The Experts below are selected from a list of 3297 Experts worldwide ranked by ideXlab platform
Chunhui Chiu - One of the best experts on this subject based on the ideXlab platform.
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hyperproduction of β glucanase exg1 promotes the bioconversion of mogrosides in saccharomyces cerevisiae mutants defective in mannoprotein deposition
Journal of Agricultural and Food Chemistry, 2015Co-Authors: Reuben Wang, Peiyin Lin, Shyuetsong Huang, Chunhui ChiuAbstract:Bacteria and fungi can secrete extracellular enzymes to convert macromolecules into smaller units. Hyperproduction of extracellular enzymes is often associated with alterations in cell wall structure in fungi. Recently, we identified that Saccharomyces cerevisiae kre6Δ mutants can efficiently convert mogroside V into mogroside III E, which has antidiabetic properties. However, the underlying efficient bioconversion mechanism is unclear. In the present study, the mogroside (MG) bioconversion properties of several cell wall structure defective mutants were analyzed. We also compared the cell walls of these mutants by transmission electron microscopy, a zymolyase sensitivity test, and a mannoprotein release assay. We found zymolyase-sensitive mutants (including kre1Δ, las21Δ, gas1Δ, and kre6Δ), with defects in mannoprotein deposition, exhibit efficient MG conversion and Excessive Leakage of Exg1; such defects were not observed in wild-type cells, or mutants with abnormal levels of glucans in the cell wall. Thus, yeast mutants defective in mannoprotein deposition may be employed to convert glycosylated bioactive compounds.
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Hyperproduction of β‑Glucanase Exg1 Promotes the Bioconversion of Mogrosides in Saccharomyces cerevisiae Mutants Defective in Mannoprotein Deposition
2015Co-Authors: Reuben Wang, Peiyin Lin, Shyuetsong Huang, Chunhui ChiuAbstract:Bacteria and fungi can secrete extracellular enzymes to convert macromolecules into smaller units. Hyperproduction of extracellular enzymes is often associated with alterations in cell wall structure in fungi. Recently, we identified that Saccharomyces cerevisiae kre6Δ mutants can efficiently convert mogroside V into mogroside III E, which has antidiabetic properties. However, the underlying efficient bioconversion mechanism is unclear. In the present study, the mogroside (MG) bioconversion properties of several cell wall structure defective mutants were analyzed. We also compared the cell walls of these mutants by transmission electron microscopy, a zymolyase sensitivity test, and a mannoprotein release assay. We found zymolyase-sensitive mutants (including kre1Δ, las21Δ, gas1Δ, and kre6Δ), with defects in mannoprotein deposition, exhibit efficient MG conversion and Excessive Leakage of Exg1; such defects were not observed in wild-type cells, or mutants with abnormal levels of glucans in the cell wall. Thus, yeast mutants defective in mannoprotein deposition may be employed to convert glycosylated bioactive compounds
A Y Polyakov - One of the best experts on this subject based on the ideXlab platform.
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post dry etching treatment of nanopillar gan ingan multi quantum wells
Journal of Alloys and Compounds, 2021Co-Authors: A Y Polyakov, L A Alexanyan, M L Skorikov, A V Chernykh, I Shchemerov, V N Murashev, Taehwan Kim, In Hwan Lee, S J PeartonAbstract:Abstract Time-resolved photoluminescence (PL), current-voltage characteristics and deep trap spectra of nanopillar GaN/InGaN multi-quantum-well (MQW) light emitting diodes (LEDs) prepared by reactive ion etching (RIE) from planar samples were studied as a function of post-RIE surface treatment. Immediately after RIE, we observe a sharp drop of intensity of the 460 nm MQW PL band and a strong increase of intensity of the defect-related 600 nm MQW band similar to the yellow band in n-GaN. KOH etching and (NH4)2S sulfur passivation treatments increased the MQW PL band intensity above the level of the planar structure and decreased the intensity of the defect 600 nm PL band, but was not effective in decreasing the RIE-induced Excessive Leakage current of the LEDs. Only annealing at ≥ 700 °C following RIE was able to strongly suppress the Excessive Leakage. Deep trap spectra suggest that the RIE-induced drop of the 460 nm PL intensity and increase of the 600 nm PL intensity are accompanied by the increase of the Ec-0.7 eV electron trap density and of Ev+0.8 eV hole trap density in the quantum wells. The first of these defects is attributed to nitrogen interstitial acceptors believed to be effective nonradiative recombination centers, while the hole traps are attributed to gallium vacancy acceptor complexes with shallow donors. Both types of defects are produced on the sidewalls of nanopillars by RIE and can be largely annealed at 700 °C, although higher annealing temperatures are needed to fully suppress their negative impact. These results are also relevant to curing the effects of dry-etch damage for micro-LEDs with small chip dimensions, a serious problem in the micro-LED field.
