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      • Chemically Activated Covalent Triazine Frameworks with Enhanced Textural Properties for High Capacity Gas Storage

        Lee, Yoon Jeong,Talapaneni, Siddulu Naidu,Coskun, Ali American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.36

        <P>Chemical activation of porous/nonporous materials to achieve high surface area sorbents with enhanced textural properties is a very promising strategy. The chemical activation using KOH, however, could lead to broad distribution of pores originating from the simultaneous pore deepening and widening pathways. Accordingly, establishing correlation between the chemical/textural properties of starting porous/nonporous materials and various pore formation mechanisms is quite critical to realize superior porosity and gas uptake properties. Here,, we show that the chemical and textural properties of starting porous organic polymers, that is, covalent triazine frameworks (CTF), have profound effect on the resulting porosity of the frameworks. The chemical activation of microporous CTF-1 using KOH at 700 degrees C enabled the preparation of chemically activated CTF-1, caCTF-1-700, which predominantly showed pore deepening, leading to an increased surface area of 2367 m(2) g(-1) and significantly enhanced gas adsorption properties with CO2 uptake capacities up to 6.0 mmol g(-1) at 1 bar and 1.45 mmol g(-1) at 0.15 bar and 273 K along with a isosteric heats of adsorption (Q(st)) of 30.6 kJ mol(-1). In addition, a remarkable H-2 uptake capacity of 2.46 and 1.66 wt % at 77 and 87 K, 1 bar along with the Q(st) value of 10.95 kJ mol-1 at zero coverage was also observed for the caCTF-1-700. Notably, the activation of mesoporous CTF-2 under the same conditions was accompanied by a decrease in its surface area and also in the conversion of mesopores into the micropores, thus leading to a pore deepening/narrowing rather than widening. We attributed this result to the presence of reactive weak spots, triazine moieties, for the chemical activation reaction within the CTF backbone. These results collectively suggest the critical role of chemical and pore characteristics of porous organic polymers in chemical activation to realize solid-sorbents for high capacity gas storage applications.</P>

      • Tetrathiafulvalene (TTF)-Annulated Calix[4]pyrroles: Chemically Switchable Systems with Encodable Allosteric Recognition and Logic Gate Functions

        Park, Jung Su,Sessler, Jonathan L. American Chemical Society 2018 Accounts of chemical research Vol.51 No.10

        <P><B>Conspectus</B></P><P>Molecular and supramolecular systems capable of switching between two or more states as the result of an applied chemical stimulus are attracting ever-increasing attention. They have seen wide application in the development of functional materials including, but not limited to, molecular and supramolecular switches, chemosensors, electronics, optoelectronics, and logic gates. A wide range of chemical stimuli have been used to control the switching within bi- and multiple state systems made up from either singular molecular entities or supramolecular ensembles. In general, chemically triggered switching systems contain at least two major functional components that provide for molecular recognition and signal transduction, respectively. These components can be connected to one another via either covalent or noncovalent linkages.</P><P>Of particular interest are switchable systems displaying cooperative or allosteric features. Such advanced control over function is ubiquitous in nature and, in the case of synthetic systems, may allow the capture and release of a targeted chemical entity or permit the transduction of binding information from one recognition site to another. Allosterically controlled complexation and decomplexation could also permit the amplification or deamplification of analyte-specific binding affinity, lead to nonlinear binding characteristics, or permit a magnification of output signals.</P><P>Our own efforts to develop chemically driven supramolecular switches, advanced logic gates, and multifunction cascade systems have focused on the use of tetrathiafulvalene (TTF) annulated calix[4]pyrroles (C4Ps). These systems, TTF-C4Ps, combine several orthogonal binding motifs within what are conformationally switchable receptor frameworks. Their basic structure and host-guest recognition functions can be controlled via application of an appropriate chemical stimulus. Homotropic or heterotropic allosteric molecular recognition behavior is often seen. This has allowed us to (1) produce self-assembled structures, (2) control switching between bi- and multistate constructs, (3) generate chemical logic gates performing chemical-based Boolean logic operations, (4) create ionically controlled three-state logic systems that release different chemical messengers and activate disparate downstream reactions, and (5) encode a variety advanced functional operations into what are relatively simple molecular-scale devices.</P><P>Looking to the future, we believe that exploiting allosteric control will expand opportunities for supramolecular chemists and allow some of the complexity seen in biology to be reproduced in simple constructs. Of particular appeal would be a capacity to release chemical messengers at will, perhaps after a prior capture and chemical modification step, that then encode for further downstream functions as seen in the case of the small molecules, such as neurotransmitters and pheromones, used by nature for the purpose of intraentity communication. Molecular scale logic devices with allosteric functions are thus the potential vanguard of a new area of study involving interactions between multiple discrete components with an emphasis on functional outcomes.</P> [FIG OMISSION]</BR>

