High Oxidizability Research Articles

Synthesis of nanostructured yttrium with the use of cluster beams and investigation of the optical and electrical properties of yttrium hydride species

The preparation of new types of nanosystems based on metallic yttrium nanoparticles, which are difficult to produce by traditional methods due to the high melting temperature and the extremely high oxi� dizability of this metal, has been investigated. The materials are prepared on an original highvacuum setup intended for the formation of metal nanoparticle beams by laser ablation. Yttrium nanoparticles are synthe� sized, and their chemical reactions with hydrogen are studied at room temperature. It is found that the reac� tion at low hydrogen pressures (~10 -3 Pa) leads to the formation of YH2 dihydride particles with metal prop� erties. An increase in the hydrogen pressure to ~100 Pa results in the transformation of metallike YH 2 nano� particles into dielectric YH 3- x (x < 1) nanoparticles. It is revealed that the last reaction corresponding to the metal-dielectric phase transition is reversible with respect to the pressure of the hydrogen atmosphere.

Kinetics and mechanism of the oxidation of the products of decene-1 oligomerization

The kinetic characteristics of the autooxidation and initiated oxidation of decene oligomers PAO-2, PAO-4, PAO-6, and PAO-10+ at 120°C were studied. The mechanism of the oxidation of PAO-2 fraction is examined in detail using a mathematical model. The key reactions in the mechanism of PAO-2 oxidation at 120, 130, and 140°C are identified and the kinetic parameters determined. It is shown that the high oxidizability of an oligomer is determined not only by the presence of double bonds and hydroperoxides in samples, but also by high rates of chain initiation and decomposition of hydroperoxides with formation of free radicals. A comparative study of the mechanism of oxidation of a PAO-2 sample prepared using an alternative technology was carried out. It is shown that both the qualitative and quantitative parameters of the oxidation stability of the produced oligomer depend on the production technology. With the aim of enhancing oxidation stability of the initial nonhydrogenated products of oligomerization, the process of oxidation of PAO-2 sample was studied in the presence of antioxidants based on sterically hindered phenols and aromatic amines. It is demonstrated that such inhibitors can be used for anti-oxidation protection of the primary oligomerization products during their storage.

CO oxidation on stepped Rh[ n(1 1 1) × (1 1 1)] single crystal electrodes: a chronoamperometric study

The CO electro-oxidation reaction has been studied on Rh[ n(1 1 1) × (1 1 1)]-type electrodes in 0.5 M H 2SO 4 using chronoamperometry. The transients recorded on Rh(1 1 1), Rh(5 5 4), Rh(5 5 3) and Rh(3 3 1) are characterized by a current plateau, visible directly after charging of the double layer, followed by a main oxidation feature, which consists of two peaks, a pre-peak and a main peak. The current density in the plateau region is nearly constant over time and, thus, is of (quasi) zeroth order in CO coverage. A plot of log( j plateau) vs. E final gives a linear relationship with a slope of ca. 45 mV dec −1, suggesting a second electron transfer as the rate determining step. Analogously to platinum, the current density plateau was ascribed to a Langmuir–Hinshelwood type reaction between CO ads and OH ads with no effective freeing of sites for OH adsorption due to relaxation of the CO adlayer. The presence of two peaks, rather than one, in the main oxidation feature can be explained by assuming a low surface mobility of CO and high oxidizability of rhodium surfaces. Indeed, dual step chronoamperometry shows that the mobility of CO on rhodium surfaces in aqueous media is very low. Since rhodium surfaces are known to oxidize readily, the pre-peak and main peak can be ascribed to CO reacting with OH, which adsorbs fast at the steps and more slowly at terrace sites. Since the geometry of the steps is nearly the same on each surface, the pre-peak appears structure insensitive, while the main peak shifts considerably with the step density. Introducing randomly distributed crystalline defects by cycling the electrodes repeatedly up to the surface oxidation region prior to each potential step experiment, results in a negative shift of the main peak, while the position of the pre-peak remains fixed. From the data presented, we conclude that the reaction nucleates at the steps and grows in the direction of the terraces.

