Recent Submissions

  • Imitation Learning based on Generative Adversarial Networks for Robot Path Planning

    Yi, Xianyong (2020-11-24) [Thesis]
    Advisor: Michels, Dominik L.
    Committee members: Wonka, Peter; Moshkov, Mikhail
    Robot path planning and dynamic obstacle avoidance are defined as a problem that robots plan a feasible path from a given starting point to a destination point in a nonlinear dynamic environment, and safely bypass dynamic obstacles to the destination with minimal deviation from the trajectory. Path planning is a typical sequential decision-making problem. Dynamic local observable environment requires real-time and adaptive decision-making systems. It is an innovation for the robot to learn the policy directly from demonstration trajectories to adapt to similar state spaces that may appear in the future. We aim to develop a method for directly learning navigation behavior from demonstration trajectories without defining the environment and attention models, by using the concepts of Generative Adversarial Imitation Learning (GAIL) and Sequence Generative Adversarial Network (SeqGAN). The proposed SeqGAIL model in this thesis allows the robot to reproduce the desired behavior in different situations. In which, an adversarial net is established, and the Feature Counts Errors reduction is utilized as the forcing objective for the Generator. The refinement measure is taken to solve the instability problem. In addition, we proposed to use the Rapidly-exploring Random Tree* (RRT*) with pre-trained weights to generate adequate demonstration trajectories in dynamic environment as the training data, and this idea can effectively overcome the difficulty of acquiring huge training data.
  • Diels-Alder Polymer Networks with Temperature-Reversible Cross-Linking-Induced Emission Yu Jiang*, and Nikos Hadjichristidis*

    Hadjichristidis, Nikos; Jiang, Yu (Angewandte Chemie, Wiley, 2020-11-19) [Article]
    A novel synthetic strategy toward reversible cross-linked polymeric materials with tunable fluorescence properties is presented. Dimaleimide-substituted tetraphenylethene (TPE-2MI), which is nonemissive due to the photo-induced electron transfer (PET) between maleimide (MI) and tetraphenylethene (TPE) groups, was used to cross-link random copolymers of methyl (MM), decyl (DM) or lauryl (LM) with furfuryl methacrylate (FM). The mixture of copolymer and TPE-2MI in DMF showed reversible fluorescence with “on/off” behavior depending on the Diels-Alder (DA)/retro-DA process, which is easily adjusted by temperature. At high temperatures, the retro-DA reaction of polymer networks is dominant, and the fluorescence is quenched by the PET mechanism. In contrast, at low temperatures, the emission recovers as the DA reaction takes over. Based on these results, a transparent PMFM/TPE-2MI film was prepared, and the emission behavior was investigated. It was found that the polymer film shows an accurate response to the external temperature and exhibited tunable fluorescent “turn on/off” behavior. These excitingresults suggest the possible application of this type of reversible cross-linked materials in many areas, including information security and transmission. An example of invisible/visible writing is given.
  • Gas-Phase Thermochemistry of MX3 and M2X6 (M = Sc, Y; X = F, Cl, Br, I) from a Composite Reaction-Based Approach: Homolytic versus Heterolytic Cleavage

