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Choi, Kyung Min,Kim, Dohyung,Rungtaweevoranit, Bunyarat,Trickett, Christopher A.,Barmanbek, Jesika Trese Deniz,Alshammari, Ahmad S.,Yang, Peidong,Yaghi, Omar M. American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.1
<P>Materials development for artificial photosynthesis, in particular, CO2 reduction, has been under extensive efforts, ranging from inorganic semiconductors to molecular complexes. In this report, we demonstrate a metal organic framework (MOF)-coated nanoparticle photocatalyst with enhanced CO2 reduction activity and stability, which stems from having two different functional units for activity enhancement and catalytic stability combined together as a single construct. Covalently attaching a CO2-to-CO conversion photocatalyst Re-I(CO)(3)(BPYDC)Cl, BPYDC = 2,2'-bipyridine-5,5'-dicarboxylate, to a zirconium MOF, UiO-67 (Re-n-MOF), prevents dimerization leading to deactivation. By systematically controlling its density in the framework (n = 0, 1, 2, 3, 5, 11, 16, and 24 complexes per unit cell), the highest photocatalytic activity was found for Re-3-MOF. Structural analysis of Re-MOFs suggests that a fine balance of proximity between photoactive centers is needed for cooperatively enhanced photocatalytic activity, where an optimum number of Re complexes per unit cell should reach the highest activity. Based on the structure-activity correlation of Ren-M0Fs, Rea-MOF was coated onto Ag nanocubes (AgCRe3-MOF), which spatially confined photoactive Re centers to the intensified near-surface electric fields at the surface of Ag nanocubes, resulting in a 7-fold enhancement of CO2-to-CO conversion under visible light with long-term stability maintained up to 48 h.</P>
Overcoming the Diffraction Limit Using Multiple Light Scattering in a Highly Disordered Medium
Choi, Youngwoon,Yang, Taeseok Daniel,Fang-Yen, Christopher,Kang, Pilsung,Lee, Kyoung Jin,Dasari, Ramachandra R.,Feld, Michael S.,Choi, Wonshik American Physical Society 2011 Physical review letters Vol.107 No.2
Zipf’s Law Distributions in Korean Financial Markets
윤성민,K. H. Chang,김경식,C. Christopher Lee,J.S. Choi 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.1
We investigate the rank distribution and the cumulative probability for stock prices, and the probability density of price returns for stocks traded the Korean Stock Exchange (KSE) and the Korean Securities Dealers Automated Quotations (KOSDAQ) market. We show that the upper tails of the distributions can be fitted with a power-law and find that the rank distribution scales approximately as a power law with exponents = −0.99 (p !small) and −1.33 (p !large) for the KSE and = −1.31 for the KOSDAQ. These values are similar to those of stock prices traded on the Tokyo Stock Exchange (TSE). In addition, the cumulative probability distribution follows a power law with the scaling exponent = −1.23 (KSE) or −1.45 (KOSDAQ). In particular, the evidence shows that the probability density of normalized price returns for two kinds of assets almost has the form of an exponential function, which is similar to the result for the TSE and the New York Stock Exchange (NYSE).
Investigations on recyclisation and hydrolysis in avibactam mediated serine β-lactamase inhibition
Choi, Hwanho,Paton, Robert S.,Park, Hwangseo,Schofield, Christopher J. Royal Society of Chemistry 2016 Organic & biomolecular chemistry Vol.14 No.17
<▼1><P>In contrast to the β-lactams, which react irreversibly, avibactam reacts reversibly with serine β-lactamases.</P></▼1><▼2><P>β-Lactams inhibit penicillin-binding proteins (PBPs) and serine β-lactamases by acylation of a nucleophilic active site serine. Avibactam is approved for clinical use in combination with ceftazidime, and is a breakthrough non β-lactam β-lactamase inhibitor also reacting <I>via</I> serine acylation. Molecular dynamics (MD) and quantum chemical calculations on avibactam-mediated inhibition of a clinically relevant cephalosporinase reveal that recyclisation of the avibactam derived carbamoyl complex is favoured over hydrolysis. In contrast, we show that analogous recyclisation in β-lactam mediated inhibition is disfavoured. Avibactam recyclisation is promoted by a proton shuttle, a ‘structural’ water protonating the nucleophilic serine, and stabilization of the negative charge developed on aminocarbonyl oxygen. The results imply the potential of calculations for distinguishing between bifurcating pathways during inhibition and in generating hypotheses for predicting resistance. The inability of β-lactams to undergo recyclisation may be an Achilles heel, but one that can be addressed by suitably functionalized reversibly binding inhibitors.</P></▼2>
High-speed synthetic aperture microscopy for live cell imaging.
