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181.
By using pH-metric and conductometric methods it has been found that tetracycline (H3TC) forms with WO
4
2–
and MoO
4
2–
ions the following complex compounds: [WO3HTC]2–, [WO3(H2TC)2]2– and [MoO3(H2TC)2]2–. Stability constants log/gb
1
k
=7.86 and log
1
k
=7.80 for [WO3HTC]2– and [MoO3HTC]2–, respectively, have been calculated from pH-metric measurements. 相似文献
182.
The results of an ab initio study of the magnetic hyperfine structure in the X (2)Pi electronic state of CCCH are reported. The potential surfaces for two components of the X (2)Pi electronic state were computed by means of an extensive configuration interaction approach. The electronically averaged hyperfine coupling constants of H and (13)C for (12)C (12)C (12)CH, (13)C (12)C (12)CH, (12)C (13)C (12)CH, and (12)C (12)C (13)CH are obtained as functions of two bending vibrational modes by the density functional theory method. The vibronic wave functions are calculated with the help of a variational approach which takes into account the Renner-Teller effect and spin-orbit coupling. The model Hamiltonian is expressed in terms of the normal bending coordinates. It is found that, due to the generally strong geometry dependence of the hyperfine coupling constants, it is necessary to carry out the vibronic averaging of the corresponding functions in order to obtain the values which can be compared to the results of the measurements. The results of the present study help to reliably interpret the experimental data previously published. They also predict the yet unobserved hyperfine structure in excited vibronic states. 相似文献
183.
Milena Polumackanycz Mateusz Kaszuba Agnieszka Konopacka Urszula Marzec-Wrblewska Marek Wesolowski Krzysztof Waleron Adam Buciski Agnieszka Viapiana 《Molecules (Basel, Switzerland)》2020,25(22)
Rosa canina L. (dog rose) is a rich source of phenolic compounds that offer great hope for the prevention of chronic human diseases. Herein, wild and commercial samples of dog rose were chemically characterized with respect to their phenolic composition by liquid chromatography coupled to diode array detection and electrospray ionization tandem mass spectrometry (LC-DAD-ESI/MS). Furthermore, in vitro antioxidant properties and antibacterial activity of dog rose fruits and leaves hydromethanolic extracts and infusions were also evaluated. The results revealed that wild and commercial fruits of dog rose are similar in terms of l(+)-ascorbic acid, total phenolics (TPC), total flavonoids (TFC) and total phenolic acids (TPAC) content, individual phenolic constituents and antioxidant activity. Moreover, the fruits had lower levels of phenolic compounds and also revealed lower biological activity than the leaves. On the other hands, the highest content of TPC, TFC, TPAC, individual phenolic constituents, DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging activity and FRAP (ferric reducing antioxidant power) were found in the leaf’s infusions. They were also the only ones to show antibacterial activity. Overall, these finding confirmed usefulness of R. canina L. leaves and fruits as a rich source of bioactive phenolic compounds with potential use in food, pharmaceutical, and cosmetic industries. 相似文献
184.
Reactions of substituted cyanoacetate anions 4 with S,S-dialayklsuccinimidosulfonium salts resulted generally in the formation of N-alkylthiomethylketenimines and α-alkylthiomethylesters. Coupling products were also obtained with anion 4d and only observed in the case of methyl phenylcyanoacetate anion 4b. The results were interpreted by the formation of instable σ-sulfurane intermediates. Homolytic cleavage of these intermediates gave radical pairs, then the coupling products. Heterocyclic clevage gave new sulfonium salts which rearranged via sulfonium ylides. 相似文献
185.
Reactions of 5-phenylthieno[3,2-b]pyran-7-one, 2-phenylbenzo[b]-thieno[3,2-b]pyran-4-one and the corresponding thiones with sodium ethylate, guanidines, hydrazines and amines are described and compared to those observed with benzopyranones. 相似文献
186.
