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971.
Electrochemical Biosensors Based on Enzymatic Reactor of Silver Solid Amalgam Powder for Measurements in Flow Systems
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An enzymatic reactor based on silver solid amalgam powder was suggested as the main part of biosensors in flow systems for the first time. Biosensors were tested with following enzymes: ascorbate oxidase, glucose oxidase, catalase, tyrosinase and laccase. The current response of each biosensor was optimized with respect to the detection potential, flow rate, the injection and reactor volume. Relative standard deviation for detection with the studied enzymes was found to be in the range of 0.81–2.1 %. The biosensor with the ascorbate oxidase reactor was used for determination of ascorbic acid in the vitamin tablets Celaskon. 相似文献
972.
Alena Pavelkova Pavel Kucharczyk Petr Stloukal Marek Koutny Vladimir Sedlarik 《先进技术聚合物》2014,25(6):595-604
The work presented here investigates the synthesis of poly(lactic acid)–poly(ethylene oxide) diisocyanate chain‐linked copolymer, and its application in the nano‐encapsulation of bioactive compounds. Study was conducted on the effect of the type of chain‐linking agent, along with molecular weight, thermal properties and hydrophilic/hydrophobic behavior, through the methods of gel permeation chromatography, Fourier transform infrared spectroscopy–attenuated total reflectance, differential scanning calorimetry, light scattering, water uptake experimentation, and water contact angle measurements. Nanoparticle formation was performed via a single solvent evaporation process, and the particles obtained were characterized by dynamic light scattering and scanning electron microscopy. Results show the significantly enhanced molecular weight of the final product after the chain‐linking reaction (up to 300,000 g/mol), as well as the non‐linear nature of the sample due to broad polydispersity, ranging from 4–13. The final products exhibited glass transition temperatures of between 30 and 44 °C, while their crystalline quality was either significantly suppressed or a completely amorphous attribute was observed. Nanoparticles in the range of 300 nm that contained metazachlor were successfully prepared, and their releasing behavior exhibited first order release kinetics. A slower rate of release was observed in samples containing 4,4′‐methylenebis(phenyl isocyanate) as a chain‐linker. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
973.
Evgenija A. Djurendić Olivera R. Klisurić Mihály Szécsi Marija N. Sakač Suzana S. Jovanović-Šanta Imre Ignáth Vesna V. Kojić Aleksandar M. Oklješa Marina P. Savić Katarina M. Penov-Gaši 《Structural chemistry》2014,25(6):1747-1758
Tetrakis-, tris-, bis-, and mono salicylic acid derivatives 1–4 were synthesized by reaction of methyl 2-hydroxy benzoate (methyl salicylate) with 2,2-bis (hydroxymethyl) propane-1,3-diol (pentaerythritol) in the presence of sodium. Yields of different salicyloyloxy derivatives were changed by varying the molar ratios of reactants. For compounds 2 and 3, X-ray structure analysis was performed, as well as molecular energy minimization, to define their conformation in terms of their energy minima. Comparison of crystal and energy minimized structures for these two compounds (2 and 3) revealed that the intramolecular hydrogen bonds play an important role, stabilizing conformation of the most part of the molecule. The antioxidant activity and cytotoxicity of the synthesized derivatives were evaluated in a series of in vitro tests, as well as 17β-hydroxysteroid dehydrogenase type 2 inhibition potency. Tetrakis salicyloyloxy derivative 1 expressed the highest antioxidant potency, tris salicyloyloxy derivative 2 was the best inhibitor of 17βHSD2 enzyme, while bis salicyloyloxy derivative 3 showed strong cytotoxicity against prostate and breast cancer cells with no cytotoxicity against healthy cells. 相似文献
974.
Membrane transport proteins are essential for cellular uptake of numerous salts, nutrients and drugs. Bilitranslocase is a transporter, specific for water-soluble organic anions, and is the only known carrier of nucleotides and nucleotide-like compounds. Experimental data of bilitranslocase ligand specificity for 120 compounds were used to construct classification models using counter-propagation artificial neural networks (CP-ANNs) and support vector machines (SVMs). A subset of active compounds with experimentally determined transport rates was used to build predictive QSAR models for estimation of transport rates of unknown compounds. Several modelling methods and techniques were applied, i.e. CP-ANN, genetic algorithm, self-organizing mapping and multiple linear regression method. The best predictions were achieved using CP-ANN coupled with a genetic algorithm, with the external validation parameter QV2 of 0.96. The applicability domains of the models were defined to determine the chemical space in which reliable predictions can be obtained. The models were applied for the estimation of bilitranslocase transport activity for two sets of pharmaceutically interesting compounds, antioxidants and antiprions. We found that the relative planarity and a high potential for hydrogen bond formation are the common structural features of anticipated substrates of bilitranslocase. These features may serve as guidelines in the design of new pharmaceuticals transported by bilitranslocase. 相似文献
975.
