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Mohamed Amine Aounallah Imen Ben Slimene-Debez Kais Djebali Dorra Gharbi Majdi Hammami Sana Azaiez Ferid Limam Olfa Tabbene 《Applied biochemistry and biotechnology》2017,181(2):650-666
A strain producing chitinase, isolated from potato stem tissue, was identified as Bacillus licheniformis by biochemical properties and 16S RNA sequence analysis. Statistical experimental designs were used to optimize nine independent variables for chitinase production by B. licheniformis AT6 strain in submerged fermentation. Using Plackett–Burman design, (NH4)2SO4, MgSO4.7H2O, colloidal chitin, MnCl2 2H2O, and temperature were found to influence chitinase production significantly. According to Box–Behnken response surface methodology, the optimal fermentation conditions allowing maximum chitinase production were (in gram per liter): (NH4)2SO4, 7; K2HPO4, 1; NaCl, 1; MgSO4.7H2O, 0.1; yeast extract, 0.5; colloidal chitin, 7.5; MnCl2.2H2O, 0.2; temperature 35 °C; pH medium 7. The optimization strategy led to a 10-fold increase in chitinase activity (505.26 ± 22.223 mU/mL versus 50.35 ± 19.62 mU/mL for control basal medium). A major protein band with a molecular weight of 61.9 kDa corresponding to chitinase activity was clearly detected under optimized conditions. Chitinase activity produced in optimized medium mainly releases N-acetyl glucosamine (GlcNAc) monomer from colloidal chitin. This enzyme also acts as an exochitinase with β-N-acetylglucosaminidase. These results suggest that B. licheniformis AT6 secreting exochitinase is highly efficient in GlcNAc production which could in turn be envisaged as a therapeutic agent or as a conservator against the alteration of several ailments. 相似文献
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Synthesis and characterisation of poly(ester-amide)s from aromatic bisoxazoline precursors 总被引:1,自引:0,他引:1
A series of novel aliphatic aromatic poly(ester-amide)s (PEA) have been synthesized by condensation reaction of aromatic bisoxazolines with aliphatic dicarboxylic compounds. These polymers have a number average molecular weight of 20,000-25,000. Depending of the aromatic structure of the bisoxazoline precursor, they are either amorphous or semi-crystalline. A good solubility in aprotic solvents was observed for all PEAs. 相似文献
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This article has been retracted. 相似文献
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H. Mosbahi M. Gassoumi Imen Saidi Houcine Mejri C. Gaquière M.A. Zaidi H. Maaref 《Current Applied Physics》2013,13(7):1359-1364
AlGaN/GaN/Si HEMTs grown by molecular beam epitaxy have been investigated using spectroscopy capacitance, direct and pulse current–voltage and small-signal microwave measurements. Passivation of the HEMT devices by SiO2/SiN with NH3 and N2O pretreatments is made in order to reduce the trapping effects. As has been found from DLTS data, some of electron traps are eliminated after passivation. This has led to an improvement in the drain current. To describe the electron transport, we have developed a charge-control model by including the deep traps observed from DLTS experiments. The thermal and trapping effects have been, on the other hand, studied from a comparison between direct-current and pulsed conditions. As a result, a gate-lag and a drain-lag were revealed indicating the presence of deep lying centers in the gate-drain spacing. Finally, small-signal microwave results have shown that the radio-frequency parameters of the AlGaN/GaN/Si transistors are improved by SiO2/SiN passivation and more increasingly with N2O pretreatment. 相似文献
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This paper is concerned with the severely ill-posed Cauchy–Stokes problem. We are interested in a data completion problem which is exploited to detect small leaks to control water loss Kim et al. (2008) [1]. This inverse problem is rephrased into an optimization one: An energy-like error functional is introduced. We prove that the optimality condition of the first order is equivalent to solving an interfacial equation which turns out to be a Cauchy-Steklov-Poincaré operator. Numerical trials highlight the efficiency of the method. 相似文献
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Two inorganic compounds entitled tetrasodium hexaaquacobalt decavanadate tetraco-sahydrate,(I), and diammonium bis[hexaaquamanganese] decavanadate tetrahydrate,(II), have been isolated by conventional solution method and structurally characterized by single-crystal X-ray diffraction methods, scanning electron microscopy, IR spectra, thermal analyses and cyclic voltammetry measurements. They crystallize with triclinic (P-1) symmetry and consists of a centrosymmetric [V10O28]6? anion. The Co2+ and Mn2+ cations in (I) and (II) respectively are octahedrally coordinated by six water molecules. Compound (I) also contains a polymeric linear array of edge-sharing [Na(OH2)6]+ and [Co(OH2)6]2+ octahedra and compound (II) exhibit a catenary structure consisting of [V10O28]6? anions linked to [Mn(OH2)6]2+ and NH4 +via hydrogen bonds. 相似文献
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This Note is concerned with the severely ill-posed Cauchy–Stokes problem. This inverse problem is rephrased into an optimization one: An energy-like error functional is introduced. We prove that the optimality condition of the first order is equivalent to solving an interfacial equation which turns out to be a Cauchy–Steklov–Poincaré operator. Numerical trials highlight the efficiency of the present method. To cite this article: A. Ben Abda et al., C. R. Mecanique 337 (2009). 相似文献
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Transesterification of β-keto esters with a wide variety of allyl, benzyl, propargyl, and alkyl alcohols using, for the first time, commercially available and inexpensive Et3N as a Brønsted base additive, is efficiently performed in toluene at reflux. The corresponding esters are exclusively obtained in 57–98% yields with no trace amounts of γ,δ-ketones, usually expected from the decarboxylative Carroll rearrangement. 相似文献