode, displacing molecules of protonated water. This allows to shift the potentials and increase of the electrolysis current in 0.2 mol∙dm–3 H2SO4 to 1.7…1.9 V. It indicates the processes of formation of peroxide radicals on the surface of the platinum anode. Further shift of the anode potential into more positive area than 2.00…2.05 V leads to a rapid increase in current density. At such potentials, dimethyl sulfoxide and dimethyl sulfone are oxidized to methane sulfonic acid with a parallel oxygen and hydrogen peroxide release. Current–voltage study has shown that the oxidation of dimethyl sulfoxide in aqueous solutions runs through the formation of dimethyl sulfone. When conducting electrochemical synthesis with control of the anode potential, it is possible to produce dimethyl sulfone without further oxidation to methane sulfonic acid. The addition of 0.2 mol∙dm–3 H2SO4 to aqueous dimethyl sulfoxide solutions inhibits oxygen release and intensifies oxidation of dipole dimethyl sulfoxide molecules adsorbed on the platinum surface. The influence of adsorption processes on the kinetics of anode processes at the platinum anode in aqueous solutions of dimethyl sulfoxide at high anode potentials has been studied.

Sex differences in renal mitochondrial function of young Sprague Dawley rats

Introduction Sex differences are implicated in many cardiovascular and renal pathologies; for instance, premenopausal females are typically less prone to renovascular damage than males. However, although mitochondrial bioenergetics per se is a well-known factor that can mediate the progression of the renal diseases, it is not known if there are sex-related dissimilarities in the performance of renal mitochondria prior to the development of any disease. The goal of this study was to test the differences in renal cortical and medullary mitochondrial function in healthy male versus female rats. Methods . Mitochondria were isolated from the kidneys collected from male and female Sprague Dawley (SD) rats procured from Charles River labs at 11 weeks of age. Mitochondrial membrane potential, superoxide and H2O2 levels were measured with luminescent or fluorescent dyes (TMRM, MCLA and Amplex Red) in mitochondria isolated from renal cortex and medulla. To measure the oxygen consumption rate (OCR) and mitochondrial calcium uptake, seahorse assay and spectrofluorimetry with CaGreen dye, respectively, were performed on isolated mitochondria. Lipid peroxide radical formation was detected using electron spin resonance spectroscopy (ESR) with in vivo spin trapping. The SOD activity and total antioxidant capacity were measured using commercially available kits. In order to analyze the expression levels of various mitochondria-related proteins, Western blot analysis was performed on snap-frozen isolated renal mitochondria. Results . Kidneys from SD male (SDM) and female rats (SDF) were divided into cortex (SDMC, FC) and medulla (SDMM, FM). We report higher membrane potential in SDFM compared to SDMM (p<0.001). H2O2 levels were elevated in both the SDFC and SDFM mitochondria compared to SDM (p<0.01), and GPX4 level was significantly increased the SDFM samples. Interestingly, superoxide production was increased in the medulla compared to the cortex for both SDM and SDF, while SOD2 expression was similar. Total SOD activity was increased in SDFC compared to all other groups (p<0.01). ESR showed similar lipid peroxide radical levels in all groups. Antioxidant capacity was reduced in SDFM tissues compared to other groups (p<0.05). Female mitochondria exhibited decreased OCR compared to males, and all OCR parameters were lower in medullary vs cortical mitochondria, independent of sex. Interestingly, calcium uptake was more active in the medulla vs cortex for both males and females, whereas the mitochondrial permeability transition pore (mPTP) opening was recorded earlier in females than males. Conclusions . We report differences in mitochondrial function in the cortex and medulla of young healthy male and female rats, primarily, in their ability to handle reactive oxygen species. The observed sex-related dissimilarities open new avenues of research aimed at establishing the mechanisms that may affect the predisposition of males and females to kidney disease development later in life.

Performance and Durability of Mn-Based Platinum Group-Metal Free Catalyst in Membrane Electrode Assemblies