The primary goal of this study was to describe and compare the criteria used to assess carcinogenic activity. The statistically-based predictive quantitative structure–activity relationship (QSAR) models based on the counter propagation artificial neural network (CPANN) algorithm, and knowledge-based expert systems based on a decision tree structural alert (SA) approach (Toxtree application), were considered. The integration of the QSAR (CPANN models) and SAR (Toxtree SA application) approach contributed to the mechanistic understanding of the QSAR model considered. The mapping technique inherent to CPANN Kohonen enables us to relate the similarities or dissimilarities within a congeneric set of chemicals with particular SAs for carcinogenicity. The focus of our investigations was the similarities and dissimilarities of the features used in the QSAR and SAR methods. Due to the complexity of the carcinogenic endpoint, the integration of different approaches allows the models to be improved and provides a valuable technique for evaluating the safety of chemicals. 相似文献
976.
Cătălin Tănase Lucia Odochian Tiberius Balaeş Gabriela Lisă Daniel Gherca Aurel Pui 《Journal of Thermal Analysis and Calorimetry》2014,115(1):947-953
This paper is aimed to analyse the thermal behaviour in air of edible mushrooms through nonisothermal (TG, DTG, DTA) and calorimetric (Berthelot calorimeter) methods. The studied mushrooms were Pleurotus ostreatus spontaneously grown and from culture and Agaricus bisporus from culture, currently used in alimentation but insufficiently investigated from this point of view. The analysis of TG–DTG–DTA curves has indicated that the degradation mechanism is complex and characteristic to every species and major differences between the cap and the stipe of investigated mushrooms have not been recorded. These species are thermally stable in the range of 30–160 °C. The thermal stability in terms of initial degradation temperature (T i °C) and the temperature corresponding to the conversion grade (T α=0.03 °C) indicate that the stipe has a thermal stability close to the cap one and that the cultivated mushrooms are more thermally stable than those spontaneously grown. The obtained results concerning the combustion of the sample using Berthelot calorimeter are in accordance with the TG–DTG–DTA analysis. The residue obtained is a measure of the mineral content and is quantitatively close. 相似文献
977.
Nikola Peřinka Markéta Držková Milena Hajná Bohumil Jašúrek Petra Šulcová Tomáš Syrový Marie Kaplanová Jaroslav Stejskal 《Journal of Thermal Analysis and Calorimetry》2014,116(2):589-595
The polyaniline dispersions stabilized with poly(N-vinylpyrrolidone) (PANI/PVP) were synthesized by oxidative polymerization with different mass ratios of PANI and PVP and different molar concentrations of the components in the polymerization mixture. The composite powders prepared from colloidal PANI/PVP dispersions were characterized by thermogravimetry and differential thermal analysis. The change in the ratio of PANI and PVP as well as the starting molar concentrations of aniline hydrochloride and oxidant has influence on the resulting properties of the dispersions. Concerning the doping, the results show that PANI/PVP powders are stable up to approximately 160 °C. Degradation of polymer chains starts at temperatures above 250 °C. The PANI/PVP composite powders with lower content of PANI exhibit slightly higher thermal stability. Further, colloidal PANI/PVP dispersions were screen-printed on aluminum foil for infrared spectroscopic characterization and on poly(ethylene terephthalate) foil for electrical measurements. The sheet resistance of printed layers measured by two-point probe was of the order of tens to thousands of kΩ sq?1. The influence of both the change in the composition and the drying temperature is discussed. 相似文献
978.
Jana Holubová Zdeněk Černošek Eva Černošková 《Journal of Thermal Analysis and Calorimetry》2014,116(2):699-702
Thermal properties and structure of bulk glasses of (As2S3)1?x(Sb4S4)x system (x varies from 0 to 60 mol%) were studied by differential scanning calorimetry and Raman spectroscopy. It was found that with increasing Sb content the glasses can be sorted out to the three groups. The structure of glasses with x ≤ 10 is build-up mainly from AsS3/2 pyramidal units and the well-known crystallization resistance of As2S3 can explain the reluctance of these undercooled liquids against crystallization. In glasses with a higher content of antimony, i.e., 10 < x ≤ 30 mol%, the vibration characteristics of As4S4 clusters appear. Undercooled melts of these glasses crystallize forming both β-As4S4 and high-temperature phases of Sb2S3. Structure of glasses with the highest antimony content (x > 30 mol%) is based on SbS3/2 structural units significantly lowering stability of their undercooled melts from which only Sb2S3 crystallizes. 相似文献
979.
Petr Brázda Eva Večerníková Eva Pližingrová Adriana Lančok Daniel Nižňanský 《Journal of Thermal Analysis and Calorimetry》2014,117(1):85-91
Thermal behavior of highly crystalline ε-Fe2O3 nanoparticles of different apparent crystallite sizes was characterized using thermogravimetry, differential thermal analysis, and analysis of evolved gas by mass spectrometry. Phase composition of the samples was monitored ex situ by X-ray powder diffraction. The results show that the thermal stability of this metastable iron oxide polymorph decreases with increasing particle size. For the particle diameter of 19(2) nm, the transformation temperature was equal to 794(5) °C, while for 28(2) nm only 755(10) °C. Surface of the nanoparticles contained adsorbed water and carbon dioxide. Elimination of these species proceeds in two steps. Water is removed at temperatures below 200 °C and CO2 in the temperature range between 200 and 450 °C. 相似文献
980.
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