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991.
Asymmetric reduction of ketimines 1 with trichlorosilane can be catalyzed by N-methylvaline-derived Lewis-basic formamides 3a-d with high enantioselectivity (< or =95% ee) and low catalyst loading (1-5 mol %) at room temperature in toluene. Appending a fluorous tag, as in 5a-c, simplifies the isolation procedure, while preserving high enantioselectivity (< or =92% ee). 相似文献
992.
A combined use of ephedrine and cinchonine as resolving agents enabled facile resolution of racemic tert-butylphenylphosphinous acid-borane (1) into the two enantiomers in ca. 31-32% yield each. The resolved 1 served as a model substrate to study stereoselective synthetic transformations of phosphinous acid-boranes yielding optically active phosphinite-borane, boranatophosphinous-sulfonic anhydride, secondary phosphine-borane, tertiary phosphine-borane, secondary phosphine oxide, and phosphinic halides. By the judicious choice of the reaction paths, either enantiomer of tert-butylphenylphosphine-borane and of tert-butylmethylphenylphosphine-borane could be stereoselectively obtained from a single enantiomer of 1. 相似文献
993.
A series of RuII or FeII trischelate complex salts containing N-methyl/aryl-2,2':4,4' ':4',4' '-quaterpyridinium ligands that has previously been subjected to quadratic nonlinear optical studies (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 13399) has now been investigated for two-photon absorbing behavior. Z-scan measurements using a 750 nm laser afford reasonably large two-photon absorption (2PA) cross-sections sigma2 of ca. 62-180 GM for the RuII complexes, but only very weak 2PA is observed for the FeII compounds. The excited-state and 2PA properties of the representative chromophore [RuII(Me2Qpy2+)3]8+ (Me2Qpy2+=N' ',N' '-dimethyl-2,2':4,4' ':4',4' '-quaterpyridinium) have also been investigated by using semiempirical intermediate neglect of differential overlap/multireference-determinant single and double configuration interaction computations with the optimized geometry obtained via density functional theory. The calculated sigma2 value of ca. 624 GM at 1.70 eV for this metal-to-ligand charge-transfer chromophore is about 10 times larger than that obtained from the Z-scan studies. 相似文献
994.
Magdalena Szutkowska Marcin Podsiado Tomasz Sadowski Pawe Figiel Marek Boniecki Daniel Pietras Tomasz Polczyk 《Molecules (Basel, Switzerland)》2021,26(5)
Ti(C,N)-reinforced alumina-zirconia composites with different ratios of C to N in titanium carbonitride solid solutions, such as Ti(C0.3,N0.7) (C:N = 30:70) and Ti(C0.5,N0.5) (C:N = 50:50), were tested to improve their mechanical properties. Spark plasma sintering (SPS) with temperatures ranging from 1600 °C to 1675 °C and pressureless sintering (PS) with a higher temperature of 1720 °C were used to compare results. The following mechanical and physical properties were determined: Vickers hardness, Young’s modulus, apparent density, wear resistance, and fracture toughness. A composite with the addition of Ti(C0.5,N0.5)n nanopowder exhibited the highest Vickers hardness of over 19.0 GPa, and its fracture toughness was at 5.0 Mpa·m1/2. A composite with the Ti(C0.3,N0.7) phase was found to have lower values of Vickers hardness (by about 10%), friction coefficient, and specific wear rate of disc (Wsd) compared to the composite with the addition of Ti(C0.5,N0.5). The Vickers hardness values slightly decreased (from 5% to 10%) with increasing sintering temperature. The mechanical properties of the samples sintered using PS were lower than those of the samples that were spark plasma sintered. This research on alumina–zirconia composites with different ratios of C to N in titanium carbonitride solid solution Ti(C,N), sintered using an unconventional SPS method, reveals the effect of C/N ratios on improving mechanical properties of tested composites. X-ray analysis of the phase composition and an observation of the microstructure was carried out. 相似文献
995.
Karol Sidor Tomasz Berniak Piotr tka Anna Rokiciska Marek Michalik Piotr Kutrowski 《Molecules (Basel, Switzerland)》2021,26(6)
The polycondensation of resorcinol and formaldehyde in a water–ethanol mixture using the adapted Stöber method was used to obtain resol resins. An optimization of synthesis conditions and the use of an appropriate stabilizer (e.g., poly(vinyl alcohol)) resulted in spherical grains. The resins were carbonized in the temperature range of 600–1050 °C and then chemically activated in an aqueous HNO3 solution, gaseous ammonia, or by an oxidation–reduction cycle (soaking in a HNO3 solution followed by treatment with NH3). The obtained carbons were characterized by XRD, the low-temperature adsorption of nitrogen, SEM, TGA, and XPS in order to determine degree of graphitization, porosity, shape and size of particles, and surface composition, respectively. Finally, the materials were tested in phenol adsorption. The pseudo-second order model perfectly described the adsorption kinetics. A clear correlation between the micropore volume and the adsorption capacity was found. The content of graphite domains also had a positive effect on the adsorption properties. On the other hand, the presence of heteroatoms, especially oxygen groups, resulted in the clogging of the pores and a decrease in the amount of adsorbed phenol. 相似文献
996.
The pH-dependent surface charging of tellurium (IV) oxide has been studied. The isoelectric point (IEP) of tellurium (IV) oxide was determined by microelectrophoresis in various 1-1 electrolytes over a concentration range of 0.001–0.1 M. In all electrolytes studied and irrespective of their concentration the zeta potential of TeO2 was negative over the pH range 3–12. In other words the IEP of TeO2 is at pH below 3 (if any). TeO2 specifically adsorbs ionic surfactants, and their presence strongly affects the zeta potential. In contrast the effect of multivalent inorganic ions on the zeta potential of TeO2 is rather insignificant (no shift in the IEP). In this respect TeO2 is very different from metal oxides. 相似文献
997.
