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961.
Marina Nídia Ferreira dos Santos Costa Marcos Antônio Pena Muniz Charles Alberto Brito Negrão Carlos Emmerson Ferreira da Costa Maria Louze Nobre Lamarão Luiz Morais José Otávio Carréra Silva Júnior Roseane Maria Ribeiro Costa 《Journal of Thermal Analysis and Calorimetry》2014,115(3):2269-2275
The Pracaxi oil—(Pentaclethra macroloba) contains high concentrations of fatty acids with emollient action that contribute to skin hydration. The use of this oil is supported by the utilization of natural resources thus enabling regional development and social contribution. The objective of this study was to characterize the P. macroloba oil by thermogravimetry (TG, DTG, and DTA), gas chromatography, Fourier transform infrared spectroscopy (FT-IR), and oxidation stability—Rancimat, aiming at the quality control of plant raw material. Three samples of crude oil sold by Amazon Oil Industry (Ananindeua, Pará, Brazil) were studied. The analysis of these oil samples showed different fatty acids, especially the behenic, oleic, linoleic, and lignoceric acids totalizing approximately 96 % of the grease composition and in smaller percentage arachidic, lauric, myristic, palmitic, and linolenic acids were found. The major acids have wide medicinal use. According to the TG/DTG curve, thermal stability was observed up to 220 °C, indicating a greater mass loss related to the dehydration and elimination of volatile substances. The thermal decomposition process occurred in the range of 430–450° C according to the DTG curve. The absorption spectrum in the infrared region (FT-IR) showed well-defined bands confirming the presence of functional groups present in the oil. Tests in a Rancimat have shown an induction period between 8 and 10 h demonstrating that the samples are in agreement with the standards required by ANP No. 14/2012 which requires at least 6 h of testing. 相似文献
962.
Adulteration of drugs is a serious issue and can have a great impact on human health. It is mainly done with the intention of boosting the effects of products. For many years, the enforcement officers in Malaysia have had difficulty deciding whether some products should be confiscated as they have not been able to produce fast reliable evidence of adulteration. For that reason, we explored the use of differential scanning calorimetry (DSC) as a potential fast detection method of commercial products marketed in Malaysia that may be adulterated. We confirmed the outcomes qualitatively with high pressure liquid chromatography. DSC was set at a heating rate of 10 °C min?1 and within a temperature range of 100–250 °C with nitrogen as a purge gas at a flow rate of 20 mL min?1 to analyse a sildenafil reference standard (RS), sildenafil tablets and sildenafil adulterated commercial products. Four sildenafil adulterated commercial products were analysed. Since the melting point of sildenafil in the mixture tended to shift, the presence of sildenafil in three of these adulterated commercial products was confirmed using the spiking method and was re-analysed using DSC. The re-analysed results indicated that the enthalphy of fusion (?H) and the resolution peak of sildenafil increased accordingly depending upon the amount of spiked sildenafil RS. Apart from these results, the DSC curves also showed different patterns for sildenafil RS and the mixtures. Therefore, we concluded that DSC can potentially be used to detect sildenafil in adulterated commercial products. 相似文献
963.
Ariadni Zianna Maja Šumar Ristović Antonis Hatzidimitriou Christos D. Papadopoulos Maria Lalia-Kantouri 《Journal of Thermal Analysis and Calorimetry》2014,118(3):1431-1440
In this study, three novel tetranuclear nickel(II) cubane-type clusters with the general formula [Ni4(L)4(μ3-CH3O)4(CH3OH)4] [L: the anion of 5-methyl-2-hydroxybenzaldehyde (1), 2-hydroxypropiophenone (2), and 2-hydroxybenzophenone (3)] were synthesized and characterized by single-crystal X-ray diffraction analysis. The crystal structure of each compound contains a tetranuclear cubane core [Ni4O4] based on an approximately cubic array of altering nickel and oxygen atoms with intracluster metal–metal separations of 3.04–3.14 Å. Each Ni(II) atom is surrounded by two oxygen atoms from the ligand (L) and by the μ3-CH3O oxygen atom that bridges three Ni atoms of the cubane core. The coordination sphere of Ni is completed with one methanol molecule and making six-coordinate with a distorted octahedral geometry. These complexes were characterized also by spectroscopy (IR and UV–Vis). Simultaneous TG/DTG–DTA techniques were used to analyze their thermal behavior under inert atmosphere, with particular attention to determine their thermal degradation pathways, which was found to be a multi-step decomposition accompanied by the release of the ligand molecules. Finally, the kinetic analysis of the decomposition processes was performed for the first step of complex (3), since only this verifies the requirement of applying an isoconversional method like Kissinger–Akahira–Sunose (KAS). For this step, we found the average value E a = 107.8 ± 4.5 kJ mol?1. 相似文献
964.
