排序方式: 共有72条查询结果,搜索用时 31 毫秒
61.
Andreia Ilie Ecaterina Andronescu Denisa Ficai Georgeta Voicu Maria Ficai Maria Maganu Anton Ficai 《Central European Journal of Chemistry》2011,9(2):283-289
The aim of this work was to increase our understanding of collagen (COLL)/ hydroxyapatite (HA) composite materials; more specifically,
we focused on the study of the influence of the precursorconcentrations over the final content of deposited HA. We found that
the increase of the precursor concentrations led to better mineralization (on the basis of the content of deposited mineral
phase). Regardless of the precursor concentrations, the content of the deposited amount was found to increase with the increase
of the number of deposited layers. Quantification of the mineral phase amount was achieved by gravimetric determination. Based
on the determined deposition equation the number of layers can be easily determined in order to obtain composite materials
with desired content of mineral phase. 相似文献
62.
63.
Denisa Tarabová Viktor Milata Jiří Hanusek 《Journal of Physical Organic Chemistry》2013,26(6):503-509
The kinetics and mechanism of the nucleophilic vinylic substitution of dialkyl (alkoxymethylidene)malonates (alkyl: methyl, ethyl) and (ethoxymethylidene)malononitrile with substituted hydrazines and anilines R1–NH2 (R1: (CH3)2N, CH3NH, NH2, C6H5NH, CH3CONH, 4‐CH3C6H4SO2NH, 3‐ and 4‐X‐C6H4; X: H, 4‐Br, 4‐CH3, 4‐CH3O, 3‐Cl) were studied at 25 °C in methanol. It was found that the reactions with all hydrazines (the only exception was the reaction of (ethoxymethylidene)malononitrile with N,N‐dimethylhydrazine) showed overall second‐order kinetics and kobs were linearly dependent on the hydrazine concentration which is consistent with the rate‐limiting attack of the hydrazine on the double bond of the substrate. Corresponding Brønsted plots are linear (without deviating N‐methyl and N,N‐dimethylhydrazine), and their slopes (βNuc) gradually increase from 0.59 to 0.71 which reflects gradually increasing order of the C–N bond formed in the transition state. The deviation of both methylated hydrazines is probably caused by the different site of nucleophilicity/basicity in these compounds (tertiary/secondary vs. primary nitrogen). A somewhat different situation was observed with the anilines (and once with N,N‐dimethylhydrazine) where parabolic dependences of the kinetics gradually changing to linear dependences as the concentration of nucleophile/base increases. The second‐order term in the nucleophile indicates the presence of a steady‐state intermediate ‐ most probably T±. Brønsted and Hammett plots gave βNuc = 1.08 and ρ = ?3.7 which is consistent with a late transition state whose structure resembles T±. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
64.
Denisa Batir-Marin Monica Boev Oana Cioanca Cornelia Mircea Ana Flavia Burlec Galba Jean Beppe Adrian Spac Andreia Corciova Lucian Hritcu Monica Hancianu 《Molecules (Basel, Switzerland)》2021,26(9)
The sterile stems belonging to the Equisetum species are often used in traditional medicine of various nations, including Romanians. They are highly efficient in treating urinary tract infections, cardiovascular diseases, respiratory tract infections, and medical skin conditions due to their content of polyphenolic derivatives that have been isolated. In this regard, this study aimed to provide the chemical composition of the extracts obtained from the Equisetum species (E. pratense, E. sylvaticum, E. telmateia) and to investigate the biological action in vitro and in vivo. For the chemical characterization of the analyzed Equisetum species extracts, studies were performed by using ultra-high-performance liquid chromatography (UHPLC-DAD). In vitro evaluation of the antioxidant activity of the plant extracts obtained from these species of Equisetum genus was determined. The neuroprotective activity of these three ethanolic extracts from the Equisetum species using zebrafish tests was determined in vivo. All obtained results were statistically significant. The results indicate that E. sylvaticum extract has a significant antioxidant activity; whereas, E. pratense extract had anxiolytic and antidepressant effects significantly higher than the other two extracts used. All these determinations indicate promising results for the antioxidant in vitro tests and neuroprotective activity of in vivo tests, particularly mediated by their active principles. 相似文献
65.
Three chiral stationary phases were prepared by dynamic coating of sulfobutylether‐β‐cyclodextrin (SBE‐β‐CD) with different degrees of substitution, onto strong anion‐exchange stationary phases. The enantioselective potential and stability of newly prepared chiral stationary phases were examined using a set of structurally different chiral analytes. Measurements were performed in RP‐HPLC. Mobile phases consisted of methanol/formic acid, pH 2.10, and methanol/10 mM ammonium acetate buffer, pH 4.00, in various volume ratios. SBE‐β‐CDs with degrees of substitution (DS) 4, 6.3, and 10 proved suitable for the enantioseparation of 14, 11, and 8 analytes, respectively. The SBE‐β‐CD DS 4 based chiral stationary phase enabled the enantioseparation of the nearly all basic and neutral compounds. Chiral stationary phases with higher sulfobutylether‐β‐cyclodextrin substitution (especially DS 10) yielded higher enantioresolution values for acidic compounds. 相似文献
66.
