排序方式: 共有126条查询结果,搜索用时 15 毫秒
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Andreia Valente Philippe Zinck Andre' Mortreux Marc Bria Marc Visseaux 《Journal of polymer science. Part A, Polymer chemistry》2011,49(17):3778-3782
The Cp*La(BH4)2(THF)2/n‐butylethylmagnesium (BEM) catalytic system has been assessed for the coordinative chain transfer copolymerization of styrene and 1‐hexene. Poly(styrene‐co‐hexene) statistical copolymers were obtained with number‐average molecular weight up to 7600 g/mol, PDI around 1.4 and 1.5 and up to 23% hexene content. The occurence of chain transfer reactions in the presence of excess BEM is established in the course of the statistical copolymerization. Thanks to this transfer process, the quantity of 1‐hexene in the copolymer is increased by a factor of about 3 for high ratio of hexene in the feed, extending the range of our concept of a chain transfer induced control of the composition of statistical copolymers to poly(styrene‐co‐hexene) copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
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Isoprene–Styrene Chain Shuttling Copolymerization Mediated by a Lanthanide Half‐Sandwich Complex and a Lanthanidocene: Straightforward Access to a New Type of Thermoplastic Elastomers 下载免费PDF全文
Dr. Andreia Valente Dr. Gregory Stoclet Dr. Fanny Bonnet Prof. André Mortreux Prof. Marc Visseaux Prof. Philippe Zinck 《Angewandte Chemie (International ed. in English)》2014,53(18):4638-4641
A lanthanide half‐sandwich complex and a ansa lanthanidocene have been assessed for isoprene–styrene chain shuttling copolymerization with n‐butylethylmagnesium (BEM). In the presence of 1 equiv BEM, a fully amorphous multiblock microstructure of soft and hard segments is achieved. The microstructure consists of poly(isoprene‐co‐styrene) blocks, with hard blocks rich in styrene and soft blocks rich in isoprene. The composition of the blocks and the resulting glass transition temperatures (Tg) can be easily modified by changing the feed and/or the relative amount of the catalysts, highlighting a new class of thermoplastic elastomers (TPEs) with tunable transition temperatures. The materials self‐organize into nanostructures in the solid state. 相似文献
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Marta Leite Andreia Freitas Anabela Marisa Azul Jorge Barbosa Saul Costa Fernando Ramos 《Analytica chimica acta》2013
Amanitins, highly toxic cyclopeptides isolated from various Amanita species, are the most potent poisons accounting for the hazardous effects on intestinal epithelium cells and hepatocytes, and probably the sole cause of fatal human poisoning. 相似文献
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The photophysical and photovoltaic properties of three alternated fluorene–thiophene copolymers were studied. With similar structure the copolymers differed by the numbers of thiophene units linked to each fluorene group:one, two and three. The electronic properties were analyzed through mobility measurements and the overall properties pointed out to the one containing the three rings as the best material, as anticipated, due to the larger number of thiophene units. However, after thermal annealing the polymer containing two thiophene rings presented the best photovoltaic efficiency, seven fold greater than the pristine material. The morphology, studied by atomic force microscopy, revealed to be one of the key factors for the performance of the materials as solar cells. 相似文献
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Benchmarking of density functionals for the kinetics and thermodynamics of the hydrolysis of glycosidic bonds catalyzed by glycosidases 下载免费PDF全文
Andreia T. Pereira António J. M. Ribeiro Pedro A. Fernandes Maria J. Ramos 《International journal of quantum chemistry》2017,117(18)
In recent years, there has been an increased interest in understanding the enzymatic mechanism of glycosidases resorting mostly to DFT and DFT/MM calculations. However, the performance of density functionals (DFs) is well known to be system and property dependent. Trends drawn from general studies, despite important to evaluate the quality of the DFs and to pave the way for the development of new DFs, may be misleading when applied to a single specific system/property. To overcome this issue, we carried out a benchmarking study of 40 DFs applied to the geometry optimization and to the electronic barrier height (E Barrier) and electronic energy of reaction (E R) of prototypical glycosidase‐catalyzed reactions. Additionally, we report calculations with SCC‐DFTB and four semiempirical MO methods applied to the same problem. We have used a universal molecular model for retaining glycosidases, comprising only a 22‐atoms system that mimics the active site and substrate. High accuracy reference geometries and energies were calculated at the CCSD(T)/CBS//MP2/aug‐cc‐pVTZ level of theory. Most DFs reproduce the reference geometries extremely well, with mean unsigned errors (MUE) smaller than 0.05 Å for bond lengths and 3° for bond