排序方式： 共有87条查询结果，搜索用时 15 毫秒
41.
Faiza Saleem Uzma Nisar Aisha Younas Faiza Jabeen Javed Iqbal Qazi Nazia Khursheed 《Natural product research》2016,30(6):720-723
In this work chitin was extracted chemically from shrimp shells. Seventeen Bacillus isolates were screened for chitinolytic activity. The chitinolytic strains of Bt. were screened at different temperatures and pHs for their hydrolytic potentials. By using a pair of specific primers, endochitinase gene was amplified from SBS Bt-5 strain through PCR, and then cloned into pTZ57 TA cloning vector and transferred in Escherichia coli DH5α strain. The sequenced gene (GenBank Accession No: HE995800) consists of 2031 nucleotides capable of encoding 676 residues. The protein consisted of three functional domains with a calculated molecular mass of 74.53 kDa and a pI value of 5.83. The amino acid sequence of chi gene showed 99% similarity to the genes of Bt MR11 endochitinase, Bt serovar kurstaki chitinase (kchi), Bt strain MR21 endochitinase and Bacillus cereus B4264. 相似文献
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Perrine-Walker F Gherbi H Imanishi L Hocher V Ghodhbane-Gtari F Lavenus J Benabdoun FM Nambiar-Veeti M Svistoonoff S Laplaze L 《Current protein & peptide science》2011,12(2):156-164
Actinorhizal symbioses are mutualistic associations between plants belonging to eight angiosperm families and soil bacteria of the genus Frankia. These interactions lead to the formation of new root organs, actinorhizal nodules, where the bacteria are hosted and fix atmospheric nitrogen thus providing the plant with an almost unlimited source of nitrogen for its nutrition. It involves an elaborate signaling between both partners of the symbiosis. In recent years, our knowledge of this signaling pathway has increased tremendously thanks to a series of technical breakthroughs including the sequencing of three Frankia genomes [1] and the implementation of RNA silencing technology for two actinorhizal species. In this review, we describe all these recent advances, current researches on symbiotic signaling in actinorhizal symbioses and give some potential future research directions. 相似文献
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Shahat AA Ibrahim AY Hendawy SF Omer EA Hammouda FM Abdel-Rahman FH Saleh MA 《Molecules (Basel, Switzerland)》2011,16(2):1366-1377
Essential oils of the fruits of three organically grown cultivars of Egyptian fennel (Foeniculum vulgare var. azoricum, Foeniculum vulgare var. dulce and Foeniculum vulgare var. vulgare) were examined for their chemical constituents, antimicrobial and antioxidant activities. Gas chromatography/mass spectrometry analysis of the essential oils revealed the presence of 18 major monoterpenoids in all three cultivars but their percentage in each oil were greatly different. trans-Anethole, estragole, fenchone and limonene were highly abundant in all of the examined oils. Antioxidant activities of the essential oils were evaluated using the DPPH radical scavenging, lipid peroxidation and metal chelating assays. Essential oils from the azoricum and dulce cultivars were more effective antioxidants than that from the vulgare cultivar. Antimicrobial activities of each oil were measured against two species of fungi, two species of Gram negative and two species of Gram positive bacteria. All three cultivars showed similar antimicrobial activity. 相似文献
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In this work, we report the antioxidant and free radical scavenging activity of 6-bromoeugenol and eugenol. EC50, the concentration providing 50% inhibition, is calculated and the antioxidant activity index (AAI) is evaluated. The antioxidant activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging method. EC50 values of 6-bromoeugenol, ascorbic acid and eugenol were 34.270 μg/mL, 54.888 μg/mL and 130.485 μg/mL, respectively. 6-Bromoeugenol showed higher AAI value (1.122) followed by ascorbic acid (0.700), then by eugenol (0.295). We also investigate the kinetics of DPPH radical scavenging activity of our products to determine the useful parameter TEC50 to evaluate their antiradical efficiency (ARE). Our results have shown high ARE. This study has provided the following ARE ( × 10? 3) order for the tested antioxidants: ascorbic acid (70.119)>6-bromoeugenol (34.842) > eugenol (21.313). Finally, we classify ascorbic acid and eugenol as fast kinetics reaction (TEC50 8.82 and 11.38 min, respectively) and 6-bromoeugenol as medium kinetics reaction (TEC50 39.24 min). 相似文献
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Ahsan Nazir Muhammad Asad Saleem Faiza Nazir Tanveer Hussain Muhammad Qasim Faizan Muhammad Usman 《Photochemistry and photobiology》2016,92(2):343-347
