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Abstract  

Isoprene polymerizes under the action of γ-radiation from a 60Co source yielding a low molecular weight polyisoprene which remains soluble in the unreacted monomer. The electronic absorption spectrum of polyisoprene oligomer in isoprene monomer has been explained using squalene, a polyisoprene hexamer, as model compound. The radiation chemical yield for polyisoprene formation has been estimated from both gravimetric and spectrophotometric data pertaining the amount of polymer formed. An average G value of 35 molecules/100 eV has been determined suggesting that the polymerization mechanism involves free radicals. The chemical structure of the resulting polyisoprene radio-oligomer has been determined by FT-IR spectroscopy and found identical to that of a reference polyisoprene sample prepared by a chemically-initiated free radical polymerization process. The structure determination by FT-IR spectroscopy has been reported in detail.

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Abstract  

Reaction rate constants of (−)-epigallocatechin gallate (EGCG) and (+)-catechin with the hydroxyl radical (·OH) were measured using the rapid flow ESR method. The rate constant of EGCG was larger twice than that of the pyrogallol or gallic acid, they are the model compounds of the B ring of EGCG. It was explained by the quantum-chemical calculation of the bond dissociation energy (BDE) of the phenolic hydroxyl group (ϕ-OH) and the spin densities of EGCG radical. The energy of the EGCG radical was lowered by the hydrogen bonding between the radical part on the B ring and the hydroxyl group on the gallate group, leading to the lowering of BDE. Linear relationship between the relative activation energy and BDE of all the polyphenols measured was observed (Evans-Polanyi equation), showing that the reaction with ·OH occurs in the same manner.

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Abstract  

Ruthenium catalysts have been prepared by incipient wetness impregnation of ruthenium(III) nitrosylnitrate, Ru(NO)(NO3)3 onto high surface area titanate supports obtained by hydrothermal treatment of TiO2 P25 in concentrated alkaline solutions. These Ru-containing catalysts were evaluated in the catalytic wet air oxidation of p-hydroxybenzoic acid (p-HBZ), a model compound representative of phenolic pollutants present in olive mills wastewaters, at 413 K and 50 bars of air. Two different titanates morphologies were tested as supports for this reaction: hydrogenotitanate nanotubes (HNT) obtained with concentrated NaOH and hydrogenotitanate nanowires (HNW) formed in the presence of highly concentrated KOH solution. The HNT and HNW supports and their corresponding supported Ru catalysts were characterized by means of N2 adsorption–desorption, XRD, UV and TEM analyses. Results showed that the use of high surface area titanate supports led to catalysts much more active than similar Ru catalysts supported on conventional TiO2 supports.

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The objective of this study was to combine the Yeast Estrogen Screen (YES) for the detection of estrogenic compounds with thinlayer chromatography. Such an approach might serve as an effective tool in effect-directed analysis, i.e., the identification of bioactive compounds in mixtures. The proposed method (planar-YES) allows the detection of estrogenic effects on the surface of a TLC plate after an exposure time of 2-3 h instead of the usual 18 h which are used for the traditional microplate-YES. The estimated limits of quantification for the estrogenic model compound 17α-ethinylestradiol (EE2) were 0.8 pg without and 1.6 pg with a prior chromatographic development of the TLC plate. The hormones 17α- ethinylestradiol (EE2), 17β-estradiol (E2) and estrone (E1) could be separated by thin-layer chromatography and were detected by means of the specific bioassay subsequently. Finally, the applicability of the method on real samples was demonstrated with the detection of estrogenic effects in sediment extracts from sediments of the river Elbe.

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The newly developed experimental OPLC separation unit 100 (OSU 100) has been used for fully on-line multiple hyphenation using the one-channel flowing eluent wall (FEW) arrangement at the inlet. OSU 100-UV and OSU 100-DAD-ESI-MS with manual injector or autosampler were used to test the connected systems (OPLC-UV; OPLC-DAD-ESI-MS), using xanthine standards (caffeine, theophylline, theobromine) and green tea leaf extract as model compounds. The mobile phase chloroform-trifluoroacetic acid-acetonitrile-methanol, 76:4:6.67:13.33 ( v / v ) is suitable for rapid and selective separation, DAD, and ESI-MS of xanthines. The detection sensitivity of OPLC-UV or OPLC-DAD was increased by hyphenation with ESI-MS coupled in series. In contrast with DAD, the extracted ion chromatogram ( m / z = 181.1 Da) after background subtraction yields readily measurable peaks from the small amounts of theophylline and theobromine in tea leaf extract. Analysis of xanthines was achieved within 10 min with less than 2 mL mobile phase. Owing to the openable adsorbent layer in OPLC the bed conditions can, moreover, be checked off-line after single or multiple fully online separations.

