Publications by authors named "Kyu Seung Lee"

11 Publications

  • Page 1 of 1

Inhibition of Photoconversion Activity in Self-Assembled ZnO-Graphene Quantum Dots Aggregated by 4-Aminophenol Used as a Linker.

Molecules 2020 Jun 17;25(12). Epub 2020 Jun 17.

Institute of Advanced Composite Materials, Korea Institute of Science and Technology, 92, Chudong-ro, Bongdong-eup, Wanju-gun, Jeollabuk-do 55324, Korea.

The aggregation of zinc oxide nanoparticles leads to an increased absorbance in the ultraviolet-visible region by an induced light scattering effect. Herein, we demonstrate the inhibition of photoconversion activity in ZnO-graphene core-shell quantum dots (QD) (ZGQDs) agglomerated by 4-aminophenol (4-AP) used as a linker. The ZnO-graphene quantum dots (QD) aggregates (ZGAs) were synthesized using a facile solvothermal process. The ZGAs revealed an increased absorbance in the wavelengths between 350 and 750 nm as compared with the ZGQDs. Against expectation, the calculated average photoluminescence lifetime of ZGAs was 7.37 ns, which was 4.65 ns longer than that of ZGQDs and was mainly due to the high contribution of a slow (τ, τ) component by trapped carriers in the functional groups of graphene shells and 4-AP. The photoelectrochemical (PEC) cells and photodetectors (PDs) were fabricated to investigate the influence of ZGAs on the photoconversion activity. The photocurrent density of PEC cells with ZGAs was obtained as 0.04 mA/cm at 0.6 V, which was approximately 3.25 times lower than that of the ZGQDs. The rate constant value of the photodegradation value of rhodamine B was also decreased by around 1.4 times. Furthermore, the photoresponsivity of the PDs with ZGAs (1.54 μA·mW) was about 2.5 times as low as that of the PDs with ZGQDs (3.85 μA·mW). Consequently, it suggests that the device performances could be degraded by the inhibition phenomenon of the photoconversion activity in the ZGAs due to an increase of trap sites.
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http://dx.doi.org/10.3390/molecules25122802DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7355606PMC
June 2020

Unveiling the composite structures of emissive consolidated p-i-n junction nanocells for white light emission.

Nanoscale 2018 Aug 8;10(29):13867-13874. Epub 2018 Jun 8.

Institute of Advanced Composite Materials, Applied Quantum Composites Research Center, Korea Institute of Science and Technology, 92 Chudong-ro, Bongdong-eup, Wanju-gun, Jeonbuk 55324, Republic of Korea.

Hybrid organic-Red-Green-Blue (RGB) color quantum dots were incorporated into consolidated p(polymer)-i(RGB quantum dots)-n(small molecules) junction structures to fabricate a single active layer for a light emitting diode device for white electroluminescence. The semiconductor RGB quantum dots, as an intrinsic material, were electrostatically bonded between functional groups of the p-type polymer organic material core surface and the n-type small molecular organic material shell surface. The ZnCdSe/ZnS and CdSe/ZnS quantum dots distributed uniformly and isotropically surrounding the polymer core which in turn was surrounded by small molecular organic materials. In the present study, we have identified the mechanisms of chemical synthesis and interactions of the p-i-n junction nanocell structure through modeling studies by DFT calculations. We have also investigated optical, structural and electrical properties along with the carrier transport mechanism of the light emitting diodes which have a single active layer of consolidated p-i-n junction nanocells for white electroluminescence.
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http://dx.doi.org/10.1039/c8nr01842aDOI Listing
August 2018

Comparison of analytical methods and residue patterns of pymetrozine in Aster scaber.

Bull Environ Contam Toxicol 2011 Dec 16;87(6):649-52. Epub 2011 Sep 16.

Department of Bio-Environmental Chemistry, Chungnam National University, 220 Kungdong Yusungku, Daejeon, 305-764, Republic of Korea.

Residues of the polar pesticide pymetrozine were compared using two methods: hydromatrix and liquid-liquid extraction (LLE). The biological half-life and the final residue level were investigated using Aster scaber over a 10-days cultivation period. The respective biological half-lives of the pesticide were 4.2 and 3.5 days at the recommended and double dose. The final residue levels were 1.28 and 1.98 mg kg(-1), respectively, at the same application rate of pymetrozine according to the GAP standard of the United Kingdom. Average recovery was higher with LLE than with the hydromatrix method. Dissipation curves of pymetrozine were influenced by the application amount and growth rate of A. scaber. The final residue level of pymetrozine could be predicted to be lower than the UK maximum residue limit for lettuce applying the GAP standard.
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http://dx.doi.org/10.1007/s00128-011-0407-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3223348PMC
December 2011

Major role of GABA(A)-receptor mediated tonic inhibition in propofol suppression of supraoptic magnocellular neurons.

