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Bhattarai Narayan,Khil Myung Seob,Oh Seung Jin,Kim Hak Yong,Kim Kwan Woo The Korean Fiber Society 2004 Fibers and polymers Vol.5 No.4
The kinetic parameters, including the activation energy E, the reaction order n, and the pre-exponential factor Z, of the degradation of the copolymers based on the poly(L-lactide) (PLLA) or poly(p-dioxanone-co-L-lactide) (PDO/PLLA) and diol-terminated poly(ethylene glycol) (PEG) segments have been evaluated by the single heating methods of Friedman and Freeman-Carroll. The experimental results showed that copolymers exhibited two degradation steps under nitrogen that can be ascribed to PLLA or PDO/PLLA and PEG segments, respectively. However, copolymers exhibited almost single degradation step in air. Although the values of initial decomposition temperature were scattered, copolymers showed the lower maximum weight loss rate and degradation-activation energy in air than in nitrogen whereas the higher value of temperature at the maximum rate of weight loss was observed in air.
Hydrophilic nanofibrous structure of polylactide; fabrication and cell affinity
Bhattarai, Shanta Raj,Bhattarai, Narayan,Viswanathamurthi, Periasamy,Yi, Ho Keun,Hwang, Pyoung Han,Kim, Hak Yong Wiley Publishers 2006 Journal of Biomedical Materials Research Part A Vol. No.
<P>Microstructure and architecture of the scaffolds along with the surface chemistry exert profound effect on biological activity (cell distribution, proliferation, and differentiation). For the biological activity, scaffolds in tissue engineering have been widely designed. The objective of this study was to develop hydrophilic nanofibrous structure of polylactides (PLLA) polymer in the form of nonwoven mat by electrospinning technique, and further evaluate the fibroblast NIH3T3 cell proliferation, morphology, and cell–matrix interaction. Hydrophilicity of the PLLA fibers was improved by adding small fraction of low molecular weight polyethylene glycol (PEG) into the electrospinning solution. Four different ratio types (100/0, 80/20, 70/30, and 50/50) of PLLA/PEG electrospun matrices were fabricated, and the pore characteristics, tensile properties, contact angle, and hydrolytic degradation were observed. Furthermore, scanning electron microscope (SEM) and fluorescence actin staining images were used for micro-observation of cell–matrix interaction and cell morphology. It was found that the electrospun mat of PLLA/PEG (80/20), composed of fibers with diameters in the range 540–850 nm, majority of pore diameter less than 100 μm, tensile strength 8 MPa, elongation 150%, porosity more than 90%, and improved hydrophilicity with slow hydrolytic degradation, is favorable for biological activity of NIH3T3 fibroblast cell. Based on these results, the correct composition of PLLA and PEG in the porous electrospun matrix (i.e., PLLA/PEG (80/20)) will be a better candidate rather than other compositions of PLLA/PEG as well as hydrophobic PLLA for application in tissue engineering. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006</P>
Biotransformation of Flavone by CYP105P2 from Streptomyces peucetius
( Niraula ),( Narayan Prasad ),( Saurabh Bhattarai ),( Na Rae Lee ),( Jae Kyung Sohng ),( Tae Jin Oh ) 한국미생물 · 생명공학회 2012 Journal of microbiology and biotechnology Vol.22 No.8
Biocatalytic transfer of oxygen in isolated cytochrome P450 or whole microbial cells is an elegant and efficient way to achieve selective hydroxylation. Cytochrome P450 CYP105P2 was isolated from Streptomyces peucetius that showed a high degree of amino acid identity with hydroxylases. Previously performed homology modeling, and subsequent docking of the model with flavone, displayed a reasonable docked structure. Therefore, in this study, in a pursuit to hydroxylate the flavone ring, CYP105P2 was co-expressed in a two-vector system with putidaredoxin reductase (camA) and putidaredoxin (camB) from Pseudomonas putida for efficient electron transport. HPLC analysis of the isolated product, together with LCMS analysis, showed a monohydroxylated flavone, which was further established by subsequent ESI/MS-MS, A successful 10.35% yield was achieved with the whole-cell bioconversion reaction in Escherichia coli. We verified that CYP105P2 is a potential bacterial hydroxylase.
