Recent Submissions

  • Assessing the Range of Validity of Current Tube Models through Analysis of a Comprehensive Set of Star–Linear 1,4-Polybutadiene Polymer Blends

    Hall, Ryan; Desai, Priyanka S.; Kang, Beom-Goo; Huang, Qifan; Lee, Sanghoon; Chang, Taihyun; Venerus, David C.; Mays, Jimmy; Ntetsikas, Konstantinos; Polymeropoulos, George; Hadjichristidis, Nikolaos; Larson, Ronald G. (Macromolecules, American Chemical Society (ACS), 2019-10-10) [Article]
    We blend newly synthesized nearly monodisperse four-arm star 1,4-polybutadienes with various well-entangled linear polymers, confirming the conclusions in Desai et al. [ Macromolecules201649 (13)49644977] that advanced tube models, namely, the hierarchical 3.0 and branch-on-branch models [Wang, Z.; J. Rheol.201054 (2)223260], fail to predict the linear rheological data when the pure linear polymers have shorter relaxation times, but within 3–4 orders of magnitude of the star polymer. However, when the linear polymer has a longer relaxation time than the star, our new work, surprisingly, finds that non-monotonic dependence of terminal relaxation behavior on composition is both observed experimentally and captured by the models. Combined with previous data from the literature, we present results from over 50 1,4-polybutadiene star–linear blends, suitable for thorough testing of rheological models of entangled polymers.
  • New Insight on the Role of Electrolyte Additives in Rechargeable Lithium Ion Batteries

    Ming, Jun; Cao, Zhen; Wu, Yingqiang; Wahyudi, Wandi; Wang, Wenxi; Guo, Xianrong; Cavallo, Luigi; Hwang, Jang-Yeon; Shamim, Atif; Li, Lain-Jong; Sun, Yang-Kook; Alshareef, Husam N. (ACS Energy Letters, American Chemical Society (ACS), 2019-10-08) [Article]
    Solid electrolyte interphase (SEI)-forming agents such as vinylene carbonate, sulfone, and cyclic sulfate are commonly believed to be film-forming additives in lithium-ion batteries that help to enhance graphite anode stability. However, we find that the film-forming effect and the resultant SEI may not be the only reasons for the enhanced graphite stability. This is because the as-formed SEI cannot inhibit Li+–solvent co-intercalation once the additive is removed from the electrolyte. Instead, we show that the Li+ solvation structure, which is modified by these additives, plays a critical role in achieving reversible Li+ (de)intercalation within graphite. This discovery is confirmed in both carbonate and ether-based electrolytes. We show that the problem of graphite exfoliation caused by Li+–solvent co-intercalation can be mitigated by adding ethene sulfate to tune the Li+ coordination structure. This work brings new insight into the role of additives in electrolytes, expanding the prevailing thinking over the past 2 decades. In addition, this finding can guide the design of more versatile electrolytes for advanced rechargeable metal-ion batteries.
  • Ultralong cycle stability of aqueous zinc-ion batteries with zinc vanadium oxide cathodes

    Wang, Lulu; Huang, Kuo-Wei; Chen, Jitao; Zheng, Junrong (Science Advances, American Association for the Advancement of Science (AAAS), 2019-10-04) [Article]
    Rechargeable aqueous zinc-ion batteries are promising candidates for large-scale energy storage but are plagued by the lack of cathode materials with both excellent rate capability and adequate cycle life span. We overcome this barrier by designing a novel hierarchically porous structure of Zn-vanadium oxide material. This Zn0.3V2O5·1.5H2O cathode delivers a high specific capacity of 426 mA·h g−1 at 0.2 A g−1 and exhibits an unprecedented superlong-term cyclic stability with a capacity retention of 96% over 20,000 cycles at 10 A g−1. Its electrochemical mechanism is elucidated. The lattice contraction induced by zinc intercalation and the expansion caused by hydronium intercalation cancel each other and allow the lattice to remain constant during charge/discharge, favoring cyclic stability. The hierarchically porous structure provides abundant contact with electrolyte, shortens ion diffusion path, and provides cushion for relieving strain generated during electrochemical processes, facilitating both fast kinetics and long-term stability.
  • Iodine-transfer polymerization and CuAAC “click” chemistry: A versatile approach toward poly(vinylidene fluoride)-based amphiphilic triblock terpolymers

