Oxidation of ultra high molecular weight polyethylene (UHMWPE) part 2: Critical examination of the total luminescence intensity (TLI) method for determining hydroperoxides

The validity of the total luminescence intensity (TLI) method for determining the amount of hydroperoxides in a UHMWPE sample has been assessed. Measurements of hydroperoxides with FTIR before and after a TLI run showed that only about 50% of the hydroperoxides were decomposed at 150 °C. It was also found that this value was not constant with ageing time, which means that the TLI value could not be representative of the total number of hydroperoxides in a sample as a function of ageing time. Thermoluminescence was also found to complicate the measurements and could, if care was not taken, give TLI values that were much too high. In addition it was found that the TLI value is actually connected with the build-up of carbonyls rather than the build-up of hydroperoxides. This last finding is consistent with part one of this study, where it was reported that CL from oxidising UHMWPE is a type of activated CL, where carbonyls are the activating species. From all of these results it is concluded that TLI is not a suitable method for determining hydroperoxides in UHMWPE.     

Thermolysis of polyethylene hydroperoxides in the melt. Part 9: Re-examination of the experimental kinetics of hydroperoxide decomposition

The experimental kinetics of decomposition of polyethylene hydroperoxides in the melt is re-examined. It is found that the rates determined are more accurate if only the “free” hydroperoxides are taken into account instead of the total hydroperoxides that include also the “associated” hydroperoxides. Then, decomposition of polyethylene hydroperoxides in the melt can be attributed unambiguously to a first-order reaction that is valid in the whole time range of the thermolysis experiments. Nevertheless, the first-order rate constant determined this way increases with the initial hydroperoxide concentration. This constitutes a significant difference with the first-order rate constants that are valid in low molecular mass chemistry and are independent of the initial concentration of the reacting species. It has already been concluded previously that this experimental first-order rate cannot be attributed to true monomolecular hydroperoxide decomposition. Hence, another or other reactions must be envisaged for the interpretation of the specific first-order decomposition of the hydroperoxides in polyethylene melts.     

Direct evidence for base-mediated decomposition of alkyl hydroperoxides (ROOH) in the gas phase

The reaction of F(-) with CH(3)OOH has been studied in the gas phase using a tandem flowing afterglow-selected ion flow tube apparatus. The reaction is rapid (k = 1.23 x 10(-9) cm(3) s(-1), 49% efficiency), and formation of HO(-) + CH(2)O + HF is the major reaction channel observed (85%). Isotopic labeling, reactions of F(-) with larger alkyl hydroperoxides, and computational studies demonstrate that the major product ion, HO(-), is formed via a concerted elimination mechanism that appears to be general to all alkyl hydroperoxides possessing an alpha-hydrogen. This mechanism represents a base-mediated decomposition of alkyl hydroperoxides in the gas phase that may have important implications for solution and biochemical reactions. The reverse reaction, CH(3)OO(-) + HF is also efficient (k = 2.43 x 10(-9) cm(3) s(-1)). The major product ensemble HO(-) + CH(2)O + HF (81%) is identical to that of the forward reaction, and represents a novel neutral-catalyzed decomposition of the anion.     

Photogenerated hydroperoxides of EPDM rubbers and their characterization

Three different ethylene/propylene/diene (EPDM) rubbers were allowed to react with singlet oxygen. This reaction leads to the production of polymeric pendant hydroperoxides only in one case. Terpolymer ethylene/propylene/5-ethylidene-2-norbornene reacts with singlet oxygen and isolated and associated secondary hydroperoxides are formed. Anthracene was used as a sensitizer for production of singlet oxygen under 365-nm irradiation. The course of hydroperoxide formation was similar in the solid state as well as in the toluene solution. Reactivity of hydroperoxides prepared was tested in their reaction with gaseous dimethyl sulfide (DMS). Both the isolated and associated hydroperoxides react with DMS by dual fast and slow process. Fast process is more significant in the case of the isolated hydroperoxides. © 1995 John Wiley & Sons, Inc.     

Preparation of a Novel Stationary Phase for Separation of Ethylbenzene Hydroperoxides

The novelty of this work is preparation of a special stationary phase for selective separation of hydroperoxides. This column can be used widely in the polymerization industries where a variety of initiators (mainly the hydroperoxides) are used. In this work, the ionic liquid-based silica particles were prepared and used as a novel stationary phase for separation of ethylbenzene hydroperoxides. The mobile phase of methanol/acetonitrile from 90:10 to 70:30 (v v^?1) was used to separate three isomers of ethylbenzene hydroperoxide. A satisfactory linearity was obtained from 1.0 to 110.0 mg mL^?1 (RSD <4.0 %). The stationary phase performed stably and produced reproducible results, highlighting its potential as a separation material.     

