Publications by authors named "Milim Lee"

9 Publications

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Sharp Turns and Fluorescent Repeats: Modular Construction and Shape-Dependent Electronic Properties of π-Conjugated Chain Molecules.

Chempluschem 2021 Feb;86(2):313-318

Department of Chemistry, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea.

In search of the design rules for structural ordering of open-chain molecules, we have built a series of zig-zag shaped π-conjugated structures with ring-fused heteroaromatics as sharp turns and tolane-based linear fragments as light-emitting units. Using only a finite number of common building blocks, an efficient "double-elongation" strategy was implemented to construct a series of π-conjugated oligomers with precise length control (55-89 % yields). Our approach takes advantage of the modular nature of the bis(triazolo)benzene synthesis and the masked reactivity of the nitro group. A combination of photophysical and DFT computational studies revealed that the bis(triazolo)benzene-tolane repeat units behave as electronically decoupled light-absorbing/emitting units (λ = 408-422 nm; Φ = 20-25 % in THF). Such context-independent photophysical properties promise their potential applications in chemical sensing and switching.
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http://dx.doi.org/10.1002/cplu.202000818DOI Listing
February 2021

Weak Links To Differentiate Weak Bonds: Size-Selective Response of π-Conjugated Macrocycle Gels to Ammonium Ions.

J Am Chem Soc 2019 04 1;141(14):5980-5986. Epub 2019 Apr 1.

Department of Chemistry , Seoul National University , 1 Gwanak-ro, Gwanak-gu , Seoul 08826 , Korea.

Molecular-level host-guest interactions can drive gel-to-sol phase transitions of the bulk material. Using supramolecular gels constructed from π-conjugated aza-crown macrocycles, we have investigated the effects of guest chemical structures on the kinetics of gel disassembly. While ammonium ions bind only weakly to the individual macrocycles in solution, gel-to-sol transitions of self-assembled macrocycles occur readily under ambient conditions. This net signal amplification process was monitored conveniently by time-dependent spectroscopic studies to reveal a straightforward correlation between the response rate and shape/size of the guest species. Well-designed weak links thus respond to subtle differences in weak bonds and translate them into visually discernible macroscopic signaling events.
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http://dx.doi.org/10.1021/jacs.9b01002DOI Listing
April 2019

Effect of Nb concentration on the spin-orbit coupling strength in Nb-doped SrTiO epitaxial thin films.

Sci Rep 2018 Apr 10;8(1):5739. Epub 2018 Apr 10.

Electronic Materials Research Center, Korea Institute of Science and Technology, Seoul, 02792, Korea.

Several oxide materials have attracted much interest for the application in spintronic devices due to unusual properties originating from the strongly correlated orbital and spin degrees of freedom. One missing part in oxide spintronics is a good spin channel featured by strong spin-orbit coupling (SOC) which enables an efficient control of the electron's spin. We have systematically investigated the dependence of the SOC strength of Sr(Nb Ti)O thin films on Nb concentration (n = 2~20 at. %) as a deeper exploration of a recent finding of the strong SOC in a heavily Nb-doped SrTiO (Sr(NbTi)O) epitaxial film. Apart from a finding of a proportionality of the SOC to n, we have observed an intriguing temperature dependence of the SOC strength and the anisotropic magnetoresistance (MR) in the intermediate n region. These phenomena are associated with the temperature dependence of Landé g-factor and the change of the band structure, which is consistent with the result of density functional theory (DFT) calculation.
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http://dx.doi.org/10.1038/s41598-018-23967-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5893625PMC
April 2018

From Foldable Open Chains to Shape-Persistent Macrocycles: Synthesis, Impact on 2D Ordering, and Stimulated Self-Assembly.

J Am Chem Soc 2018 04 21;140(13):4726-4735. Epub 2018 Mar 21.

Department of Chemistry , Seoul National University , 1 Gwanak-ro, Gwanak-gu, Seoul 08826 , Korea.

Small molecule self-assembly at surfaces offers an efficient route to highly ordered organic films that can be programmed for a variety of chemical and electronic applications. The success of these materials depends on the ability to program intermolecular interactions to guide precise structural ordering. Toward this objective, we have designed and synthesized a series of bis(triazolo)benzene-based π-conjugated molecules. Our synthesis exploits a last-stage C-C cross-coupling reaction to close up zigzag-shaped linear precursors to cyclized products, so that direct side-by-side comparisons can be made for their structure-dependent self-assembly behavior at surfaces and response to external stimuli. Indeed, scanning tunneling microscopy (STM) analysis revealed distinct differences as the conformational flexibility of the molecular backbone and the chemical structure of the peripheral groups are varied. Specifically, alkyl chains adsorb and form interdigitated structures, whereas oligo ethylene glycol (OEG) chains remain desorbed and thus shift self-assembly to more densely packed π-conjugated cores. While the macrocycles self-assemble immediately and spontaneously, their linear precursors exhibit slower self-assembly kinetics, which could be attributed to the difference in the degree of conformational freedom. We also found that perturbation by the STM tip and the addition of cosolutes profoundly impacted the kinetics of self-assembly and surface patterning. This highly unusual behavior highlights the importance of noncovalent interactions that are inherently weak in solution but can be made strong for symmetric and conformationally restricted molecules confined within 2D surfaces.
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http://dx.doi.org/10.1021/jacs.8b01805DOI Listing
April 2018