Kim, Moonseok,Choi, Youngwoon,Fang-Yen, Christopher,Sung, Yongjin,Dasari, Ramachandra R,Feld, Michael S,Choi, Wonshik Optical Society of America 2011 Optics letters Vol.36 No.2
<P>We present a high-speed synthetic aperture microscopy for quantitative phase imaging of live biological cells. We measure 361 complex amplitude images of an object with various directions of illumination covering an NA of 0.8 in less than one-thirteenth of a second and then combine the images with a phase-referencing method to create a synthesized phase image. Because of the increased depth selectivity, artifacts from diffraction that are typically present in coherent imaging are significantly suppressed, and lateral resolution of phase imaging is improved. We use the instrument to demonstrate high-quality phase imaging of live cells, both static and dynamic, and thickness measurements of a nanoscale cholesterol helical ribbon.</P>
Video-rate tomographic phase microscopy.
Fang-Yen, Christopher,Choi, Wonshik,Sung, Yongjin,Holbrow, Charles J,Dasari, Ramachandra R,Feld, Michael S SPIE--the International Society for Optical Engine 2011 JOURNAL OF BIOMEDICAL OPTICS Vol.16 No.1
<P>Tomographic phase microscopy measures the 3-D refractive index distribution of cells and tissues by combining the information from a series of angle-dependent interferometric phase images. In the original device, the frame rate was limited to 0.1 frames per second (fps) by the technique used to acquire phase images, preventing measurements of moving or rapidly changing samples. We describe an improved tomographic phase microscope in which phase images are acquired via a spatial fringe pattern demodulation method, enabling a full tomogram acquisition rate of 30 fps. In addition, in this system the refractive index is calculated by a diffraction tomography algorithm that accounts for the effects of diffraction in the 3-D reconstruction. We use the instrument to quantitatively monitor rapid changes in refractive index within defined subregions of cells due to exposure to acetic acid or changes in medium osmolarity.</P>
First-principles investigation of wet-chemical routes for the hydrogenation of graphene
Horbatenko, Yevhen,Choi, Min,Ruoff, Rodney S.,Bielawski, Christopher W.,Park, Noejung Elsevier 2015 Carbon Vol.93 No.-
<P><B>Abstract</B></P> <P>To investigate the microscopic mechanism for the wet-chemical hydrogenation of graphene, first principles density functional calculations were performed for the hydrogen transfer reaction between the graphene surface and a mixture of hydrogen carrier and electron donor. For the hydrogen transfer from CH<SUB>3</SUB>OH to graphene, as commonly used in Birch-type reductions, the presence of alkali atoms is important not only because they donate electrons but also stabilize the CH<SUB>3</SUB>O<SUP>−</SUP>. On the other hand, when a hydrogen carrier becomes charge neutral after the transfer, as for the case of CH<SUB>3</SUB>NH<SUB>3</SUB> <SUP>+</SUP>, the presence of alkali atoms is not essential, and the supply of electrons from an external source can lead to as favorable thermodynamics as that of alkali atoms. We suggest that, based on these results, a potentially more efficient experimental procedure can be designed.</P>
Analyzing Somatic Genome Rearrangements in Human Cancers by Using Whole-Exome Sequencing
Yang, L.,Lee, M.S.,Lu, H.,Oh, D.Y.,Kim, Y.,Park, D.,Park, G.,Ren, X.,Bristow, Christopher A.,Haseley, Psalm S.,Lee, S.,Pantazi, A.,Kucherlapati, R.,Park, W.Y.,Scott, Kenneth L.,Choi, Y.L.,Park, Peter University of Chicago Press [etc.] 2016 American journal of human genetics Vol.98 No.5
<P>Although exome sequencing data are generated primarily to detect single-nucleotide variants and indels, they can also be used to identify a subset of genomic rearrangements whose breakpoints are located in or near exons. Using >4,600 tumor and normal pairs across 15 cancer types, we identified over 9,000 high confidence somatic rearrangements, including a large number of gene fusions. We find that the 50 fusion partners of functional fusions are often housekeeping genes, whereas the 30 fusion partners are enriched in tyrosine kinases. We establish the oncogenic potential of ROR1-DNAJC6 and CEP85L-ROS1 fusions by showing that they can promote cell proliferation in vitro and tumor formation in vivo. Furthermore, we found that similar to 4% of the samples have massively rearranged chromosomes, many of which are associated with upregulation of oncogenes such as ERBB2 and TERT. Although the sensitivity of detecting structural alterations from exomes is considerably lower than that from whole genomes, this approach will be fruitful for the multitude of exomes that have been and will be generated, both in cancer and in other diseases.</P>