Proton exchange membrane fuel cells (PEMFCs) have drawn increasing attention in automotive and residential applications. To significantly reduce the cost of the PEMFC stacks, current platinum-group metal (PGM) catalysts must be replaced by PGM-free catalysts. Although Fe-based PGM-free catalysts (Fe-N-C) have exhibited promisingly high activity for the oxygen reduction reaction (ORR)1, they suffer from insufficient stability. Additionally, a major issue associated with Fe-containing catalysts is that dissolved iron ions can facilitate Fenton’s reaction thus forming a strong radical known to degrade the ionomer and membrane2.Mn-based catalysts have recently been developed, aiming to improve the catalyst durability and mitigate the Fenton’s reaction3. However, the catalyst stability and integration into membrane electrode assemblies (MEAs) have yet to be studied. In this work, density function theory (DFT) has been applied to study the active sites and their degradation mechanism. Computational fluid dynamic (CFD) modeling was also applied to study water, oxygen and proton transport in the electrode. Electrode fabrication optimizations were conducted based on the guidance from the CFD results. The optimizations include ionomer content, electrode porosity and MEA fabrication approaches It has been found that Mn-based catalysts showed improved MEA durability compared to Fe-based catalysts due to the higher carbon graphitization degree, reduced de-metallization and mitigation of peroxide radical formation. However, there is still a significant performance degradation compared to PGM-based MEAs. X-ray absorption has been applied to examine the catalyst and corresponding MEAs before and after durability. The degradation is primarily attributed to the oxidation and agglomeration of active sites. Acknowledgement: The project is financially supported by the Department of Energy’s HFTO under the Grant DE-EE0008075. Reference:1. Wu, K.L. More, C.M. Johnston, P. Zelenay, Science, 332, 443, 2011.2. F Coms, H Xu, T. McCallum, C. Mittelsteadt, ECS Trans. 64, 389, 2014.3. Li, J.; Chen, M.; Cullen, D. A.; Hwang, S.; Wang, M.; Li, B.; Liu, K.; Karakalos, S.; Lucero, M.; Zhang, H.; Lei, C.; Xu, H.; Sterbinsky, G. E.; Feng, Z.; Su, D.; More, K. L.; Wang, G.; Wang, Z.; Wu, G., Atomically dispersed manganese catalysts for oxygen reduction in proton-exchange membrane fuel cells. Nature Catalysis 2018, 1 (12), 935-945.

A detailed ellipsometric porosimetry and positron annihilation spectroscopy study of porous organosilicate-glass films with various ratios of methyl terminal and ethylene bridging groups

Abstract Organosilicate-glass films with a varying ratio of terminal methyl and bridging ethylene groups are synthesized using 1,2-bis(trimethoxysilyl)ethane/methyltrimethoxysilane mixtures and sol-gel technology. The films are characterized by Fourier Transform Infrared spectroscopy, Ellipsometric Porosimetry and Positron Annihilation Spectroscopy. The hard bake at 400 °C generates the final pore structure, which depends on the curing environment. It is shown that ethylene bridge is destructed during the hard bake in the air via formation of peroxide radicals that form ≡SiOH during the transformation. Continuous hard bake leads to condensation of silanol groups and form a structure similar to the ordinary silica. The pore size of highly porous materials (>30%) is larger in air cured films. Destruction of the ethylene bridge makes the films matrix soft and micropores collapse due to the capillary forces during the template evaporation. It leads to the film shrinkage, increases the size of internal voids. The air cured samples showed better mechanical properties than N2 cured ones although in the last case ethylene bridging groups were preserved. The reason is that the collapse of micropores increase the internal density and creates more favorable condition for condensation of silanol groups.

Sustainable Electrochemical Depolymerization of Lignin in Reusable Ionic Liquids

Lignin’s aromatic building blocks provide a chemical resource that is, in theory, ideal for substitution of aromatic petrochemicals. Moreover, degradation and valorization of lignin has the potential to generate many high-value chemicals for technical applications. In this study, electrochemical degradation of alkali and Organosolv lignin was performed using the ionic liquids 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and triethylammonium methanesulfonate. The extensive degradation of the investigated lignins with simultaneous almost full recovery of the electrolyte materials provided a sustainable alternative to more common lignin degradation processes. We demonstrate here that both the presence (and the absence) of water during electrolysis and proton transport reactions had significant impact on the degradation efficiency. Hydrogen peroxide radical formation promoted certain electrochemical mechanisms in electrolyte systems “contaminated” with water and increased yields of low molecular weight products significantly. The proposed mechanisms were tentatively confirmed by determining product distributions using a combination of liquid chromatography-mass spectrometry and gas-chromatography-mass spectrometry, allowing measurement of both polar versus non-polar as well as volatile versus non-volatile components in the mixtures.

