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11.
Alves Lourdes A. Felipe Maria G. A. Silva JoÃo B. Almeida E. Silva Silvio S. Prata Arnaldo M. R. 《Applied biochemistry and biotechnology》1998,70(1):89-98
Applied Biochemistry and Biotechnology - In order to remove or reduce the concentrations of toxic substances present in the sugarcane bagasse hemicellulose hydrolysate for xyloseto-xylitol... 相似文献
12.
Irene Yarovsky Marie-Isabel Aguilar Milton T. W. Hearn 《Journal of chromatography. A》1994,660(1-2):75-84
The molecular dynamics method has been applied to investigate the conformations of n-butyl ligands immobilised onto an amorphous silica surface analogous to those utilised with silica-based RP-HPLC sorbents. Three systems were constructed which corresponded to ligand densities of 1.64, 2.67 and 3.69 μmol/m2. A number of parameters related to the structure of the sorbent materials were derived in order to characterise the molecular properties of each system. These parameters included the hydrocarbon layer thickness, the frequency of gauche conformations, the distance distribution for carbon atoms and the diffusion coefficients of individual atoms in the n-butyl ligands. From these properties, the positions of chains with respect to the surface as well as their mobility were estimated. It was found that at higher densities, the n-butyl chains are predominantly perpendicular to the surface while at low density they are highly tilted or lying almost parallel to the surface. The degree of ligand flexibility decreased with increasing surface density. Mobility of individual carbon atoms as well as chain disorder increased with distance from the surface for all ligand densities. The simulated properties of n-butyl chains immobilised to a silica surface correlated well with results obtained by Fourier transform IR and 13C-cross polarisation magic angle spinning NMR experimental methods and statistical predictions of the behaviour of immobilised chains. 相似文献
13.
García F Hopkins AD Kowenicki RA McPartlin M Tesa Y 《Dalton transactions (Cambridge, England : 2003)》2004,(14):2051-2052
The reaction of (Me(3)Si)(3)SiK[middle dot]18-crown-6 with SbCl(3)(3 : 1 equiv.) provides a simple route to the title complex [(Me(3)Si)(3)SiSb](4). The potassium base initially acts as a nucleophile and then as a coupling agent, forming Sb-Sb bonds. 相似文献
14.
[reaction: see text] The reaction of o-quinodimethanes (oQDMs) with alkoxy alkynyl Fischer carbene complexes is highly dependent on the carbene complex. Thus, for arylalkynyl carbene complexes, the initial [4 + 2]-cycloadduct evolves opening a new entry to the benzo[b]fluorene skeleton, which is present in many natural products. However, for alkenylalkynyl carbene complexes, the reaction takes place through the double bond, instead of the triple bond, in an unprecedented fashion, leading to new functionalized alkynyl carbene complexes. 相似文献
15.
An extracellular xylanase produced by a Mexican Aspergillus strain was purified and characterized. Aspergillus sp. FP-470 was able to grow and produce extracellular xylanases on birchwood xylan, oat spelt xylan, wheat straw, and corncob, with higher production observed on corncob. The strain also produced enzymes with cellulase, amylase, and pectinase activities on this substrate. A 22-kDa endoxylanase was purified 30-fold. Optimum temperature and pH were 60 degrees C and 5.5, respectively, and isoelectric point was 9.0. The enzyme has good stability from pH 5.0 to 10.0, retaining >80% of its original activity within this range. Half-lives of 150 min at 50 degrees C and 6.5 min at 60 degrees C were found. K(m) and activation energy values were 3.8 mg/mL and 26 kJ/mol, respectively, using birchwood xylan as substrate. The enzyme showed a higher affinity for 4-O-methyl-D-glucuronoxylan with a K(m) of 1.9 mg/mL. The enzyme displayed no activity toward other polysaccharides, including cellulose. Baking trials were conducted using the crude filtrate and purified enzyme. Addition of both preparations improved bread volume. However, addition of purified endoxylanase caused a 30% increase in volume over the crude extract. 相似文献
16.
Bond AD García F Jantos K Lawson GT McPartlin M Wright DS 《Chemical communications (Cambridge, England)》2002,(12):1276-1277
The novel, deca-lithium cage [(mtaNHLi)(As2(Nmta)5)-Li(4).2thf]2 (1) (mtaN = 5-methylthiazolyl, C4H4N2S) contains an imido-bridged tetraanion [(mtaN)2As(mu-Nmta)-As(Nmta)2]4-, which represents a new type of multi-functional imido group 15 ligand framework (homologous with group 15 anions of the type [As(NR)3]3-). 相似文献
17.
Bashall A Bond AD Doyle EL García F Kidd S Lawson GT Parry MC McPartlin M Woods AD Wright DS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(15):3377-3385
Amination of [ClP(micro-NtBu)](2) (1) using NH(3) in THF gives the cyclophospha(III)zane dimer [H(2)NP(micro-NtBu)](2) (2), in good yield. (31)P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et(3)N show that almost quantitative formation of the cyclic tetramer [[P(micro-NtBu)](2)(micro-NH)](4) (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre-organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58-67 % using various reaction scales. The isolation of the major by-product of the reaction (ca. 0.5-1 % of samples of 3), the pentameric, host-guest complex [[P(micro-NtBu)(2)](2)(micro-NH)](5)(HCl).2 THF] (4.2 THF), gives a strong indication of the mechanism involved. In situ (31)P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl(-) ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent- and anion-dependent. The X-ray structures of 2 and 4.2 THF are reported. 相似文献
18.
Aguilar CN Favela-Torres E Viniegra-González G Augur C 《Applied biochemistry and biotechnology》2002,102(1-6):407-414
Undesirable protease production by Aspergillus niger Aa-20 in submerged culture and solid-state culture was evaluated using different concentrations of tannic acid as sole carbon
source in a model system designed for tannase production. Protease production was found to be dependent on the culture system
used (submerged culture or solid-state culture) and on the initial tannic acid concentration. Expression of protease activity
in submerged culture was higher (up to 10 times) than activity obtained in solid-state culture, using identical culture medium
composition. In submerged culture, the lowest final protease activity (0.13 IU) was obtained with the highest tannic acid
concentration, while in solid-state culture protease activity was not affected by changes in initial substrate concentration.
Absence of detectable proteolytic activity in solid-state culture is related to high production of tannase enzyme. Hence,
the use of solid-state culture for fungal enzyme production may allow for higher and more stable enzyme titers present in
culture extracts. 相似文献
19.
Several on-column sample preconcentration modes--large-volume sample stacking using the EOF pump (LVSEP), LVSEP with anion-selective exhaustive injection (LVSEP-ASEI) and field-amplified sample injection with sample matrix removal using the electroosmotic flow (EOF) pump (FAEP)--were used to analyze some nonsteroidal anti-inflammatory drugs (NSAIDs) by capillary electrophoresis, and then compared. Methanol was the background electrolyte solvent to suppress the EOF. The effect of the type and length of the solvent plug, and the sample injection time were investigated in FAEP to determine the conditions that provided the best response. LVSEP, LVSEP-ASEI, and FAEP improved the sensitivity of the peak area by 100-, 1200-, and 1800-fold, respectively. The methodology developed, in combination with solid-phase extraction (SPE), was applied to the analysis of water samples. 相似文献
20.