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排序方式: 共有239条查询结果,搜索用时 343 毫秒
31.
Monodispersed silver (Ag) nanoparticles (NPs) were obtained by applying an electric field on unipolar-charged Ag NPs fabricated using a heterogeneous condensation technique in gas media. Well defined and charged Ag NPs were separated based on their sizes and were collected on quartz substrates. Thin films consisting of monodispersed Ag NPs with size ranging from 35 to 120 nm were prepared by varying an applied electric field during the fabrication process. Scanning electron microscope results showed that the samples have uniform size distribution. Coherent oscillations of conduction band electrons in gas medium induced by electromagnetic field and coupling of all similar plasmon resonances due to uniform Ag NPs size produced unique and interesting optical properties. Narrow extinction widths (~41 to ~69 nm) were observed compared to the width of polydispersed Ag sample. The ability to prepare samples in gas media and tune the plasmon resonance by merely varying an electric field during fabrication makes the method simple, fast, and highly economical. 相似文献
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Zhengbin Li Soo Moon Ro Balaji Sundara Sekar Eunhee Seol Suman Lama Sun Gu Lee Guangyi Wang Sunghoon Park 《Biotechnology and Bioprocess Engineering》2016,21(6):695-703
1,3-propanediol oxidoreductase (DhaT), which catalyzes the conversion of 3-hydroxypropionaldehyde (3-HPA) to 1,3-propanediol (1,3-PD) with the oxidation of NADH to NAD+, is a key enzyme in the production of 1,3-PD from glycerol. DhaT is known to be severely inactivated by its physiological substrate, 3-HPA, due to the reaction of 3-HPA with the thiol group of the cysteine residues. In this study, using site-directed mutagenesis, four cysteine residues in Klebsiella pneumoniae J2B DhaT were substituted to alanine, the amino acid commonly found in cysteine’s positions in other DhaT, individually and in combination. Among the total of 15 mutants developed, a double mutant (C28A_C107A) and a triple mutant (C28A_C93A_C107A) exhibited approximately 50 and 16% higher activity than the wild-type counterpart, respectively, after 1 h incubation with 10 mM 3-HPA. According to detailed kinetic studies, the double mutant had slightly better kinetic properties (V max , K cat , and K m for both 3-HPA and NADH) than wild-type DhaT. This study shows that DhaT stability against 3-HPA can be increased by cysteine-residue removal, albeit to a limited extent. 相似文献
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Noureddine L Azzam R Nemer G Bielawski J Nasser M Bitar F Dbaibo GS 《Prostaglandins & other lipid mediators》2008,86(1-4):49-55
Ceramide has been implicated in regulatory processes vital for cell survival under different stressors, most notably hypoxia. Little has been done to investigate the contributions of the different ceramide species to the regulation of cell survival. This study aims to highlight the patterns of variation in total ceramide and its species in the growing and hypoxic mouse heart. Mus musculus mice were placed in a hypoxic environment at birth. Control animals remained in room air. The hearts were extracted at different time points: 1 day, 1 week, 4 weeks, and 8 weeks. The total ceramide content and the amounts of component species were assayed by a modified diacylglycerol kinase assay and high-performance liquid chromatography-tandem mass spectroscopy, respectively. Data was collected from both ventricles in hypoxic and control conditions. There was significant polycythemia in the hypoxic versus control animals with a nearly twofold increase in hematocrit levels. Hypoxic right ventricle (RV) mass significantly increased over that of controls at different age groups. When ceramide content was compared in the hypoxic versus control animals, there was a significant increase at day 1 and a significant decrease at week 4 in the left ventricle, whereas a significant decrease was found in the RV at 1 week, 4 weeks, and 8 weeks. There was also a differential involvement of the RV with regard to levels of N-palmitoyl-D-erythro-sphingosine (C16-Cer) and its synthetic precursor dihydro-N-palmitoyl-D-erythro-sphinganine (DHC-16-Cer). The decrease in C16-Cer observed in both hypoxic and control RV's over time was paralleled by a significant increase in DHC-16-Cer in hypoxic (142.1+/-15.0 pmol; p<0.05) but not control (52.8+/-4.0 pmol) RV's suggesting a role for DHC-16-Cer in the RV adaptive response to hypoxia. Another species, N-arachidoyl-D-erythro-sphingosine (C20-Cer), was specifically and significantly decreased in the hypoxic RV. These studies support the presence of distinct roles for different ceramide species and their precursors. A better assessment of cyanotic congenital heart disease in light of the mechanism and timing of cardiomyocyte death, will lead to punctual interventions and even novel cardioprotective strategies. 相似文献
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The aim of this study was to investigate the effect of Eudragit RS 30D, talc, and verapamil hydrochloride on dissolution and mechanical properties of beads coated with "drug-layered matrices". This was accomplished with the aid of a three-factor multiple-level factorial design using percent drug release in 1 and 2 h, T(50), tensile strength, brittleness, stiffness and toughness as the responses. Beads were coated in a fluidized-bed coating unit. Surface morphology and mechanical properties were evaluated by surface profilometry and texture analysis, respectively. No cracks, flaws and fissures were observed on the surfaces. The mechanical properties were dependent on the talc/polymer ratio. The release of verapamil from the beads was influenced by matrix components. Increasing the level of both talc and Eudragit decreased the percent drug released from 67% to 4.8% and from 80.7% to 6.7% in 1 and 2 h, respectively, and increased T(50) from 0.8 to 25.7 h. It was concluded that beads could be efficiently coated with "drug-layered matrices". The release of drug, however, depends on a balance between the levels of drug, talc, and polymer, whereby desired dissolution and mechanical properties could be controlled by the talc/polymer ratio and the level of drug loading. 相似文献
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Steven A. Safren Katie B. Biello Laura Smeaton Matthew J. Mimiaga Ann Walawander Javier R. Lama Aadia Rana Mulinda Nyirenda Virginia M. Kayoyo Wadzanai Samaneka Anjali Joglekar David Celentano Ana Martinez Jocelyn E. Remmert Aspara Nair Umesh G. Lalloo Nagalingeswaran Kumarasamy James Hakim Thomas B. Campbell for the PEARLS Study Team 《PloS one》2014,9(8)
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Annarita Poli Vincenzo Schiano Moriello Enrico Esposito Licia Lama Agata Gambacorta Barbara Nicolaus 《Biotechnology letters》2005,26(21):1635-1638
A haloalkalophilic Halomonas strain CRSS, isolated from salt sediments in Antarctica, produced exocellular polysaccharides (EPS) up to 2.9gg-1 dry cells. Acetate was the most efficient carbon source for EPS production. The composition of media strongly affected the nature of the polymers; a mannan and a xylo-mannan, were obtained when cells were grown on complex media. Acetate was the most efficient carbon source for EPS production and in presence of this substrate, a new polysaccharide, a fructo-glucan, was produced. The EPS fraction was composed by glucose, fructose, glucosamine and galactosamine in relative proportions of 1:0.7:0.3:trace.Revisions requested; Revisions received 6 September 2004 相似文献