The system of ordinary differential equations for the method of the gentlest ascent dynamics (GAD) is tested to determine the saddle points of the potential energy surface of some molecules. The method has been proposed earlier [E and Zhou in Nonlinearity 24:1831 (2011)]. We additionally use the metric of curvilinear internal coordinates. By a number of examples, we explain the possibilities of a GAD curve; it can find the transition state of interest by a gentlest ascent, directly or indirectly, or not. A GAD curve can be a model of a reaction path, if it does not contain a turning point for the energy. We further discuss generalized GAD formulas for the search of saddle points of a higher index. We calculate diverse examples. 相似文献
965.
Structure‐Based Design of Inhibitors of the Aspartic Protease Endothiapepsin by Exploiting Dynamic Combinatorial Chemistry
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Milon Mondal Nedyalka Radeva Dr. Helene Köster Dr. Ahyoung Park Dr. Constantinos Potamitis Dr. Maria Zervou Prof. Dr. Gerhard Klebe Dr. Anna K. H. Hirsch 《Angewandte Chemie (International ed. in English)》2014,53(12):3259-3263
Structure‐based design (SBD) can be used for the design and/or optimization of new inhibitors for a biological target. Whereas de novo SBD is rarely used, most reports on SBD are dealing with the optimization of an initial hit. Dynamic combinatorial chemistry (DCC) has emerged as a powerful strategy to identify bioactive ligands given that it enables the target to direct the synthesis of its strongest binder. We have designed a library of potential inhibitors (acylhydrazones) generated from five aldehydes and five hydrazides and used DCC to identify the best binder(s). After addition of the aspartic protease endothiapepsin, we characterized the protein‐bound library member(s) by saturation‐transfer difference NMR spectroscopy. Cocrystallization experiments validated the predicted binding mode of the two most potent inhibitors, thus demonstrating that the combination of de novo SBD and DCC constitutes an efficient starting point for hit identification and optimization. 相似文献
966.
In Situ Electrodeposition of an Asymmetric Sol–Gel Membrane Based on an Octadecyltrimethoxysilane Langmuir Film
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Maria Hitrik Prof. Ovadia Lev Prof. Daniel Mandler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(38):12104-12113
The unique properties of Langmuir film formation were utilized in assembling a thin skin of an asymmetric membrane. An octadecyltrimethoxysilane (ODTMS) Langmuir monolayer was formed at the air–water interface and served as the substrate for growing a bulky sol–gel polymer in situ. The latter was based on the electrochemical deposition of tetramethoxysilane dissolved in the water subphase by means of horizontal touch electrochemistry. The resultant asymmetric layer that consisted of a thin hydrophobic ODTMS Langmuir film connected to a bulk hydrophilic sol–gel network was studied in situ and ex situ by using various techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy (EIS), scanning electron microscopy, transmission electron microscopy (TEM), and goniometry. We found that a porous hydrophilic film grew on top of a hydrophobic layer as was evident from TEM, contact angle, and EIS analyses. The film thickness and film permeability could be controlled by changing the deposition conditions such as the potential window applied and its duration. Hence, this method offers an alternative approach for assembling asymmetric films for various applications 相似文献
967.
Dr. Antonio Zucca Dr. Luca Maidich Laura Canu Dr. Giacomo L. Petretto Prof. Sergio Stoccoro Prof. Maria Agostina Cinellu Dr. Guy J. Clarkson Dr. Jonathan P. Rourke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(18):5501-5510
Rollover cyclometalation involves bidentate heterocyclic donors, unusually acting as cyclometalated ligands. The resulting products, possessing a free donor atom, react differently from the classical cyclometalated complexes. Taking advantage of a “rollover”/“retro‐rollover” reaction sequence, a succession of oxidative addition and reductive elimination in a series of platinum(II) complexes [Pt(N,C)(Me)(PR3)] resulted in a rare C(sp2)?C(sp3) bond formation to give the bidentate nitrogen ligands 3‐methyl‐2,2′‐bipyridine, 3,6‐dimethyl‐2,2′‐bipyridine, and 3‐methyl‐2‐(2′‐pyridyl)‐quinoline, which were isolated and characterized. The nature of the phosphane PR3 is essential to the outcome of the reaction. This route constitutes a new method for the activation and functionalization of C?H bond in the C(3) position of bidentate heterocyclic compounds, a position usually difficult to functionalize. 相似文献
968.