Ex vivo low-density lipoprotein oxidizability and in vivo lipid peroxidation in patients on CAPD

Chronic renal failure is associated with accelerated atherosclerosis and a high incidence of cardiovascular disease. Oxidative modification of low-density lipoprotein (LDL) is considered a key event in atherogenesis. We studied the ex vivo oxidizability of LDL exposed to Cu2+ ions (lag time, rate of propagation, maximum conjugated diene formation) and its relationship with LDL density, fatty acids, and antioxidants, along with plasma malondialdehyde (MDA) and autoantibodies against Cu2+-, MDA-, and hypochlorous acid-modified LDL and plasma antioxidants in 17 continuous ambulatory peritoneal dialysis (CAPD) patients and 21 healthy control subjects. LDL alpha- and gamma-tocopherol and total polyunsaturated fatty acid (PUFA) concentrations were significantly higher in the CAPD patients. LDL density was shifted to small, dense LDL. LDL oxidizability was comparable to that of healthy subjects. Lag time correlated positively with LDL alpha-tocopherol and inversely with both total PUFA concentrations and density; the rate of oxidation and LDL density correlated positively with total PUFA and total fatty acid concentrations, respectively. Ratios of autoantibody titers against oxidized to native LDL did not differ between the two groups. While plasma alpha- and gamma-tocopherol concentrations and tocopherol to cholesterol ratios were significantly higher, vitamin C concentrations were very low in the CAPD patients. MDA concentrations were 1.7 times higher than in healthy subjects. (1) Ex vivo LDL oxidizability is normal in CAPD patients as a result of efficient protection by LDL-associated lipophilic antioxidants, although the LDL composition is altered toward high oxidizability; and (2) the plasma antioxidant screen is insufficient due to impaired vitamin C status.

Effects of Ozone on Resin Acids in Thermomechanical Pulp and Paper Mill Circulation Waters

The present study investigated ozonation as means to remove resin acids from pulp and paper mill circulation waters. Ozone selectively oxidizes resin acids in debarking, thermomechanical pulping (TMP), and newsprint machine (PM) circulation waters. The relative ozone dose of 0.2 mgO3/initial mgCOD eliminated over 90% of total resin acid concentration in all tested waters, despite the initial resin acid or organic matter concentration. With that ozone dose, the removal of organic material (measured as COD) was only about 30%. Because of the different COD concentrations of tested waters, the absolute amount of ozone needed for over 90% resin acid reduction was 2000 mg/1 for debarking water, 600 mg/1 for TMP water, and 300 mg/1 for PM water, when initial COD concentrations were 10,000, 3000, and 1500 mg/1, respectively. In theory, abietane type resin acids should be more susceptible to ozone attack than pimarane type resin acids, because of their conjugated double bond structure. In the experiments, a high oxidizability of pimarane type resin acids, as compared to abietane type resin acids, was found.

Photo-oxidation of aromatic polymers

The photodegradation of aromatic polymers involves several distinctive reactions including both direct photolytic pathways and photo-oxidative processes. To account for such a complexity, the photoreactivity of four aromatic polymers is detailed. The mechanisms of photochemical evolution were probed using various techniques such as FTIR and UV spectroscopies, chemical derivatization reactions, physical treatments of irradiated films and mass spectrometric analysis of the low molecular weight fragments. A dual photochemistry, largely dependent upon the spectral distribution of the excitation light source, is well evidenced with bisphenol-A polycarbonate (PC). Excitation of PC at short wavelengths involves two consecutive photo-Fries rearrangements of the aromatic carbonate units; on irradiation at long wavelengths, photoproducts are shown to result from the photo-induced oxidation on the side chain and from the phenyl rings oxidation. The photo-oxidation of poly(butylene terephthalate) (PBT) largely involves pure photolytic pathways; on the opposite, the dominant photo-oxidative pathway of phenoxy resins (PR) is attributed to the high oxidizability of methylene groups in α-position to the oxygen atom of the ether groups. It is shown at last that the photo-oxidation of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) largely involves the oxidation of phenyl rings.

Photo-oxidation of aromatic polymers

The photodegradation of aromatic polymers involves several distinctive reactions including both direct photolytic pathways and photo-oxidative processes. To account for such a complexity, the photoreactivity of four aromatic polymers is detailed. The mechanisms of photochemical evolution were probed using various techniques such as FTIR and UV spectroscopies, chemical derivatization reactions, physical treatments of irradiated films and mass spectrometric analysis of the low molecular weight fragments. A dual photochemistry, largely dependent upon the spectral distribution of the excitation light source, is well evidenced with bisphenol-A polycarbonate (PC). Excitation of PC at short wavelengths involves two consecutive photo-Fries rearrangements of the aromatic carbonate units; on irradiation at long wavelengths, photoproducts are shown to result from the photo-induced oxidation on the side chain and from the phenyl rings oxidation. The photo-oxidation of poly(butylene terephthalate) (PBT) largely involves pure photolytic pathways; on the opposite, the dominant photo-oxidative pathway of phenoxy resins (PR) is attributed to the high oxidizability of methylene groups in α-position to the oxygen atom of the ether groups. It is shown at last that the photo-oxidation of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) largely involves the oxidation of phenyl rings.

