The effects of aqueous solvent structure on the mutarotation kinetics of glucose

The mutarotation rates of glucose in aqueous mixtures of tetrahydrofuran andtert-butanol in the mole fraction (x_i) range 0i<0.2 have been measured at 5° intervals in the range 5–35°C. The kinetic deuterium isotope effects have been determined for the same solvent compositions at 25 and 35°C. A statistical analysis of the Arrhenius plots indicates that the experimental errors, although small, are too large for the establishment of any compensation behavior between H and S which has often been claimed for reactions in mixed aqueous solvents. Nevertheless, it appears that H exhibits a complex solvent composition dependence, and the solvent effects on the measured rate constants differ markedly from those found for aqueous solutions ofN,N-dimethyl-formamide and dimethyl sulfoxide. There is a deuterium isotope rate effect for solvent mixtures in which 0i<0.1, over and above the usually observed kinetic isotope effect. This additional effect decreases with rising temperature. The results are discussed in terms of competing water ordering effects in ternary mixtures containing water, a hydrophilic solute, and a hydrophobic solute.     

Catalysts for metathesis of olefins obtained through [Mo3O4(C2O4)3 (H2O)3]2? coordinated to γ-Al2O3

New highly active catalysts for the metathesis of olefins have been obtained through the interaction of [Mo₃O₄ (C₂O₄)₃ (H₂O)₃]^2– anion with Al₂O₃ surface and further activation in H₂ or CO atmosphere.

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[Mo₃O₄ (C₂O₄)₃ (H₂O)₃]^2– Al₂O₃ H₂ CO .

     

Kinetic Spectrophotometric Determination of Total Iron in Natural Water by Flow Injection Analysis Using On-Line Preconcentration

A new flow injection catalytic spectrophotometric method for on-line preconcentration and determination of total iron in natural water is described. The method is based on a combination of iron-catalyzed oxidation of diaminoditolyl by potassium bromate and the use of on-line preconcentration of iron onto 8-hydroxy-quinoline immobilized on silica gel. The corresponding calibration graph is linear over the range of 2.0–110ngmL^–1 for Fe(III) using a time-based technique for 5min preconcentration. The relative standard deviation of 11 measurements of 60ngmL^–1 Fe(III) was 0.67%. The method was applied to the determination of iron in natural water. The results obtained by the proposed method were compared with those obtained by ICP-AES. The t-test showed no significant differences between the two methods at a confidence level of 95%.     

Kinetic-morphological peculiarities of solid-state isomerization of complexes

The thermal solid-state isomerizations of Copy₂Cl₂ (py=pyridine), Nien₂(NO₂)₂ and Nien₂(NCS)₂ (en=ethylenediamine) were studied by thermal analysis, thermomicroscopy, X-ray diffraction and IR-spectroscopy. It was shown that the reactions proceed by nuclear formation and growth. The kinetic-morphological peculiarities of the processes suggest that the process-determining stage is a phase stage, i. e. structural transformation. The topography and kinetics of processes are therefore determined by the crystal structures of the initial material and the reaction product, and by the contact conditions at the interface. The stress relaxation processes affect the morphology of the products and the kinetics of the transformation.

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Zusammenfassung Thermische Isomerisierungsreaktionen in fester Phase wurden durch thermische Analyse, Thermomikroskopie, Röntgenbeugung und IR-Spektroskopie an CoPy₂Cl₂ (Py=Pyridin), Nien₂(NO₂)₂ und Nien₂(NCS)₂ (en=Ethylendiamin) untersucht. Es wird gezeigt, dass die Reaktionen durch Keimbildung und Wachstum ablaufen. Die kinetischen und morphologischen Charakteristika der Prozesse weisen darauf hin, dass der geschwindigkeitsbestimmende Schritt ein Phasenschritt, d. h. eine Strukturumwandlung ist. Deshalb sind Topographie und Kinetik der Vorgänge durch die Kristallstrukturen des Ausgangsstoffe und des Reaktionsprodukts und durch die Kontaktbedingungen an der Grenfläche bestimmt. Die Spannungsrelaxationsprozesse beeinflussen die Morphologie der Produkte und die Umwandlungskinetik.

