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1.
Mäkinen EM  Hopia AI 《Lipids》2000,35(11):1215-1223
In order to study antioxidant action on lipid hydroperoxide decomposition, the effects of α-tocopherol (TOH) and ascorbyl palmitate on the decomposition rate and reaction sequences of 9- and 13-cis,trans methyl linoleate hydroperoxide (cis,trans ML-OOH) decomposition in hexadecane were studied at 40°C. Decomposition of cis,trans ML-OOH as well as the formation and isomeric configuration of methyl linoleate hydroxy and ketodiene compounds were followed by high-performance liquid chromatographic analysis. TOH effectively inhibited the decomposition of ML-OOH. The decomposition rate was two times slower at 0.2 mM and more than 10 times slower at 2 and 20 mM of TOH. Ascorbyl palmitale (0.2, 2, and 20 mM) slightly accelerated the decomposition of ML-OOH. Both compounds had an effect on the reaction sequences of ML-OOH decomposition. At high levels TOH inhibited the isomerization of cis,trans ML-OOH to trans,trans ML-OOH through peroxyl radicals and increased the formation of hydroxy compounds. Further, the majority of the hydroxy and ketodiene compounds formed had a cis,trans configuration, indicating that cis,trans ML-OOH decomposed through alkoxyl radicals without isomerization. These results suggest that when inhibiting the decomposition of hydroperoxides, TOH can act as a hydrogen atom donor to both peroxyl and alkoxyl radicals. In the presence of ascorbyl palmitate, cis,trans ML-OOH decomposed rapidly but without isomerization. In contrast to TOH, the majority of hydroxy compounds were cis,trans, but the ketodiene compounds were trans,trans isomers. This indicates that ascorbyl palmitate reduced cis,trans ML-OOH to the corresponding hydroxy compounds. However, the simultaneous formation of trans,trans ketodiene compounds suggests that ML-OOH decomposition, similar to the control sample, also occurred in these samples. Thus, under these experimental conditions, the reduction of ML-OOH to more stable hydroxy compounds did not occur to an extent significant enough to inhibit the radical chain reactions of ML-OOH decomposition.  相似文献   

2.
The antioxidant effects of α-and γ-tocopherols (at 0, 10, 100, 500, and 1000 ppm) were evaluated in a model system based on the autoxidation of methyl linoleate in bulk for 4 d at 40°C. Samples were collected every 24 h and analyzed for the 9 cis,trans, 9 trans,trans, 13 cis,trans, and 13 trans,trans isomers of hydroperoxide, hydroxy, and ketodiene oxidation products by high-performance liquid chromatography. Results showed that both α- and γ-tocopherols are effective hydrogen donors as evidenced by their abilities to inhibit the formation of hydroperoxides, hydroxy compounds, and ketodienes and the cis,trans to trans,trans isomerization of hydroperoxides. Compared with γ-tocopherol, α-tocopherol was a more efficient antioxidant at very low concentrations (10 ppm) but a less efficient antioxidant at the high concentrations (100–1000 ppm). This paradoxical behavior is explained on the basis of differences in ease of hydrogen donation between the two tocopherol homologs. Although α-tocopherol shows some loss of efficiency with increasing concentration, it is not a prooxidant when compared to the control void of antioxidants.  相似文献   

3.
The results of extensive molecular dynamics simulations and theoretical considerations of the adsorption of methane–methyl mercaptan mixtures in slit-shaped carbon nanopores are presented. We observe significant mobility of both methane and mercaptan molecules within the pore volume, between pores, and between adsorbed and gas phases for a wide range of temperatures and pressures. Although mercaptans adsorb preferentially relative to methane, the process remains reversible, provided non-oxidizing conditions are maintained. A mercaptan/methane ratio of the order of 200 ppm in the adsorbed phase is sufficient for the gas phase to have a mercaptan concentration above the human threshold for detection. The reversibility of the adsorption process and low concentration of mercaptans makes it unlikely that these would be harmful for adsorbed natural gas storage systems.  相似文献   

