Peroxy Species Research Articles

Peroxy acids in photo-oxidized polypropylene

The presence of peracids among the peroxy species formed during the photo-oxidation of isotactic polypropylene (PP) has been proven both chemically and spectroscopically. The fast reaction of organic sulphides (dimethyl-sulphide in particular) with peracids has been employed to remove the latter selectively from the preoxidized PP. Thus treated PP exhibited spectral changes in the IR carbonyl region indicating the disappearance of peracids from the system. The ability of such PP samples to form stable 2,2,6,6-tetramethylpiperidine nitroxyls from the corresponding amine solutions is considerably lower than that of untreated polymer. The formation of nitroxyls in HALS stabilized systems is discussed in this connection. A mechanism of peracid genesis in oxidizing PP is put forward based on the assumption of methyl group attack by macroalkoxy-radicals with subsequent macro-aldehyde/peracid formation.

Probing the distribution of peroxy species derived from oxometalates by electrochemistry and spectroscopy

La voltammetrie cyclique et la spectrometrie UV-visible sont utilisees pour controler l'interaction entre le peroxyde d'hydrogene avec le tungstophosphate afin de caracteriser les differents types de composes peroxy formes

ChemInform Abstract: Epoxidations of Olefins by Peroxy Intermediate Generated in situ from CCl4 and Superoxide.

AbstractSuperoxide reacts with CCl4 in aprotic solvents [condition (A)] to yield an active peroxy species CClr‐COO", which can oxidize olefins (I), (III), (V), (VII) or (IX) to the corresponding epoxides (II) [either from (Ia) or from (Ib)], (IV), (VI), (VIII), or (X) as the main products.

ChemInform Abstract: A NEW METHOD OF MAKING TITANIA GELS AND THEIR MICROSTRUCTURE

AbstractAerohydro‐ Gele werden durch Reaktion von H2O, mit folgenden Alkoxiden erhalten: Ti(OEt)4, Ti(OPr)4, Ti(OBu)4 und [(CH3)2CHO]4Ti.

A New Method of Making Titania Gels and Their Microstructure

The reaction of H2O2 with alkoxides results in aerohydro gels of titania. These gels appear to form by a complex polymerization process involving peroxy species. The gels are porous and appear to have a fibrillar microstructure.

Excited species generation in horseradish peroxidase-mediated oxidation of glutathione

Photoemissive excited species are produced by the horseradish peroxide (HRP)-catalyzed oxidation of reduced glutathione (GSH), without exogenously added hydroperoxide under aerobic conditions. The emitted low-level chemiluminescence consisted of two phases. Ligh emission occured at wavelengths beyond 610 nm (≥90 intensity), indicative of singlet oxygen 1O 2. Deuterium oxide enhanced photoemission 4.4-fold. Ascorbate inhibited chemiluminescence completely. In the absence of GSH or when GSH was replaced by the disulfide, no red chemiluminescence was observed. The glutathionyl radical GS· is most likely to be involved in both phases of light emission. Further, the superoxide radical plays a role, as substantiated by the inhibitory effect of superoxide dismutase. Both phases of photemission were abolished by glutathione peroxidase: thus hydroperoxides are regarded as essential intermediates for the formation of excited species. Catalase abolished phase I and did not affect phase II. In contrast, glutathione S-transferase 1–2 (showing peroxidase activity towards organic hydroperoxides but not towards H 2O 2) inhibited phase II, whereas phase I was still present. Glutathione sulfonate and the disulfide GSSG were detected as oxidation products from GSH under conditions where phase II chemiluminescence was observed. HRP Compound III accumulated during the reduction. It is concluded that phase I is dependent on exogenously added or ednogenously generated H 2O 2, whereas phase II does not require H 2O 2 but an organic peroxy species. A mechanisms based on chain reactions involving oxygen addition to the thiyl radical is proposed. Sulfenyl peroxy Species are suggested as transient intemediates in reactions finally leading to the generation of excited states such as singlet molecular oxygen.

