The linkage between reversible Friedel–Crafts acyl rearrangements and the Scholl reaction

Structural Chemistry - Friedel–Crafts acyl rearrangements in PPA (at 80–240 °C) and Scholl reactions in AlCl3/NaCl (at 140–220 °C) of...     

Synthesis,characterization and kinetic computations of fullerene (C60)–CuO on the mechanism decomposition of ammonium perchlorate

CuO, C₆₀–CuO, and Al/C₆₀–CuO nanostructures were synthesized and characterized by scanning electron microscope (SEM)/energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR). differential scanning calorimetry (DSC)/thermogravimetric analysis (TGA) measurements were performed to study the influence of these additives on ammonium percolate (AP) thermal decomposition. From the comparison of DSC and TGA plots, the catalytic effect of CuO and C₆₀–CuO has been clearly noticed in which the lower temperature decomposition of AP was decreased from 331 °C to 315 °C, 310 °C, and 303 °C (in the presence of CuO, C₆₀–CuO, and Al/C₆₀–CuO, respectively) and the HTD was dropped from 430 °C (pure AP) to 352 °C, 335 °C, and 317 °C (for the compounds AP/CuO, AP/C₆₀–CuO, and AP/Al/C₆₀–CuO, respectively). The kinetics of the samples were investigated by isoconversional models and compared with an iterative procedure. The results of pure AP indicated a complex decomposition process involving three decomposition steps with specific reaction mechanism. The nanocatalysts incorporated in the AP have clearly affected its decomposition process in which the reaction mechanism and the number of stages were changed.     

Non-isothermal crystallization kinetics and degradation kinetics studies on barium thioglycolate end-capped poly(ε-caprolactone)

Journal of Thermal Analysis and Calorimetry - The poly(ε-caprolactone) (PCL) was synthesized by ring-opening polymerization at 160 °C under nitrogen atmosphere for 2 h...     

Nickel nanoparticles generated by pulsed laser ablation in liquid CO2

Research on Chemical Intermediates - Nickel nanoparticles with various structures were synthesized by a pulsed laser ablation process in liquid CO2 at 17 °C and 5.2 MPa. A...     

Melt processed polyethylene/fullerene nanocomposites with highly improved thermo-oxidative stability

The thermo-oxidative stability of melt processed polyethylene composites with the two fullerenes C₆₀ and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was studied with the aim of comparing the stabilization effect of both fullerenes on three different polyethylenes (PE). The results obtained show that, irrespective of the specific polyethylene being considered, C₆₀ loadings as low as 1.0 wt% cause a dramatic increase in the thermo-oxidative stability of the corresponding composites (up to 64.8 °C at T2% and 113.8 °C at T5%, TX% being the temperature corresponding to a mass loss of X wt%), in agreement with previous reports. Furthermore, and more importantly, this work shows for the first time that the thermo-oxidation stability effect caused by PCBM is even higher than that of C₆₀, the difference between both being particularly significant in the early stages of degradation, i.e. for mass losses ≤2 wt%. For example, polyethylene composites with 1.0 wt% PCBM show T2% values which are systematically higher than those of the corresponding composites with 1.0 wt% C₆₀, the difference between the T2% values of the two composites being 38.8 °C, 67.1 °C and 26.4 °C in the three different polyethylenes considered. Therefore, when compared with C₆₀, PCBM is particularly more effective at delaying the beginning of the thermo-oxidative degradation. According to our results, PCBM loadings as low as 1.0 wt% can increase the thermo-oxidative stability of polyethylene composites by more than 130 °C and these are, as far as we know, the highest thermo-oxidative stability results induced by nanoparticles ever reported in the literature for polyethylene.     

