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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>

        • Chemically-Modulated Photoluminescence of Graphene Oxide for Selective Detection of Neurotransmitter by “Turn-On” Response

          Jeon, Su-Ji,Kwak, Seon-Yeong,Yim, DaBin,Ju, Jong-Min,Kim, Jong-Ho American Chemical Society 2014 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.136 No.31

          <P>Designing artificial nanomaterials capable of selectively detecting targets without the use of expensive and fragile antibodies is of great interest in the applications of nanomedicine. Here, we show that the photoluminescence (PL) of graphene oxide (GO) was chemically modulated for the selective detection of a neurotransmitter without the use of antibodies. GO was functionalized with nitrotriacetic acid (NTA) on which four different metal ions were chelated (M-NTA-GO), which led to its different PL responses to neurotransmitters. In particular, the Cu-NTA-GO hybrid was able to selectively detect norepinephrine at nanomolar concentrations in a simple manner via its “turn-on” PL. Moreover, it was successfully applied to the selective detection of norepinephrine secreted from living PC-12 cells.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2014/jacsat.2014.136.issue-31/ja504276z/production/images/medium/ja-2014-04276z_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja504276z'>ACS Electronic Supporting Info</A></P>

        • Fully Solution-Processed Transparent Conducting Oxide-Free Counter Electrodes for Dye-Sensitized Solar Cells: Spray-Coated Single-Wall Carbon Nanotube Thin Films Loaded with Chemically-Reduced Platinum Nanoparticles

          Kim, Sang Yong,Kim, Yesel,Lee, Kyung Moon,Yoon, Woo Sug,Lee, Ho Seok,Lee, Jong Tae,Kim, Seung-Joo,Ahn, Yeong Hwan,Park, Ji-Yong,Lee, Tai Kyu,Lee, Soonil American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.16

          <P>We report fully solution-processed fabrication of transparent conducting oxide-free counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) by combining spray-coating of single-wall carbon nanotubes (SWCNTs) and chemical reduction of chloroplatinic acid precursor to platinum nanoparticles (Pt NPs) with formic acid. The power conversion efficiency of a semitransparent DSSC with such SWCNT-based CE loaded with Pt NPs is comparable to that of a control device with a conventional CE. Quantification of Pt loading shows that network morphology of entangled SWCNTs is efficient in forming and retaining chemically reduced Pt NPs. Moreover, electron microscopy and electrochemical impedance spectroscopy results show that mainly Pt NPs, which are tens of nanometers in diameter and reside at the surface of SWCNT CEs, contribute to electrocatalytic activity for triiodide reduction, to which we attribute strong correlation between power conversion efficiency of DSSCs and time constant deduced from equivalent-circuit analysis of impedance spectra.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-16/am5019447/production/images/medium/am-2014-019447_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5019447'>ACS Electronic Supporting Info</A></P>

        • Versatile Processing of Metal-Organic Framework-Fluoropolymer Composite Inks with Chemical Resistance and Sensor Applications

          Kim, Jin-Oh,Kim, Jin Yeong,Lee, Jeong-Chan,Park, Steve,Moon, Hoi Ri,Kim, Dong-Pyo American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.4

          <P>We report a new class of metal-organic framework (MOF) inks with a water-repellent, photocurable fluoropolymer (PFPE) having up to 90 wt % MOF loading. These MOF inks are enabled to process various MOFs through spray coating, pen writing, stencil printing, and molding at room temperature. Upon UV curing, the hydrophobic PFPE matrix efficiently blocks water permeation but allows accessibility of chemicals into the MOF pores, thereby freeing the MOF to perform its unique function. Moreover, by introducing functional MOFs we successfully demonstrated a water-tolerant chemosensor for a class of aromatic pollutants in water and a chemical-resistant thermosensor for visualizing temperature image. This approach would open up innumerable opportunities for those MOFs that are otherwise dormant.</P> [FIG OMISSION]</BR>

        • Selective Activation of Methane on Single-Atom Catalyst of Rhodium Dispersed on Zirconia for Direct Conversion

          Kwon, Yongwoo,Kim, Tae Yong,Kwon, Gihun,Yi, Jongheop,Lee, Hyunjoo American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.48

          <P>Direct methane conversion into value-added products has become increasingly important. Because of inertness of methane, cleaving the first C–H bond has been very difficult, requiring high reaction temperature on the heterogeneous catalysts. Once the first C–H bond becomes activated, the remaining C–H bonds are successively dissociated on the metal surface, hindering the direct methane conversion into chemicals. Here, a single-atom Rh catalyst dispersed on ZrO<SUB>2</SUB> surface has been synthesized and used for selective activation of methane. The Rh single atomic nature was confirmed by extended X-ray fine structure analysis, electron microscopy images, and diffuse reflectance infrared Fourier transform spectroscopy. A model of the single-atom Rh/ZrO<SUB>2</SUB> catalyst was constructed by density functional theory calculations, and it was shown that CH<SUB>3</SUB> intermediates can be energetically stabilized on the single-atom catalyst. The direct conversion of methane was performed using H<SUB>2</SUB>O<SUB>2</SUB> in the aqueous solution or using O<SUB>2</SUB> in gas phase as oxidants. Whereas Rh nanoparticles produced CO<SUB>2</SUB> only, the single-atom Rh catalyst produced methanol in aqueous phase or ethane in gas phase.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2017/jacsat.2017.139.issue-48/jacs.7b11010/production/images/medium/ja-2017-11010p_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja7b11010'>ACS Electronic Supporting Info</A></P>

