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Bibliographies thématiques / Structure and Prototropy

Littérature scientifique sur le sujet « Structure and Prototropy »

Auteur : Grafiati

Publié le 6 septembre 2023

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Articles de revues sur le sujet "Structure and Prototropy"

1

Cornejo, J., et M. C. Hermosin. « Structural alteration of sepiolite by dry grinding ». Clay Minerals 23, n^o 4 (décembre 1988) : 391–98. http://dx.doi.org/10.1180/claymin.1988.023.4.06.

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AbstractThe effects of dry grinding on the structure of sepiolite were studied by XRD, surface area measurement, TG-DTA and IR spectroscopy techniques. The results show that the sepiolite framework is rather resistant to mechanical stress and its alteration by dry grinding occurs through three successive, overlapping processes: (i) thinning of the fibrous particles without structural alteration; (ii) distortion of the parallel units of sepiolite fibres, affecting essentially the particle surface which transforms into an amorphous protective coating; (iii) disruption of the inner structure and a prototropy effect, producing an amorphous phase with some residual order.

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Sheshashena Reddy, T., N. Rameshwar, B. Bhudevi et A. Ram Reddy. « Structure dependent prototropy in 4-hydroxy-3-formylideneamino-1-methyl/phenylquinolin-2-ones ». Spectrochimica Acta Part A : Molecular and Biomolecular Spectroscopy 73, n^o 5 (septembre 2009) : 916–21. http://dx.doi.org/10.1016/j.saa.2009.04.019.

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Grigg, Ronald, Jasothara Markandu, Trevor Perrior, Sivagnanasundram Surendrakumar et William J. Warnock. « Effect of structure on tandem 1,2-prototropy-cycloaddition versus tandem cyclisation-cycloaddition reactions of oximes. » Tetrahedron Letters 31, n^o 4 (janvier 1990) : 559–62. http://dx.doi.org/10.1016/0040-4039(90)87034-w.

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4

Colsch, Benoit, Annelaure Damont, Christophe Junot, François Fenaille et Jean-Claude Tabet. « Experimental evidence that electrospray-produced sodiated lysophosphatidyl ester structures exist essentially as protonated salts ». European Journal of Mass Spectrometry 25, n^o 3 (25 mars 2019) : 333–38. http://dx.doi.org/10.1177/1469066719838924.

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Sodiated lysoglycerophosphatidylethanolamine (LGPE) and lysoglycerophosphatidylcholine (LGPC) species dissociate under low collision energy by covalent bond cleavage resulting in product ions with either sodium retention or without sodium retention. For explaining these fragmentations, sodium chelation by heteroatoms (as charge-solvated structures) is often considered, and consequently, under keV collision conditions, sodium is “spectator” of cleavages (charge remote fragmentation). However, cleavage of such charge-solvated forms under low-energy conditions should result in sodium desolvation rather than covalent bond cleavage. In the present study, protonated salts are proposed as the main representative structures of the sodiated LGPE and LGPC forms. These structures are generated from sodiation of zwitterionic and betaine forms of LGPE and LGPC molecules, respectively. Experimental evidence to determine which structure is involved in the dissociations is provided, especially by comparing the dissociation of LGPL sodiated forms with that of sodiated polyethylene glycols. Energy-resolved mass spectrometry breakdown experiments were performed on a quadrupole time-of-flight instrument to demonstrate that both LGPE and LGPC sodiated forms exist as protonated salt structures. From such structures, proton migration by prototropy can result in different bond cleavages whereas the salt moiety remains spectator of these processes.

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Perrin, Monique, Alain Thozet, Pilar Cabildo, Rosa Ma Claramunt, Eduard Valenti et José Elguero. « Molecular structure and tautomerism of 3,5-bis(4-methylpyrazol-1-yl)-4-methylpyrazole ». Canadian Journal of Chemistry 71, n^o 9 (1 septembre 1993) : 1443–49. http://dx.doi.org/10.1139/v93-186.