Neurosci Lett 2011 Apr 3;494(2):119-23. Epub 2011 Mar 3.

Department of Physiology, Brain Research Institute, College of Medicine, Chungnam National University, 6 Munhwa-Dong, Joong-Gu, Daejeon 301-131, Republic of Korea.

Using slice patch clamp recording, we examined the effects of general anesthetic propofol (2,6-diisoprophlphenol) on dual modality of GABA(A) inhibition in supraoptic nucleus (SON) magnocellular neurosecretory cells (MNCs): conventional quantal synaptic transmission (IPSCs, I(phasic)) and persistent tonic form of inhibitory current (I(tonic)). Propofol (10 μM) enhanced I(tonic) as shown by an inward shift in I(holding) (16.46±2.93 pA, n=27) and RMS increase (from 3.37±0.21 pA to 4.68±0.33 pA, n=27) in SON MNCs. Propofol also prolonged the decay time of IPSCs with decreased IPSCs frequency but no significant changes in IPSCs amplitude. Overall, propofol (1-10 μM) caused much smaller increase in mean I(phasic) than mean I(tonic) at all tested concentrations. In consistent with the enhancement of GABA(A) currents, propofol attenuated ongoing firing activities of SON MNCs by ∼65% of control. Selective inhibition of I(phasic) by a GABA(A) antagonist, gabazine (1 μM), failed to block the propofol suppression of the firing activities, while inhibition of I(tonic) and I(phasic) by bicuculline (20 μM) efficiently blocked the propofol-induced neurodepression in SON MNCs. Taken together, our results showed that propofol facilitated I(tonic) with marginal increase in mean I(phasic), and this could be a mechanism reducing the intrinsic SON MNCs excitability during propofol anesthesia.
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http://dx.doi.org/10.1016/j.neulet.2011.02.072DOI Listing
April 2011

Active packing method for blue light-emitting diodes with photosensitive polymerization: formation of self-focusing encapsulates.

Opt Express 2008 Mar;16(6):3680-5

School for Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510631, China.

A novel light-emitting diode (LED) packaging method, named the active packaging (AP) method, is presented in this paper. In this method, during the LED packaging process, the light emitted from a GaN LED chip itself is employed to package the LED encapsulant, thereby eliminating the need to utilize a mold. Current injection into a bare LED chip, triggers a photosensitive epoxy to polymerize, leading to the formation of mushroom lamp cap on the LED chip. The emission properties of LEDs fabricated by this method, including their emission beam profiles and light outputs, were characterized. The results showed that a self-focusing effect happened with the addition of an epoxy on the chip. The simulation demonstrated that the geometry the encapsulant controlled the beam pattern of emission. Further, the self-focusing effect was believed to be caused by the combination of the threshold energy of epoxy polymerization, the beam pattern and the power output of the LED chip.
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http://dx.doi.org/10.1364/oe.16.003680DOI Listing
March 2008

Serotonin inhibits GABA synaptic transmission in presympathetic paraventricular nucleus neurons.

Neurosci Lett 2008 Jul 10;439(2):138-42. Epub 2008 May 10.

Research Institute of Medical Sciences, Department of Physiology, College of Medicine, Chungnam National University, 6 Munhwa-dong, Joong-gu, Daejeon, 301-131, Republic of Korea.

Activation of serotonin (5-hydroxytryptamine, 5-HT) receptors produces various autonomic and neuroendocrine responses in the hypothalamic paraventricular nucleus (PVN), including increased blood pressure and heart rate. However, the role(s) of 5-HT on the local GABA synaptic circuit have not been well understood in the PVN, where the inhibitory neurotransmitter GABA plays a key role in the modulation of sympathoexcitatory outflow. In the present study, we examined the effects of 5-HT on GABA synaptic transmission in presympathetic PVN neurons projecting to spinal cord using patch-clamp electrophysiology combined with tract-tracing techniques. Bath application of 5-HT (0.01-100 microM) reversibly decreased the frequency of spontaneous GABAergic inhibitory postsynaptic currents (sIPSC) in a concentration dependent manner (IC50, 0.07 microM), with no significant changes in the amplitudes and decay kinetics of sIPSC. The sIPSC inhibition of 5-HT was mimicked by 5-HT1A agonist, 8-OH-DPAT (8-hydroxy-2(di-n-propylamino)tetralin, 10 microM), and blocked by 5-HT1A antagonist WAY-100635 but not by 5-HT1B antagonist SB224289. 5-HT also reduced the frequency of miniature IPSC (mIPSC) (2.59+/-0.51 Hz, control vs. 1.25+/-0.31 Hz, 5-HT, n=16) in similar extent with 5-HT induced reduction of sIPSC frequency (sIPSCs, 55.8+/-6.2%, n=11 vs. mIPSCs, 52.30+/-5.85%, n=16; p>0.5). All together, our results indicate that 5-HT can inhibit presynaptic GABA release via presynaptic 5-HT1A receptors in presympathetic PVN neurons projecting to spinal cord.
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http://dx.doi.org/10.1016/j.neulet.2008.05.012DOI Listing
July 2008

White light emitting diodes realized by using an active packaging method with CdSe/ZnS quantum dots dispersed in photosensitive epoxy resins.

