Song Yi Park

Ulsan National Institute of Science and Technology, Urusan, Ulsan, South Korea

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Publications (12)28.7 Total impact

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    ABSTRACT: Single crystal silicon nanoparticles (Si-NPs) of 20 nm were produced via a laser pyrolysis at a virtually complete conversion from SiH4 into Si-NPs. SF6 was used as the photosensitizer to transfer laser beam energy to silicon precursors, dramatically enhancing crystallinity of Si-NPs and their production efficiency. By using their well-developed crystalline structure, the directional volume expansion of Si-NPs was confirmed during lithiation. Lithiation/delithiation kinetics of our Si-NPs was superior to that of their amorphous counterparts due to the footprinted Li+ pathways formed during amorphization.
    J. Mater. Chem. A. 09/2014;
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    ABSTRACT: We demonstrate a practical route to synthesize Ge nanoparticles (NPs) in multi-gram quantities via the laser pyrolysis of GeH4 gas. The size of the as-produced Ge NPs can be precisely controlled in the range of 19.0 to 65.9 nm via a subsequent etching procedure using a dilute H2O2 solution. Stable water dispersions of Ge NPs yield particles with a Ge/GeO2 core-shell structure, however, the oxide shell can easily be removed and passivated by treatment with HCl. The feed materials used in this process are readily available and lead to non-toxic, water-based dispersions of Ge NPs. The scalability and convenience of this procedure make it attractive as a method to obtain Ge NP dispersions for use in applications such as optoelectronic devices and biosensors.
    Nanoscale 07/2014; · 6.23 Impact Factor
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    ABSTRACT: The introduction of fluorine (F) atoms onto conjugated polymer backbone has verified to be an effective way to enhance the overall performance of polymer-based bulk-heterojunction (BHJ) solar cells, but the underlying working principles are not yet fully uncovered. As our attempt to further understand the 'F' impact, herein we have reported two novel fluorinated analogues of PCDTBT, viz. PCDTFBT (1F) and PCDT2FBT (2F), through inclusion of either one or two F atoms into the benzothiadiazole (BT) unit of the polymer backbone and the characterization of their physical properties, especially their performance in solar cells. Together with a profound effect of fluorination on the optical property, nature of charge transport, and molecular organization, F atoms are effective in lowering both the HOMO and LUMO levels of the polymers without a large change in the energy bandgaps. PCDTFBT-based BHJ solar cell shows a power conversion efficiency (PCE) of 3.96 % with high open-circuit voltage (VOC) of 0.95 V, mainly due to the deep HOMO level (-5.54 eV). To the best of our knowledge, the resulting VOC is comparable to the record VOC values in single junction devices. Furthermore, to our delight, the best PCDTFBT-based device, prepared using 2 % v/v diphenyl ether (DPE) additive, reaches the PCE of 4.29 %. On the other hand, doubly-fluorinated polymer PCDT2FBT shows the only moderate PCE of 2.07 % with a decrease in VOC (0.88 V), in spite of the further lowering of the HOMO level (-5.67 eV) with raising the number of F atoms. Thus, our results highlight that an improvement in efficiency by tuning the energy levels of the polymers by means of molecular design can be expected only if their truly optimized morphologies with fullerene in BHJ systems are materialized.
    ACS Applied Materials & Interfaces 04/2014; · 5.01 Impact Factor
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    ABSTRACT: Activation of the Wnt pathway is known to promote tumorigenesis and tumor metastasis, and targeting Wnt pathway inhibition has emerged as an attractive approach for controlling tumor invasion and metastasis. The major pathway for inhibiting Wnt is through the degradation of beta-catenin by the GSK3-beta/CK1/Axin/APC complex. It was found that Hep3B hepato-carcinoma cells respond to anthocyanins through GSK3-beta-induced suppression of beta-catenin; however, they cannot dephosphorylate GSK3-beta without AMPK activation. We tested the effects of anthocyanins on proliferation and apoptosis by MTT and Annexin V-PI staining in vitro. Mouse xenograft models of hepato-carcinomas were established by inoculation with Hep3B cells, and mice were injected with 50 mg/kg/ml of anthocyanins. In addition, protein levels of p-GSK3-beta, beta-catenin, p-AMPK, MMP-9, VEGF, and Ang-1 were also analyzed using western blot. Anthocyanins decrease phospho-GSK3-beta and beta-catenin expression in an in vivo tumor xenograft model, increase AMPK activity in this model, and inhibit cell migration and invasion, possibly by inhibiting MMP-2 (in vitro) and the panendothelial marker, CD31 (in vivo). To elucidate the role of the GSK3-beta/beta-catenin pathway in cancer control, we conditionally inactivated this pathway, using activated AMPK for inhibition. Further, we showed that AMPK siRNA treatment abrogated the ability of anthocyanins to control cell proliferation and metastatic potential, and Compound C, an AMPK inhibitor, could not restore GSK3-beta regulation, as exhibited by anthocyanins in Hep3B cells. These observations imply that the AMPK-mediated GSK3-beta/beta-catenin circuit plays crucial roles in inhibiting cancer cell proliferation and metastasis in anthocyanin-treated hepato-carcinoma cells of Meoru origin.
