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991.
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
992.
W. Wojnowski J. Pikies K. Peters E.-M. Peters D. Thiery H. G. Von Schnering 《无机化学与普通化学杂志》1994,620(2):377-384
Formation and Structures of N-(tri-t-butoxysilyl)aniline Compounds Para-substituted N-(tri-t-butoxysilyl)anilines (t-BuO)3SiNRC4H4X-p, R = H, CH3, with substituents of high electron affinity (X = CN, NO2) were prepared by a one-pot reaction of tri-t-butoxychlorsilane, potassium t-butanolate and substituted anilines. Corresponding compounds with substituents of low electron affinity (X = OMe, H) preferably were prepared by metalation of anilines with sodium amide. Four crystal structures were determined. N-(tri-t-butoxysilyl)-p-nitro-aniline, N-methyl-(N-tri-t-butoxysilyl)-p-nitroaniline and N-(tri-t-butoxysilyl)-p-cyanoaniline crystallize at 298 K monoclinically, N-(tri-t-butoxysilyl)aniline crystallizes orthorhombically. 相似文献
993.
E. L. Anderson M. M. Thomason H. T. Mayfield W. Bertsch 《Journal of separation science》1979,2(6):335-342
A versatile two-dimensional gas chromatograph is described, consisting of 2 separate ovens, one intermediate trap, an auxiliary inlet, and the necessary hardware to effect off-line switching according to the principle of Deans. The unit has been designed for use with high resolution glass capillary columns. The performance of individual instrumental components was critically evaluated. Results showed that low dead volume glass to metal connections were required in the manifold and detector lines to minimize extra-column effects. The mass of the intermediate trap must be low to allow rapid heating. Operational parameters are discussed and examples of some applications are shown. 相似文献
994.
ZHANG Cong-jie CAO Ze-xing ** ZHANG Qian-er . State Key Laboratory for Physical Chemistry of Solid Surface Department of Chemistry Center for Theoretical Chemistry Xiamen University Xiamen P. R. China . Department of Chemistry Shanxi Normal University Linfen P. R. China 《高等学校化学研究》2003,(4)
IntroductionCarbon chains are among the most attractivecandidates as the carriers of the diffuse interstellarbands ( DIBs) [1] .To detect the carbon chains indark clouds and carbon stars[2 ] ,itis very importantto understand their electronic spectra.Maier andhis coworkers have measured the polyacetylenicradicals C2 n H( n=1— 4) and C2 n-1H( n=2— 6) bythe rotational spectroscopy[3 ,4] and the species n≤ 4have been detected in dark interstellar clouds[5,6] .In neon matrices,the B2 Π← X2… 相似文献
995.
The development of a slurry sampling method for the determination of calcium, copper, iron, magnesium and zinc in fish tissue samples by flame atomic absorption spectrometry is described. In comparison with microwave-assisted digestion, the proposed method is simple, requires short time and eliminates total sample dissolution before analysis. Suspension medium was optimized for each analyte to obtain quantitative recoveries from fish tissue samples without matrix interferences. Nevertheless, iron recoveries higher than 46% were not found. Treatment of samples slurried in nitric acid by microwave irradiation for 15-30 s at 75-285 W permitted to achieve efficient recoveries for calcium, iron, magnesium and zinc. Further improvement in the matrix effects for iron determination was accomplished by the use of an additional step of short microwave-assisted suspension treatment. However, standard addition method was required for calcium and copper determination, being necessary hydrochloric acid as suspension medium for the last one. Although copper could not be determined in the certified reference material using microwave-assisted digestion, the accuracy of the slurry sampling method was verified for all the investigated analytes. Detection limits were 22.8 ± 8.0, 0.884 ± 0.092, 5.07 ± 0.76, 35.5 ± 0.7 and 1.17 ± 0.04 μg g−1 for calcium, copper, iron, magnesium and zinc, respectively. The standard deviations obtained using slurry sampling method and microwave-assisted digestion were not significantly different, and the mean relative standard deviation of the over-all method (n = 3) of the slurry sampling method for different concentration levels was below 12%. 相似文献
996.
