排序方式: 共有193条查询结果,搜索用时 15 毫秒
81.
Experimental and Theoretical DFT Study on Synthesis of Sterically Crowded 2,3,3,(4)5‐Tetrasubstituted‐4‐nitroisoxazolidines via 1,3‐Dipolar Cycloaddition Reactions Between Ketonitrones and Conjugated Nitroalkenes
下载免费PDF全文
![点击此处可从《Journal of heterocyclic chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Radomir Jasiński Kamila Mróz Agnieszka Kącka 《Journal of heterocyclic chemistry》2016,53(5):1424-1429
1,3‐Dipolar cycloaddition reactions between ketonitrones ( 1a , 1b , 1c , 1d , 1e ) and β‐substituted nitroalkenes ( 2a , 2b , 2c , 2d ) proceed under mild conditions, with complete regioselectivity, and lead with high yields to sterically crowded 2,3,3,5‐tetrasubstituted‐4‐nitroisoxazolidines ( 3a , 3b , 3c , 3d , 3e , 3f ). Reaction course may be interpreted on the basis of nature of local, nucleophile–electrophile interactions. Moreover, density functional theory (DFT) simulations of reaction paths suggest that these reactions should be considered as polar, “one‐step two‐stage” cycloadditions. Subsequently, it has been found that similar reactions between ketonitrones and α‐substituted nitroalkenes do not allow to obtain the expected 2,3,3,4‐tetrasubstituted‐4‐nitroisoxazolidines. 相似文献
82.
Ray Asit Jena Sudipta Sahoo Ambika Kamila Pradeep Kumar Nayak Sanghamitra Panda Pratap Chandra 《Chemistry of Natural Compounds》2021,57(6):1150-1152
Chemistry of Natural Compounds - 相似文献
83.
Kamila Saasiska Maciej Celiski Kamila Mizera Mateusz Barczewski Pawe Kozikowski Micha K. Leszczyski Agata Domaska 《Molecules (Basel, Switzerland)》2021,26(4)
In this paper, the fire behavior of unsaturated polyester resin (UP) modified with L-histidinium dihydrogen phosphate-phosphoric acid (LHP), being a novel intumescent fire retardant (IFR), was investigated. Thermal and thermomechanical properties of the UP with different amounts of LHP (from 10 to 30 wt. %) were determined by thermogravimetric analysis (TG) as well as dynamic mechanical thermal analysis (DMTA). Reaction to small flames was studied by horizontal burning (HB) test, while fire behavior and smoke emission were investigated with the cone calorimeter (CC) and smoke density chamber. Further, the analysis of volatile products was conducted (TGA/FT-IR). It was observed that the addition of LHP resulted in the formation of carbonaceous char inhibiting the thermal decomposition, burning rate and smoke emission. The most promising results were obtained for the UP containing 30 wt. % of LHP, for which the highest reduction in maximum values of heat release rate (200 kW/m2) and total smoke release (3535 m2/m2) compared to unmodified polymer (792 kW/m2 and 6895 m2/m2) were recorded. However, some important disadvantage with respect to water resistance was observed. 相似文献
84.
Kamila Bendová 《Archive for Mathematical Logic》2001,40(1):19-23
Even if the ordering of all natural number is (known to be) not definable from multiplication of natural numbers and ordering
of primes, there is a simple axiom system in the language such that the multiplicative structure of positive integers has a unique expansion by a linear order coinciding with the
standard order for primes and satisfying the axioms – namely the standard one.
Received: 3 December 1998 相似文献
85.
Ekaterina М. Zueva Мaria М. Petrova Aliia V. Shamsieva Kamila R. Trigulova Elvira I. Musina Robert R. Fayzullin Artem S. Bogomyakov Victor I. Ovcharenko Andrey A. Karasik 《International journal of quantum chemistry》2020,120(8):e26145
A combination of experimental (SQUID magnetometry) and quantum-chemical (BS-DFT, CASSCF(n,m)/NEVPT2, DDCI3) methods is used to probe the influence of terminal ligands on magnetic exchange coupling in the series of [Cu2(μ2-OAc)4L2] complexes with O-donor terminal ligands extended by two novel complexes containing phosphine oxide ligands. The possibilities and limitations of these approaches are discussed. The influence of terminal ligands on magnetic superexchange interaction was quantified by two contributions—the first contribution is associated with structural changes within the {Cu(μ2-OAc)4Cu} core, while the second contribution is due to the difference in the electronic influence of different terminal ligands at a given core geometry. Both contributions were found to be approximately of the same order of magnitude. These results indicate that magnetic exchange coupling, known to be highly sensitive to the distortions in core geometry, is not solely determined by the core structure. Our findings are consistent with the fact that various one- and multiparameter magnetostructural correlations reported in the literature have only a qualitative predictive capability. 相似文献
86.
Agata G?uszyńska Kamila Bajor Izabella Czerwińska Dominika Kalet Bernard Juskowiak 《Tetrahedron letters》2010,51(41):5415-5418
Two new ligands based on anthracene or carbazole planar skeletons, and a phenyloxazoline moiety linked by a vinyl bridge are synthesized as potential DNA-interacting drugs. Their spectral characteristics and DNA binding affinity are assessed. 相似文献
87.