    Patil, Yogesh Raghunath; Zapsas, Georgios; Gnanou, Yves; Hadjichristidis, Nikolaos (Journal of Polymer Science Part A: Polymer Chemistry, Wiley, 2019-10-01) [Article]
    This study presents the synthesis and properties of linear PVDF-based amphiphilic triblock terpolymers with PS and PEO, [PVDF-b-PS-b-PEO], by adopting a procedure that involves: (a) iodine-transfer polymerization (ITP) of VDF with 1-iodoperfluorohexane (C6F13I) serving as chain-transfer agent (CTA) to afford C6F13-PVDF-I, (b) ITP of styrene with the C6F13-PVDF-I macromolecular-CTA to obtain C6F13-PVDF-b-PS-I diblock copolymer, (c) end-group exchange from iodo- to azido-group by nucleophilic substitution reaction with NaN3, and (d) copper-catalyzed azide-alkyne cycloaddition (CuAAC) with alkyne-terminated PEO to achieve C6F13-PVDF-b-PS-b-PEO triblock terpolymers. The 1H and 19F NMR spectroscopy confirmed the presence of all blocks, while gel permeation chromatography traces showed the living nature of ITP technique. The self-assembly of these terpolymers was investigated in films (atomic force microscopy and DSC), as well as in aqueous and organic solvents (DLS). The analysis of crystalline phases based on the FTIR spectroscopy indicated the conversion of PVDF α-phase into α + β-phases and β + γ-phases upon the incorporation of PS and PEO blocks, respectively. The synthesized amphiphilic copolymers were evaluated (fluorescence spectroscopy) as carriers of small hydrophobic molecules in water. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019
  • A new tricrystalline triblock terpolymer by combining polyhomologation and ring-opening polymerization. synthesis and thermal properties

    Ladelta, Viko; Zapsas, Georgios; Gnanou, Yves; Hadjichristidis, Nikolaos (Journal of Polymer Science Part A: Polymer Chemistry, Wiley, 2019-10-01) [Article]
    New tricrystalline triblock terpolymers, polyethylene-block-poly(ε-caprolactone)-block-poly(L-lactide) (PE-b-PCL-b-PLLA), were synthesized by ROP of ε-caprolactone (CL) and L-lactide (LLA) from linear ω-hydroxyl polyethylene (PE-OH) macroinitiators. The linear PE-OH macroinitiators were prepared by C1 polymerization of methylsulfoxonium methylide (polyhomologation). Tin(II) 2-ethylhexanoate was used as the catalyst for the sequential ROP of CL and LLA in one-pot polymerization at 85 °C in toluene (PE-OH macroinitiators are soluble in toluene at 80 °C). 1H NMR spectra confirmed the formation of PE-b-PCL-b-PLLA triblock terpolymers through the appearance of the characteristic proton peaks of each block. GPC traces showed the increase in the number average molecular weight from PE-OH macroinitiator to PE-b-PCL, and PE-b-PCL-b-PLLA corroborating the successful synthesis. The existence of three crystalline blocks was proved by DSC and XRD spectroscopy. © 2019 The Authors. Journal of Polymer Science Part A: Polymer Chemistry published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019
  • 17% Efficient Organic Solar Cells Based on Liquid Exfoliated WS2 as a Replacement for PEDOT:PSS

    Lin, Yuanbao; Adilbekova, Begimai; Firdaus, Yuliar; Yengel, Emre; Faber, Hendrik; Sajjad, Muhammad; Zheng, Xiaopeng; Yarali, Emre; Seitkhan, Akmaral; Bakr, Osman; El Labban, Abdulrahman; Schwingenschlögl, Udo; Tung, Vincent; McCulloch, Iain; Laquai, Frédéric; Anthopoulos, Thomas D. (Advanced Materials, Wiley, 2019-10-01) [Article]
    The application of liquid-exfoliated 2D transition metal disulfides (TMDs) as the hole transport layers (HTLs) in nonfullerene-based organic solar cells is reported. It is shown that solution processing of few-layer WS2 or MoS2 suspensions directly onto transparent indium tin oxide (ITO) electrodes changes their work function without the need for any further treatment. HTLs comprising WS2 are found to exhibit higher uniformity on ITO than those of MoS2 and consistently yield solar cells with superior power conversion efficiency (PCE), improved fill factor (FF), enhanced short-circuit current (JSC), and lower series resistance than devices based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and MoS2. Cells based on the ternary bulk-heterojunction PBDB-T-2F:Y6:PC71BM with WS2 as the HTL exhibit the highest PCE of 17%, with an FF of 78%, open-circuit voltage of 0.84 V, and a JSC of 26 mA cm−2. Analysis of the cells' optical and carrier recombination characteristics indicates that the enhanced performance is most likely attributed to a combination of favorable photonic structure and reduced bimolecular recombination losses in WS2-based cells. The achieved PCE is the highest reported to date for organic solar cells comprised of 2D charge transport interlayers and highlights the potential of TMDs as inexpensive HTLs for high-efficiency organic photovoltaics.
  • MAPbI3 Single Crystals Free from Hole-Trapping Centers for Enhanced Photodetectivity