Peroxidation Radical Formation and Regiospecificity of Recombinated Anabaena sp. Lipoxygenase and Its Effect on Modifying Wheat Proteins

Peroxidation radical formation and the regiospecificity of recombinated lipoxygenase from Anabaena sp. PCC7120 (ana-rLOX) were characterized by using ESR and HPLC-MS. It was found that ana-rLOX oxygenated at the C-13 position of the substrate linoleic acid (LA); at C-13 and C-16 of α-linolenic acid (ALA); at C-9, C-12, and C-15 of arachidonic acid (AA); at C-12, C-15, and C-18 of eicosapentaenoic acid (EPA); and at C-14 and C-16 of docosahexaenoic acid (DHA), respectively. A total of 7, 14, 30, 28, and 18 radical adducts for LA, ALA, AA, EPA, and DHA were respectively identified by HPLC-MS. The functional characteristics of wheat protein, such as foaming capacity (FC), foam stability (FS), emulsifying activity index (EAI), emulsifying stability index (ESI), increased with enzymatic reactions. However, the average particle size of wheat proteins decreased with addition of ana-rLOX/LA. The ana-rLOX was also positivele effective in improving dough properties. These results provided clear evidence that ana-rLOX from Anabaena sp. could effectively improve the quality of wheat flour, which suggested that the enzyme could be applied as flour improver.

Oxidative degradation of acid doped polybenzimidazole membranes and fuel cell durability in the presence of ferrous ions

Phosphoric acid doped polybenzimidazole membranes have been explored as proton exchange membranes for high temperature polymer electrolyte membrane fuel cells. Long-term durability of the membrane is of critical concern and has been evaluated by accelerated degradation tests under Fenton conditions. In this study effects of phosphoric acid and ferrous ions were investigated by measurements of the weight loss, intrinsic viscosity and size exclusion chromatography (SEC) of the polymer membranes. Ferrous ions resulted in, as expected, catalytic formation of peroxide radicals and hence the accelerated polymer degradation in terms of weight loss and molecular weight decrease. The presence of phosphoric acid as an inevitable dopant of the membranes, on the other hand, significantly impeded the membrane degradation by means of metal ion complexing, decreased pH, and acid–base interactions with the amino groups of the polymer. Fuel cell durability tests with contaminations of ferrous ions did show considerable performance degradation, however, primarily due to the catalyst deterioration rather than the membrane degradation.

Influence of chemical compositions and molecular weights of humic acids on Cr(VI) photo-reduction

Humic acids (HA) strongly affect the fate of trace metals in soils and aquatic environments. One of the remarkable properties of HA is its ability to reduce Cr(VI), an extremely toxic anion. However, it is unclear which HA components are involved in Cr(VI) reduction and possess the photo-induced properties. In this study, an ultrafiltration technique was used to fractionate HAs into four fractions of different nominal molecular weights (Mw): >100, 50–100, 10–50 and <10kDa. Each HA fraction was characterized by spectroscopic analyses followed by examining Cr(VI) removal on each fraction of HA at pH 1–5. Spectroscopic results indicated that low-Mw HA was enriched with polar and aromatic domains. These polar, including polar C in aliphatic region, and aromatic groups were the major sites for Cr(VI) reduction because they disappeared rapidly upon interaction with Cr(VI). As a result, low Mw of HA exhibited greater efficiency of Cr(VI) reduction. Light induced the rapid transfer of electrons between chromate-phenol/carboxyl ester, or the formation of peroxide radicals or H2O2 through the ready decay of peroxy radicals associated with polar substituents, explained the rapid scavenging of Cr(VI) on polar and aromatic groups of HAs under illumination.

Chemical and radiation-chemical radical reactions in lignocellulose materials

Chemical and radiation-chemical radical reactions in lignocellulose materials were explored by 3-cm and 2-mm ESR spectroscopy. Background (intrinsic) singlet signals at g=2.003 from wood pulp and lignin and those arising during reaction of lignocellulose materials with acids and chlorine were attributed to radicals with conjugated CC bonds. The 2-mm ESR signal with 3D anisotropy of g-factor from o-semiquinone radical ions formed in reaction of lignin with NaOH was recorded for the first time. The singlet signals derived from cellulose γ-irradiated at 77 K and marked out during post-thermal reactions were assigned to radicals with conjugated bonds. In wetted cellulose, a triplet signal with α β H ≅2.7 mT and imposed quadruplet structure (0.5–0.7 mT) from three γ-protons was detected at 300 K and attributed to С 4-radicals. The triplet signals derived from С 2- and С 3-radicals in pyranose cycles of cellulose exhibited higher values of α β H (3.0–3.2 mT) and lower thermal stability (up to 250 K). In radiolyzed cotton pulp, detected were ESR signals derived from formyl radicals formed upon rupture of the С 5С 6 bond in pyranose cycles. Heating up irradiated samples under О 2 was accompanied by formation of peroxide radicals. Photoinduced recombination of trapped electrons with С 1-radicals was found to proceed as a chain reaction with a kinetic length of about 25 units. Photolysis ( λ≥360 nm) of radiolyzed cellulose enhanced the disclosure of pyranose cycles and, as a result, the evolution of CO 2 by a factor of 2–2.5.