Gas Chromatographic Method for Routine Determination of Oleanolic and Ursolic Acids in Medicinal Plants 总被引:1,自引:0,他引:1
Summary A rapid and simple gas chromatographic method has been established for routine analysis of free oleanolic and ursolic acids in dried samples of medicinal herbs. Soxhlet extraction of triterpenes was followed by solid-phase extraction (SPE). Amounts of the compounds were measured by gas chromatography after silylation of the purified samples. Experiments were performed to establish the optimum conditions (e.g. solvent, and mode and duration of extraction) for calibration curve linearity, sensitivity, reproducibility, and recovery. The conditions used for derivatization and gas chromatographic analysis resulted in an improvement on literature data. The method devised enables accurate routine measurement of many samples in quite a short time (e.g. for chemotaxonomical screening, or quality control of herbal drugs). The practical application of the method was illustrated on five Lamiaceae species. 相似文献
997.
M. G. Voronkov O. M. Trofimova Yu. I. Bolgova L. V. Klyba L. I. Larina A. I. Albanov V. A. Pestunovich N. F. Chernov K. B. Petrushenko 《Chemistry of Heterocyclic Compounds》2003,39(12):1639-1644
We have synthesized 1- and 2-(trimethylsilylmethyl)- and 1- and 2-(trimethoxysilylmethyl)benzotriazoles by reaction of 1,2,3-benzotriazolylsodium with trimethyl- or trimethoxy(chloromethyl)silane. We obtained 1- and 2-(silatranylmethyl)benzotriazoles by transesterification of the latter with triethanolamine. 相似文献
998.
共混合聚(醚-酯)多嵌段共聚物的表面表征及其血液相容性研究 总被引:2,自引:0,他引:2
本文通过X-射线光电子能谱(XPS)、表面接触角、表面ξ电位和血液相容性实验,研究了聚(醚-酯)多嵌段共聚物及其共混物的表面组成和性质与血液相容性的关系。实验结果表明,疏水性的PET-PTMO多嵌段共聚物的血液相容性很差,并且与表相中软段的富集量无关;当亲水性的PET-PEO多嵌段共聚物与疏水性的PET-PTMO多嵌段共聚物共混后,发现存在着一个最佳的共混比例,此时材料表面的血小板粘附量大大降低。对于共混物,表相△[C—O)/[C—O]和表面ξ电位可以较好地与血小板粘附量相关联。以上结果清楚地表明,材料表面的亲-疏水性平衡、软段深度层次分布及表面电位是影响血液相容性的重要因素。 相似文献
999.
金橙G螯合形成树脂分离富集地质样品中的微量贵金属 总被引:10,自引:0,他引:10
主要研究了金橙G螯合形成树脂分离富集地质样品中金、铂、钯的最佳实验条件。在柱高大于16cm,0.1mol/L HCl介质的样品溶液以小于或等于0.5mL/min流速过柱,用0.1mol/L HCl的3%硫脲溶液以小于或等于0.5mL/min流速洗脱金、铂、钯(和铑),都能同时定量富集。用火焰原子吸收光谱法测定,回收率均在95% ̄110%之间。经地质样品加标准回收实验,结果令人满意。证明这种以磺酸基 相似文献
1000.
Gold-gold interactions in small polynuclear complexes are analysed using extended Hückel calculations. They are influenced by the nature of the ligand donor atoms, by the bridging ligands, but most by the formal oxidation state of the metal. Au---Au bonds are much stronger in complexes of Au(II) and Au(III), but a weak interaction between two d10 centres exists for Au(I) complexes, owing to mixing of the s and p orbitals with the d orbitals. Phosphines induce stronger metal-metal bonds when coordinated trans to the Au---Au bond in [Au(II)[(CH2)2PPh2]L]2 (Ph = phenyl), but have the opposite effect when bonded orthogonally to the metal-metal axis in Au(I) binuclear species. When two gold atoms are bridged by a single carbon atom, belonging either to mesityl (Mes = 2,4,6-Me3C6H2) or CR2, the former produces stronger Au(I)---Au(I) interactions, reflected in shorter distances. Formal oxidation states are proposed for the gold atoms in two mixed-valence clusters, [Au4(C6F5)2((PPh3)2CH})2(PPh3)2](ClO4)2 and [{(2,4,6-C6F3H2)Au(CH2PPh2CH2)2Au{in2-Au(CH2PPh2CH2)2Au](ClO4)2. The results suggest a higher oxidation state for the outer gold atoms, in both the T-shaped tetranuclear cluster and the Au6 linear chain. 相似文献