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51.
[formula: see text] A spherical host with D2d symmetry consisting of a tetrathia[3.3.3.3]paracyclophane and two 18-crown-6 moieties was synthesized. Its crystal structure shows a central cavity with a diameter of 1.96 A and a depth of 6.75 A. A Na+ ion could rest in the cavity center but prefers core binding to external binding in one of the crown units. An intramolecular kinetic equilibrium was reached with the Na+ ion switching between the two crown units with an energy barrier of 14.1 +/- 3 kcal/mol. 相似文献
52.
Qiong Yu Lai Ji Zheng LuXiao Bo Su Xiao Yang Ji 《Journal of solid state chemistry》2002,165(2):312-316
Spinel compound LiNi1−xMnxVO4 (0≤x≤0.4) had been prepared by using the moist chemical method. X-ray diffraction spectra showed that the lattice constant increased with x in the LiNi1−xMnxVO4, XPS spectra indicating that Li1s had a chemical shift towards lesser binding energy, and manganese in LiNi1−xMnxVO4 existing as the mixed valence of Mn2+ and Mn3+. The electrochemical charge and discharge testing at a current density of 0.1 mA/cm2 between the potentials of 4.0 and 3.0 V vs Li/Li+ in 1 mol/dm3 LiPF6/EC+DEC (1:1 by volume) at 25°C showed that LiNi1−xMnxVO4 cell has a better rechargeability, but a lower cell voltage of 4.0 V vs Li/Li+ than that without the doping sample, and the capacity and the cycle efficiency of the Li/LiNi1−xMnxVO4 cells increased with x in the LiNi1−xMnxVO4. 相似文献
53.
The m6A‐RNA modification is a dynamic and reversible process, which has emerged as a new RNA code for the regulation of gene expression. The functional network of methyltransferases (writers), demethylases (erasers), and binding proteins (readers) modulate the level of m6A modification. Dysfunction of RNA methylation has been associated with various fundamental biological processes and human diseases. Herein, we briefly introduce an understanding‐enabled manipulation on m6A‐RNA modification with an emphasis on the use of small‐molecule intervention. 相似文献
54.
Ding L Liu W Wang W Glinka CJ Worcester DL Yang L Huang HW 《Langmuir : the ACS journal of surfaces and colloids》2004,20(21):9262-9269
A neutron diffraction method applicable to nonlamellar phases of substrate-supported lipid membranes is described and validated. When prepared on a flat substrate, the resulting nonlamellar phases have layered symmetry which provides some advantages over powder diffraction for detailed structure determination. This approach recently led to the detection of a rhombohedral phase and a distorted hexagonal phase of lipids. Here the determination of intensity and phase information for such phases is demonstrated by application to the hexagonal phase of diphytanoyl phosphatidylcholine (DPhPC). The hexagonal symmetry is used to verify the data reduction procedure for the intensities of the diffraction peaks. Diffraction intensities measured while varying the D2O/H2O ratio in the relative humidity was used to solve the phase problem. The neutron scattering length density distribution of the hexagonal phase was constructed and analyzed to elucidate the packing of the lipid molecules. The structure of DPhPC in the hexagonal phase is of interest in connection with its stalk structure in the rhombohedral phase. We also found that the incorporation of tetradecane into the DPhPC hexagonal phase is limited, similar to the case for dioleoyl phosphatidylethanolamine. 相似文献
55.
Chen-Hui Li Wen-Wei Lai Keh Ying Hsu Teh-Chou Chang 《Journal of polymer science. Part A, Polymer chemistry》1993,31(1):27-34
A series of semi-aromatic poly(ether-ester)s containing cinnamic group was prepared from 4,4′-diacrylic acid-α,ω-phenoxyalkanes with diols in the presence of diphenylchlorophosphate (DPCP) and pyridine as a catalyst and solvent. The phase behavior of these polymers was studied by differential scanning calorimetry (DSC), optical polarizing microscopy equipped with a heating stage, and wide-angle x-ray diffraction (WAXD). All of the poly(ether-ester)s, except P3 , show nematic or smectic thermotropic liquid crystalline behaviour under optical polarizing microscopic observation. These polymers can undergo photocrosslinking reaction upon heating, as examined by IR, solubility, and DSC analysis. © 1993 John Wiley & Sons, Inc. 相似文献
56.