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The title compound C12N6H14, 1, crystallizes in the space group P21/n (a = 8.222(2) Å, b = 27.336(8) Å, c = 5.574(2) Å, α = 90.00°, β = 100.97(4)°, γ = 90.00°), Z = 4, d = 1.308 g cm−3. The conformation about the N—C bonds linking the pyrazole rings can be defined as EZ, with "pyridine-like" nitrogen atoms in an anti disposition [Formula: see text] and "pyridine-like" and "pyrrole-like" nitrogen atoms in a syn disposition [Formula: see text] with regard to the central pyrazole. Intermolecular hydrogen bonds between the central and the terminal pyrazole ring of configuration Z form centrosymmetric dimers. They pack in sheets nearly parallel to the (−2 3 1) plane. Its tautomerization barrier has been determined in methanol-d4; the value, 11.9 kcal mol−1, is similar to those of 3,5-dimethyl-4-chloropyrazole (12.8 kcal mol−1) and 3,5-dimethyl-4-nitropyrazole (12.1 kcalmol−1). These values together with the shape of the conformational potential surface (calculated using the AM1 Hamiltonian) suggest that, in compound 1, prototropy and rotation about the N—C bonds linking the three pyrazole rings take place simultaneously.

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Star, Alexander, Israel Goldberg et Benzion Fuchs. « Diazadioxadecalin and salen podands and macrocycles within dynamic combinatorial virtual libraries : structure, prototropy, complexation and enantioselective catalysis ». Journal of Organometallic Chemistry 630, n^o 1 (juillet 2001) : 67–77. http://dx.doi.org/10.1016/s0022-328x(01)00882-8.

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Szymańska, Małgorzata, et Irena Majerz. « Prototropy, Intramolecular Interactions, Electron Delocalization, and Physicochemical Properties of 1,8-dihydroxy-9-anthrone—DFT-D3 Study of Substituent Effects ». Molecules 28, n^o 1 (1 janvier 2023) : 344. http://dx.doi.org/10.3390/molecules28010344.

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1,8-dihydroxy-9-anthrone are tricyclic compounds with a ketone group in the middle ring and two hydroxyl groups substituted in the side-aromatic rings what results in formation of two intramolecular hydrogen bonds in which the oxygen atom from the ketone group is the proton acceptor. 1,8-dihydroxy-9-anthrones in which intramolecular proton transfer between C10 and CO in the middle ring occurs, can exist in a tautomeric keto-enol equilibrium. For anthralin, the most important representative of this group, this equilibrium has been studied previously, but it has not been studied for its derivatives. Substituents in the middle ring change the geometry of 1,8-dihydroxy-9-anthrones so they are also expected to affect the keto-enol equilibrium. It is also important to study the effect of intramolecular hydrogen bonds on the structure of both tautomeric forms. It was found that the nature of the substituent in the middle ring could affect the antioxidant properties of the investigated compound.

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Lacalli, T. C. « Prototroch structure and innervation in the trochophore larva of Phyllodoce (Polychaeta) ». Canadian Journal of Zoology 64, n^o 1 (1 janvier 1986) : 176–84. http://dx.doi.org/10.1139/z86-028.

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The prototroch and prototroch nerve in trochophores of two Phyllodoce species are described at the ultrastructural level and interpreted with reference to the observed normal behavior of larvae during swimming. The prototroch is a complex structure consisting of four tiers of cells of which the second bears the main locomotory cilia. Cells in the other tiers also have cilia but are notable chiefly for the slender processes they send to the prototroch nerve and which evidently contribute to the sheath that surrounds the nerve. Neurociliary synapses were not observed, but the prototroch arrests when the frontal organ is touched and in response to cholinergic drugs. The arrests are only partial in that the cilia continue to beat, but in a restricted register. The mechanism responsible was not identified, but several possibilities are discussed. While the capacity to arrest could be intrinsic to the main trochal cells (i.e., tier 2), the absence of obvious regions of contact between these cells and the prototroch nerve increases the likelihood that the other tiers are also involved. The arrests could in fact result simply from physical interference between the cilia of adjacent tiers. The arrest response in Phyllodoce is compared with that seen in trochal bands in other spiralian larvae.

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Ma, Jiani, Jan-Michael Mewes, Kyle T. Harris, Timothy M. Dore, David Lee Phillips et Andreas Dreuw. « Unravelling the early photochemical behavior of (8-substituted-7-hydroxyquinolinyl)methyl acetates through electronic structure theory and ultrafast transient absorption spectroscopy ». Physical Chemistry Chemical Physics 19, n^o 2 (2017) : 1089–96. http://dx.doi.org/10.1039/c6cp05499d.

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Sergienko, V. S., V. L. Abramenko et Yu E. Gorbunova. « Prototropic Tautomerism of Salicylideneimines. Crystal Structure of 3,5-Dichlorosalicylideneallylimine ». Crystallography Reports 65, n^o 1 (janvier 2020) : 53–55. http://dx.doi.org/10.1134/s106377452001023x.

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