Nitrogen doped-ZnO/n-GaN heterojunctions

Nitrogen-doped ZnO nanorods were prepared by electrodeposition using two different Zn precursors (zinc nitrate and zinc acetate), while all other growth conditions (dopant precursor, concentration, growth temperature, and bias) were identical. We have shown that the precursor used affects the properties of the ZnO nanorods, and that the presence of rectifying properties in n-GaN/N:ZnO heterojunctions is strongly related to the use of nitrate precursor for ZnO growth. The difference in the properties of ZnO obtained from two precursors is attributed to the differences in native defect and impurity concentrations, which could affect the electronic properties of the samples. © 2011 American Institute of Physics.published_or_final_versio

Solution-based growth of ZnO nanorods for light-emitting devices: Hydrothermal vs. electrodeposition

ZnO nanorods have been grown by two inexpensive, solution-based, low-temperature methods: hydrothermal growth and electrodeposition. Heterojunction n-ZnO nanorods/p-GaN light-emitting diodes have been studied for different nanorod growth methods and different preparation of the seed layer. We demonstrate that both the nanorod properties and the device performance are strongly dependent on the growth method and seed layer. All the devices exhibit light emission under both forward and reverse bias, and the emission spectra can be tuned by ZnO nanorod deposition conditions. Electrodeposition of rods or a seed layer results in yellow emission, while conventional hydrothermal growth results in violet emission. © The Author(s) 2010. This article is published with open access at Springerlink.com.published_or_final_versionSpringer Open Choice, 01 Dec 201

Plasma treatment of p-GaN/n-ZnO nanorod light-emitting diodes

Conference vol. 8987 entitled: Oxide-based Materials and Devices VZinc oxide (ZnO) is a material of great interest for short-wavelength optoelectronic applications due to its wide band gap (3.37 eV) and high exciton binding energy (60 meV). Due to the difficulty in stable p-type doping of ZnO, other p-type materials such as gallium nitride (GaN) have been used to form heterojunctions with ZnO. p-GaN/n-ZnO heterojunction devices, in particular light-emitting diodes (LED) have been extensively studied. There was a huge variety of electronic properties and emission colors on the reported devices. It is due to the different energy alignment at the interface caused by different properties of the GaN layer and ZnO counterpart in the junction. Attempts have been made on modifying the heterojunction by various methods, such as introducing a dielectric interlayer and post-growth surface treatment, and changing the growth methods of ZnO. In this study, heterojunction LED devices with p-GaN and ZnO nanorods array are demonstrated. The ZnO nanorods were grown by a solution method. The ZnO nanorods were exposed to different kinds of plasma treatments (such as nitrogen and oxygen) after the growth. It was found that the treatment could cause significant change on the optical properties of the ZnO nanorods, as well as the electronic properties and light emissions of the resultant LED devices. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.Link_to_subscribed_fulltex

Effects of purpurin on proton-pumping ATPase and morphological transition in Candida albicans

This journal suppl. is Special Issue: Abstracts of the 18th Congress of the International Society for Human and Animal MycologyOpportunistic human fungal pathogen Candida albicans poses a serious threat to human health. The unicellular microbe exists as part of the normal microbiota on the skin and mucosal surfaces of oral cavity, digestive tract, and urogenital system, but can become invasive and cause local and/or disseminated diseases (candidiasis) in immunocompromised patients with high morbidity and mortality rates (40–60%). Clinical usefulness of the current limited arsenal of antifungal agents has been hampered by toxic side effects, poor pharmacokinetics, and emergence of drug-resistant isolates, indicating a dire need of new antifungal agents. In our earlier study, we have first reported the potent in vitro anti-Candidal activity of purpurin (an anthraquinone pigment found in madder root) against six pathogenic Candida species. One striking virulence trait of C. albicans is its ability to grow and switch between budded yeast and filamentous forms (hyphae), and this yeast-tohypha transition is closely linked with external pH. It is thus conceivable that perturbation of pH homeostasis can be attractive in the management of candidiasis through indirect modulation of morphogenesis. To this end, we extended the investigation and demonstrated the inhibitory actions of purpurin on pH homeostasis and hyphal growth in C. albicans SC5314. At sub-MIC levels (￡0.5 lg ml-1), purpurin suppressed glucosemediated proton pumping ATPase activity in a concentration-dependent manner, and partially inhibited yeast-to-hypha transition and biofilms. Physiological disturbance of cellular metabolism could be excluded as C. albicans growth was not affected. Safe concern and high selectivity of purpurin for C. albicans were justified by its non-toxic nature to primary human gingival fibroblasts (2•MIC; viability = 94%) and keratinocytes (1•MIC; viability = 95%). Therefore, purpurin may represent a potential candidate that deserves further investigations in the development of antifungal strategies against candidiasis - for example, combinational use of purpurin with antifungal agents possessing different modes of action may reduce the likelihood of acquired drug resistance.link_to_OA_fulltex

