9,240 research outputs found
Enantioselective resolution of racemic compounds by cell surface displayed lipase
No full textRecombinant Escherichia coli (E. coli) displaying lipase on the cell surface was examined as a whole cell biocatalyst for enantioselective resolution of racemic compounds. The Pseudomonas fluorescens lipase was displayed on the cell surface of E. coli by fusing the lipase gene to the Salmonella typhimurium outer membrane protein C (OmpC) gene by C-terminal deletion-fusion strategy. The localization of truncated OmpC-lipase fusion protein was confirmed by confocal microscopy and whole cell lipase activity. As an application for enantioselective biocatalyst. whole cell bioconversion was examined using cell surface displayed lipase. When racemic ethyl 3-hydroxybutyrate, methyl mandelate and cis-3-acetoxy-4-phenylazetidin-2-one were used as substrates, (R)-3-hydroxybutyric acid, (S)-mandelic acid and (3S, 4R)-cis-3-hydroxy-4-phenylazetidin-2-one were successfully obtained with the enantiomeric excess of greater than 99%. The cell surface displayed lipase was found to be maintained without much loss of activity and selectivity during 10 repeated reactions over 120 h. These results suggest that cell surface displayed lipase has a high enantioselectivity, broad substrate specificity and reusability, which makes it an excellent system for the production of various optically active compounds. (C) 2004 Elsevier Inc. All rights reserved.This work was supported by Ministry of Commerce, Industry
and Energy through the Intelligence Bioinformatics
and Application Center (TGW 10011093) at the Korea Research
Institute of Bioscience and Biotechnology, Center
for Ultramicrochemical Process Systems, and by the BK21
project. Further support from IBM through the Shared University
Research Program is appreciated
Application of 3D T1Black-Blood Imaging in the Diagnosis of Leptomeningeal Carcinomatosis: Potential Pitfall of Slow-Flowing Blood Reply
No full textTemperature-sensitive pluronic/poly(ethylenimine) nanocapsules for thermally triggered disruption of intracellular endosomal compartment
No full textPluronic hydrogel nanoparticles cross-linked with poly(ethylenimine) (PEI) were synthesized by a modified emulsification/solvent evaporation method. Pluronic F-127 preactivated at the terminal group with p-nitrophenyl chloroformate was dissolved in dichloromethane, and the organic solution was emulsified in deionized water containing PEI by sonication. Primary amine groups of PEI in the aqueous phase were conjugated and/or crosslinked with activated Pluronic F-127 in the vicinity of the water/dichloromethane interface, resulting in the formation of shell-cross-linked Pluronic/PEI nanocapsules. Pluronic/PEI nanocapsules exhibited a volume transition behavior over a temperature range of 24-33 degrees C. The thermally reversible swelling/deswelling of Pluronic/PEI nanocapsules was caused by temperature-dependent hydrophobic interaction of cross-linked and/or grafted Pluronic polymer chains in the nanocapsules. Pluronic/PEI nanocapsules were utilized to break up intracellular endosomal compartments by swelling-induced destabilization of the endosomal membrane triggered by a cold-shock treatment.the Ministry of Health and
Welfare, Korea
Measurements of the curvatures of random surfaces by scattering experiments: the case of bicontinuous microemulsions
No full textA small-angle neutron scattering (SANS) study is made on a three-component isometric (equal volume fractions of water and oil) ionic microemulsion system, composed of AOT/brine/decane. SANS measurements are made as a function of volume fraction of surfactant within the one-phase channel next to the three-phase region at the hydrophile-lipophile balance (HLB) salinity and at a constant temperature. A previous SANS contrast variation experiment indicated that the microstructure of this type of isometric microemulsion at and around the HLB temperature is bicontinuous in water and oil, with a mono-layer of surfactant film situated at the oil-water interface, having zero mean curvature. We analyze SANS data taken with an oil-water contrast in terms of a modified Berk random wave model. We choose a spectral function which is an inverse 8-th order polynomial in wave number k, containing three length scales 1/a, 1/b, and 1/c. The spectral function has finite second and fourth moments. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function for the micro-phase-separated microemulsions. The model shows good agreement with the intensity data;in an absolute scale. We then use the three parameters so obtained to calculate the average square mean curvature and the average Gaussian curvature of the interface. We determine the variation of these curvatures and the underlying spectral functions as a function of the surfactant volume fraction and discuss their implication on the degree of local order of the bicontinuous structure. We also show 3-d morphologies of two of the microemulsions generated by this model
The Gaussian curvature of the oil-water interface in an isometric bicontinuous microemulsion