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, , ₂l₂, Nien₂(NO₂)₂ Nien₂(NCS)₂, en= , = . , . - , . , . .

     

Thermal effects on glass As2Se3·As2Te3

The DTA trace of the chalcogenide glass As₂Se₃·As₂Te₃ shows a single glass transition at 142 °C, a single crystallization exotherm depending on the heating rate, and two melting endotherms, at 290 °C and 312 °C. The X-ray diffraction for a crystallized sample indicates the presence of two solid solution phases: Te in As₂Se₃ (rich in Se) and Se in As₂Te₃ (rich in Te), confirming that the single crystallization peak of the initially homogeneous phase (singleT _g ) represents two coincident peaks superimposed. The crystallization of the glass phase is also clearly manifested in the time-dependence of the electrical conductivity and microphotography.

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Zusammenfassung Die DTA-Kurve von chalcogenidem Glas As₂Se₃·As₂Te₃ läßt eine Glastransformation bei 142 °C, eine von der Aufheizgeschwindigkeit abhängige exotherme Kristallisation und zwei endotherme Schmelzvorgänge bei 290 und 312 °C erkennen. Röntgendiffraktometrie der kristallisierten Probe zeigt das Vorliegen von zwei Phasen fester Lösungen:Te in As₂Se₃ (reich an Se) und Se in As₂Te₃ (reich an Te). Das steht in Übereinstimmung damit, daß der Kristallisationspeak der ursprünglich homogenen Phase (einT _g -Wert) zwei sich überlagernde Peaks repräsentiert. Die Kristallisation der Glasphase ist klar an der Zeitabhängigkeit der elektrischen Leitfähigkeit und durch Mikrophotographie zu erkennen.

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As₂Se₃·As₂Te₃ 142 °, 290 312 dg. : As₂Se₃ ( ) Se As₂Te₃ ( ), , ( _g ), . .

     

Ammoxidation of halogen-substituted toluenes on V-P-oxide catalysts

The ammoxidation of various halogen-substituted toluenes on crystalline vanadium phosphate catalysts was investigated. The monophosphates and the NH₄VOP₂O₇ are transformed into new NH₄-containing V-P-oxides. The (VO)₂P₂O₇ used is stable in time on stream. These structures are very active and selective ammoxidation catalysts.

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. NH₄VOP₂O₇ V-P , NH₄. (VO)₂P₂O₇ . .

     

Characteristics of Diffraction Gratings Fabricated by the Two-Beam Interference Method Using Photosensitive Hybrid Gel Films

Diffraction gratings of arbitrary periods have been fabricated by the two-beam interference method using photosensitive ZrO₂ gel films and characterized. The ZrO₂ gel films were formed on Si or silica glass substrates from sols that were derived from Zr-butoxide modified chemically with benzoylacetone. The gel films were irradiated with two interference beams from a He-Cd laser (325 nm) and then leached in ethyl alcohol. The above process gave uniform surface-relief gratings of periods ranging from 1.0 to 0.5 m, depending on the incidence angle of the interference beams. The diffraction efficiency, measured in the Littrow configuration using a He-Ne laser (633 nm), showed polarization dependence for the grating of 0.5 m period but not for the gratings of 1.0 m period. The maximum diffraction efficiency was 18% for the grating of 1.0 m period and 28% for that of 0.5 m period in the reflection mode. The present study has proved that the photosensitive gel films are versatile in fabrication of optical devices.     

