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961.
Lucía Álvarez-Rodríguez Prof. Dr. Javier A. Cabeza Dr. Pablo García-Álvarez Prof. Dr. Mar Gómez-Gallego Laura González-Álvarez Alba D. Merinero Prof. Dr. Miguel A. Sierra 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(6):1588-1594
The formation of the five-membered-ring germylene complexes [M(CO)5{Ge(tBu2bzamC(OEt)Me)tBu}] ( 3M ; M=Cr, W), which occurs readily at room temperature from the germylene Ge(tBu2bzam)tBu ( 1 t Bu ) and Fischer carbenes [M(CO)5{C(OEt)Me}] ( 2M ; M=Cr, W), has been found to be reversible. Upon heating at 60 °C, complexes 3M undergo epimerization to an equilibrium mixture of 3M and 3′M . At that temperature, the chromium epimers (but not the tungsten ones) release CO to end in the mixed germylene–Fischer carbene complexes [Cr(CO)4{C(OEt)Me}{Ge(tBu2bzam)tBu}] (cis- 4Cr and trans- 4Cr ). The latter decompose at 120 °C to [Cr(CO)5{Ge(tBu2bzam)tBu}] ( 6Cr ). Because the formation of cis- 4Cr and trans- 4Cr from 3Cr or 3′Cr requires the presence of free 1 t Bu and 2Cr in the reaction solutions, the reactions of 1 t Bu with 2M to give 3M (and 3′M at 60 °C) should be reversible. This proposal has been proven by germylene-exchange crossover reactions in which free 1 t Bu and [M(CO)5{Ge(tBu2bzamC(OEt)Me)CH2SiMe3}] ( 5′M ; M=Cr, W) were formed when complexes 3M were treated at room temperature with the germylene Ge(tBu2bzam)CH2SiMe3 ( 1tmsm ). A clear differential behavior between N-heterocyclic carbenes (NHCs) and amidinatogermylenes ( 1 t Bu and 1tmsm ) in their reactivity against group 6 metal Fischer carbene complexes is demonstrated. The higher electron-donor capacity of amidinatogermylenes with respect to NHCs and the bias of the former to get involved in ring expansion processes are responsible for this differential behavior. 相似文献
962.
Dr. Pilar Hoyos Dr. Almudena Perona Dr. Olga Juanes Dr. Ángel Rumbero Dr. María J. Hernáiz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(28):7593-7624
Glycodendrimers are an important class of synthetic macromolecules that can be used to mimic many structural and functional features of cell-surface glycoconjugates. Their carbohydrate moieties perform key important functions in bacterial and viral infections, often regulated by carbohydrate–protein interactions. Several studies have shown that the molecular structure, valency and spatial organisation of carbohydrate epitopes in glycoconjugates are key factors in the specificity and avidity of carbohydrate–protein interactions. Choosing the right glycodendrimers almost always helps to interfere with such interactions and blocks bacterial or viral adhesion and entry into host cells as an effective strategy to inhibit bacterial or viral infections. Herein, the state of the art in the design and synthesis of glycodendrimers employed for the development of anti-adhesion therapy against bacterial and viral infections is described. 相似文献
963.
Ángel M. Montaña Stefano Ponzano Consuelo Batalla Mercè Font-Bardia 《Tetrahedron》2012,68(39):8276-8285
An α-benzyloxyketone forming part of a strained cyclopentane carbon framework when treated with 10 equiv of anhydrous NaOH in absolute ethanol, for 2 h, affords in a 65% yield a new 2-benzyl-2-hydroxyketone, resulting from an unprecedented double benzylic rearrangement. This new rearrangement could be interpreted as an initial benzylic 1,4-shift between the O-enolate alkoxide of the ketone group and the oxygen atom of the benzyloxy ether, followed by a Curtin type benzylic 1,2-shift. Apart from the novelty and the synthetic application of this transformation it is worth noting the complete regio- and stereoselectivity observed. The structures of both substrate and product have been confirmed by X-ray diffraction studies. A tentative mechanism is herein proposed. 相似文献
964.
M. José González-Álvarez Natalia Mayordomo Laura Gallego-Yerga Carmen Ortiz Mellet Francisco Mendicuti 《Tetrahedron》2012,68(14):2961-2972
Steady-state and time-resolved fluorescence techniques have been employed in the study of the complexation of methyl 2-naphthalenecarboxylate (2MN), a fluorescent probe, with 2I,3I-O-(o-Xylylene)-per-O-Me-α-, -β-, and -γ-cyclodextrins (Xmα-, Xmβ-, and XmγCDs, respectively), which have also the capability of self-aggregate. The influence of the xylylene moiety was assessed by comparing the data of 2MN complexation by Xmα-, Xmβ-, and XmγCD with those obtained for their fully permethylated mα-, mβ-, and mγCD counterparts. The 2MN emission spectrum shows two overlapping electronic bands whose ratio of intensities, R, is very sensitive to the polarity of the surrounding medium. The stoichiometry, the complex formation constants and the ΔH0 and ΔS0 parameters upon inclusion were obtained from the variations in R and 〈τ〉 as a function of CD concentration and temperature. 2MN forms 1:1 stoichiometry complexes with all the CDs. Molecular Mechanics and Molecular Dynamics calculations were performed to simulate the complexation processes in the presence of water, determine their preferred structures, and ascertain the host–guest interactions at play. 相似文献
965.