Jacques E. Desnoyers Gérald Perron Lévon Avédikian Jean-Pierre Morel 《Journal of solution chemistry》1976,5(9):631-644
The enthalpies of solution of urea (U) in water (W)-tert-butanol (TBA) mixtures and of TBA in W-U mixtures, the enthalpies of dilution of TBA in W, and the enthalpies of mixing of U and TBA aqueous solutions were measured with a solution calorimeter and a flow microcalorimeter. Enthalpies of transfer of U and TBA to the mixed solvents were derived. Also, pair and triplet interaction parameters between the various solutes were derived from the mixing and dilution experiments. The enthalpic pair parameter hU-TBA is positive, suggesting that the main contribution to this parameter is the decrease in hydrophobic hydration of TBA in the presence of U. 相似文献
187.
In an investigation of novel tricyclic systems, synthesis of several thieno[2,3-b][1,4]benzoxazepines and thieno[3,2-b][1,5]benzoxazepines were effected by ring closure of appropriately amino aldehyde compounds. A new oxazepine fused with two heterocyclic rings, the dithieno[3,2-b:2,3-f][1,4]oxazepine, is described. 相似文献
188.
J.L. Meunier A. Morel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):341-352
For the first order transition of the Ising model below , Isakov has proven that the free energy possesses an essential singularity in the applied field. Such a singularity in the
control parameter, anticipated by condensation theory, is believed to be a generic feature of first order transitions, but
too weak to be observable. We study these issues for the temperature driven transition of the q states 2D Potts model at . Adapting the droplet model to this case, we relate its parameters to the critical properties at and confront the free energy to the many informations brought by previous works. The essential singularity predicted at the
transition temperature leads to observable effects in numerical data. On a finite lattice, a metastability domain of temperatures
is identified, which shrinks to zero in the thermodynamical limit.
Received 30 March 1999 相似文献
189.
Milena Hugenschmidt Ksenia Kutonova Elvia P. Valadez Sánchez Sarah Moulai Hartmut Gliemann Stefan Bräse Christof Wöll Dagmar Gerthsen 《Particle & Particle Systems Characterization》2020,37(11):2000209
The first example of layer-by-layer growth of a metal–organic framework (MOF) directly on transmission electron microscopy (TEM) grids is described. ZIF-8 is deposited on thin amorphous carbon films and subjected to a structure analysis by (scanning) TEM ((S)TEM). This method serves as a two-in-one synthesis and TEM sample-preparation technique and allows straightforward analysis of ZIF-8 crystallites. Artifacts resulting from sample preparation are completely avoided by this approach. The morphological properties, crystal structure, and the chemical composition of the material are investigated with high spatial resolution by a variety of methods of (analytical) electron microscopy. Furthermore, the incorporation of metallic nanoparticles in ZIF-8 by integrating a corresponding step into the layer-by-layer deposition process is examined. The formation of ZIF-8 crystals on the film proceeds as under the absence of nanoparticle-forming synthesis steps. However, the nanoparticles rather cover the supporting amorphous carbon film than being incorporated in the ZIF-8 material. This information cannot be obtained from standard characterization techniques but requires the application of analytical (S)TEM techniques. 相似文献
190.
Mignani AG Ciaccheri L Ottevaere H Thienpont H Conte L Marega M Cichelli A Attilio C Cimato A 《Analytical and bioanalytical chemistry》2011,399(3):1315-1324
Because of its high price, extra virgin olive oil is frequently targeted for adulteration with lower quality oils. This paper
presents an innovative optical technique capable of quantifying and discriminating the adulteration of extra virgin olive
oil caused by lower-grade olive oils. An original set-up for diffuse-light absorption spectroscopy in the wide 400–1,700 nm
spectral range was experimented. It made use of an integrating sphere containing the oil sample and of optical fibers for
illumination and detection; it provided intrinsically scattering-free absorption spectroscopy measurements. This set-up was
used to collect spectroscopic fingerprints of authentic extra virgin olive oils from the Italian Tuscany region, adulterated
by different concentrations of olive-pomace oil, refined olive oil, deodorized olive oil, and refined olive-pomace oil. Then,
a straightforward multivariate processing of spectroscopic data based on principal component analysis and linear discriminant
analysis was applied which was successfully capable of predicting the fraction of adulterant in the mixture, and of discriminating
its type. The results achieved by means of optical spectroscopy were compared with the analysis of fatty acids, which was
carried out by standard gas chromatography. 相似文献