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排序方式: 共有210条查询结果,搜索用时 15 毫秒
201.
202.
We discuss quantum deformations of Riemann surfaces whose fundamental groups are Abelian (the exceptional Riemann surfaces). We prove uniformization theorems, state deformation estimates, and study the dependence of quantum Riemann surfaces on the deformation parameter.Supported in part by NSF grant DMS-9206936.Supported in part by DOE grant DE-FG02-88ER25065. 相似文献
203.
Ionic liquids with the weakly coordinating perfluoroalkoxyaluminate anions, Al(ORF)4-, are obtained by a metathesis reaction of LiAl(ORF)4 and [bmim]Cl or [bmpyr]Cl in high yields. The compounds [bmim][Al(hfip)4] and [bmpyr][Al(hfip)4] have surprisingly low viscosities at elevated temperatures (60 degrees C) and an exceptionally high electrochemical window, which might render them useful for certain applications. 相似文献
204.
We have developed a new method for the synthesis of functionalized symmetrical trisulfides based on (5,5‐dimethyl‐2‐thioxo‐1,3,2‐dioxa‐phosphorin‐2‐yl)disulfanyl derivatives prepared from readily available 5,5‐dimethyl‐2‐sul‐fanyl‐2‐thioxo‐1,3,2‐dioxaphosphorinane or bis(5,5‐dimethyl‐2‐thioxo‐1,3,2‐dioxaphosphorinan‐2‐yl) disulfide. The symmetrical trisulfides can be obtained from aliphatic and aromatic thiols and l ‐cysteine derivatives under mild conditions with high yield and purity. 相似文献
205.
We report a microfluidic technique for high-throughput generation of droplets of nanolitre volume in parallel channels with online control of the volumes, volume fraction and distribution of droplet volumes with the use of two external valves. 相似文献
206.
Berski S Sensato FR Polo V Andrés J Safont VS 《The journal of physical chemistry. A》2011,115(4):514-522
The oxygen atom transfer reaction from the Mimoun-type complex MoO(η(2)-O(2))(2)OPH(3) to ethylene C(2)H(4) affording oxirane C(2)H(4)O has been investigated within the framework of the Bonding Evolution Theory in which the corresponding molecular mechanism is characterized by the topological analysis of the electron localization function (ELF) and Thom's catastrophe theory (CT). Topological analysis of ELF and electron density analysis reveals that all Mo-O bonds in MoO(η(2)-O(2))(2)OPH(3) and MoO(2)(η(2)-O(2))OPH(3) belong to closed-shell type interactions though negative values of total energy densities E(e)(r(BCP)) imply some covalent contribution. The peroxo O(i)-O(j) bonds are characterized as charge-shift or protocovalent species in which pairs of monosynaptic basins V(3)(O(i)), V(3)(O(j)) with a small electron population of ~0.25e each, are localized between core basins C(O(i)), C(O(j)). The oxygen transfer reaction from molybdenum diperoxo complex MoO(η(2)-O(2))(2)OPH(3) to C(2)H(4) system can be described by the following consecutive chemical events: (a) protocovalent peroxo O(2)-O(1) bond breaking, (b) reduction of the double C(1)=C(2) bond to single C(1)-C(2) bond in ethylene, (c) displacement of oxygen O(1) with two nonbonding basins, V(i=1,2)(O(1)), (d) increase of a number of the nonbonding basins to three (V(i=1,2,4)(O(1))); (e) reorganization and reduction in the number of nonbonding basis to two basins (V(i=1,4)(O(1))) resembling the ELF-topology of the nonbonding electron density in oxirane, (e) formation of the first O(1)-C(2) bond in oxirane, (f) C(2)-O(1)-C(2) ring closure, (g) formation of singular nonbonding basin V(O(2)) in new Mo=O(2) bond. The oxygen atom is transferred as an anionic moiety carrying a rather small electronic charge ranging from 0.5 to 0.7e. 相似文献
207.
Slawomir Jarosz Stanislaw Skóra Artur Stefanowicz Mateusz Mach Jadwiga Frelek 《Journal of carbohydrate chemistry》2013,32(8):961-974
ABSTRACT Reaction of sugar derived phosphonates [Sug-C(O)CH2P(O)(OMe)2] with sugar aldehydes (Sug'-CHO) provides the higher enones of the general formula Sug-C(O)CH=CH-Sug' with the trans configuration of the double bond. The phosphonate method is superior to the previously used phosphorane methodology [Sug-C(O)CH=PPh3 + Sug'-CHO] since sugar phosphonates can be prepared in much higher yields and are much more nucleophilic than corresponding phosphoranes. The sugar enones are reduced to appropriate allylic alcohols with zinc borohydride; the stereoselectivity of this process is >97:3 (with the D-glycero isomer predominating) when the carbonyl group is placed at the α-position to the sugar ring. CD spectroscopy was used for the determination of the configuration of higher sugar allylic alcohols. 相似文献
208.
Magdalena Jakubczyk Slawomir Michalkiewicz Agata Skorupa Kinga Krajcarz 《Molecules (Basel, Switzerland)》2022,27(24)
The electrochemical properties of methylisothiazolinone (MIT), the most widely used preservative, were investigated by cyclic (CV) and differential pulse voltammetry (DPV) to develop a new method for its determination. To our knowledge, this is the first demonstration of a voltammetric procedure for the determination of MIT on a boron-doped diamond electrode (BDDE) in a citrate–phosphate buffer (C-PB) environment. The anodic oxidation process of methylisothiazolinone, which is the basis of this method, proved to be diffusion-controlled and proceeded with an irreversible two-electron exchange. The radical cations, as unstable primary products, were converted in subsequent chemical reactions to sulfoxides and sulfones, and finally to more stable final products. Performed determinations were based on the DPV technique. A linear calibration curve was obtained in the concentration range from 0.7 to 18.7 mg L−1, with a correlation coefficient of 0.9999. The proposed procedure was accurate and precise, allowing the detection of MIT at a concentration level of 0.24 mg L−1. It successfully demonstrated its suitability for the determination of methylisothiazolinone in household products without the need for any separation steps. The proposed method can serve as an alternative to the prevailing chromatographic determinations of MIT in real samples. 相似文献
209.
210.