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排序方式: 共有78条查询结果,搜索用时 15 毫秒
21.
Sofia Lindblad Flóra Boróka Németh Dr. Tamás Földes Dr. Daniel von der Heiden Herh G. Vang Zakarias L. Driscoll Emily R. Gonnering Prof. Imre Pápai Prof. Nathan Bowling Prof. Mate Erdelyi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(55):13748-13756
[Bis(pyridine)iodine(I)]+ complexes offer controlled access to halonium ions under mild conditions. The reactivity of such stabilized halonium ions is primarily determined by their three-center, four-electron [N−I−N]+ halogen bond. We studied the importance of chelation, strain, steric hindrance and electrostatic interaction for the structure and reactivity of halogen bonded halonium ions by acquiring their 15N NMR coordination shifts and measuring their iodenium release rates, and interpreted the data with the support of DFT computations. A bidentate ligand stabilizes the [N−I−N]+ halogen bond, decreasing the halenium transfer rate. Strain weakens the bond and accordingly increases the release rate. Remote modifications in the backbone do not influence the stability as long as the effect is entirely steric. Incorporating an electron-rich moiety close by the [N−I−N]+ motif increases the iodenium release rate. The analysis of the iodine(I) transfer mechanism highlights the impact of secondary interactions, and may provide a handle on the induction of stereoselectivity in electrophilic halogenations. 相似文献
22.
S.?Mate?i? Mu?ani?Email author M.?Su?eska 《Journal of Thermal Analysis and Calorimetry》2009,96(2):523-529
The ageing of double base rocket propellants (DB rocket propellants), which is a consequence of chemical reactions and physical
processes that take place over time, has significant effect on their relevant properties (e.g. chemical composition, mechanical
properties, ballistic properties, etc.). The changes of relevant properties limit the safe and reliable service life of DB
rocket propellants. This is the reason why numerous research efforts are devoted to finding out reliable methods to measure
the changes caused by ageing, to assess the quality at a given moment of time, and to predict remaining life-time of DB rocket
propellants.
In this work we studied dynamic mechanical properties of DB rocket propellant artificially aged at elevated temperatures,
in order to detect and quantify changes in dynamic mechanical properties caused by the ageing. Dynamic mechanical properties
were studied using dynamic mechanical analyser (DMA).
The results obtained have shown that the ageing causes significant changes of DMA curve’s shape and positions. These changes
are quantified by following some characteristic points on DMA curves (e.g. glass transition temperatures; storage modulus,
loss modulus and tanδ at characteristic temperatures, etc.). It has been found out that the most sensitive parameters to the
ageing process are: storage modulus at viscoelastic and softening region, peak width and height on loss modulus curve, glass
transition and softening temperature, and tanδ at viscoelastic region. 相似文献
23.
A.A. Kamel CM. Ma M.S. El-Aasser F.J. Micale J.W. Vanderhoff 《Journal of Dispersion Science and Technology》2013,34(2-3):315-330
The electrophoretic mobility behavior of well-characterized polystyrene latex particles, carrying one type of surface functional endgroups, has been studied as a function of pH. At low pH, the interaction of protons with the functional endgroups increased in the order: Hydroxyl > carboxyl > sulfate; at high pH the order of interaction was reversed; and at intermediate pH no interactions were observed. The particles of the polystyrene latexes in their different forms at the intermediate pH range, dispersed in deionized water, all exhibited the same mobility irrespective of the functional endgroup. The origin of charge in these systems is explained as being the result of either the preferential adsorption of hydroxyl ions or an electron - injection mechanism due to the overlap of local intrinsic molecular - ion states in polystyrene and water. At low concentrations of functional endgroups, the surface properties of the polystyrene latexes are largely dependent upon the hydrophobic nature of the surface. 相似文献
24.
Tobias Frank Johannes CM Schlachetzki Bettina G?ricke Katrin Meuer Gundula Rohde Gunnar PH Dietz Mathias B?hr Armin Schneider Jochen H Weishaupt 《BMC neuroscience》2009,10(1):49-10
Background
The hematopoietic Granulocyte-Colony Stimulating Factor (G-CSF) plays a crucial role in controlling the number of neutrophil progenitor cells. Its function is mediated via the G-CSF receptor, which was recently found to be expressed also in the central nervous system. In addition, G-CSF provided neuroprotection in models of neuronal cell death. Here we used the retinal ganglion cell (RGC) axotomy model to compare effects of local and systemic application of neuroprotective molecules. 相似文献25.
We give a necessary and sufficient condition for a certain set of infinite products of linear operators to be zero. We shall investigate also the case when this set of infinite products converges to a non-zero operator. The main device in these results is a weighted version of the König Lemma for infinite trees in graph theory.
26.
27.