    Minenkova, Irina; Osina, Evgeniya L.; Cavallo, Luigi; Minenkov, Yury (Inorganic Chemistry, American Chemical Society (ACS), 2020-11-19) [Article]
    A domain-based local-pair natural-orbital coupled-cluster approach with single, double, and improved linear-scaling perturbative triple correction via an iterative algorithm, DLPNO-CCSD(T1), was applied within the framework of the Feller-Peterson-Dixon approach to derive gas-phase heats of formation of scandium and yttrium trihalides and their dimers via a set of homolytic and heterolytic dissociation reactions. All predicted heats of formation moderately depend on the reaction type with the most and least negative values obtained for homolytic and heterolytic dissociation, respectively. The basis set size dependence, as well as the influence of static correlation effects not covered by the standard (DLPNO-)CCSD(T) approach, suggests that exploitation of the heterolytic dissociation reactions with the formation of M3+ and X- ions leads to the most robust heats of formation. The gas-phase formation enthalpies ΔHf°(0 K)/ΔHf°(298.15 K) and absolute entropies S°(298.15 K) were obtained for the first time for the Sc2F6, Sc2Br6, and Sc2I6 species. For ScBr3, ScI3, Sc2Cl6, and Y2Cl6, we suggest a reexamination of the experimental heats of formation available in the literature. For other compounds, the predicted values were found to be in good agreement with the experimental estimates. Extracted MX3 (M = Sc, Y; X = F, Cl, Br, and I) 0 K atomization enthalpies indicate weaker bonding when moving from fluorine to iodine and from yttrium to scandium. Likewise, the stability of yttrium trihalide dimers degrades when going from fluorine to iodine. Respective scandium trihalide dimers are less stable, with 0 K dimer dissociation energy decreasing in the row fluorine - chlorine - bromine ≈ iodine. Correlation of the (n - 1)s2p6 electrons on bromine and iodine, inclusion of zero-point energy, relativistic effects, and the effective-core-potential correction as well as amelioration of the DLPNO localization inaccuracy are shown to be of similar magnitude, which is critical if accurate heats of formation are a goal.
  • Introducing a Cantellation Strategy for the Design of Mesoporous Zeolite-like Metal–Organic Frameworks: Zr-sod-ZMOFs as a Case Study

    Alsadun, Norah Sadun; Mouchaham, Georges; Guillerm, Vincent; Czaban-Jozwiak, Justyna; Shkurenko, Aleksander; Jiang, Hao; Bhatt, Prashant; Parvatkar, Prakash Tukaram; Eddaoudi, Mohamed (Journal of the American Chemical Society, American Chemical Society (ACS), 2020-11-19) [Article]
    Herein we report novel mesoporous zirconium-based metal-organic frameworks (MOFs) with zeolitic sodalite (sod) topology. Zr-sod-ZMOF-1 and -2 are constructed based on a novel cantellation design strategy. Distinctly, organic linkers are judiciously designed in order to promote the deployment of the 12-coordinated Zr hexanuclear molecular building block (MBB) as a tetrahedral secondary building unit, a prerequisite for zeolite-like nets. The resultant Zr-sod-ZMOFs exhibit mesopores with a diameter up to ≈43 Å, while the pore volume of 1.98 cm3·g-1 measured for Zr-sod-ZMOF-1 is the highest reported experimental value for zeolite-like MOFs based on MBBs as tetrahedral nodes.
  • Molecularly-porous ultrathin membranes for highly selective organic solvent nanofiltration

    Huang, Tiefan; Moosa, Basem; HOANG, PHUONG; Liu, Jiangtao; Chisca, Stefan; Zhang, Gengwu; Alyami, Mram Z.; Khashab, Niveen M.; Nunes, Suzana Pereira (Nature Communications, Springer Science and Business Media LLC, 2020-11-18) [Article]
    AbstractEngineering membranes for molecular separation in organic solvents is still a big challenge. When the selectivity increases, the permeability tends to drastically decrease, increasing the energy demands for the separation process. Ideally, organic solvent nanofiltration membranes should be thin to enhance the permeant transport, have a well-tailored nanoporosity and high stability in harsh solvents. Here, we introduce a trianglamine macrocycle as a molecular building block for cross-linked membranes, prepared by facile interfacial polymerization, for high-performance selective separations. The membranes were prepared via a two-in-one strategy, enabled by the amine macrocycle, by simultaneously reducing the thickness of the thin-film layers (<10 nm) and introducing permanent intrinsic porosity within the membrane (6.3 Å). This translates into a superior separation performance for nanofiltration operation, both in polar and apolar solvents. The hyper-cross-linked network significantly improved the stability in various organic solvents, while the amine host macrocycle provided specific size and charge molecular recognition for selective guest molecules separation. By employing easily customized molecular hosts in ultrathin membranes, we can significantly tailor the selectivity on-demand without compromising the overall permeability of the system.
  • Polyurethanes from Direct Organocatalytic Copolymerization of p-Tosyl Isocyanate with Epoxides.