Ezetimibe ameliorates steatohepatitis via AMP activated protein kinase-TFEB-mediated activation of autophagy and NLRP3 inflammasome inhibition.

Autophagy 2017 Oct 21;13(10):1767-1781. Epub 2017 Sep 21.

a Department of Internal Medicine , Yonsei University College of Medicine , Seoul , Korea.

Impairment in macroautophagy/autophagy flux and inflammasome activation are common characteristics of nonalcoholic steatohepatitis (NASH). Considering the lack of approved agents for treating NASH, drugs that can enhance autophagy and modulate inflammasome pathways may be beneficial. Here, we investigated the novel mechanism of ezetimibe, a widely prescribed drug for hypercholesterolemia, as a therapeutic option for ameliorating NASH. Human liver samples with steatosis and NASH were analyzed. For in vitro studies of autophagy and inflammasomes, primary mouse hepatocytes, human hepatoma cells, mouse embryonic fibroblasts with Ampk or Tsc2 knockout, and human or primary mouse macrophages were treated with ezetimibe and palmitate. Steatohepatitis and fibrosis were induced by feeding Atg7 wild-type, haploinsufficient, and knockout mice a methionine- and choline-deficient diet with ezetimibe (10 mg/kg) for 4 wk. Human livers with steatosis or NASH presented impaired autophagy with decreased nuclear TFEB and increased SQSTM1, MAP1LC3-II, and NLRP3 expression. Ezetimibe increased autophagy flux and concomitantly ameliorated lipid accumulation and apoptosis in palmitate-exposed hepatocytes. Ezetimibe induced AMPK phosphorylation and subsequent TFEB nuclear translocation, related to MAPK/ERK. In macrophages, ezetimibe blocked the NLRP3 inflammasome-IL1B pathway in an autophagy-dependent manner and modulated hepatocyte-macrophage interaction via extracellular vesicles. Ezetimibe attenuated lipid accumulation, inflammation, and fibrosis in liver-specific Atg7 wild-type and haploinsufficient mice, but not in knockout mice. Ezetimibe ameliorates steatohepatitis by autophagy induction through AMPK activation and TFEB nuclear translocation, related to an independent MTOR ameliorative effect and the MAPK/ERK pathway. Ezetimibe dampens NLRP3 inflammasome activation in macrophages by modulating autophagy and a hepatocyte-driven exosome pathway.
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http://dx.doi.org/10.1080/15548627.2017.1356977DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5640190PMC
October 2017

Ezetimibe, an NPC1L1 inhibitor, is a potent Nrf2 activator that protects mice from diet-induced nonalcoholic steatohepatitis.

Free Radic Biol Med 2016 10 12;99:520-532. Epub 2016 Sep 12.

Severance Biomedical Science Institute, Yonsei Biomedical Research Institute, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea. Electronic address:

Oxidative stress is important for the pathogenesis of nonalcoholic fatty liver disease (NAFLD), a chronic disease that ranges from hepatic steatosis to nonalcoholic steatohepatitis (NASH). The nuclear factor erythroid 2-related factor 2-Kelch-like ECH associated protein 1 (Nrf2-Keap1) pathway is essential for cytoprotection against oxidative stress. In this study, we found that oxidative stress or inflammatory biomarkers and TUNEL positive cells were markedly increased in NASH patients compared to normal or simple steatosis. In addition, we identified that the hepatic mRNA levels of Nrf2 target genes such as Nqo-1 and GSTA-1 were significantly increased in NASH patients. Ezetimibe, a drug approved by the Food and Drug Administration for the treatment of hypercholesterolemia, improves NAFLD and alleviates oxidative stress. However, the precise mechanism of its antioxidant function remains largely unknown. We now demonstrate that ezetimibe activates Nrf2-Keap1 pathway which was dependent of autophagy adaptor protein p62, without causing cytotoxicity. Ezetimibe activates AMP-activated protein kinase (AMPK), which in turn phosphorylates p62 (p-S351) via their direct interaction. Correspondingly, Ezetimibe protected liver cells from saturated fatty acid-induced apoptotic cell death through p62-dependent Nrf2 activation. Furthermore, its role as an Nrf2 activator was supported by methione- and choline- deficient (MCD) diet-induced NASH mouse model, showing that ezetimibe decreased the susceptibility of the liver to oxidative injury. These data demonstrate that the molecular mechanisms underlying ezetimibe's antioxidant role in the pathogenesis of NASH.
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http://dx.doi.org/10.1016/j.freeradbiomed.2016.09.009DOI Listing
October 2016

Multichromophoric π-Conjugation: Modular Design for Gated and Cascade Energy Transfer.

