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141.
A Calix[6]arene scaffold was functionalized to provide a tridentate binding site at the small rim and three bidentate chelate sites at the large rim of the cone to generate a heteropolytopic ligand. Its complexation to one equivalent of Zn(II) at the small rim yields a funnel complex displaying both host-guest properties and preorganization of the three chelate groups at the large rim. These two aspects allowed the full control of the binding events to regioselectively form dinuclear Zn(II) and heteropolynuclear Zn(II)/Cu(I) complexes. The heteropolynuclear systems all rely on the host-guest relationship thanks to the induced-fit behavior of the calix cavity. With the short guest MeCN, the large rim is preorganized into a trigonal tris-triazole core and accommodates a single Cu(I) ion. A long guest breaks this spatial arrangement, and three Cu(I) ions can then be bound at the tris-bidentate triazole-dimethylamine site at the large rim. In a noncoordinating solvent however, the tetranuclear complex is submitted to scrambling and the addition of exogenous π-acceptor ligands is required to control the binding of Cu(I) in a well-defined environment. Hindrance selectivity was then induced by the accessibility at the small rim site. Indeed, while CO can stabilize Cu(I) at both coordination sites, PPh(3) cannot fit into the cavity and forces Cu(I) to relocate at the large rim. The resulting well-defined symmetrical tetranuclear complex thus arises from the quite remarkable selective supramolecular assembly of nine partners (1 Zn(II), 3 Cu(I), 1 calixarene, 1 guest alkylamine, 3 PPh(3)). 相似文献
142.
Benoit Perthame Athanasios E. Tzavaras 《Archive for Rational Mechanics and Analysis》2000,155(1):1-48
For scalar conservation laws, the kinetic formulation makes it possible to generate all the entropies from a simple kernel.
We show how this concept replaces and simplifies greatly the concept of Young measures, avoiding the difficulties encountered
when working in L
p
. The general construction of the two kinetic functions that generate the entropies of 2 × 2 strictly hyperbolic systems
is also developed here. We show that it amounts to building a “universal” entropy, i.e., one that can be truncated by a “kinetic
value” along Riemann invariants. For elastodynamics, this construction can be completed and specialized using the additional
Galilean invariance. This allows a full characterization of convex entropies. It yields a kinetic formulation consisting of
two semi-kinetic equations which, as usual, are equivalent to the infinite family of all the entropy inequalities.
Accepted May 29, 2000?Published online November 16, 2000 相似文献
143.
We show that every core graph with a primitive automorphism group has the property that whenever it is a retract of a product of connected graphs, it is a retract of a factor. The example of Kneser graphs shows that the hypothesis that the factors are connected is essential. In the case of complete graphs, our result has already been shown in [4, 17], and it is an instance where Hedetniemi's conjecture is known to hold. In fact, our work is motivated by a reinterpretation of Hedetniemi's conjecture in terms of products and retracts. 相似文献
144.
Martin Poncelet Prof. Dr. Benoit Driesschaert 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(38):16593-16596
A stable triarylmethyl spin probe whose electron paramagnetic resonance (EPR) spectrum is highly sensitive to molecular tumbling is reported. The strong anisotropy of the hyperfine coupling tensor with the central carbon of a 13C1-labeled triarylmethyl radical enables the measurement of the probe rotational correlation time with applications to measure microviscosity and molecular dynamics. 相似文献
145.
Dr. Benoit Colasson Prof. Alberto Credi Dr. Barbara Ventura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(2):534-542
The interlocking of ring and axle molecular components in rotaxanes provides a way to combine chromophoric, electron-donor and electron-acceptor moieties in the same molecular entity, in order to reproduce the features of photosynthetic reaction centers. To this aim, the photoinduced electron transfer processes involving a 1,8-naphthalimide chromophore, embedded in several rotaxane-based dyads, were investigated by steady-state and time-resolved absorption and luminescence spectroscopic experiments in the 300 fs–10 ns time window. Different rotaxanes built around the dialkylammonium/ dibenzo[24]crown-8 ether supramolecular motif were designed and synthesized to decipher the relevance of key structural factors, such as the chemical deactivation of the ammonium-crown ether recognition, the presence of a secondary site for the ring along the axle, and the covalent functionalization of the macrocycle with a phenothiazine electron donor. Indeed, the conformational freedom of these compounds gives rise to a rich dynamic behavior induced by light and may provide opportunities for investigating and understanding phenomena that take place in complex (bio)molecular architectures. 相似文献
146.
The elastic behaviour with temperature near the commensurate incommensurate phase transition of [N (CH3)4 Zn Cl4] have been investigated by Brillouin scattering and compared to ultrasonic results. Elastic and attenuation anomalies observed at 8 MHz are not found at Brillouin frequency. Photoelastic coefficients have been measured. 相似文献
147.
148.
Jacob D. Porter Eric Greve Abdulmohsen Alsafran Adam R. Benoit Sergey V. Lindeman Chris Dockendorff 《Tetrahedron》2018,74(37):4823-4836
Bifunctional catalysts containing discrete metal pi-acid and amine sites were designed and investigated for the direct intermolecular addition of aldehydes and ketones to unactivated alkynes. Copper(I)-based catalysts were prioritized based on intramolecular (Conia-ene type) reactions, and complexes were designed with tridentate ligands and potentially hemilabile heterocyclic spacers. The structures of the designed catalysts were computed using density functional theory (DFT), and the relative energies of putative catalytic intermediates were estimated and used to prioritize catalyst designs. Novel bifunctional precatalysts containing a thiazole spacer were synthesized via a 9-step sequence and combined with transition metals before screening for the direct addition of aldehydes and ketones to several internal and terminal alkynes. Despite the lack of desired intermolecular reactions, DFT calculations of putative catalyst intermediates appears to be a promising strategy for the design and prioritization of bifunctional catalysts for CC bond formation. 相似文献
149.
Morgane Sayes Guillaume Benoit Prof. André B. Charette 《Angewandte Chemie (International ed. in English)》2018,57(41):13514-13518
Herein, we report a user‐friendly and metal‐free UV‐A light mediated borocyclopropanation of styrenes using continuous flow technology. A broad range of styrene derivatives can be cyclopropanated in good yields within 1 h residence time to produce highly valuable cyclopropylboronate esters with modest to good diastereoselectivities. The reaction is also applicable to α‐substituted styrenes. Mechanistic studies support a photoredox process during which xanthone, a well‐known organic photosensitizer, can easily reach a photoexcited state that is available for both an oxidative and a reductive quenching. 相似文献
150.
This review provides an overview of the various synthetic pathways of the N-CF3 group. This pattern can be generated either from fluoride ions or from electrophilic, nucleophilic, or radical trifluoromethylation. This article mainly focuses on the most recent and prominent studies. 相似文献