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排序方式: 共有350条查询结果,搜索用时 15 毫秒
311.
Dr. Andre Nicolai Petelski Silvana Carina Pamies María Josefina Verónica Márquez Prof. Dr. Gladis Laura Sosa Prof. Dr. Nélida María Peruchena 《Chemphyschem》2022,23(13):e202200151
Melamine (M) is a popular triamine triazine compound in the field of supramolecular materials. In this work, we have computationally investigated how substituents can be exploited to improve the binding strength of M supramolecules. Two types of covalent modifications were studied: the substitution of an H atom within an amine group −NHR, and the replacement of the whole −NH2 group (R=H, F, CH3 and COCH3). Through our dispersion-corrected density functional theory computations, we explain which covalent modification will show the best self-assembling capabilities, and why the binding energy is enhanced. Our charge density and molecular orbital analyses indicate that the best substituents are those that generate a charge accumulation on the endocyclic N atom, providing an improvement of the electrostatic attraction. At the same time the substituent assists the main N−H⋅⋅⋅N hydrogen bonds by interacting with the amino group of the other monomer. We also show how the selected group notably boosts the strength of hexameric rosettes. This research, therefore, provides molecular tools for the rational design of emerging materials based on uneven hydrogen-bonded arrangements. 相似文献
312.
A new simple “one-pot” synthesis of some 3-benzoylamino-5-oxo-5, 6, 7, 8-tetrahydrocoumarins from 1, 3-cyclohexanediones, hippuric acid, acetic anhydride and triethyl orthoformate or other one-carbon synthetic equivalent is described. 相似文献
313.
Ana C.F. Ribeiro Luís M.P. Veríssimo Abílio J.F.N. Sobral Victor M.M. Lobo Miguel A. Esteso 《Comptes Rendus Chimie》2013,16(5):469-475
Diffusion coefficients of silver salts in aqueous solutions are estimated from Onsager-Fuoss and Pikal models, using different values of the mean distance of closest approach of ions, a, determined from different theoretical procedures. The influence of this parameter on the diffusion of these systems is discussed. 相似文献
314.
Dr. Vellaisamy Sridharan Pascual Ribelles Verónica Estévez Prof. Mercedes Villacampa Prof. M. Teresa Ramos Prof. Paramasivan T. Perumal Prof. J. Carlos Menéndez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(16):5056-5063
The indium trichloride‐catalyzed reaction between aromatic imines and α,β‐unsaturated N,N‐dimethylhydrazones in acetonitrile afforded 1,2,3,4‐tetrahydroquinolines bearing a hydrazone function at C4 through a one‐pot diastereoselective domino process that involves the formation of two C? C bonds and the controlled generation of two stereocenters, one of which is quaternary. This reaction constitutes the first example of an α,β‐unsaturated dimethylhydrazone that behaves as a dienophile in a hetero Diels–Alder reaction. The related reaction between anilines, aromatic aldehydes, and methacrolein dimethylhydrazone in CHCl3 with BF3?Et2O as catalyst afforded polysubstituted 1,2,3,3a,4,8b‐hexahydropyrrolo[3,2‐b]indoles as major products through a fully diastereoselective ABB′C four‐component domino process that generates two cycles, three stereocenters, two C? C bonds, and two C? N bonds in a single operation. 相似文献
315.
316.
Sridharan V Ribelles P Estévez V Villacampa M Ramos MT Perumal PT Menéndez JC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(16):5056-5063
The indium trichloride-catalyzed reaction between aromatic imines and α,β-unsaturated N,N-dimethylhydrazones in acetonitrile afforded 1,2,3,4-tetrahydroquinolines bearing a hydrazone function at C4 through a one-pot diastereoselective domino process that involves the formation of two C-C bonds and the controlled generation of two stereocenters, one of which is quaternary. This reaction constitutes the first example of an α,β-unsaturated dimethylhydrazone that behaves as a dienophile in a hetero Diels-Alder reaction. The related reaction between anilines, aromatic aldehydes, and methacrolein dimethylhydrazone in CHCl(3) with BF(3)?Et(2)O as catalyst afforded polysubstituted 1,2,3,3a,4,8b-hexahydropyrrolo[3,2-b]indoles as major products through a fully diastereoselective ABB'C four-component domino process that generates two cycles, three stereocenters, two C-C bonds, and two C-N bonds in a single operation. 相似文献
317.
Notario R Roux MV Cuevas G Cardenas J Leyva V Juaristi E 《The journal of physical chemistry. A》2006,110(24):7703-7712
318.
319.
We present a detailed study of the work function of pristine and doped single-walled carbon nanotubes (SWCNTs) using a novel screened exchange hybrid density functional. We find that SWCNTs with diameters larger than 0.9 nm tend asymptotically and smoothly to the graphene limit of 4.6 eV. On the other hand, the work function of narrow tubes exhibits a strong dependence on their diameter and chiral angle. Boron or nitrogen doping, with concentrations from 1% to 2%, not only changes the electronic behavior by introducing new states around the Fermi level, but also produces a significant change of the work function that can vary between 3.9 (N doping) and 5.2 eV (B doping). 相似文献
320.
It has been shown that for each Killing–Yano (KY)-form accepted by an n-dimensional (pseudo)Riemannian manifold of arbitrary signature, two different gravitational currents can be defined. Conservation
of the currents are explicitly proved by showing co-exactness of the one and co-closedness of the other. Some general geometrical
facts implied by these conservation laws are also elucidated. In particular, the conservation of the one-form currents implies
that the scalar curvature of the manifold is a flow invariant for all of its Killing vector fields. It also directly follows
that, while all KY-forms and their Hodge duals on a constant curvature manifold are the eigenforms of the Laplace–Beltrami
operator, for an Einstein manifold this is certain only for KY 1-forms, (n − 1)-forms and their Hodge duals. 相似文献