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991.
Alena Rudolph Dino AlbericoRobert Jordan Ming PanFabio E.S. Souza Boris Gorin 《Tetrahedron letters》2013
A new synthetic strategy towards the C27–C35 subunit of Eribulin (1) has been devised to include a protected 1,2-amino alcohol at C34–C35. Early introduction of the C35 amino group in the synthesis of 1 increases the efficiency of the route. This new approach can be accomplished on a multi-gram scale and allows for the successful synthesis of Eribulin. 相似文献
992.
Two-state and continuous phase transitions in lipid bilayers A time-resolved X-ray diffraction study
Structural changes associated with transition from one phase to another have been examined in several lipid-water systems using time-resolved X-ray diffraction methods. Two types of transition mechanism can be recognized on the basis of scattering originating from the packing of the hydrocarbon chains. Two-state transitions are characterized by coexistence of the wide-angle scattering patterns of the initial and final phases throughout the transition region. Continuous transitions, on the other hand, take place through a series of intermediate states that are believed to arise from deformation of the hydrocarbon chain lattice as one phase transforms into another. Two-state processes are observed as subgel to liquid crystal transitions, and continuous transformations are typical of subgel to gel phase transitions. Examples of these transition types are presented and other transitions that do not appear to conform to either of these mechanisms are described. 相似文献
993.
994.
Vladimir B. Kobychev Nadezhda M. Vitkovskaya Elena Yu. Larionova Boris A. Trofimov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2931-2940
The ab initio calculations of 1-methoxy-2-propene ( 1 ), 1-methylthio-2-propene ( 2 ), and their anions are performed using the RHF/6-31+G* geometry optimization followed by MP2/6-31+G* energy calculations. Both 1 and 2 are found to rearrange toward 1-substituted 1-propenes with a comparable exothermic effect. However, the proton abstraction energies of 1 and 2 differ significantly. So, the acidity of propene is just slightly affected by the OCH 3 group while the SCH 3 group decreases its proton abstraction energy by 17.5 kcal/mol. Changes in charge distribution, bond lengths and bond orders suggest the negative hyperconjugation to stabilize anions of 2 but not that of 1 . This divergence is explained with a difference in sulfur and oxygen electronegativity. The d -functions of both sulfur and oxygen act in polarization. The Z -isomer of anion 1 is found to be by 2.9 kcal/mol more stable than its E -isomer, this could provide a predominant kinetic formation of the less stable Z -isomer of 1-methoxy-1-propene under base catalysis. 相似文献
995.
Nina K. Gusarova Svetlana F. Malysheva Natal’ya A. Belogorlova Alexander V. Artem’ev Vladimir A. Kuimov Boris A. Trofimov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):98-104
Abstract Red phosphorus reacts with 4-methoxystyrene in the KOH-DMSO superbase system (130 °C, 3 h, Ar) in the presence of a small quantity of H2O to give tris[2-(4-methoxyphenyl)ethyl]phosphane oxide as the main product in 30% yield. Microwave activation of the reaction (600 W, 6 min) affords basically a mixture of the phosphane oxide and tris[2-(4-methoxyphenyl)ethyl]phosphane (in a ratio of 1:1). When the mixture is exposed to air (r.t., 24 h), the phosphane oxide is formed in 85% yield. GRAPHICAL ABSTRACT 相似文献
996.
Vadim Yu. Kukushkin Elena A. Aleksandrova Boris V. Zhadanov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):433-435
Abstract The interaction of the complexes (Et4 N)[Pt(R2 SO)X3] (R = Me, Et, CH2 Ph, X [dbnd] C1; R [dbnd] Me, X [dbnd] Br) and cis-[Pt(Me2 SO)2 Cl2] with concentrated HX (X [dbnd] Cl. Br) results in the reduction of the coordinated sulfoxides and oxidation of Pt(II) to Pt(IV). As a result [Pt(R2 S)X5 and [Pt(R2S)2 X4] are formed. Ligands R2 S can be removed from the complexes and isolated in a free state. 相似文献
997.