Activation of molecular oxygen in trifluoroacetic acid

The interaction of molecular oxygen with aqueous trifluoroacetic acid (TFA) led to an increase in pH. This effect was explained by a decrease in the concentration of the protonated CF3CO2H 2 + and H3O+ species after oxygen was fed in the reactor. Quantum-chemical calculations show that a radical pair can be formed in an activation-free exothermal reaction involving the radical residue of the acid, the CF3CO2H 2 + ...3O2...CF3CO 2 − peroxide radical, and the acid molecule in the CF3C 2 · ...HOO· collision complex. It was assumed that the activation of molecular oxygen in aqueous TFA solutions, providing the activity of the system in oxidations of various organic and inorganic substrates, is related to the formation of peroxide radicals in them.

Mechanical, vulcametric, and thermal properties of the different 5‐ethylidene 2‐norbornene content of ethylene‐propylene‐diene‐monomer vulcanized with different types and compositions of peroxides

AbstractEthylene‐propylene‐diene‐monomer (EPDM) rubber is an important commercial polymer. The vulcanization process significantly changes its thermal, mechanical, and vulcametric properties. This study was carried out to find optimum formulation of EPDM composite for a better application in automotive industry. Sixteen EPDM polymer samples having different 5‐ethylidene 2‐norbornene (ENB) and ethylene contents were vulcanized with different types and compositions of peroxide and coagents. The mechanical and vulcametric properties of these samples were measured and compared. The type of peroxide, coagent, and EPDM grade affected the mechanical, thermal, and vulcametric properties of the EPDM rubber to some extend. Use of aromatic peroxide and coagent increased the thermal stability slightly. Mechanical properties were changed very slightly with the change of peroxide type for the same content of peroxide and coagent. Scorch time and cure time decreased with initial increase of the peroxide content. EPDM compound vulcanized with BBPIB peroxide and TAC/S coagent has higher cure time than EPDM compound vulcanized with DMBPHa peroxide and TMPTMA coagent. Coran method was used for the modeling of experimental data. Velocity constant for the formation of peroxide radical and polymer radical were found for each case. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Relations of Oligotrophic Bacteria to Oxygen

Polluted air and the derived photochemical smog are the sources of free radicals in the atmosphere. Organic peroxides present in the smog mediate formation of peroxide radical. Oxygen species are formed by purely physical mechanisms, for instance, energy consumption converts molecular oxygen to an excited singlet state. Six active oxygen species are known: ozone, atomic oxygen, perhydroxyl, superoxide, and singlet oxygen. Singlet oxygen is the most harmful oxygen product for living cells, while hydrogen peroxide is the least harmful. Molecular oxygen is hardly toxic for prokaryotes due to an efficient protection of microbial cells by specific enzymes. This work experimentally confirms the harmlessness of molecular oxygen.

Chemiluminescence study of commercial type-B gelatines

The chemiluminescence emission of type-B commercial gelatines films was studied under different conditions. The influence of the gel strength resistance or bloom value of the gelatines on the characteristics of the emission has been investigated. Gelatine material of better quality, bloom 225, gives lower emission than the bloom 75 gelatine material under all the conditions employed in this work. The level of hydroperoxide concentration, determined in the gelatine films, correlates with the emission intensity. A mechanism of hydroperoxide and peroxide radical formation has been proposed in a similar way to that of the autooxidation reactions that take place on N-alkyl amide products. The emission is enhanced drastically in the presence of oxygen and at temperatures above the T g of the gelatine materials. This fact confirms the important role of oxygen mobility in the material. Also, at temperatures higher than T g the disproportionation reaction between peroxide radicals, responsible of the emission, is favoured.