Asymmetric polysulfone membranes were prepared by wet phase inversion method with different demixing rate of casting solutions. The influent factor of demixing rate was focused on the polarity of additive in the polysulfone/N-methyl-2-pyrrolidone/water ternary system. With increasing the polarity of alcohols in the casting solution, the decrease in skin layer thickness was observed and then a poor separation performance of membranes can be obtained. It was found that the polar additive caused the rapidly demixing of casting solution in coagulation bath and formed porous asymmetric membranes with defective skin layer. In the other case, chloroform was used as the non-polar additive in casting solution. With increasing the mount of chloroform in the casting solution, the increase in skin layer thickness was observed and then lead to a good separation performance of these membranes. It was found that of the non-polar additive delays the demixing rate of casting solution in this ternary system. The separation performance of these asymmetric membranes were characterized by the measurement of dehydration of ethanol/water mixture by pervaporation and observed the morphology by scanning electron microscopy. It was found that the separation performance of asymmetric polysulfone membrane strongly depends on the polarity of adding solvent in polysulfone/N-methyl-2-pyrrolidone/water ternary system. 相似文献
57.
The complex species of UO2(HA)(H2A)+ and UO2(HA)2 were identified in the ascorbic acid solution of uranyl ion at pH<2.1 and pH>2.1, respectively. Polarographic wave was proved to be the simultaneous reduction of UO2+2 and UO2(HA)(H2A)+ at pH <2.1. However, at pH>2.1, the wave is due to the reduction of U02(HA)2 The stability constants of the two complex species were found to be 5.1×10+ and 1.0×105, respectively. The hydrolysis constant of uranyl ion in the solution of ascorbic acid was determined. 相似文献
58.
Xiang-Hua Lai 《Tetrahedron letters》2004,45(23):4469-4472
Mono(6-(p-toluenesulfonyl))permethylated β-cyclodextrin, a versatile precursor for a wide variety of mono-functionalized permethyl β-cyclodextrins, has been generated successfully by the direct methylation of monotosylated cyclodextrin. This afforded a convenient synthesis of mono(6A-N-allylamino-6A-deoxy)permethylated β-cyclodextrin. Hydrosilylation of the chiral selector with (EtO)3SiH and reaction of the resultant reactive siloxane with pristine silica gel afforded a facile entry into a structurally well-defined chiral HPLC stationary phase. 相似文献
59.
The isolation and identification of eleven crystalline components from the aerial part of Cynanchum taiwanianum Yamazaki (Asclepiadaceae) are described. Their structures were determined on the basis of spectral evidence and chemical transformation. Besides caffeic acid, β-amyrin, and methyl phaeophorbide a, the isolated flavonoid components are classified into two groups, i.e. kaempferol derivatives (kaempferol, astragalin, afzelin, trifolin) and quercetin derivatives (quercetin, isoquercitrin, quercitrin, hyperin). 相似文献
60.
Wen-Feng Liaw Chia-Huei Lai Ming-Hsi Chiang Cheng-Kang Hsieh Gcne-Hsiang Lee Shie-Ming Peng 《中国化学会会志》1993,40(5):437-444
Diphenyldichalcogenides (PhE)2 (E = Te, Se) react with Fe(0)-phenylchalcogenolate [PPN] [PhEFe(CO)4] to yield the products of oxidative addition, Fe(II)-mixed-phenylchalcogenolate fac- [PPN][Fe(CO)3(TePh)n(ScPh)3-n] (n = 1, 2). Reactions of [PPN][REFe(CO)4] (E=Se, R=Me; E=S, R=Et) and diphenyldichalcogenides yielded ligand-exchange products [PPN][PhEFe(CO)4] (E=Te, Se, S). The compounds [Fe(CO)3(TePh)(ScPh)2]? (l) and [Fe(CO)3(TePh)2 (2) crystallize in the isomorphous monoclinic space group C2/e, with a = 32.035(8), b = 11.708(6), c = 28.909(6) Å, Z = 8, R = 0.048, and Rw = 0.044 (1); with a = 32.089(5), b= 11.745(2), c = 28.990(8) Å, Z = 8, R = 0.048, and Rw = 0.048 (2). The complexes 1 and 2 crystallize as discrete cations of PPN+ and anions of [Fe(CO)3(TcPh)u(ScPh)3-n] (n=1, 2), and one half solvent molecule THF. The geometry around Fe(II) is a distorted octahedron with three carbonyl groups and three phenylchalcogenolate ligands occupying facial positions. 相似文献