Dorota aewska Paula Zarba Justyna Gody Agata Doroz-Ponka Annika Frank David Reiner-Link Marek Bajda Dorota Stary Szczepan Mogilski Agnieszka Olejarz-Maciej Maria Kaleta Holger Stark Barbara Malawska Katarzyna Kie-Kononowicz 《Molecules (Basel, Switzerland)》2021,26(12)
Neurodegenerative diseases, e.g., Alzheimer’s disease (AD), are a key health problem in the aging population. The lack of effective therapy and diagnostics does not help to improve this situation. It is thought that ligands influencing multiple but interconnected targets can contribute to a desired pharmacological effect in these complex illnesses. Histamine H3 receptors (H3Rs) play an important role in the brain, influencing the release of important neurotransmitters, such as acetylcholine. Compounds blocking their activity can increase the level of these neurotransmitters. Cholinesterases (acetyl- and butyrylcholinesterase) are responsible for the hydrolysis of acetylcholine and inactivation of the neurotransmitter. Increased activity of these enzymes, especially butyrylcholinesterase (BuChE), is observed in neurodegenerative diseases. Currently, cholinesterase inhibitors: donepezil, rivastigmine and galantamine are used in the symptomatic treatment of AD. Thus, compounds simultaneously blocking H3R and inhibiting cholinesterases could be a promising treatment for AD. Herein, we describe the BuChE inhibitory activity of H3R ligands. Most of these compounds show high affinity for human H3R (Ki < 150 nM) and submicromolar inhibition of BuChE (IC50 < 1 µM). Among all the tested compounds, 19 (E153, 1-(5-([1,1′-biphenyl]-4-yloxy)pentyl)azepane) exhibited the most promising in vitro affinity for human H3R, with a Ki value of 33.9 nM, and for equine serum BuChE, with an IC50 of 590 nM. Moreover, 19 (E153) showed inhibitory activity towards human MAO B with an IC50 of 243 nM. Furthermore, in vivo studies using the Passive Avoidance Task showed that compound 19 (E153) effectively alleviated memory deficits caused by scopolamine. Taken together, these findings suggest that compound 19 can be a lead structure for developing new anti-AD agents. 相似文献
998.
Secondary metabolites of fungi can be responsible for allergies; therefore, the identification of compounds produced by these organisms is very important. Fungi produce large amounts of secondary metabolites, which belong to groups of chemicals such as: dicarboxylic acids, hydroxy acids, alcohols, hydrocarbons, esters, fatty acids, sterols, amino acids and mycotoxins. The presence of all these compounds in human proximity contributes to many diseases. Therefore, the aim of the study was a qualitative and quantitative analysis of hydroxy and dicarboxylic acids produced by fungi occurring in student hostel in Poland, in the province of Pomerania. The following species of fungi were subjected to extraction: Aspergillus niger, Aspergillus fumigatus, Aspergillus candidus, Rhizopus sp., Geotrichum candidum, and Penicillium chrysogenum. A mixture of ethyl acetate and methanol was used for the extraction. The obtained extracts were further analyzed by gas chromatography mass spectrometry (GC–MS). In all samples of fungi, the presence of a total of 22 acids, including 13 dicarboxylic and 9 hydroxy acids, was confirmed. Most acids (17 different acids) were identified in A. fumigatus. Only 10 acids were identified in the mycelium of G. candidum and A. niger. Acids which were identified in all samples of the mycelium were 22-hydroxydocosanoic acid, 24-hydroxytetracosanoic acid and adipic acid. The most abundant compounds were 22-hydroxydocosanoic acid in A. fumigatus, A. candidus, Rhizopus sp., G. candidum and P. chrysogenum, and succinic acid in A. niger. More experiments are needed to understand the physiological role of hydroxy and dicarboxylic acids. We hope that our results are an important contribution to further studies on the human health. 相似文献
999.
In the paper, a Lagrange optimal control problem governed by a fractional Dirichlet problem with the Riemann–Liouville derivative is considered. To begin with, based on some variational method, the existence and continuous dependence of solution to the aforementioned Dirichlet problem is investigated. Then, continuous dependence is applied to show the existence of optimal solution to the Lagrange problem. An important point is that the solution to Dirichlet problem does need to be unique; therefore, the above dependence should be understood as a continuity of some multifunction—the concept of the Kuratowski–Painlevé limit of the sequence of sets is used to formulate this property. 相似文献
1000.
Marek Arendarczyk 《Extremes》2017,20(2):451-474
In this paper, we study the asymptotic behavior of supremum distribution of some classes of iterated stochastic processes \(\{X(Y(t)) : t \in [0, \infty )\}\), where \(\{X(t) : t \in \mathbb {R} \}\) is a centered Gaussian process and \(\{Y(t): t \in [0, \infty )\}\) is an independent of {X(t)} stochastic process with a.s. continuous sample paths. In particular, the asymptotic behavior of \(\mathbb {P}(\sup _{s\in [0,T]} X(Y (s)) > u)\) as \(u \to \infty \), where T>0, as well as \(\lim _{u\to \infty } \mathbb {P}(\sup _{s\in [0,h(u)]} X(Y (s)) > u)\), for some suitably chosen function h(u) are analyzed. As an illustration, we study the asymptotic behavior of the supremum distribution of iterated fractional Brownian motion process. 相似文献