Dr. Daniel Umereweneza Dr. Yoseph Atilaw Dr. Stefan Peintner Anastasia Rudenko Dr. Catarina Bourgard Dr. Ruisheng Xiong Prof. Théoneste Muhizi Prof. Per Sunnerhagen Prof. Adolf Gogoll Prof. Mate Erdelyi 《European journal of organic chemistry》2023,26(8):e202201280
Three new compounds, the silphiperfolanol angelate ester umutagarananol ( 1 ), the macrocyclic pyrrolizidine alkaloids umutagarinine A and B ( 2 – 3 ), and five known secondary metabolites ( 4 – 8 ) were isolated from the CH2Cl2−MeOH (1 : 1) extract of the roots and the stem bark of Solanecio mannii (Hook. f.) (Asteraceae). The isolated compounds were characterized by NMR and IR spectroscopic, and mass spectrometric analyses, whereas the relative stereochemistry of 4 was established by NAMFIS-based combined computational and solution NMR analysis. Synthetic modification of 5 provided two new compounds, 2-angeloyloxy-4,8-epoxypresilphiperfolane ( 9 ) and 2-angeloyloxy-4,8-epoxypresilphi-perfolane ( 10 ). The crude extracts and the isolated constituents showed weak antibacterial activities (EC50 0.7–13.3 mM) against the Gram-negative Escherichia coli and the Gram-positive Bacillus subtilis. Compounds 2 , 3 and 4 exhibited strong cytotoxicity against MCF-7 human breast cancer cells, with EC50 values of 35.6, 21.7 and 12.5 μM, respectively. 相似文献
28.
29.
Bojan Kozlev
ar Elizabeta Mate Zvonko Jagli
i Lea Glaar Amalija Golobi
Peter Strauch Jan Moncol Nives Kitanovski Primo egedin 《Polyhedron》2009,28(13):2759-2765
Several copper(II) methanoato complexes, namely mononuclear [Cu(O2CH)2(2-mpy)2] (1) (2-mpy = 2-methylpyridine), binuclear [Cu2(μ-O2CH)4(2-mpy)2] (2), and the polynuclear {[Cu(μ-O2CH)2(2-mpy)2][Cu2(μ-O2CH)4]}n (3) and {Na2[Cu(μ-O2CH)2(O2CH)2][Cu2(μ-O2CH)4]}n (4), have been synthesized. The mononuclear complex 1 is formed by two asymmetric chelate methanoate anions and two 2-methylpyridine molecules, giving a highly distorted ‘elongated octahedral’ coordination sphere. Complex 1 decomposes outside the mother-liquid, transforming into a regular isolated binuclear paddle-wheel complex 2 with four intra-binuclear bridging methanoates and two axial 2-mpy ligands. The polynuclear complex 3 is formed of alternate mononuclear and binuclear building blocks resembling the central cores of 1 and 2, but with significant differences, especially for the methanoates of the mononuclear units. The oxygen atom of the mononuclear unit in the octahedral axial position in 3 is simultaneously coordinated to the axial position of the binuclear paddle-wheel central core, thus enabling a chain type of structure. A chain of alternate mononuclear and binuclear building blocks, as in the neutral compound 3, are found as well in the ionic polymeric compound 4, though two types of bridges are found in 4, while there is only one type in 3. Namely, the axial position of the octahedral mononuclear unit in 4 is occupied by the methanoate oxygen atom that is already a part of the binuclear paddle-wheel unit, while one equatorial methanoate from the mononuclear unit serves as a triatomic bridge to the axial position of the binuclear building block. A very strong antiferromagnetic interaction is found for all the complexes with the paddle-wheel building blocks [Cu2(μ-O2CH)4] 2–4 (−2J = 444–482 cm−1), attributed to the methanoate intra-binuclear bridges. On the other hand, this strong antiferromagnetism, found already at room temperature, reduces the intensity of the EPR S = 1 spin signals reported for the isolated paddle-wheel complex 2. For the polymeric 3, only the spin S = ½ signals are found in the EPR spectra, and they are assigned to the mononuclear building blocks. No signals with a clear origin are however seen in the room temperature EPR spectrum of the polymeric analogue 4, only the S = ½ signals in the low temperature spectra. This feature is suggested to be due to a specific influence between the adjacent S = 1 (binuclear) and S = ½ (mononuclear) species via their bridges. 相似文献
30.
In this paper, we introduce a particular class of nonlinear and non-separable multiscale representations which embeds most of these representations. After motivating the introduction of such a class on one-dimensional examples, we investigate the multi-dimensional and non-separable case where the scaling factor is given by a non-diagonal dilation matrix M. We also propose new convergence and stability results in L p and Besov spaces for that class of nonlinear and non-separable multiscale representations. We end the paper with an application of the proposed study to the convergence and the stability of some nonlinear multiscale representations. 相似文献