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21.
Manabe K Iimura S Sun XM Kobayashi S 《Journal of the American Chemical Society》2002,124(40):11971-11978
Dehydration reactions in water have been realized by a surfactant-type catalyst, dodecylbenzenesulfonic acid (DBSA). These reactions include dehydrative esterification, etherification, thioetherification, and dithioacetalization. In these reactions, DBSA and substrates form emulsion droplets whose interior is hydrophobic enough to exclude water molecules generated during the reactions. Detailed studies on the esterification revealed that the yields of esters were affected by temperature, amounts of DBSA used, and the substrates. Esters were obtained in high yields for highly hydrophobic substrates. On the basis of the difference in hydrophobicity of the substrates, unique selective esterification and etherification in water were attained. Furthermore, chemospecific, three-component reactions under DBSA-catalyzed conditions were also found to proceed smoothly. This work not only may lead to environmentally benign systems but also will provide a new aspect of organic chemistry in water. 相似文献
22.
The kinetics of the thermal decomposition of solid complexes of the type Ni(NCS)2L2 (L=pyridine,β-picoline and quinoline), of pseudooctahedral configuration, were studied by using isothermal methods, on the basis of losses of weight, in the temperature range 90–191?. The most suitable reaction order for all the complexes under investigation was found to ben=2/3, i.e. the total decomposition rate is determined by the chemical process proper. The calculated values ofE a(in kcal · mole?1) decrease in the following order: Ni(NCS)2py2 (29.4)>Ni(NCS)2(β-pic)2 (27.6)>Ni(NCS)2Q2 (24.3). With increasing volume of the ligand L the reaction rate also increases, and this suggests that the reaction proceeds by dissociative activation. For all the investigated complexes it was found that δH>E A; this may be explained by a several-step mechanism and the complex Ni(NCS)2L is then considered an intermediate. 相似文献
23.
Electrodes containing glucose oxidase or xanthine oxidase adsorbed on modified glassy carbon electrodes or on conductive complexes, accumulate charge in the presence of substrates, the discharge of which gives the chronoamperometric stripping current. This current is 15 times higher than the stationary current after preconcentration for 8 min. A ten-fold increase in sensitivity of the determination of glucose or hypoxanthine is observed. The stripping current of electrodes based on cytochrome b2 adsorbed on a graphite electrode is 25 times higher than the stationary current. The electrode is useful for lactate determinations for more than 7 days. 相似文献
24.
The present short review deals with electroanalytical aspects of electrochemical response of ascorbic acid (Vitamin C) at conducting and electrogenerated polymer modified electrodes. Two main topics are considered: (i) electrocatalytic oxidation of ascorbate at conducting polymer modified electrodes, leading to electroanalytical techniques for ascorbate assay, and (ii) retardation of ascorbate penetration through a layer of electrogenerated polymers, leading to permselective coatings and their diverse uses, especially for biosensing devices. 相似文献
25.
Mathematical Notes - In this paper, we define the Dirichlet series $$ \zeta_{u_T j} (s)$$ , $$ j = 1, \dots, r$$ , absolutely converging in the half-plane $$ \operatorname{Re} s> 1/2 $$ and... 相似文献
26.
27.
Nadica Ivošević DeNardis Vera Žutić Vesna Svetličić Ranieri Urbani 《Electroanalysis》2007,19(4):473-478
In situ amperometric characterization of an aggregating system in terms of molecular adsorption and single microparticle interactions at the electrode interface is demonstrated using a model system: alginate/Ca(II) in an aqueous electrolyte solution. Recording of chronoamperometric curves of oxygen reduction at the dropping mercury electrode is designed for detection of dip‐shaped signals of individual gel microparticles. By addition of Ca(II) decrease of alginate adsorption is accompanied by appearance of signals indicating vesicle type association of alginate molecules and microparticles of gel phase. AFM imaging provided evidence of initial stage in calcium alginate gel formation. 相似文献
28.
A. P. Jucys E. P. Na
lnas P. S.
virblis 《International journal of quantum chemistry》1972,6(3):465-472
A general theory of the extended method of calculation of atomic structures having complex configurations is presented. It is based on the correspondence between the radial integrals of the ordinary method and the linear combinations of those of the extended method. The rules for going over from the ordinary method to the extended one are given. 相似文献
29.
Tomislav P. Živković 《Theoretical chemistry accounts》1988,73(2-3):207-219
A new method for the calculation of bond orders in alternant hydrocarbons is presented. The method requires a summation over the contributions of various superposition diagrams. Quantitatively, the method is almost as reliable as PPP, and due to its simplicity it can be used for fast and relatively accurate calculation of bond orders. In addition some simple rules are derived, which in many cases can be used to predict the signs of bond orders between nonbonded atoms.Dedicated to Professor J. Koutecký on the occasion of his 65th birthdayResearch supported by the Robert A. Welch Foundation of Houston, Texas 相似文献
30.
Summary
UV Densitometric Method for the Determination of Estrogens and Androgens in Pharmaceutical Preparations
A convenient method for the determination of estradiol benzoate/testosterone propionate and of ethynylestradiol/methyltestosterone mixtures from ampoules and lingualets, is described. The procedure is simple since the method involves direct reading from the thin-layer plate, avoiding thus the elution of the spot.After TL Chromatographie separation of active substances, densitometric measurements were performed with a HPTL scanner at 254 nm, whereby good and precise results were obtained. The standard deviation was found to range from 0.022 to 0.183, whereas the relative standard deviation ranged from 0.93 to 2.7%.The results obtained show that the method is applicable to routine analysis. 相似文献