The challenge of ambient air–processed organometallic halide perovskite : technology transfer from spin coating to meniscus blade coating of perovskite thin films

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Antifungal Activity of Baicalein Against Candida krusei Does Not Involve Apoptosis

The present study was designed to evaluate the antifungal activity of baicalein against Candida krusei isolates. Using a broth microdilution assay, baicalein exhibited potent in vitro antifungal activity against C. krusei isolates with a minimum inhibitory concentration of 2. 7 μg/ml. Flow cytometric study indicated that baicalein depolarized mitochondrial membrane potential in a concentration-dependent manner. However, mechanistic analyses showed that the intracellular reactive oxygen species (ROS) level was virtually unchanged, and massive DNA fragmentation was not observed in C. krusei isolates after baicalein treatment even at a concentration which was apoptotic in C. albicans. Taken together, we conclude that the antifungal activity of baicalein in C. krusei isolates occurs through perturbation in mitochondrial homeostasis without causing elevation of the intracellular ROS level and does not involve apoptosis. © 2010 Springer Science+Business Media B.V.link_to_subscribed_fulltex

Novel antifungal activity of purpurin against Candida species in vitro

The antifungal activity of purpurin (1,2,4-trihydroxy-9,10-anthraquinone), a natural red anthraquinone pigment in madder root (Rubia tinctorum L.), was evaluated by a broth microdilution assay against a total of 24 Candida isolates representing six species. The minimum inhibitory concentration (MIC) range of purpurin was 1.285.12 μg/ml. Mechanistic studies using the rhodamine 6G extrusion assay indicated that purpurin inhibited the energy-dependent efflux pumps of the Candida isolates in a dose-dependent manner. Furthermore, purpurin demonstrated a dose-dependent depolarization of mitochondrial membrane potential, one of the biochemical checkpoints regulating cell death in eukaryotic cells, suggesting a possible linkage between purpurin antifungal mechanism and Candida apoptosis. © 2010 ISHAM.link_to_subscribed_fulltex

Entrapment of a Trigonopsis variabilis D-amino acid oxidase variant F54Y for oxidative deamination of cephalosporin C

Trigonopsis variabilis D-amino acid oxidase (TvDAAO) is an enzyme used in the industrial bioconversion of cephalosporin C (CPC) into 7-aminocephalosporanic acid, a crucial biosynthetic nucleus for a wide spectrum of semi-synthetic cephem antibiotics. Using homology modeling and site-directed mutagenesis, we have previously shown that the TvDAAO variant F54Y possesses improved catalytic activity and thermostability. To further explore its industrial application, the conditions for immobilization of the enzyme were examined in the present investigation. The results showed that entrapment in a calcium alginate (Ca-alginate) matrix using 2% alginate, 500mM CaCl 2, and 15min stabilization appeared to be optimal for the immobilization of F54Y. The entrapped enzyme allowed complete CPC conversion. The entrapped enzyme also showed good operational stability and retained at least 90% of its original activity after 20 reaction cycles. To conclude, the entrapment of F54Y in Ca-alginate appeared to be a simple and efficient biocatalysis system with potential application in the antibiotics industry. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.link_to_subscribed_fulltex

A single Phe54Tyr substitution improves the catalytic activity and thermostability of Trigonopsis variabilis d-amino acid oxidase

The industrial importance of Trigonopsis variabilis d-amino acid oxidase (TvDAAO) is represented by its biocatalytic oxidative deamination of cephalosporin C (CPC) to yield glutaryl-7-aminocephalosporanic acid (GL-7-ACA). The process has been incorporated into a two-step bioconversion to produce 7-aminocephalosporanic acid, the crucial synthetic nucleus for several semi-synthetic cephalosporin antibiotics. A homology model of TvDAAO indicated that residue F54 is in a close proximity to the in silico docked CPC. Substitution of this F54 to Tyr (F54Y) resulted in 6-fold improvement in k cat,app and ~2.5-fold increase in K i of GL-7-ACA. Heat treatment (55°C, 60min) did not decrease the activity of F54Y. It is suggested that the Tyr substitution might initiate hydrogen bond formation with the amino group of CPC and facilitate deamination. Faster substrate turnover, reduced GL-7-ACA inhibition and improved thermostability of the F54Y substitution render it a useful candidate in industrial production of semi-synthetic cephems. © 2009 Elsevier B.V.link_to_subscribed_fulltex

Investigation of low-bandgap nonfullerene acceptor-based polymer solar cells with very low photovoltage loss

202105 bchyVersion of RecordPublishe