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31.
Darian E Hnizdo V Fedorowicz A Singh H Demchuk E 《Journal of computational chemistry》2005,26(7):651-660
A method of statistical estimation is applied to the problem of evaluating the absolute entropy of internal rotation in a molecule with two torsional degrees of freedom. The configurational part of the entropy is obtained as that of the joint probability density of an arbitrary form represented by a two-dimensional Fourier series, the coefficients of which are statistically estimated using a sample of the torsional angles of the molecule obtained by a stochastic simulation. The internal rotors in the molecule are assumed to be attached to a common frame, and their reduced moments of inertia are initially calculated as functions of the two torsional angles, but averaged over all the remaining internal degrees of freedom using the stochastic-simulation sample of the atomic configurations of the molecule. The torsional-angle dependence of the reduced moments of inertia can be also averaged out, and the absolute internal-rotation entropy of the molecule is obtained in a good approximation as the sum of the configurational entropy and a kinetic contribution fully determined by the averaged reduced moments of inertia. The method is illustrated using Monte Carlo simulations of isomers of stilbene and halogenated derivatives of propane. The two torsional angles in cis-stilbene are found to be much more strongly correlated than those in trans-stilbene, while the degree of the angular correlation in propane increases strongly on substitution of hydrogen atoms with chlorine. 相似文献
32.
33.
Karoll Ferrer Katy Díaz Miroslav Kvasnica Andrs F. Olea Mauricio Cuellar Luis Espinoza 《Molecules (Basel, Switzerland)》2021,26(4)
The metabolism of brassinosteroid leads to structural modifications in the ring skeleton or the side alkyl chain. The esterification and glycosylation at C-3 are the most common metabolic pathways, and it has been suggested that conjugate brassinosteroids are less active or inactive. In this way, plants regulate the content of active brassinosteroids. In this work, the synthesis of brassinosteroid 24-norcholane type analogs conjugated at C-3 with benzoate groups, carrying electron donor and electron attractant substituents on the aromatic ring, is described. Additionally, their growth-promoting activities were evaluated using the Rice Lamina Inclination Test (RLIT) and compared with that exhibited by brassinolide (used as positive control) and non-conjugated analogs. The results indicate that at the lowest tested concentrations (10−8–10−7 M), all analogs conjugated at C-3 exhibit similar or higher activities than brassinolide, and the diasteroisomers with S configuration at C-22 are the more active ones. Increasing concentration (10−6 M) reduces the biological activities of analogs as compared to brassinolide. 相似文献
34.
The potential of an N-Troc-protected sialic acid donor, equipped with phenylsulfenyl functionality as a leaving group, has been explored. As a result, the entitled donor was proven to be highly reactive and to have broad applicability toward the synthesis of variant sialo-glycans, which have N-glycolyl, de-N-acetyl, 1,5-lactam and 8-O-sulfo sialic acid analogs. 相似文献
35.
Syntheses of Two Potential Ligands for Tc-99m Labeling as Diagnosis Agents of Alzheimer''''s Disease
Two types of ligands-biphenyl and stilbene derivatives, whichcan be labeled with Tc-99m for the diagnosis of Alzheimer'sdisease (AD) have been synthesized successfully. The key stepsin these two syntheses involved Suzuki reaction and Wittig reac-tion respectively. The new discovered debromination reactionmay be expanded to the compounds with double or triple bondadjacent to the carbon atom bearing the bromine atoms. Thesetypes of syntheses provide a route to a series of biphenyl andstilbene derivatives that will benefit the search of new imagingagents for AD. 相似文献
36.
Jia Rong Li Li Jun Zhang Xi Quan Yang Qing Li Dong Wang Chun Xia Wang Da Xin Shi Qi Zhang 《中国化学快报》2008,19(1)
Two different skeletons of heterocyclic compounds, quinoline and quinazolinone analogs could be obtained by a novel one-potsynthesis from substituted 3-amino-lH-benzo[f]chromene-2-carbonitrile derivatives and cyclohexanone in DMF in the catalyst ofanhydrous zinc chloride under reflux. A plausible mechanism was proposed. 相似文献
37.
A. G. Shavva G. L. Starova S. I. Selivanov S. N. Morozkina 《Chemistry of Heterocyclic Compounds》2008,44(2):148-152
By X-ray crystallographic analysis and NMR spectroscopy it was demonstrated that the conformations of several D-homo-6-oxa-8α
analogs of steroidal estrogens are similar in the crystal and in solution. The distances between the hydrogen atoms in these
molecules, calculated by the ab initio and MM+ methods, correspond to the experimental data.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 202–207, February, 2008. 相似文献
38.
Yue‐Qi Mo Xian‐Yu Deng Xi Jiang Qiu‐Hong Cui 《Journal of polymer science. Part A, Polymer chemistry》2009,47(13):3286-3295
Poly(3,6‐silafluorene) is a typical wide band‐gap conjugated polymer with ultraviolet light emission. The blue electroluminescence from the 3,6‐silafluorene‐based copolymers via intrachain energy transfer was reported in this study. The monomer containing vinylene, anthracene, and tri‐arylamine moieties incorporated into the poly(3,6‐silafluorene) backbone can form efficient deep‐blue emitting copolymers with EL efficiency of 1.1–1.9%. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3286–3295, 2009 相似文献
39.
Yaghoub Haghighatnia Saeed Balalaie Hamid Reza Bijanzadeh 《Helvetica chimica acta》2012,95(5):818-824
Some new amidated fentanyl (=N‐[1‐(2‐phenylethyl)piperidin‐4‐yl]‐N‐phenylpropanamide) analogs with a 4‐(N‐phenylamido)piperidine scaffold and additional amide bonds have been designed and synthesized through Ugi four‐component reaction (Ugi‐4CR). Good‐to‐high yields, diversity‐oriented synthesis, and possible applications in drug discovery are advantages of this approach. 相似文献
40.
In this paper, we report the efficient and regioselective synthesis of 2-aminopyrrole-4-carboxylates as derivatives of conformationally restricted analogues of γ-amino butyrates (GABA) via a zinc perchlorate catalyzed amination-annulation of α-cyanomethyl-β-ketoesters under mild reaction conditions in water. 相似文献