Novel separation method for highly sensitive speciation of cancerostatic platinum compounds by HPLC–ICP–MS

A high-performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC–ICP–MS) method is presented for analysis of cisplatin, monoaquacisplatin, diaquacisplatin, carboplatin, and oxaliplatin in biological and environmental samples. Chromatographic separation was achieved on pentafluorophenylpropyl-functionalized silica gel. For cisplatin, carboplatin, and oxaliplatin limits of detection of 0.09, 0.10, and 0.15 g L^–1, respectively, were calculated at m/z 194, using aqueous standard solutions. (3 L injection volume). The method was utilized for model experiments studying the stability of carboplatin and oxaliplatin at different chloride concentrations simulating wastewater and surface water conditions. It was found that a high fraction of carboplatin is stable in ultrapure water and in solutions containing 1.5 mol L^–1 Cl^–, whereas oxaliplatin degradation was increased by increasing the chloride concentration. In order to support the assessment of oxaliplatin eco-toxicology, the method was tested for speciation of patient urine. The urine sample contained more than 17 different reaction products, which demonstrates the extensive biotransformation of the compound. In a second step of the study the method was successfully evaluated for monitoring cancerostatic platinum compounds in hospital waste water.     

Unexpected variations of the rate of catalytic ethylene hydrogenation on nickel versus the flow-rate of the reacting mixture

Different shapes of the plot rate vs. flow-rate can be obtained for ethylene hydrogenation on nickel. They relate to the presence of oxygen traces and the way they are introduced into the reacting mixture. A previous statement according to which active centers are produced by the conversion of oxygen into water is thus confirmed.

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. . , . ., , .

     

Structure of vanadium phosphate anion in solutions from17O,51V and31P NMR data

¹⁷O,⁵¹V and³¹P NMR studies indicate that the anion structure of sodium vanadophosphate in an aqueous solution is close to that in crystals of the (CN₃H₆)₈HPV₁₄O₄₂ 7H₂O salt.

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¹⁷O,⁵¹V,³¹P , (CN₃H₆)₈HPV₁₄O₄₂ 7H₂O.

     

Application of thermal analysis to the investigation of catalysts

A short review of the possibilities of application of thermal analysis to the investigation of catalysts is given: analysis of catalysts, investigation of the processes during the preparation of catalysts, desactivation of catalysts, and interaction of reactants or catalytic poisons with the catalysts. Several examples are mentioned.

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Zusammenfassung Eine kurze Übersicht über die Möglichkeiten des Einsatzes der Thermoanalyse zur Prüfung von Katalysatoren wird gegeben: Analyse der Katalysatoren, Prüfung der Vorgänge während der Herstellung von Katalysatoren, Inaktivierung von Katalysatoren, Wechselwirkungen zwischen Reagenzien oder Katalysatorengiften und den Katalysatoren. Eine Anzahl von Beispielen wird erwähnt.

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Résumé On piésente une rapide vue d'ensemble sur les possibilités d'application de l'analyse thermique à l'étude des catalyseurs: l'analyse des catalyseurs, l'étude des processus ayant lieu lors de la préparation des catalyseurs, la désactivation des catalyseurs, l'interaction de réactifs ou de poisons sur les catalyseurs. Plusieurs exemples sont mentionnés.

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. , , —, —, — , . , — . .

     

Investigation of the influence of metal oxides on the thermal degradation of chlorine-containing polymers by thermogravimetry

The influence of oxides of zinc, magnesium, antimony and aluminium on the thermal degradations of polychloroprene, chlorinated polyethylene and epichlorhydrin homopolymer has been investigated. The investigations showed that these metal oxides can change the thermal stabilities and degradation processes of chlorine-containing polymers. A considerable acceleration of the dehydrochlorination of these polymers was found in the presence of zinc oxide.

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Zusammenfassung Es wurde der Einfluß von Zink-, Magnesium-, Antimon- und Aluminiumoxid auf den thermischen Zerfall von Polychloropren, chloriertem Polyäthylen und Epichlorhydrin-homopolymeren untersucht. Die Untersuchungen zeigen, daß diese Metalloxide die thermische Stabilität und die Zersetzungsprozesse von chlorhaltigen Polymeren verändern können. In Gegenwart von Zinkoxid wurde eine bedeutende Beschleunigung der Dehydrochlorierung dieser Polymere festgestellt.

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, , , . , . .

