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741.
742.
An improved synthesis for the preparation of diastereomerically pure dihydrothebainone (1) from thebaine (3) is reported. A 41% overall yield was realized over three steps via direct transformation of dihydrothebaine-Ø (4) to thebainone-A (6) with 6N HCl. 相似文献
743.
Marian Żenkiewicz Agnieszka Richert Rafał Malinowski Krzysztof Moraczewski 《Polymer Testing》2013,32(2):209-214
Results of investigation of mass losses, geometrical surface structure changes and variations in crystallinity of poly(lactic acid) (PLA), poly(?-caprolactone) (PCL) and commercially available material (PHB) consisting of poly(3,4-hydroxybutyrate) and poly(lactic acid) are presented. These structural changes occurred due to degradation of these polymers in the presence of the following enzymes: proteinase K, protease, esterase or lipase. Independently of the enzyme type, the largest mass loss was found for PLA and the smallest for PHB. Thus, under the experimental conditions, the processes of enzymatic degradation proceeded most rapidly in PLA, more slowly in PCL, and the most slowly in PHB. It was also found that proteinase K caused the largest mass losses, protease caused smaller mass losses, and both esterase and lipase produced the least mass losses, while lipase did not bring about mass loss in PHB. Images of surfaces of individual samples, obtained by scanning electron microscopy (SEM), indirectly confirmed the results of the mass loss examination. Crystallinity of the studied polyesters increased with degradation in the presence of proteinase K and protease, while changes in the crystallinity due to esterase and lipase were not observed. The presented results illustrate well the relative susceptibilities of the individual polyesters toward degradation induced by various enzymes. 相似文献
744.
The effects of wall-normal single point oscillations in turbulent boundary layers at very high Reynolds number are investigated by numerical simulation. The impact on the friction drag and on the turbulent structures is analyzed. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
745.
Dr. Marian Olaru Ralf Kather Dr. Emanuel Hupf Dr. Enno Lork Dr. Stefan Mebs Prof. Dr. Jens Beckmann 《Angewandte Chemie (International ed. in English)》2018,57(20):5917-5920
Transmetallation of Pb(OAc)4 with R2Hg ( 1 ), followed by treatment with HCl in Et2O, provided RPbCl3 ( 2 ), the first kinetically stabilized monoorganolead trihalide that resists reductive elimination under ambient conditions. The kinetic stabilisation relies on an intramolecularly coordinating O‐donor substituent (R=6‐Ph2P(O)‐Ace‐5‐). The gram‐scale preparation of 2 was key for the synthesis of unsymmetrically substituted diaryllead dichlorides RR′PbCl2 ( 3 a , R′=Ph; 3 b , R′=4‐MeOC6H4; 3 c , R′=4‐Me2NC6H4). 相似文献
746.
Marian Rauser Daniel P. Warzecha Prof. Dr. Meike Niggemann 《Angewandte Chemie (International ed. in English)》2018,57(20):5903-5907
In analogy to the classical reaction of C?B bonds with peroxides, the first oxidative functionalization of aminoboranes through a 1,2‐N migration was realized. Readily available aliphatic nitro compounds are thereby transformed into N‐ and O‐functionalized hydroxylamines in a single synthetic operation. Addition of hazardous peroxides is avoided. Instead, the insertion of O2, as the terminal oxidant, into Zn?C bonds provides the necessary peroxides. The required zinc organyls, in turn, are formed through a boron‐to‐zinc exchange, from an organoboronic ester byproduct of the nitro‐to‐aminoborane transformation. 相似文献
747.
Dr. Marian Olaru Daniel Duvinage Dr. Enno Lork Dr. Stefan Mebs Prof. Dr. Jens Beckmann 《Angewandte Chemie (International ed. in English)》2018,57(32):10080-10084
Kinetically stabilized congeners of carbenes, R2C, possessing six valence electrons (four bonding electrons and two non‐bonding electrons) have been restricted to Group 14 elements, R2E (E=Si, Ge, Sn, Pb; R=alkyl or aryl) whereas isoelectronic Group 15 cations, divalent species of type [R2E]+ (E=P, As, Sb, Bi; R=alkyl or aryl), were unknown. Herein, we report the first two examples, namely the bismuthenium ion [(2,6‐Mes2C6H3)2Bi][BArF4] ( 1 ; Mes=2,4,6‐Me3C6H2, ArF=3,5‐(CF3)2C6H3) and the stibenium ion [(2,6‐Mes2C6H3)2Sb][B(C6F5)4] ( 2 ), which were obtained by using a combination of bulky meta‐terphenyl substituents and weakly coordinating anions. 相似文献
748.
Alexander Krok Marian Peciar Roman Fekete 《Particuology》2014,(5):116-131
During the production of pharmaceutical tablets using powder compaction, certain common problems can occur, such as sticking, tearing, cutting, and lamination. In the past, the compressibility of the powder was calculated only along the axis of the device; consequently, critical areas of the material throughout the volume could not be identified. Therefore, finite element method (FEM) can be used to predict these defects in conjunction with the use of an appropriate constitutive model. This article summarizes the current research in the field of powder compaction, describes the Drucker-Prager Cap model calibration procedure and its implementation in FEM, and also examines the mechanical behavior of powder during compaction. In addition, the mechanical behavior of pharmaceutical powders in relation to changes in friction at the wall of the system is examined, and the dependence of lubrication effect on the geometry of the compaction space is also investigated. The influence of friction on the compaction process for the flat-face, fiat-face radius edge, and standard convex tablets is examined while highlighting how the effects of friction change depending on the shape of these tablets. 相似文献
749.
In this paper we assess the efficacy of a laser system, emitting at 635 nm, in methylene blue–mediated photodynamic inactivation of Pseudomonas aeruginosa that contaminates wounds, using diffuse reflectance spectrometry. The spectral plots of the contaminated wounds were recorded before and after laser irradiation, and the refractive index and extinction coefficient were determined by Kramers-Kronig analysis of reflectance spectra. The changes in optical parameter values after the treatment were corroborated with bacterial counts determined by bacteriological examination. The results revealed that the combined treatment 635-nm laser–methylene blue is an efficient way to destroy the bacteria that contaminate the wounds. 相似文献
750.
Marian Olszowy Ewa Markiewicz Czesław Pawlaczyk Ewa Nogas-Ćwikiel 《Phase Transitions》2013,86(11-12):1099-1106
Dielectric response of poly(vinyl chloride), (PVC), loaded with different amount of Ba0.3Na0.7Ti0.3Nb0.7O3 (BNTN) ceramic powders was investigated in frequency range 100 Hz–1 MHz and temperature range 100–450 K. Ceramic solid solution of barium titanate and sodium niobate with composition Ba0.3Na0.7Ti0.3Nb0.7O3 was obtained from BaCO3, TiO2, Na2CO3 and Nb2O5 by conventional method. Powders were prepared by grinding of ceramics. The obtained ceramics, used to produce BNTN–PVC composites, are characterized by the relaxor behaviour with a broad peak of dielectric permittivity ε′ at T m ≈ 230 K. The microstructure of the powders was observed and the grain size was estimated using scanning electron microscope Hitachi S-4700. The EDS analysis confirms the qualitative and quantitative chemical composition of powders and ceramics. The BNTN–PVC composite samples of 0-3 connectivity were prepared from ceramic and polymer powders by hot-pressing method. The dielectric response of the composites displays features originated from the PVC polymer modified by those of BNTN ceramics. The relaxation time of the α-process of PVC obeys the Vogel–Fulcher law and decreases with increasing volume fraction of the ceramics. 相似文献