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991.
Summary A new method was developed for preparing an aqueous colloidal dispersion ofΒ-carotene. This method consists of preparing a solid mixture ofΒ-carotene and polyvinylpyrrolidone (PVP) from their chloroform solution by evaporating the solvent and dissolving the mixture
into water.
From filtration experiment and electron microscopic observation it was found thatΒ-carotene in its aqueous dispersion exists as colloidal particles with a diameter of about 100 ?. Spectroscopic data evidenced
thatΒ-carotene is molecularly dispersed in solid of PVP. It was considered that PVP acts as a solid solvent forΒ-carotene and, at the same time, a stabilizing agent for its aqueous dispersion. Instead of PVP, such a hydrophilic-oleophilic
substance as methylcellulose, polyvinylmethylether or Aerosol OT could be also used as the dispersing agent. Other materials
thanΒ-carotene could be dispersed by similar technique.
Zusammenfassung Es wird eine neue Methode zur Pr?paration einer w?\rigen Kolloid-Dispersion vonΒ-Carotin beschrieben. Diese Methode besteht aus Herstellen einer festen Mischung ausΒ-Carotin und Polyvinylpyrrolidon (PVP) aus der Chloroforml?sung durch Verdampfen des L?sungsmittels und anschlie\ende L?sung der Mischung in Wasser. Aus Filtration und elektronenmikroskopischen Aufnahmen l?\t sich zeigen, da\ dasΒ-Carotin molekulardispers im festen PVP verteilt ist. Das PVP wirkt offensichtlich als festes L?sungsmittel fürΒ-Carotin und gleichzeitig als stabilisiertes Agens für die w?\rige Dispersion. Anstelle von PVP k?nnen auch derartige hydrophile-oleophile Substanzen wie Methylcellulose, Polyvinylmethyl?ther oder Aerosol OT verwendet werden. Es k?nnen auch andere Materialien alsΒ-Carotin auf gleiche Weise dispergiert werden.相似文献
992.
993.
994.
Michael addition of allylsilane to α-nitro olefin in the presence of AlCl3 proceeded smoothly at low temperature to give unsaturated nitronic acid, which was converted into the γδ-enone using aqueous Ti (III). Transformation with the latter provided a convenient new synthesis of cyclopentenone. 相似文献
995.
Takashi Hayashita Norio Teramae Toshiharu Kuboyama Shigeo Nakamura Hiromasa Yamamoto Hiroshi Nakamura 《Journal of inclusion phenomena and macrocyclic chemistry》1998,32(2-3):251-265
Recent progress in chromoionophores based on (1) spherand and hemispherand, (2) cryptand, and (3) dibenzo-16-crown-5 and calix[4]crown which selectively respond to alkali metal ions in aqueous media is reviewed in relation to their molecular structure and photometric function. The design concept of the chromoionophores for colorimetry in aqueous media is discussed in the light of their acid dissociation and metal complex formation equilibria. 相似文献
996.
To examine the nature of the adsorption and desorption branches in hysteretic adsorption isotherms of gases on mesoporous materials, we measured the temperature dependence of the adsorption and desorption isotherms of argon, oxygen, and carbon dioxide onto MCM-41 with a pore diameter of 4.4 nm. The results clearly show that in the open-ended cylindrical pores of MCM-41, capillary condensation rather than evaporation takes place near a thermodynamical equilibrium transition, as opposed to the general statement that capillary evaporation can occur via a meniscus formed at the pore mouth, and, thus, takes place at equilibrium. 相似文献
997.
Cheng Yang Gaku Fukuhara Asao Nakamura Yumi Origane Tadashi Mori Takehiko Wada Yoshihisa Inoue 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):433-437
The complexation behavior of 6-amino-6-deoxy-γ-cyclodextrin (CD), 6A,6X-diamino-6A,6X-deoxy-γ-CDs and 3A-amino-3A-deoxy-altro-γ-CD with 2-anthracenecarboxylic acid (AC) was studied by NMR, UV–vis and circular dichroism spectroscopy. These modified γ-CD derivatives were found to form stable 1:2 host-guest ternary complexes with AC in aqueous solution. Compared with native
γ-CD, the primary-face-aminated γ-CDs exhibited remarkably enhanced overall association constants as a result of the additional electrostatic interactions
between the oppositely charged host and guest. In contrast, the ternary complex formation of the secondary-face-aminated γ-CD with AC was hindered. 相似文献
998.
999.
Organocopper reagents provide the most general synthetic tools in organic chemistry for nucleophilic delivery of hard carbanions to electrophilic carbon centers. A number of structural and mechanistic studies have been reported and have led to a wide variety of mechanistic proposals, some of which might even be contradictory to others. With the recent advent of physical and theoretical methodologies, the accumulated knowledge on organocopper chemistry is being put together into a few major mechanistic principles. This review will summarize first the general structural features of organocopper compounds and the previous mechanistic arguments, and then describe the most recent mechanistic pictures obtained through high-level quantum mechanical calculations for three typical organocuprate reactions, carbocupration, conjugate addition, and S(N)2 alkylation. The unified view on the nucleophilic reactivities of metal organocuprate clusters thus obtained has indicated that organocuprate chemistry represents an intricate example of molecular recognition and supramolecular chemistry, which chemists have long exploited without knowing it. Reasoning about the uniqueness of the copper atom among neighboring metal elements in the periodic table will be presented. 相似文献
1000.
Eishun Tsuchida Hiroshi Nishikawa Eiichi Terada 《Journal of polymer science. Part A, Polymer chemistry》1976,14(4):825-832
The oxidative polymerization catalyzed by Cu(II)-poly(vinylpyridine) derivatives and the effect of the nonpolar field formed by the polymer ligand on the catalysis was studied in dimethyl sulfoxide (DMSO) solvent. The catalytic activity of the Cu complex increases in the following order; Cu-(styrene-vinylpyridine copolymer) (St·VP) complex > Cu-partially quarternized (by benzyl chloride) poly(vinylpyridine)(BCQP) complex > Cu-poly(vinylpyridine) (PVP) complex > Cu-pyridine (Py) complex > Cu-partially quarternized (by ethyl bromide) poly(vinylpyridine) (EBQP) complex. This order is the same as that of the reoxidation rate constant of the catalyst. Acceleration of ko process in Cu-St>VP and Cu-BCQP systems, where the active site is in the nonpolar field formed by the polymer ligand, is explained by an increase in strength of the coordination bonds. 相似文献