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101.
V.?V.?Novokshonov Nguen?Chyong?Hoi N.?S.?ShaglaevaEmail author 《Russian Journal of General Chemistry》2017,87(6):1172-1174
Reaction of β-cyclodextrin with allyl bromide in dimethyl sulfoxide affords 2-О-allyl-β-cyclodextrin, while in dimethylformamide 6-О-allyl-β-cyclodextrin is formed. Optimal conditions of the reaction were found allowing to obtain the target products in quantitative yield. 相似文献
102.
Kleeberg C Cheung MS Lin Z Marder TB 《Journal of the American Chemical Society》2011,133(47):19060-19063
Reaction of [(IPr)Cu-OtBu] (1) with pinB-SiMe(2)Ph (2) leads to the Cu-silyl complex [(IPr)Cu-SiMe(2)Ph] (3). Insertion of CO(2) into the Cu-Si bond of 3 is followed by transformation of the resulting silanecarboxy complex [(IPr)Cu-O(2)CSiMe(2)Ph] (4) to the silanolate complex [(IPr)Cu-OSiMe(2)Ph] (5) via extrusion of CO. As 5 reacts readily with 2 to regenerate 3, a catalytic CO(2) reduction to CO is feasible. The individual steps were studied by in situ(13)C NMR spectroscopy of a series of stoichiometric reactions. Complexes 3, 4, and 5 were isolated and fully characterized, including single-crystal X-ray diffraction studies. Interestingly, the catalytic reduction of CO(2) using silylborane 2 as a stoichiometric reducing agent leads not only to CO and pinB-O-SiMe(2)Ph but also to PhMe(2)Si-CO(2)-SiMe(2)Ph as an additional reduction product. 相似文献
103.
Ming Zhao Sin Ting Lau Xiao Qi Zhang Wen Cai Ye Po Sing Leung Chun‐Tao Che Zhi‐Xiu Lin 《Helvetica chimica acta》2011,94(11):2099-2105
Bruceine K ( 1 ), a pentacyclic C20‐quassinoid bearing a unique 12,20‐epoxy moiety, and bruceine L ( 2 ), along with the ten known compounds (6S,7E)‐6,9,10‐trihydroxy‐ and (6S,7E)‐6,9‐dihydroxymegastigma‐4,7‐dien‐3‐one ( 3 and 4 , resp.), cleomiscosins A–C, luteoline, quercetine, bruceantinol, pinoresinol, and thevetiaflavone, were isolated from the ripe fruits of Brucea javanica. Bruceines K ( 1 ) and L ( 2 ) were determined to be (1β,2α,11β,12β,14ξ,15β)‐12,20‐epoxy‐1,2,11,13,14,15‐hexahydroxypicras‐3‐en‐16‐one and (1β,2α,11β,12β,15β)‐13,20‐epoxy‐1,2,11,12‐tetrahydroxy‐16‐oxo‐15‐(senecioyloxy)picras‐3‐en‐21‐oic acid methyl ester (senecioic acid=3‐methylbut‐2‐enoic acid), respectively, on the basis of NMR (1H‐ and 13C‐NMR, DEPT, 1H,1H‐COSY, NOESY, HMQC, and HMBC) and ESI‐MS data. Among the known compounds, (6S,7E)‐6,9,10‐trihydroxy‐ and (6S,7E)‐6,9‐dihydroxymegastigma‐4,7‐dien‐3‐one ( 3 and 4 , resp.), cleomiscosin C, luteoline, quercetine, and thevetiaflavone were isolated for the first time from the Brucea plants. 相似文献
104.