     

Oxidative stability of lubricants for dry circuit sliding contacts

The thin film oxidation resistance of isoparaffin and two polyol esters synthetic lubricants was studied by high pressure differential scanning calorimetry. The oxidation induction time of each lubricant was measured by isothermally heating the sample in an oxygen environment. Arrhenius plots were constructed to predict the service life of the lubricant at low temperatures. The results indicate that polyol esters exhibit better oxidative stability than isoparaffins.

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Zusammenfassung Mittels Hochdruck-Differential-Scanning-Kalorimetrie wurde die Dünnschicht-Oxydationswiderstandsfestigkeit von Isoparaffin- und zwei synthetischen Polyolesterschmiermitteln untersucht. Die Oxydationsinduktionszeit jedes Schmiermittels wurde durch isothermes Erhitzen der Probe in Sauerstoff gemessen. Zur Vorhersage der Lebensdauer der Schmiermittel bei niedrigen Temperaturen wurden die entsprechenden Arrhenius-Diagramme erstellt. Die Ergebnisse zeigen, dass Polyolester über eine bessere oxydative Stabilität verfügen als Isoparaffine.

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, . . . , , .

     

Determination of liquid adsorption and desorption on and from solids by means of the derivatograph

This paper presents a method for calculation of the adsorption and immersion heats of water on a silica gel surface from the DTA curve obtained with a modified derivatograph. The adsorption and desorption heats have also been determined. The relationship between the adsorption heat and the amount of water adsorbed is presented.

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Zusammenfassung Eine Methode zur Berechnung der Adsorptions- und Immersionswärmen von Wasser an Silikagel aus den mit einem modifizierten Derivatographen gemessenen DTA-Kurven wird beschrieben. Adsorptions- und Desorptionswärmen wurden bestimmt. Die Beziehung zwischen der Adsorptionswärme und der Menge des adsorbierten Wassers wird angegeben.

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, , . . .

     

Role of the surface of silica gel in the radiation chemical conversions of adsorbed hydrocarbons

The action of gamma radiation on the systems benzene-silica gel and hexane-silica gel has been studied by EPR for different ratios of the components. It is shown that H-atoms detached from the surface OH groups during irradiation react with the adsorbed hydrocarbons to give C₆H ₇ ^. (C₆H₆D in the case of deuterated silica gel) and C₆H ₁₃ ^. radicals. It is ascertained that the SiO^. radicals also formed with the H-atoms during irradiation react with the adsorbate. Confirmation that H-atoms and SiO^. radicals participate in the radiation chemical conversions of adsorbed hydrocarbons is obtained by experiments with silica gels previously dehydrated at various temperatures. A possible mechanism of energy migration within the silica beads is discussed.     

Probing the surface polarity of native celluloses using genuine solvatochromic dyes

The surface polarity of native celluloses has been investigated by the following solvatochromic dyes: dicyano-bis (1,10)-phenanthroline iron (II) Fe(phen)2 (CN)2 (1), bis(4-N,N-dimethylamino)-benzophenone (2), and cou-marine 153 (3). Linear Solvation Energy (LSE) relationships and the UV/Vis data have been used to characterize the surface polarity of different native cellulose batches in terms of the empirical Kamlet–Taft polarity parameters (hydrogen bond acidity), (hydrogen bond basicity), and * (dipolarity/polarizability). , , *and calculated Reichardt's E T (30) values are reported for various native and regenerated cellulose samples with different degrees of crystallinity. The degree of crystallinity of the cellulose samples has been determined by X-ray. The microcrystalline environment of cellulose can be exactly parameterized in terms of the , and *values. It shows a fairly strong acidity and a low dipolarity/polarizability. For the amorphous sections smaller and larger * values are observed. The correspondence of the empirical polarity parameters determined has been discussed in relation to results from pyrene fluorescence and zetapotential measurements.     