Nanotechnology 2008 Apr 4;19(14):145202. Epub 2008 Mar 4.

National Research Laboratory for Nano-Bio-Photonics, BK21 Physics Program and Department of Physics, Chungbuk National University, Cheongju 361-763, Korea.

White light emitting diodes (LEDs) have been realized using the active packaging (AP) method. The starting materials were bare InGaN LED chips and CdSe/ZnS core-shell quantum dots (QDs) dispersed in photosensitive epoxy resins. Such hybrid LED devices were fabricated using QD mixtures with one ('single'), two ('dual') or four ('multi') emission wavelengths. The AP method allows for convenient adjustment of multiple parameters such as the CIE-1931 coordinate (x, y), color temperature, and color rending index (CRI). All samples show good white balance, and under a 20 mA working current the luminous efficacies of the single, dual, and multi hybrid devices were 8.1 lm W(-1), 5.1 lm W(-1), and 6.4 lm W(-1), respectively. The corresponding quantum efficiencies were 4.1%, 3.1%, and 3.1%; the CRIs were 21.46, 43.76, and 66.20; and the color temperatures were 12 000, 8190, and 7740 K. This shows that the CRI of the samples can be enhanced by broadening the QD emission band, as is exemplified by the 21.46 CRI of the single hybrid LED compared to the 66.20 value for the multi hybrid LED. In addition, we were able to increase the CRI of the single hybrid LED from 15.31 to 32.50 by increasing the working currents from 1 to 50 mA.
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http://dx.doi.org/10.1088/0957-4484/19/14/145202DOI Listing
April 2008

Inhibitory effects of coronary vasodilator papaverine on heterologously-expressed HERG currents in Xenopus oocytes.

Acta Pharmacol Sin 2007 Apr;28(4):503-10

Department of Physiology, College of Medicine, Chungnam National University, Daejeon 301131, Korea.

Aim: To characterize the effects of papaverine on HERG channels expressed in Xenopus oocytes as well as cardiac action potential in rabbit ventricular myocytes.

Methods: Conventional microelectrodes were used to record action potential in rabbit ventricular myocytes. HERG currents were recorded by 2-electrode voltage clamp technique in Xenopus oocytes injected with HERG cRNA.

Results: Papaverine increased the cardiac action potential duration in rabbit ventricular myocytes. It blocked heterologously-expressed HERG currents in a concentration-dependent manner (IC50 71.03+/-4.75 micromol/L, NH 0.80, n=6), whereas another phosphodiesterase inhibitor, theophylline (500 micromol/L), did not. The blockade of papaverine on HERG currents was not voltage-dependent. The slope conductance measured as a slope of the fully activated HERG current-voltage curves decreased from 78.03+/-4.25 muS of the control to 56.84+/-5.33, 36.06+/-6.53, and 27.09+/-5.50 microS (n=4) by 30, 100, and 300 micromol/L of papaverine, respectively. Papaverine (100 micromol/L) caused a 9 mV hyperpolarizing shift in the voltage-dependence of steady-state inactivation, but there were no changes in the voltage-dependence of HERG current activation. Papaverine blocked HERG channels in the closed, open, and inactivated states.

Conclusion: These results showed that papaverine blocked HERG channels in a voltage- and state-independent manner, which may most likely be the major mechanism of papaverine-induced cardiac arrhythmia reported in humans.
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http://dx.doi.org/10.1111/j.1745-7254.2007.00507.xDOI Listing
April 2007

Modulating effect of ginseng saponins on heterologously expressed HERG currents in Xenopus oocytes.

Acta Pharmacol Sin 2005 May;26(5):551-8

Department of Physiology, College of Medicine, Chungnam National University, Daejeon 301-131, Korea.

Aim: To examine the effects of ginseng saponins on the heterologously expressed human ether-a-go-go related gene (HERG) that encodes the rapid component of the delayed rectifier K+ channel.

Methods: A two-electrode voltage clamp technique was used. HERG currents were recorded in Xenopus oocytes injected with HERG cRNA.

Results: Crude saponins of Korean red ginseng (GS) induced a minimal increase of the maximal HERG conductance without changes in the voltage-dependent HERG current activation and inactivation curves. GS, however, decelerated HERG current deactivation in a concentration-dependent manner, which was more noticeable with panaxitriol (PT) than panaxidiol (PD). Consistently, ginseng saponins increased the HERG deactivation time constants with the order of potency of Rg1 (a major component of PT)>Rf1>Rb1 (a major component of PD). Re had little effect on HERG deactivation. During a cardiac action potential, GS increased the outward HERG current.

