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121.
Summary The chromatographic technique of frontal analysis is applied to measuring adsorption from binary liquid mixtures by silica gel. The complete adsorption isotherm of a solvent mixture is obtained by measuring the break-through curves for a series of small concentration steps of the mobile phase. This method offers a direct way to determine the composition of the stationary phase in liquid-solid chromatography with mixed mobile phases. The surface excess isotherms of all binary systems formed by benzene, cyclohexane, and 1,2-dichloroethane, at the solution-silica gel interface at 25 °C are presented. The data of the three systems are shown to be thermodynamically mutually consistent. 相似文献
122.
Eva Schneiderman Bruno Perly Elwood Brooks Apryll M. Stalcup 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(1-2):43-50
The characterization of binary and ternary complexes of benzoate, lauryl hexaoxyethylene (C12E6) and -CD is presented. The complexation equilibrium was characterized by UV-Vis spectrophotometry, titration microcalorimetry, capillary electrophoresis, and 2D ROESY 1H-NMR. Results suggested that -CD forms one complex with C12E6in the stoichiometric ratio of -CD : C12E61.5 : 1, with a stability constant 1.3 × 105 M-1.5. The 2-D ROESY 1H-NMR spectrum indicated that C12E6is included inside the -CD cavity. The primary binding site of C12E6 is on the lauryl subunit of this molecule. Analogous to a previously reported study of -CD, the combination of -CD and C12E6precipitated from the solution. Addition of benzoate seemed to dissolve the precipitate and nearly doubled the apparent stability constant of the complex. Results from the various techniques supported formation of ternary complexes between -CD, C12E6, and benzoate. 相似文献
123.
S. I. Oshevski 《Russian Chemical Bulletin》2002,51(7):1171-1176
The possibility of specific cleavage of a single-stranded DNA fragment due to cooperative action of two oligonucleotide derivatives bearing chemical groups (at the 3"-phosphate and 5"-thiophosphate ends, respectively) located close to each other in a complementary complex is demonstrated. 相似文献
124.
Christopher M. Timperley Krystal E. Casey Stuart Notman David J. Sellers Nancy E. Williams Nichola H. Williams Gareth R. Williams 《Journal of fluorine chemistry》2006,127(12):1554-1563
Eighteen new fluorogenic analogues of organophosphorus nerve agents were synthesised and characterised. They included analogues of tabun, sarin, cyclosarin, soman, VX, and Russian VX, with the 7-oxy-4-methylcoumarin or 7-oxy-4-(trifluoromethyl)coumarin leaving group. These analogues inhibited acetylcholinesterase (AChE) effectively in vitro and therefore have potential as tools for the identification of novel organophosphatases in biological systems. Analogues of VX and Russian VX with the 7-amino-4-methylcoumarin group, although poor AChE inhibitors, may have utility for screening enzyme libraries for phosphoramidases capable of cleaving P-N bonds. 相似文献
125.
The multilayer adsorption on the solid/liquid interface in binary mixtures was studied by adsorption space filling with constant
and variable layer thickness. Adsorption from benzene/n-heptane mixtures was examined on hydrophilic and hydro-phobic surfaces.
The free enthalpy of adsorption, Δ21
G=f (x
1), was calculated from the adsorption excess isotherm by integration of the Gibbs equation. Supposing that the free enthalpy
is mainly due to adsorption in the first layer, the composition of this layer can be calculated from the Δ21
G=f (x
1) function. It was established that the adsorption layer thickness in benzene/heptane mixtures increases significantly with
increasing benzene content. This statement was supported by X-ray diffraction on hydrophobic clay minerals.
Received: 2 April 1997 Accepted: 10 June 1997 相似文献
126.
Arginase isolated from beef liver was covalently attached to a polyacrylamide bead support bearing carboxylic groups activated
by a water-soluble carbodiimide. The most favorable carbodiimide wasN-cyclohexyl-Nt’-(methyl-2-p-nitrophenyl-2-oxoethyl) aminopropyl carbodiimide methyl bromide, but for practical purposes,N-cyclohexyl-Nt’-morpholinoethyl carbodiimide methyl tosylate was used. The optimal conditions for the coupling procedure were
determined. The catalytic activity of the immobilized arginase was 290–340 U/g solid or 2.9–3.4 U/mL wet gel. The pH optimum
for the catalytic activity was pH 9.5, the apparent temperature maximum was at 60°C and Kmapp was calculated to be 0.37M L-arginine. Immobilization markedly improved the conformational stability of arginase. At 60°C,
the pH for maximal stability was found to be 8.0. The immobilized arginase was used for the production of L-ornithine and
D-arginine. 相似文献
127.
Yong Wang Zheng-bao He Zuo-wan Zhou 《高分子科学》2007,(6):565-572
The objectives of this paper are to understand the crystallization behavior of polypropylene(PP)composites with surface modified tetra-needle-shaped zinc oxide whisker(T-ZnOw).T-ZnOw was surface modified with different coupling agents,such as silane coupling agents(KH-550,KH-560)and titanate coupling agent(NDZ-105),in order to improve the compatibility between PP and T-ZnOw.DSC and POM were used to characterize the melt and crystallization behavior and the crystalline structures of the composites,respectively.The results show that the surface modified T-ZnOw acts as a nucleating agent of PP crystallization,depending on the coupling agent used for modification.KH-550 and KH-560 have more apparent role in improving the interfacial interaction than NDZ-105 and induce PP crystallization at higher temperature and with smaller spherulites size.The results also suggest that the crystallization behavior depends on not only the content of coupling agent,but also the content of the surface modified T-ZnOw used in the composites. 相似文献
128.
分光光度法同时测定中草药中的钼和铜 总被引:2,自引:2,他引:2
本文建立了在混合显色剂(PF+PAN)的胶束体系中,利用分光光度法同时测定中草药中的钼和铜。实验表明:在混合体系中,钼量在0~10μg/25mL,铜量在0~50μg/25mL的范围内符合比尔定律,ε′Mo=9.2×104L·mol-1·cm-1;ε′Cn=1.5×104L·mol-1·cm-1。该法用于中草药样品的分析,结果满意,回收率可达92~111%。 相似文献
129.
Tidjani Ngadi 《International journal of quantum chemistry》2003,94(2):65-74
In this article, we make a connection between the Rumer transformation, used in the study of the genetic code‐doublets, and the negation of classic logic. A unified classification is given, relying on two Klein's 4‐groups describing the symmetries of the 16 doublets of nitrogenous bases and those of the 16 binary connectives of classic logic, both groups being subgroups of a larger noncommutative group with eight elements we identify as the dihedral group D4. Also, some connections with other works are briefly considered. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
130.
采用络合反应,消除电镀锡溶液中金属离子对分离柱的污染,应用离子色谱法检测电镀液中SO4^2-的含量,回收率为95%-104%。 相似文献