In-silico and In-vitro based studies of Streptomyces peucetius CYP107N3 for oleic acid epoxidation
( Saurabh Bhattarai ),( Narayan Prasad Niraula ),( Jae Kyung Sohng ),( Tae Jin Oh ) 생화학분자생물학회(구 한국생화학분자생물학회) 2012 BMB Reports Vol.45 No.12
Certain members of the cytochromes P450 superfamily metabolize polyunsaturated long-chain fatty acids to several classes of oxygenated metabolites. An approach based on in silico analysis predicted that Streptomyces peucetius CYP107N3 might be a fatty acid-metabolizing enzyme, showing high homology with epoxidase enzymes. Homology modeling and docking studies of CYP107N3 showed that oleic acid can fit directly into the active site pocket of the double bond of oleic acid within optimum distance of 4.6 □ from the Fe. In order to confirm the epoxidation activity proposed by in silico analysis, a gene coding CYP107N3 was expressed in Escherichia coli. The purified CYP107N3 was shown to catalyze C9-C10 epoxidation of oleic acid in vitro to 9,10-epoxy stearic acid confirmed by ESI-MS, HPLC-MS and GC-MS spectral analysis. [BMB Reports 2012; 45(12): 736-741]
Stabilization of gold nanoparticles by hydrophobically-modified polycations
Remant Bahadur, K. C.,Aryal, Santosh,Bhattarai, Shanta Raj,Bhattarai, Narayan,Kim, Chi Hun,Kim, Hak Yong Informa UK (TaylorFrancis) 2006 Journal of Biomaterials Science. Polymer Edition Vol.17 No.5
<P>Surface-modified gold nanoparticles have pronounced benefits in the biomedical field due to their significant interaction with delivery materials. In the present study we used hydrophobically-modified polycations (i.e., N-acylated chitosan) to stabilize gold nanoparticles. Aliphatic hydrophobic groups, having carbon chains of different lengths, were first grafted onto the backbone of chitosan by N-acylation with fatty-acid chlorides in order to increase its hydrophobicity. Gold nanoparticles stabilized with native chitosan and N-acylated chitosan were prepared by the graft-onto approach. Chemical modification and its quantification were studied by Fourier-transform infrared (FT-IR) spectroscopy. Further, the stabilized gold nanoparticles were characterized by different physico-chemical techniques such as UV-Vis, FT-IR, TEM, TGA and DLS. Spectral studies of gold nanoparticles show the backbone and the side chain functional groups of chitosan were not cleaved during the conjugation process. TEM observations revealed that the modified chitosan gold nanoparticles were well dispersed and spherical in shape with average size around 10-12 nm in triply-distilled water at pH 7.4, whereas the native chitosan gold nanoparticles appeared as clusters with 9.9 nm as average diameter and were dispersed only in dilute HCl. The size of modified chitosan gold nanoparticles varied depending on the length of grafting molecules.</P>
Mechanical Behaviors and Characterization of Electrospun Polysulfone/Polyurethane Blend Nonwovens
Cha Dong-Il,Kim Kwan-Woo,Chu Gong-Hee,Kim Hak-Yong,Lee Keun-Hyung,Bhattarai Narayan The Polymer Society of Korea 2006 Macromolecular Research Vol.14 No.3
In the present study we investigated the relationship between the morphology and mechanical properties of electrospun polysulfone (PSF)/polyurethane (PU) blend nonwovens, by using the electrospinning process to prepare three types of electrospun nonwovens: PSF, PU and PSF/PU blends. The viscosity, conductivity and surface tension of the polymer solutions, were measured by rheometer, electrical conductivity meter and tensiometer, respectively. The electrospun PSF/PU blend nonwovens were characterized by scanning electron microscopy (SEM) and with a universal testing machine. The SEM results revealed that the electrospun PSF nonwoven had a structure consisting of cross-bonding between fibers, whereas the electrospun PU nonwoven showed a typical, point-bonding structure. In the electrospun PSF/PU blend nonwovens, the exact nature of the point-bonding structure depended on the PU contents. The mechanical properties of the electrospun PSF/PU blend nonwoven were affected by the structure or the morphology. With increasing PU content, the mechanical behaviors, such as Young's modulus, yield stress, tensile strength and strain, of the electrospun PSF/PU blend nonwovens were by up to 80%.