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Naringenin is a natural widespread flavanone occurring in different foodstuffs that presents several important biological activities. Although its properties are well documented, its mechanisms of action are still controversial. The present article reports a conformational analysis of naringenin, using the semiempirical AM1 and ab initio methods, at the Hartree–Fock level of theory. The 3-21G, 3-21G*, 6-31G, and 6-31G** basis sets were used. The electron correlation effects were included through the Møller–Plesset second-order perturbation theory. The solvation of naringenin has been investigated through the standard SCRF, the supermolecule (SM), and the combined SM/SCRF models. The results have shown that there are two degenerate forms of naringenin, differing mainly by the orientation of a hydroxyl group (C4—OH). The energy barrier for the interconversion between them is ca. 6 kcal.mol–1, suggesting some conjugation between the -system of the aromatic B ring and the hydroxyl group (C4—OH). 相似文献
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We consider the diffraction of a time-harmonic acoustic plane wave by a rigid half-plane in a viscous fluid medium. The linearized equations of viscous fluid flow and the no-slip condition on the half-plane are used to derive a pair of disjoint Wiener-Hopf equations for the fluid stresses and velocities. The Wiener-Hopf equations are solved in conjunction with a requirement that the stresses are integrable near the edge of the half-plane. Specific wave components of the scattered velocity field are given analytically. A Padé approximation to the Wiener-Hopf kernel function is used to derive numerical results that show the effect of viscosity on the velocity field in the immediate vicinity of the edge of the half-plane. 相似文献
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Rodrigo S. Corrêa Marcelo H. dos Santos Tanus J. Nagem Javier Ellena 《Structural chemistry》2010,21(3):555-563
Oxygenated xanthones have been extensively investigated over the years, but there are few reports concerning their crystal
structure. Our chemical investigations of Brazilian plants resulted in the isolation of four natural products named 1-hydroxyxanthone
(I), 1-hydroxy-7-methoxyxanthone (II), 1,5-dihydroxy-3-methoxyxanthone (III), and 1,7-dihydroxy-3,8-dimethoxyxanthone (IV).
The structures of these compounds were established on the basis of single crystal X-ray diffraction. The xanthone nucleus
conformation is essentially planar with the substituents adopting the orientations less sterically hindered. In addition,
classical intermolecular hydrogen bonds (O–H···O) present in III and IV give rise to infinite ribbons. However, the xanthone
I does not present any intermolecular hydrogen bonds, meanwhile the xanthone II presents only a non-classical one (C–H···O).
The crystal packing of all xanthone structures is also stabilized by π–π interactions. The fingerprint plots, derived from
the Hirshfeld surfaces, exhibited significant features of each crystal structures. 相似文献
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Abstract Linear dynamic analysis of lattice structures using transfer matrices and joint coupling matrices is presented. A lattice structure is defined as a network of one-dimensional members that are connected by joints. Two examples are considered to illustrate how transfer matrices and joint coupling matrices may be used to compute natural frequencies of vibration. These two examples indicate that the transfer matrix and joint coupling matrix analysis is numerically accurate over a wide range of frequencies and becomes increasingly efficient, compared to the finite element method, as the frequency increases. Some suggestions for further improvements in computational efficiency and some comments about applicability to numerical analysis of wave propagation problems are given. 相似文献
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Antonio C. Doriguetto Marcelo H. Santos Javier A. Ellena Tanus J. Nagem 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(9):1095-1097
The natural compound 5,10‐dihydroxy‐2,2‐dimethylpyrano[3,2‐b]xanthen‐6(2H)‐one (6‐deoxyjacareubin), C18H14O5, was isolated from leaves of Vismia latifolia (Guttiferae family). The compound has four six‐membered rings. The molecule has two planar benzenoid and one planar pyranoid ring, plus a pyranoid ring in a distorted chair conformation. The crystal is stabilized by one intra‐ and one intermolecular hydrogen bond. 相似文献
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Antnio C. Doriguetto Javier Ellena Marcelo H. Dos Santos Maria E. C. Moreira Tanus J. Nagem 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(6):o350-o352
Single crystals of the phenylcoumarin named mammeigin (or mammea A/AA cycle D) [systematic name: 5‐hydroxy‐8,8‐dimethyl‐6‐(3‐methylbutanoyl)‐4‐phenyl‐2H,8H‐pyrano[2,3‐f]chromen‐2‐one], C25H24O5, were obtained in the course of a chemotaxonomic study of the Guttiferae family. Mammeigin was extracted from the fruits of Kilmeyera pumila. The structure reveals an infinite three‐dimensional network stabilized by non‐classical intermolecular hydrogen bonds. 相似文献
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The linearized equations of viscous fluid flow are used to analyze the diffraction of a time-harmonic acoustic plane wave by a circular aperture in a rigid plane screen. Arbitrary aperture size and arbitrary angle of incidence are considered. Sets of dual integral equations are derived for the diffracted velocity and pressure fields, and are solved by analytic reduction to sets of linear algebraic equations. In the case of normal incidence, numerical results are presented for the fluid velocity in the aperture and the power absorption due to viscous dissipation. The theoretical results for power absorption are compared to previously obtained results from high amplitude acoustic experiments in air. The conditions under which the dissipation predicted by linear theory becomes significantare quantified in terms of the fluid viscosity and sound speed, the acoustic frequency, and the aperture radius. 相似文献