    Yang, Chen; El Demellawi, Jehad K.; Yin, Jun; Velusamy, Dhinesh; Emwas, Abdul-Hamid M.; El-Zohry, Ahmed M.; Gereige, Issam; AlSaggaf, Ahmed; Bakr, Osman; Alshareef, Husam N.; Mohammed, Omar F. (ACS Energy Letters, American Chemical Society (ACS), 2019-10-01) [Article]
    Perovskite single crystals (PSCs) are considered the next breakthrough in optoelectronics research due to their free-grain boundary and much lower density of trap states compared to those of their polycrystalline counterparts. However, the inevitable formation of triiodide-based intrinsic defects during high-temperature crystal growth is one of the major challenges impeding the further development of optoelectronic devices based on PSCs. Here, we not only identified the existence of these triiodide ions as hole-trapping centers and their tremendous negative impact on the performance of PSCs, but more importantly, we used a reduction treatment to prevent their formation during crystal growth. The removal of such defect centers resulted in much higher charge carrier mobility and longer carrier lifetime than the untreated counterparts, leading to enhanced photodetection properties. The I3–-free MAPbI3 single crystal (MSC) devices consistently generated a more than 100 times higher photocurrent than that generated by I3–-rich devices under the same light intensity.
  • Structure-activity relationships in metal organic framework derived mesoporous nitrogen-doped carbon containing atomically dispersed iron sites for CO2 electrochemical reduction

    Sun, Xiaohui; Wang, Riming; Ould-Chikh, Samy; Osadchii, Dmitrii; Li, Guanna; Aguilar, Antonio; Hazemann, Jean-louis; Kapteijn, Freek; Gascon, Jorge (Journal of Catalysis, Elsevier BV, 2019-09-25) [Article]
    Mesoporous nitrogen-doped carbon nanoparticles with atomically dispersed iron sites (named mesoNC-Fe) are synthesized via high-temperature pyrolysis of an Fe containing ZIF-8 MOF. Hydrolysis of tetramethyl orthosilicate (TMOS) in the MOF framework prior to pyrolysis plays an essential role in maintaining a high surface area during the formation of the carbon structure, impeding the formation of iron (oxide) nanoparticles. To gain inside on the nature of the resulting atomically dispersed Fe moieties, HERFD-XANES, EXAFS and valence-to-core X-ray emission spectroscopies have been used. The experimental spectra (both XAS and XES) combined with theoretical calculations suggest that iron has a coordination sphere including a porphyrinic environment and OH/H2O moieties responsible for the high activity in CO2 electroreduction. DFT calculations demonstrate that CO formation is favored in these structures because the free energy barriers of *COOH formation are decreased and the adsorption of *H is impeded. The combination of such a unique coordination environment with a high surface area in the carbon structure of mesoNC-Fe makes more active sites accessible during catalysis and promotes CO2 electroreduction.
  • Facile synthesis of poly(trimethylene carbonate) by alkali metal carboxylate-catalyzed ring-opening polymerization