    Gnanou, Yves; Jia, Mingchen; Hadjichristidis, Nikos; Feng, Xiaoshuang (Angewandte Chemie (International ed. in English), Wiley, 2020-11-17) [Article]
    The direct copolymerization of p -tosyl isocyanate (TSI) with epoxides, initiated by onium salts in the presence of trialkylborane, to produce polyurethanes is reported. The rate of copolymerization and the (regio)selectivity were investigated in relation to the trialkylborane and initiator used. Under optimized conditions such copolymerizations have been successfully performed for a wide range of epoxides, including ethylene oxide, propylene oxide, 1-octene oxide, cyclohexene oxide, and allyl glycidyl ether. These copolymerizations afford a new category of polyurethanes, clear of side products such as cyclic oxazolidinone, isocyanurate, and poly(isocyanate) linkages. The experimental conditions used in this work are compatible with those for the organocatalytic (co)polymerization of other oxygenated monomers and CO 2 , holding the potential for their terpolymerization with p -tosyl isocyanate and the development of new materials with unprecedented properties.
  • Liquid nanoparticles: manipulating the nucleation and growth of nanoscale droplets.

    Wang, Ruoxu; Han, Fei; Chen, Bo; Liu, Lingmei; Wang, Shaoyan; Zhang, Hua; Han, Yu; Chen, Hongyu (Angewandte Chemie (International ed. in English), Wiley, 2020-11-15) [Article]
    By manipulating the nucleation and growth of solid materials, the synthesis of various sophisticated nanostructures has been achieved. Similar methodology, if applied to liquid, could enable the mass-production and control of ultra-small droplets at the scale of nanoparticles (10 -18  L or below). It would be highly desirable since droplets plays a fundamental role in numerous applications. Here we present a general strategy to synthesize and manipulate nanoscale droplets, similar to what has been done to solid nanoparticles in the classis solution-synthesis. It was achieved by a solute-induced phase separation which initiates the nucleation of droplets from a homogeneous solution. These liquid nanoparticles have great potentials to be manipulated like their solid counterparts, borrowing from the vast methodologies of nanoparticle synthesis, such as burst nucleation, seeded growth and co-precipitations. LNPs also serve as a general synthetic platform, to fabricate nanoreactors, drug-loaded carriers, and other hollow nanostructures with a variety of shell materials.
  • A nanobody-functionalized organic electrochemical transistor for the rapid detection of SARS-CoV-2 or MERS antigens at the physical limit

    Guo, Keying; Wustoni, Shofarul; Koklu, Anil; Díaz-Galicia, Escarlet; Moser, Maximilian; Hama, Adel; Alqahtani, Ahmed A.; Nazir Ahmad, Adeel; Alhamlan, Fatimah Saeed; McCulloch, Iain; Arold, Stefan T.; Grunberg, Raik; Inal, Sahika (Cold Spring Harbor Laboratory, 2020-11-13) [Preprint]
    The COVID-19 pandemic highlights the need for rapid protein detection and quantification at the single-molecule level in a format that is simple and robust enough for widespread point-of-care applications. We here introduce a modular nanobody-organic electrochemical transistor architecture that enables the fast and specific detection and quantification of single-molecule to nanomolar protein antigen concentrations in complex bodily fluids. The sensor combines a new solution-processable organic semiconductor material in the transistor channel with the high-density and orientation-controlled bioconjugation of nanobody fusion proteins on disposable gate electrodes. It provides results after a 10 minutes exposure to 5 μL of unprocessed samples, maintains high specificity and single-molecule sensitivity in human saliva or serum, and is rapidly reprogrammed towards any protein target for which nanobodies exist. We demonstrate the use of this highly modular platform for the detection of green fluorescent protein, SARS-CoV-1/2, and MERS-CoV spike proteins and validate the sensor for COVID-19 screening in unprocessed clinical nasopharyngeal swab and saliva samples.
  • A nanobody-functionalized organic electrochemical transistor for the rapid detection of SARS-CoV-2 or MERS antigens at the physical limit