New protocol for oxidation in water: micellar oxidation systems composed of novel amphiphilic hydroperoxides

A series of novel amphiphilic hydroperoxides, alpha-alkoxyalkyl hydroperoxides (alpha-AHPs) and their related hydroperoxides, were designed and prepared with the intention of developing new oxidizing agents bearing a micelle-forming character in water. After their fundamental physical and interfacial properties were elucidated, both oxidation of benzyl sulfide and epoxidation of geraniol promoted by these hydroperoxides were investigated in detail under various conditions. Effective oxidation ofbenzyl sulfide to the corresponding sulfoxide was achieved in aqueous micellar systems composed of alpha-AHPs la-d and a catalytic amount of MoO2(acac)2 at 30 degrees C. Up to 100% conversion was observed under the optimum conditions. In the case of epoxidation of geraniol in water, the corresponding 2,3-epoxide was selectively formed in good yields. Because the conversion of each substrate in the micellar systems was higher than that in nonmicellar media, the solubilization of substrates into micelles was certainly effective in promoting oxidations of insoluble substrates in aqueous media. Micellar oxidation systems composed of novel amphiphilic hydroperoxides afford a new protocol in order to derive safer conditions under which these reactions may be carried out.     

Oxidation of ultra high molecular weight polyethylene (UHMWPE) part 3: Decomposition of hydroperoxides with SO2 and its effect on the chemiluminescence signal

Samples of slightly oxidised UHMWPE were treated with SO₂ to decompose hydroperoxides prior to chemiluminescence measurements. It was found that the effect was quite substantial, but it was not just due to the elimination of hydroperoxides; a stabilising effect was also manifested. This effect increased with an increasing concentration of hydroperoxides in the samples. The stabilising effect could not be seen in fresh samples or when the hydroperoxides were decomposed by heating the sample in nitrogen. In addition, a stabilising effect was also observed for samples in which the hydroperoxides were reduced by DMS. It was concluded that the stabilisation was due to the formation of H₂SO₄ in the case of SO₂ and DMSO in the case of DMS. Both these substances can act as stabilisers against oxidative degradation of polymers and were evenly distributed in the sample films after the reaction with the hydroperoxides.     

Colorimetric determination of lipid hydroperoxides in oils and fats with microperoxidase

The use of the peroxidase-like activity of microperoxidase for the calorimetric determination of lipid hydroperoxides in oils and fats has been investigated. The principle of the determination is that 4-aminoantipyrine and N,N-diethylaniline are coupled oxidatively by the hydroperoxides through the action of microperoxidase, yielding a violet colour with maximum absorbance at 554 nm. The response of the microperoxidase system is enhanced by the presence of acetonitrile. The method has been successfully applied to the determination of methyl linoleate hydroperoxide, tert-butyl hydroperoxide and the hydroperoxides in oil and fat samples (soybean oil, linseed oil, olive oil, salad oil, butter and lard). The results agreed closely with those obtained by the iodometric method. The proposed method permitted the determination of the hydroperoxides at 0.5-0.05 mumole levels, with the same sensitivity regardless of sample type tested, with satisfactory reproducibility compared with that obtained by the conventional assay methods.     

Study on Aromatic Phosphines for Novel Fluorometry of Hydroperoxides (II) -The Determination of Lipid Hydroperoxides with Diphenyl-1-Pyrenylphosphine -

Abstract

A new fluorometric determination of hydroperoxides was proposed. Non-fluorescent diphenyl-1-pyrenyl-phosphine (DPPP) was oxidized quantitatively by hydroperoxides to a strong fluorescent DPPP oxide. A sensitive assay for lipid hydroperoxides was developed based on the reaction. The reaction of lipid hydroperoxides with DPPP was conducted in the dark in the mixture of chloroform and methanol at 60°C within 60 min. The contents of hydroperoxides showed linear relation to the fluorescence intensities in a wide concentration range. The sensitivity was 10,000 times higher than conventional iodometry. The correlation constant between peroxide values obtained by iodometry and by this method was 0.9993 (n=10). The sample size was minimized to less than 3 mg per tube.     