4.
The initial steps in the autoxidation of CLA methyl ester are poorly understood. The aim of this study was to determine the stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of a good hydrogen atom donor. For this purpose, 9-cis, 11-trans CLA methyl ester was autoxidized in the presence of α-tocopherol under atmospheric oxygen at 40°C in the dark. The CLA methyl ester hydroperoxides were isolated, reduced to the corresponding hydroxy derivatives, and separated by HPLC. The stereochemistry of seven hydroxy-CLA methyl esters was investigated. The position of the hydroxy group was determined by GC-MS. The geometry as well as the position of the double bonds in the alkyl chain was determined by NMR. In addition, the 13C NMR spectra of six hydroxy-CLA methyl esters were assigned using COSY, gradient heteronuclear multiple bond correlation, gradient heteronuclear single quantum correlation, and total correlation spectroscopy experiments. The autoxidation of 9-cis, 11-trans CLA methyl ester in the presence of a good hydrogen atom donor is stereoselective in favor of one geometric isomer, namely the 13-(R,S)-hydroperoxy-9-cis, 11-trans-octadecadienoic acid methyl ester. Three types of conjugated diene hydroperoxides are formed as primary hydroperoxides: trans,trans hydroperoxides (12-OOH-8t,10t and 9-OOH-10t,12t), a cis,trans hydroperoxide with the trans double bond adjacent to the hydroperoxide-bearing carbon atom (13-OOH-9c,11t), and a new type of cis,trans lipid hydroperoxide with the cis double bond adjacent to the hydroperoxide-bearing carbon atom (8-OOH-9c,11t). In addition, three nonkinetic hydroperoxides (13-OOH-9t,11t, 8-OOH-9t,11t, and 9-OOH-10t,12c) are formed. This study supports the theory that CLA methyl ester autoxidizes at least partly through an autocatalytic free radical reaction. The complexity of the hydroperoxide mixture is due to formation of two different pentadienyl radicals. Moreover, the stereoslectivity in favor of one geometric isomer can be explained by the selectivity of the two previous steps: the preferential formation of a W-conformer of the pentadienyl radical over the Z-conformer, and regioselectivity of the oxygen addition to the pentadienyl radical.  相似文献   

5.
Radical polymerization of methyl methacrylate (MMA) in the presence of methyl -(bromomethyl) acrylate yielded poly-(MMA) bearing the 2-methoxycarbonylallyl end group through chain reaction involving bimol ecular termination. The molecular weight of the resultant polymer was effectively controlled with a small amount of the bromomethylacrylate added; the chain transfer constant was estimated to be 0.9. The poly (MMA) with the unsaturated end group (
  相似文献   

6.
The atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with poly vinylacetate macroinitiator (PVAc-CCl3) and CuCl/PMDETA as catalyst was successfully carried out in bulk and solution. The apparent propagation rate constant () and concentration of active species ([P°]) were higher in the bulk. In solution they increased with polarity of solvent. Two different molecular weights of macroinitiators were used in ATRP of MMA. The linear relation of Ln[M]0/[M] versus time was only confirmed for the low molecular weight macroinitiator. The ratio of was calculated in the bulk reaction with the low molecular weight macroinitiator, this ratio was 1.77 × 1014 M−1 s−1 for larger macroinitiator in solution. The MWD of block copolymers were sharper with lower molecular weight macroinitiator in the solution, but it appeared broader in the bulk polymerization. Our results indicated that smaller molecular weight macroinitiator was more efficient and formed a block copolymer with lower PDI. Thermal analysis and microstructure of the block copolymers are investigated by 1H NMR, FT-IR, TGA and DSC. The chain tacticity of the MMA units is found not to be sensitive to the kinetic of the reactions with two different molecular weights of macroinitiator. DSC measurement shows two different transitions at 39 and 108 °C assigned to PVAc and PMMA blocks. The TGA profile shows a three-step degradation. The initial small weight loss that occurs around 220 °C and two large weight loss around 238 and 310 °C are attributed to dechlorination step and decomposition of the PMMA and PVAc blocks.  相似文献   