    Guo, Keying; Wustoni, Shofarul; Koklu, Anil; Díaz-Galicia, Escarlet; Moser, Maximilian; Hama, Adel; Alqahtani, Ahmed A.; Nazir Ahmad, Adeel; Alhamlan, Fatimah Saeed; McCulloch, Iain; Arold, Stefan T.; Grunberg, Raik; Inal, Sahika (Cold Spring Harbor Laboratory, 2020-11-13) [Preprint]
    The COVID-19 pandemic highlights the need for rapid protein detection and quantification at the single-molecule level in a format that is simple and robust enough for widespread point-of-care applications. We here introduce a modular nanobody-organic electrochemical transistor architecture that enables the fast and specific detection and quantification of single-molecule to nanomolar protein antigen concentrations in complex bodily fluids. The sensor combines a new solution-processable organic semiconductor material in the transistor channel with the high-density and orientation-controlled bioconjugation of nanobody fusion proteins on disposable gate electrodes. It provides results after a 10 minutes exposure to 5 μL of unprocessed samples, maintains high specificity and single-molecule sensitivity in human saliva or serum, and is rapidly reprogrammed towards any protein target for which nanobodies exist. We demonstrate the use of this highly modular platform for the detection of green fluorescent protein, SARS-CoV-1/2, and MERS-CoV spike proteins and validate the sensor for COVID-19 screening in unprocessed clinical nasopharyngeal swab and saliva samples.
  • Optically Pure C1-Symmetric Cyclic(alkyl)(amino)carbene Ruthenium Complexes for Asymmetric Olefin Metathesis

    Morvan, Jennifer; Vermersch, François; Zhang, Ziyun; Falivene, Laura; Vives, Thomas; Dorcet, Vincent; Roisnel, Thierry; Crévisy, Christophe; Cavallo, Luigi; Vanthuyne, Nicolas; Bertrand, Guy; Jazzar, Rodolphe; Mauduit, Marc (Journal of the American Chemical Society, American Chemical Society (ACS), 2020-11-13) [Article]
    An expedient access to the first optically pure ruthenium complexes containing C1-symmetric cyclic (alkyl)(amino)carbene ligands is reported. They demonstrate excellent catalytic performances in asymmetric olefin metathesis with high enantioselectivities (up to 92% ee). Preliminary mechanistic insights provided by density functional theory models highlight the origin of the enantioselectivity.
  • Active and stable Fe-based catalyst, mechanism, and key role of alkali promoters in ammonia synthesis