      • Coal Chemical Looping Gasification for Syngas Generation Using an Iron-Based Oxygen Carrier

        Guo, Qingjie,Cheng, Yu,Liu, Yongzhuo,Jia, Weihua,Ryu, Ho-Jung American Chemical Society 2014 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.53 No.1

        <P>The chemical-looping gasification (CLG) of coal is a clean and effective technology for syngas generation. Sharing principles with chemical-looping combustion (CLC), CLG also uses oxygen carriers to transfer lattice oxygen to the fuel. Investigations into CLG with different O/C ratios are carried out in a fluidized bed reactor with steam used as the gasification–fluidization medium. The effect of the active component content of the oxygen carrier on the gas selectivity is performed, and reaction mechanisms between the Fe<SUB>2</SUB>O<SUB>3</SUB> oxygen carrier and coal with steam as the gasification agent are discussed. Moreover, we also assessed the reactivity of the CaO-decorated iron-based oxygen carrier particles in multicycle reactions. The carbon conversion efficiency is increased from 55.74 to 81% with increasing O/C ratio, whereas the content of H<SUB>2</SUB> first decreases and then increases. The addition of CaO can increase the carbon conversion efficiency and the gasification rate substantially and reduce the generation rate of H<SUB>2</SUB>S from 1.89 × 10<SUP>–3</SUP> to 0.156 × 10<SUP>–3</SUP> min<SUP>–1</SUP>. Furthermore, X-ray diffraction (XRD) images indicate that the CaO-decorated iron-based oxygen carrier particles were completely regenerated after six redox cycles. Finally, the peak fitting of gasification reaction rate curves is used to explore the reaction mechanism between coal char and the CaO-decorated iron-based oxygen carrier, indicating that the reactions in the CLG include three stages: the complex reactions involved an oxygen carrier, coal char, and steam; the gasification of coal char; and the reduction of Fe<SUB>3</SUB>O<SUB>4</SUB> to FeO. The two-segment modified random pore model (MRPM) fits the experiment data well.</P>

      • Development of a Highly Visual, Simple, and Rapid Test for the Discovery of Novel Insulin Mimetics in Living Vertebrates

        Lee, Jinho,Jung, Da-Woon,Kim, Woong-Hee,Um, Jung-In,Yim, Soon-Ho,Oh, Won Keun,Williams, Darren R. American Chemical Society 2013 ACS CHEMICAL BIOLOGY Vol.8 No.8

        <P>Diabetes mellitus is a global epidemic with major impacts on human health and society. Drug discovery for diabetes can be facilitated by the development of a rapid, vertebrate-based screen for identifying new insulin mimetic compounds. Our study describes the first development of a zebrafish-based system based on direct monitoring of glucose flux and validated for identifying novel anti-diabetic drugs. Our system utilizes a fluorescent-tagged glucose probe in an experimentally convenient 96-well plate format. To validate our new system, we identified compounds that can induce glucose uptake via activity-guided fractionation of the inner shell from the Japanese Chestnut (<I>Castanea crenata</I>). The best performing compound, UP3.2, was identified as fraxidin and validated as a novel insulin mimetic using a mammalian adipocyte system. Additional screening using sets of saponin- and triazine-based compounds was undertaken to further validate this assay, which led to the discovery of triazine PP-II-A03 as a novel insulin mimetic. Moreover, we demonstrate that our zebrafish-based system allows concomitant toxicological analysis of anti-diabetic drug candidates. Thus, we have developed a rapid and inexpensive vertebrate model that can enhance diabetes drug discovery by preselecting hits from chemical library screens, before testing in relatively expensive rodent assays.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/acbcct/2013/acbcct.2013.8.issue-8/cb4000162/production/images/medium/cb-2013-000162_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cb4000162'>ACS Electronic Supporting Info</A></P>


        Photon-Triggered Current Generation in Chemically-Synthesized Silicon Nanowires

        Kim, Jungkil,Kim, Ha-Reem,Lee, Hoo-Cheol,Kim, Kyoung-Ho,Hwang, Min-Soo,Lee, Jung Min,Jeong, Kwang-Yong,Park, Hong-Gyu American Chemical Society 2019 NANO LETTERS Vol.19 No.2