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electrical properties and deep trap spectra in ga2o3 films grown by halide vapor phase epitaxy on p type diamond substrates
Journal of Applied Physics, 2021Co-Authors: A Y Polyakov, I Shchemerov, E B Yakimov, V I Nikolaev, S A Tarelkin, A I Pechnikov, Sergey Stepanov, A E Nikolaev, Nikolay V LuparevAbstract:Films of Ga2O3 were grown by Halide Vapor Phase Epitaxy (HVPE) on bulk heavily B-doped (001)-oriented diamond substrates using thin interlayers of Al2O3 deposited by HVPE or AlN/AlGaN deposited by metalorganic chemical vapor deposition. The growth with AlN/AlGaN was dominated by the formation of a highly conducting ɛ-phase with poor crystalline quality. For these samples, Excessive Leakage of Schottky diodes and of the Ga2O3/diamond heterojunction prevented meaningful electrical characterization. The film grown with the Al2O3 interlayer was mainly composed of (−201) β-Ga2O3 with an admixture of the ɛ-phase. The film had a low density of residual shallow donors, 5 × 1015 cm−3, with deep electron traps spectra consisting of the well documented centers for β-Ga2O3 near Ec 0.27, Ec 0.7, and Ec 1 eV, all of which are often ascribed to native defects or their complexes. The electrical properties of heterojunctions were mostly determined by the properties of the Ga2O3 films. Both Schottky diodes and heterojunctions showed measurable photosensitivity for 259 nm wavelength excitation, but very low photocurrent for near-UV (365 nm wavelength excitation).
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structural defects responsible for Excessive Leakage current in schottky diodes prepared on undoped n gan films grown by hydride vapor phase epitaxy
Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials Processing Measurement and Phenomena, 2014Co-Authors: A Y Polyakov, E B Yakimov, Nikolai B Smirnov, A V Govorkov, A S Usikov, H Helava, Yu N Makarov, In Hwan LeeAbstract:Schottky diodes fabricated on undoped n-GaN films grown by hydride vapor phase epitaxy showed more than two orders of magnitude higher reverse current if the films contained open core defects. The open core defects were revealed by scanning electron microscope observation in secondary electrons, microcathodoluminescence (MCL), and electron beam induced current (EBIC) modes. Plan-view EBIC imaging showed that such films contained a relatively high density of large (∼10 μm in diameter) dark defects that were absent in good films with low Leakage current. In plan-view scanning electron microscope images, pits with the density similar to the density of dark defects were observed. Cross-sectional MCL observation showed that the pits terminated the vertical micropipes starting near the interface with the substrate. Some of the micropipes closed approximately halfway through the grown thickness. The regions of micropipes, either closed or not, showed a higher intensity of bandedge and defect MCL bands. Possible reasons for the formation of such structures are discussed.
E B Yakimov - One of the best experts on this subject based on the ideXlab platform.
