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Park K.-H.,Chonnam National University | Jin E.-M.,Chonnam National University | Gu H.-B.,Chonnam National University | Yoon S.-D.,Chonnam National University | And 2 more authors.
Applied Physics Letters | Year: 2010

Zirconia (ZrO2) nanofibers added mesoporous titania (TiO 2) photoelectrode has been synthesized for dye-sensitized solar cells to enhance the efficiency of cell. The ZrO2 nanofibers had reduced the resistance of the photoelectrode as well as enhancement of the absorption spectra in the ultraviolet (UV), visible, and near infrared (IR) region. The internal resistance of the photoelectrode is one of the important factor to affects the power conversion efficiency directly. The ZrO2 nanofibers provide the more photon harvest and optimal electron pathway. Finally, about 200% increases in conversion efficiency has been achieved. © 2010 American Institute of Physics.


Park Y.,Kangwon National University | Kim N.H.,Kangwon National University | Cho S.B.,Agency for Defense Development | Kim J.M.,Agency for Defense Development | And 6 more authors.
Journal of Molecular Structure | Year: 2010

The passivating layer (also called the solid electrolyte interface, SEI) plays a key role in the performances of Li-ion batteries. In this work, we studied the surface reactions of Li[Ni0.31Co0.32Mn 0.28Al0.09]O2 with the organic electrolyte in the overcharge state by means of FTIR, XPS, XAS, and 2D correlation analysis. The FTIR and XPS results revealed that several types of compounds are formed on the cathode surface. These results also suggest that the organic solvents are decomposed to a greater extent than the Li-salt during the overcharge state. Based on the 2D correlation analysis, we can deduce the following sequence of events: 287.0 (due to C-O) → 290.0 (due to carbonate) → 288.5 (due to CO) → 291.5 (due to C-Fx) → 284.5 eV (due to CC or CH). © 2010 Elsevier B.V. All rights reserved.


Kim J.Y.,Chonnam National University | Park K.,Chonnam National University | Bae S.Y.,Samsung | Kim G.C.,Jeonnam Nano Bio Research Center | And 2 more authors.
Journal of Materials Chemistry | Year: 2011

To investigate the relationship between the linker length and the catalytic activities of metal-decorated CNTs, three samples were prepared with different linker molecules, viz. NaSH, HSCH2CH2SH, and C 2H2N2S3. The structures of the prepared samples were characterized using transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The analysis of the TEM images and XRD patterns showed that the Pd nanoparticles strongly adhered to the outside of the CNTs, with average particle sizes of ∼3 nm, ∼5 nm, and ∼6 nm for samples A, B and C, respectively. The XPS spectra revealed that the Pd species on the Pd-decorated CNTs consisted of Pd0, Pd2+ and Pd4+. The oxidized Pd species were formed by the interaction of the electron-donor Pd 0 atoms with the electrophilic neighboring protons (H+) during the sample preparation. The oxidized Pd species become more abundant with increasing linker length, causing a decrease of their catalytic activities in organic and electrocatalytic reactions. Nevertheless, all of the samples exhibited higher activity in organic and electrocatalytic reactions than that of the reference systems. © 2011 The Royal Society of Chemistry.


Pyo A.,Chonnam National University | Kim Y.H.,Chonnam National University | Park K.,Chonnam National University | Kim G.C.,Jeonnam Nano Bio Research Center | And 2 more authors.
Applied Organometallic Chemistry | Year: 2012

The mechanism of decarboxylative coupling of phenylpropiolic acid and methyl 4-iodobenzoate was investigated by gas chromatographic analysis and monitoring the decarboxylation reaction by FT-IR spectroscopy. Among many possible pathways, we found that the mechanism involves two possible pathways, namely the decarboxylation of phenylpropiolic acid and that proceeding through the carboxylated palladium complex. Copyright © 2012 John Wiley & Sons, Ltd.