Photochemical and Photobiotogical Studies with Acridine and Phenanthridine Hydroperoxides in Cell-free DNA

Abstract— The acridine and phenanthridine hydroperoxides 3 and 7 were synthesized as photochemical hydroxyl radical sources for oxidative DNA damage studies. The generation of hydroxyl radicals upon UVA irradiation (Λ. = 350 nm) was verified by trapping experiments with 5,5-di-methyl-1-pyrroline N -oxide and benzene. The enzymatic assays of the damage in cell-free DNA from bacteriophage PM2 caused by the acridine and phenanthridine hydroperoxides 3 and 7 under near-UVA irradiation revealed a wide range of DNA modifications. Particularly, extensive single-strand break formation and DNA base modifications sensitive to formamidopyrimidine DNA glycosylase (Fpg protein) were observed. In the photooxida-tion of calf thymus DNA, up to 0.69±0.03% 8-oxo-7,8-dihydroguanine was formed by the hydroperoxides 3 and 7 on irradiation, whose yield was reduced up to 40% in the presence of the hydroxyl radical scavengers mannitol and fert-butanol. The acridine and phenanthridine hydroperoxides 3 and 7 also induce DNA damage through the type I photooxidation process, for which photoinduced electron transfer from 2'-deoxyguanosine to the singlet states of 3 and 7 was estimated by the Rehm-Weller equation to possess a negative Gibb's free energy of cα -5 kcal/ mol. Control experiments with the sensitizers acridine 1 and the acridine alcohol 4 in calf thymus and PM2 DNA confirmed the photosensitizing propensity of the UVA-ab-sorbing chromophores. The present study emphasizes that for the development of selective and efficient photochemical hydroxyl radical sources, chromophores with low photosensitizing ability must be chosen to avoid type I and type II photooxidation processes.     

Synthesis of allylic hydroperoxides and EPR spin-trapping studies on the formation of radicals in iron systems as potential initiators of the sensitizing pathway

Many terpenes used as fragrance compounds autoxidize when exposed to air, forming allylic hydroperoxides that have the potential to be skin contact allergens. To trigger the immunotoxicity process that characterizes contact allergy, these hydroperoxides are supposed to bind covalently to proteins in the skin via radical pathways. We investigated the formation of reactive radical intermediates from 7-hydroperoxy-3,7-dimethylocta-1,5-dien-3-ol and 2-hydroperoxylimonene, responsible for the sensitizing potential acquired by autoxidized linalool and limonene. Both compounds were synthesized through new short and reproducible synthetic pathways. The hydroperoxide decomposition catalyzed by Fe(II)/Fe(III) redox systems, playing a key role in degradating peroxides in vivo, was examined by spin-trapping-EPR spectroscopy. Alkoxyl and carbon-centered free radicals derived from the hydroperoxides were successfully trapped by the spin-trap 5,5-dimethyl-1-pyrroline N-oxide, whereas peroxyl radicals were characterized by spin-trapping studies with 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide. Using liquid chromatography combined with mass spectrometry, we demonstrated the formation of adducts, via radical mechanisms induced by Fe(II)/Fe(III), between the hydroperoxides and N-acetylhistidine methyl ester, a model amino acid that is prone to radical reactions. Free radicals derived from these hydroperoxides can thus induce amino acid chemical modifications via radical mechanisms. The study of these mechanisms will help to understand the sensitizing potential of hydroperoxides.     

Use of 9,10-diphenylanthracene as a contrast agent in chemiluminescence imaging: The observation of spreading of oxidative degradation in thin polypropylene films

Thin films of polypropylene were doped with a chemiluminescence (CL) activator, 9,10-diphenylanthracene (DPA), and were thermally oxidised in a CL imaging apparatus to determine whether heterogeneous oxidation processes such as spreading of oxidation could be observed. The presence of DPA resulted in significantly more intense CL images compared with undoped polymer, due to the efficient chemically induced electron exchange luminescence reaction between DPA and hydroperoxides. Hence, the CL images from DPA-doped PP were used to locate the position of hydroperoxides in the oxidising polymer. For thermal oxidation at 150 and 140 °C hydroperoxides were observed to form in localised regions of the films, whilst other areas remained hydroperoxide free. As the oxidation time increased the concentration of hydroperoxides in these areas increased and they were observed to spread to the remainder of the polymer. Time-resolved line maps from the images indicated that zones with high concentration of hydroperoxides travel through the polymer during oxidation. Integrals of CL images from the thermal oxidation of DPA-doped polymers indicated that a significant degree of oxidation had occurred by the end of the “induction period” for a conventional CL-intensity oxidation-time profile. This is a likely reason why spreading of oxidation has not previously been observed for undoped PP films.     