UV radiations are high‐energy radiations present in sunlight that can damage human skin. Protection against these radiations becomes vital especially in those areas of the globe where UV index is quite high that makes the inhabitants more prone to dangerous effects of UV radiations. Clothing materials are good blockers of UV radiations, particularly when the fabric cover factor is high and/or the fabrics contain suitable UV‐blocking finishes. In this study, effect of application of aqueous and methanolic extracts of two different plants, i.e., Achyranthes aspera and Alhagi maurorum on UV protection properties of cotton fabric was investigated. The results showed that the fabric samples treated with extracts of both the plants have excellent UV protection properties as indicated by their ultraviolet protection factor. It was concluded that both the aqueous and methanolic plant extracts are very effective in blocking UVA and UVB radiations, when applied on cotton fabrics. The UV protection performance of Achyranthes aspera extracts was much better as compared to that of Alhagi maurorum, and methanolic extracts of both the plants outperformed the aqueous extracts in terms of UV protection. 相似文献
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For determination of film thickness with a reflectometer, the incident light is usually perpendicular to the film. Often, however, measuring heads are used that keep the aperture of the optical fiber constant or even microscopes are used to increase the lateral resolution in film thickness determination. Analogous to a fixed angle of incidence α the thickness determination is influenced in both cases. In contrast to a fixed angle now all angles between 0° and the aperture angle αapt are present for a measuring head or a microscope objective. We demonstrate here, how the aperture of the measuring head affects the thickness determination and give a quantitative estimation of the influence by assigning an effective angle of incidence αeff to a measuring head with aperture angle αapt. 相似文献
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We present NMR results of Pr1−xSrxMnO3 and their lacunar samples, and also present results of the single crystalline layered manganites La1.2Sr1.8Mn2O7 and La1.2Sr1.6Ca0.2Mn2O7. In Pr1−xSrxMnO3, a single resonance line is observed for 0.27 ≤ x ≤ 0.4, which indicates the sample to be in a metallic state. In the Pr and Sr deficient samples, the NMR line arising from Mn2+ is observed. Introducing deficiency to Pr or Sr sites, a charge disproportionation of the type 2Mn3+→ Mn2+ + Mn4+ probably occurs. For La1.2Sr1.8Mn2O7 and La1.2Sr1.6Ca0.2Mn2O7 compounds, the NMR spectra under an external field of 1.5 T are broad and spread with several distinct lines in the frequency range 310–420 MHz. This is different from the results of La1−xSrxMnO3 and Pr1−xSrxMnO3 with a metallic state, where a single line has been observed. The distinct NMR lines are ascribed to Mn4+, Mn3+ and metallic phase, taking account of the results for La1−xSrxMnO3 and Pr1−xSrxMnO3. In addition to the NMR line from the metallic phase, the observation of Mn3+ and Mn4+ lines suggests a phase separation at low temperature in La1.2Sr1.8Mn2O7 and La1.2Sr1.6Ca0.2Mn2O7. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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W. Boujelben M. Ellouze A. Cheikh‐Rouhou J. Pierre Q. Cai W.B. Yelon K. Shimizu C. Dubourdieu 《physica status solidi (a)》2002,191(1):243-254
Strontium substituted praseodymium manganite Pr0.7Sr0.3MnO3 powder was synthesized by a solid state reaction method at 1400 °C. Neutron diffraction analysis at room temperature and at 14.5 K shows that our sample belongs to the Pnma space group at both temperatures. At low temperature, the refinement gave 3.368μB for the Mn atoms and 0.273μB for the Pr atom, aligned ferromagnetically along the crystallographic y‐axis. Magnetic measurements show that our sample exhibits a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature, TC, is found to be 250 K. Electrical studies show a semiconductor–metal transition at Tϱ = 260 K. This transition temperature is observed in the vicinity of the Curie temperature TC. Magneto‐transport properties show a sharp drop in resistivity as a function of the magnetic applied field. Our sample displays a magnetoresistance effect at 8 T of about 80% in the vicinity of the Curie temperature TC. 55Mn NMR measurements at 4.2 K confirm the metallic behavior at low temperature. The time average resonance frequency indicates that electron hopping between Mn3+ and Mn4+ occurs over the whole crystal. 相似文献
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W. Boujelben A. Cheikh‐Rouhou M. Ellouze J.C. Joubert 《physica status solidi (a)》2000,177(2):503-510
We present the electrical properties of polycrystalline samples Pr1—xSrxMnO3 (0 ≤ x ≤ 0.5). These properties are correlated to the ratio of the Mn3+/Mn4+ cations. The transport properties of the Pr1—xSrxMnO3 samples could be explained on the basis of double exchange mechanism between pairs of Mn3+ and Mn4+ cations, with conductivity occurring by electron hopping between manganese ions along Mn–O–Mn bonds. A semiconductor‐to‐metal transition is observed as a function of temperature for the mixed valence samples Pr1—xSrxMnO3 (0.25 ≤ x ≤ 0.4) with a metallic‐like behaviour above a critical temperature Tϱ. A semiconductor‐like one is observed for all the range of temperature (50 to 300 K) for (0 ≤ x ≤ 0.2 and x= 0.5). Below the Curie temperature Tc, for the ferromagnetic regimes, the spin disorder scattering process has been observed to play an important role in resistivity behaviour. The evolution of activated energies with the carrier concentration has been investigated. 相似文献