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11.
Summary The capillary gas chromatographic retention behavior of -pinene and tricyclene has been investigated on stationary phases of different polarities. On all but one of the columns employed, tricyclene eluted before -pinene; only permethylated -cyclodextrins dissolved in moderately polar polisiloxanes gave a reversed elution order. The intermolecular interactions which caused the unexpected retention behavior were investigated in detail, applying methods of computer simulation. To achieve this, we have developed a calculation algorithm on the basis of molecular mechanical optimizations and programmed it in a macro. This makes it possible to systematically investigate a given configuration space in which all the possible interactions can take place. It was shown that permethylated -cyclodextrin as host molecule for both guest molecules offers an optimum cavity size. As a result the number of energetically favorable contacts between host and guest molecules as well as the strength of the interactions in this stationary phase were larger. As a consequence the elution order, normally only influenced by the vapor pressure of the compounds at a given temperature, was changed. Nonspecific interactions played an especially important role for these kinds of substances. 相似文献
12.
M. Yoshida M. Asano M. Kumakura R. Katakai T. Mashimo H. Yuasa K. Imai H. Yamanaka 《Colloid and polymer science》1990,268(8):726-730
A sequential polydepsipeptide containing a tripeptide sequence L-alanyl-Lalanyl-ethyl L-glutamyl and an-hydroxy acid L-lactic acid, poly(Ala-Ala-Glu(OEt)-Lac), was synthesized to prepare the microspherical particles by the solvent evaporation process. In this case, the solvents play the most important role for the preparation of polydepsipeptide microspheres and, as an example, when 200 mg of the polydepsipeptide dissolved in 10 ml of 98/2% chloroform/dichloroacetic acid mixture was stirred at 400 rpm and 30 C, the microspherical particles with mean diameter of 58m were formed after pouring into 200 ml of 1% (w/v) poly(vinyl alcohol) solution. 17-Estradiol was incorporated into the particles, and the resulting particles were found to contain 5 mg of drug per 25 mg of the particle. The in vivo release of drug from the microspherical formulation was evaluated by measuring the pharmacological influence on rat prostate. It was found that the sufficient amount of drug, keeping the effective pharmacological influence, is supplied during the first 12-week period, followed by an incomplete supplying of drug intil the implant is perfectly degraded in vivo in the 25th week from the start of implantation. 相似文献
13.
R. Sakamoto 《Colloid and polymer science》1984,262(10):788-792
Solvent effects on the phase separation of poly(-benzyl L-glutamate) to liquid crystal and isotropic solution have been observed in various helicogenic solvents. The temperature-composition phase diagrams have been determined for each solution. The critical concentrations,
2
*
, at which the phase separation occours have been compared in various solvents. In dimethylformamide in which the polymer is molecularly dispersed, the observed
2
*
value has agreed with that calculated by Flory's theory. In some solvents in which the polymer aggregates in a head-to-tail mode such as chloroform, the observed
2
*
values have been considerably small. It is assumed that the polymer aggregates behave as longer particles than the original particles. In dioxane in which the polymer aggregates highly both in a head-to-tail and a side-by-side modes, the
2
*
value has been a little larger than that in chloroform. In this case the relationship between the aggregation and the liquid crystal formation is so complicated that further investigation is necessary. In aromatic solvents such asm-cresol that dissolves the polymer almost molecularly, the
2
*
is smaller than that in dimethylformamide. Therefore, the intermolecular interactions between the phenyl groups in the side groups of the polymer and those in solvent molecules must be considered.The author is grateful to Mr. K. Sano and Mr. M. Watanabe for their observation of the liquid crystal formation. 相似文献
14.
Summary The interfering effect of the -radiation of radioactive isotopes of the rare earths on the non-destructive neutron activation analysis of g amounts of uranium, using the 106 KeV--line of 239Np and NaI (Tl). detector, is estimated. The errors introduced by the interfering isotope in the analysis of uranium, are determined as a function of the ratio of the concentration in the sample of the interfering element and uranium. In addition, the possibilities of determining the quantitative effect of these elements are described. The use of the proposed method is demonstrated by the analysis of some geological samples.
Zerstörungsfreie Neutronenaktivierungsanalyse von Uran über die 106 KeV--Strahlung von Neptunium-239II. Einfluß der Seltenen Erden
Zusammenfassung Es wird die Störung bestimmt, die die -Strahlung der radioaktiven Isotope Seltener Erden bei der zerstörungsfreien Neutronenaktivierungsanalyse von Mikrogramm-Mengen Uran über die 106 KeV--Linie des 239Np mit Hilfe eines NaJ(Tl)-Detektors hervorrufen kann. Die Fehler in der Analyse von Uran, die das Störisotop verursachen kann, werden als Funktion des Verhältnisses der Konzentration des Störelements zu der des Urans in der Probe bestimmt. Es werden Möglichkeiten beschrieben, den Einfluß störender Elemente quantitativ zu erfassen. Die Brauchbarkeit der vorgeschlagenen Methode wurde durch Analyse einiger geologischer Objekte bewiesen.