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electrical properties and deep trap spectra in ga2o3 films grown by halide vapor phase epitaxy on p type diamond substrates
Journal of Applied Physics, 2021Co-Authors: A Y Polyakov, I Shchemerov, E B Yakimov, V I Nikolaev, S A Tarelkin, A I Pechnikov, Sergey Stepanov, A E Nikolaev, Nikolay V LuparevAbstract:Films of Ga2O3 were grown by Halide Vapor Phase Epitaxy (HVPE) on bulk heavily B-doped (001)-oriented diamond substrates using thin interlayers of Al2O3 deposited by HVPE or AlN/AlGaN deposited by metalorganic chemical vapor deposition. The growth with AlN/AlGaN was dominated by the formation of a highly conducting ɛ-phase with poor crystalline quality. For these samples, Excessive Leakage of Schottky diodes and of the Ga2O3/diamond heterojunction prevented meaningful electrical characterization. The film grown with the Al2O3 interlayer was mainly composed of (−201) β-Ga2O3 with an admixture of the ɛ-phase. The film had a low density of residual shallow donors, 5 × 1015 cm−3, with deep electron traps spectra consisting of the well documented centers for β-Ga2O3 near Ec 0.27, Ec 0.7, and Ec 1 eV, all of which are often ascribed to native defects or their complexes. The electrical properties of heterojunctions were mostly determined by the properties of the Ga2O3 films. Both Schottky diodes and heterojunctions showed measurable photosensitivity for 259 nm wavelength excitation, but very low photocurrent for near-UV (365 nm wavelength excitation).
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structural defects responsible for Excessive Leakage current in schottky diodes prepared on undoped n gan films grown by hydride vapor phase epitaxy
Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials Processing Measurement and Phenomena, 2014Co-Authors: A Y Polyakov, E B Yakimov, Nikolai B Smirnov, A V Govorkov, A S Usikov, H Helava, Yu N Makarov, In Hwan LeeAbstract:Schottky diodes fabricated on undoped n-GaN films grown by hydride vapor phase epitaxy showed more than two orders of magnitude higher reverse current if the films contained open core defects. The open core defects were revealed by scanning electron microscope observation in secondary electrons, microcathodoluminescence (MCL), and electron beam induced current (EBIC) modes. Plan-view EBIC imaging showed that such films contained a relatively high density of large (∼10 μm in diameter) dark defects that were absent in good films with low Leakage current. In plan-view scanning electron microscope images, pits with the density similar to the density of dark defects were observed. Cross-sectional MCL observation showed that the pits terminated the vertical micropipes starting near the interface with the substrate. Some of the micropipes closed approximately halfway through the grown thickness. The regions of micropipes, either closed or not, showed a higher intensity of bandedge and defect MCL bands. Possible reasons for the formation of such structures are discussed.
Reuben Wang - One of the best experts on this subject based on the ideXlab platform.
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hyperproduction of β glucanase exg1 promotes the bioconversion of mogrosides in saccharomyces cerevisiae mutants defective in mannoprotein deposition
Journal of Agricultural and Food Chemistry, 2015Co-Authors: Reuben Wang, Peiyin Lin, Shyuetsong Huang, Chunhui ChiuAbstract:Bacteria and fungi can secrete extracellular enzymes to convert macromolecules into smaller units. Hyperproduction of extracellular enzymes is often associated with alterations in cell wall structure in fungi. Recently, we identified that Saccharomyces cerevisiae kre6Δ mutants can efficiently convert mogroside V into mogroside III E, which has antidiabetic properties. However, the underlying efficient bioconversion mechanism is unclear. In the present study, the mogroside (MG) bioconversion properties of several cell wall structure defective mutants were analyzed. We also compared the cell walls of these mutants by transmission electron microscopy, a zymolyase sensitivity test, and a mannoprotein release assay. We found zymolyase-sensitive mutants (including kre1Δ, las21Δ, gas1Δ, and kre6Δ), with defects in mannoprotein deposition, exhibit efficient MG conversion and Excessive Leakage of Exg1; such defects were not observed in wild-type cells, or mutants with abnormal levels of glucans in the cell wall. Thus, yeast mutants defective in mannoprotein deposition may be employed to convert glycosylated bioactive compounds.
