Bibliographies thématiques / Supra-molecular Framework

Littérature scientifique sur le sujet « Supra-molecular Framework »

Auteur : Grafiati

Publié le 7 septembre 2023

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Articles de revues sur le sujet "Supra-molecular Framework"

Arletti, Rossella, Simona Quartieri, Giovanna Vezzalini, Ettore Fois et Gloria Tabacchi. « HP-induced supra-molecular organization of guest molecules in FER-type zeolites ». Acta Crystallographica Section A Foundations and Advances 70, a1 (5 août 2014) : C1469. http://dx.doi.org/10.1107/s2053273314085301.

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The response to pressure of a synthetic all-silica ferrierite (Si-FER) and of a natural ferrierite from Monastir (Sardinia, Italy) (Mon-FER, Na0.56 K1.19 Mg2.02 Ca0.52 Sr0.14)(Al6.89Si29.04)O72 ·17.86 H2O) is here investigated combining HP synchrotron XRPD experiments and molecular dynamics simulations. The experiments were carried out by using penetrating (methanol:ethanol:water 16:3:1, m.e.w.; ethanol:water 1:3, e.w.) and non-penetrating (silicone oil, s.o.) pressure transmitting media (PTM). In Si-FER compressed in e.w., both water (w.) and ethanol molecules (e.) enter the pore system even at 0.2 GPa. The structural refinement of the data collected at 0.8 GPa reveals 8 w. and 4 e. molecules in the 10- and 6-membered ring channels, in tight agreement with the results of MD simulations. In Si-FER compressed at 0.2 GPa in m.e.w., only water molecules penetrate the 10-membered ring channels (15 per u.c.), organized in chains running along the channel axis. The interactions among the guest species and the framework oxygen atoms are very weak, due to the hydrophobicity of the framework. Upon decompression, the intruded extra-molecules are not completely released, so giving rise to new materials with different extra-framework contents. The results obtained for Si-FER compressed in m.e.w. and s.o. were compared to those obtained for Mon-FER, demonstrating that the zeolite composition and the PTM strongly influence the overall elastic parameters of the investigated samples. Specifically, Mon-FER shows a much higher rigidy than Si-FER in both media, due to the stiffening effect of the numerous extraframework species present in the natural sample. The higher rigidity of Si-FER in m.e.w. with respect to s.o. can be explained by the penetration, in the former case, of the PTM molecules, which contribute to stiffen the framework.

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Yan, Li, Wei Liu, Chuanbi Li, Yifei Wang, Li Ma et Qinqin Dong. « Hydrogen bonded supra-molecular framework in inorganic–organic hybrid compounds : Syntheses, structures, and photoluminescent properties ». Journal of Molecular Structure 1035 (mars 2013) : 240–46. http://dx.doi.org/10.1016/j.molstruc.2012.11.046.

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FENG, ZHAO-QING, et GEN-MING JIN. « PROBING THE SYMMETRY ENERGY AT SUPRA-SATURATION DENSITIES FROM PION EMISSION IN HEAVY-ION COLLISIONS ». International Journal of Modern Physics E 19, n^o 08n09 (septembre 2010) : 1686–93. http://dx.doi.org/10.1142/s0218301310016107.

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Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, the emission of pion in heavy-ion collisions in the region 1 A GeV as a probe of nuclear symmetry energy at supra-saturation densities is investigated systematically, in which the pion is considered to be mainly produced by the decay of resonances Δ(1232) and N *(1440). The π-/π+ yields are calculated for selected Skyrme parameters SkP, SLy6, Ska and SIII, and also for the cases of different stiffness of symmetry energy with the parameter SLy6. Preliminary results compared with the measured data by the FOPI collaboration favor a hard symmetry energy of the potential term proportional to (ρ/ρ0)γs with γs = 2.

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Yan, Li, Chuanbi Li et Xiaoli Chen. « Hydrogen bonded supra-molecular framework in inorganic–organic hybrid compounds of Mn(II) and Zn(II) : Syntheses, structures, and photoluminescent studies ». Journal of Molecular Structure 1058 (janvier 2014) : 277–83. http://dx.doi.org/10.1016/j.molstruc.2013.11.026.

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Shi, Shikao, Ji Zhou, Shitian Han, Yanli Peng et Jianping Ye. « Optical Properties of Porphyrin Chromophores Assembled in Nano-Lamellar Zirconium Phosphate ». Journal of Nanoscience and Nanotechnology 8, n^o 3 (1 mars 2008) : 1359–63. http://dx.doi.org/10.1166/jnn.2008.18196.