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Abstract  

Thermogravimetry is often used to study polymer degradation. Most often the information obtained may have some practical application but is of limited value for the determination of fundamental processes which may be occurring. A kinetic expression or activation parameters for a complex process which may involve consecutive or parallel reactions provides almost no information about any of the reactions that might be occurring. However, for single, well-defined processes, thermogravimetry, in conjugation with other analytical methods, can be effectively utilized in the determination of reaction mechanism. The thermal degradation of vinylidene chloride barrier polymers corresponds to the elimination of hydrogen chloride initiated at an allylic dichloromethylene unit in the mainchain. This process is uncomplicated by competing reactions. Thermogravimetry may be utilized to obtain meaningful rate constants and activation parameters for the degradation. This in conjunction with mass spectral analysis of evolved gas, characterization of both the polymer and degradation residue by ultraviolet, infrared and 1H and 13C NMR spectroscopy, and the study of model compounds has permitted a detailed description of the degradation process. General purpose poly(styrene) is a commodity polymer widely used in the food packaging industry as well as many others. If processed at excessively high temperature, it undergoes thermal degradation to expel styrene monomer which can impart negative flavor and aroma characteristics to packaged food items. The degradation reaction has been fully detailed using thermogravimetry in conjugation with evolved gas analysis, size exclusion chromatography and NMR spectroscopy.

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Abstract

Kinetic or rather thermokinetic analysis of thermal decomposition with releasing gaseous products is a current subject of discussion in many works and still devotes much attention to the property and meaningfulness of the single kinetics triplet determination. Analysis of thermogravimetric data by the relative rate of reaction/process were used to examine the frequently studied process of thermal dissociation of calcium carbonate as a model compound and comparing with published data for chemically defined compounds (azo-peroxyesters) and complex polyolefins–liquid paraffin mixtures. Two methods of correlation between parameters of the model were observed: thermodynamic and analytical expression. It was shown that these relations depend on course of the process. For analyzed model substance, enthalpy of reaction can be deduced on the basis of relation between coefficients in three-parameter equation. For large values of coefficients it is not possible, but other type of correlation was proved. Also, the relative rate of CO2 gasification (Boudouard reaction) of brown and bituminous coals was analyzed and compared to that of its pyrolysis.

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Abstract  

Humic acids represent a complicated mixture of miscellaneous molecules formed as a product of mostly microbial degradation of dead plant tissues and animal bodies. In this work, lignite humic acids were enriched by model compounds and the model-free method suggested by Šimon was used to evaluate their stability over the whole range of conversions during the first thermooxidative degradation step. The kinetic parameters obtained were used to predict the stability at 20 and 180�C, respectively, which served for the recognition of processes induced by heat and those naturally occurring at lower temperatures. Comparison of the conversion times brought a partial insight into the kinetics and consequently into the role of individual compounds in the thermooxidative degradation/stability of the secondary structure of humic acids. It has been demonstrated that aromatic compounds added to humic acids, except pyridine, increased stability of humic acids and intermediate chars. The same conclusion can be drawn for acetic and palmitic acids. Addition of glucose or ethanol decreased the overall humic stability; however, the char of the former showed the highest stability after 40% of degradation.

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Abstract  

Thermal behaviour of cure-accelerated phenol-formaldehyde (PF) resins was studied using the addition of commercial mixture of water soluble oil shale alkylresorcinols (AR) to PF resin, 5-MR being as model compound. The acceleration effect of AR is based on the promotion of condensation of resin methylol groups and subsequent reaction of released formaldehyde with AR. Commercial PF resins SFŽ-3013VL and SFŽ-3014 from the Estonian factory VKG Resins have been used. The chemical structure of resins was characterised by 13C NMR spectroscopy. TG-DTA analysis was carried out using labsysTM instrument Setaram. By TG-DTA measurements, the shift of exothermic and endothermic peaks and the changes of mass loss rate in the ranges of 1.5–10 g AR/100 g PF resin were studied. The effect of AR on the curing behaviour of PF resins was also followed by gel time. Testing of the plywood when using PF resin with 5 mass% of AR shows that the press time could be reduced by about 15%.

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Abstract

Different contents of promoter (Co) in Co–Ni–Mo–B amorphous catalysts were prepared by chemical reduction of the precursors of metal salts with a sodium borohydride aqueous solution. The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Adding a proper content of the promoter Co into Ni–Mo–B amorphous catalyst could increase the MoO2 content and decrease the particle size, but doping excess Co would cover some of the active sites and increase the particle size of the catalysts. The effect of Co content on the catalytic hydrodeoxygenation activity of the amorphous catalysts was studied using phenol as a model compound. The main route for the HDO of phenol on these amorphous catalysts was hydrogenation–dehydration and the content of aromatic compounds in HDO products was decreased obviously. The pseudo first-order reaction rate constant of the phenol HDO on Co–Ni–Mo–B amorphous catalyst was much greater than that of MoS2 when adding proper promoter Co.

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