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排序方式: 共有211条查询结果,搜索用时 15 毫秒
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Andriy B. Zaborovskiy Ruslan E. Prystansky Vitaliy I. Timokhin 《Journal of organometallic chemistry》2004,689(18):2912-2919
The interaction of (Me3Si)3SiH with O2 is known to afford (Me3SiO)2Si(H)SiMe3 in which the two oxygen atoms arise from the same oxygen molecule. In order to investigate the mechanism of this unusual reaction, the oxidation rates were measured in the temperature range 30-70 °C by following oxygen uptake in the presence and absence of hydroquinone as inhibitor. The rate constant for the spontaneous reaction of (Me3Si)3SiH with O2 was determined at 70 °C to be ∼3.5 × 10−5 M−1 s−1. A sequence of the propagation steps is proposed by combining the previous and present experimental findings with some theoretical results obtained at the semiempirical level. These calculations showed that the silylperoxyl radical (Me3Si)3SiOO undergoes three consecutive unimolecular steps to give (Me3SiO)2Si()SiMe3. Evidence has been obtained that the rate determining step is the rearrangement of silylperoxyl radical to a dioxirand-like pentacoordinated silyl radical. Our findings are of considerable importance for the understanding of the oxidation of hydrogen-terminated silicon surfaces. 相似文献
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We review our recent work on the direct calculation of the interfacial free energy, gamma, of the crystal-melt interface via molecular dynamics computer simulation for a number of model systems. The value of gamma as a function of crystal orientation is determined using a thermodynamic integration technique employing moving cleaving walls [Phys. Rev. Lett. 2000, 85, 4751]. The calculation is sufficiently precise to resolve the small anisotropy in gamma, which is crucial in determining the kinetics and morphology of dendritic growth. We report values of gamma for the hard-sphere and Lennard-Jones systems, as well as recent results on the series of inverse-power potentials. For the inverse sixth-, seventh-, and eighth-power systems, we determine gamma for both fcc and bcc crystal structures. For these systems, the bcc-melt gamma is lower than that for fcc crystals by about 25%, consistent with recent experiments and computer simulations on fcc-forming systems that show preferential formation of bcc nuclei in the initial stages of crystallization. In addition, we show that our results give a molecular interpretation of Turnbull's rule, which is the empirical relationship between gamma and the enthalpy of fusion. 相似文献
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Ruslan P. Liferovich 《Journal of solid state chemistry》2004,177(6):2188-2197
Ternary lanthanide scandates (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho) have been synthesized at ambient pressure. Their structure has been investigated at room temperature by Rietveld analysis of powder X-ray diffraction data. The Ln-scandates are orthorhombic perovskites, adopting space group Pbnm (? 62), a≈b≈√2ap, c≈2ap, Z=4. Heavy lanthanides (Er-Lu), and Y do not form perovskites at ambient conditions. Compositionally driven phase transitions were not observed. The unit-cell parameters decrease with increasing ScO6 octahedron rotation and atomic number of the Ln cation. In common with lanthanide orthoferrites, the uniform structural evolution is interrupted at the middle-heavy part of the lanthanide sequence. This is probably due to an interplay between: (i) enlargement of the ScO6 octahedra relative to BO6 in other perovskites (e.g., FeO6 in GdFeO3); (ii) reduction in size of the first coordination sphere of Ln3+ coincident with the lanthanide contraction; (iii) coincident expansion of the second coordination sphere due to screening effects of OI1 on OI2, and entry of Sc to the lanthanide coordination sphere; (iv) complex mixing between oxygen and lanthanide lanthanide f- and scandium d-orbitals. In the series studied, Ln3+ are in eight-fold coordination (tetragonal antiprism), and are considerably displaced from the center of the LnO8 polyhedron along [001]. Evolution of the crystallochemical characteristics through the Ln orthoscandate series is complex due to both the antipathetic distortions of A- and B-site coordination polyhedra and interaction of the orbitals of oxygen, Ln and Sc. Empirically obtained limits of Goldschmidt and observed viiito tolerance factors for ternary LnBO3 compounds adopting the Pbnm structure are 0.795 and 0.841, respectively. 相似文献
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Ruslan Bikmurzin Rimant Bandzevi
it Arnas Maralka Andrius Maneikis Lilija Kaldien 《Molecules (Basel, Switzerland)》2022,27(14)
β-glucans are known as biological response modifiers. However, different sources can result in structural differences and as a result differences in their biological activity. The hot water extraction method allows to obtain, high molecular weight β-glucans without altering their structure by using strong chemicals, such as alkalis or acids. Analysis of β-glucans by FT-IR and NMR spectroscopy in solid state is superior to analysis in solution as it allows researchers to study the preserved structure of the extracted polysaccharides. FT-IR spectroscopy was used in this study to make side-by-side comparison analysis of hot water extracted β-glucans from different yeast sources. NMR spectroscopy was used to confirm findings made by FT-IR spectroscopy. Extracted β-glucans exhibit characteristic structure of β-1,3/1,6-linked glucans with noticeable levels of proteins, possibly in a form of oligopeptides, chitin and other impurities. β-glucans obtained from C. guilliermondii, P. pastoris and S. pastorianus exhibited higher protein content. Differences in mannan, chitin and α-glucan content were also observed; however, the species-specific structure of obtained β-glucans could not be confirmed without additional studies. Structural analysis of high molecular weight β-glucans in solid state by FT-IR spectroscopy is difficult or limited due to band intensity changes and overlapping originating from different molecules. 相似文献
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Oleg Tkachenko Abdur Rahim Andrey Baraban Ruslan Sukhov Inna Khristenko Yoshitaka Gushikem Yuriy Kholin 《Journal of Sol-Gel Science and Technology》2013,66(1):145-154
A sol–gel based hybrid process was developed by manipulating different techniques in sol–gel process to synthesize γ-alumina and (CuO, CuO + ZnO) doped γ-alumina spherical particles. Catalysts having spherical geometry have an important advantage over powders or pellets which are impervious to fluids, when packed in a reactor. Boehmite sol was used as alumina precursor for synthesizing porous γ-alumina and doped materials. γ-alumina particles having 5 wt% CuO, 4 wt% CuO + 1 wt% ZnO, 3 wt% CuO + 2 wt% ZnO and 2 wt% CuO + 3 wt% ZnO were prepared by adding required amounts of Cu(NO3)2 and Zn(NO3)2 solutions prior to gelation of the sol. Methanol dehydration studies were carried out by employing these synthesized catalysts. Hundred percent conversion of methanol to dimethyl ether was observed with (4 wt% CuO + 1 wt% ZnO)-γ-alumina and (5 wt% CuO)-γ-alumina microspheres at 325 and 350 °C, respectively. 相似文献