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61.
62.
A straightforward asymmetric synthesis of the cage oxygenated structure of (+)-harringtonolide has been accomplished for the first time. The key steps involved (i) a templated stereoselective IMDA reaction to build a highly functionalized cyclohexene ring D, (ii) functionalization of the cycloadduct, (iii) ring-closing metathesis providing the five-membered ring C, and finally (iv) a challenging one-step cascade cyclization of an epoxy-alcohol toward the target structure, whose mechanism was investigated. 相似文献
63.
Bistable space–time discrete systems commonly possess a large variety of stable stationary solutions with periodic profile. In this context, it is natural to ask about the fate of trajectories composed of interfaces between steady configurations with periodic pattern and in particular, to study their propagation as traveling fronts. Here, we investigate such fronts in piecewise affine bistable recursions on the one-dimensional lattice. By introducing a definition inspired by symbolic dynamics, we prove the existence of front solutions and uniqueness of their velocity, upon the existence of their ground patterns. Moreover, the velocity dependence on parameters and the co-existence of several fronts with distinct ground patterns are also described. Finally, robustness of the results to small $C^1$ -perturbations of the piecewise affine map is argued by mean continuation arguments. 相似文献
64.
Hagen Poddig Jens Hunger Sirko Kamusella Hans‐Henning Klauss Anja U. B. Wolter Gaël Bastien Laura T. Corredor Bohrquez Thomas Doert 《无机化学与普通化学杂志》2019,645(8):631-637
The new calcium iron iridium hydrogarnet Ca3(Ir2–xFex)(FeO4)2–x(H4O4)1+x (0 ≤ x ≤ 1) was obtained by hydrothermal synthesis under strongly oxidizing alkaline conditions. The compound adopts a garnet‐like crystal structure and crystallizes in the acentric cubic space group I4 3d (no. 220) with a = 12.5396(6) Å determined at T = 100 K for a crystal with a refined composition Ca3(Ir1.4Fe0.6)(FeO4)1.4(O4H4)1.6. Iridium and iron statistically occupy the octahedrally coordinated metal position, the two crystallographically independent tetrahedral sites are partially occupied by iron. Hydroxide groups are found to cluster as hydrogarnet defects, i.e. partially substituting oxide anions around the empty tetrahedral metal sites. The presence of hydroxide ions was confirmed by infrared spectroscopy and the hydrogen content was quantified by carrier gas hot extraction; the overall composition was verified by energy dispersive X‐ray spectroscopy. The structure model is supported by 57Fe‐Mössbauer spectroscopic data evidencing different Fe sites and a magnetic ordering of the octahedral iron sublattice at room temperature. The thermal decomposition proceeds via three steps of water loss and results in Ca2Fe2O5, Fe2O3 and Ir. Mössbauer and magnetization data suggest magnetic order at ambient temperature with complex magnetic interactions. 相似文献
65.
Jérôme Bastien Claude-Henri Lamarque 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(5):393-407
Persoz’s gephyroidal model, which consists of elementary rheological models (dry friction element and linear spring), can
be covered by the existence and uniqueness theory for maximal monotone operators. Moreover, classical results of numerical
analysis allow one to use a numerical implicit Euler scheme, with convergence order of the scheme equal to one. Some numerical
simulations are presented. 相似文献
66.
First Total Synthesis,Structure Revision,and Natural History of the Smallest Cytochalasin: (+)‐Periconiasin G
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Mehdi Zaghouani Dr. Caroline Kunz Laura Guédon Dr. Florent Blanchard Dr. Bastien Nay 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15257-15260
The total synthesis of the smallest cytochalasin isolated so far, periconiasin G, which bears a seven‐membered ring in lieu of the usual macrocycle, has been performed from both enantiomers of citronellal, relying on an intramolecular Diels–Alder reaction in favor of the natural endo stereochemistry. We show that, among the four synthesized stereoisomers, including the exo isomers, the one matching the NMR data of the natural product was not that assigned in the original report, imposing structure revision. The natural product, previously isolated from a plant‐mutualistic fungus, was biologically investigated taking into account its natural history, showing significant effects against the phytopathogenic fungus Botrytis cinerea and thus opening new opportunities in combating this pest. 相似文献
67.