    BMC Complementary and Alternative Medicine 03/2014; 14(1):109. · 2.08 Impact Factor
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    ABSTRACT: The present study investigated the regulatory mechanisms by which epigallocatechin-3-gallate (EGCG) exerts vascular endothelial growth factor (VEGF)-, p53- and AMP-activated protein kinase (AMPK)-associated pro-apoptotic and migration-suppressing effects on colon cancer cells. EGCG decreased the expression levels of VEGF and matrix metalloproteinase (MMP)-9. EGCG treatment induced apoptosis in the presence of wild-type and mutant p53, indicating that a p53-independent pathway may contribute to EGCG-induced apoptosis in these cells. EGCG showed migration-suppressing effects, suggesting that this activity may also have p53-dependent and -independent components. The interaction between p53 and VEGF in the EGCG-treated cells was investigated using pifithrin-α. Notably, the suppression of p53 activity blocked the ability of EGCG to inhibit VEGF and MMP-9 in the cells expressing wild-type p53, but not mutant p53, indicating that the effects of EGCG on VEGF may be p53-dependent or -independent. Finally, although AMPK and VEGF did not appear to co-localize, the results indicated that AMPK controls VEGF in EGCG-treated cells regardless of the p53 status.
    Oncology letters 11/2013; 6(5):1346-1350. · 0.24 Impact Factor
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    ABSTRACT: Curcumin, the major phytochemical in turmeric, exerts anti‑proliferative, anticancer and anti‑inflammatory activities in various types of cancer cells. Curcumin has been demonstrated to induce apoptosis through multiple signaling pathways; however, its association with survival pathways, including the Wnt signaling pathway, is not fully understood. The Wnt signaling pathway is involved in diverse functions, including cell development, growth and proliferation. This pathway is important for cancer cell survival and metastasis. β‑catenin and GSK3β play a key role in the Wnt signaling pathway and therefore, various members of the Wnt signaling pathway have been hypothesized to represent potential targets for anticancer therapy. In the present study, the effect of curcumin on the suppression of migration and proliferation of Hep3B hepatocarcinoma cells was investigated via suppression of Wnt signaling in vitro and in vivo. 12‑O‑tetradecanoylphorbol‑13‑acetate (TPA)‑induced cell migration was observed to be suppressed by curcumin treatment. In addition, curcumin suppressed TPA‑induced activation of Wnt signaling. These results indicate that curcumin induces anti‑migratory activity, which functions via the Wnt signaling pathway.
    Molecular Medicine Reports 05/2013; · 1.17 Impact Factor
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    ABSTRACT: Two naphtho[1,2-b:5,6-b 0 ]dithiophene-based copolymers, poly[4,9-bis(2-ethylhexyloxy)naphtho[1,2-b:5,6-b 0 ]dithiophene-2,7-diyl-alt-[4,6-{(1-thieno[3,4-b]thiophen-2-yl)-2-ethylhexan-1-one}] (P1) and poly[4,9-bis(2-ethylhexyloxy)naphtho[1,2-b:5,6-b 0 ]dithiophene-2,7-diyl-alt-[4,6-{(1-(3-fluorothieno[3,4-b]thiophen)-2-yl)-2-ethylhexan-1-one}] (P2), were designed and synthesized for use in polymer solar cells (PSCs). We systematically investigated the synthesis, thermal stability, optical and electrochemical properties, field-effect carrier mobilities, and photovoltaic characteristics of these polymers. The field-effect mobilities of P1 and P2 were determined to be 5.8 Â 10 À4 and 1.2 Â 10 À3 cm 2 V À1 s À1 , respectively. Among the naphtho[1,2-b:5,6-b 0 ]dithiophene-based copolymers studied here, P2 showed the best photovoltaic performance, with an open-circuit voltage (V oc) of 0.71 V, a short-circuit current density (J sc) of 13.52 mA cm À2 , a fill factor (FF) of 0.51, and a power conversion efficiency of 4.88% under AM 1.5 irradiation (100 mW cm À2).
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    ABSTRACT: Activation of the mammalian target of rapamycin (mTOR) pathway promotes tumorigenesis, and inhibiting the mammalian target of rapamycin complex 1 (mTORC1) has emerged as an attractive target for suppressing tumor growth. We found that selenium treatment of HT-29 colon cancer cells suppressed mTORC1 through Akt-independent and -dependent pathways. In Akt-independent mTORC1 inhibition in selenium-treated colon cancer cells, adenosine monophosphate-activated protein kinase (AMPK) alpha(1) was crucial for suppression of mTORC1 activity. In contrast, the Akt-dependent mTORC1 inhibition by selenium did not require AMPKalpha(1). The importance of the AMPKalpha(1)-mTORC1 pathway in mediating the antiproliferative action of selenium was examined in xenograft tumors, and the suppression of mTORC1 as well as Akt was concomitant with an increase in AMPKalpha(1) activity. These findings suggest that the antiproliferative effect of selenium is mediated by an Akt-independent AMPKalpha(1)/mTORC1 pathway or by the Akt/tuberous sclerosis complex 2 /mTORC1 pathway.