No full textSmall-angle neutron scattering (SANS) measurements are made on a three-component isometric (equal volume fractions of water and oil) microemulsion system, composed of AOT/water (0.4% NaCl)/D-octane, in the one-phase channel near the three-phase region at and around the hydrophile-lipophile balance temperature. A previous SANS contrast variation experiment indicated that the microstructure of this type of isometric microemulsion is bicontinuous in water and oil with the surfactant film at the interface having a zero mean curvature. We analyze SANS data taken with an oil-water contrast in terms of a modified Berk's random wave model. We choose a spectral function which is an inverse sixth-order polynomial, with three parameters a, b and c, as introduced by Lee and Chen earlier. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function appropriate for the microemulsion system. The model analysis results in good agreement with the intensity data in an absolute scale. We then use the three parameters. so obtained to calculate the average Gaussian curvature of the interface. We discuss the variation of the average Gaussian curvature as a function of the surfactant volume fraction and its implication on the degree of local order of the bicontinuous structure. We also show a 3-D reconstructed morphology of the most disordered microemulsion
ELECTRONIC PROPERTY OF NA-DOPED EPITAXIAL GRAPHENES ON SIC
Get PDFThe electronic property of epitaxial graphenes with Na adsorption or intercalation is studied with the use of pseudopotential density functional method. It is found that the charge transfer and the Na binding energy show strong coverage dependence. Calculated energetics shows that Na prefers the intercalation between the buffer and top graphene layers to the adsorption on top graphene layer. The buffer layer is inert to Na adsorption on top graphene layer but it is charged when Na atoms are intercalated. This indicates that the conduction of epitaxial graphenes can be affected significantly by Na intercalation.X1119sciescopu
Re-emergent direct-indirect band gap transitions in carbon nanotubes under shear strains
No full textElectronic structures of single-walled carbon nanotubes under varying shear strains are studied with the use of pseudopotential density functional method. We present a new scheme to induce shear strains in one-dimensional materials like nanotubes without introducing artificial edge atoms. It is found that the band gap of semiconducting zigzag nanotubes exhibits reemerging direct-indirect transitions as they are twisted. The breaking of the three-fold rotational symmetry and the electron-hole symmetry of corresponding graphitic band structures under shear is shown to be the origin of the behavior in the band gap. (C) 2008 Elsevier Ltd. All rights reserved.X114sciescopu
SELF-ASSEMBLED METAL ATOM CHAINS ON GRAPHENE NANORIBBONS
Get PDFElectronic and magnetic properties of alkali and alkaline-earth metal doped graphene nanoribbons (GNRs) are studied by the pseudopotential density functional method. Strong site dependence is observed in metal adsorption on GNRs, and the adsorbed metal atoms are found to spontaneously form atomic chains in a particular form of GNRs. Such doped GNRs exhibit intriguing magnetic properties such as hysteresis and spin compensation as metal atoms switch from one edge to another at alternating gate voltages. Our study shows that the metal atoms can be used as reagents that can identify the edge atomic structures of GNRs and also as gate-driven spin valves that control the spin current in GNRs.X1170sciescopu
A traffic control algorithm for Clos network type ATM switches
No full textThis paper presents a new traffic control algorithm for asynchronous transfer mode (ATM) switches composed of Clos network type switch fabric. In most traffic control algorithms previously proposed, an ATM switch has been considered as a single node, although the switch fabric of an ATM switch is usually of a network type. In this paper, we suggest a new control algorithm that is designed not only for the ATM network but also for the switch fabric and that can maintain high speed even in cases where buffer capacity of the switch fabric is limited. Main modules of the suggested algorithm are a traffic status detection mechanism based on non-parametric statistical tests, a cell-loss detection mechanism, and a cluster-based fair share computation procedure. Results of simulation experiments show that the suggested algorithm satisfactorily adjusts traffic rate of available bit rate services according to changes in traffic rate used by quality of service (QoS) guaranteed services. The results also show that the algorithm prevents cell losses relatively well and keeps the delay time of QoS guaranteed services short enough
Surface-enhanced Raman scattering (SERS) spectra of sodium benzoate and 4-picoline in Ag colloids prepared by gamma-irradiation
No full textPVP-protected silver colloids were prepared by gamma-irradiation and chemical reduction method. Surface-enhanced Raman scattering (SERS) spectra of sodium benzoate and 4-picoline in Ag colloids prepared by gamma-irradiation were recorded. The SERS spectra of sodium benzoate were successfully recorded in Ag colloids, whereas the Raman spectra did not appear without Ag colloids. The Raman spectra of 4-picoline were not detected without Ag colloids, while the SERS spectra of 4-picoline were increased by adding Ag colloids. The carboxylate group of sodium benzoate and N donor of 4-picoline were adsorbed on the surface of Ag nanoparticles. (c) 2004 Elsevier B.V. All fights reserved.The work was supported by the Science Foundation
of Hannam University, 2004
- …
