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191.
192.
Chantal Galaup Joëlle Azma Pierre Tisns Claude Picard Patricia Ramos Olga Juanes Ernesto Brunet JuanCarlos Rodríguez‐Ubis 《Helvetica chimica acta》2002,85(6):1613-1625
Two macrobicyclic ligands derived from an 18‐membered tetralactam ring and 2,2′‐bipyridine or 2,6‐bis(pyrazol‐1‐yl)pyridine moieties, 1 and 2 , respectively, form stable complexes with GdIII, EuIII, and TbIII ions in aqueous solution. The ligand‐based luminescence is retained in the GdIII cryptates, whereas this radiative deactivation is quenched in the EuIII and TbIII cryptates by ligand‐to‐metal energy transfer, resulting in the usual metal‐centered emission spectra. Singlet‐ and triplet‐state energies, emission‐decay lifetimes, and luminescence yields were measured. [Tb⊂ 1 ]3+ cryptate shows a long luminescence lifetime (τ=1.12 ms) and a very high metal luminescence quantum yield (Φ=0.25) in comparison with those reported in the literature for Tb3+ complexes sensitized by a bipyridine chromophore. By comparison to [Ln⊂ 1 ]3+, [Ln⊂ 2 ]3+ presents markedly lower luminescence properties, due to worse interaction between the 2,6‐bis(pyrazol‐1‐yl)pyridine unit and the metal ion. Moreover, the luminescent metal and the triplet ligand energy levels of [Eu⊂ 2 ]3+ do not match. The effects of H2O molecules coordinated to the metal centre and of thermally activated decay processes on nonradiative deactivation to the ground‐state are also reported. 相似文献
193.
Ernesto Schulz Lang Robert Alan Burrow Lenice de Loureno Marques 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(3):m95-m96
The title compound, [Au(C10H9N4O2S)(C18H15P)], is nearly linear at AuI, with Au—N = 2.0707 (18) Å, Au—P = 2.2310 (8) Å and N—Au—P 171.93 (5)°. The molecules are linked by intermolecular N—H⃛O bonds. 相似文献
194.
Betweenness measures provide quantitative tools to pick out fine details from the massive amount of interaction data that is available from large complex networks. They allow us to study the extent to which a node takes part when information is passed around the network. Nodes with high betweenness may be regarded as key players that have a highly active role. At one extreme, betweenness has been defined by considering information passing only through the shortest paths between pairs of nodes. At the other extreme, an alternative type of betweenness has been defined by considering all possible walks of any length. In this work, we propose a betweenness measure that lies between these two opposing viewpoints. We allow information to pass through all possible routes, but introduce a scaling so that longer walks carry less importance. This new definition shares a similar philosophy to that of communicability for pairs of nodes in a network, which was introduced by Estrada and Hatano [E. Estrada, N. Hatano, Phys. Rev. E 77 (2008) 036111]. Having defined this new communicability betweenness measure, we show that it can be characterized neatly in terms of the exponential of the adjacency matrix. We also show that this measure is closely related to a Fréchet derivative of the matrix exponential. This allows us to conclude that it also describes network sensitivity when the edges of a given node are subject to infinitesimally small perturbations. Using illustrative synthetic and real life networks, we show that the new betweenness measure behaves differently to existing versions, and in particular we show that it recovers meaningful biological information from a protein-protein interaction network. 相似文献
195.
Rafael Fernández Dr. Abdessamad Grirrane Dr. Irene Resa Dr. Amor Rodríguez Dr. Ernesto Carmona Prof. Eleuterio Álvarez Dr. Enrique Gutiérrez‐Puebla Prof. Ángeles Monge Prof. Juan Miguel López del Amo Dr. Hans‐Heinrich Limbach Agustí Lledós Prof. Feliu Maseras Prof. Diego del Río Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(4):924-935
New zincocenes [ZnCp′2] ( 2 – 5 ) with substituted cyclopentadienyl ligands C5Me4H, C5Me4tBu, C5Me4SiMe2tBu and C5Me4SiMe3, respectively, have been prepared by the reaction of ZnCl2 with the appropriate Cp′‐transfer reagent. For a comparative structural study, the known [Zn(C5H4SiMe3)2] ( 1 ), has also been investigated, along with the mixed‐ring zincocenes [Zn(C5Me5)(C5Me4SiMe3)] ( 6 ) and [Zn(C5Me5)(C5H4SiMe3)] ( 7 ), the last two obtained by conproportionation of [Zn(C5Me5)2] with 5 or 1 , as appropriate. All new compounds were characterised by NMR spectroscopy, and by X‐ray methods, with the exception of 7 , which yields a side‐product ( C ) upon attempted crystallisation. Compounds 5 and 6 were also investigated by 13C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp′ ligands, while 3 and 4 exhibit slipped‐sandwich geometries. Compounds 5 and 6 have rigid, η5/η1(σ) structures, in which the monohapto C5Me4SiMe3 ligand is bound to zinc through the silyl‐bearing carbon atom, forming a Zn? C bond of comparable strength to the Zn? Me bond in ZnMe2. Zincocene 5 has dynamic behaviour in solution, but a rigid η5/η1(σ) structure in the solid state, as revealed by 13C CPMAS NMR studies, whereas for 6 the different nature of the Cp′ ligands and of the ring substituents of the η1‐Cp′ group (Me and SiMe3) have permitted observation for the first time of the rigid η5/η1 solution structure. Iminoacyl compounds of composition [Zn(η5‐C5Me4R)(η1‐C(NXyl)C5Me4R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl=2,6‐dimethylphenylisocyanide) have also been obtained and characterised. 相似文献
196.