RUI P. BONIFÁCIO EDUARDO J. M. FILIPE CLARE McCABE MARGARIDA F. COSTA GOMES AGÍLIO A. H. PÁDUA 《Molecular physics》2013,111(15):2547-2553
The solubility of xenon in n-hexane and n-perfluorohexane has been studied using both molecular simulation and a version of the SAFT approach (SAFT-VR). The calculations were performed close to the saturation line of each solvent, between 200 K and 450 K, which exceeds the smaller temperature range where experimental data are available in the literature. Molecular dynamics simulations, associated with Widom's test particle insertion method, were used to calculate the residual chemical potential of xenon in n-hexane and n-perfluorohexane and the corresponding Henry's law coefficients. The simulation results overestimate the solubility of xenon in both solvents when simple geometric combining rules are used, but are in good agreement if a binary interaction parameter is included. With the SAFT-VR approach we are able to reproduce the experimental solubility for xenon in n-hexane, using simple Lorentz-Berthelot rules to describe the unlike interaction. In the case of n-perfluorohexane as a solvent, a binary interaction parameter was introduced, taken from previous work on (xe + C2F6) mixtures. Overall, good agreement is obtained between the simulation, theoretical and experimental data. 相似文献
966.
Marta González Roi Álvarez Rodríguez Maria Magdalena Cid Carlos Silva López 《Journal of computational chemistry》2012,33(13):1236-1239
The mechanism of the acetylene homologation procedure accidentally discovered and further developed by Crabbé and coworkers is unknown. Kinetic isotope effect (KIE) experiments, however, suggest that an intramolecular hydrogen shift is the key step of the transformation. In this work, we present a computational study of this mechanism. We found that the reaction proceeds via an unexpected stepwise retro‐imino‐ene rearrangement. This mechanism justifies the role of Cu(I) as a reaction catalyst and is also compatible with the KIE experiments reported. © 2012 Wiley Periodicals, Inc. 相似文献
967.
968.
Ángel Manu Martínez Dr. Inés Alonso Dr. Nuria Rodríguez Dr. Ramón Gómez Arrayás Prof. Dr. Juan C. Carretero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(22):5733-5742
A new mode of reactivity of 1,3-diynes in rhodium-catalyzed oxidative annulation reactions has enabled the rapid assembly of extended π systems from readily available picolinamide derivatives. The process involves a double C−H bond activation and the iterative annulation of two 1,3-diyne units, with each alkyne moiety engaged in an orchestrated insertion sequence with high regiocontrol, leading to the formation of five new C−C bonds and the construction of four fused rings in a single operation. Either isoquinoline-1-carboxamides or fused polycyclic systems can be accessed by a switch in the regioselectivity of the second diyne insertion depending on the reaction conditions. DFT theoretical calculations have elucidated that the cooperative participation of both rhodium and copper in substrate activation, favored in the presence of excess of the copper(II) salt, is key to such a reversal of regioselectivity and subsequent multiple cyclization leading to fused polycyclic products. The role of copper was found to be essential in assisting both multiple insertion and rhodium-walking sequences, with the implication of intermediates with a Rh−Cu bond (2.60 Å). 相似文献
969.
Dr. Carlos Alberto López Dr. María Consuelo Álvarez-Galván Dr. María Victoria Martínez-Huerta Dr. María Teresa Fernández-Díaz Dr. José Antonio Alonso 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(17):4496-4500
The hybrid methylammonium (MA) lead halide MAPbX3 perovskites present an appealing optoelectronic behavior with applications in high-efficiency solar cells. The orientation of the organic MA units may play an important role in the properties, given the degrees of freedom for internal motion of MA groups within the PbX6 network. The present neutron powder diffraction study reveals the dynamic features of the MA units in the hybrid perovskite series MAPb(Br1−xClx)3, with x=0, 0.33, 0.5, 0.67, and 1. From difference Fourier maps, the H and C/N positions were located within the PbX6 lattice; the refinement of the crystal structures unveiled the MA conformations. Three different orientations were found to exist as a function of the chlorine content (x) and, therefore, of the cubic unit-cell size. These conformations are stabilized by H-bond interactions with the halide ions, and were found to agree with those reported from theoretical calculations. 相似文献
970.
Vanessa C. Arias-Coronado Dr. Raquel Pereira-Cameselle Ani Ozcelik Dr. Maria Talavera Prof. Dr. Ángeles Peña-Gallego Dr. J. Lorenzo Alonso-Gómez Prof. Dr. Sandra Bolaño 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(59):13496-13499
Spirobifluorene derivatives find use in many end-user applications. Therefore, further expansion of their scope is the focus of many research studies. However, although the optical properties of spirobifluorenes can be greatly tuned through incorporation of metal complexes, to date, spirobifluorene metallaaromatics remain unknown. Taking advantage of the versatility of our methodology for the synthesis of metallaaromatic systems, this work reports the first metallaaromatic spirobifluorene compound. The presence of an Ir atom was found to redshift the absorption maximum by ca. 1.1 eV compared to bare spirobifluorene. Additionally, X-ray analysis as well as anisotropy of the current-induced density calculations revealed this compound to be of aromatic nature. The high stability in solution, solid state, under air, and at high temperature, as well as distinct optical properties of this new class of compounds are expected to open new frontiers for chiroptical and optoelectronic applications. 相似文献