Collapsed polymers in solution represent an oft-overlooked area of polymer physics, however recent studies of biopolymers in the bloodstream have suggested that the physics of polymer globules are not only relevant but could potentially lead to powerful new ways to manipulate single molecules using fluid flows. In the present article, we investigate the behavior of a collapsed polymer globule under the influence of linear combinations of shear and elongational flows. We generalize the theory of globule-stretch transitions that has been developed for the specific case of simple shear and elongational flows to account for behavior in arbitrary flow fields. In particular, we find that the behavior of a globule in flow is well represented by a two-state model wherein the critical parameters are the transition probabilities to go from a collapsed to a stretched state P(g-s) and vice versa P(s-g). The collapsed globule to stretch transition is described using a nucleation protrusion mechanism, and the reverse transition is described using either a tumbling or a relaxation mechanism. The magnitudes of P(g-s) and P(s-g) govern the state in which the polymer resides; for P(g-s) ≈ 0 and P(s-g) ≈ 1 the polymer is always collapsed, for P(g-s) ≈ 0 and P(s-g) ≈ 0 the polymer is stuck in either the collapsed or stretched state, for P(g-s) ≈ 1 and P(s-g) ≈ 0 the polymer is always stretched, and for P(g-s) ≈ 1 and P(s-g) ≈ 1 the polymer undergoes tumbling behavior. These transition probabilities are functions of the flow geometry, and we demonstrate that our theory quantitatively predicts globular polymer conformation in the case of mixed two-dimensional flows, regardless of orientation and representation, by comparing theoretical results to Brownian dynamics simulations. Generalization of the theory to arbitrary three-dimensional flows is discussed as is the incorporation of this theory into rheological equations. 相似文献
105.
106.
Copper doped zinc sulfide nanoparticles were prepared by chemical precipitation method. The size of the particles was varied by changing the concentration of capping agent. The XRD studies indicate that most of the samples are cubic in nature. The broadening of peaks tends to increase with increasing capping agent concentration showing decrease in particle size. The crystalline size computed using Scherrer formula is found to be in range of 3–10 nm. Absorption spectra show absorption edge in UV region. The edge was found to shift towards shorter wavelength as the capping agent concentration is increased. This indicates increased effective band gap and hence reduced particle size. The nanoparticle size has been estimated in the range 5–10 nm using effective mass approximation model. For electroluminescence (EL) study of ZnS:Cu nanocrystals, the EL cells were prepared by placing ZnS:Cu nanoparticles between SnO2 coated conducting glass plate and aluminum foil. Alternating voltage of various frequencies was applied and EL brightness (B) at different voltages (V) was measured and reported in this paper. 相似文献
107.
J. Hubert S. Bordeleau K. C. Tran S. Michaud B. Milette R. Sing J. Jalbert D. Boudreau M. Moisan J. Margot 《Fresenius' Journal of Analytical Chemistry》1996,355(5-6):494-500
The use of microwave induced plasmas, particularly of surface wave plasmas, as detectors in atomic emission spectrometry for elemental analysis is reviewed. Surface wave plasmas have been produced at low HF power and used as gas chromatographic detectors. The analytical performances for the detection of non-metals with a Fourier transform spectrometer and a two-channel filter unit are reported. The excitation behavior of non-metals in helium-based mixed gas-plasmas has also be studied. In particular, the effect of power and of nitrogen concentration on the bromine emission has been systematically investigated. A nine-fold improvement of the detection limits for bromine can be obtained in a high power (900 W) helium-nitrogen (0.1–0.2%) plasma. 相似文献
108.
The reaction of bisgermavinylidene [(Me3SiN?PPh2)2C?Ge→Ge?C(PPh2?NSiMe3)2] ( 1 ) with AdNCO (Ad = Adamantyl) afforded the [2 + 2] cycloadditon product [(Me3SiN?PPh2)2CGeC(O) NAd] ( 2 ). Similar reaction of 1 with Ph3SiOH in tetrahydrofuran (THF) yielded the base‐stabilized germanium(II) triphenylsiloxide [H2C(PPh2?NSiMe3)2Ge(OSiPh3)2] ( 3 ). The results suggested that reactive germavinylidene may exist in solution and is capable of forming addition reaction products. The X‐ray structures of 2 and 3 were determined. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
109.
110.
D. L. Phillips C. Zhao W. M. Kwok Y.L. Li X. Guan D. Wang 《光散射学报》2005,17(3):251-253
pacc:8240,8760E Acombinedexperimentalandtheoretical studyofthephotochemistryofCHBr3inpurewa terandinacetonitrile/watermixedsolventsisre portedthatelucidatesthereactionsandmecha nismsresponsibleforthephotochemicalconver sionofthehalogenatomsinCHBr3intothre… 相似文献