    Carcinogenesis 02/2010; 31(6):1092-9. · 5.64 Impact Factor
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    ABSTRACT: AMP-activated protein kinase (AMPK), a highly conserved protein in eukaryotes, functions as a major metabolic switch to maintain energy homeostasis. It also intrinsically regulates the mammalian cell cycle. Moreover, the AMPK cascade has emerged as an important pathway implicated in cancer control. In this study we investigated the effects of curcumin on apoptosis and the regulatory effect of the AMPK-cyclooxygenase-2 (COX-2) pathway in curcumin-induced apoptosis. Curcumin has shown promise as a chemopreventive agent because of its in vivo regression of various animal-model colon cancers. This study focused on exploiting curcumin to apply antitumorigenic effects through modulation of the AMPK-COX-2 cascade. Curcumin exhibited a potent apoptotic effect on HT-29 colon cancer cells at concentrations of 50 micromol/L and above. These apoptotic effects were correlated with the decrease in pAkt and COX-2, as well as the increase in p-AMPK. Cell cycle analysis showed that curcumin induced G(1)-phase arrest. Further study with AMPK synthetic inhibitor Compound C has shown that increased concentrations of Compound C would abolish AMPK expression, accompanied by a marked increase in COX-2 as well as pAkt expression in curcumin-treated HT-29 cells. By inhibiting AMPK with Compound C, we found that curcumin-treated colon cancer cells were no longer undergoing apoptosis; rather, they were proliferative. These results indicate that AMPK is crucial in apoptosis induced by curcumin and further that the pAkt-AMPK-COX-2 cascade or AMPK-pAkt-COX-2 pathway is important in cell proliferation and apoptosis in colon cancer cells.
    Annals of the New York Academy of Sciences 09/2009; 1171:489-94. · 4.38 Impact Factor
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    ABSTRACT: AMPK (AMP-activated protein kinase) is highly conserved in eukaryotes, where it functions primarily as a sensor of cellular energy status. Recent studies indicate that AMPK activation strongly suppresses cell proliferation in non-malignant cells as well as in tumor cells. In this study, quercetin activated AMPK in MCF breast cancer cell lines and HT-29 colon cancer cells, and this activation of AMPK seemed to be closely related to a decrease in COX-2 expression. The application of a COX-2 inhibitor or cox-2-/- cells supported the idea that AMPK is an upstream signal of COX-2, and is required for the anti-proliferatory and pro-apoptotic effects of quercetin. The suppressive or growth inhibitory effects of quercetin on COX-2 were abolished by treating cancer cells with an AMPK inhibitor Compound C. These results suggest that AMPK is crucial to the anti-cancer effect of quercetin and that the AMPK-COX-2 signaling pathway is important in quercetin-mediated cancer control.
    Experimental and Molecular Medicine 04/2009; 41(3):201-7. · 2.57 Impact Factor
  • Song Yi Park, Ock Jin Park
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    ABSTRACT: It has been well known that resveratrol inhibits the proliferation of various cancer cells. AMP-activated protein kinase (AMPK), a sensor of cellular energy status, has emerged as a potent target for cancer prevention and/or treatment. It has been found that the activation of AMPK by resveratrol was crucial for the inhibition of HT-29 colon cancer cells. Resveratrol strongly inhibited phosphorylation of Akt. The possibility whether AMPK activation was essential to the inhibition of p-Akt was investigated in resveratrol-treated cancer cells. The inhibitory effect of resveratrol on Akt was not observed when AMPK activities were blocked by the treatment with AMPK siRNA at a relatively lower level of resveratrol. However, the higher concentrations of resveratrol inhibited Akt without the activation of AMPK. Therefore, it was concluded that resveratrol could modulate Akt AMPK-dependently or AMPK-independently. The inhibition of Akt along with the activation of AMPK may contribute to the unraveling anti-cancer mechanism of resveratrol. KeywordsAkt–AMP-activated kinase–LY294002–resveratrol–HT-29 colon cancer cell
    Food science and biotechnology 19(6):1537-1541. · 0.70 Impact Factor
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    ABSTRACT: Suppressing the mammalian target of rapamycin (mTOR) pathway has emerged as an attractive method for controlling cancer growth and preventing cancers. Epigallocatechin-3-gallate (EGCG) is a well-known chemopreventive polyphenol, and its effects on AMP-activated protein kinase (AMPK) activation were previously reported. In this study the regulatory mechanisms of EGCG on mTOR and Akt, 2 cancer survival signals, and the interrelationships among mTORC1, Akt, and AMPK were examined. It was found that the suppression of mTORC1 by EGCG requires signals from AMPK, however, the inhibition of Akt with EGCG seems to be AMPK independent. Further, there was no clear indication of Akt as an upstream regulator of mTOR in EGCG treated HT-29 colon cancer cells.
    Food science and biotechnology 22(1). · 0.70 Impact Factor