    Almaksoud, Walid; Rai, Rohit Kumar; Morlanes, Natalia Sanchez; Harb, Moussab; Ahmad, Rafia; Ould-Chikh, Samy; Anjum, Dalaver H.; Hedhili, Mohamed N.; Al-Sabban, Bedour E.; Albahily, Khalid; Cavallo, Luigi; Basset, Jean-Marie (Journal of Catalysis, Elsevier BV, 2020-11-13) [Article]
    Worldwide NH3 production reached 0.18 Gton in 2019, and 1-2 % of the global CO2 emissions are due to large-scale NH3 synthesis (1 billion tons of CO2 / year). A catalyst for ammonia synthesis has been obtained by pyrolysis of iron phthalocyanine (FePc) precursor under N2, followed by impregnation with alkali metals (Na, Li, K, and Cs) and H2 treatment. Characterization (XPS, XRD, HR-TEM, ICP-OES, TGA, CHNS analysis, and BET) revealed nano-sized core-shell structures formed during H2 treatment, with Fe in the core and promoters (“Cs2O” and “K2O”) with carbon on the shell. The alkali metals partially inhibit the methanation process of carbon. These Fe NPs were found to be very active and stable catalysts, as compared to the commercial iron-based catalyst KM1 (Haldor-Topsoe). Activities of promoted catalysts follow the order: K>Cs>Na∼Li, with more than 6% of NH3 at 400 °C and 7 MPa, and contact time (WHSV) of 12000 ml.g-1.h-1 with K. The apparent activation energy was found to be 31 kJ.mol-1 and 34 kJ.mol-1 for 3-K-FePc700 and 10-Cs-FePc700 suggesting the facile activation of N2 on the catalysts surface. DFT-based predicted atomic and electronic structures reveal a similarity in the partial charge distribution on surface Fe species with K or Cs. Surprisingly the main effect of alkali is related to the geometrical repartition of alkali, leading to a larger number of exposed iron atoms, active sites, in the case of K than Cs. The alkali (present as metal oxide) leaves at medium coverage of the surface some exposed Fe(0) for N2 non-dissociative chemisorption (end-on type). The free energy profile demonstrates that the thermodynamic stability of the reaction intermediates for nitrogen reduction reaction (NRR) increases with pressure indicating better feasibility of the reaction at higher pressures.
  • Diels–Alder Polymer Networks with Temperature-Reversible Cross-Linking-Induced Emission

    Jiang, Yu; Hadjichristidis, Nikos (Angewandte Chemie International Edition, Wiley, 2020-11-12) [Article]
    A novel synthetic strategy toward reversible cross-linked polymeric materials with tunable fluorescence properties is presented. Dimaleimide-substituted tetraphenylethene (TPE-2MI), which is non-emissive due to the photo-induced electron transfer (PET) between maleimide (MI) and tetraphenylethene (TPE) groups, was used to cross-link random copolymers of methyl (MM), decyl (DM) or lauryl (LM) with furfuryl methacrylate (FM). The mixture of copolymer and TPE-2MI in DMF showed reversible fluorescence with “on/off” behavior depending on the Diels-Alder (DA)/retro-DA process, which is easily adjusted by temperature. At high temperatures, the retro-DA reaction of polymer networks is dominant, and the fluorescence is quenched by the PET mechanism. In contrast, at low temperatures, the emission recovers as the DA reaction takes over. Based on these results, a transparent PMFM/TPE-2MI film was prepared, and the emission behavior was investigated. It was found that the polymer film shows an accurate response to the external temperature and exhibited tunable fluorescent “turn on/off” behavior. These exciting results suggest the possible application of this type of reversible cross-linked materials in many areas, including information security and transmission. An example of invisible/visible writing is given.
  • σ/π Plasticity of NHCs on the Ruthenium–Phosphine and Ruthenium═Ylidene Bonds in Olefin Metathesis Catalysts

    Azofra Mesa, Luis; Vummaleti, Sai V. C.; Zhang, Ziyun; Poater, Albert; Cavallo, Luigi (Organometallics, American Chemical Society (ACS), 2020-11-12) [Article]
    The nature of the Ru bonding environment in a set of Grubbs catalysts has been studied by means of density functional theory (DFT). On the one hand, for a set of 20 [Ru(═CH2)(NHC)(PCy3)][Cl]2 second-generation adducts, the results show that calculated 31P NMR shieldings exhibit a good correlation with the calculated R(Ru–P) bond lengths, which are in turn strongly correlated with the calculated PCy3 ligand dissociation energies. Bond energy decomposition analysis (EDA) also indicates that there is a strong correlation between the σ and π orbital interaction energies for the Ru–PCy3 bond, while no correlation was found for the case of the bond between the Ru moiety and the N-heterocyclic carbene (NHC) ligands, Ru–NHC. Furthermore, π orbital interaction energies of the Ru–PCy3 bond were found to be strongly correlated with the calculated PCy3 ligand dissociation energies, as well as with the R(Ru–P) bond lengths, confirming the significance of the π back-donation component from Ru to PCy3 in determining the lability of the PCy3 ligand in the studied adducts. On the other, for a set of 17 [Ru(═CHR)(NHC)x(PCy3)2–x][Cl]2 first (x = 0)- and second-generation (x = 1) complexes, DFT results show that changes occurring in the 13C NMR shielding of the Ru═ylidene bond are mainly due to σ(Ru═C) → π*(Ru═C) molecular orbital (MO) transitions. Good correlations are observed between σ(13C) and the energy gaps of the MOs involved in such transitions, between the binding energies of the ylidene moiety and the rest of the Ru fragment, as well as with the R(Ru═C) bond lengths. Finally, our novel preliminary results suggest that, once the metallacycle intermediate is formed by reaction with ethylene, 13C′(β) NMR shielding retains the NMR information from σ(13C) in the 16e species, in contrast to what happens with the 13C(α) NMR shielding.
  • Resolving Different Physical Origins toward Crystallite Imperfection in Semiconducting Polymers: Crystallite Size vs Paracrystallinity