    Takojima, Kaoru; Saito, Tatsuya; Vevert, Cedric; Ladelta, Viko; Bilalis, Panagiotis; Watanabe, Jun; Hatanaka, Shintaro; Konno, Takashi; Yamamoto, Takuya; Tajima, Kenji; Hadjichristidis, Nikolaos; Isono, Takuya; Satoh, Toshifumi (Polymer Journal, Springer Science and Business Media LLC, 2019-09-24) [Article]
    Alkali metal carboxylates, including sodium acetate, sodium benzoate, and sodium sorbate, which are all readily available and widely used as food additives, were found to promote the ring-opening polymerization (ROP) of trimethylene carbonate (TMC) to produce poly(trimethylene carbonate) (PTMC). The sodium acetate-catalyzed ROP of TMC proceeded in the presence of an alcohol initiator under solvent-free conditions at 70 °C, even at very low catalyst loadings of 0.01–0.0001 mol%. The controlled nature of this ROP system enabled the synthesis of PTMCs with predicted molecular weights ranging from 2400 to 11 700 g mol−1 and narrow dispersities (~1.23). Importantly, ROP is initiated by an alcohol initiator, allowing PTMC production with desired functional groups, such as azido, alkyne, and methacrylate groups, at the α-chain end. Furthermore, the poly(L-lactic acid)-b-PTMC-b-poly(L-lactic acid) triblock copolymer, a biodegradable thermoplastic elastomer, was successfully synthesized in one pot via the sodium acetate-catalyzed ring-opening block copolymerization of TMC and L-lactide with a 1,3-propanediol initiator.
  • Halogen Vacancies Enable Ligand-Assisted Self-Assembly of Perovskite Quantum Dots into Nanowires.

    Pan, Jun; Li, Xiyan; Gong, Xiwen; Yin, Jun; Zhou, Dianli; Sinatra, Lutfan; Huang, Renwu; Liu, Jiakai; Chen, Jie; Dursun, Ibrahim; El-Zohry, Ahmed M.; Saidaminov, Makhsud I.; Sun, Hong-Tao; Mohammed, Omar F.; Ye, Changhui; Sargent, E.; Bakr, Osman (Angewandte Chemie (International ed. in English), Wiley, 2019-09-19) [Article]
    Interest has been growing in defects of halide perovskites in view of their intimate connection with key material optoelectronic properties. In perovskite quantum dots (PQDs), the influence of defects is even more apparent than in their bulk counterparts. By combining experiment and theory, we report herein a halide-vacancy-driven, ligand-directed self-assembly process of CsPbBr3 PQDs. With the assistance of oleic acid and didodecyldimethylammonium sulfide, surface-Br-vacancy-rich CsPbBr3 PQDs self-assemble into nanowires (NWs) that are 20-60 nm in width and several millimeters in length. The NWs exhibit a sharp photoluminescence profile (≈18 nm full-width at-half-maximum) that peaks at 525 nm. Our findings provide insight into the defect-correlated dynamics of PQDs and defect-assisted fabrication of perovskite materials and devices.
  • Generating Triple Crystalline Superstructures in Melt Miscible PEO-b-PCL-b-PLLA Triblock Terpolymers by Controlling Thermal History and Sequential Crystallization

    Palacios, Jordana K.; Liu, Guoming; Wang, Dujin; Hadjichristidis, Nikolaos; Müller, Alejandro J. (Macromolecular Chemistry and Physics, Wiley, 2019-09-11) [Article]
    The morphology, crystallization behavior, and properties of multi-crystalline polymer systems based on triple crystalline biodegradable PEO-b-PCL-b-PLLA triblock terpolymers are reviewed. The triblock terpolymers, with increasing poly(l-lactide) (PLLA) content, exhibit a triple crystalline nature. Upon cooling from melt, the PLLA block crystallizes first and templates the spherulitic morphology of the terpolymer. Then, the poly(ε-caprolactone) (PCL) block crystalizes and, finally, the poly(ethylene oxide) (PEO) block. These triblock terpolymers are melt miscible according to small angle X-ray scattering (SAXS) results. Thus, the crystallization of PCL and PEO blocks takes place within the interlamellar zones of the PLLA spherulites that are formed previously. Therefore, the lamellae of PLLA, PCL, and PEO exist side-by-side within a unique spherulite, constituting a novel triple crystalline superstructure. The theoretical analysis of SAXS curves implies that only one lamella of either PCL or PEO can occupy the interlamellar space in between two contiguous lamellae of PLLA. Several complex competitive effects such as plasticizing, nucleation, anti-plasticizing, and confinement take place during the isothermal crystallization of each block in the terpolymers. New results on how successive self-nucleation and annealing thermal treatment can be used as an additional suitable technique to properly separate the three crystalline phases in these triple crystalline triblock terpolymers are also included.
  • Ligand Effects in Pd-Catalyzed Intermolecular Alkyne Hydroarylations