Patricia Lara Margarita Paneque Prof. Dr. Manuel L. Poveda Prof. Dr. Laura L. Santos Dr. José E. V. Valpuesta Verónica Salazar Dr. Ernesto Carmona Prof. Dr. Salvador Moncho Gregori Ujaque Dr. Agustí Lledós Prof. Dr. Celia Maya Dr. Kurt Mereiter Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(36):9046-9057
Experimental and theoretical studies on equilibria between iridium hydride alkylidene structures, [(TpMe2)Ir(H){?C(CH2R)ArO }] (TpMe2=hydrotris(3,5‐dimethylpyrazolyl)borate; R=H, Me; Ar=substituted C6H4 group), and their corresponding hydride olefin isomers, [(TpMe2)Ir(H){R(H)C? C(H)OAr}], have been carried out. Compounds of these types are obtained either by reaction of the unsaturated fragment [(TpMe2)Ir(C6H5)2] with o‐C6H4(OH)CH2R, or with the substituted anisoles 2,6‐Me2C6H3OMe, 2,4,6‐Me3C6H2OMe, and 4‐Br‐2,6‐Me2C6H2OMe. The reactions with the substituted anisoles require not only multiple C? H bond activation but also cleavage of the Me? OAr bond and the reversible formation of a C? C bond (as revealed by 13C labeling studies). Equilibria between the two tautomeric structures of these complexes were achieved by prolonged heating at temperatures between 100 and 140 °C, with interconversion of isomeric complexes requiring inversion of the metal configuration, as well as the expected migratory insertion and hydrogen‐elimination reactions. This proposal is supported by a detailed computational exploration of the mechanism at the quantum mechanics (QM) level in the real system. For all compounds investigated, the equilibria favor the alkylidene structure over the olefinic isomer by a factor of between approximately 1 and 25. Calculations demonstrate that the main reason for this preference is the strong Ir–carbene interactions in the carbene isomers, rather than steric destabilization of the olefinic tautomers. 相似文献
197.
198.
Cavalli A Masetti M Recanatini M Prandi C Guarna A Occhiato EG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(10):2836-2845
Density functional theory (DFT) has been used to define the energy profiles of the Nazarov reaction involving cyclic systems. The calculations were carried out at the B3LYP/6-311G** level of theory and the solvent (dichloromethane) contribution was estimated by using the recently developed SM5.43R solvation model. DFT calculations were first carried out to determine the energy profiles associated with the electrocyclization reactions of 3-hydroxy- and 3-ethoxypentadienyl cations in which one of the double bonds is embedded in O-heterocyclic and carbocyclic systems. In particular, the effects on the reaction rate of modifications to the substrate, as well as the presence of the heteroatom in the cycle, have been investigated. The torquoselectivity of the electrocyclization reaction was then explored with substituted O-heterocycles to understand the factors that control the stereochemical outcome of the process that preferentially provides 2,5-trans-disubstituted products. These DFT-based results rationally explain most of the experimental observations related to the Nazarov reaction of the substrates herein investigated and could be useful in the rational interpretation, and likely in the prediction, of the outcome of Nazarov reactions involving other cyclic systems. 相似文献
199.
200.
The selective cleavage of methoxy protecting groups next to hydroxy groups is achieved using a radical hydrogen abstraction reaction as the key step. Under the reaction conditions, the hydroxy group generates an alkoxyl radical that reacts with the sterically accessible adjacent methoxy group, which is transformed into an acetal. In the second step, the acetals are hydrolyzed to give alcohols or diols. A one-pot hydrogen abstraction-hydrolysis procedure was also developed. Good yields were usually achieved, and the mild conditions of this methodology were compatible with different functional groups and sensitive substrates such as carbohydrates. 相似文献