Chemistry 2016 May 24;22(19):6610-6. Epub 2016 Mar 24.

Department of Chemistry, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul, 08826, Korea.

Multichromophore arrays allow for cascade energy transfer. As an isoelectronic analogue of indacenyl, bis(triazolo)benzene features a fused tricyclic skeleton that rigidly places two π-extended triazoles in close proximity. Such triazole-based fluorophores behave as electronically independent modules in the ground states, but become tightly coupled upon photoexcitation for highly efficient excitation energy transfer (EET) that can be gated by external stimuli. Taking this donor-acceptor fluorophore system a step further, we have designed and implemented a cascade EET. Here, the initial excitation takes part in a circular relay to arrive at the longest-wavelength emitting site as the final destination. Modularly constructed triazoloarenes should serve as versatile platforms for chemically controlled optical signaling.
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http://dx.doi.org/10.1002/chem.201600318DOI Listing
May 2016

Resin bonding of metal brackets to glazed zirconia with a porcelain primer.

Korean J Orthod 2015 Nov 20;45(6):299-307. Epub 2015 Nov 20.

Department of Orthodontics, College of Dentistry, Yonsei University, Seoul, Korea. ; The Institute of Cranio-Facial Deformity, College of Dentistry, Yonsei University, Seoul, Korea.

Objective: The aims of this study were to compare the shear bond strength between orthodontic metal brackets and glazed zirconia using different types of primer before applying resin cement and to determine which primer was more effective.

Methods: Zirconia blocks were milled and embedded in acrylic resin and randomly assigned to one of four groups: nonglazed zirconia with sandblasting and zirconia primer (NZ); glazed zirconia with sandblasting, etching, and zirconia primer (GZ); glazed zirconia with sandblasting, etching, and porcelain primer (GP); and glazed zirconia with sandblasting, etching, zirconia primer, and porcelain primer (GZP). A stainless steel metal bracket was bonded to each target surface with resin cement, and all specimens underwent thermal cycling. The shear bond strength of the specimens was measured by a universal testing machine. A scanning electron microscope, three-dimensional optical surface-profiler, and stereoscopic microscope were used to image the zirconia surfaces. The data were analyzed with one-way analyses of variance and the Fisher exact test.

Results: Group GZ showed significantly lower shear bond strength than did the other groups. No statistically significant differences were found among groups NZ, GP, and GZP. All specimens in group GZ showed adhesive failure between the zirconia and resin cement. In groups NZ and GP, bonding failed at the interface between the resin cement and bracket base or showed complex adhesive and cohesive failure.

Conclusions: Porcelain primer is the more appropriate choice for bonding a metal bracket to the surface of a full-contour glazed zirconia crown with resin cement.
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http://dx.doi.org/10.4041/kjod.2015.45.6.299DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4664906PMC
November 2015

The regulation of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase by autophagy in low-glycolytic hepatocellular carcinoma cells.

Biochem Biophys Res Commun 2015 Jul 30;463(3):440-6. Epub 2015 May 30.

Department of Nuclear Medicine, Severance Hospital, Yonsei University College of Medicine, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-752, South Korea. Electronic address:

The glycolytic phenotype is a dominant metabolic phenomenon in cancer and is reflected in becoming aggressive. Certain hepatocellular carcinoma lack increased glycolysis and prefer to uptake acetate than glucose for metabolism. Autophagy plays a role in preserving energies and nutrients when there is limited external nutrient supply and maintains glucose level of blood though supporting gluconeogenesis in the liver. As the role of autophagy and gluconeogenesis in HCC following the glycolic activity was not clear, we cultured HCC cells with different glycolytic levels in Hank's balanced salt solution (HBSS) to induce autophagy and conducted the activity of gluconeogenesis. Both autophagy and gluconeogenesis were induced in low glycolytic HCC cells (HepG2). In glycolytic Hep3B cells, only autophagy without gluconeogenesis was induced upon starvation. When autophagy was blocked, the level of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) was reduced in HepG2 cells and not in Hep3B. Altogether, we investigated contribution of hepatic gluconeogenesis to the metabolic phenotype of HCC cells and the role of autophagy as a potential mechanism regulating gluconeogenesis in low glycolytic HCC.
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http://dx.doi.org/10.1016/j.bbrc.2015.05.103DOI Listing
July 2015