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161.
Dr. Dorian Didier Dr. Pierre‐Olivier Delaye Marwan Simaan Biana Island Dr. Guillaume Eppe Dr. Hendrik Eijsberg Amir Kleiner Prof. Dr. Paul Knochel Prof. Dr. Ilan Marek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(4):1038-1048
The copper‐catalyzed carbomagnesiation reaction of cyclopropenyl esters 1 leads to various substituted cyclopropanes species 3 in good yields with very high diastereoselectivities. The reaction proceeds through a syn‐chelated carbomagnesiation reaction and could be extended to various cyclopropenylmethyl ester derivatives 5 . The potential of this approach was illustrated by the preparation of two consecutive all‐carbon quaternary stereocenters. However, the carbometalation reaction needs to be performed at temperature ranging from ?35 to ?20 °C to avoid subsequent fragmentation reaction into stereodefined β,γ‐nonconjugated unsaturated esters 4 . Alternatively, the carbocupration reaction with organocopper species could also be performed to leads to configurationally stable cyclopropyl copper species 2[Cu] . Additionally, when the Lewis acid character of the copper center is decreased (i.e., RCuCNLi), the reaction proceed with an anti‐selectivity. The diastereodivergent behavior of these organometallic species is of synthetic interest, since both diastereomers syn‐ 3 and anti‐ 3 can be obtained, at will, from the same precursor cyclopropenyl esters 1 . 相似文献
162.
Marek Grzybowski Vincent Hugues Dr. Mireille Blanchard‐Desce Prof. Dr. Daniel T. Gryko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12493-12501
Structurally unique π‐expanded diketopyrrolopyrroles (EDPP) were designed and synthesized. Strategic placement of a fluorene scaffold at the periphery of a diketopyrrolopyrrole through tandem Friedel–Crafts‐dehydration reactions resulted in dyes with supreme solubility. The structure of the dyes was confirmed by X‐ray crystallography verifying a nearly flattened arrangement of the ten fused rings. Despite the extended ring system, the dye still preserved good solubility and was further functionalized by using Pd‐catalyzed coupling reactions, such as the Buchwald–Hartwig amination. Photophysical studies of these new functional dyes revealed that they possess enhanced properties when compared with expanded DPPs in terms of two‐photon absorption cross‐section. It is further demonstrated that in addition to the initial diacetals, the final electrophilic cyclization step can also be applied to diketones. By placing two amine groups at peripheral positions of the resulting dyes, values of two‐photon absorption cross‐section on the level of 2000 GM around 1000 nm were achieved, which in combination with high fluorescence quantum yield (Φfl), generated a two‐photon brightness of approximately 1600 GM. These characteristics in combination with strong red emission (665 nm) make these new π‐expanded diketopyrrolopyrroles of major promise as two‐photon dyes for bioimaging applications. Finally, the corresponding N‐alkylated DPPs displayed a solid‐state fluorescence. 相似文献
163.
Two perpendicular projections of rising bubbles were observed in counter-current downstream diverging flow. Evidently, the bubbles did not enter the boundary layer at the channel wall and a plug liquid flow assumption was acceptable in our experimental equipment. This confirmed that the experiment was appropriate for simulation of bubble rises in a quiescent liquid column. Recent data obtained by a high-speed camera permitted recording over a period of 60 s. Image analysis by a tailor-made program provided a time-series of quantities related to the position, size, and shape of bubbles. In addition to determination of the aspect ratio of the equivalent oblate ellipsoid, deviation from this shape was investigated in respect of the difference between the bubble’s centre of mass and the geometrical centre of bubble projection. Autocorrelation of the data indicated that the bubble inclination oscillated harmonically with a frequency of 5–10 Hz; cross correlation showed that the horizontal shift of the centre of mass, as well as the horizontal velocity, increased with increasing bubble inclination, and the vertical shift of the centre of mass increased with an increases in the absolute value of the bubble inclination. There is no significant phase shift in the oscillation of these quantities. The bulky bottom side of the bubbles is in accordance with the model of bubble oscillation induced by instability of the equilibrium of gravity and surface tension forces. The oscillation frequency dependence on surface forces (Eötvös number) is evident, while viscosity does not play a significant role in low-viscosity liquids. Therefore, vortex-shedding is more likely to be an effect of the oscillation and not its cause. 相似文献
164.