α-Tocopherol reduces lipopolysaccharide-induced peroxide radical formation and interleukin-6 secretion in primary murine microglia and in brain

The purpose of this study was to determine if α-tocopherol—a reactive oxygen species (ROS) scavenging agent—inhibits LPS-induced oxidative stress and interleukin-6 (IL-6) production in murine microglia and brain. LPS increased intracellular peroxides and IL-6 in a dose-dependent fashion in primary microglia. The LPS-induced increase in ROS and IL-6 was reduced by pretreatment of α-tocopherol. Intraperitoneal injection (i.p.) of LPS induced lipid peroxidation and IL-6 in brain. Importantly, three daily injections (20 mg) of α-tocopherol increased brain α-tocopherol and decreased LPS-induced lipid peroxidation and IL-6 in brain. Taken together, these data indicate that α-tocopherol can mitigate inflammatory cytokine production in the brain.

Foxing – A New Approach to an Old Problem

An investigation was conducted to elucidate the nature of foxings. A connection has been found between foxing formation and paper production, duration of its exposing to light, level of its dusting and storage conditions. UV investigations revealed that foxings show heavy fluorescence at the initial stage of development; luminescence decreases as the colour intensity increases. ESR-spectroscopic technique has revealed the presence of peroxide radicals in the area of foxings. In the initial stage of formation, their amount in stains was the double of that in the surrounding areas. In some fox spots a little bit more iron and copper is found than out of them. Fe(III) exists usually as slightly soluble oxides in dust and impurities. Cellulose oxidation by air O2 is resulting in the formation of peroxide radicals that are able to reduce Fe(III) to Fe(II) in acid media. Fe2+ containing compounds are much more soluble, therefore they can diffuse from dust particles and impurities into the surrounding fibres. The oxidation process increases in the area of Fe(II) diffusion, as the ions of Fe2+ are the radical forming centers. The products of cellulose oxidation can undergo reactions of condensation with compounds that contain nitrogen, thus forming brown-coloured products.

ESR study and copolymer analysis of acrylamide‐methacrylamide solid solutions

AbstractWhen acrylamide‐methacrylamide mixed crystals are irradiated by ultraviolet (UV) rays, a copolymeric sample is obtained containing both monomeric constituents. For identification and quantitative analysis of these copolymers, a modified form of UV spectroscopy was used. The greatest advantage of UV spectroscopy for copolymer analysis lies in its rapid application. A comparison of the spectrum of the unknown compositions with spectra of known systems by using a calibration curve and the shifts in absorption maxima in different concentrations are valuable aids in establishing the composition. Electron spin resonance (ESR) provides a correlation between the obtained copolymer composition and the shape of the signal of the responsible radical. ESR spectra obtained for UV‐irradiated acrylamide‐methacrylamide mixed crystals reveal that during polymerization both radicals are present. As methacrylamide percentage increases in the mixture, the signal becomes similar to the 9‐line spectrum of pure methacrylamide. When there is 90% methacrylamide present in the original mixture, a 5‐line signal is observed, with even‐numbered peaks in the methacrylamide signal appearing now as shoulders. When the methacrylamide percentage is about 16%, a characteristic 3‐line signal of acrylamide is dominant. As the methacrylamide percentage increases in the original mixture of the copolymers, ESR signals indicate a decrease in the rate constant values for second‐order decay at 60°C. The stability of the formed radicals was studied by admitting oxygen to the copolymeric samples as well as to the homopolymeric systems. Since the peroxidic radicals are more active in the hydrogen abstraction process, they decay more rapidly than the macro radical itself by a bimolecular termination reaction. As the methacrylamide percentage increases in the copolymeric mixtures, the peroxide radical formation becomes more difficult. This indicates that polymethacrylamide brings more stability in copolymerization reactions with acrylamide. The polymerization rate of both monomers and their mixed crystals were enhanced by adding chlorine gas before irradiation. Chlorine acts as an agent for slowing down the radical decay as well as accelerating the radical initiation reactions.

Link between the structure of amorphous-crystalline polymers and the features of oxidation of polymer radicals formed by gamma irradiation

The ESR method has been used to study the oxidation of the primary radicals formed by γ-irradiation in polyvinylidene fluoride and polyethlene. It has been established that in them only some of the primary alkyl radicals may be oxidized with formation of peroxide radicals. In polyvinylidene fluoride radicals of three types are found: stable non-oxidizable fluoroalkyl, stable peroxide and unstable peroxide. It is assumed that they are localized respectively within the crystallites, on the surface and in the amorphous regions of the polymer, the concentration ratio of the stable peroxide to alkyl radicals being a measure of the specific surface of the crystallites. It is shown that this ratio for polyvinylidene fluoride is constant in time and depends on the structure of the sample changing on orientation drawing, thermal treatment and impact loading of the polymer. It has been established that high and low density polyethylene samples are characterized by different values of this ratio.