Using the thermochemical approach to interpret the kinetics of heterogeneous reactions and the mechanism of congruent dissociative decomposition of solids developed in the 1980s and (re)analyzing the experimental data available in the literature over the last 90 years, a novel mechanism for the catalytic oxidation of H2 by PtO2 is proposed. In place of the conventional Langmuir–Hinshelwood and Eley–Rideal adsorption reaction mechanisms, our model is based on the reactions: PtO2(s) + 2H2 ? Pt(g) + 2H2O and Pt(g) + O2 ? PtO2(g) → PtO2(s). The first reaction determines the kinetics of H2 oxidation and the second determines the kinetics of restoration of the PtO2 layer. Thermochemical consideration of kinetic features of this model enables (for first time in the history of this reaction) the enthalpy and equilibrium constants for H2 oxidation on platinum to be calculated. The results are in good agreement with experimental data. In addition, the proposed mechanism explains the origin of the surface-retexturing effect, the impact of autocatalysis, the influence of H2O vapor on oxidation rate, and the three-fold variation of the Arrhenius E parameter with temperature. This all convincingly demonstrates the value of the thermochemical approach in interpreting heterogeneous reactions. 相似文献
998.
Dr. Ramiz A. Boulos Nikki Y. T. Man Dr. Nigel A. Lengkeek Prof. Katherine A. Hammer Dr. Niki F. Foster Natalie A. Stemberger Prof. Brian W. Skelton Pan Yu Wong Prof. Boris Martinac Prof. Thomas V. Riley Prof. Allan J. McKinley Prof. Scott G. Stewart 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(52):17980-17988
Herein we describe the preparation and structure‐activity relationship studies on range of stilbene based compounds and their antibacterial activity. Two related compounds, each bearing carboxylic acid moieties, exhibit good activity against several bacterial strains, including methicillin‐resistant Staphylococcus aureus MRSA (ATCC 33592 and NCTC 10442). Compound 10 was most active against Moraxella catarrhalis with minimum inhibitory concentrations (MICs) of 0.12–0.25 μg mL?1 and against Staphylococcus spp. with MICs ranging from 2–4 μg mL?1. The derivative 17 showed increased activity with MICs of 0.06–0.25 μg mL?1 against M. catarrhalis and 0.12–1 against Staphylococcus spp. This level of activity is similar to that reported for S. aureus for antibiotics, such as vancomycin, with MICs of ≤2.0 μg mL?1 and clindamycin with MICs of ≤0.5 μg mL?1. As an indicator of toxicity, 17 was tested for its ability to lyse sheep erythrocytes, and showed low haemolytic activity. Such results highlight the value of tris(stilbene) compounds as antibacterial agents providing suitable properties for further development. 相似文献
999.
Oleg I. Zhukov Boris I. Drevko 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):663-666
3-Thia(selena)pentane-1,5-diones react with Lewis acids by heteroatom. In these reactions soft Lewis acids such as tin tetrachloride and antimony pentachloride form adducts but hard Lewis acid such as phosphorus pentachloride oxidizes chalcogen atom of 3-thia(selena)-pentane-1,5-dione. Carbon analogues of these diketones form pyrylium salts in the reactions with these Lewis acids. 相似文献
1000.
Felicia Seichter Andreas Wilk Katharina Wörle Seong-Soo Kim Josef A. Vogt Ulrich Wachter Peter Radermacher Boris Mizaikoff 《Analytical and bioanalytical chemistry》2013,405(14):4945-4951
The 12CO2/13CO2 isotope ratio is a well-known marker in breath for a variety of biochemical processes and enables monitoring, e.g., of the glucose metabolism during sepsis. Using animal models—here, at a mouse intensive care unit—the simultaneous determination of 12CO2 and 13CO2 within small volumes of mouse breath was enabled by coupling a novel low-volume hollow waveguide gas cell to a compact Fourier transform infrared spectrometer combined with multivariate data evaluation based on partial least squares regression along with optimized data preprocessing routines. 相似文献