Search results for "54"
showing 10 items of 2200 documents
Crystal structure of 12-benzylsulfanyl-2,9-dibromo-6H-dibenzo[b,g][1,8]naphthyridin-11-one
2015
The hetero-tetra-cene skeleton of the title mol-ecule, C23H14Br2N2OS, is defined by linear annulation of four six-membered rings, including two N heteroatoms. This moiety is nearly planar (r.m.s. deviation = 0.055 Å), with a slight twist of 4.1 (2)° between the two halves of the aromatic system. The dihedral angle between the least-squares plane of the skeleton and the benzyl group is 24.5 (3)°; the C-S-C angle involving the benzyl-sulfanyl group is 99.2 (4)°. In the crystal, mol-ecules are π-stacked in an anti-parallel fashion along [110], with a distance between the aromatic planes of 3.47 (2) Å. Inter-molecular N-H⋯O hydrogen bonds form chains extending parallel to [001] and bridge the a…
Development of a Method for Anodic Degradation of Lignin for the Analysis of Paleo‐Vegetation Proxies in Speleothems
2022
Synthesis, Thermal, and Optical Properties of Tris(5‐aryl‐1,3,4‐oxadiazol‐2‐yl)‐1,3,5‐triazines, New Star‐Shaped Fluorescent Discotic Liquid Crystals
2019
Abstract The synthesis of tris(aryloxadiazolyl)triazines (TOTs), C 3‐symmetrical star‐shaped mesogenes with a 1,3,5‐triazine center, 5‐phenyl‐1,3,4‐oxadiazole arms, and various peripheral alkoxy side chains is reported. Threefold Huisgen reaction on a central triazine tricarboxylic acid and suitable aryltetrazoles yields the title compounds. Selected analogues with a benzene center are included in this study and allow for an evaluation of the impact of the central unit on the physical properties. Thermal (differential scanning calorimetry, DSC; polarization optical microscopy, POM), optical (UV/Vis, fluorescence), electric (time of flight, TOF), and structural (single crystal; wide‐angle X‐…
Sintesis y evaluación biológica de nuevos derivados de tipo imidazolina y etanolamina fluorados
2011
Una de las principales áreas de interés de la química orgánica es la búsqueda de nuevos compuestos con actividad biológica. En este sentido cabe destacar el especial interés que despiertan los compuestos nitrogenados debido a que constituyen una de las familias más numerosas entre las biomoléculas y que están implicados en múltiples procesos a nivel metabólico y estructural. Un ejemplo representativo los constituyen los compuestos de tipo etanolamina, ampliamente estudiados por sus variadas y numerosas aplicaciones. Por una parte han servido como modelo para el diseño de peptidomiméticos derivados de hidroxietilamina, que resultan interesantes como inhibidores de proteasas. Algunos de ellos…
Reacciones de Friedel-Crafts enantioselectivas catalizadas por complejos de metales de transición del grupo (IV) y binol
2010
La reacción de Friedel-Crafts es un poderoso proceso de formación de enlaces carbono-carbono de gran importancia en síntesis orgánica. La aplicación de la versión asimétrica catalítica de esta reacción a la alquilación de arenos ricos en electrones, como indoles o pirroles, puede proporcionar acceso a importantes productos enantioméricamente enriquecidos alquilados y constituyen un tema de actual interés, ya que estos arenos se han identificado como estructuras "privilegiadas" o farmacóforos. Los complejos Zr(IV) y Hf(IV)-BINOL generados in situ han sido evaluados como catalizadores en la alquilación de Friedel-Crafts enantioselectiva de indoles y pirroles con diferentes cetonas α, β-insatu…
Uso de la calculadora gvSIG 1.10
2010
Uso de la calculadora gvSIG 1.10
Multiple facets of inverse continuity
2021
International audience; Inversion of various inclusions that characterize continuity in topological spaces results in numerous variants of quotient and perfect maps. In the framework of convergences, the said inclusions are no longer equivalent, and each of them characterizes continuity in a different concretely reflective subcategory of convergences. On the other hand, it turns out that the mentioned variants of quotient and perfect maps are quotient and perfect maps with respect to these subcategories. This perspective enables use of convergence-theoretic tools in quests related to quotient and perfect maps, considerably simplifying the traditional approach. Similar techniques would be un…
Group topologies coarser than the Isbell topology
2011
Abstract The Isbell, compact-open and point-open topologies on the set C ( X , R ) of continuous real-valued maps can be represented as the dual topologies with respect to some collections α ( X ) of compact families of open subsets of a topological space X . Those α ( X ) for which addition is jointly continuous at the zero function in C α ( X , R ) are characterized, and sufficient conditions for translations to be continuous are found. As a result, collections α ( X ) for which C α ( X , R ) is a topological vector space are defined canonically. The Isbell topology coincides with this vector space topology if and only if X is infraconsonant. Examples based on measure theoretic methods, t…
Variations of selective separability II: Discrete sets and the influence of convergence and maximality
2012
A space $X$ is called selectively separable(R-separable) if for every sequence of dense subspaces $(D_n : n\in\omega)$ one can pick finite (respectively, one-point) subsets $F_n\subset D_n$ such that $\bigcup_{n\in\omega}F_n$ is dense in $X$. These properties are much stronger than separability, but are equivalent to it in the presence of certain convergence properties. For example, we show that every Hausdorff separable radial space is R-separable and note that neither separable sequential nor separable Whyburn spaces have to be selectively separable. A space is called \emph{d-separable} if it has a dense $\sigma$-discrete subspace. We call a space $X$ D-separable if for every sequence of …
Existence de points fixes enlacés à une orbite périodique d'un homéomorphisme du plan
1992
Let f be an orientation-preserving homeomorphism of the plane such that f-Id is contracting. Under these hypotheses, we establish the existence, for every periodic orbit, of a fixed point which has nonzero linking number with this periodic orbit.