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排序方式: 共有102条查询结果,搜索用时 15 毫秒
1.
Jean Guillon Jean-Michel Leger Cecilia Dapremont Lou Apollonia Denis Pascal Sonnet Stéphane Massip 《Supramolecular chemistry》2013,25(5):319-329
The synthesis of new 25,27-dialkyloxy-5,17-diarylcalix[4]arenes-crown-6 1a–f in 1,3-alternate conformation by Suzuki cross-coupling reaction is reported. Their conformation was determined using 1H, 13C, 2D NMR and ROESY analysis, and X-ray crystallography. Extraction experiments using a two-phase solvent method involving sodium, potassium or cesium picrate showed good extraction of the cesium cation. The X-ray crystal structures of 1,3-alternate 25,27-dipropoxy-5,17-diphenylcalix[4]arene-crown-6 ether 1a and its cesium picrate complex were established. Solid-state data were used to determine the complexation behavior of these new ligands. The efficiency of calixarenes 1a–f for cesium ion extraction could be ascribed to the rigidity and flatness linkages caused by the aryl groups at the lower rim of the aromatic moieties in the calixarene skeleton. In addition, the introduction of these aromatic moieties in positions 5 and 17 enhanced the solubility of the metal complexes in organic media. 相似文献
2.
EI Rodriguez Martinez CI Barriga-Paulino MI Zapata CC Chinchilla AM López-Jiménez CM Gómez 《BMC neuroscience》2012,13(1):104-23
ABSTRACT: BACKGROUND: The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old). RESULTS: The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0--20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults. CONCLUSIONS: The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages. 相似文献
3.
The regiochemical outcomes for s-BuLi/TMEDA deprotonations of N-Boc-2-azabicyclo[2.1.1]hexanes had been shown to be temperature dependent. Computational methods have been applied to advance understanding of the complexes that the reagents form, the character of the deprotonations, and hence the experimentally observed regiochemical biases. The tertiary anion is formed more readily than the secondary anion and is also the more stable anion. Computations for the enthalpy of proton abstraction from the analogous N-methoxycarbonyl structure also indicate greater stability for the tertiary carbamate anion. 相似文献
4.
5.
Philip E. Sonnet 《Journal of heterocyclic chemistry》1970,7(5):1101-1108
Both 2- and 3-pyrrolemethanols hearing electron-withdrawing ring substituants react with alcohols in the presence, of acid to produce ethers. Dipyrrylmethanes are formed only as byproducts under these conditions. Other reactions of these pyrrolemethanols are described. 相似文献
6.
Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
7.
Riccardo Rosso André M. Sonnet Epifanio G. Virga 《Continuum Mechanics and Thermodynamics》2002,14(1):127-136
kinks created in a biological membrane by the interaction with a movable bead. We arrive at the evolution equations for both the
bead and the membrane, whence we conclude that the force exerted on the bead by a fixed membrane points in the direction along
which the curvature of the membrane is more concentrated. This is the first step towards understanding the basic mechanism
behind the dynamics of protein aggregation which takes place on biological membranes.
Received November 6, 2001 / Published online February 4, 2002 相似文献
8.
AM Jayannavar 《Pramana》2002,58(2):173-181
We present a simple model of transmission across a metallic mesoscopic ring. In one of its arm an electron interacts with
a single magnetic impurity via an exchange coupling. We show that entanglement between electron and spin impurity states leads
to reduction of Aharonov-Bohm oscillations in the transmission coefficient. The spin-conductance is asymmetric in the flux
reversal as opposed to the two-probe electrical conductance which is symmetric. In the same model, in contradiction to the
naive expectation of a current magnification effect, we observe enhancement as well as suppression of this effect depending
on the system parameters. The limitations of this model to the general notion of dephasing or decoherence in quantum systems
are pointed out. 相似文献
9.
10.
Krow GR Shoulders MD Edupuganti R Gandla D Yu F Sonnet PE Sender M Choudhary A DeBrosse C Ross CW Carroll P Raines RT 《The Journal of organic chemistry》2012,77(12):5331-5344
Proline derivatives with a C(γ)-exo pucker typically display a high amide bond trans/cis (K(T/C)) ratio. This pucker enhances n→π* overlap of the amide oxygen and ester carbonyl carbon, which favors a trans amide bond. If there were no difference in n→π* interaction between the ring puckers, then the correlation between ring pucker and K(T/C) might be broken. To explore this possibility, proline conformations were constrained using a methylene bridge. We synthesized discrete gauche and anti 5-fluoro- and 5-hydroxy-N-acetylmethanoproline methyl esters from 3-syn and 3-anti fluoro- and hydroxymethanopyrrolidines using directed α-metalation to introduce the α-ester group. NBO calculations reveal minimal n→π* orbital interactions, so contributions from other forces might be of greater importance in determining K(T/C) for the methanoprolines. Consistent with this hypothesis, greater trans amide preferences were found in CDCl(3) for anti isomers en-MetFlp and en-MetHyp (72-78% trans) than for the syn stereoisomers ex-MetFlp and ex-MetHyp (54-67% trans). These, and other, K(T/C) results that we report here indicate how substituents on proline analogues can affect amide preferences by pathways other than ring puckering and n→π* overlap and suggest that caution should be exercised in assigning enhanced pyrrolidine C(γ)-exo ring puckering based solely on enhanced trans amide preference. 相似文献