The Experts below are selected from a list of 26361 Experts worldwide ranked by ideXlab platform

Duncan F. Wass - One of the best experts on this subject based on the ideXlab platform.

  • Small Molecule Activation by Intermolecular Zr(IV)-Phosphine Frustrated Lewis Pairs
    Journal of the American Chemical Society, 2016
    Co-Authors: Owen J. Metters, Sebastian J. K. Forrest, Hazel A. Sparkes, Ian Manners, Duncan F. Wass
    Abstract:

    We report intermolecular transition metal frustrated Lewis pairs (FLPs) based on zirconocene aryloxide and phosphine moieties that exhibit a broad range of Small Molecule Activation chemistry that has previously been the preserve of only intramolecular pairs. Reactions with D2, CO2, THF, and PhCCH are reported. By contrast with previous intramolecular examples, these systems allow facile access to a variety of steric and electronic characteristics at the Lewis acidic and Lewis basic components, with the three-step syntheses of 10 new intermolecular transition metal FLPs being reported. Systematic variation to the phosphine Lewis base is used to unravel steric considerations, with the surprising conclusion that phosphines with relatively Small Tolman steric parameters not only give highly reactive FLPs but are often seen to have the highest selectivity for the desired product. DOSY NMR spectroscopic studies on these systems reveal for the first time the nature of the Lewis acid/Lewis base interactions in transition metal FLPs of this type.

  • Small Molecule Activation by Intermolecular Zr(IV)-Phosphine Frustrated Lewis Pairs
    2016
    Co-Authors: Owen J. Metters, Sebastian J. K. Forrest, Hazel A. Sparkes, Ian Manners, Duncan F. Wass
    Abstract:

    We report intermolecular transition metal frustrated Lewis pairs (FLPs) based on zirconocene aryloxide and phosphine moieties that exhibit a broad range of Small Molecule Activation chemistry that has previously been the preserve of only intramolecular pairs. Reactions with D2, CO2, THF, and PhCCH are reported. By contrast with previous intramolecular examples, these systems allow facile access to a variety of steric and electronic characteristics at the Lewis acidic and Lewis basic components, with the three-step syntheses of 10 new intermolecular transition metal FLPs being reported. Systematic variation to the phosphine Lewis base is used to unravel steric considerations, with the surprising conclusion that phosphines with relatively Small Tolman steric parameters not only give highly reactive FLPs but are often seen to have the highest selectivity for the desired product. DOSY NMR spectroscopic studies on these systems reveal for the first time the nature of the Lewis acid/Lewis base interactions in transition metal FLPs of this type

  • frustrated lewis pairs beyond the main group synthesis reactivity and Small Molecule Activation with cationic zirconocene phosphinoaryloxide complexes
    Journal of the American Chemical Society, 2011
    Co-Authors: Andy M Chapman, Mairi F Haddow, Duncan F. Wass
    Abstract:

    The extension of the frustrated Lewis pair (FLP) concept to the transition series with cationic zirconocene–phosphinoaryloxide complexes is demonstrated. Such complexes mimic the reactivity of main group FLPs in reactions such as heterolytic hydrogen cleavage, CO2 Activation, olefin and alkyne addition, and ring-opening of tetrahydrofuran. The interplay between sterics and electronics is shown to have an important role in determining the reactivity of these compounds with hydrogen in particular. The Zr–H species generated from the heterolytic Activation of hydrogen is shown to undergo insertion reactions with both CO2 and CO. Crucially, these transition metal FLPs are markedly more reactive than main group systems in many cases, and in addition to the usual array of reactions they demonstrate unprecedented reactivity in the Activation of Small Molecules. This includes SN2 and E2 reactions with alkyl chlorides and fluorides, enolate formation from acetone, and the cleavage of C–O bonds to facilitate SN2 ty...

Daniel G Nocera - One of the best experts on this subject based on the ideXlab platform.

  • double hangman iron porphyrin and the effect of electrostatic nonbonding interactions on carbon dioxide reduction
    Journal of Physical Chemistry Letters, 2020
    Co-Authors: Charles G Margarit, Naomi G Asimow, Miguel I Gonzalez, Daniel G Nocera
    Abstract:

    Hangman porphyrins influence the reaction rates of Small Molecule Activation by positioning a functional group in the secondary coordination sphere of the metal center. Electrocatalysis by hangman ...