Simultaneous Determination of Hydrogen Peroxide and Organic Hydroperoxides in Water

The kinetics of the reactions of H 2 O 2 and of methyl, ethyl, tert -butyl, and cumene hydroperoxides with I m were investigated in the presence and absence of molybdate as catalyst. These results were utilized to develop an analytical method for the simultaneous determination of H 2 O 2 and organic hydroperoxides in aqueous solutions. The total amount of H 2 O 2 and organic hydroperoxides can be determined by the spectrophotometric measurement of $ {\rm I}_3^ - $ formed quantitatively during 30 min of heating at 60°C. Catalase selectively decomposes H 2 O 2 in solutions containing organic hydroperoxides. The total amount of the latter can therefore be determined iodometrically after H 2 O 2 decomposition. In the oxidation of leuco crystal violet to crystal violet by H 2 O 2 and organic hydroperoxides, horseradish peroxidase exerts similar activities in the reactions involving methyl and ethyl hydroperoxides and H 2 O 2 , but its activity is much lower with tert -butyl and cumene hydroperoxide. It was observed that acetate buffer is unsuitable for pH adjustment in this type of hydroperoxide determination in consequence of the slow oxidation of the dye in the blank solution.     

Cholesterol Hydroperoxides as Substrates for Cholesterol‐Metabolizing Cytochrome P450 Enzymes and Alternative Sources of 25‐Hydroxycholesterol and other Oxysterols

The interaction of the primary autoxidation products of cholesterol, namely 25‐ and 20ξ‐hydroperoxides, with the four principal cholesterol‐metabolizing cytochrome P450 enzymes is reported. Addition of cholesterol 25‐hydroperoxide to the enzymes CYP27A1 and CYP11A1 induced well‐defined spectral changes while generating 25‐hydroxycholesterol as the major product. The 20ξ‐hydroperoxides induced spectral shifts in CYP27A1 and CYP11A1 but glycol metabolites were detected only with CYP11A1. CYP7A1 and CYP46A1 failed to give metabolites with any of the hydroperoxides. A P450 hydroperoxide‐shunt reaction is proposed, where the hydroperoxides serve as both donor for reduced oxygen and substrate. CYP27A1 was shown to mediate the reduction of cholesterol 25‐hydroperoxide to 25‐hydroxycholesterol, a role of potential significance for cholesterol‐rich tissues with high oxidative stress. CYP27A1 may participate in the removal of harmful autoxidation products in these tissues, while providing a complementary source of 25‐hydroxycholesterol, a modulator of immune cell function and mediator of viral cell entry.     

Swallow-tailed perylene derivative: a new tool for fluorescent imaging of lipid hydroperoxides

A swallow-tailed perylene derivative including a triphenylphosphine moiety was synthesized and applied to the detection and the live-cell imaging of lipid hydroperoxides. The novel probe, named Spy-LHP, reacted rapidly and quantitatively with lipid hydroperoxides to form the corresponding oxide, Spy-LHPOx, which emits extremely strong fluorescence (Phi approximately 1) in the visible range (lambda(em) = 535 nm, 574 nm). Spy-LHP was highly selective for lipid hydroperoxides, and the addition of other reactive oxygen species (ROS) including hydrogen peroxides, hydroxyl radical, superoxide anion, nitric oxide, peroxynitrite, and alkylperoxyl radical, caused no significant increase in the fluorescence intensity. The probe exhibited good localization to cellular membranes and was successfully applied to the confocal laser scanning microscopy (CLSM) imaging of lipid hydroperoxides in live J774A.1 cells, in which lipid peroxidation was proceeded by the stimulation of 2,2-azobis(2-amidinopropane)dihydrochloride (AAPH). These findings establish Spy-LHP as a promising new tool for investigating the physiology of lipid hydroperoxides.     