    Jiao, Xuechen; Statz, Martin; Lai, Lianglun; Schott, Sam; Jellett, Cameron; McCulloch, Iain; Sirringhaus, Henning; McNeill, Christopher R. (The Journal of Physical Chemistry B, American Chemical Society (ACS), 2020-11-10) [Article]
    The crystallization and aggregation behaviors of semiconducting polymers play a critical role in determining the ultimate performance of optoelectronic devices based on these materials. Due to the soft nature of polymers, crystallite imperfection exists ubiquitously. To this aspect, crystallinity is often used to represent the degree of crystallite imperfection in a reciprocal relation. Despite of the importance, the discussion on crystallinity is still on the phenomenological level and ambiguous in many cases. As two major contributors to crystallite imperfection, crystallite size and paracrystallinity are highly intertwined and hardly separated, hindering more accurate and trustworthy structural analysis. Herein, with the aid of synchrotron-based X-ray diffraction, combined with environmentally controlled heating capability, the evolution of crystallite size and paracrystallinity of two prototypical polythiophene-based thin films have been successfully measured. Strikingly, the paracrystallinity of poly(3-hexylthiophene-2,5-diyl) (P3HT) crystallites remains unchanged with annealing, while the paracrystallinity of poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) becomes diminished with crystallite growth. This work delivers a promising gesture to semiconducting polymers community, confirming that it is possible to experimentally separate crystallite size and paracrystallinity, both of which are highly intertwined. With this progress, investigation on the correlation between further detailed microstructural parameters and device performance can be achieved.
  • All-Carbon Quaternary Stereocenters α to Azaarenes via Radical-Based Asymmetric Olefin Difunctionalization.

    Yin, Yanli; Li, Yunqiang; Goncalves, Theo; Zhan, Qiangqiang; Wang, Guanghui; Zhao, Xiaowei; Qiao, Baokun; Huang, Kuo-Wei; Jiang, Zhiyong (Journal of the American Chemical Society, American Chemical Society (ACS), 2020-11-05) [Article]
    A radical-based asymmetric olefin difunctionalization strategy for rapidly forging all-carbon quaternary stereocenters α to diverse azaarenes is reported. Under cooperative photoredox and chiral Brønsted acid catalysis, cyclopropylamines with α-branched 2-vinylazaarenes can undergo a sequential two-step radical process, furnishing various valuable chiral azaarene-substituted cyclopentanes. The use of the rigid and confined C2-symmetric imidodiphosphoric acid catalysts achieves high enantio- and diastereo-selectivities for these asymmetric [3 + 2] cycloadditions.
  • A New Synthetic Methodology of Site-Specific Functionalized Polypeptides: Metal-Free, Highly Active and Selective at Room Temperature