7.
The structure-retention correlation of various C24 bile acid isomers was studied by the addition of methyl β-cyclodextrin (Me-β-CD) to mobile phases in reversed-phase high-performance liquid chromatography (HPLC). The compounds examined include a series of monosubstituted bile acids related to cholanoic acids differing from one another in the position and configuration of an oxygen-containing function (hydroxyl or oxo group) at the position C-3, C-6, C-7, or C-12 and the stereochemistry of the A/B-ring fusion (trans 5α-H and cis 5β-H) in the steroid nucleus. The inclusion HPLC with Me-β-CD was also applied to biologically important 4β- and 6-hydroxylated bile acids substituted by three to four hydroxyl groups in the 5β-steroid nucleus. These bile acid samples were converted into their fluorescence prelabeled 24-pyrenacyl ester derivatives and chromatographed on a Capcell Pak C18 column eluted with methanol-water mixtures in the presence or absence of 5 mM Me-β-CD. The effects of Me-β-CD on the retentions of each compound were correlated quantitatively to the decreasing rate of capacity factors and the relative strength of host-guest inter-actions. On the basis of the retention data, specific and nonspecific hydrogen-bonding interactions between the bile acids and the Me-β-CD were discussed.  相似文献   

8.
The inhibition effect of methyl violet (MV) on the corrosion of cold rolled steel (CRS) in 1.0 M sulfuric acid (H2SO4) was investigated by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) methods. The results show that MV is a good inhibitor, and inhibition efficiency increases with inhibitor concentration, while decreases with the temperature. The adsorption of MV on CRS surface obeys Langmuir adsorption isotherm equation. The thermodynamic parameters of adsorption enthalpy (ΔH°), adsorption free energy (ΔG°) and adsorption entropy (ΔS°) are calculated and discussed. Potentiodynamic polarization curves show that MV acts as a mixed-type inhibitor in sulfuric acid. EIS exhibits one capacitive loop which indicates that the corrosion reaction is controlled by charge transfer process. Inhibition efficiency values obtained from weight loss, polarization and EIS are in reasonably good agreement. The adsorbed film on CRS surface containing optimum dose of MV was investigated by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Depending on the results, the inhibitive mechanism is proposed from the viewpoint of adsorption theory.  相似文献   

9.
Niobium (V) ethoxide [Nb(OC2H5)5] catalyzed the rearrangement of methyl 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoate (Me-HPODE) to epoxy hydroxy isomers. At low temperature (5°C) in aprotic solvent, Me-HPODE was converted to the diastereomeric α, β-epoxy alcohols, methyl 11(R,S),12(R,S)-epoxy-13(S)-hydroxy-9(Z)octadecenoate. These products are referred to as oxylipids and structurally resemble those obtained from the vanadium- and epoxygenase-catalyzed rearrangement of Me-HPODE but are distinct from products obtained from ferrous iron-, hematin-, and hemoglobin-catalyzed rearrangements. Because the product of the niobium-catalyzed rearrangement of Me-HPODE was predominantly the erythro diastereomer, the rearrangement is distinguished from that produced by a titanium catalyst, in which the threo diastereomer [methyl 11(R), 12(R)-epoxy-13(S)-hydroxy-9(Z)-octadecenoate] predominates, and from that produced by a vanadium catalyst, in which both diastereomers are produced in equal proportion. The synthesis of alcohol epoxide by Nb(OC2H5)5 was inhibited by traces of water, but inclusion of molecular sieves in the reaction medium did not improve yield, as the alcohol epoxide rearranged to ketonic materials.  相似文献   

