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排序方式: 共有430条查询结果,搜索用时 17 毫秒
1.
Wan-Guo Wei 《Tetrahedron》2005,61(50):11882-11886
The first total synthesis of (±)-terreinol is described. An intramolecular Pd(II)-catalyzed cycloisomerization of a 2-(1′-alkynyl)benzyl alcohol via an apparent 6-endo diagonal pathway led to the 1H-isochromene ring system, which was further converted to the desired spiro ketal via an iodine-mediated intramolecular spiro-cyclization. 相似文献
2.
The enzyme cellulase fromAspergillus oryzae was resolved into four multiple forms, using anion exchange chromatography on DEAE Sephadex A-50 and gel filtration on Sephadex G-75. The stages of fractionation were followed by electrophoresis on cellulose acetate strips. These enzyme forms are characterized by different enzyme activities and isoelectric points.
Herrn Univ.-Prof. Dr.Hans Tuppy zum 65. Geburtstag herzlichst gewidmet. 相似文献
3.
The effect of the biomass presence on the overall circulation velocity, the linear velocities both in the riser and the downcomer
and the overall gas hold-up was studied in a three-phase internal loop airlift reactor (ILALR). The measured data were compared
with those obtained using a two-phase system (air—water). All experiments were carried out in a 40 dm3 ILALR at six different biomass concentrations (ranging from 0 g dm−3 to 7.5 g dm−3), at a temperature of 30°C, under atmospheric pressure. Air and water were used as the gas and liquid model media, respectively.
Pellets of Aspergillus niger produced during the fermentation of glucose to gluconic acid in the ILALR were considered solid phase. In addition, liquid
velocities were measured during the fermentation of glucose to gluconic acid using Aspergillus niger. All measurements were performed in a bubble circulation regime. At given experimental conditions the effect of the biomass
on the circulation velocities in the ILALR was negligible. However, increasing of the biomass concentration led to lower values
of the total gas hold-up.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
4.
A series of different weight ratios of guar gum viz. 5, 10, 20 and 30 were incorporated into polyurethane/polyacrylonitrile (PU/PAN, 50/50) semi interpenetrating polymer networks (SIPNs) using polyethylene glycol-400, 4,4′-diphenyl methane diisocyanate, acrylonitrile, benzoyl peroxide and new metallic catalyst. The obtained polymer composites were subjected to biodegradation studies using specific fungi Aspergillus niger. The composites are characterized for physico-mechanical properties like density and tensile behaviour of the specimens before and after biodegradation. The positron annihilation lifetime spectroscopy (PALS) was used to monitor the content of free volume before and after biodegradation. The extent of degradation was examined by change in tensile behaviour and surface morphology. The influences of fungi on mechanical and morphological behaviour of filled IPNs are found to be interesting. The free volume changes in the composite systems correlates well with the mechanical properties. 相似文献
5.
M. Costa-Ferreira A. Dias C. Maximo M. J. Morgado G. Sena-Martins J. Cardoso Duarte 《Applied biochemistry and biotechnology》1994,44(3):231-242
Production of xylanolytic enzymes by anAspergillus niger CCMI 850 isolate was investigated in batch cultures. The effect of the composition of a fermentation medium that did not
include chemical inducers, on β-xylanase, β-xylosidase, α-l-arabinofuranosidase, and total cellulase activity was studied. With 4% xylan as the carbon source, about 65 U/mL of β-xylanase
was obtained, whereas the total cellulase activity was undetectable, under the specified conditions. This β-xylanase activity
represents the highest reported for a wild-type strain ofA. niger. The effect of pH and temperature on the activity of β-xylanase was studied. Partial characterization of the β-xylanase showed
that with insoluble birchwood as substrate theK
m
andV
max were 0.3 mM and 19 μmol/min, respectively. Aspects of using the crude β-xylanase preparation for applications in the pulp and paper industry
were discussed. 相似文献
6.