angles. Among the DFs, wB97X‐D, CAM‐B3LYP, B3P86, and PBE1PBE have the best performance in geometry optimizations (MUE = 0.02 Å). Conversely, semiempirical MO and SCC‐DFTB methods yielded less accurate geometries (MUE between 0.09 and 0.17 Å). The inclusion of D3 correction has a small, but still relevant, influence in the geometry predicted by some DFs. Regarding E Barrier, 11 DFs (MPW1B95, CAM‐B3LYP, M06 ‐ 2X, PBE1PBE, wB97X ‐ D, B1B95, BMK, MN12 – SX, M05, M06, and M11) presented errors below 1 kcal.mol?1, in relation to the reference energy. Most of these functionals belong to the family of hybrid functionals (H‐GGA, HH‐GGA, and HM‐GGA), which shows a positive influence of HF exchange in the determination of E Barrier. The inclusion of D3 correction has not affected significantly the E Barrier and E R. The use of geometries at the accurate but expensive MP2/aug‐cc‐pVTZ level of theory has a small, albeit not insignificant, influence in the E Barrier when compared with energies calculated with geometries determined with the DFs (usually a few tenths of kcal.mol?1, with exceptions). In general, semiempirical MO methods and DFTB are associated with larger errors in the determination of E Barrier, with unsigned errors from 6.9 to 24.7 kcal.mol?1. 相似文献
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Luís Cruz Joana L.C. Sousa Andreia Marinho Nuno Mateus Victor de Freitas 《Tetrahedron letters》2017,58(2):159-162
The synthesis and structural characterization by LC–MS and NMR of novel pyranoluteolinidin derivatives are reported. The compounds result from the reactions between luteolinidin and three different carboxylic acids in wine model-like solutions. The three pigments possess different substituents attached to the D ring (methyl, catechol and dimethylaminophenyl groups) and the same catechol group in the B ring, yielding a wide spectrum of colors from yellow to pink-purple. 相似文献
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Neves P Leite A Rangel M de Castro B Gameiro P 《Analytical and bioanalytical chemistry》2007,387(4):1543-1552
Partition coefficients of moxifloxacin in liposomes of dimyristoyl-L-α-phosphatidylcholine or dimyristoyl-L-α-phosphatidylglycerol and water were determined by spectrophotometry and fluorimetry. The K
p values obtained were larger than those reported for most of the other fluoroquinolones, a consequence of the structural changes
observed in the molecule of moxifloxacin, which in turn change its acid/base properties. Introduction of a methoxy group at
position 8 and a diazabicyclonyl ring at position 7 in the basic fluoroquinolone structure alters the charge distribution
at the physiological pH of 7.4, and these changes seem to be responsible for its improved antibacterial potency and broader
spectrum of activity. Location studies have also been performed using fluorescence and electron paramagnetic resonance (EPR)
spectroscopies. The results show that moxifloxacin must be located near the phospholipid headgroups, similar to other fluoroquinolones,
but contributions from a hydrophobic component were also detected. These results suggest that the enhanced activity of this
drug may be related to a more facilitated entrance into the bacterial cell, perhaps including a mediator step involving electrostatic
interaction with a hydrophobic component; this step then controls the extent or orientation of insertion and improves the
electrostatic interaction. 相似文献
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The Influence of the Amide Linkage in the FeIII‐Binding Properties of Catechol‐Modified Rosamine Derivatives 下载免费PDF全文
Carla Queirós Dr. Andreia Leite Maria G. M. Couto Dr. Luís Cunha‐Silva Prof. Giampaolo Barone Prof. Baltazar de Castro Prof. Maria Rangel Dr. André M. N. Silva Dr. Ana M. G. Silva 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15692-15704
The two new fluorescent ligands RosCat1 and RosCat2 contain catechol receptors connected to rosamine platforms through an amide linkage and were synthesized by using microwave‐assisted coupling reactions of carboxyl‐ or amine‐substituted rosamines with the corresponding catechol units and subsequent deprotection. RosCat1 possesses a reverse amide, whereas RosCat2 has the usual oriented amide bond (HNCO vs. CONH, respectively). The ligands were characterized by means of NMR spectroscopy, mass‐spectrometry, and DFT calculations and X‐ray crystallography studies for RosCat1 . The influence of the amide linkage on the photophysical properties of the fluorescent ligands was assessed in different solvents and showed a higher fluorescence quantum yield for RosCat1 . The coordination chemistry of these ligands with a FeIII center has been rationalized by mass‐spectrometric analysis and semiempirical calculations. Octahedral FeIII complexes were obtained by the chelation of three RosCat1 or RosCat2 ligands. Interestingly, the unconventional amide connectivity in RosCat1 imposes the formation of an eight‐membered ring on the chelate complex through a “salicylate‐type” mode of coordination. 相似文献