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The supra-molecular assemblies and optical properties of the symmetrical neutral porphyrin chromophore, meso-tetra(4-pyridyl)porphine, bound to a modified α-zirconium phosphate framework have been studied. The interlayer distance of the cetyltrimethylammonium zirconium phosphate framework is 39.6 Å. After the addition of meso-tetra(4-pyridyl)porphine to the framework, the X-ray powder diffraction (XRPD) patterns show that the interlayer distance of the framework is 30.3 Å, demonstrating the formation of novel assemblies. In the framework, organic chromophores are assumed to align in a canted monolayer. The interaction of organic chromophores with the frame-work causes noticeable red shifts of the Soret absorption band from 416 to 427 nm. In contrast, the luminescence peak is blue shifted from 660 nm in aqueous media to 648 nm when mesotetra(4-pyridyl)porphine is bound to the framework. Furthermore, the emission yield of the organic chromophore in the framework is dramatically enhanced compared to that of organic aqueous solutions. The spectroscopic change of meso-tetra(4-pyridyl)porphine is ascribed to the unique microenvironments of the nano-lamellar framework. The juxtaposition of the porphyrin chromophores in the framework tunes their electronic interactions. In comparison, the organic chromophores also attempted to bind with another modified α-zirconium phosphate, n-butylammonium zirconium phosphate. However, the chromophores could not enter into n-butylammonium zirconium phosphate due to its smaller interlayer distance (18.8 Å).

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Kawamura, Yasuhiko, Takaaki Ishiduka et Masao Tsukayama. « One-Way Geometrical Isomerization of 1,1-Diarylethenes Induced by Photosensitized Electron Transfer ». International Journal of Modern Physics B 17, n^o 08n09 (10 avril 2003) : 1492–97. http://dx.doi.org/10.1142/s0217979203019216.

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One-way geometrical isomerization around a C=C bond of 1,1-diary1-2-t-butylethene is achieved upon photoirradiation of cyanoaromatics as a light-absorbing sensitizer. In the thermochemical view, there is no difference between both E and Z isomers of the ethene. Key intermediate is a putative distonic radical cation which is a unique one having a spatially separate radical and ionic centers on the molecular framework. Generation of such an intermediate is due to the presence of a π-donating substituent on an aromatic ring and a bulky t-butyl group. Molecular oxygen interacts as superoxide with the C=C bond of the radical cation in a [supra + antara] manner to give a decomposition product, i.e. a benzophenone derivative and pivalaldehyde, via a dioxetane and competitively, one geometrical isomer of the ethene is afforded by splitting oxygen before making two bonds with the ethene radical cation and superoxide.

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Kawamura, Yasuhiko, Takahiro Abe et Masao Tsukayama. « One-Way and Two-Way Geometrical Isomerizations of 1, 1-Diarylketone Oxime O-Methyl Ethers Induced by Photosensitized Electron Transfer ». International Journal of Modern Physics B 17, n^o 08n09 (10 avril 2003) : 1487–91. http://dx.doi.org/10.1142/s0217979203019204.

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Under an oxygen atmosphere, the E and Z isomer ratio of N-methoxy-4-methoxyphenyl-4'-methylphenylmethanimine (one of the title compounds; initially, ⌈E⌉/⌈Z⌉ = 1/1) reached to 4/96 upon irradiation (> 360 nm) of 9, 10-dicyanoanthracene (DCA) as a photosensitizer in acetonitrile. Key intermediate is presumed to be a putative distonic radical cation which is a unique one having a spatially separate radical and ionic centers on the molecular framework. The whole scenario of the reaction was supported by molecular orbital calculations. An excited singlet state of DCA generated by light absorption was quenched by oxime ethers to give the DCA anion radical and radical cations of E- and Z-oxime ethers. Then the subsequent single electron transfer from the DCA anion radical to molecular oxygen generates superoxide anion radical, which reacted with distonic radical cations of E- and Z-oxime ethers bya ⌈supra + antara⌉ manner. Geometry selection occurs at a stage of just making a new bond between nitrogen and oxygen terminals in the ensuing peroxyaminy1-1,4-diradical. The final oxime ether is afforded by releasing molecular oxygen without successful single bond formation. Instead, ring closure to azadioxetane gives rise to formation of byproducts, benzophenones and methyl nitrite, by decomposion of it in a metathesis fashion.

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Altayyar, Mansour, Jennifer A. Nasser, Dimitra Thomopoulos et Michael Bruneau. « The Implication of Physiological Ketosis on The Cognitive Brain : A Narrative Review ». Nutrients 14, n^o 3 (25 janvier 2022) : 513. http://dx.doi.org/10.3390/nu14030513.