        <P>A porous Si segment in a Si nanowire (NW), when exposed to light, generates a current with a high on/off ratio. This unique feature has been recently used to demonstrate photon-triggered NW devices including transistors, logic gates, and photodetection systems. Here, we develop a reliable and simple procedure to fabricate porous Si segments in chemically synthesized Si NWs for photon-triggered current generation. To achieve this, we employ 100 nm-diameter chemical-vapor-deposition grown Si NWs that possess an n-type high doping level and extremely smooth surface. The NW regions uncovered by electron-beam resist become selectively porous through metal-assisted chemical etching, using Ag nanoparticles as a catalyst. The contact electrodes are then fabricated on both ends of such NWs, and the generated current is measured when the laser is focused on the porous Si segment. The current level is changed by controlling the power of the incident laser and bias voltage. The on/off ratio is measured up to 1.5 × 10<SUP>4</SUP> at a forward bias of 5 V. In addition, we investigate the porous-length-dependent responsivity of the NW device with the porous Si segment. The responsivity is observed to decrease for porous segment lengths beyond 360 nm. Furthermore, we fabricate nine porous Si segments in a single Si NW and measure the identical photon-triggered current from each porous segment; this single NW device can function as a high-resolution photodetection system. Therefore, our fabrication method to precisely control the position and length of the porous Si segments opens up new possibilities for the practical implementation of programmable logic gates and ultrasensitive photodetectors.</P> [FIG OMISSION]</BR>

      • Enzyme-Inspired Formulation of the Electrolyte for Stable and Efficient Vanadium Redox Flow Batteries at High Temperatures

        Abbas, Saleem,Hwang, Jinyeon,Kim, Heejin,Chae, Seen Ae,Kim, Ji Won,Mehboob, Sheeraz,Ahn, Ahreum,Han, Oc Hee,Ha, Heung Yong American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.30

        <P>Histidine, inspired by vanadium bromoperoxidase enzyme, has been applied as a homogeneous electrocatalyst to the positive electrolyte of vanadium redox flow battery (VRFB) to improve the performance and stability of VRFB at elevated temperatures. The histidine-containing electrolyte is found to significantly improve the performance of VRFB in terms of thermal stability estimated by the remaining amount of VO<SUB>2</SUB><SUP>+</SUP> in the electrolyte (61 vs 43% of a pristine one), energy efficiency at a high current density of 150 mA cm<SUP>-2</SUP> (78.7 vs 71.2%), and capacity retention (73.2 vs 27.7%) at 60 °C. The mechanism of the catalytic functions of histidine with the chemical species in the electrolyte has been investigated for the first time by multinuclear NMR spectroscopy and first-principles calculations. The analyzed data reveal that histidine improves the kinetics of both charge and discharge reactions through different affinity toward the reactants and products as well as suppresses the precipitation of VO<SUB>2</SUB><SUP>+</SUP> by impeding the polymerization of vanadium ions. These findings are in good agreement with the improved chemical and electrochemical performance of the histidine-containing VRFB. Our results show a new type of chemical/electrochemical mechanism in the improved redox flow battery performance that may be essential in a new research arena for better performance of electrochemical systems.</P> [FIG OMISSION]</BR>

      • Chemical Doping Effects in Multilayer MoS<sub>2</sub> and Its Application in Complementary Inverter

        Yoo, Hocheon,Hong, Seongin,On, Sungmin,Ahn, Hyungju,Lee, Han-Koo,Hong, Young Ki,Kim, Sunkook,Kim, Jae-Joon American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.27

        <P>Multilayer MoS<SUB>2</SUB> has been gaining interest as a new semiconducting material for flexible displays, memory devices, chemical/biosensors, and photodetectors. However, conventional multilayer MoS<SUB>2</SUB> devices have exhibited limited performances due to the Schottky barrier and defects. Here, we demonstrate poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) doping effects in multilayer MoS<SUB>2</SUB>, which results in improved electrical characteristics (∼4.6× higher on-current compared to the baseline and a high current on/off ratio of 10<SUP>6</SUP>). Synchrotron-based study using X-ray photoelectron spectroscopy and grazing incidence wide-angle X-ray diffraction provides mechanisms that align the edge-on crystallites (97.5%) of the PDPP3T as well as a larger interaction with MoS<SUB>2</SUB> that leads to dipole and charge transfer effects (at annealing temperature of 300 °C), which support the observed enhancement of the electrical characteristics. Furthermore, we demonstrate a complementary metal-oxide-semiconductor inverter that uses a p-type MoSe<SUB>2</SUB> and a PDPP3T-doped MoS<SUB>2</SUB> as charging and discharging channels, respectively.</P> [FIG OMISSION]</BR>

      • Room-Temperature, Ambient-Pressure Chemical Synthesis of Amine-Functionalized Hierarchical Carbon–Sulfur Composites for Lithium–Sulfur Battery Cathodes