Kim J.D.,Chonnam National University | Pyo A.,Chonnam National University | Park K.,Chonnam National University | Kim G.C.,Jeonnam Nano Bio Research Center | And 2 more authors.
Bulletin of the Korean Chemical Society | Year: 2013

We present here an efficient and simple method for preparation of highly active Pd heterogeneous catalyst (CNT-Pd), specifically by reaction of dichlorobis(triphenylphosphine)palladium (Pd(PPh3)2Cl 2) with thiolated carbon nanotubes (CNTs). The as-prepared CNT-Pd catalysts demonstrated an excellent catalytic activity for the carbon-carbon (C-C) cross-coupling reactions (i.e. Suzuki, Stille, and decarboxylative coupling reactions) under mild conditions. The CNT-Pd catalyst could easily be removed from the reaction mixture; additionally, in the decarboxylative coupling of iodobenzene and phenylpropiolic acid, it showed a six-times recyclability, with no loss of activity. Moreover, once its activity had decreased by repeated recycling, it could easily be reactivated by the addition of phosphine ligands. The remarkable recyclability of the decarboxylative coupling reaction is attributable to the high degree of dispersion of Pd catalysts in CNTs. Aggregation of the Pd catalysts is inhibited by their strong adhesion to the thiolated CNTs during the chemical reactions, thereby permitting their recycling. Copyright © 2005 KCSNET.


Kim J.D.,Chonnam National University | Yun H.,Chonnam National University | Kim G.C.,Jeonnam Nano Bio Research Center | Lee C.W.,Chonnam National University | Choi H.C.,Chonnam National University
Applied Surface Science | Year: 2013

A facile approach to the synthesis of novel CNT-Ag and GO-Ag antibacterial materials, in which thiol groups are utilized as linkers to secure silver (Ag) nanoparticles to the CNT and GO surfaces without agglomeration, is reported. The resulting CNT-Ag and GO-Ag samples were characterized by performing TEM, XRD, Auger, XPS, and Raman measurements, which revealed that in these antibacterial materials size-similar and quasi-spherical Ag nanoparticles are anchored to the CNT and GO surfaces. The Ag nanoparticles in CNT-Ag and GO-Ag have narrow size distributions with average diameters of 2.6 and 3.5 nm respectively. The antibacterial activities of CNT-Ag and GO-Ag against Escherichia coli were assessed with the paper-disk diffusion method and by determining the minimal inhibitory concentrations (MICs). CNT-Ag was found to have higher antibacterial activity than the reference Ag colloid. Moreover, both CNT-Ag and GO-Ag retain more than 50% of their original antibacterial activities after 20 washes with detergent, which indicates their potential as antibacterial materials for laboratory and medical purposes. © 2013 Elsevier B.V. All rights reserved.


Hong C.K.,Chonnam National University | Ko H.-S.,Chonnam National University | Han E.-M.,Chonnam National University | Yun J.-J.,Jeonnam Nano Bio Research Center | Park K.-H.,Chonnam National University
Nanoscale Research Letters | Year: 2013

We have successfully introduced green phosphors LaPO4:Ce, Tb (G4) or (Mg, Zn)Al11O19:Eu (G2) into TiO2 photoelectrode of dye-sensitized solar cells. The conversion efficiency of the G4-doped device was enhanced by 30% compared with the pristine TiO2photoelectrode. The green phosphor doped at 5-wt.% ratio contributed to the reduction of resistances of the surface and interface of the photoelectrode and to the great enhancement of the absorption spectrum in UV-visible and near-infrared regions. The internal resistances and absorbance of the photoelectrode directly affect the power conversion efficiency. Green phosphor plays an important role towards the realization of high-efficiency dye-sensitized solar cells. © 2013 Hong et al.