A sensitive method for determination of allergenic fragrance terpene hydroperoxides using liquid chromatography coupled with tandem mass spectrometry

Different compositions of monoterpenes are utilized for their pleasant scent in cosmetics and perfumes. However, the most commonly used fragrance terpenes easily oxidize upon contact with air, forming strongly skin‐sensitizing hydroperoxides. Due to their thermolability and low UV absorbance, detection methods for hydroperoxides are scarce. For the first time, a simple and sensitive method using LC/ESI‐MS/MS was developed to quantitatively determine hydroperoxides from the common fragrance compounds linalool, linalyl acetate, and limonene. The method was applied to autoxidized petitgrain oil and sweet orange oil. A separation was accomplished using a C₃ column. The method LOD for the investigated hydroperoxides in the essential oils was below 0.3 μg/mL, corresponding to 0.3 ppm. For prevention purposes and according to EU regulations, concentrations in cosmetics exceeding 100 ppm in “rinse‐off” and 10 ppm in “stay‐on” products of linalool and limonene must be labeled. However, the products may still contain allergens, such as hydroperoxides, formed by oxidative degradation of their parent terpenes. The sensitivity and selectivity of the presented LC/MS/MS method enables detection of hydroperoxides from the fragrance terpenes linalool, linalyl acetate, and limonene. However, for routine measurements, the method requires further validation.     

聚乙烯醇-亚铁氰化钾修饰电极测定油/水型乳液中氢过氧化物含量

建立了聚乙烯醇(PVA)-亚铁氰化钾修饰电极方波伏安法测定油/水(O/W)型乳液中氢过氧化物含量的方法。对电极修饰条件和氢过氧化物测量的主要参数进行了研究。结果表明,当亚铁氰化钾浓度为0.08 mol/L,分别修饰1μL亚铁氰化钾和1μL0.2%PVA时,修饰电极的电流响应值最强。在优化实验条件下,亚铁氰化钾氧化峰电流的降低值与氢过氧化物浓度在1.48×10-6～1.34×10-4mol/L范围内呈良好的线性关系,R2=0.9981,检出限为1.7×10-7mol/L。所建立的方法稳定性好,精密度高,能灵敏、准确地测量O/W型乳液中氢过氧化物含量。     

REACTIVITY OF PHOTOCHEMICALLY-GENERATED LIPID HYDROPEROXIDES IN CELL MEMBRANES WITH GLUTATHIONE PEROXIDASE

The ability of glutathione peroxidase (Gpx) to catalyze the reductive inactivation of photochemically-generated lipid hydroperoxides (LOOHs) was investigated, using hematoporphyrin derivative (HPD) as a photosensitizing agent and erythrocyte ghosts as membrane targets. Glutathione peroxidase was reactive toward photoperoxidized membranes only after their exposure to phospholipase A2 (PLA2). Iodometrically-determined LOOH values were typically 30-40% greater than values measured by enzymatic assay using Gpx and glutathione reductase. A consistent result was obtained when photooxidized membranes were treated with PLA2 and GSH/Gpx followed by iodometric assay, viz. persistence of approximately 40% of the starting LOOH. Whereas photooxidized egg phosphatidylcholine liposomes underwent total LOOH loss when incubated with PLA2 and GSH/Gpx, no net loss was observed with photooxidized cholesterol/dimyristoyl-phosphatidylcholine liposomes. The results suggest that cholesterol hydroperoxides in ghost membranes account for the Gpx-resistant fraction of LOOHs.     

Kinetics and thermodynamics of the exchange reactions of peroxy radicals with hydroperoxides

The enthalpies and equilibrium constants of the exchange reactions of peroxy radicals with hydroperoxides of various structures are calculated. The experimental data on the reactions of hydrogen atom abstraction by the peroxy radicals from the hydroperoxides are analyzed, and the kinetic parameters characterizing these reactions are calculated using the intersecting parabolas method. The activation energies and rate constants for nine reactions of H atom abstraction by a peroxy radical from the OOH group of a peroxide are calculated using the above parameters. The geometric parameters of the transition states for the reactions are calculated. The low triplet repulsion plays an important role in the fast occurrence of the reactions. The polar interaction in the transition state is manifested in the reactions of the peroxy radicals with hydroperoxides containing a polar group.     

α-Substituted diisopropylbenzene hydroperoxides for low-temperature SBR polymerization

Four pure hydroperoxides were evaluated as initiators for the polymerization of styrene–butadiene rubber (SBR) at 5°C. These materials were the meta and para isomers of mono- and dihydroperoxy-diisopropylbenzene. Results showed that the monohydroperoxides produced somewhat faster reactions than a control hydroperoxide, p-menthane hydroperoxide. Response to mercaptan level adjustments was good, providing polymer with a Mooney viscosity in the 50 to 60 range. The reaction rate with the dihydroperoxides was slower, but again provided polymer with a satisfactory viscosity. Basic physical property measurements on polymers prepared with the pure hydroperoxides or control hydroperoxides showed only minor differences. It is anticipated that these differences can be eliminated by small adjustments in the compound recipe.