The paper presents a study of the effect of a constant magnetic field (CMF) on the basic processes of quercetin electrochemical reactions. According to the observation made in previous studies, the presence of a double bond in the C-ring of quercetin enhances the antioxidant properties of that compound, whereas the presence of −OH groups also affects the antioxidant properties. Using cyclic voltammetry it was found that the constant magnetic field improves the efficiency of quercetin electrooxidation, especially of the third stage of the process, i. e. the stage in which the oxidation of the OH groups in the A-ring is the most difficult. The use of HPLC confirmed the electrochemical measurements and the results of cyclic voltammetry studies. The beneficial effect of the magnetic field on the efficiency of quercetin oxidation was confirmed by the results of impedance spectroscopy measurements. 相似文献
165.
Cysteine protease from grapevine (Vitis vinifera) belongs to those resistant proteins, which survive the process of vinification and can therefore be detected as wine components. Its amino acid sequence shows a homology to other members of the papain family, but the enzyme has only partially been explored so far. In order to get more biochemical information with the help of mass spectrometry (MS), wine proteins were collected by ultrafiltration and separated by gel permeation chromatography. The purified enzyme surprisingly displayed a high molecular mass value of around 200 kDa, indicating a possible oligomeric status and aggregation, as it entered only negligibly the separating 10% gel during polyacrylamide gel electrophoresis. The isoelectric point (pI) value of 3.6 was determined by chromatofocusing. Matrix‐assisted laser desorption/ionization (MALDI)‐MS was employed to evaluate the cleavage specificity and usefulness of the isolated cysteine protease in protein and peptide research. A potential applicability could be anticipated from the efficient digestion performance in volatile ammonium formate buffers at pH 3. Common peptides were digested and the resulting products analyzed by MS/MS sequencing. Then, mixtures of protein standards and extracted barley nuclear proteins were processed in the same way. Grape cysteine protease is nonspecific but shows a certain preference for Arg, Lys, and also Leu residues. Compared with papain, it seems not to require fully the presence of a large hydrophobic residue adjacent to that at the cleavage site. The enzyme is suitable for protein research as it produces peptides of a reasonable length in acidic pH. 相似文献
166.
Al-Shantir Omar Csáki Štefan Ondro Tomáš Keppert Martin Minárik Peter Vrabec Marek Trník Anton 《Journal of Thermal Analysis and Calorimetry》2020,142(5):1759-1766
Journal of Thermal Analysis and Calorimetry - This paper presents mechanical-acoustic study of samples made from electroporcelain mixture (type C 130) under five different compression... 相似文献
167.
Dr. Shantanu Ganesh Kulkarni Kristýna Jelínková Dr. Marek Nečas Dr. Zdeňka Prucková Dr. Michal Rouchal Dr. Lenka Dastychová Dr. Petr Kulhánek Dr. Robert Vícha 《Chemphyschem》2020,21(18):2084-2095
Stilbene derivatives are well-recognised substructures of molecular switches based on photochemically and/or thermally induced (E)/(Z) isomerisation. We combined a stilbene motif with two benzimidazolium arms to prepare new sorts of supramolecular building blocks and examined their binding properties towards cucurbit[n]urils (n=7, 8) and cyclodextrins (β-CD, γ-CD) in water. Based on the 1H NMR data and molecular dynamics simulations, we found that two distinct complexes with different stoichiometry, i. e., guest@β-CD and guest@β-CD2, coexist in equilibrium in a water solution of the (Z)-stilbene-based guests. We also demonstrated that the bis(benzimidazolio)stilbene guests can be transformed from the (E) into the (Z) form via UV irradiation and back via thermal treatment in DMSO. 相似文献
168.
169.
170.
Marek Mac Tomasz Uchacz Tomasz Wróbel Andrzej Danel Ewa Kulig 《Journal of fluorescence》2010,20(2):525-532
Novel fluorescing dyes 1,3,4-triphenyl-6-(1,4,7,10-tetraoxa-13-aza-cyclopentadec-13-ylmethyl)-1H-pyrazolo[3,4-b]quinoline (K1) and 2-[(2-hydroxyethyl)-(1,3,4-triphenyl-1H-pyrazolo[3,4-b]quinolin-6-ylmethyl)-amino]ethanol (L1) have been synthesized and investigated by the means of steady state and time-resolved fluorescence techniques. These compounds
act as sensors for the fluorescence detection of small inorganic cations (lithium, sodium, barium, magnesium and calcium)
in solvents of different polarities (THF and acetonitrile). The mechanism, which allows application of these compounds as
sensors, is an electron transfer from the electro-donative part of molecule to the acceptor part (fluorophore), which is retarded
upon complexation of the electro-donative part by inorganic cations. We found that crown ether-containing compound is very
sensitive to the addition of any investigated ions but amino alcohol-containing one exhibits better selectivity to the addition
of two-valued cations. Two kinds of the complexes (LM+ and L2M+) were found in the investigated systems. In addition, the dyes may be used as fluorescence indicators in solvents of lower
polarity like tetrahydrofuran. 相似文献