10.
Low levels (≤0.1%) of squalene were anticipated in oils from the blubber of the harp seal Phoca groenlandica. The traditional roule of saponification and analytical examination of the total unsaponifiables was unattractive. A method developed for squalene in olive oil, reportedly present in the range of 0.3–0.7%, was based on total conversion of the oil to methyl ester of fatty acids by alkali transesterification, followed by hydrogenation over Adam's catalyst (PtO2). The analysis of the fully saturated methyl esters and any squalane produced concurrently was by gas—liquid chromatography. This method was satisfactory for the small amounts, 0.03% or less, of squalene in seal oil and is also illustrated for olive oil. A flame-ionization detector excessive response of approximately 25% was observed for all levels of squalene tested. The calculated factor of 1.22 should be applied to the peak area for squalane due to the higher response of hydrocarbons relative to the methyl esters of fatty acids and the system of oil components if reporting as fatty acids. Presented in part at the Annual Meeting of the Canadian Section of the American Oil Chemists' Society, London, Oct. 15–18, 1999.  相似文献   

11.
A unique Rh/TiO_2 solid acid catalyst modified with H_2SO_4 was synthesized and evaluated in the esterification reaction of propylene glycol methyl ether and decomposition of methyl orange(MO) in aqueous phase under halogen lamp irradiation. For this purpose, rhodium(Rh) nanoparticles were loaded on SO_4~(2-)/TiO_2 via the photo-deposition method. It was found that SO_4~(2-)/Rh–TiO_2 exhibited stronger catalytic activity than SO_4~(2-)/TiO_2. The new catalysts were characterized by X-ray powder diffraction(XRD), Brunauer–Emmett–Teller(BET), Transmission electron microscopy(TEM) and high-resolution(HRTEM), X-ray photoelectron spectroscopy(XPS) and Fourier Transform infrared spectroscopy(FTIR). Results from XRD and BET show that SO_4~(2-)/Rh–TiO_2 has higher specific surface area and smaller pore size than SO42-/TiO_2. The distribution of loaded Rh was found to be uniform with a particle size of 2–4 nm. Data from XPS reveal that Rh primarily exists as Rh~0 and Rh~(3+)in Rh–TiO_2 and SO_4~(2)-/Rh–TiO_2. These valence forms of Rh likely contribute to the enhanced catalytic activity. Furthermore, FT-IR spectra of the catalysts show an abundance of surface hydroxyl groups, which help the formation of hydroxyl radicals and the enhancement of surface acid density. The results show that more acid sites are formed on the sulfated Rh–TiO_2, and these acidic sites are largely responsible for improving the catalytic performance. This superior SO_4~(2-)/Rh–TiO_2 catalyst has potential applications in reactions requiring efficient acid catalysts, including esterification reactions and waste water treatment.  相似文献   

12.
Summary α-Amino, ω-carboxyl heterodifunctional poly(methyl methacrylate) was prepared by a living anionic polymerization of methyl methacrylate using N,N'-diphenylethylenediamine monolithium amide and succinic anhydride as an initiator and terminator, respectively. Its intramolecular cyclization was carried out to obtain a well-defined cyclic poly(methyl methacrylate). Received: 27 June 2001/Accepted: 16 July 2001  相似文献   

13.
Graft copolymers of poly(methyl methacrylate) and polyamide-6 (PMMA-g–PA6) were investigated via in situ anionic polymerization of ε-caprolactam, using PMMA precursors with N-carbamated caprolactam pendants (PMMA–CCL) as macroactivators and sodium caprolactamate as catalyst. Three grades of PMMA–CCLs obtained by free radical copolymerization were used for synthesizing the PMMA-g–PA6 copolymers with different PMMA content. The resulting graft copolymer was characterized by Fourier-transform infrared spectroscopy and selective extraction. Scanning electron microscopy is used to clarify the phase morphology of obtained polymer by fracture surface. The thermal property, crystallinity and dimensional stability of graft copolymer were studied using differential scanning calorimetry, X-ray diffraction and water absorption measurement. The results show the Tg of graft copolymer is higher than that of neat PA6, but the onset and peak points of graft copolymer melting point are shifted to lower temperature. The percentage crystallinity and water absorption of PMMA-g–PA6 copolymer decrease with increasing PMMA content, but the crystal structure of PA6 is scarcely affected by the presence of PMMA. Graft copolymers have improved dimensional stabilities relative to neat PA6. Upon the incorporation of 19.9 wt% PMMA into PA6, the water absorption of PMMA-g–PA6 copolymer has been reduced from 4.8 for neat PA6 to 2.1%.  相似文献   

