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排序方式: 共有243条查询结果,搜索用时 31 毫秒
41.
42.
Juan Chen Stepan Stepanovic Dr. Apparao Draksharapu Prof. Dr. Maja Gruden Prof. Dr. Wesley R. Browne 《Angewandte Chemie (International ed. in English)》2018,57(12):3207-3211
Non‐heme (L)FeIII and (L)FeIII‐O‐FeIII(L) complexes (L=1,1‐di(pyridin‐2‐yl)‐N,N‐bis(pyridin‐2‐ylmethyl)ethan‐1‐amine) underwent reduction under irradiation to the FeII state with concomitant oxidation of methanol to methanal, without the need for a secondary photosensitizer. Spectroscopic and DFT studies support a mechanism in which irradiation results in charge‐transfer excitation of a FeIII?μ‐O?FeIII complex to generate [(L)FeIV=O]2+ (observed transiently during irradiation in acetonitrile), and an equivalent of (L)FeII. Under aerobic conditions, irradiation accelerates reoxidation from the FeII to the FeIII state with O2, thus closing the cycle of methanol oxidation to methanal. 相似文献
43.
Nicolaou KC Stepan AF Lister T Li A Montero A Tria GS Turner CI Tang Y Wang J Denton RM Edmonds DJ 《Journal of the American Chemical Society》2008,130(39):13110-13119
The molecular design, chemical synthesis, and biological evaluation of two distinct series of platensimycin analogues with varying degrees of complexity are described. The first series of compounds probes the biological importance of the benzoic acid subunit of the molecule, while the second series explores the tetracyclic cage domain. The biological data obtained reveal that, while the substituted benzoic acid domain of platensimycin is a highly conserved structural motif within the active compounds with strict functional group requirements, the cage domain of the molecule can tolerate considerable structural modifications without losing biological action. These findings refine our present understanding of the platensimycin pharmacophore and establish certain structure-activity relationships from which the next generation of designed analogues of this new antibiotic may emerge. 相似文献
44.
Noncovalent Interaction of Graphene with Heterocyclic Compounds: Benzene,Imidazole, Tetracene,and Imidazophenazines
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Dr. Eugene Zarudnev Dr. Stepan Stepanian Ludwik Adamowicz Dr. Victor Karachevtsev 《Chemphyschem》2016,17(8):1204-1212
Noncovalent functionalization of graphene with organic molecules offers a direct route to multifunctional modification of this nanomaterial, leading to its various possible practical applications. In this work, the structures of hybrids formed by linear heterocyclic compounds such as imidazophenazine (F1) and its derivatives (F2‐F4) with graphene and the corresponding interaction energies are studied by using the DFT method. Special attention is paid to the hybrids where the attached molecule is located along the graphene zigzag ( GZZ) and armchair ( GAC ) directions. The interaction energies corresponding to the graphene hybrids of the F1‐F4 compounds for the two directions are found to be distinct, while tetracene (being a symmetrical molecule) shows a small difference between these binding energies. It is found that the back‐side CH3 and CF3 groups have an important influence on the arrangements of F1 derivatives on graphene and on their binding energies. The contribution of the CF3 group to the total binding energy of the F3 molecule with graphene is the largest (3.4 kcal mol?1) (the GZZ direction) while the CH3 group increases this energy of F2 only by 2.0 kcal mol?1 (the GAC direction). It is shown that replacing the carbons with other atoms or adding a back‐side group enables one to vary the polarizability of graphene. 相似文献
45.
A highly efficient regiodivergent method for the synthesis of N-fused heterocycles via transition-metal-catalyzed rearrangement of 3-iminocyclopropenes has been developed. 相似文献
46.
