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31.
Alessandra Farina Stefano Valdo Meille Maria Teresa Messina Pierangelo Metrangolo Giuseppe Resnati Giuseppe Vecchio 《Angewandte Chemie (International ed. in English)》1999,38(16):2433-2436
Halogen bonds , attractive intermolecular interactions between perfluoroalkyl bromides and bromide ions, are present in cocrystals of (−)-sparteinium hydrobromide ( 1 ) and (S)-1,2-dibromohexafluoropropane ( 2 ; shown schematically), and result in enantiopure and infinite supramolecular helices. The perfluorocarbon–hydrocarbon self-assembly allows the resolution of racemic 2 . 相似文献
32.
This paper regards the existence of entropy waves for a model example of nonstrictly hyperbolic system which degenerates on a sonic line. This construction is an important tool to approach the convergence of the vanishing viscosity and of other similar approximations to the weak solutions of the hyperbolic systems, via the compensated compactness techniques. 相似文献
33.
Stefano Cicchi Dr. Pierangelo Fabbrizzi Dr. Giacomo Ghini Dr. Alberto Brandi Prof. Paolo Foggi Prof. Agnese Marcelli Dr. Roberto Righini Prof. Chiara Botta Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(3):754-764
A series of dendrimeric compounds bearing pyrene units were synthesized to afford light‐harvesting antennae based on the formation of intramolecular excimers. The synthetic plan profited from the efficiency of the Huisgen reaction, the 1,3‐dipolar cycloaddition of azides and terminal alkynes, which allowed ready assembly of the different building blocks. The three molecular antennae obtained, of increasing generation, revealed efficient energy transfer both in solution and in the solid state. 相似文献
34.
Natural Abundance 15N and 13C Solid‐State NMR Chemical Shifts: High Sensitivity Probes of the Halogen Bond Geometry
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Paolo Cerreia Vioglio Luca Catalano Dr. Vera Vasylyeva Prof. Carlo Nervi Prof. Michele R. Chierotti Prof. Giuseppe Resnati Prof. Roberto Gobetto Prof. Pierangelo Metrangolo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16819-16828
Solid‐state nuclear magnetic resonance (SSNMR) spectroscopy is a versatile characterization technique that can provide a plethora of information complementary to single crystal X‐ray diffraction (SCXRD) analysis. Herein, we present an experimental and computational investigation of the relationship between the geometry of a halogen bond (XB) and the SSNMR chemical shifts of the non‐quadrupolar nuclei either directly involved in the interaction (15N) or covalently bonded to the halogen atom (13C). We have prepared two series of X‐bonded co‐crystals based upon two different dipyridyl modules, and several halobenzenes and diiodoalkanes, as XB‐donors. SCXRD structures of three novel co‐crystals between 1,2‐bis(4‐pyridyl)ethane, and 1,4‐diiodobenzene, 1,6‐diiodododecafluorohexane, and 1,8‐diiodohexadecafluorooctane were obtained. For the first time, the change in the 15N SSNMR chemical shifts upon XB formation is shown to experimentally correlate with the normalized distance parameter of the XB. The same overall trend is confirmed by density functional theory (DFT) calculations of the chemical shifts. 13C NQS experiments show a positive, linear correlation between the chemical shifts and the C?I elongation, which is an indirect probe of the strength of the XB. These correlations can be of general utility to estimate the strength of the XB occurring in diverse adducts by using affordable SSNMR analysis. 相似文献
35.
This work discusses the choice of a reference frame for beam section stiffness properties. Established concepts as the center of elasticity, the center of stiffness and the center of compliance are discussed and contextualized. An interpretation of univocally defined generalized strain transformations is given in terms of minimization of appropriate norms of the stiffness and compliance matrices of the beam section that univocally define special reference points. Transformations of generalized strain perturbations that preserve the angular strain are sought. They are subsequently constrained to represent a change of reference point, and further restricted to lie in the plane of the section. Each transformation is univocally defined and given a clear mathematical and geometrical interpretation. It is recognized that transformations that decouple forces and linear strains from moments and angular strains cannot be described as a mere change of reference point. 相似文献
36.
37.
This paper is concerned with the low Mach number limit for the compressible Navier-Stokes equations in an exterior domain.We present here an approach based on Strichartz estimate defined on a non trapp... 相似文献
38.
Maria Teresa Messina Pierangelo Metrangolo Silvio Quici Amedea Manfredi Tullio Pilati 《Supramolecular chemistry》2013,25(4):405-410
Abstract 4′-(4-Methylphenyl)-2,2′:6′,2″-terpyridine (1) self-assembles with dihaloperfluoroarenes (2). A chemo- and site-selective supramolecular synthesis occurs which preserves in the solid cocrystal the most stable s-trans, s-trans conformation of the pure terpyridine module. The single crystal X-ray structure of 3a, prepared from 1 and 1,4-diiodotetrafluorobenzene (2a) (monoclinic, a = 14.608(1), b = 13.276(1), c = 13.970(2) Å, β = 109.808(8)°, U = 2549.4 (4) Å3, T = 291 (1) K, space group C2/c Z = 4; μ(Mo-Kα) = 2.519 mm?1; d calc.: 1.890 g cm?3; 5748 reflections measured, 3715 unique (Rint = 0.024) which were used in all calculations; the final R and wR (F 2) were 0.043 and 0.069, respectively) shows the presence of infinite ribbons where the two modules alternate in a zigzag arrangement. 相似文献
39.
Giuseppe Gattuso Rosalba Liantonio Pierangelo Metrangolo Franck Meyer Andrea Pappalardo 《Supramolecular chemistry》2013,25(3):235-243
1,3-Bis(α-picolyloxy)-p-tert-butylcalix[4]crown-5 in the cone conformation (2), 1,8-diiodoperfluorooctane or 1,6-diiodoperfluorohexane, and potassium iodide ternary mixtures undergo in solution self-sorting and afford crystalline “supramolecular salts”. These hybrid materials consist of supercation [K+ ? 2] and superanion [I–(CF2) n –I…I? …I–(CF2) n –I…I? …] (n = 6,8) components. In the supercations the potassium ion is embedded in the ionophoric pocket created by the heteroatoms present at the lower rim. In the superanions the iodide ions form infinite fluorous polyanionic chains as a result of a self-assembly process which relies on halogen bonding. Both cation encapsulation and anion-perfluorocarbon halogen bonding were detected in solution by 1H and 19F NMR, and in the gas phase by ESI MS. 相似文献
40.
Cavallotti C Metrangolo P Meyer F Recupero F Resnati G 《The journal of physical chemistry. A》2008,112(40):9911-9918
19F NMR measurements and theoretical calculations were performed to study paramagnetic complexes of iodoperfluorocarbons with stable nitroxide radicals. Contrary to what is usually measured for diamagnetic halogen-bonded complexes involving iodoperfluorocarbons, it was found that the formation of complexes with the 2,2,6,6-tetramethyl(piperidin-1-yloxyl) (TEMPO) radical determines downfield shifts in the 19F NMR spectra. The experimental finding was confirmed by calculating nuclear shielding using density functional theory and correcting the isotropic diamagnetic (19)F chemical shift with contact interactions evaluated from the hyperfine coupling tensor. The computational analysis of the interaction between CF3I and TEMPO, by using DFT and MP2 theories, showed that the occurrence of the halogen bond between the interacting partners is associated with a significant charge transfer to CF3I and that the measured downfield shift is due to the occurring spin transfer. 相似文献