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931.
Polygalacturonases are part of the group of enzymes involved in pectin degradation. The aim of this work was to investigate
some of the factors affecting polygalacturonase production by an Aspergillus giganteus strain and to characterize this pectinolytic activity. Several carbon sources, both pure substances and natural substrates,
were tested in standing cultures, and the best results were obtained with orange bagasse and purified citrus pectin. On citrus
pectin as sole carbon source, the highest extracellular activity (9.5 U/ml and 40.6 U/mg protein) was obtained in 4.5-day-old
cultures shaken at 120 rpm, pH 3.5 and 30°C, while on orange bagasse, the highest extracellular activity (48.5 U/ml and 78.3 U/mg
protein) was obtained in 3.5-day-old cultures shaken at 120 rpm, pH 6.0 and 30°C. Optimal polygalacturonase activity was observed
in assays conducted at pH 5.5–6.5 and 55–60°C. The activity showed good thermal stability, with half-lives of 90 and 30 min
when incubated at 55 and 60°C, respectively. High stability was observed from pH 4.5 to 8.5; more than 90% of the activity
remained after 24 h in this pH range. 相似文献
932.
Bennett SM Tang Y McMaster D Bright FV Detty MR 《The Journal of organic chemistry》2008,73(17):6849-6852
4-(Hydroxymethyl)phenyl benzyl selenoxide (4) sequestered in a halide-permeable, Class II xerogel formed from 10/90 (mol/mol) 3-aminopropyltriethoxysilane/tetraethoxysilane catalyzes the bromination of organic substrates (4-pentenoic acid, 3,5-dihydroxybenzoic acid, 1,3,5-trimethoxybenzene, N-phenylmorpholine, and N,N-dimethylaniline) with NaBr and H2O2. Catalyst performance (reaction rate) when sequestered within the halide-permeable xerogel is 23-fold greater in comparison to xerogel-free catalyst in solution. The catalyst is easily separated from the reaction mixture via filtration and the recovered catalyst can be reused without loss of activity through formation of the first 80 mol of product per mole of catalyst. 相似文献
933.
Two solvent-modified MEKC methods were developed for the quantitative analysis of heterocyclic amines synthesised using intramolecular ring closure via catalysed hydroamination. The first method was capable of resolving six of the amines (precursors and products) with a sample-to-sample injection time of 2 min employing a 20 mM borate buffer, pH 9.2 with 20 mM SDS and 5% v/v n-butanol (n-BuOH). A second low-pH method using 20 mM phosphate buffer, 100 mm SDS, 5% v/v n-BuOH and 20% v/v iso-propanol (i-PrOH) was able to resolve an additional pair of compounds with a sample-to-sample time of 3.5 min. Application of the first method to the analysis of a sample containing catalyst as well as amines placed directly in a 96-well plate showed excellent performance, with migration time and peak height and area reproducibility being less than 0.9 and 9.6%, respectively. The quantity of conversion by catalyst was calculated to be 68 +/- 7%, which was in excellent agreement with the 67 +/- 5% obtained by more conventional (1)H NMR experiments, with the added advantage that this method is also cheaper, quicker and more amendable to high-throughput screening of combinatorial libraries. 相似文献
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938.
Clara Fredeline Rajemiarimoelisoa Cédric Boyère Léonie Pellissier Marine Peuchmaur Hanitra Ranjana Randrianarivo Danielle Aurore Doll Rakoto 《Natural product research》2016,30(13):1557-1560
In this study, we report for the first time the presence of alkaloids belonging to β-carboline type in the pods of the endemic Albizia polyphylla from Madagascar. Three major alkaloids were isolated and structurally identified as: 1-methyl-β-carboline, (+)-(R)-1-methyl-1,2,3,4-tetrahydro-β-carboline and (–)-(S)-1,2-dimethyl-1,2,3,4-tetrahydro-β-carboline. 相似文献
939.
Summary: The reactivity ratios r1 and r2 in copolymerizations of styrene and parasubstituted styrenes, for which r1 = 1/r2, are in contradiction with diffusion control for their propagation reactions. The cross propagation rate constants k12copol in copolymerization of styrene with p-chlorostyrene, p-methylstyrene and p-methoxystyrene have been shown to increase with their nucleophilicity parameter N. This is also not compatible with diffusion controlled cross propagation and propagation, but agrees with similar rate constants of propagation for these monomers. The capping rate constants k12capp of reactions of poly(p-methylstyrene)± and poly(p-methoxystyrene)± with π-nucleophiles also increase with N, but with a much larger selectivity. This shows that k12copol and k12capp are not identical. The k, from 109 to 6 109 L mol−1 s−1, obtained with p-chlorostyrene, styrene and p-methylstyrene by the Diffusion Clock (DC) method are not consistent with those derived from the ionic species concentration (ISC method) for indene, 2,4,6-trimethylstyrene and p-methoxystyrene of the order of 104 – 105 L mol−1 s−1, also measured for living polymerization. These last values are in agreement with those measured previously in nonliving systems, and with an approximate compensation between the reactivity of a monomer and that of the corresponding carbocation. 相似文献
940.
Hélène Angellier Jean-Luc Putaux Sonia Molina-Boisseau Danielle Dupeyre Alain Dufresne 《Macromolecular Symposia》2005,221(1):95-104
Aqueous suspensions of nanocrystals can be obtained by acid hydrolysis of native waxy maize starch granules. The disruption of waxy maize starch granules by 2.2N HCl hydrolysis has been followed by scanning and transmission electron microscopy and laser granulometry. The mechanical properties of composite materials made of poly(styrene-co-butyl acrylate) filled with starch nanocrystals were characterized by dynamic mechanical analysis. These nanocrystals appeared to be an interesting reinforcing phase in a thermoplastic matrix. 相似文献