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        • 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 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>

        • Graphene-Assisted Chemical Etching of Silicon Using Anodic Aluminum Oxides as Patterning Templates

          Kim, Jungkil,Lee, Dae Hun,Kim, Ju Hwan,Choi, Suk-Ho American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.43

          <P>We first report graphene-assisted chemical etching (GaCE) of silicon by using patterned graphene as an etching catalyst. Chemical-vapor-deposition-grown graphene transferred on a silicon substrate is patterned to a mesh with nanohole arrays by oxygen plasma etching using an anodic- aluminum-oxide etching mask. The prepared graphene mesh/silicon is immersed in a mixture solution of hydrofluoric acid and hydro peroxide with various molecular fractions at optimized temperatures. The silicon underneath graphene mesh is then selectively etched to form aligned nanopillar arrays. The morphology of the nanostructured silicon can be controlled to be smooth or porous depending on the etching conditions. The experimental results are systematically discussed based on possible mechanisms for GaCE of Si.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-43/acsami.5b07773/production/images/medium/am-2015-077734_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b07773'>ACS Electronic Supporting Info</A></P>

        • Novel Flexible Transparent Conductive Films with Enhanced Chemical and Electromechanical Sustainability: TiO<sub>2</sub> Nanosheet–Ag Nanowire Hybrid

          Sohn, Hiesang,Kim, Seyun,Shin, Weonho,Lee, Jong Min,Lee, Hyangsook,Yun, Dong-Jin,Moon, Kyoung-Seok,Han, In Taek,Kwak, Chan,Hwang, Seong-Ju American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.3

          <P>Flexible transparent conductive films (TCFs) of TiO2 nanosheet (TiO2 NS) and silver nanowire (Ag NW) network hybrid were prepared through a simple and scalable solution-based process. The as-formed TiO2 NS-Ag NW hybrid TCF shows a high optical transmittance (TT: 97% (90.2% including plastic substrate)) and low sheet resistance (R-s: 40 Omega/sq). In addition, the TiO2 NS Ag NW hybrid TCF exhibits a long-time chemical/aging and electromechanical stability. As for the chemical/aging stability, the hybrid TCF of Ag NW and TiO2 NS reveals a retained initial conductivity (Delta R-S/R-S < 1%) under ambient oxidant gas over a month, superior to that of bare Ag NW (Delta R-s/R-s > 4000%) or RuO2 NS Ag NW hybrid (Delta R-s/R-s > 200%). As corroborated by the density functional theory simulation, the superb chemical stability of TiO2 NS-Ag NW hybrid is attributable to the unique role of TiO2 NS as a barrier, which prevents Ag NW's chemical corrosion via the attenuated adsorption of sulfidation molecules (H2S) on TiO2 NS. With respect to the electromechanical stability, in contrast to Ag NWS (Delta R/R-0 similar to 152.9%), our hybrid TCF shows a limited increment of fractional resistivity (Delta R/R-0 similar to 14.4%) after 200 000 cycles of the 1R bending test (strain: 6.7%) owing to mechanically welded Ag NW networks by TiO2 NS. Overall, our unique hybrid of TiO2 NS and Ag NW exhibits excellent electrical/optical properties and reliable chemical/electromechanical stabilities.</P>

        • 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>

        • 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>

        • 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>

        • Embedding Covalency into Metal Catalysts for Efficient Electrochemical Conversion of CO<sub>2</sub>

          Lim, Hyung-Kyu,Shin, Hyeyoung,Goddard, William A.,Hwang, Yun Jeong,Min, Byoung Koun,Kim, Hyungjun American Chemical Society 2014 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.136 No.32

          <P>CO<SUB>2</SUB> conversion is an essential technology to develop a sustainable carbon economy for the present and the future. Many studies have focused extensively on the electrochemical conversion of CO<SUB>2</SUB> into various useful chemicals. However, there is not yet a solution of sufficiently high enough efficiency and stability to demonstrate practical applicability. In this work, we use first-principles-based high-throughput screening to propose silver-based catalysts for efficient electrochemical reduction of CO<SUB>2</SUB> to CO while decreasing the overpotential by 0.4–0.5 V. We discovered the covalency-aided electrochemical reaction (CAER) mechanism in which <I>p</I>-block dopants have a major effect on the modulating reaction energetics by imposing partial covalency into the metal catalysts, thereby enhancing their catalytic activity well beyond modulations arising from <I>d</I>-<I>block</I> dopants. In particular, sulfur or arsenic doping can effectively minimize the overpotential with good structural and electrochemical stability. We expect this work to provide useful insights to guide the development of a feasible strategy to overcome the limitations of current technology for electrochemical CO<SUB>2</SUB> conversion.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2014/jacsat.2014.136.issue-32/ja503782w/production/images/medium/ja-2014-03782w_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja503782w'>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>

        • Nano-Storage Wires

          Lee, Dong Jun,Kim, Eunji,Kim, Daesan,Park, Juhun,Hong, Seunghun American Chemical Society 2013 ACS NANO Vol.7 No.8

          <P>We report the development of “nano-storage wires” (NSWs), which can store chemical species and release them at a desired moment <I>via</I> external electrical stimuli. Here, using the electrodeposition process through an anodized aluminum oxide template, we fabricated multisegmented nanowires composed of a polypyrrole segment containing adenosine triphosphate (ATP) molecules, a ferromagnetic nickel segment, and a conductive gold segment. Upon the application of a negative bias voltage, the NSWs released ATP molecules for the control of motor protein activities. Furthermore, NSWs can be printed onto various substrates including flexible or three-dimensional structured substrates by direct writing or magnetic manipulation strategies to build versatile chemical storage devices. Since our strategy provides a means to store and release chemical species in a controlled manner, it should open up various applications such as drug delivery systems and biochips for the controlled release of chemicals.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-8/nn402082v/production/images/medium/nn-2013-02082v_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn402082v'>ACS Electronic Supporting Info</A></P>

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