        Chae, Changju,Kim, Jinmin,Kim, Ju Young,Ji, Seulgi,Lee, Sun Sook,Kang, Yongku,Choi, Youngmin,Suk, Jungdon,Jeong, Sunho American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.5

        <P>Recently, the achievement of newly designed carbon-sulfur composite materials has attracted a tremendous amount of attention as high-performance cathode materials for lithium-sulfur batteries. To date, sulfur materials have been generally synthesized by a sublimation technique in sealed containers. This is a well-developed technique for the synthesizing of well-ordered sulfur materials, but it is limited when used to scale up synthetic procedures for practical applications. In this study, we suggest an easily scalable, room-temperature/ambient-pressure chemical pathway for the synthesis of highly functioning cathode materials using electrostatically assembled, amine-terminated carbon materials. It is demonstrated that stable cycling performance outcomes are achievable with a capacity of 730 mAhg(-1) at a current density of 1 C with good cycling stability by a virtue of the characteristic chemical/physical properties (a high conductivity for efficient charge conduction and the presence of a number of amine groups that can interact with sulfur atoms during electrochemical reactions) of composite materials. The critical roles of conductive carbon moieties and amine functional groups inside composite materials are clarified with combinatorial analyses by X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy.</P>

      • Mechanistic Insights into Tunable Metal-Mediated Hydrolysis of Amyloid-β Peptides

        Derrick, Jeffrey S.,Lee, Jiwan,Lee, Shin Jung C.,Kim, Yujeong,Nam, Eunju,Tak, Hyeonwoo,Kang, Juhye,Lee, Misun,Kim, Sun Hee,Park, Kiyoung,Cho, Jaeheung,Lim, Mi Hee American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.6

        <P>An amyloidogenic peptide, amyloid-beta (A beta), has been implicated as a contributor to the neurotoxicity of Alzheimer's disease (AD) that continues to present a major socioeconomic burden for our society. Recently, the use of metal complexes capable of cleaving peptides has arisen as an efficient tactic for amyloid management; unfortunately, little has been reported to pursue this strategy. Herein, we report a novel approach to validate the hydrolytic cleavage of divalent metal complexes toward two major isoforms of A beta (A beta(40) and A beta(42)) and tune their proteolytic activity based on the choice of metal centers (M = Co, Ni, Cu, and Zn) which could be correlated to their anti-amyloidogenic properties. Such metal-dependent tunability was facilitated employing a tetra-N-methylated cyclam (TMC) ligand that imparts unique geometric and stereochemical control, which has not been available in previous systems. Co(II)(TMC) was identified to noticeably cleave A beta peptides and control their aggregation, reporting the first Co(II) complex for such reactivities to the best of our knowledge. Through detailed mechanistic investigations by biochemical, spectroscopic, mass spectrometric, and computational studies, the critical importance of the coordination environment and acidity of the aqua-bound complexes in promoting amide hydrolysis was verified. The biological applicability, of Co(II)(TMC) was also illustrated via its potential blood-brain barrier permeability, relatively low cytotoxicity, regulatory capability against toxicity induced by both A beta(40) and A beta(42) in living cells, proteolytic activity with A beta peptides under biologically relevant conditions, and inertness toward cleavage of structured proteins. Overall,, our approaches and findings on reactivities of divalent metal complexes toward Afi, along with the mechanistic insights, demonstrate the feasibility of utilizing such metal complexes for amyloid control.</P>

      • A Photocatalyst–Enzyme Coupled Artificial Photosynthesis System for Solar Energy in Production of Formic Acid from CO<sub>2</sub>

        Yadav, Rajesh K.,Baeg, Jin-Ook,Oh, Gyu Hwan,Park, No-Joong,Kong, Ki-jeong,Kim, Jinheung,Hwang, Dong Won,Biswas, Soumya K. American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.28

        <P>The photocatalyst–enzyme coupled system for artificial photosynthesis process is one of the most promising methods of solar energy conversion for the synthesis of organic chemicals or fuel. Here we report the synthesis of a novel graphene-based visible light active photocatalyst which covalently bonded the chromophore, such as multianthraquinone substituted porphyrin with the chemically converted graphene as a photocatalyst of the artificial photosynthesis system for an efficient photosynthetic production of formic acid from CO<SUB>2</SUB>. The results not only show a benchmark example of the graphene-based material used as a photocatalyst in general artificial photosynthesis but also the benchmark example of the selective production system of solar chemicals/solar fuel directly from CO<SUB>2</SUB>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-28/ja3009902/production/images/medium/ja-2012-009902_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja3009902'>ACS Electronic Supporting Info</A></P>

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