Elastic properties and mechanical relaxation behaviors of PVDF (poly (vinylidene fluoride)) at temperatures between −20 and 100 °C and at 2 MHz ultrasonic frequency

The elastic properties of PVDF have been investigated as a function of temperature. The propagation velocity and absorption of longitudinal and transverse ultrasonic waves have been measured at a constant frequency of 2 MHz and temperatures between –20 and 100 °C. Hence, the temperature dependences of storage and loss elastic constants have been obtained for temperatures between –20 and 100 °C. It has been seen that the relaxation behavior is affected from the form of mechanical disturbance. For the longitudinal mode, only one relaxation peak at 42 °C, but for transverse mode three relaxation peaks at 28 °C, 60 °C, and 94 °C have been observed. The results have been compared with the literature values obtained previously for PVDF. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2862–2873, 2005     

Isolation,purification, and characterization of thermophilic laccase from the xerophyte <Emphasis Type="Italic">Cereus pterogonus</Emphasis>

Three laccase temperature isoforms were isolated and purified to homogeneity from the xerophyte plant species Cereus pterogonus. This catalytically active protein exhibited an apparent molecular mass of 137 kDa, 90 kDa, and 43 kDa. Under reducing conditions the enzyme yielded a subunit molecular mass of 43 kDa alone, suggesting that the enzyme is a multimer of its subunits. The enzyme exhibited an optimum pH of 10 with 2,6-dimethoxyphenol used as a substrate. The 137 and 90 kDa forms yielded optimum activity at 90°C; whereas the 43 kDa molecular form yielded optimum activity at 60°C. The enzyme kinetic constant Km remained closely similar for all three enzyme forms, whereas Vmax varied by 25 % overall. The catalytic activity remained above its t_1/2 value in excess of the 30 min denaturation assay period at 60°C and 90°C. These high-temperature isoforms of the plant laccase enzyme with alkaline pH optima can find great industrial use.     

Glucose Oxidase-dextran Conjugates with Enhanced Stabilities Against Temperature and pH

Multipoint covalent bonding of glucose oxidase (EC 1.1.3.4) to hydrophilic natural polymer dextran and optimization of procedures to obtain, with enhanced temperature and pH stabilities, were studied. Purified enzyme was conjugated with various molecular weight dextrans (17.5, 75, and188 kD) in a ratio of 20:1, 10:1, 1:1, 1:5, 1:10, 1:15, and 1:20. After 1 h of incubation at pH 7, the activities of purified enzyme and conjugates were determined at different temperatures (25°C, 30°C, 35°C, 40°C, 50°C, 60°C, 70°C, and 80°C), and the results were evaluated for thermal resistance. Increases in temperature from 25°C to 50°C did not change the activities of the conjugates. The conjugate, which was prepared with 75 kDa dextran in a molar ratio of 1:5, showed the highest thermal resistance and even the activity still remains at 80°C at pH 7.0. This conjugate also displayed activity in a wide pH range (pH 4.0–7.0) at high temperatures. Conjugate, which was synthesized with 75 kDa dextran in a molar ratio of 1:5, appears to be feasible and useful for biotechnological applications.     

Kinetics of Lime Pretreatment of Sugarcane Bagasse to Enhance Enzymatic Hydrolysis

The objective of this work was to determine the optimum conditions of sugarcane bagasse pretreatment with lime to increase the enzymatic hydrolysis of the polysaccharide component and to study the delignification kinetics. The first stage was an evaluation of the influence of temperature, reaction time, and lime concentration in the pretreatment performance measured as glucose release after hydrolysis using a 2³ central composite design and response surface methodology. The maximum glucose yield was 228.45 mg/g raw biomass, corresponding to 409.9 mg/g raw biomass of total reducing sugars, with the pretreatment performed at 90°C, for 90 h, and with a lime loading of 0.4 g/g dry biomass. The enzymes loading was 5.0 FPU/dry pretreated biomass of cellulase and 1.0 CBU/dry pretreated biomass of β-glucosidase. Kinetic data of the pretreatment were evaluated at different temperatures (60°C, 70°C, 80°C, and 90°C), and a kinetic model for bagasse delignification with lime as a function of temperature was determined. Bagasse composition (cellulose, hemicellulose, and lignin) was measured, and the study has shown that 50% of the original material was solubilized, lignin and hemicellulose were selectively removed, but cellulose was not affected by lime pretreatment in mild temperatures (60–90°C). The delignification was highly dependent on temperature and duration of pretreatment.     

