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991.
Yu Ping ZHANG Wen Jun GONG Li Qun FAN Yi Jun ZHANG Kwang Pill LEE 《中国化学快报》2006,17(11):1485-1488
A porous monolithic sol-gel column with the solution of methacryloxypropyltrimethoxysilane in toluene with an acid catalyst was prepared in the presence and absence of sodium dodecyl sulfate. In situ polymerization was carried out byγ-ray irradiation within the capillary. Theγ-radiation-initiated synthesis could generate radicals directly on the monomer avoiding use of any initiator. The chromatographic behavior of the capillary monolithic columns were studied in the modes of CEC, p-CEC and low pressure-driven separation, all the tests exhibited reversed-phase character. It provided a viable alternative to either thermally initiated or photo polymerization method for the preparation of monolithic columns. 相似文献
992.
Xin Rong QIN* Quan LI Yu Yuan XIE State Key Laboratory of Drug Research Shanghai Institute of Materia Medica Shanghai Institutes for Biological Sciences Chinese Academy of Science Shanghai 《中国化学快报》2001,(9)
The proteinogenic (-amino acids constitute an important section of the "chiral pool", being inexpensive in the L-form (but available if necessary as the D enantiomers), structurally varied and chemically versatile1, they are useful starting materials for chiral reagents, auxiliaries and ligands2. Any high-yielding transformation of an (-amino acids which proceeds without racemization is thus of potential importance, especially if it generates another reactive center and may be applied to the s… 相似文献
993.
994.
995.
In the present paper, Na_2SO_4-Al_2(SO_4)_3-H_2O system has been studied by ~(23)Na and ~(27)Al NMR quantitative method. It has been shown that the existence of double salt can be easily identified by this method. 相似文献
996.
Masayoshi Nakasako Masamitsu Wada Satoru Tokutomi Kotaro T. Yamamoto Jun Sakai Mikio Kataoka Fumio Tokunaga † Masaki Furuya 《Photochemistry and photobiology》1990,52(1):3-12
Abstract— The quaternary structure of pea phytochrome type I (PI) dimer in the red-light-absorbing form was studied by small-angle X-ray scattering (SAXS) technique and rotary-shadowing electron microscopy. Structural parameters for PI 114 kDa chromopeptide dimer and its tryptically digested N-terminal 59 kDa chromopeptide monomer, such as average electron density, molecular volume and the second moment of electron density distribution, were determined in terms of SAXS using the contrast variation method. Furthermore, by means of model simulation for the scattering profiles of the chromopeptides, most plausible structural models for both peptides were constructed. The distance between the chromophoric domains was estimated to be about 70 A in the resultant model for 114 kDa chromopeptide dimer. Furthermore, the model was consistent with the electron-micrographic images of both the intact PI dimer and the PI 114 kDa chromopeptide dimer, so that the N-terminal 7 kDa fragment did not significantly contribute the low-resolution images of the dimer. 相似文献
997.
Okada Y Yokozawa M Akiba M Oishi K O-kawa K Akeboshi T Kawamura Y Inokuma S Nakamura Y Nishimura J 《Organic & biomolecular chemistry》2003,1(14):2506-2511
A variety of aromatic compounds with both activating and deactivating substituents were brominated with sodium monobromoisocyanurate (SMBI) 1, diethyl ether, diethyl ether-methanesulfonic acid, trifluoroacetic acid, or sulfuric acid were employed as solvents. Thus nitrobenzene was conveniently brominated in sulfuric acid, benzene was readily monobrominated in diethyl ether-methanesulfonic acid, and phenol was selectively brominated at the ortho position under mild conditions in refluxing diethyl ether. With substituents that are easily protonated, trifluoroacetic acid may be employed as solvent in the reaction with 1, in contrast NBS was ineffective in trifluoroacetic acid. This renders 1 a superior reagent relative to NBS. In addition to aromatics, alkenes, ketones and esters were also brominated with 1. Diethyl malonate was brominated with 1 and then subjected to a Bingel reaction with NaH to afford the desired methanofullerene in reasonable yield. 相似文献
998.
Yuan LF Yang J Wang H Zeng C Li Q Wang B Hou JG Zhu Q Chen DM 《Journal of the American Chemical Society》2003,125(1):169-172
Orientationally ordered structures of two-dimensional (2D) C(60) at low temperature have been investigated theoretically and experimentally. Using total energy optimization with a phenomenological potential, we find the ground state is a close packed hexagonal lattice in which all the molecules have the same orientation. Several local minima of the potential energy surface are found to be associated with other 1 x 1 lattices as well as 2 x 2 lattices. The energies of the orientational domain boundaries of the 1x1 lattices are also computed, and two kinds of which yield negative values. A majority of these theoretical findings are confirmed by our low-temperature scanning tunneling microscopy study of a 2D C(60) array supported on a self-assembled monolayer. 相似文献
999.
The rheological properties of titanium dioxide dispersed in water are measured over a wide range of powder concentrations, temperatures, and pH values. The value of intrinsic viscosity of titanium dioxide measured with an Ubbelohde capillary viscometer is 3.55, which is useful for determining the shape and aggregation property of the particles. The yield stress and steady shear viscosity of titanium dioxide with broad and narrow particle size distributions were measured over a wide range of solid volume fractions on a Brabender rheometer. It is observed that the rheological properties of the suspensions are quite different due to the difference in particle size distributions. Quemada, Casson, and Zhou's models were used to fit the experimental data and useful parameters were obtained. Calculated data are also in good agreement with the experimental data. As expected, the shear viscosity and yield stress decrease with increasing temperature. But when the temperature is around 50 degrees C, yield stress increases with increasing temperature while shear viscosity exhibits a complex behavior. The phenomena are very interesting and special. The Peclet number was used to analyze the shear thickening behavior. Models were also used to describe the shear viscosity under different temperatures and the master plots of the reduced variables eta/eta(infinity) vs t(c)gamma; at different temperatures are superimposed, which means the agreement is fair and the models are suitable to describe the rheological properties of titanium dioxide suspensions. pH effects were investigated on a Rheometrics RFS-II rheometer and it was found that pH can change the surface charge of the particles, which also affects the rheological behavior. The pH at which maximum shear viscosity and yield stress occur is in concordance with the isoelectric point. Copyright 2001 Academic Press. 相似文献
1000.
We have investigated the effect of salt concentration and temperature on the average aggregation number and micro-polarity of the interior of micelles of sodium dodecyl sulfate (SDS). sodium tetradecyl sulfate (STDS) and lithium dodecyl sulfate (LiDS). The transient fluorescence decay of micelle-solubilized pyrene has been measured and analyzed. An exponent weighted average aggregation number <n>e was obtained by this technique. For SDS and STDS in NaCl solution, <n>e increases as the temperature is lowered or salt concentration is increased <n>e increased from ~ 50 to ~ 250 over [NaCl] = 0 to 0.8 M. Due to the strong counterion binding of lithium in the micellar solution, the LiDS micelle is much, smaller and does not increase appreciabily even at [LiCl] =0.8 M. From the fluorescence spectrum fine structure of pyrene and the fluorescence decay of the monomer and excimer, we can understand the local polarity and the water penetration to the interior of the micelle upon addition of salts and with changing temperature. The interior of the micelle becomes more nonpolar as the salt concentration is increased and the temperature is lowered. A complete kinetic analysis of the time–dependence of the fluorescence is given. The kinetic analysis is in agreement with the results reached by fluorescence spectral analysis. 相似文献