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991.
992.
The polyaluminum chloride containing Ca was prepared by adding Ca before and after the aluminium polymerization, respectively. The effects of Ca on the hydrolysis and polymerization of aluminum, the characteristic of aluminum species, the ζ potential and viscosity of PAC were also studied. The experimental results show that the introduction of Ca retards the formation of Al precipitates during the hydrolysis and polymerization of aluminum and increases the contents of Alm and Al13 in PAC. Aluminum species can complex with Ca to form heteronuclear hydroxo complexes, which decreases the chemical shifts of Alm and Al13 in NMR. The ζ potential and the viscosity of PAC increase with the rise of Ca/Al molar ratio. Comparing with adding Ca after the aluminium polymerization, there are much more Al-Ca heteronuclear hydroxo complexes formed by adding Ca before the polymerization, which leads to a more obvious influence of Ca/Al molar ratio on the ζ potential and the viscosity of PAC. 相似文献
993.
Leena Rahkamo Matti Siika-Aho Marianna Vehviläinen Matti Dolk Liisa Viikari Pertti Nousiainen Johanna Buchert 《Cellulose (London, England)》1996,3(1):153-163
Hardwood dissolving pulp was treated with purified
Trichoderma reesei
endoglucanases and cellobiohydrolases. Endoglucanases were more efficient in hydrolysing pulp carbohydrates than were the cellobiohydrolases at the same protein dosage. Endoglucanases also lowered the viscosity and improved the alkaline solubility more dramatically. There was a clear correlation between the alkaline solubility and viscosity, and therefore the solubility could only be improved by lowering the viscosity of the pulp. At the same degree of cellulose degradation, endoglucanase II was found to be most effective in reducing the viscosity and thus improving the solubility. Cellobiohydrolases had a less pronounced effect on the viscosity or solubility. 相似文献
994.
Chong LT Bandyopadhyay P Scanlan TS Kuntz ID Kollman PA 《Journal of computational chemistry》2003,24(12):1371-1377
Direct hydroxide attack on the scissile carbonyl of the substrate has been suggested as a likely mechanism for esterase antibodies elicited by phosphonate haptens, which mimic the transition states for the alkaline hydrolysis of esters.1 The unique amidase activity of esterase antibody 43C9 has been attributed to nucleophilic attack by an active-site histidine residue.2 Yet, the active site of 43C9 is strikingly similar to those of other esterase antibodies, particularly 17E8. We have carried out quantum mechanical calculations, molecular dynamics simulations, and free energy calculations to assess the mechanism involving direct hydroxide attack for 43C9. Results support this mechanism and suggest that the mechanism is plausible for other antiphosphonate antibodies that catalyze the hydrolysis of (p-nitro)phenyl esters. 相似文献
995.
Methodi L. Chetkarov Fawzy D. Hatour Dimiter N. Kolev 《Monatshefte für Chemie / Chemical Monthly》1984,115(11):1321-1327
TheSomogyi—Nelson colorimetric method is applied in a new manner which is more suitable for following the kinetics of cellobiose hydrolysis catalyzed by -glucosidase (EC 3.2.1.21). TheSomogyi—Nelson colour reagent, which is a mixture of the solutions of the reagent ofSomogyi and that ofNelson in a volume ratio of 1:1, is added to the enzyme-substrate solution at the very start of the reaction. The colour reagent reacts with the product (D-glucose). Under the reaction conditions (0.1M acetate buffer,pH = 5.0 and temperature 37°C) the colour reagent does not affect the enzyme activity. The method excludes any inhibition of the product, owing to the continuous removal of the latter by the colour reagent. The method suggested has been applied to monitor cellobiose hydrolysis with -glucosidase, contained in four cellulase enzyme preparations from various fungal sources. The values of theMichaelis parameters (Km, V) were determined.