Biochemistry and Physiology of Bioluminescent Bacteria

This chapter describes the biochemistry and physiology of bioluminescent bacteria. The function of bioluminescent bacteria is to emit light in biological systems. The chapter explains the variety of habitats in which these bacteria are found, the light-emitting system may play an important role in their ecology or physiology. The luciferase in bacteria, unlike that of any other luminous group (except, perhaps, the fungi), is related to the respiratory pathway, functioning as a shunt for electrons directly to oxygen at the level of reduced flavin. This luciferase is an external flavin mono-oxygenase or mixed-function oxidase, electrons for reduction of flavin mononucleotide (FMN) are provided by the reducing power derived from the electron-transport pathway. The light-emitting reaction then proceeds via the reaction of molecular oxygen with reduced flavin to form an intermediate luciferase-flavin peroxy species, whose breakdown provides energy sufficient to leave one of the products in an electronically excited singlet state, with subsequent light emission. The bacterial (luciferase-bound) peroxide chromophore, which has been isolated and characterized, provides a model in this respect for the different bioluminescent reactions.

Interaction of cytokinins with lipid-associated oxy free radicals during senescence: a prospective mode of cytokinin action

In senescence physiology, experimental data indicate causative relationships among cytokinin, lipoxygenation, anti-oxidation, and lipid-associated free radical scavenging. During both normal and induced senescence, there is a rise in lipoxygenase (LOX) which catalyzes the oxidation of polyunsaturated fatty acids containing the cis, cis-1,4-pentadiene configuration. These include linoleic and linolenic acids, which are of common occurrence in plants and inter alia may be situated in membranal phospholipids. Lipoxygenation causes the production of free radicals such as the superoxide, fatty acid, and peroxy species. Cytokinin (CK) lowers LOX and superoxide dismutase activities significantly in senescing foliage and is mimicked by the endogenous lipid antioxidant, α-tocopherol (vitamin E), in its chlorophyll-retaining and LOX-lowering effects. Further experimentation indicated that CK interaction with free radicals may occur in two ways, (i) CK may act as a direct free radical scavenger by virtue of the fact that the hydrogens of the α-carbon atom in the amine bond can be extracted, resulting in the formation of an amide: [Formula: see text][Formula: see text] (this mechanism may also, in part, explain polyamine effects), (ii) CK may serve as an incipient preventative of free radical formation by inhibiting oxidation of plant purine compounds, which at certain stages of breakdown release superoxide and hydroxyl free radicals. This effect is probably associated with a lowering of substrate affinity for xanthine oxidase. This assumption is further borne out by similar senescence-retarding effects of selective xanthine oxidase inhibitors such as allopurinol. These observations collectively indicate that prevention of free radical formation and (or) their direct scavenging should be included in the multifactorial antisencscence mode of action of cytokinin.

Quantitative measurements of hydroperoxy and alkylperoxy radicals in gas-phase oxidation reactions from overlapping electron paramagnetic resonance spectra

Two numerical methods are presented for the analysis of overlapping electron spin resonance spectra of peroxy radicals obtained by freezing. One is devoted to the determination of a simple lineshape parameter and the other uses a data collecting and processing system and a least-squares fitting treatment. Examples are provided for quantitative measurements of peroxy species obtained during gas-phase oxidation of hydrocarbons and heterogeneous decomposition of hydrogen peroxide.

Polymer reactions, 8. Oxidative pyrolysis of poly(propylene)

AbstractPoly(propylene) has been oxidized at temperatures between 240 and 289°C. The products were GC separated and on‐line identified by an interfaced GC peak identification system. The major products are CO2, H2O, acetaldehyde, acetone, butanal, formaldehyde, methanol and other ketones and aldehydes. Most of the products can be accounted for by well‐known reactions of alkoxyl and peroxyl radicals; the major products are derived from the secondary alkoxy and peroxy species. Oxygen starvation is manifested in diffusion limited products of olefins and dienes, and the increase of CO2 and H2O formation in pure oxygen atmosphere. The first order rate constant at 240°C is 2,4·10−3 S−1 with an overall activation energy of ca. 16 kcal·mol−1 (67 kJ·mol−1). If one assumes the oxidative pyrolysis to share the same reaction pathways as autoxidation at lower temperatures, then the observed rate constants and activation energy may be calculated from kinetic parameters measured earlier for autoxidation of poly(propylene) from 71 to 140°C. Good agreement was obtained implying a similarity of oxidative degradation of the polymers spanning a large temperature range.