    Zhao, Wei; Lv, Yanfeng; Li, Ji; Feng, Zihao; Ni, Yonghao; Hadjichristidis, Nikos (Angewandte Chemie International Edition, Wiley, 2020-11-03) [Article]
    Functionalized polypeptides have attracted tremendous interest in recent years and found many stimulating applications due to their tunable physicochemical characteristics including hydrophilicity and stimuli-responsive behavior. The development of new strategies to produce these polymers without metallic contaminants is crucial for their applications in high-value and sensitive domains, such as biomedical, microelectronic, food packaging and personal beauty care fields. Herein, a highly efficient strategy to access well-defined site-specific functionalized polypeptides is developed by combining Michael reaction with hydrogen-bonding organocatalytic ROP of NCA. A library of chain-end and chain-middle functionalized polypeptides (14 examples) with predesigned molecular weights and low polydispersities are readily prepared with this approach. Specifically, the whole synthetic process is metal-free, fulfilling high activity and selectivity at room temperature.
  • SELECTIVITY OF METATHESIS REACTIONS CATALYZED BY SUPPORTED COMPLEXES OF GROUP VI

    Wackerow, Wiebke (2020-11) [Dissertation]
    Advisor: Basset, Jean-Marie
    Committee members: Huang, Kuo-Wei; Ruiz-Martinez, Javier; Astruc, Didier
    The general objective of this thesis is the analysis of selective reactions for group VI grafted metal complexes via methods and principles of SOMC. For this objective, three approaches have been chosen. The first chapter is an introduction to the topic of selectivity in catalysis, emphasizing heterogeneous catalysis and more specifically the different approaches to support catalysts on surfaces. The concept of catalysis by design is introduced as a new way to use the surface as a ligand. Chapter 2 presents the results of a library of well-defined catalysts of group VI with identical catalytic functionality, but different ligand environment. The results reveal, that metal-carbynes are able to switch their catalytic reactivity based on the substrate that they are contacted with. The difference in reaction mechanisms and the differing reactivities towards the substrates are presented. It can be concluded that the classical ROMP is selectively achieved with cyclic alkene substrates leading to polymers whereas cyclic alkanes yield exclusively higher and lower homologues of the substrate without polymeric products. Chapter 3 presents the study of olefin metathesis of cis-2-pentene with metal-carbynes of group VI, where the selectivity of the catalyst library towards yield of cis-/trans products is analyzed. It is presented, that the ligand environment of the catalysts is showing an influence in the selectivity. Rates of cis/trans isomerization of the products are high and are approaching thermodynamic equilibrium at high conversion. Product isomerization, thermodynamic equilibrium and reactivity differences between liquid phase and gas phase products are analyzed. Chapter 4 presents the full characterization of tungsten-hydrides by selective transformation into tungsten-hydroxides. These newly discovered well-defined tungstenhydroxides are fully characterized by ICP, TEM, DRIFT, double quantum and triple quantum solid-state NMR. The presented results allow to predict that tungsten-hydrides on KCC-1700 are present as two distinct species. Catalysis results with cyclooctane show, that due to burial of the complexes in the KCC-1700 surface the tungsten-hydrides are less active towards cyclic alkane metathesis reactions with bulky cyclooctane than the metalcarbyne complexes. Chapter 5 is giving a conclusion of results and an outlook for catalytic applications of the generated tungsten-hydroxides of chapter 4.
  • Structural transformation of highly active metal–organic framework electrocatalysts during the oxygen evolution reaction