    Voccia, Maria; Falivene, Laura; Cavallo, Luigi; Tubaro, Cristina; Biffis, Andrea; Caporaso, Lucia (Organometallics, American Chemical Society (ACS), 2019-09-11) [Article]
    The use of palladium(II) catalysts for the synthesis of aryl alkenes by addition of aromatic C–H bonds to alkynes has received a great interest in the literature. The mechanistic features of the reaction have been largely discussed, but no systematic study has been reported so far, particularly for what concerns the role of ligands. In this work, we performed a detailed theoretical study in order to fill this gap. To this extent, three different systems have been considered, with the aim to emphasize how the steric and electronic metal environment affects the catalytic activity and, most notably, steers the reaction selectivity toward the two main products of single and double alkyne insertion into the aromatic C–H bond. Moreover, given the crucial role of the acid media, two acids have been considered, namely, trifluoroacetic acid and tetrafluoroboric acid, to understand the effect of the acid strength and coordinative power on the competition between the different pathways.
  • Gas sensitivity amplification of interdigitated chemocapacitors through etching

    Oikonomou, P.; Botsialas, A.; Papanikolaou, N.; Kazas, I.; Ntetsikas, Konstantinos; Polymeropoulos, Georgios; Hadjichristidis, Nikolaos; Sanopoulou, M.; Raptis, I. (IEEE Sensors Journal, Institute of Electrical and Electronics Engineers (IEEE), 2019-09-02) [Article]
    In polymer coated planar Inter Digitated Electrodes (IDEs), the gas sensing sensitivity is much lower than the sensitivity of parallel plate capacitors. Here, we introduce a simple patterning step for the modification of the geometry of the dielectric substrate of the planar IDEs, and increase of the contribution of the sensitive layer to the output signal. The proposed methodology is investigated through simulation and verified by experimental data. Polymer coated IDEs with different dimensions of spatial wavelength were studied experimentally upon exposure to analytes of varying polarity. The sensing performance of the fabricated structures compare very well with theoretically estimated values obtained through finite element simulations. The maximum performance gain is also calculated by simulation demonstrating the potential of the technology.
  • Towards the online computer-aided design of catalytic pockets

    Falivene, Laura; Cao, Zhen; Petta, Andrea; Serra, Luigi; Poater, Albert; Oliva, Romina; Scarano, Vittorio; Cavallo, Luigi (Nature Chemistry, Springer Science and Business Media LLC, 2019-09-02) [Article]
    The engineering of catalysts with desirable properties can be accelerated by computer-aided design. To achieve this aim, features of molecular catalysts can be condensed into numerical descriptors that can then be used to correlate reactivity and structure. Based on such descriptors, we have introduced topographic steric maps that provide a three-dimensional image of the catalytic pocket—the region of the catalyst where the substrate binds and reacts—enabling it to be visualized and also reshaped by changing various parameters. These topographic steric maps, especially when used in conjunction with density functional theory calculations, enable catalyst structural modifications to be explored quickly, making the online design of new catalysts accessible to the wide chemical community. In this Perspective, we discuss the application of topographic steric maps either to rationalize the behaviour of known catalysts—from synthetic molecular species to metalloenzymes—or to design improved catalysts.
  • General Mild Reaction Creates Highly Luminescent Organic-Ligand-Lacking Halide Perovskite Nanocrystals for Efficient Light-Emitting Diodes.