Jérôme Bastien 《Archive of Applied Mechanics (Ingenieur Archiv)》2014,84(6):851-880
A wheel subjected to two friction forces, one exerted by the ground and one exerted by the brake pad, is studied. A formalism using multivalued operators allows us to write the constitutive laws of this wheel in the form of a differential inclusion, for which we have the existence and the uniqueness of the solution, as well as the convergence of the associated numerical scheme. This wheel may be connected by itself to a chassis. The chassis may also be connected to two of these wheels. In these two cases, we again obtain a well-posed differential inclusion, in terms of existence, uniqueness, and convergence of the numerical scheme. In a more general manner, numerous applications can be proposed in the domain of the nonlinear dynamics of wheeled vehicles. 相似文献
68.
69.
The synthesis of the chiral diaza-9-crown-3 derivatives 1 (S,S) and 2 (R,R) is described. These sensors were designed as luminescent chemosensors for lithium where the fluorescence emission from the naphthalene moieties was ‘switched on’ upon Li+ recognition by the crown ether moiety in organic solvents, showing excellent selectivity over other group I and group II cations. Even though the recognition of Li+ was not achieved in water (pH 7.4) or aqueous alcohol solution, the fluorescence (which was switched on at pH 7.4) was substantially modulated by spherical anions, where the fluorescence emission was quenched in the presence of Br− and I− but less by Cl− and not by acetate. This indicates that the emission was quenched by heavy-atom affect. The recognition of Li+ was also investigated by 1H NMR in CD3CN and by observing the changes in the circular dicromism spectra. For the former, the resonances for the crown ether moiety and α-methyl protons adjacent to the ring were sifted upfield and broadened, whereas for 1 the intensity of the CD signal for the π-π transition was substantially modulated upon Li+ recognition. 相似文献
70.
Akshay Kumar Hippolyte Durand Elisa Zeno Cyril Balsollier Bastien Watbled Cecile Sillard Sbastien Fort Isabelle Baussanne Naceur Belgacem Daniel Lee Sabine Hediger Martine Demeunynck Julien Bras Gaël De Paëpe 《Chemical science》2020,11(15):3868
Cellulose nanofibrils (CNF) are renewable bio-based materials with high specific area, which makes them ideal candidates for multiple emerging applications including for instance on-demand drug release. However, in-depth chemical and structural characterization of the CNF surface chemistry is still an open challenge, especially for low weight percentage of functionalization. This currently prevents the development of efficient, cost-effective and reproducible green synthetic routes and thus the widespread development of targeted and responsive drug-delivery CNF carriers. We show in this work how we use dynamic nuclear polarization (DNP) to overcome the sensitivity limitation of conventional solid-state NMR and gain insight into the surface chemistry of drug-functionalized TEMPO-oxidized cellulose nanofibrils. The DNP enhanced-NMR data can report unambiguously on the presence of trace amounts of TEMPO moieties and depolymerized cellulosic units in the starting material, as well as coupling agents on the CNFs surface (used in the heterogeneous reaction). This enables a precise estimation of the drug loading while differentiating adsorption from covalent bonding (∼1 wt% in our case) as opposed to other analytical techniques such as elemental analysis and conductometric titration that can neither detect the presence of coupling agents, nor differentiate unambiguously between adsorption and grafting. The approach, which does not rely on the use of 13C/15N enriched compounds, will be key to further develop efficient surface chemistry routes and has direct implication for the development of drug delivery applications both in terms of safety and dosage.DNP-enhanced solid-state NMR unravels the surface chemistry of functionalized nanocellulose. 相似文献