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Hyperproduction of β‑Glucanase Exg1 Promotes the Bioconversion of Mogrosides in Saccharomyces cerevisiae Mutants Defective in Mannoprotein Deposition
2015Co-Authors: Reuben Wang, Peiyin Lin, Shyuetsong Huang, Chunhui ChiuAbstract:Bacteria and fungi can secrete extracellular enzymes to convert macromolecules into smaller units. Hyperproduction of extracellular enzymes is often associated with alterations in cell wall structure in fungi. Recently, we identified that Saccharomyces cerevisiae kre6Δ mutants can efficiently convert mogroside V into mogroside III E, which has antidiabetic properties. However, the underlying efficient bioconversion mechanism is unclear. In the present study, the mogroside (MG) bioconversion properties of several cell wall structure defective mutants were analyzed. We also compared the cell walls of these mutants by transmission electron microscopy, a zymolyase sensitivity test, and a mannoprotein release assay. We found zymolyase-sensitive mutants (including kre1Δ, las21Δ, gas1Δ, and kre6Δ), with defects in mannoprotein deposition, exhibit efficient MG conversion and Excessive Leakage of Exg1; such defects were not observed in wild-type cells, or mutants with abnormal levels of glucans in the cell wall. Thus, yeast mutants defective in mannoprotein deposition may be employed to convert glycosylated bioactive compounds
Peiyin Lin - One of the best experts on this subject based on the ideXlab platform.
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hyperproduction of β glucanase exg1 promotes the bioconversion of mogrosides in saccharomyces cerevisiae mutants defective in mannoprotein deposition
Journal of Agricultural and Food Chemistry, 2015Co-Authors: Reuben Wang, Peiyin Lin, Shyuetsong Huang, Chunhui ChiuAbstract:Bacteria and fungi can secrete extracellular enzymes to convert macromolecules into smaller units. Hyperproduction of extracellular enzymes is often associated with alterations in cell wall structure in fungi. Recently, we identified that Saccharomyces cerevisiae kre6Δ mutants can efficiently convert mogroside V into mogroside III E, which has antidiabetic properties. However, the underlying efficient bioconversion mechanism is unclear. In the present study, the mogroside (MG) bioconversion properties of several cell wall structure defective mutants were analyzed. We also compared the cell walls of these mutants by transmission electron microscopy, a zymolyase sensitivity test, and a mannoprotein release assay. We found zymolyase-sensitive mutants (including kre1Δ, las21Δ, gas1Δ, and kre6Δ), with defects in mannoprotein deposition, exhibit efficient MG conversion and Excessive Leakage of Exg1; such defects were not observed in wild-type cells, or mutants with abnormal levels of glucans in the cell wall. Thus, yeast mutants defective in mannoprotein deposition may be employed to convert glycosylated bioactive compounds.
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Hyperproduction of β‑Glucanase Exg1 Promotes the Bioconversion of Mogrosides in Saccharomyces cerevisiae Mutants Defective in Mannoprotein Deposition
2015Co-Authors: Reuben Wang, Peiyin Lin, Shyuetsong Huang, Chunhui ChiuAbstract:Bacteria and fungi can secrete extracellular enzymes to convert macromolecules into smaller units. Hyperproduction of extracellular enzymes is often associated with alterations in cell wall structure in fungi. Recently, we identified that Saccharomyces cerevisiae kre6Δ mutants can efficiently convert mogroside V into mogroside III E, which has antidiabetic properties. However, the underlying efficient bioconversion mechanism is unclear. In the present study, the mogroside (MG) bioconversion properties of several cell wall structure defective mutants were analyzed. We also compared the cell walls of these mutants by transmission electron microscopy, a zymolyase sensitivity test, and a mannoprotein release assay. We found zymolyase-sensitive mutants (including kre1Δ, las21Δ, gas1Δ, and kre6Δ), with defects in mannoprotein deposition, exhibit efficient MG conversion and Excessive Leakage of Exg1; such defects were not observed in wild-type cells, or mutants with abnormal levels of glucans in the cell wall. Thus, yeast mutants defective in mannoprotein deposition may be employed to convert glycosylated bioactive compounds