Changes in Secondary Metabolite Contents Following Crude Drug Preparation

Crude drug is commonly prepared by directly drying of freshly harvested plant organ or after slicing. These processes may decrease or maintain the content of the desired metabolites presence in the crude drug. Plant rhizome can be directly sliced followed by drying or after storage at certain period. Certain rhizome can maintain the secondary metabolites after being stored for three months (12 weeks), while others decreased just after being stored for two weeks. Drying process can be performed under the sun or in an air circulated oven with temperature not higher than 60 °C. Phenolic content of crude drugs on the other hand is the lowest if it is dried at 60 °C. Drying at 40 °C, 80 °C and 100 °C produce crude drug with higher phenolic content compared to those dried at 60 °C. This may associated with the activity of peroxidase that has optimal activity at 60° C. At above 60 °C, the activity of peroxidase may decrease due to the degradation of the enzyme. Moist treatment of fresh material may increase the content of the secondary metabolites. Boiling of Cosmos caudatus leaves increased the content of the flavonoid glycoside. However, part of the flavonoid was presence in the aliquot that hamper further step of crude drug preparation. Steaming of potato peels increased the chlorogenic acid content. From these observations, steaming can be considered as one of pre-treatment steps in the preparation of crude drugs prior drying process. The increase of flavonoid glycoside in Cosmos caudatus leaves upon boiling has been confirmed not due to the increase the extractability of the flavonoid. The increase of key enzyme activity that involved in the biosynthetic pathway upon moist-heat treatment need to be further studied     

Synthesis,characterization, and antioxidant activity of some new N4-arylsubstituted-5-methoxyisatin-β-thiosemicarbazone derivatives

Research on Chemical Intermediates - Firstly, thiosemicarbazides were prepared by the reaction of hydrazine monohydrate with isothiocyanates in cold dry ethanol at 0&nbsp;°C for...     

OPERANDO X-RAY DIFFRACTION ANALYSIS OF THE MnOx–ZrO2 CATALYST DURING OXIDATION OF PROPANE

Journal of Structural Chemistry - A series of MnOx–ZrO2 catalysts is prepared by coprecipitation with variation of the calcinationtemperature from 400&nbsp;°C to...     

Tea-leaves based nitrogen-doped porous carbons for high-performance supercapacitors electrode

Journal of Solid State Electrochemistry - Nitrogen-doped porous activated carbons have been fabricated through a simple and efficient carbonization method at 700&nbsp;°C with the waste...     

Hydrothermal synthesis of Ag-doped BiOI nanostructure used for photocatalysis

Research on Chemical Intermediates - A series of Ag-doped BiOI photocatalysts with different Ag contents was successfully synthesized by a hydrothermal method at 120&nbsp;°C for...     

Selective hydrothermal synthesis of ammonium vanadates(V) and (IV,V)

Transition Metal Chemistry - The reduction of vanadium pentoxide with formamide under hydrothermal–microwave treatment at 180–210&nbsp;°C allows for the selective synthesis of...     

A determination of the effective temperatures for the dissociation of the proton bound dimer of dimethyl methylphosphonate in a planar differential mobility spectrometer

The dissociation of the proton bound dimer of dimethyl methylphosphonate to the protonated and neutral molecule has been studied in a planar differential mobility spectrometer. The internal energy of the ions is the sum of the thermal component and the electric field component and results in an effective temperature, T_eff, that is significantly greater than that of the ambient atmosphere temperature, T. The measured rate constant for dissociation, which rises exponentially with field strength, together with activation energy and pre-exponential factor previously determined under thermal conditions, allow the calculation of T_eff as a function of electric field strength. T_eff is a linear function of electric field intensity at constant T over the range of T from 60 °C to 140 °C. The efficiency of the available collision energy in causing dissociation decreases with increasing T, from 52% at 60 °C to 40% at 140 °C.     

Determination of radiological hazard parameters and radioactivity concentrations in bauxite samples: the case of the Sutlegen Mine Region (Antalya,Turkey)

Journal of Radioanalytical and Nuclear Chemistry - Iron phosphate glasses with melting temperatures of?~?1300&nbsp;°C were developed to immobilize spent nuclear fuels. The...     

Synthesis of helical and straight carbon nanofibers by chemical vapor deposition using alkali chloride catalysts

Microchimica Acta - Carbon nanofibers were synthesized by chemical vapor deposition using alkali chloride catalysts at a temperature range from 500 to 700&nbsp;°C. Depending on the...     

The non-isothermal kinetics of zinc ferrite reduction with carbon monoxide

Journal of Thermal Analysis and Calorimetry - This study aims to reduce zinc ferrite using carbon monoxide in the temperature range of 25–1000&nbsp;°C using temperature-programmed...