    Zhang, Bin-Bin; Yuan, Shuai; Ma, Ju-Ping; Zhou, Yang; Hou, Jingshan; Chen, Xueyuan; Zheng, Wei; Shen, Huaibin; Wang, Xue-Chun; Sun, Baoquan; Bakr, Osman; Liao, Liang-Sheng; Sun, Hong-Tao (Journal of the American Chemical Society, American Chemical Society (ACS), 2019-08-31) [Article]
    The presence of labile bulky insulating hydrocarbon ligands in halide perovskite nanocrystals (NCs) passivates surface traps but concurrently makes charge transport difficult in optoelectronic devices. Early efforts routinely rely on the replacement of long-chain ligands with short-chain cousins, leading to notable changes in NC's sizes and photophysical properties and thus making it hard to obtain devices with nearly designed emissions. Here we report a general solution-phase ligand-exchange strategy to produce organic-ligand-lacking halide perovskite NCs with high photoluminescence (PL) quantum yields and good stability in ambient air. We demonstrate that the ligand exchange can be achieved by a well-controlled mild reaction of thionyl halide with the carboxylic and amine groups on the NC's surface, resulting in nearly dry NCs with well-passivated surfaces and almost unaltered emission characteristics. Consequently, we achieve exceptionally high-performance blue perovskite NC light-emitting diodes (LEDs) with an external quantum efficiency of up to 1.35% and an extremely narrow full width at half-maximum of 14.6 nm. Our work provides a systematic framework for preparing high-quality organic-ligand-lacking perovskite NC inks that can be directly cast as films featuring effective charge transport, thereby providing the foundation for further development of a wide range of efficient perovskite optoelectronic devices.
  • General Mild Reaction Creates Highly Luminescent Organic-Ligand-Lacking Halide Perovskite Nanocrystals for Efficient Light-Emitting Diodes.

    Zhang, Bin-Bin; Yuan, Shuai; Ma, Ju-Ping; Zhou, Yang; Hou, Jingshan; Chen, Xueyuan; Zheng, Wei; Shen, Huaibin; Wang, Xue-Chun; Sun, Baoquan; Bakr, Osman; Liao, Liang-Sheng; Sun, Hong-Tao (Journal of the American Chemical Society, American Chemical Society (ACS), 2019-08-31) [Article]
    The presence of labile bulky insulating hydrocarbon ligands in halide perovskite nanocrystals (NCs) passivates surface traps but concurrently makes charge transport difficult in optoelectronic devices. Early efforts routinely rely on the replacement of long-chain ligands with short-chain cousins, leading to notable changes in NC's sizes and photophysical properties and thus making it hard to obtain devices with nearly designed emissions. Here we report a general solution-phase ligand-exchange strategy to produce organic-ligand-lacking halide perovskite NCs with high photoluminescence (PL) quantum yields and good stability in ambient air. We demonstrate that the ligand exchange can be achieved by a well-controlled mild reaction of thionyl halide with the carboxylic and amine groups on the NC's surface, resulting in nearly dry NCs with well-passivated surfaces and almost unaltered emission characteristics. Consequently, we achieve exceptionally high-performance blue perovskite NC light-emitting diodes (LEDs) with an external quantum efficiency of up to 1.35% and an extremely narrow full width at half-maximum of 14.6 nm. Our work provides a systematic framework for preparing high-quality organic-ligand-lacking perovskite NC inks that can be directly cast as films featuring effective charge transport, thereby providing the foundation for further development of a wide range of efficient perovskite optoelectronic devices.
  • A Supramolecular View on the Cooperative Role of Brønsted and Lewis Acid Sites in Zeolites for Methanol Conversion.

    Bailleul, Simon; Yarulina, Irina; Hoffman, Alexander E J; Dokania, Abhay; Abou-Hamad, Edy; Chowdhury, Abhishek Dutta; Pieters, Giovanni; Hajek, Julianna; De Wispelaere, Kristof; Waroquier, Michel; Gascon, Jorge; Van Speybroeck, Veronique (Journal of the American Chemical Society, American Chemical Society (ACS), 2019-08-30) [Article]
    A systematic molecular level and spectroscopic investigation is presented to show the cooperative role of Brønsted acid and Lewis acid sites in zeolites for the conversion of methanol. Extra-framework alkaline-earth metal containing species and aluminum species decrease the number of Brønsted acid sites, as protonated metal clusters are formed. A combined experimental and theoretical effort shows that postsynthetically modified ZSM-5 zeolites, by incorporation of extra-framework alkaline-earth metals or by demetalation with dealuminating agents, contain both mononuclear [MOH]+ and double protonated binuclear metal clusters [M(μ-OH)2M]2+ (M = Mg, Ca, Sr, Ba, and HOAl). The metal in the extra-framework clusters has a Lewis acid character, which is confirmed experimentally and theoretically by IR spectra of adsorbed pyridine. The strength of the Lewis acid sites (Mg > Ca > Sr > Ba) was characterized by a blue shift of characteristic IR peaks, thus offering a tool to sample Lewis acidity experimentally. The incorporation of extra-framework Lewis acid sites has a substantial influence on the reactivity of propene and benzene methylations. Alkaline-earth Lewis acid sites yield increased benzene methylation barriers and destabilization of typical aromatic intermediates, whereas propene methylation routes are less affected. The effect on the catalytic function is especially induced by the double protonated binuclear species. Overall, the extra-framework metal clusters have a dual effect on the catalytic function. By reducing the number of Brønsted acid sites and suppressing typical catalytic reactions in which aromatics are involved, an optimal propene selectivity and increased lifetime for methanol conversion over zeolites is obtained. The combined experimental and theoretical approach gives a unique insight into the nature of the supramolecular zeolite catalyst for methanol conversion which can be meticulously tuned by subtle interplay of Brønsted and Lewis acid sites.
  • Tetracrystalline Tetrablock Quarterpolymers: Four Different Crystallites under the Same Roof.