The ammoxidation of propylene and isobutene over a tin-vanadium-phosphorus oxide catalyst

Studies have been made of the ammoxidation of propylene and isobutene over a tin oxide-vanadia-phosphorus oxide catalyst. Values of the kinetic parameters based on initial rates are reported for the ammoxidation of the olefins to unsaturated nitriles and to other products. The results are consistent with a mechanism in which the abstraction of an allylic hydrogen from the adsorbed olefins by adsorbed peroxy species is rate determining. The reaction is suggested to occur at Sn 4+ surface sites from which electron transfer to neighboring vanadium ions is possible.

Grafting of acrylic acid onto radiation‐peroxidized polypropylene film in the presence of ferrous ion

AbstractAcrylic acid has been grafted from aqueous solution onto 70 μ isotactic polypropylene‐film previously peroxidized by irradiating in air with both 400 keV electrons and γ‐radiation from a 60Co source. Ferrous ion has been used to induce the redox decomposition of the macromolecular peroxy species at temperatures between 0 and 40°C. It has been shown that the effect of low [Fe2+] is to increase grafting rates, but that at [Fe2+] > 8 × 10−4 molal the retarding effect of the reducing ion becomes increasingly important. At constant [Fe2+] a pronounced maximum in rate is observed at around 50 wt‐% of acrylic acid; this may be related to increased swelling of the polymer matrix at this point. The initial rate of grafting increases as the square root of the preirradiation dose and, in the preirradiation dose rate range, 1.6–8.0 Mrad/sec, is independent of the dose rate. The grafting rate during the later stages of the reaction, however, increases as the preirradiation dose rate decreases. In the temperature range 0–40°C, the overall activation energy is 19 kcal/mole; from this value, the activation energy of initiation has been estimated to be around 20 kcal/mole.

ESR study of radiation damage in TPX polymer (poly‐4‐methylpentene‐1)

AbstractElectron spin resonance spectroscopy has been used to study the effects of 15 MeV electrons, x‐rays, and ultraviolet radiation on poly‐4‐methylpentene‐1 (TPX) both at 77°K and at room temperature. At least seven identifiably different paramagnetic species are observable in unstabilized oxygen‐free TPX after irradiation, and additional species exist in the stabilized grades. The species which predominates under most conditions is interpreted as being due to the loss of hydrogen from a main‐chain tertiary carbon atom; interpretations of most of the other species are also given. Oxygen is found to diffuse rapidly into the polymer and to react with the free radicals to form peroxy species. In the absence of oxygen the radiation damage is expected to lead ultimately to crosslinking or double‐bond formation, or with oxygen to degradation. The general nature of the free radicals produced by electron or x‐ray irradiation is the same, but there are significant differences for ultraviolet irradiation. The observed spectra for irradiated TPX and their interpretations are in good agreement with the spectra and later interpretations for irradiated polypropylene, but are in less satisfactory agreement with the published papers on polybutene‐1 and poly‐3‐methylbutene‐1.

The Transfer of the Oxygen Atom of Water in an Aqueous Solution of Iron and Copper Sulfates

Abstract When an oxygen-18 enriched aqueous solution of ferrous, ferric and cupric sulfates was heated between 130 and 200°C, the oxygen-18 content decreased in the order of FeII>FeIII>CuII in water; and it increased in the sulfate group and in the molecular oxygen of the gaseous phase. A transfer of oxygen from water to the sulfate group was also observed, even in a nitrogen atmosphere. The oxygen transfer was promoted in all the cases in the presence of molecular oxygen, and it increased further in the presence of benzene. Since the exchange reaction of oxygen does not occur between water and sulfate ions, the above facts may be attributed to the reactions between water and the thermal decomposition products of the sulfate group, and between water and the hydrogen peroxide produced. The peroxy species, produced by the oxidation of the decomposition products, are more reactive in such a transfer of oxygen, since the reaction is promoted in the presence of oxygen. The peroxides in the autoxidation of benzene seem also to be reactive in it.