Search results for "Polarity"
showing 10 items of 196 documents
Conformational properties of oxazoline-amino acids
2016
Abstract Oxazoline-amino acids (Xaa-Ozn) occur in natural peptides of potentially important bioactivity. The conformations of the model compounds: Ac-(S)-Ala-Ozn(4R-Me), Ac-(S)-Ala-Ozn(4S–Me), and (gauche+, gauche−, anti) Ac-(S)-Val-Ozn(4R-Me) were studied at meta-hybrid M06-2X/6–311++G(d,p) method including solvent effect. Boc- l -Ala- l -Ozn-4-COOMe and Boc- l -Val- l -Ozn-4-COOMe were synthesized and studied by FT-IR and NMR-NOE methods. The conformations in crystal state were gathered from the Cambridge Structural Data Base. The main conformational feature of the oxazoline amino acids is the conformation β2 (ϕ,ψ ∼ −161°, −6°), which predominates in weakly polar environment and still is …
Synthesis and characterization of a new spirooxindole grafted pyrrolidino/piperidine moiety
2021
In this text, we synthesized and characterized a new spirooxindole grafted pyrrolidino/piperidine moieties. The new hit obtained via one-pot reaction of the chalcone based cyclohexanone with the isatin and (R)-piperidine-2-carboxylic acid in MeOH under reflux for 48 h. The compound exclusively obtained in regio-selective and diastereo-selective manner. The chemical feature of the target compound is confirmed by 1H NMR and 13C NMR spectroscopy. In addition, we reported for the first time the X-ray single crystal structure of isatin. Its molecular packing depends mainly on strong O…H hydrogen bonds and π-π stacking interactions as well as weak H…H and H…C contacts. Using DFT calculations, is…
ChemInform Abstract: Diaryldistyrylpyrazines: Solvatochromic and Acidochromic Fluorophores.
2014
Diaryldimethylpyrazines are the starting materials for the synthesis of C2-symmetric donor- or acceptor-substituted distyrylpyrazines. The optical properties of these cruciform-shaped dyes are dominated by the distyrylpyrazine units; the photophysics is controlled by the styryl substitution, the diaryl substituents on the central pyrazine only having a small effect. Protonation occurs on the pyrazine and/or lateral amines or azines, thereby altering the absorption and emission properties. Hypso- and bathochromism as well as fluorescence quenching depend on the nature of the terminal substituent. This, and a significant positive solvatochromism of the fluorescence, allow optical sensing of t…
Infrared bandshapes of intramolecularly H-bonded systems, 2,4,6-tribromophenol
1983
Abstract A detailed quantitative analysis of the IR bandshape of the ν S (OH) vibration of 2,4,6-tribromophenol in a series of solvents of varying polarity is presented. A distinct dependence of band parameters on solvent polarity has been found. Various contributions to the bandshape are discussed.
Diaryldistyrylpyrazines: Solvatochromic and Acidochromic Fluorophores
2013
Diaryldimethylpyrazines are the starting materials for the synthesis of C2-symmetric donor- or acceptor-substituted distyrylpyrazines. The optical properties of these cruciform-shaped dyes are dominated by the distyrylpyrazine units; the photophysics is controlled by the styryl substitution, the diaryl substituents on the central pyrazine only having a small effect. Protonation occurs on the pyrazine and/or lateral amines or azines, thereby altering the absorption and emission properties. Hypso- and bathochromism as well as fluorescence quenching depend on the nature of the terminal substituent. This, and a significant positive solvatochromism of the fluorescence, allow optical sensing of t…
Effect of polarity and elongational flow on the morphology and properties of a new nanobiocomposite
2015
Nanocomposites are a new class of biodegradable polymer materials with an ultrafine phase dispersion of the order of a few nanometers in a biodegradable polymer matrix that shows very interesting properties often very different from those of conventional filled polymers. In this work the effect of the polarity of the organomodified montmorillonite and of the elongational flow on the morphology and the rheological and mechanical properties of a new nanobiocomposite having as a matrix a biodegradable copolyester based bland has been investigated. The morphology of the nanocomposite with the more polar organomodified clay shows a more exfoliated morphology due to the major compatibility with t…
Spatial and temporal pattern of neuroblasts, proliferation, and Engrailed expression during early brain development in Tenebrio molitor L. (Coleopter…
2003
Abstract In insects, the knowledge of embryonic brain development is still fragmentary, and comparative data are scarce. In this study, we explored aspects of embryonic brain development in the coleopteran Tenebrio molitor . A detailed description is provided of the spatial and temporal pattern of the embryonic brain neuroblasts during 18–60% of embryonic development. Approximately 125 brain NBs have been identified in each hemisphere of the brain at about 40% of embryonic development. A subset of five neuroblasts, among them the two progenitors of the mushroom bodies and two progenitors of the larval antennal lobe, are morphologically identifiable by their larger size. As revealed by incor…
Hinterland-Verging Thrusting in the Northern Sicily Continental Margin: Evidences for a Late Collisional Stage of the Sicilian Fold and Thrust Belt?
2018
The Sicilian Fold and Thrust Belt developed during Neogene-Quaternary times characterized by main African-wards tectonic transport direction. Recent investigations highlighted extensive hinterland-verging tectonic structures active during late Pliocene-Pleistocene time suggesting a late collisional stage of the Sicilian Fold and Thrust Belt that could be a precursor of a change in the subduction polarity in the central belt of Mediterranean.
Macrophages as an Emerging Source of Wnt Ligands: Relevance in Mucosal Integrity
2019
The Wnt signaling pathway is a conserved pathway involved in important cellular processes such as the control of embryonic development, cellular polarity, cellular migration, and cell proliferation. In addition to playing a central role during embryogenesis, this pathway is also an essential part of adult homeostasis. Indeed, it controls the proliferation of epithelial cells in different organs such as intestine, lung, and kidney, and guarantees the maintenance of the mucosa in physiological conditions. The origin of this molecular pathway is the binding between Wnt ligands (belonging to a family of 19 different homologous secreted glycoproteins) and their specific membrane receptors, from …
Evolució de la sintaxi dels contextos de polaritat negativa en castellà i català
2007
In this paper we would like to compare the evolution of the syntax of polar contexts in Catalan and Spanish. By doing so, it would be possible to explain the greater syntactic disponibility of Catalan quantifiers and the important constraints for the same class of words in Spanish. After presenting in the first section the main theoretical questions about polarity in natural languages, we will describe in the second section the syntax of corresponding contexts in Middle Ages for both languages. Then, in the third section we will attend to the evolution towards current situation in order to understand the nature of modern differences between Catalan and Spanish on this area of their syntax.