14.
Glycidyl methacrylate-functionalized methyl methacrylate–butyl acrylate (GACR) core–shell structure copolymers were synthesized to toughen polylactide (PLA). With an increase in GACR content, the PLA/GACR blends showed decreased tensile strength and modulus; however, the elongation at break and the impact strength were significantly increased compared with that of PLA. The brittle fracture of neat PLA was gradually transformed into ductile fracture by the addiction of GACR. From dynamic mechanical analysis, the rigidity of the PLA/GACR blends was decreased with the increase of GACR content. The addition of GACR decreased the degree of crystallinity of PLA. The GACR was found to aggregate to form clusters with size increasing with increasing GACR content by transmission electron microscope analysis. The clusters dispersed in PLA matrix uniformly. It was found that PLA demonstrated large area, plastic deformation (shear yielding) and cavities in the blend upon being subjected the tensile and impact tests, which was an important energy-dissipation process and led to a toughened and transparent blend.  相似文献   

15.
Work on interdiffusion has been mainly carried out in binary systems in the past, and this work has focused on polymer–solvent (S) systems and polymer blends. To understand and predict the interdiffusion of two solids in the presence of one S, we present a new mathematical model based on the Onsager approach. Within our model, interdiffusion kinetics are described with a modification of the reptation model for long polymer chains, and the chemical potential gradient is used as the driving force behind mass transfer. The chemical potential is calculated with a Flory–Huggins approach. The model was validated with 29 Raman spectroscopy experiments in poly(vinyl acetate)–poly(methyl methacrylate)–toluene systems at 20 °C. Monomer mobilities (L i,0s) were determined for both polymers to show the independence of L i,0 from the chain length. The L i,0s were found to be strongly dependent on the S content. With the knowledge of phase equilibria and L i,0s, interdiffusion in the ternary polymer–polymer–S system could be predicted by the introduced model. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47092.  相似文献   

16.
Graphene oxide (GO)–TiO2 hybrid materials with enhanced photocatalytic properties were synthesized by a one-step combustion method using urea and titanyl nitrate as the fuel and oxidizer, respectively. During the synthesis procedure, the precursors containing GO, fuel, and oxidizer were maintained at different combustion temperatures (300–450 °C) for 10 min to ignite the combustion reaction. The effects of combustion temperatures on the weight loss, chemical status and photocatalytic properties were studied by thermogravimetry and differential scanning calorimetry, X-ray photoelectron spectroscopy, Raman, and photoluminescence. GO in the GO–TiO2 hybrids were not oxidized, but thermally reduced by decomposition of partial oxygen-containing groups. Meantime, the nitrogen doping of GO was achieved. Compared to the neat TiO2 obtained at same condition, GO–TiO2 hybrid obtained at 350 °C exhibited enhanced photodegradation performance, which is attributed to the effective photo-generated electron transferring from TiO2 to partially reduced GO, which confirmed by the photoluminescence quenching of TiO2.  相似文献   