Franciele Maria Pelissari Paulo José do Amaral Sobral Florencia Cecilia Menegalli 《Cellulose (London, England)》2014,21(1):417-432
Cellulose nanofibers were isolated from banana peel using a combination of chemical treatments, such as alkaline treatment, bleaching, and acid hydrolysis. The suspensions of chemically treated fibers were then passed through a high-pressure homogenizer 3, 5, and 7 times, to investigate the effect of the number of passages on the properties of the resulting cellulose nanofibers. The cellulose nanofibers isolated in this study had a dry basis yield of 5.1 %. Transmission electron microscopy showed that all treatments effectively isolated banana fibers in the nanometer scale. The micrographs of the process steps used to isolate the nanofibers revealed gradual removal of amorphous components. Increasing number of passages in the homogenizer shortened the cellulose nanofibers while furnishing more stable aqueous suspensions with zeta potential values ranging from ?16.1 to ?44.1 mV. All the samples presented aspect ratio in the range of long nanofibers, hence being potentially applicable as reinforcing agents in composites. X-ray diffraction studies revealed that homogenized nanofiber suspensions were more crystalline than non-homogenized suspensions. Fourier transform infrared spectroscopy confirmed that alkaline treatment and bleaching removed most of the hemicellulose and lignin components present in the banana fibers. Thermal analyses revealed that the developed nanofibers exhibit enhanced thermal properties. In general, the nanoparticles isolated from the banana peel have potential application as reinforcing elements in a variety of polymer composite systems. 相似文献
969.
Thermal Ethane Activation by Bare [V2O5]+ and [Nb2O5]+ Cluster Cations: on the Origin of Their Different Reactivities
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Dr. Xiao‐Nan Wu Dr. Shi‐Ya Tang Dr. Hai‐Tao Zhao Dr. Thomas Weiske Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6672-6677
The gas‐phase reactivity of [V2O5]+ and [Nb2O5]+ towards ethane has been investigated by means of mass spectrometry and density functional theory (DFT) calculations. The two metal oxides give rise to the formation of quite different reaction products; for example, the direct room‐temperature conversions C2H6→C2H5OH or C2H6→CH3CHO are brought about solely by [V2O5]+. In distinct contrast, for the couple [Nb2O5]+/C2H6, one observes only single and double hydrogen‐atom abstraction from the hydrocarbon. DFT calculations reveal that different modes of attack in the initial phase of C?H bond activation together with quite different bond‐dissociation energies of the M?O bonds cause the rather varying reactivities of [V2O5]+ and [Nb2O5]+ towards ethane. The gas‐phase generation of acetaldehyde from ethane by bare [V2O5]+ may provide mechanistic insight in the related vanadium‐catalyzed large‐scale process. 相似文献
970.
Juliano Fiorelli Catarina Abdala Gomide Francisco Antonio Rocco Lahr Maria Fátima do Nascimento Diogo de Lucca Sartori Julian Eduardo Mejia Ballesteros Stephen Bonila Bueno Ugo Leandro Belini 《Cellulose (London, England)》2014,21(5):3269-3277
Anatomical and physico-chemical properties of residual natural fibers (sugarcane bagasse, coconut fibers and peanut hulls) were characterized in order to evaluate their potential for use in the production of particleboard. The bulk density was determined by helium pycnometer and the chemical characteristics by using an electronic pH meter (for pH determination) on fibers dissolved in acidic and neutral detergents (to determine the levels of cellulose, hemicellulose and lignin). The anatomical characteristics were established using scanning electron microscopy coupled with an X-ray detector system, as well as energy dispersive X-ray spectroscopy. Results indicated similarities and differences between physico-chemical and anatomical characteristics of the residual lignocellulosic fibers when compared with the Pinus sp. wood commercially employed in particleboard production. Bulk density and pH for residual lignocellulosic fibers and Pinus sp. wood presented analogous values. Similar amounts of cellulose and lignin were identified between waste fibers and Pinus sp. wood. The presence of silica was identified in coconut fiber, peanut hull and sugarcane bagasse waste fibers, and may affect the mechanical characteristics of panels. Coconut and sugarcane bagasse fibers show surface pores with diameters ranging from 1.2 to 2.1 μm, below the 5 μm identified for Pinus sp. wood. Both fibers present pores distributed over their entire surface, whereas peanut hull fibers have no pores on their surface. This characteristic contributes to resin dispersion among particles, reflecting positively on the physical–mechanical properties of the panels. Particleboards produced with residual lignocellulosic fibers present similar physical–mechanical properties to those of Pinus sp. wood panels. 相似文献