    Hadjichristidis, Nikolaos; Ladelta, Viko; Zapsas, Georgios; Abou-Hamad, Edy; Gnanou, Yves (Angewandte Chemie (International ed. in English), Wiley, 2019-08-27) [Article]
    Multicrystalline block copolymers having three or more crystalline segments are essential materials for the advancement of physics in the field of crystallinity. Due to the challenging synthesis of multicrystalline polymers only a limited number of tricrystalline terpolymers are reported until now. We report, for the first time, the synthesis of poly(ethylene)-b-poly(ethylene oxide)-b-poly(ε-caprolactone)-b-poly(L-Lactide) (PE-b-PEO-b-PCL-b-PLLA) tetracrystalline tetrablock quarterpolymer, by combining polyhomologation, ring-opening polymerization, and an organic/metal “catalyst switch” strategy.1H NMR spectroscopy and gel-permeation chromatography confirm the formation of the tetrablock quarterpolymer, while differential scanning calorimetry, X-ray diffraction, and wide-line separation solid-state NMR spectroscopy reveal the existence of four different crystalline domains.
  • Aromaticity Driven Electrocatalytic Water Oxidation by a Phosphorus-Nitrogen PN3-Pincer Cobalt Complex

    Das, Pradip K.; Bhunia, Sarmistha; Chakraborty, Priyanka; Rana, Atanu; Dey, Abhishek; Huang, Kuo-Wei (ChemRxiv, 2019-08-27) [Preprint]
    Water oxidation is the primary step in both natural and artificial photosynthesis to convert solar energy in into chemical fuels. Herein, we report the first cobalt-based pincer catalyst for electrolytic water oxidation at neutral pH with high efficiency under electrochemical conditions. Most importantly, ligand (pseudo)aromaticity is identified to play an important role in the electrocatalysis. A significant potential jump (~300 mV) was achieved towards a lower positive value when the aromatized cobalt complex was transformed to a (pseudo)dearomatized cobalt species. This complex catalyzes the water oxidation in its high valent oxidation state at a much lower overpotential (~ 340 mV vs. NHE) based on the onset potential (0.5 mA/cm<sup>2</sup>) of catalysis at pH 10.5, outperforming all the other literature systems. These observations may provide a new strategy for the design of earth-abundant transition metal-based water oxidation catalysts.
  • Photoacoustic Detection of Superoxide Using Oxoporphyrinogen and Porphyrin

    Merkes, Jean Michél; Rueping, Magnus; Kiessling, Fabian; Banala, Srinivas (ACS sensors, American Chemical Society (ACS), 2019-08-23) [Article]
    The superoxide (O2•-) ion is a highly reactive oxygen species involved in many diseases; hence, its noninvasive detection is desirable to identify the onset of pathological processes. Here, we employed photoacoustic (PA) spectroscopy, which enables imaging at ultrasound resolution with the sensitivity of optical modality, for the first time to detect O2•-, using stimuli-responsive contrast agents. meso-(3,5-Di-tert-butyl 4-hydroxyphenyl) porphyrins and oxoporphyrinogens were used as PA contrast agents, which trap the O2•- and enable its detection. The trapped O2•- increased the PA signal amplitude of chromophores up to 9.6-fold, and induced a red-shift in the PA signal maxima of up to 225 nm. Therefore, these trigger-responsive probes may be highly valuable as smart diagnostic PA probes to investigate pathological events stimulated by O2•- species.

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