    Zhao, Shenlong; Tan, Chunhui; He, Chun-Ting; An, Pengfei; Xie, Feng; Jiang, Shuai; Zhu, Yanfei; Wu, Kuang-Hsu; Zhang, Binwei; Li, Haijing; Zhang, Jing; Chen, Yuan; Liu, Shaoqin; Dong, Juncai; Tang, Zhiyong (Nature Energy, Springer Science and Business Media LLC, 2020-10-26) [Article]
    Metal–organic frameworks (MOFs) are increasingly being investigated as electrocatalysts for the oxygen evolution reaction (OER). Despite their promising catalytic activity, many fundamental questions concerning their structure−performance relationships—especially those regarding the roles of active species—remain to be answered. Here we show the structural transformation of a Ni0.5Co0.5-MOF-74 during the OER by operando X-ray absorption spectroscopy analysis and high-resolution transmission electron microscopy imaging. We suggest that Ni0.5Co0.5OOH0.75, with abundant oxygen vacancies and high oxidation states, forms in situ and is responsible for the high OER activity observed. The ratio of Ni to Co in the bimetallic centres alters the geometric and electronic structure of as-formed active species and in turn the catalytic activity. Based on our understanding of this system, we fabricate a Ni0.9Fe0.1-MOF that delivers low overpotentials of 198 mV and 231 mV at 10 mA cm−2 and 20 mA cm−2, respectively
  • Intrinsic efficiency limits in low-bandgap non-fullerene acceptor organic solar cells

    Karuthedath, Safakath; Gorenflot, Julien; Firdaus, Yuliar; Chaturvedi, Neha; De Castro, Catherine S. P.; Harrison, George T.; Khan, Jafar Iqbal; Markina, Anastasia; Albalawi, Ahmed; Peña, Top Archie Dela; Liu, Wenlan; Liang, Ru-Ze; Sharma, Anirudh; Paleti, Sri Harish Kumar; Zhang, Weimin; Lin, Yuanbao; Alarousu, Erkki; Anjum, Dalaver H.; Beaujuge, Pierre; De Wolf, Stefaan; McCulloch, Iain; Anthopoulos, Thomas D.; Baran, Derya; Andrienko, Denis; Laquai, Frédéric (Nature Materials, Springer Science and Business Media LLC, 2020-10-23) [Article]
    In bulk heterojunction (BHJ) organic solar cells (OSCs) both the electron affinity (EA) and ionization energy (IE) offsets at the donor–acceptor interface should equally control exciton dissociation. Here, we demonstrate that in low-bandgap non-fullerene acceptor (NFA) BHJs ultrafast donor-to-acceptor energy transfer precedes hole transfer from the acceptor to the donor and thus renders the EA offset virtually unimportant. Moreover, sizeable bulk IE offsets of about 0.5 eV are needed for efficient charge transfer and high internal quantum efficiencies, since energy level bending at the donor–NFA interface caused by the acceptors’ quadrupole moments prevents efficient exciton-to-charge-transfer state conversion at low IE offsets. The same bending, however, is the origin of the barrier-less charge transfer state to free charge conversion. Our results provide a comprehensive picture of the photophysics of NFA-based blends, and show that sizeable bulk IE offsets are essential to design efficient BHJ OSCs based on low-bandgap NFAs.
  • Enzymatic Formation of an Artificial Base Pair Using a Modified Purine Nucleoside Triphosphate

    Flamme, Marie; Röthlisberger, Pascal; Levi-Acobas, Fabienne; Chawla, Mohit; Oliva, Romina; Cavallo, Luigi; Gasser, Gilles; Marlière, Philippe; Herdewijn, Piet; Hollenstein, Marcel (ACS Chemical Biology, American Chemical Society (ACS), 2020-10-22) [Article]
    The expansion of the genetic alphabet with additional, unnatural base pairs (UBPs) is an important and long-standing goal in synthetic biology. Nucleotides acting as ligands for the coordination of metal cations have advanced as promising candidates for such an expansion of the genetic alphabet. However, the inclusion of artificial metal base pairs in nucleic acids mainly relies on solid-phase synthesis approaches, and very little is known about polymerase-mediated synthesis. Herein, we report the selective and high yielding enzymatic construction of a silver-mediated base pair (dImC-AgI-dPurP) as well as a two-step protocol for the synthesis of DNA duplexes containing such an artificial metal base pair. Guided by DFT calculations, we also shed light into the mechanism of formation of this artificial base pair as well as into the structural and energetic preferences. The enzymatic synthesis of the dImC-AgI-dPurP artificial metal base pair provides valuable insights for the design of future, more potent systems aiming at expanding the genetic alphabet.

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