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Optimal cognitive functions are necessary for activities of daily living and self-independence. Cognitive abilities are acquired during early childhood as part of progressive neurodevelopmental milestones; unfortunately, regressive changes can occur as part of physiological aging, or more ominously, pathological diseases, such as Alzheimer’s disease (AD). Cases of AD and its milder subset, mild cognitive impairment (MCI), are rising and would impose a burdensome impact beyond the individual level. Various dietary and nutritional approaches have potential for promising results in managing cognitive deterioration. Glucose is the core source of bioenergy in the body; however, glucose brain metabolism could be affected in aging cells or due to disease development. Ketone bodies are an efficient alternate fuel source that could compensate for the deficient glycolytic metabolism upon their supra-physiologic availability in the blood (ketosis), which, in turn, could promote cognitive benefits and tackle disease progression. In this review, we describe the potential of ketogenic approaches to produce cognitive benefits in healthy individuals, as well as those with MCI and AD. Neurophysiological changes of the cognitive brain in response to ketosis through neuroimaging modalities are also described in this review to provide insight into the ketogenic effect on the brain outside the framework of purely molecular explanations.

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Porto, Michele, Paolino Caputo, Valeria Loise, Giovanni De Filpo, Cesare Oliviero Rossi et Pietro Calandra. « Polysaccharides-Reinforced Bitumens : Specificities and Universality of Rheological Behavior ». Applied Sciences 9, n^o 24 (17 décembre 2019) : 5564. http://dx.doi.org/10.3390/app9245564.

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The rheological properties of bitumens can be modified by the addition of specific chemical additives. Taking into account the molecular complex aggregation pattern, we hypothesized that macromolecules characterized by long, flexible, and hydrophilic chains can establish soft bridges connecting the different polar aggregates of asphaltenes, strengthening their overall hierarchical supra-structures, and consequently increasing rheological performance at higher temperatures. Here, we propose the use of low cost and high availability polysaccharides as chemical additives to improve the rheological characteristics of a bitumen and to strengthen its thermal resistance. Fourteen different low-cost and high-availability polysaccharides, (flours, gums, and extracts from vegetable products) have been tested. While alghae euchemae have proved to be the most effective additive, corn and 00 flours are the least effective. Attempts to explain their differences have been made considering their chemical interactions with the polar molecules of asphaltenes within the complex framework of their supramolecular hierarchical structures. Through Arrhenius analysis, a correlation between activation energy and preexponential factor has been found, which can be useful for practical purposes, together with an unexpected consistency with the behavior of simple liquids, despite the striking differences in structure. Furthermore, a qualitative model has been suggested. The added value of this work is the focus on polysaccharides constituting low-cost, high availability materials which are sometimes even found as waste in industrial processes, all factors which, together with the environmental issues connected with their use, can be considered for large-scale applications.

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Lloyd, David, Miguel A. Aon et Sonia Cortassa. « Why Homeodynamics, Not Homeostasis ? » Scientific World JOURNAL 1 (2001) : 133–45. http://dx.doi.org/10.1100/tsw.2001.20.

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Ideas of homeostasis derive from the concept of the organism as an open system. These ideas can be traced back to Heraclitus. Hopkins, Bernard, Hill, Cannon, Weiner and von Bertalanffy developed further the mechanistic basis of turnover of biological components, and Schoenheimer and Rittenberg were pioneers of experimental approaches to the problems of measuring pool sizes and dynamic fluxes. From the second half of the twentieth century, a biophysical theory mainly founded on self-organisation and Dynamic Systems Theory allowed us to approach the quantitative and qualitative analysis of the organised complexity that characterises living systems. This combination of theoretical framework and more refined experimental techniques revealed that feedback control of steady states is a mode of operation that, although providing stability, is only one of many modes and may be the exception rather than the rule. The concept of homeodynamics that we introduce here offers a radically new and all-embracing concept that departs from the classical homeostatic idea that emphasises the stability of the internal milieu toward perturbation. Indeed, biological systems are homeody- namic because of their ability to dynamically self-organise at bifurcation points of their behaviour where they lose stability. Consequently, they exhibit diverse behaviour; in addition to monotonic stationary states, living systems display complex behaviour with all its emergent characteristics, i.e., bistable switches, thresholds, waves, gradients, mutual entrainment, and periodic as well as chaotic behaviour, as evidenced in cellular phenomena such as dynamic (supra)molecular organisation and flux coordination. These processes may proceed on different spatial scales, as well as across time scales, from the very rapid processes within and between molecules in membranes to the slow time scales of evolutionary change. It is dynamic organisation under homeodynamic conditions that make possible the organised complexity of life.

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