Conclusion: Ginseng saponins enhance HERG currents, which could be in part a possible mechanism of the shortening cardiac action potential of ginseng saponins.
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http://dx.doi.org/10.1111/j.1745-7254.2005.00116.xDOI Listing
May 2005

Effects of estradiol-17beta and progesterone supplementation on in vitro nuclear maturation of canine oocytes.

Theriogenology 2005 Mar;63(5):1342-53

Department of Theriogenology and Biotechnology, College of Veterinary Medicine, Seoul National University, Seoul 151-742, Republic of Korea.

Unlike in other domestic animals, in vitro maturation (IVM) of canine oocytes has had limited success. The present study investigated the effect of the estrous cycle and estradiol-17beta (E2) or progesterone (P4) supplementation on in vitro nuclear maturation of canine oocytes recovered from domestic dog ovaries in various reproductive states (follicular, luteal or anestrous stages). Oocytes were cultured in serum-free tissue culture medium (TCM)-199 supplemented with various concentrations of E2 (Exp. 1: 0, 0.1, 1.0 or 2.0 microg/ml) or P4 (Exp. 2; 0, 0.5, 1.0 or 2.0 microg/ml) for 72 h to determine the effective concentration of hormones. In Exp. 3, in order to investigate the synergistic effect of E2 and P4 supplementation, three groups of oocytes were cultured with 2 microg/ml E2 plus various concentrations of P4 (0, 0.5, 1.0 or 2.0 microg/ml). As results, the rate of maturation to metaphase II (MII) stage was significantly higher (P < 0.05) in oocytes from the follicular stage supplemented with 2 microg/ml E2 (14.7%) compared to the other groups (1.5-8.2%). Significantly higher (P < 0.05) maturation rate to MII stage was observed in oocytes from the follicular stage supplemented with 1.0 (10.0%) or 2.0 microg/ml (10.8%) P4 compared to the other groups (0-4.8%). Furthermore, more (P < 0.05) oocytes from the follicular stage supplemented with 2.0 microg/ml of E2 and P4 (16.6%) were matured to MII stage compared to oocytes from the follicular stage supplemented with 2.0 microg/ml E2 alone (10.4%) or the other groups of oocytes (0-7.8%). Interestingly, compared to 2.0 microg/ml E2 alone (10.4%), supplementation of 2 microg/ml E2 + 0.5 microg/ml P4 (3.4%) decreased the maturation of oocytes from the follicular stage to MII stage. In conclusion, the present study demonstrated that supplementation of the culture medium with E2 or P4 alone significantly increased maturation of canine oocyte to MII and that P4 supplementation with E2 further promote or decrease oocyte maturation compared to E2 alone depending on P4 concentration.
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http://dx.doi.org/10.1016/j.theriogenology.2004.07.019DOI Listing
March 2005

Effect of beta-mercaptoethanol or epidermal growth factor supplementation on in vitro maturation of canine oocytes collected from dogs with different stages of the estrus cycle.

J Vet Sci 2004 Sep;5(3):253-8

Department of Theriogenology and Biotechnology, College of Veterinary Medicine, Seoul National University, Seoul 151-742, Korea.

Supplementation of beta-mercaptoethanol (beta-ME) in in vitro maturation (IVM) medium was shown to improve embryo development and quality in several species. Epidermal growth factor (EGF) was also shown to improve IVM of human oocyte and embryo development after in vitro fertilization (IVF). The effect of these two compounds were suggested to be mediated through the synthesis of glutathione (GSH) which is known to play an important role in protecting the cell or embryos from oxidative damage. Thus, it is suggested that supplementation of canine IVM medium with beta-ME or EGF may be of benefit due to its positive role in IVM of various mammalian oocytes and embryo development, including cattle, pigs, rodents and humans. This study investigates the effect of ovarian estrus stage on canine oocyte quality and supplementation of medium with beta-ME or EGF on IVM of canine oocytes. As results, a significantly higher percentage of oocytes progressed to metaphase II (MII) stage in 50 or 100 microM of beta-ME supplemented oocytes collected from the follicular stage. The maturation rate to metaphase I (MI) stage was also significantly higher in oocytes collected from follicular stage and cultured with 25 or 100 microM compared to other experimental groups. After IVM culture, oocytes recovered from dogs with the follicular stage and matured in TCM-199 supplemented with 20 ng/ml EGF yielded better oocyte maturation to MII phase compared to other groups. Taken together, supplementation of beta-ME (50 or 100 microM) or EGF (20 ng/ml) improved IVM of canine oocytes to MII stage.
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September 2004