Triantafyllos Roukas 《Applied biochemistry and biotechnology》1998,74(1):43-53
The production of citric acid from carob pod extract byA. niger in surface fermentation was investigated. A maximum citric acid concentration (85.5 g/L), citric acid productivity (4.07
g/L/d), specific citric acid production rate (0.18 g/g/d), and specific sugar uptake rate (0.358 g/g/d) was achieved at an
initial sugar concentration of 200 g/L, pH of 6.5, and a temperature of 30°C. Other kinetic parameters, namely, citric acid
yield, biomass yield, specific biomass production rate, and fermentation efficiency were maximum at pH 6.5, temperature 30°C,
and initial sugar concentration 100 g/L. The external addition of methanol into the carob pod extract at a concentration up
to 4% (v/v) improved the production of citric acid. 相似文献
7.
Geciane Toniazzo Débora de Oliveira Cláudio Dariva Enrique Guillermo Oestreicher Octávio A. C. Antunes 《Applied biochemistry and biotechnology》2005,123(1-3):837-844
The main objective of this work was to investigate the biotransformations of (−)α-pinene, (−)β-pinene, and (+) limonene by
Aspergillus niger ATCC 9642. The culture conditions involved—concentration of cosolvent (EtOH), substrate applied, and sequential addition
of substrates—were investigated. Adaptation of the precultures with small amounts of substrate was also studied. The experiments
were performed in conical flasks with liquid cultures. This strain of A. niger was able to convert only (−)β-pinene into α-terpineol. An optimum conversion of (−)β-pinene into α-terpineol of about 4%
was obtained when the substrate was applied as a diluted solution in EtOH and sequential addition of substrate was used. 相似文献
8.
Complete 1H and 13C NMR assignments of aurasperone A and fonsecinone A, two bis-naphthopyrones produced by Aspergillus aculeatus 总被引:1,自引:0,他引:1
Campos FR Barison A Daolio C Ferreira AG Rodrigues-Fo E 《Magnetic resonance in chemistry : MRC》2005,43(11):962-965
Complete assignments of 1H and 13C NMR chemical shifts of the polyketides aurasperone A and fonsecinone A were made by means of nuclear Overhauser enhancement and heteronuclear NMR correlation experiments. These compounds were isolated for the first time from Aspergillus aculeatus, an endophytic fungus obtained from leaves of Melia azedarach(Meliaceae). 相似文献
9.
Conidia of Aspergillus niger were immobilized in calcium alginate gel for the production of citric acid. First, the type of the preactivation medium,
together with the preactivation period, was investigated. It was found that A. niger requires a 2-d preactivation period at a 0.05 g/L NH4NO3 concentration. Second, preactivated cells were used to determine the effects of nitrogen concentration and the flow rate
of oxygen and air on the production of citric acid. Maximum citric acid production was attained with medium containing 0.01
g/L of NH4NO3. The rate of citric acid production in the nitrogenous medium was 33% higher when oxygen was used instead of air during the
production phase. This corresponds to an increase of 85% when compared to production when neither oxygen nor air was fed into
the system. In the nonnitrogenous medium citric acid concentration remained similar regardless of the use of air or oxygen.
However, in the nonnitrogenous production medium, citric acid production was not influenced considerably when oxygen was used
instead of air. The advantage of using immobilized cells is that production is achieved easily in the continuous system. Therefore,
citric acid production was also tested using a packed-bed bioreactor, and an increase in productivity by a factor of 22 was
achieved compared to the batch system. 相似文献
10.
S1 nuclease fromAspergillus oryzae (EC 3.1.30.1) was coupled to gelatin-alginate composite matrix using the residual free aldehyde groups on the surface of
glutaraldehyde crosslinked matrix. The immobilized enzyme retained approximately 10% activity of the soluble enzyme. When
partially purified enzyme was bound to the matrix, the immobilized preparation did not show any detectable enzyme activity.
However, the activity could be restored when the coupling was carried out in the presence of a coprotein or substrate. The
optimum pH of the immobilized S1 nuclease shifted to 3.8 from 4.3 for the soluble enzyme. Also, optimum temperature increased
to 65°C after immobilization. Bound S1 nuclease showed increased pH and temperature stabilities. Immobilization brought about
a twofold decrease in the Michaelis-Menton constant (K
m). 相似文献