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51.
Maxit B Giermanska J Ly I Bendejacq D Mondain-Monval O Ponsinet V 《Langmuir : the ACS journal of surfaces and colloids》2011,27(5):1990-1995
We report on the structures exhibited by two different diblock poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) copolymers in water, a selective solvent. Using a combination of X-ray scattering and freeze fracture-transmission electron microscopy (FF-TEM), we show that these structures can be widely swollen while retaining their initial morphology and a high degree of long-range order. The analysis of the FF-TEM pictures also evidences the presence of water crystallites of regular size and shape within the confined water domains. We relate the growth of these crystallites to the high local ionic strength of the water swelling the PAA brushes. Moreover, the confinement of the crystallites growth shows that the swollen phases have a very robust structure, potentially useful for confining colloidal particles. 相似文献
52.
53.
As part of a research program directed toward the synthesis of Lycopodium alkaloids, a multigram scale asymmetric synthesis of intermediate 11 was achieved in 11 steps from pyridine (17). In addition to our alkene metathesis strategy, a key feature of this synthetic approach consists of a Fukuyama's Diels-Alder cycloaddition between 1,2-dihydropyridine and acrolein using MacMillan's catalyst (18) on a 50 g scale. This led to a 12-step catalytic asymmetric synthesis of (+)-luciduline (1). A broader subset of Lycopodium alkaloids could also be obtained, as demonstrated by the derivatization of 11 into advanced intermediates for the synthesis of some of these natural products. 相似文献
54.
Mehdi Ez-Zoubir Virginie Ratovelomanana-Vidal Véronique Michelet 《Journal of organometallic chemistry》2011,696(1):433-4841
The efficiency of an Ir(I)/HI system has been studied. The association of hydroiodic acid with iridium has been tested in the catalytic hydroiodination of alkynes. The use of [Ir(cod)Cl]2 dimer led to clean hydroiodination reactions and afforded the corresponding vinyliodides as a mixture of derivatives, where the Markovnikov type adduct was found to be the major product (80/20 to 93/7 ratio), in good yields. The mechanism was investigated and two main pathways seemed to be involved, one based on an initial oxidative addition of HI to the Ir(I) complex and the other one based on a π-activation of the alkyne moiety. The corresponding vinyliodides were engaged in Pd-catalyzed cross-coupling (Sonogashira and Suzuki-Miyaura) reactions under organoaqueuous conditions. 相似文献
55.
The aim of this article is to propose a mathematical model describing the electronic structure of crystals with local defects in the framework of the Thomas–Fermi–von Weizsäcker (TFW) theory. The approach follows the same lines as that used in Cancès et al. (Commun Math Phys 281:129–177, 2008) for the reduced Hartree–Fock model, and is based on thermodynamic limit arguments. We prove, in particular, that it is not possible to model charged defects within the TFW theory of crystals. 相似文献
56.
Bertrand Parvitte Christophe Risser Raphael Vallon Virginie Zéninari 《Applied physics. B, Lasers and optics》2013,111(3):383-389
This paper aims to demonstrate the quantitative simulation of photoacoustic signals using finite element modelling software. The software Comsol Multiphysics is used to calculate the response of a differential Helmholtz resonator cell previously modeled using an electrical analogy. Quality factors and resonance frequencies are compared with experimental ones. Moreover, for the first time, the absorption coefficient of the gas sample and the laser intensity are also used to quantitatively predict photoacoustic signal that can be obtained in such a configuration. 相似文献
57.
We have developed an efficient catalytic enantioselective hydrogenation of pyridine derivatives. Enhanced reactivity was possible by an optimization of the electronic properties of the catalyst through ligand modification. This methodology shows the particular reactivity of N-iminopyridinium ylides that provides access to substituted piperidines in good enantiomeric excesses. 相似文献
58.
Recent crystal structures of nicotine bound to the acetylcholine binding protein (AChBP) ended a long debate confirming that the pyridine nitrogen of nicotine is indeed hydrogen-bonded to receptor residues through a bridging water molecule. Here, we describe the first direct experimental evaluation of the hydrogen-bond affinity of the nicotinium pyridine nitrogen. The equilibrium constant of its association with a phenol is 1 order of magnitude greater than the association of the acetylcholine carbonyl oxygen. 相似文献
59.
The Neumann realization for the Schr?dinger operator with magnetic field is considered in a bounded two-dimensional domain
with corners. This operator is associated with a small semi-classical parameter h or, equivalently, with a large magnetic field.We investigate the behavior of its eigenpairs as h tends to zero, like in a semi-classical limit. We prove, in the situation where the domain is a polygon and the magnetic
field is constant, that the lowest eigenvalues are exponentially close to those of model problems associated with the corners.
We approximate the corresponding eigenvectors by linear combinations of functions concentrated in corners at the scale
If the domain has curved sides and the magnetic field is smoothly varying, we exhibit a full asymptotics for eigenpairs in
powers of
Communicated by Christian Gérard
Submitted: October 13, 2005 Accepted: December 19, 2005 相似文献
60.
[reaction: see text] Various alpha-C-substituted 1,4-dideoxy-1,4-imino-d-galactitols were prepared efficiently from 1-O-acetyl-2,3,5,6-tetra-O-benzyl-d-glucofuranose by a four-step sequence involving as the key step the highly syn-selective TMSOTf-catalyzed addition of silylated nucleophiles to a glycofuranosylamine. Cross-metathesis of the alpha-C-allylated iminogalactofuranose derivative with an original uridin-5'-yl vinylphosphonate led to novel UDP-galactofuranose mimics. Such compounds are of interest as potential inhibitors of the mycobacterial galactan biosynthesis pathway. 相似文献