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991.
Naringinase from Penicillium species—containing α-l-rhamnosidase and β-d-glucosidase activity—immobilized on silicate carriers can be used as a mild and effective means to cleave naturally occurring
glycosides into their aglycones and sugar components. The procedure was tested with flavonoid-, anthraquinone-, and steroidglycosides.
Since the solubility of such compounds is limited in aqueous solutions, a simple batch procedure has been developed to convert
solid substrates suspended in only small amounts of buffer to the desired products with high yields. 相似文献
992.
Electroformed nickel tubing was deactivated by chemical vapor deposition of silicon from silane gas and subsequent treatment with cyclooctamethyltetrasiloxane (D4). Standard activity tests performed on the uncoated tube and also on columns coated with crosslinked and uncrosslinked, nonpolar stationary phase, show that good quality flexible columns can be prepared from nickel tubing. The inner surface of the silicon coated tube was characterized by Auger depth profile analysis. 相似文献
993.
2,2-Dimethyl-3-(2-methyl-3-indolyl)cyclopropylacetic acid, its amide and esters, and the corresponding alcohol, viz., the product of ester reduction by LiAlH4, were synthesized. The chemoselectivity of N- and O-alkylation of these compounds was studied. Selective monoalkylation at the nitrogen atom of the heterocycle, O-alkylation to the side chain, or dialkylation at both nucleophilic sites can be carried out under conditions of phase-transfer catalysis. The N-acylation at the indole fragment of nitrile of this acid occurs only under the Vilsmeier—Haak formylation conditions. 相似文献
994.
Summary The applicability of capillary electrochromatography to the automated analysis of pesticides and phthalate esters that are
of environmental concern was assessed. Reversed phase packing materials were compared. Column to column and run to run reproducibility
was established. Peak height with an internal standard gave the best reproducibility. Faster analysis than alternative HPLC
methods was demonstrated for a mixture of the insecticide pirimicarb and related pyrimidines. The relationship between the
concentration of an analyte in a sample and at the detector was determined by the use of radio-labelled14C-pirimicarb. The volume fraction of the liquid zone was 0.64. The possibility of electroosmosis through the pores is discussed
with reference to the Rice-Whitehead model for electroosmotic flow in a capillary. A new parameter, the effective pore size
is used in equations for electroosmosis through porous packings. 相似文献
995.
Summary Conductance measurements for NaI, KI, RbI, and CsI in water/N,N-dimethylformamide mixtures over the whole composition range at 298.15K are reported. The data were analyzed employing theFuoss-Justice equation in terms of limiting molar conductances (o),Walden products (o), and association constants (K
A). The results indicate that the salts are weakly associated in the above solvent mixture. Variation in theWalden products with solvent composition are briefly discussed. The results were also compared with values reported previously for some alkali metal chlorides and bromides.
Untersuchungen zur elektrischen Leitfähigkeit einiger Alkalimetalliodide in wäßrigen N,N-Dimethylformamidlösungen bei 298.15K
Zusammenfassung Die elektrische Leitfähigkeite von NaI, KI, RbI und CsI wurde in N,N-Dimethylformamid-Wasser-Mischungen verschiedener Zusammensetzung bei 298.15K gemessen. Die erhaltenen Daten wurden analysiert und bezüglich der Grenzäquivalenzleitfähigkeiten (o), derWalden-Produkte (o) und der Assoziationskonstanten (K A) ausgewertet. Die Ergebnisse zeigen, daß diese Salze in den verwendeten Lösungsmittelgemischen nur schwach assoziiert sind. Die Änderungen derWalden-Produkte in Abhängigkeit der Lösungsmittelzusammensetzung werden kurz diskutiert. Abschließend werden die Resultate mit Ergebnissen früherer Messungen, in denen das Verhalten von Alkalimetallchloriden und Alkalimetallbromiden untersucht wurde, verglichen.相似文献
996.
V. V. Semenov N. F. Cherepennikova A. N. Kornev E. V. Naamova N. P. Makarenko S. Ya. Xhorshev G. A. Domrachev O. A. Bochkova 《Russian Chemical Bulletin》1996,45(10):2431-2437
Oligo(phenylcobaltcarbonylsilane) was prepared from oligo(phenylsilane) and dicobalt octacarbonyl. The reaction proceeds with elimination of H2 and CO and insertion of cobalt carbonyl fragments into the silicone backbone of oligosilane. Oligosilane containing cobalt carbonyl groups in side organic substituents was obtained from oligolmethyl(phenylethynyl)Isilane and CO2(CO)8. The reaction of 1,2-bis(phenylethyny1)tetramethyldisilane with Co2(CO)8 proceeds with the sequential attachment of cobalt carbonyl fragments to ethynyl groups to form disilane derivatives [2-CCPhCo2(CO)6] Thermal decomposition of cobalt-containing oligosilanes affords a mixture of paramagnets and ferromagnets.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 10, pp. 2561–2567, October, 1996. 相似文献
997.
998.
Enol and keto tautomers of methyl 3-oxo pentanoate could be separated on a HP-5 capillary column. The chromatographic peaks
were identified by examining characteristic mass ions arose from the corresponding enol and keto molecular ions. The study
showed that the area percentage of enol tautomer is a function of temperature of the column. Treating the column as a reactor,
the energy of activation for the on-column tautomerization could be extracted (35.1 kJ mol−1) by monitoring the loss of the enol tautomer, because the reaction is found to obey pseudo first-order kinetics. The enthalpy
and the entropy changes (ΔH = −3.98 kJ mol−1, ΔS = −7.89 J K−1mol−1) for the enol-to-keto reaction in the stationary phase were also obtained. 相似文献
999.
Shaik Lateef SrinivasuluReddyKrishna Mohan Rudraraju Rameshraju SrinivasuluReddyJayarama Reddy 《Helvetica chimica acta》2006,89(6):1254-1257
Both aliphatic and aromatic amino sulfonamides such as mafenide ( 1a ) were synthesized in good yields (80–86%) by direct electrochemical hydrogenation of the corresponding nitriles in an undivided cell containing a Ni cathode, a Pt anode, and Raney Ni as catalyst (Table 1). The reaction can be performed without external supply of pressurized gas by in situ generation of H2. Slightly elevated temperatures (45°) and low current densities (10 mA/cm2) are favorable conditions for this type of electrochemical nitrile hydrogenation. Our synthetic protocol does not require high‐pressure equipment or chemical hazards, is environmentally very friendly, and more economical than traditional methods. The concentration of adsorbed H. radicals on the catalyst surface can be easily controlled by adjusting the electric potential, which may lead to improved product selectivity and, at the same time, reduces the risk of explosion and fire. 相似文献
1000.
痕量砷流动注射在线还原氢化物发生原子吸收测定 总被引:5,自引:0,他引:5
方法采用流动注射停流技术使水及土壤浸出液中As(V)在线还原为As(Ⅲ),不经手工还原,用氢化物发生原子吸收光谱法直接测定砷的含量。含4mol/L HCl的样品溶液与30%碘化钾溶液在编结式反应器中混合,并在采样环中停流40s,达完全还原后注入到载流中与硼氢化钠反应,采样速度55次/h,检出限(3δ)0.1μg/L,对自来水和土壤浸出液的加标回收结果满意。 相似文献