Park A.R.,Seoul National University | Son H.,Seoul National University | Min K.,Seoul National University | Park J.,Seoul National University | And 4 more authors.
Molecular Microbiology | Year: 2015

Summary: Several Fusarium species produce the polyketide mycotoxin zearalenone (ZEA), a causative agent of hyperestrogenic syndrome in animals that is often found in F.graminearum-infected cereals in temperate regions. The ZEA biosynthetic cluster genes PKS4, PKS13, ZEB1 andZEB2 encode a reducing polyketide synthase, a non-reducing polyketide synthase, an isoamyl alcohol oxidase and a transcription factor respectively. In this study, the production of two isoforms (ZEB2L and ZEB2S) from the ZEB2 gene in F.graminearum via an alternative promoter was characterized. ZEB2L contains a basic leucine zipper (bZIP) DNA-binding domain at the N-terminus, whereas ZEB2S is an N-terminally truncated form of ZEB2L that lacks the bZIP domain. Interestingly, ZEA triggers the induction of both ZEB2L and ZEB2S transcription. ZEB2L and ZEB2S interact with each other to form a heterodimer that regulates ZEA production by reducing the binding affinity of ZEB2L for the ZEB2L gene promoter. Our study provides insight into the autoregulation of ZEB2 expression by alternative promoter usage and a feedback loop during ZEA production; this regulatory mechanism is similar to that observed in higher eukaryotes. Zearalenone (ZEA) is an estrogenic mycotoxin produced by several Fusarium species. ZEB2 is a key regulator of ZEA biosynthesis. ZEB2L and ZEB2S, two isoforms formed from the ZEB2 gene, are involved in autoregulation via alternative promoter usage. ZEB2L oligomers function as direct activators of ZEA biosynthetic cluster genes, and ZEB2S inhibits ZEB2L transcription by forming ZEB2L-ZEB2S heterodimers, eliminating the DNA-binding activity of ZEB2L oligomers. © 2015 John Wiley & Sons Ltd.


Lim D.-S.,Eulji University | Kim S.-R.,Chosun University | Choi B.-D.,Chosun University | Jeong S.-J.,Chosun University | And 5 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2012

It was previously reported that in Ras transformed NIH3T3 cells, dynamin II acts as an intermediate messenger in the Ras signal transduction pathway leading to membrane ruffling and cell migration. However, these results do not provide sufficient evidence of a relationship between dynamin II and the Ras signal transduction pathway leading to membrane ruffling and cell migration. The results showed that a dynamin II association with myosin II as a signaling molecule is involved in NIH3T3 cell migration through the Ras/PI3K signaling pathway, and is associated with the p85 subunit of PI3K. Confocal microscopy also revealed co-localization between dynamin II and paxillin after PDGF stimulation. In addition, immunofluorescence results showed that dynamin II was colocalized with the actin filament. After stimulating the NIH3T3 cells with PDGF and treating them with an actin inhibitor, such as Cytochalasin D, it was observed that dynamin II with the myosin II complex inhibited binding to the actin. Therefore, dynamin II is localized in focal adhesion when cell migration is triggered and binds to the actin filament component, suggesting that it is a good candidate nanomolecule to regulate the cell attachment and migration to the materials such as implants etc. Copyright © 2012 American Scientific Publishers.


PubMed | Jeonnam Nano Bio Research Center, Daejeon University and Seoul National University
Type: Journal Article | Journal: Molecular microbiology | Year: 2015

Several Fusarium species produce the polyketide mycotoxin zearalenone (ZEA), a causative agent of hyperestrogenic syndrome in animals that is often found in F.graminearum-infected cereals in temperate regions. The ZEA biosynthetic cluster genes PKS4, PKS13, ZEB1 andZEB2 encode a reducing polyketide synthase, a non-reducing polyketide synthase, an isoamyl alcohol oxidase and a transcription factor respectively. In this study, the production of two isoforms (ZEB2L and ZEB2S) from the ZEB2 gene in F.graminearum via an alternative promoter was characterized. ZEB2L contains a basic leucine zipper (bZIP) DNA-binding domain at the N-terminus, whereas ZEB2S is an N-terminally truncated form of ZEB2L that lacks the bZIP domain. Interestingly, ZEA triggers the induction of both ZEB2L and ZEB2S transcription. ZEB2L and ZEB2S interact with each other to form a heterodimer that regulates ZEA production by reducing the binding affinity of ZEB2L for the ZEB2L gene promoter. Our study provides insight into the autoregulation of ZEB2 expression by alternative promoter usage and a feedback loop during ZEA production; this regulatory mechanism is similar to that observed in higher eukaryotes.

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