        • SCISCIESCOPUS

          Including Bioconcentration Kinetics for the Prioritization and Interpretation of Regulatory Aquatic Toxicity Tests of Highly Hydrophobic Chemicals

          Kwon, Jung-Hwan,Lee, So-Young,Kang, Hyun-Joong,Mayer, Philipp,Escher, Beate I. American Chemical Society 2016 Environmental science & technology Vol.50 No.21

          <P>Worldwide, regulations of chemicals require short-term toxicity data for evaluating hazards and risks of the chemicals. Current data requirements on the registration of chemicals are primarily based on tonnage and do not yet consider properties of chemicals. For example, short-term ecotoxicity data are required for chemicals with production volume greater than 1 or 10 ton/y according to REACH, without considering chemical properties. Highly hydrophobic chemicals are characterized by low water solubility and slow bioconcentration kinetics, which may hamper the interpretation of short-term toxicity experiments. In this work, internal concentrations of highly hydrophobic chemicals were predicted for standard acute ecotoxicity tests at three trophic levels, algae, invertebrate, and fish. As demonstrated by comparison with maximum aqueous concentrations at water solubility, chemicals with an octanolwater partition coefficient (Kow) greater than 106 are not expected to reach sufficiently high internal concentrations for exerting effects within the test duration of acute tests with fish and invertebrates, even though they might be intrinsically toxic. This toxicity cutoff was explained by the slow uptake, i.e., by kinetics, not by thermodynamic limitations. Predictions were confirmed by data entries of the OECDs screening information data set (SIDS) (n = 746), apart from a few exceptions concerning mainly organometallic substances and those with inconsistency between water solubility and Kow. Taking error propagation and model assumptions into account, we thus propose a revision of data requirements for highly hydrophobic chemicals with log Kow > 7.4: Short-term toxicity tests can be limited to algae that generally have the highest uptake rate constants, whereas the primary focus of the assessment should be on persistence, bioaccumulation, and long-term effects.</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>

        • Highly Sensitive, Simple, and Cost- and Time-Effective Method to Determine the Absolute Configuration of a Secondary Alcohol Using Competing Enantioselective Acylation Coupled with LC/MS

          Lee, Seoung Rak,Park, Hyun Bong,Kim, Ki Hyun American Chemical Society 2018 ANALYTICAL CHEMISTRY - Vol.90 No.22

          <P>The absolute-configuration determination of natural products and synthetic compounds with stereogenic centers is very important because stereoisomers dramatically and differentially affect many crucial properties, such as physical behaviors and biological functions. Despite several established methods for determining the absolute configuration, significant unmet needs for new methods still exist owing to the specific limitations of established methodologies. Here, we present a simple, optimized, new chemical-derivative method that utilizes competing enantioselective acylation followed by LC/MS analysis, and we demonstrate its successful application in determining the absolute configuration of a secondary alcohol in natural products with multiple reactive functional groups. This new development relies on the enantiomeric pair of homobenzotetramisole (HBTM) catalysts exhibiting adequate kinetic resolution for acylation of the secondary alcohol, and then the fast reaction was quantitatively confirmed via LC/MS as the characterization technique for the enantioselective transformations. Our new approach was successfully applied to determine the absolute configuration of one secondary alcohol in compound <B>1</B>, which has other hydroxyl groups to be reacted. The identified stereocenter of <B>1</B> was verified by previously established methods including quantum chemical electronic-circular-dichroism (ECD) calculations, computational NMR-chemical-shift calculations followed by DP4+ calculations, and modified Mosher’s method. In addition, our method was applied to five known naturally occurring compounds, which led to the successful verification of their absolute configurations. Our newly developed method using the HBTM catalyst provides a highly sensitive, simple, and cost- and time-effective approach and an applicable and convenient analytical method for determining the absolute configuration of one secondary alcohol in natural products.</P> [FIG OMISSION]</BR>

        • Achieving Selective and Efficient Electrocatalytic Activity for CO<sub>2</sub> Reduction Using Immobilized Silver Nanoparticles

          Kim, Cheonghee,Jeon, Hyo Sang,Eom, Taedaehyeong,Jee, Michael Shincheon,Kim, Hyungjun,Friend, Cynthia M.,Min, Byoung Koun,Hwang, Yun Jeong American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.43

          <P>Selective electrochemical reduction of CO<SUB>2</SUB> is one of the most sought-after processes because of the potential to convert a harmful greenhouse gas to a useful chemical. We have discovered that immobilized Ag nanoparticles supported on carbon exhibit enhanced Faradaic efficiency and a lower overpotential for selective reduction of CO<SUB>2</SUB> to CO. These electrocatalysts were synthesized directly on the carbon support by a facile one-pot method using a cysteamine anchoring agent resulting in controlled monodispersed particle sizes. These synthesized Ag/C electrodes showed improved activities, specifically decrease of the overpotential by 300 mV at 1 mA/cm<SUP>2</SUP>, and 4-fold enhanced CO Faradaic efficiency at −0.75 V vs RHE with the optimal particle size of 5 nm compared to polycrystalline Ag foil. DFT calculations enlightened that the specific interaction between Ag nanoparticle and the anchoring agents modified the catalyst surface to have a selectively higher affinity to the intermediate COOH over CO, which effectively lowers the overpotential.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-43/jacs.5b06568/production/images/medium/ja-2015-06568y_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b06568'>ACS Electronic Supporting Info</A></P>

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