Part I: Z. Anal. Chem. 257, 23 (1971). 相似文献
15.
In distinction to Extended Hückel Theory which predicts as the most stable conformation of free zwitterionic GABA a totally extended form, PCILO and SCF ab initio studies show that the intrinsically preferred conformation of the isolated molecule is a highly folded one, resulting from strong interactions between the two charged ends. Computations are also carried out for hydrated GABA in the supermolecule approach allowing moreover for the flexibility of binding of some of the water molecules of the first hydration shell. They predict the coexistence in solution of a large number of conformations showing different degrees of folding (or extension), a result confirmed by recent NMR studies. This and a number of similar results show that we have to adapt our thinking on the role of conformations in pharmacological activity to this situation, which was frequently obscured by the more abundant results of X-ray crystallography yielding a single conformation. 相似文献
16.
František Kopecký Božena Kopecká Pavol Kaclík 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):215-217
The solubility of nimodipine was measured in aqueous solutions of the following cyclodextrins: -cyclodextrin (-CD), hydroxypropyl--CD (HP--CD), -cyclodextrin (-CD), random substituted methyl--CD (M--CD), three hydroxypropyl--CDs (HP--CD) with mutually different average degree of substitution, and hydroxypropyl--cyclodextrin (HP--CD). From the determined linear solubility diagrams the values of the binding constant K11 of the inclusion complexes of nimodipine with the respective CDs were evaluated. The -CDs efficiently solubilized sparingly soluble nimodipine, the highest value of K11 was found for M--CD (1680 M-1), followed by -CD (550 M-1) and HP--CDs, where the higher degree of substitution lowered K11. Only slight solubilization of nimodipine was observed in the solutions of the -CDs and HP--CD. 相似文献
17.
The adsorption of ovalbumin, -globulin, and lysozyme on uniform spherical hematite and chromium hydroxide particles in aqueous media has been studied as a function of the pH at a constant ionic strength. The uptake of ovalbumin and -globulin was greatest at their isoelectric points and differed little at 10–2 and 10–3 mol dm–3 NaNO3. The adsorption of lysozyme was strongly influenced by the ionic strength.The deposition of ovalbumin on hematite in the presence of Mg (NO3)2 was significantly greater than that with NaNO3 under otherwise comparable conditions. Dialysis experiments with ovalbumin against magnesium nitrate solutions showed Mg2+ to be specifically bound to the protein.The shapes of isotherms indicated monolayer coverage for ovalbumin and multilayer coating for lysozyme for both adsorbents. The shapes of isotherms of -globulin on hematite point to a rearrangement of the protein on the particle surface, while a monolayer was found on chromium hydroxide particles.Supported by the NSF Grant CHE-9108420Part of a Ph.D. thesis 相似文献
18.
-Butyrolactone (hereafter abbreviated GBL) is produced by the two-stage hydrogenation of maleic anhydride(MAH) in the liquid phase: the hydrogenation of MAH to succinic anhydride(SAH) in the first stage and the subsequent hydrogenation of SAH to GBL in the second stage. A novel ruthenium catalyst system consisting of Ru salts, trialkylphosphine and p-toluene sulfonic acid (p-TsOH) was found very effective for the hydrogenation of SAH affording GBL, which exhibited excellent catalyst performance, exceeding 97% selectivity for GBL and high activity. 相似文献
19.
The formation and properties of the products of the radiation-induced chemical reduction of silver ions in aqueous solutions containing sodium polyacrylate were investigated. The absorption spectra of these species exhibit a band at 290 mn and a band in the visible region. The latter shifts from 470 nm to -800 nm with time or after the addition of silver ions. The species obtained (clusterites) arc linear silver clusters bound to the carboxyl groups of the ion exchanger. The red shift of the visible band is due to the increase in their size. The mechanism of the formation and the structure of the clusterites are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1429–1435, June, 1996. 相似文献
20.
Highly efficient kinetic resolution of racemic secondary alkyl diazoacetates in intramolecular carbon-hydrogen insertion reactions has been achieved using chiral dirhodium(ii) carboxamidates. Products formed from catalytic diazo decomposition of racemic 2-octyl diazoacetate and, separately, its (2R)- and (2S)-enantiomeric forms, as well as bothcis- andtrans-2-methylcyclohexyl diazoacetates, have been systematically evaluated. Enantioselectivities up to 99 %ee have been obtained for -lactone formation. -Lactone production has been observed and, although minor with cyclohexyl diazoacetates, is the major insertion pathway for diazo decomposition of 2-octyl diazoacetate.Dedicated to Academician of the RAS N. S. Zefirov (on his 60th birthday).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1798–1803, September, 1995.Financial support for this research from the National Institutes of Health (GM 46503) and the National Science Foundation of the United States is gratefully acknowledged. We thank D. A. Pierson for her preparation of 2-methylcyclohexyl diazoacetates and preliminary studies of their diazo decomposition and A. Melekhov from the Higher College of Chemistry for his preparation and catalytic studies of rac-2-octyl diazoacetate. 相似文献