Study by Fourier Transform Infrared Spectroscopy of the Electroadsorption of CO on the Ferrous Metals. 1. Iron

The electroadsorption and electrooxidation of CO on Fe have been studied at the following pH values: 14, 9.2, 6.9, and 3. In spite of the high oxidizability of Fe, a cathodic cleaning sufficed to produce an unoxidized surface on which CO could chemisorb. Over the whole pH range 3−14 chemisorbed CO was detected on the electrode surface as evidenced by an IR band at 1916−1993 cm-1, which was assigned to linear (on-top) CO. Its intensity was about 0.2%, from which a surface coverage of 5−10% was estimated. This low CO coverage inhibited both hydrogen evolution and the electrooxidation of Fe itself, which was interpreted by assuming that the cathodic cleaning reduced the native Fe oxides only over a small fraction of the surface and that CO chemisorption, H2 evolution, and start of Fe electrooxidation take place only on this small fraction of the surface.

Oxidizability and subsequent cytotoxicity of chylomicrons to monocytic U937 and endothelial cells are dependent on dietary fatty acid composition

Oxidized chylomicrons may be a metabolic factor involved in the injury of the arterial wall and may constitute a potential link between postprandial lipemia and atherogenesis. It was of interest to study the influence of dietary fatty acid composition on the oxidizability and subsequent cytotoxicity of chylomicrons on cultured cells. Human chylomicrons were obtained from healthy volunteers 3 h after ingestion of a triglyceride-rich meal containing mainly either polyunsaturated fatty acids (soya oil) or monounsaturated fatty acids (olive oil) or saturated fatty acids (partly hydrogenated palm oil). Polyunsatured fatty acid (PUFA)-rich chylomicrons exhibited a high oxidizability, whereas chylomicrons enriched with monounsaturated or saturated fatty acids were relatively resistant to oxidation. The cytotoxicity of various types of chylomicrons submitted to oxidation has been tested comparatively on cultured human monocytic U937 cells and endothelial cells. Chylomicrons enriched with saturated and monounsaturated fatty acids were not or only slightly cytototoxic to cultured cells, whereas PUFA-rich chylomicrons (highly susceptible to oxidation) were highly cytotoxic. The influence of cholesterol on the oxidizability and subsequent cytotoxicity of PUFA-rich chylomicrons has been investigated by using comparatively a soya diet supplemented or not with cholesterol. PUFA-rich cholesterol-rich chylomicrons were slightly more oxidizable and more cytotoxic than PUFA-rich (cholesterol-poor) chylomicrons, thus suggesting that the cytotoxicity of PUFA-rich chylomicrons may be due to oxidation derivatives of PUFA (for the major part) and to oxysterols (for a minor part). Furthermore, the cytotoxic effects of oxidized PUFA-rich chylomicrons and of mildly oxidized LDL were in similar range (even higher for PUFA-rich chylomicrons when expressed per lipoprotein particle), thus suggesting that oxidized PUFA-rich chylomicrons may play a nonnegligible role in cytotoxic events occurring during atherogenesis. In conclusion, our study demonstrates, for the first time to our knowledge, that 1: (nonlipolyzed) chylomicrons can be cytotoxic to cultured cells; 2 the cytotoxicity of (nonlipolyzed) chylomicrons is relative to their oxidation state; 3 the oxidizability (and subsequent cytotoxicity) of chylomicrons is dependent on their PUFA content (depending itself on dietary fatty acid composition).

Animal and Plant Fats Selectively Modulate Oxidizability of Rabbit LDL and LDL-Mediated Disruption of Endothelial Barrier function1

Enrichment of lipoproteins with fatty acids derived from animal and/or plant fats may modify the oxidizability of lipoproteins and their effects on endothelial barrier function. To test this hypothesis, rabbits were fed for 30 days diets containing 2 g corn oil/100 g diet (low fat diet) or low fat supplemented with 16 g/100 g diet of corn oil, corn oil with added cholesterol, milk fat, chicken fat, beef tallow or lard. Compared with those fed the low fat, serum and LDL cholesterol concentrations were significantly lower in rabbits fed corn oil and greater in animals fed corn oil with added cholesterol or chicken fat. In contrast to the cholesterol data, lipid hydroperoxide levels were highest in oxidized LDL derived from rabbits fed corn oil or lard. LDL vitamin E levels were highest in rabbits fed corn oil with added cholesterol. The significant elevations in linoleic acid [18:2(n-6)] in serum and LDL may partially explain the high oxidizability of LDL in rabbits fed corn oil. LDL isolated from animals fed corn oil, lard or milk fat had significantly greater albumin transfer across cultured endothelial monolayers compared with those of the low fat diet group. Their oxidative modification further contributed to endothelial barrier dysfunction. Dietary cholesterol supplementation to the corn oil diet decreased the oxidizability of LDL and partially protected the oxidized LDL-mediated endothelial cell dysfunction as compared with the corn oil diet group. These data suggest that beef tallow and chicken fat are the least atherogenic fats if oxidative modification of LDL is a critical issue in atherosclerosis.