17.
New titanium dioxide (TiO2) based catalysts were prepared by impregnating commercial zeolites in pellets form using a sol–gel technique. Characterization was done with chemical analysis, X-Ray diffraction, scanning electron microscopy, and BET measurements, together with volatile organic compounds (VOC) adsorption equilibrium experiments. TiO2 happened to fix on the inert binder leading to a close intimacy of mixing with the zeolites crystallites, without significant modification of support properties. A diffusion cell was used to produce dilute polluted air streams for dynamic experiments, in which adsorption and photodegradation phases were alternatively carried out. Regeneration of adsorbent was evaluated regarding experimental conditions. Through a comparison with the results obtained on impregnated mesoporous borosilicate beads, it was clarified that zeolite supports had no effect on 1-butanol (BuOH) photooxidation mechanisms. Yet, evidence for mass transfer limitation was found, and attributed to intracrystalline diffusion in zeolites.  相似文献   

18.
To analyze the interplay between crystallization and liquid–liquid phase separation (LLPS), isothermal crystallization behavior of poly(ethylene glycol) (PEG) in blends with isotactic poly(methyl methacrylate) (i-PMMA) was investigated by differential scanning calorimetry (DSC). The blend system had an upper critical solution temperature (UCST) type phase diagram. When the crystallization occurred simultaneously with LLPS, the overall crystallization rate was enhanced at high crystallization temperatures Tc, relatively compared with that of neat PEG. This behavior was interpreted by the combination of the effects of spinodal quench depth ?Ts and usual supercooling degree ?Tc, according to the theory of Mitra and Muthukumar, namely, the crystallization rate is enhanced by the concentration fluctuation-assisted nucleation at high Tc. In the crystallization after LLPS proceeded, on the other hand, the overall crystallization rate was slow and less dependent on the blend composition. In addition, it was revealed by small-angle X-ray scattering measurements that amorphous i-PMMA was excluded from the interlamellar region of PEG crystals in SQ as well as WQ.  相似文献   

19.
In this study, the changes in the structural and physicochemical properties of an α-crystalline phase (often called an "α-gel") were assessed in a sodium methyl stearoyl taurate (SMT)/behenyl alcohol/water system. The α-gels were characterized focusing on the effects of the alcohol/surfactant ratio and water concentration. Water molecules solubilized in the interlayer of the α-crystalline phase resulting in expanded interlayer spacing. Beyond the solubilization limit of 85 %, water molecules were trapped in the matrix of the α-crystalline phase in non-equilibrium (i.e., two phases). Accordingly, different self-diffusion coefficients for the solubilized and trapped water molecules were measured using a Fourier transform pulsed gradient spin echo technique to monitor the 1H NMR spectra. It was concluded that the two self-diffusion coefficients correspond to the water solubilized in the interlayer, i.e., "slow water," and trapped in the matrix of the α-crystalline phase, i.e., "fast water."  相似文献   

20.
Having considered the mechanical and optical properties related to microstructure, the authors of the present work did a study of the in situ interface formation between polyacrylonitrile/poly(methyl methacrylate) (PAN/PMMA) core–shell nanofibers and PMMA resin so as to prepare reinforced PMMA nanocomposites (NCs). The NCs were produced using the dip-coating method. The core–shell nanofibers were generated via phase separation of PAN/PMMA solution during the conventional electrospinning. The results of attenuated total reflection-Fourier transform infrared spectroscopy, transmission electron microscope, and energy dispersive X-ray spectrometer confirmed the formation of core–shell structure of the PAN/PMMA nanofibers. According to the findings of the study, the NCs reinforced with 1.7% volume fractions (v f) of the core–shell nanofibers, having the composition of 50/50 (PAN/PMMA), had the highest tensile and bending properties. The obtained results showed that by increasing the v f of nanofibers from 1.7 to 2.9%, the tensile and bending moduli increased by 29.9 and 44.2%, respectively. Increasing v f to 5.7% decreased the just-mentioned properties. Moreover, the transparency of NCs decreased by less than 1, 10, and 18%, respectively, when the aforementioned volume fractions were applied. The theoretical values for the tensile modulus were calculated using the models proposed by Manera, Pan, and Halpin–Tsai–Nielsen. The best prediction was made when the model proposed by Halpin–Tsai–Nielsen was applied.  相似文献   

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