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91.
《中国化学会会志》2018,65(4):452-458
Lipase‐catalyzed synthesis of lauroyl glucose ester was continuously performed in a biphasic system consisting of supercritical CO2 and an ionic liquid (IL). Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy are employed to identify the product lauroyl glucose ester. The effects of reaction pressure, temperature, substrate flow rate, the amount of enzyme, and the amount of IL on the glucose conversion rate are investigated. The highest glucose conversion of up to 95.5% could be achieved at the optimal condition, which is higher than that in the pure IL. The enzyme activity in the biphasic system was 18.19 μmol/g/min, which is much higher than that in the pure IL. The continuous reaction in the binary system could last for 10 h at high enzyme activity. The combination of supercritical CO2 and ILs could not only improve the reaction rate and yield, which are attributed to the fast mass transfer rate and enhanced enzyme activity and lifespan, but also make the product separation and enzyme/ILs recycling easier. 相似文献
92.
Stefano Colonna Vincenza PirontiPiero Pasta Francesca Zambianchi 《Tetrahedron letters》2003,44(4):869-871
Cyclohexanone monooxygenase catalyzed the oxidation of tertiary, secondary and hydroxylamines to N-oxides, hydroxylamines and nitrones respectively. 相似文献
93.
应用EPR和13C NMR技术系统地研究了糖与氨基酸反应的产物。EPR波谱分析表明,反应产物的结构主要取决于氨基酸的结构。13C NMR波谱的化学位移表明、反应产物的结构应该是2,5-哌嗪二酮,糖是作为1,4位取代的配位基。本文还提出了一种可能的反应机制。 相似文献
94.
Based on structural data of lipid A from Chlamydia trachomatis strains, chemically pure tetra- and pentaacyl 1,4′-bisphosphoryl as well as the related 4′-monophosphoryl derivatives of lipid A were synthesized. (R)-3-Hydroxyicosanoic acid as a chiral constituent was prepared via Noyori-reduction of methyl-3-oxoicosanoic acid. Synthetic intermediates were O-acylated with myristoic acid residues at positions 3 and 3′ and N-acylated with (R)-3-hydroxyicosanoic acid at both glucosamine units. Efficient purification methods for highly hydrophobic long-chain tri-, tetra- and pentaacyl progenitors of lipid A have been developed. Purity and homogeneity of the synthetic target compounds were confirmed by NMR and MS-data as well as a sensitive immunostaining approach. The tetra- and pentaacyl species serve as biomedical probes to investigate the endotoxic potential of chlamydial lipid A and to clarify its role in Chlamydia associated infections. 相似文献
95.
Mohamed Al-Bagoury 《European Polymer Journal》2004,40(11):2617-2627
Semicontinuous emulsion copolymerization of sugar-carrying methacrylate, 3-O-methacryloyl-1,2:5,6-di-O-isopropylidene-α-d-glucofuranose (3-MDG), and butyl acrylate (BA) was investigated at 70 °C with the pre-emulsion addition technique. The effect of the emulsifier concentration and its distribution on the particle size (D) as well as on the evolution of the number of particles (Np) during the polymerization was studied. The influence of the initiator concentration and its addition manner on the colloidal features was also investigated. The chemical stability and the properties of the sugar latexes were studied in the presence of sodium bicarbonate as a buffer. The effect of the seed-stage on the particle size and its distribution was analyzed. The thermal, mechanical (such as film formation and stress-strain behavior), and rheological properties of the final sugar latexes were determined as well. 相似文献
96.
97.
L. Jaroškoá L'. Fišera I. Matejková P. Ertl N. Prónayová 《Monatshefte für Chemie / Chemical Monthly》1994,125(12):1413-1425
Summary The stereoselectivity of the nitrone cycloaddition with 1-substituted 3,3-methylene-5,5-dimethyl-2-pyrrolidinones1 is discussed. C,N-Diarylnitrones give mixtures of diastereomeric spirocycloadducts3 and4, in which3 always dominates. In contrast, N-methylnitrones react under the formation of4 as major products. Cycloaddition of C-benzoyl nitrones7 with1 affords exclusively single isoxazolidines8. Semi-empirical quantum mechanical methods (AM1) were used to rationalize the regio- and stereoselectivity of the reactions.
Stereoselektivität der 1,3-dipolaren Cycloaddition von Nitronen an 1-substituierte 3,3-Methylen-5,5-dimethyl-2-pyrrolidinone
Zusammenfassung Die Stereoselektivität der Cycloaddition von Nitronen mit 1-substituierten 3,3-Methylen-5,5-dimethyl-pyrrolidinonen (1) wird diskutiert. C,N-Diarylnitrone ergeben Mischungen der diastereomeren Spirocycloaddukte3 und4, wobei3 immer überwiegt. Im Gegensatz dazu entsteht bei der Reaktion von N-Methylnitronen4 als Hauptprodukt. Die Cycloaddition von C-Benzoylnitronen (7) mit1 liefert ausschließlich Isoxazolidine vom Typ8. Zum besseren Verständnis der Regio- und Stereoselektivität der Reaktionen wurden semiempirische quantenmechanische Berechnungen (AM1) durchgeführt.相似文献
98.
T. A. Berezina V. A. Reznikov L. B. Volodarsky I. Yu. Bagryanskaya Yu. V. Gatilov 《Russian Chemical Bulletin》1990,49(1):116-121
The reactions of heterocyclic paramagnetic aldonitrone,viz., 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with mono- and disubstituted alkynes afford unstable isoxazoline derivatives.
The reactions with monosubstituted alkynes yield predominantly 5-substituted regioisomers. The resulting isoxazoline derivatives
are readily (and often spontaneously) converted into enaminoketones,viz, imidazolidine-1-oxyl derivatives. In the presence of tolan, the title paramagnetic aldonitrone gives a dimer in which one
imidazoline ring undergoes profound transformation. The structure of the resulting dimer was established by X-ray diffraction
analysis.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 112–117, January, 2000. 相似文献
99.
Conformational analysis of peptides containing a glucose-derived furanoid sugar amino acid (Gaa) by detailed NMR and constrained MD studies revealed that peptides with repeating Gaa-Leu-Val units had conformational signatures very similar to those of linear homooligomers of Gaa. 相似文献
100.
Sucrose fatty acid esters, useful as mild surfactants, have been synthesised in good yields in a solvent-free medium. High contents of monoesters and low saponification rate have been observed. The co-melting of sucrose and a multivalent cation soap such as magnesium or zinc soaps, under basic conditions, allowed the formation of a homogeneous reaction mixture, where solid sucrose was fully dissolved. The kinetic monitoring profiles are similar to reactions in homogeneous solutions, with fast initial formation of monoesters. As a consequence, conversion of sucrose in sucrose esters occurred in good yields. The specificity of multivalent cation soaps compared to monovalent cation soaps, for example, potassium stearate, was pointed out. 相似文献