Eine kinetische Methode zur Verfolgung der Hydrolyse von Cellobiose durch ß-Glucosidasen
Zusammenfassung Die kolorimetrische Methode nachSomogyi undNelson wird nach einem neuen Verfahren zur Verfolgung der Kinetik der hydrolytischen Spaltung von Cellobiose, katalysiert durch -Glucosidase (EC 3.2.1.21), angewandt. Das Farbreagenz nachSomogyi undNelson (Mischung der Reagenzien vonSomogyi undNelson im Volumenverhältnis 1:1) wird der Enzym-Substrat-Lösung zu Beginn der Reaktion hinzugefügt. Das Farbreagenz tritt mit derD-Glukose in Reaktion, wobei unter den gegebenen Reaktionsbedingungen (0,1M Azetatpuffer,pH = 5,0 und 37°C) die Enzymaktivität nicht beeinflußt wird. Die entwickelte Methode wurde zur Verfolgung der Hydrolyse von Cellobiose durch ß-Glucosidasen, die in vier Enzympräparaten aus verschiedenen Pilzstämmen enthalten waren, angewandt. Es wurden dieMichaelis-Parameter (Km, V) bestimmt.相似文献
996.
Hydrolysis of inulin was investigated employing various solid acids as hydrolytic catalysts. The catalytic performances of
several ion exchange resins were compared. The effects of the particle size and porosity on the hydrolysis reaction were found
to be significant, indicating that the intraparticle diffusion of reactants controls the reaction rate. Theoretical models
were developed, therefore, to analyze the effects of intraparticle diffusion occurring in a sequential reaction. The results
were found to be consistent with experimental observations regarding the adverse effects of pore diffusion and the reaction
pattern. 相似文献
997.
I. V. Ukrainets O. V. Gorokhova L. V. Sidorenko N. L. Bereznyakova 《Chemistry of Heterocyclic Compounds》2007,43(1):58-62
A preparative method of obtaining 1-substituted 4-methyl-2-oxo-1,2-dihydroquinoline-3-carboxylic acids is proposed. Features
of their spatial structure have been studied.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 69–74, January, 2007. 相似文献
998.
Bura Renata Mansfield Shawn D. Saddler John N. Bothast Rodney J. 《Applied biochemistry and biotechnology》2002,98(1-9):59-72
Corn fiber, a by-product of the corn wet-milling industry, represents a renewable resource that is readily available in significant
quantities and could potentially serve as a low-cost feedstock for the production of fuel-grade alcohol. In this study, we
used a batch reactor to steam explode corn fiber at various degrees of severity to evaluate the potential of using this feedstock
in the bioconversion process. The results indicated that maximum sugar yields (soluble and following enzymatic hydrolysis)
were recovered from corn fiber that was pretreated at 190°C for 5 min with 6% SO2. Sequential SO2-catalyzed steam explosion and enzymatic hydrolysis resulted in very high conversion (81%) of all polysaccharides in the corn
fiber to monomeric sugars. Subsequently, Saccharomyces cerevisiae was able to convert the resultant corn fiber hydrolysates to ethanol very efficiently, yielding 90–96% of theoretical conversion
during the fermentation process. 相似文献
999.
A. A. Kline T. N. Rogers M. E. Mullins B. C. Cornilsen Lj. M. Sokolov 《Journal of Sol-Gel Science and Technology》1994,2(1-3):269-272
Attenuated Total Reflectance (ATR) FTIR has been used to follow sol-gel synthesis kinetics for tetraethylorthosilicate (TEOS), ethanol, and water solutions yielding pure silicate materials. Aluminosilicates have also been made using TEOS:ethanol:water solutions doped with Al(III). Effective rate constants have been fitted to a kinetic model suggested by the literature for pure silicate materials. This model has been extended to include the effect of Al(III) on the rate constants. The effects of solution pH, temperature, and varying TEOS/Ethanol mole ratios have been investigated. Reliable effective rate constants for metal doped sol-gel solutions will lead to better control of the morphological and chemical properties of multi-component glass materials. 相似文献
1000.
National Renewable Energy Laboratory (NREL) designed a shrinking-bed reactor to maintain a constant bulk packing density of
cellulosic biomass. The high solid-to-liquid ratio in the pretreatment process allows a high sugar yield and avoids the need
to flush large volumes of solution through the reactor. To scale up the shrinking-bed reactor, NREL investigated a pilot-scale
screw conveyor reactor in which an interrupted flight between screws was employed to mimic the “shrinking-bed” effect. In
the experiments with the screw conveyor reactor, overmixing and uneven flow occurred. These phenomena produce negative effects
on biomass hydrolysis. The flow behavior inside the reactor was analyzed to allow redesign of the screw to achieve adequate
mixing and even flow. In the present study, computational fluid dynamics (CFD) was utilized to simulate the fluid flow in
the porous media, and a new screw design was proposed. CFD analysis performed on the redesigned reactor indicated that an
even flow pattern was achieved. 相似文献