Gelmboldt VO Ganin EV Fonari MS Simonov YA Koroeva LV Ennan AA Basok SS Shova S Kählig H Arion VB Keppler BK 《Dalton transactions (Cambridge, England : 2003)》2007,(27):2915-2924
Two novel compounds, (L(1)H)(2)[SiF(6)] x 2H(2)O (1) and (L(2)H)(2)[SiF(5)(H(2)O)](2) x 3H(2)O (2), resulting from the reactions of H(2)SiF(6) with 4'-aminobenzo-12-crown-4 (L(1)) and monoaza-12-crown-4 (L(2)), respectively, were studied by X-ray diffraction and characterised by IR and (19)F NMR spectroscopic methods. Both complexes have ionic structures due to the proton transfer from the fluorosilicic acid to the primary amine group in L(1) and secondary amine group incorporated into the macrocycle L(2). The structure of 1 is composed of [SiF(6)](2-) centrosymmetric anions, N-protonated cations (L(1)H)(+), and two water molecules, all components being bound in the layer through a system of NH[...]F, NH[...]O and OH[...]F hydrogen bonds. The [SiF(6)](2-) anions and water molecules are assembled into inorganic negatively-charged layers via OH[dot dot dot]F hydrogen bonds. The structure of 2 is a rare example of stabilisation of the complex anion [SiF(5)(H(2)O)](-), the labile product of hydrolytic transformations of the [SiF(6)](2-) anion in an aqueous solution. The components of 2, i.e., [SiF(5)(H(2)O)](-), (L(2)H)(+), and water molecules, are linked by a system of NH[...]F, NH[...]O, OH[...]F, OH[dot dot dot]O hydrogen bonds. In a way similar to 1, the [SiF(5)(H(2)O)](-) anions and water molecules in 2 are combined into an inorganic negatively-charged layer through OH[...]F and OH[...]O interactions. 相似文献
47.
48.
Kashtanov S Zhuang GV Augustsson A Nordgren J Luo Y Ross PN Guo J 《The journal of physical chemistry. B》2007,111(40):11658-11661
The electronic structure of pol(ethylene oxide) (PEO) in a thin (<1 mu) film sample was experimentally probed by X-ray emission spectroscopy. Both nonresonant and resonant X-ray emission spectra were simulated by using density functional theory (DFT) applied to four different models representing different conformations in the polymer. Calculated spectra were compared with experimental results for the PEO film. It was found that the best fit was obtained with the polymer conformation in PEO electrolytes from which the salt (LiMF6, M = P, As, or Sb) had been removed. This conformation is different from the crystalline bulk polymer and implies that film casting, commonly used to form electrolytes for Li polymer batteries, induces the same conformation in the polymer not depending upon the presence of salt. 相似文献
49.
Oleksandr V. Golovchenko Stepan G. Pilyo Vladimir S. Brovarets Alexander N. Chernega Boris S. Drach 《Heteroatom Chemistry》2004,15(6):454-458
Available 2‐acylamino‐3,3‐dichloroacrylonitriles, when treated with hydrazine hydrate, provide 2‐alkyl‐ or 2‐aryl‐5‐hydrazino‐1,3‐oxazole‐4‐carbonitriles that readily add alkyl or aryl isothiocyanates and the adducts formed recyclize on heating. Finally, the synthesis results in 5‐alkyl(aryl)amino‐1,3,4‐thiadiazol‐2‐yl(acylamino)acetonitriles or the products of their further cyclization, 2‐(5‐amino‐1,3‐ oxazol‐2‐yl)‐1,3,4‐thiadiazole derivatives. The structures of the novel substituted 1,3,4‐thiadiazoles are corroborated spectroscopically as well as by X‐ray diffraction method. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:454–458, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20041 相似文献
50.
Alexander Svidlov Mikhail Drobotenko Alexander Basov Eugeny Gerasimenko Anna Elkina Mikhail Baryshev Yury Nechipurenko Stepan Dzhimak 《Entropy (Basel, Switzerland)》2021,23(11)
Fluctuations in viscosity within the cell nucleus have wide limits. When a DNA molecule passes from the region of high viscosity values to the region of low values, open states, denaturation bubbles, and unweaving of DNA strands can occur. Stabilization of the molecule is provided by energy dissipation—dissipation due to interaction with the environment. Separate sections of a DNA molecule in a twisted state can experience supercoiling stress, which, among other things, is due to complex entropic effects caused by interaction with a solvent. In this work, based on the numerical solution of a mechanical mathematical model for the interferon alpha 17 gene and a fragment of the Drosophila gene, an analysis of the external environment viscosity influence on the dynamics of the DNA molecule and its stability was carried out. It has been shown that an increase in viscosity leads to a rapid stabilization of the angular vibrations of nitrogenous bases, while a decrease in viscosity changes the dynamics of DNA: the rate of change in the angular deviations of nitrogenous bases increases and the angular deformations of the DNA strands increase at each moment of time. These processes lead to DNA instability, which increases with time. Thus, the paper considers the influence of the external environment viscosity on the dissipation of the DNA nitrogenous bases’ vibrational motion energy. Additionally, the study on the basis of the described model of the molecular dynamics of physiological processes at different indicators of the rheological behavior of nucleoplasm will allow a deeper understanding of the processes of nonequilibrium physics of an active substance in a living cell to be obtained. 相似文献