Carbonization of candidate high‐temperature matrix materials for carbon/carbon composites

AbstractCarbon precursors used for preparing carbon/carbon composite (CCC) matrix binders undergo component elimination and carbonization during heating, which affects the ultimate carbon product. We analyzed the structural and compositional changes of two polymeric precursors N,N′‐(1,3‐phenylenedimethylidene)bis(3‐ethynylaniline) and 4,4′‐bis(3,4‐dicyanophenoxy)biphenyl during high‐temperature annealing under inert atmosphere. The samples were analyzed using x‐ray diffraction, x‐ray photoelectron spectroscopy and microRaman scattering. The precursor molecules cross‐link during curing and annealing, to form glassy carbons. The carbon structure after the annealing was reflected by the high oxidizability of the carbon in air. Deconvolution of the C 1s and O 1s XPS spectra showed that the surface oxygen was present primarily as hydroxyl and carbonyl groups, and that the amounts of surface oxygen correlated with the extent of graphitization. Addition of iron in the form of ferrocene in the precursor accelerated graphitization at all temperatures. The results are compared to those for other polymer precursors and graphite.

The doping of conjugated bond organic polymers by xenon difluoride oxidants

We have created a new universal method of chemical doping of Π-conjugated polymers, using polyacetylen (PA) and poly-p-phenelene (PPPh), by oxidential system XeF 2-acid (HA) using the mole equation 1:2 in inert solvent [1]. The scheme of the process is shown below: P+1/2 n XeF 2+I/n HA → P n+(A −) n+1/2 n Xe+1/n HF P -elemental main - chain link - CH(PA) or (PPPh); n -degree of doping; A -anion: BF 4 − ; SbF 6 − ; OSO 2F − ; OSO 2CH 3 −; OSO 2CF 3 −; OCOCF 3 −. The analyses of the products were carried out with the help of IR spectroscopy and thermography. The polymers doped by BF 4 −; AsF 6 −; SbF 6 −; OSO 2F −are stable under room temperature in non-aqueous conditions. The methods based on the XeF 2 ability to generate cation-radicals during the oxidation of organic compounds. XeF 2 high oxidizability in the super-acid environment allows to obtain polymers with extremly high degree of doping. In whole, this method allows to carry out controlled chemical doping of the polymers by large quantity of the anions and may be proposed as convenient method of obtaining the electroconductive polymers.

The Bessis reticular cell, the hemoglobin ‘switch’ and the role of fetal hemoglobin: A hypothesis

With the help of diverse factors, definitive erythropoiesis is induced by the junction of a pluripotential stem-cell with a specialized macrophage. In the normal adult marrow the latter becomes the reticular cell forming the core of an ‘erythroblastic island’. It stays in close contact with all the erythroid cells descending from the stem-cell until their full maturation. While this contact lasts, only alpha and beta (delta) globin chains are produced. The production of gamma chains is inhibited. Stress forces the reticular cell to let the erythroid cells go. The stronger the stress, the earlier the separation. When free from the reticular cell, the erythroid cells stop producing beta chains and switch to form gamma ones. Increase in the volume of blood circulation is a potent stress. Since it is relatively enormous in the embryo and the fetus, most hemoglobin produced at these periods will be fetal. The important quality of fetal hemoglobin is its high oxidizability. It permits the senescent fetal red cell to be hemolysed intravascularly before any membrane alterations appear. The heme is dealt with by the placenta. Since no erythrophagocytosis has occurred, no bilirubin is formed. This process prevents bilirubin, which is toxic to the fetal liver, to reach it.

Cyclopentadienylation of allyl-chlorine enriched PVC and degradation thereof

Pendant cyclopentadienyl groups (Cp) have been introduced by treatment with Me2CpAl into poly(vinyl chlorides) the allyl chlorine contents of which was augmented by mild chemical dehydrochlorination [PVC(A)]. Heating the cyclopentadienylated products [PVC(A)-Cp] led to gels, most likely by Diels-Alder addition, because the networks could be broken by strong dieno-philes, e.g., maleic anhydride. The thermal stability of PVC(A)'s was improved upon Me2CpAl treatment due to the substitution of thermally unstable allylic chlorines by Cp groups. The thermooxidative stability of PVC(A)-Cp was reduced relative to that of PVC(A) on account of the high oxidizability of Cp groups in the resin.