Caira MR Dumitrascu F Draghici C Dumitrescu D Cristea M 《Molecules (Basel, Switzerland)》2005,10(2):360-366
The synthesis, characterization and X-ray crystal structure of 2-(4-chloro-phenyl)-7-methylpyrrolo[1,2-b]pyridazine are reported. The compound crystallizes in the space group P2(1)/c (No.14) with a =3.8568(1), b = 11.0690(3), c = 26.4243(7) A, beta =92.777(1) degrees and Z = 4. Accurate molecular parameters for the novel heterocyclic system were obtained from intensity data collected at 113K. The molecule assumes a planar conformation in the crystal and the packing is based on pi-pi stacking with interplanar spacing 3.400 ?, typical of aromatic molecules with potential for displaying useful optical properties. 相似文献
67.
A simple two-step method for the selective preparation of anomerically pure 1α- and 1β-(indol-2-yl)deoxyribose derivatives was developed. The synthesis was based on the Sonogashira reaction of 1α- and 1β-ethynyldeoxyribose and 2-haloanilines followed by a Pd-complex catalyzed cyclization to the corresponding indolyldeoxyribosides. 相似文献
68.
Larisa Calu Mihaela Badea Denisa Falcescu Daria Duca Dana Marinescu Rodica Olar 《Journal of Thermal Analysis and Calorimetry》2013,111(3):1725-1730
In order to develop new metallo-antimicrobials the complexes of type MLCl·nH2O ((1) M: Co, n = 0; (2) M: Ni, n = 2; (3) M: Cu, n = 2.5; (4) M: Zn, n = 0, HL: Schiff base derived from acetylacetone and 3-amino-4H-1,2,4-triazole) were synthesized by template condensation. The features of complexes have been assigned from microanalytical, IR and UV–Vis-NIR data. The species heating in air evidenced processes as melting, water and hydrochloride endothermic elimination as well as oxidative degradation of the Schiff base. The temperature ranges as well as modification in the electronic spectra of dehydrated intermediates indicate the presence of both coordination and crystallisation water molecules. The final product of decomposition was the most stable metal oxide as powder X-ray diffraction indicated. 相似文献
69.
Denisa Partelová Jozef Uhrovčík Juraj Lesný Miroslav Horník Pavol Rajec Peter Kováč Stanislav Hostin 《Chemical Papers》2014,68(11):1463-1473
The aim of the presented work was to evaluate the uptake and distribution of 2-fluoro-2-deoxy-d-glucose spiked with 18F (2-[18F]FDG) in tissues of tobacco plants (Nicotiana tabacum L.) by positron emission tomography and multivariate data analysis after the immersion of the petiole of excised leaf or root of a tobacco plant in a glucose solution. From individual experiments it was found that increasing glucose concentration (c glu) in the applied solution resulted in significantly higher 2-[18F]FDG diffusion and translocation within the leaf parenchyma. More than a four times increase of the 2-[18F]FDG translocation into the aboveground parts of the tobacco plant in case of the root immersion in solution with 100-times higher c glu in comparison with the control (c glu = 0.00762 mg cm?3) was determined. These facts were not confirmed only visually on basis of the obtained 3D images, but also by the increasing coincidence transfer factor (TFc) values defined by the ratio of the number of analyzed coincidences in the non-immersed parts of leaf or plant to coincidences in leaf petiole or root immersed in the solution. Cluster and principal component analysis suggest that the 2-[18F]FDG uptake by the petiole of excised leaf and root system was realized by different mechanisms; also, the 3D image quality is influenced by the initial radioactivity of the applied solution. 相似文献
70.
Oxidative Catalysis Using the Stoichiometric Oxidant as a Reagent: An Efficient Strategy for Single‐Electron‐Transfer‐Induced Tandem Anion–Radical Reactions 下载免费PDF全文
Ing. František Kafka Ing. Martin Holan M.Sc. Denisa Hidasová Dr. Radek Pohl Dr. Ivana Císařová Dr. Blanka Klepetářová Dr. Ullrich Jahn 《Angewandte Chemie (International ed. in English)》2014,53(37):9944-9948
Oxidative single‐electron transfer‐catalyzed tandem reactions consisting of a conjugate addition and a radical cyclization are reported, which incorporate the mandatory terminal oxidant as a functionality into the product. 相似文献