Kamila Šťastná Vít Fiala Jan John 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(3):735-739
Because of the energy loss of α-particles by self-absorption, α-spectrometry requires thin, uniform, and nearly weightless
samples. Several methods exist for sample preparation, e.g., electrodeposition or co-precipitation. Unfortunately, the methods
yielding the best energy resolution are not always quantitative and are usually relatively demanding and time-consuming. This
fact makes application of α-spectrometry for screening tests with radiotracers complicated. For its simplicity and fastness,
the possibility to prepare samples for α-spectrometry by direct evaporation of simple aliquots of aqueous or organic solutions
and the influence of the presence of volatile organic diluent or tensioactive agent was investigated. Also, the influence
of coating the samples with Mylar film was evaluated. The sample preparation techniques were compared based on the counting
efficiency and energy resolution achieved. The performance of the selected method was tested on assessment of the efficiency
of americium extraction by BTBP (bis-triazine-bipyridine) extractant. 相似文献
88.
Tomas Cajka Chris Sandy Veronika Bachanova Lucie Drabova Kamila Kalachova Jana Pulkrabova Jana Hajslova 《Analytica chimica acta》2012
In this work, a new rapid method for the determination of 135 pesticide residues in green and black dry tea leaves and stalks employing gas chromatography coupled to tandem mass spectrometry (GC–MS/MS) with a triple quadrupole was developed and validated. A substantial simplification of sample processing prior to the quantification step was achieved: after addition of water to a homogenised sample, transfer of analytes into an acetonitrile layer was aided by the addition of inorganic salts. Bulk co-extracts, contained in the crude organic extract obtained by partition, were subsequently removed by liquid–liquid extraction using hexane with the assistance of added 20% (w/w) aqueous NaCl solution. The importance of matrix hydration prior to the extraction for achieving good recoveries was demonstrated on tea samples with incurred pesticide residues. For most of the analytes, recoveries in the acceptable range of 70–120% and repeatabilities (relative standard deviations, RSDs) ≤20% were achieved for both matrices at spiking levels of 0.01, 0.1 and 1 mg kg−1. Under optimised GC–MS/MS conditions, most of the analytes gave lowest calibration level ≤0.01 mg kg−1, permitting the control at the maximum residue levels (MRLs) laid down in Regulation (EC) No 396/2005. The developed method was successfully applied to the determination of pesticide residues in real tea samples. 相似文献
89.
Barbara Grzeszczyk Kamila Poławska Yasser M. Shaker Sebastian Stecko Adam Mames Magdalena Woźnica Marek Chmielewski Bartłomiej Furman 《Tetrahedron》2012,68(52):10633-10639
Kinugasa reactions between terminal acetylenes and six-membered ring nitrones when one or both components are chiral, proceed in a low to moderate yield and with a high diastereoselectivity affording mostly one, dominant β-lactam product. The first step of the reaction is controlled by the configuration of the nitrone, whereas the protonation of the C-7 center of the carbacepham skeleton in the second step depends on: a) the configuration of the bridgehead carbon atom formed in the first step, b) epimerization process in the presence of a base, and c) on the configuration of the stereogenic center in the acetylenic partner. In the case of the nitrone derived from dihydroisoquinoline, the reaction proceeds in a more complex way affording not only β-lactams, but also products derived from the alternative regio-1,3-cycloaddition, or nucleophilic addition of the acetylene to the double bond of the nitrone. 相似文献
90.
Anna Palko-abuz Maria Baszczyk Kamila
roda-Pomianek Olga Wesoowska 《Molecules (Basel, Switzerland)》2021,26(15)
Isobavachalcone (IBC) is an active substance from the medicinal plant Psoralea corylifolia. This prenylated chalcone was reported to possess antioxidative, anti-inflammatory, antibacterial, and anticancer activities. Multidrug resistance (MDR) associated with the over-expression of the transporters of vast substrate specificity such as ABCB1 (P-glycoprotein) belongs to the main causes of cancer chemotherapy failure. The cytotoxic, MDR reversing, and ABCB1-inhibiting potency of isobavachalcone was studied in two cellular models: human colorectal adenocarcinoma HT29 cell line and its resistant counterpart HT29/Dx in which doxorubicin resistance was induced by prolonged drug treatment, and the variant of MDCK cells transfected with the human gene encoding ABCB1. Because MDR modulators are frequently membrane-active substances, the interaction of isobavachalcone with model phosphatidylcholine bilayers was studied by means of differential scanning calorimetry. Molecular modeling was employed to characterize the process of membrane permeation by isobavachalcone. IBC interacted with ABCB1 transporter, being a substrate and/or competitive inhibitor of ABCB1. Moreover, IBC intercalated into model membranes, significantly affecting the parameters of their main phospholipid phase transition. It was concluded that isobavachalcone interfered both with the lipid phase of cellular membrane and with ABCB1 transporter, and for this reason, its activity in MDR cancer cells was presumptively beneficial. 相似文献