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101.
Butkovskaya NI Pouvesle N Kukui A Mu Y Le Bras G 《The journal of physical chemistry. A》2006,110(21):6833-6843
The mechanism of the gas-phase reaction of OH radicals with hydroxyacetone (CH3C(O)CH2OH) was studied at 200 Torr over the temperature range 236-298 K in a turbulent flow reactor coupled to a chemical ionization mass-spectrometer. The product yields and kinetics were measured in the presence of O2 to simulate the atmospheric conditions. The major stable product at all temperatures is methylglyoxal. However, its yield decreases from 82% at 298 K to 49% at 236 K. Conversely, the yields of formic and acetic acids increase from about 8% to about 20%. Other observed products were formaldehyde, CO2 and peroxy radicals HO2 and CH3C(O)O2. A partial re-formation of OH radicals (by approximately 10% at 298 K) was found in the OH + hydroxyacetone + O2 chemical system along with a noticeable inverse secondary kinetic isotope effect (k(OH)/k(OD) = 0.78 +/- 0.10 at 298 K). The observed product yields are explained by the increasing role of the complex formed between the primary radical CH3C(O)CHOH and O2 at low temperature. The rate constant of the reaction CH3C(O)CHOH + O2 --> CH3C(O)CHO + HO2 at 298 K, (3.0 +/- 0.6) x 10(-12) cm3 molecule(-1) s(-1), was estimated by computer simulation of the concentration-time profiles of the CH3C(O)CHO product. The detailed mechanism of the OH-initiated oxidation of hydroxyacetone can help to better describe the atmospheric oxidation of isoprene, in particular, in the upper troposphere. 相似文献
102.
Rafael Doležal Natálie Karásková Karel Musil Martin Novák Nadezhda V. Maltsevskaya Dávid Maliňák 《Analytical letters》2018,51(15):2401-2414
The biological activity of drugs on organisms is associated with the pharmacokinetic properties, such as the ability to penetrate through environments of varying polarity such as cellular organelles. In this area, particular attention is turned to the physicochemical properties that determine the potential of drugs to pass across the blood–brain barrier and thus to act on the central nervous system. In this study, special effort has been devoted to the simulation of passive diffusion of seven drugs (propranolol, ibuprofen, atenolol, promazine, chlorpromazine, imipramine, and desipramine) through the blood–brain barrier by high-performance liquid chromatography (HPLC) using a column with an immobilized artificial membrane. Gradient reverse elution was used to develop a linear correlation model for the capacity factors kIAM and the in vivo logarithmic values of brain-to-blood drug concentration ratios (log BB) with R of 0.9851. Eleven additional pharmaceuticals were determined by the same method to predict their potential to penetrate the blood–brain barrier. The reported analytical method represents an alternative tool for rapid and noninvasive assessment of the absorption properties of chemicals, especially for the development of novel drugs. The retention of the studied compounds on the immobilized artificial membrane column was also compared with three other C18-based stationary phases. Herein, the results of the HPLC determination of drugs using an immobilized artificial membrane are briefly discussed with respect to a general application of the method for evaluating a broader spectrum of pharmaceutical compounds. 相似文献
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Enchev Venelin Markova Nadezhda Marinov Marin Stoyanov Neyko Rogojerov Marin Ugrinov Angel Wawer Iwona Pisklak Dariusz Maciej 《Structural chemistry》2017,28(3):757-772
Structural Chemistry - The synthesis and structure elucidation of two new compounds, 2-(methylthio)-1,3-diazaspiro[4.4]non-2-ene-4-one (1) and 2-(methylthio)-1,3-diazaspiro[4.4]non-2-ene-4-thione... 相似文献
105.
Dina Orazbayeva Bulat Kenessov Jacek A. Koziel Dayana Nassyrova Nadezhda V. Lyabukhova 《Chromatographia》2017,80(8):1249-1256
There is a great demand for simple, fast and accurate methods for quantification of volatile organic contaminants in soil samples. Solid-phase microextraction (SPME) has a huge potential for this purpose, but its application is limited by insufficient accuracy caused by a matrix effect. The aim of this research was to develop the method for BTEX quantification in soil using combined standard addition (SA) and internal standard (IS) calibration. Deuterated benzene (benzene-d6) was used as the internal standard for all analytes. The optimized method includes spiking replicate samples with different concentrations of BTEX standards and the same concentration of benzene-d6, equilibration of soil samples at 40 °C during 2 h, and SPME–GC–MS analysis. Precision and accuracy of IS and SA methods were compared on different soil matrices. Combined SA + IS method provided more precise calibration plots compared to the conventional SA calibration. The SA + IS calibration provided more precise and accurate results compared with a reference method based on solvent extraction followed by GC–MS when applied to BTEX quantification in real soil samples (spiked with diesel fuel and aged). Recoveries of BTEX from soil samples spiked with known concentrations of analytes using the developed method were in the range of 73–130% with RSD values less than 15% for all BTEX. The proposed simultaneous standard addition and internal standard approach can be advantageous and adopted for improved quantification of other toxic VOCs in soil. 相似文献
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Nadezhda A. Ivanova 《Tetrahedron letters》2008,49(43):6179-6181
Isomeric mixtures of bromo- and iodohydrins produced via bromohydroxylation and iodohydroxylation of exo-methylene derivative 2 undergo an intramolecular aldol cyclization-dehydration sequence under Reformatsky reaction conditions to give cyclopentenone 1. 相似文献