Enthalpies of solution of thymine and uracil in water and dimethylsulfoxide

Enthalpies of solution of thymine and uracil in water and in dimethylsulfoxide (DMSO) were measured calorimetrically in the temperature range 25–40°C. H _s ^o at 25°C for thymine and uracil in water were found to be 23.1±0.5 and 29.5±0.3 kJ-mol^–1, respectively. In DMSO, H _s ^o were 7.9±0.1 and 10.2±0.1 kJ-mol^–1, respectively. In aqueous solution C _p ^o for the two nucleic acid bases were relatively large and positive with C _p ^o of thymine being larger. Both transfer quantities H _t ^o and C _p,t ^o for the proceses H₂ODMSO for the two nucleic acid bases were negative. It is proposed that, the differences in the values obtained for the two bases is due principally to increased order in the water adjacent to the methyl group in thymine.     

Selective Solid Phase Extraction and Pre-Concentration of Heavy Metals from Seawater by Physically and Chemically Immobilized 4-Amino-3-Hydroxy-2-(2-Chlorobenzene)-Azo-1-Naphthalene Sulfonic Acid Silica Gel

4-Amino-3-hydroxy-2-(2-chlorobenzene)-azo-1-naphthalene sulfonic acid (AHCANSA) was used as a chelating modifier to improve the reactivity of the silica gel surface in terms of selective binding and extraction of heavy metal ions. The surface coverage values were found to be 0.488 and 0.473mmolg^–1 for the newly modified physically adsorbed silica gel phase (I) and chemically immobilized-AHCANSA phase (II), respectively. The modified silica gel phases (I, II) were tested for stability in different acidic buffer solutions (pH 1–6) and found to be highly resistant to hydrolysis and leaching by buffer solutions above pH 2. The application of these two phases as solid extractors for a series of mono-, di-, and tri-valent metal ions from aqueous solutions was also performed with different controlling factors such as the pH value of metal ion solutions and equilibrium shaking time. The mmolg^–1 metal capacity values determined by silica gel phases (I, II) were found to confirm high affinity and selectivity characters for binding with heavy metal ions such as Cr³⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ in a range of 0.250–0.483. The tested alkali and alkaline earth metals, Na⁺, K⁺, Mg²⁺ and Ca²⁺, were found to exhibit little interaction and binding ability with the modified silica gel phases. The selectivity characters incorporated into the modified silica gel phases were further utilized and applied in solid phase extraction and pre-concentration of trace concentration levels (1.0µgmL^–1 and 2.00–2.50ngmL^–1) from real seawater samples. The percentage recovery values determined for Cr³⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were found to be in the range of 95.2–98.1±2.0–5.0%, and the pre-concentration recovery values for the same tested heavy metal ions were found to be in the range of 92.5–97.1±3.0–6.0% for the two newly modified silica gel phases with a pre-concentration factor of 500.Received December 20, 2002; accepted May 14, 2003 published online September 1, 2003     

Selenium speciation by coupling vesicle mediated HPLC with off-line ETAAS and on-line focused microwave digestion HG-AAS detection

A novel High Performance Liquid Chromatography (HPLC) method for the separation of selenium species with specific detection by off-line Electrothermal Atomization Atomic Absorption Spectrometry (ETAAS) or on-line focused microwave digestion (MW) Hydride Generation Atomic Absorption Spectrometry (HG-AAS) is described. Vesicular mobile phases of the cationic surfactant didodecyldimethylammonium bromide (DDAB) have been evaluated for the liquid chromatographic separation of inorganic selenium (selenite and selenate) and different selenoaminoacids (selenocystine, selenomethionine and selenoethionine) on a C₁₈ reversed-phase column modified by DDAB molecules. The effects of different parameters (pH, buffer and vesicle concentrations) of the mobile phase on the retention times have been determined. The detection limit for selenium with the proposed off-line HPLC-ETAAS method has been found to be 5 g/L of Se. The detection limit using HPLC-on line focused microwave digestion-HG-AAS has been found to be 1 g/L of Se, with a precision (repeatability) better than ± 5%. The latter proved to be an exceptional on-line real-time chromatographic detector for selenium speciation purposes.