  • role of proton coupled electron transfer in o o bond Activation
    Accounts of Chemical Research, 2007
    Co-Authors: Joel Rosenthal, Daniel G Nocera
    Abstract:

    The selective reduction of oxygen to water requires four electrons and four protons. The design of catalysts that promote oxygen reduction therefore requires the management of both electron and proton inventories. Pacman and Hangman porphyrins provide a cleft for oxygen binding, a redox shuttle for oxygen reduction, and functionality for tuning the acid–base properties of bound oxygen and its intermediates. With proper control of the proton-coupled electron transfer events, O–O bond breaking of oxygen, and more generally oxygenated substrates, may be achieved with high efficiencies. The rule set developed for oxygen reduction may be applied to a variety of other Small Molecule Activation reactions of consequence to energy conversion.

  • molecular chemistry of consequence to renewable energy
    Inorganic Chemistry, 2005
    Co-Authors: Jillian L Dempsey, Joel Rosenthal, Arthur J Esswein, David R Manke, Jake D Soper, Daniel G Nocera
    Abstract:

    Energy conversion cycles are aimed at driving unfavorable, Small-Molecule Activation reactions with a photon harnessed directly by a transition-metal catalyst or indirectly by a transition-metal catalyst at the surface of a photovoltaic cell. The construction of such cycles confronts daunting challenges because they rely on chemical transformations not understood at the most basic levels. These transformations include multielectron transfer, proton-coupled electron transfer, and bond-breaking and -making reactions of energy-poor substrates. We have begun to explore these poorly understood areas of molecular science with transition-metal complexes that promote hydrogen production and oxygen bond-breaking and -making chemistry of consequence to water splitting.

  • proton coupled electron transfer a unifying mechanism for biological charge transport amino acid radical initiation and propagation and bond making breaking reactions of water and oxygen
    Biochimica et Biophysica Acta, 2004
    Co-Authors: Christopher J Chang, Niels H. Damrauer, Michelle C Y Chang, Daniel G Nocera
    Abstract:

    Abstract Redox-driven proton pumps, radical initiation and propagation in biology, and Small-Molecule Activation processes all involve the coupling of electron transfer to proton transport. A mechanistic framework in which to interpret these processes is being developed by examining proton-coupled electron transfer (PCET) in model and natural systems. Specifically, PCET investigations are underway on the following three fronts: (1) the elucidation of the PCET reaction mechanism by time-resolved laser spectroscopy of electron donors and acceptors juxtaposed by a proton transfer interface; (2) the role of amino acid radicals in biological catalysis with the radical initiation and transport processes of E. coli ribonucleotide reductase (RNR) as a focal point; and (3) the application of PCET towards Small–Molecule Activation with emphasis on biologically relevant bond-breaking and bond-making processes involving oxygen and water. A review of recent developments in each of these areas is discussed.

  • hydrogen produced from hydrohalic acid solutions by a two electron mixed valence photocatalyst
    Science, 2001
    Co-Authors: Alan F Heyduk, Daniel G Nocera
    Abstract:

    Energy conversion cycles are aimed at driving unfavorable, Small-Molecule Activation reactions with a photon harnessed by a transition metal complex. A challenge that has occupied researchers for several decades is to create molecular photocatalysts to promote the production of hydrogen from homogeneous solution. We now report the use of a two-electron mixed-valence dirhodium compound to photocatalyze the reduction of hydrohalic acid to hydrogen. In this cycle, photons break two RhII–X bonds of a LRh0–RhIIX2 core in the presence of a halogen trap to regenerate the active LRh0–Rh0 catalyst, which reacts with hydrohalic acid to produce hydrogen.

Rui Cao - One of the best experts on this subject based on the ideXlab platform.

  • Structure Effects of Metal Corroles on Energy-Related Small Molecule Activation Reactions
    ACS Catalysis, 2019
    Co-Authors: Haitao Lei, Jia Meng, Haoquan Zheng, Wei Zhang, Rui Cao
    Abstract:

    The increasing global energy and environmental crises make it urgent to find and use renewable, clean, and environmentally benign new energy resources. New energy conversion schemes based on Small Molecule Activation reactions, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR), have been proposed. For example, catalytic water splitting provides a promising way to convert solar energy to chemical energy, which is stored as the hydrogen fuel. Hydrogen oxidation in fuel cells is an energy-releasing process to generate electric energy and water as the only product. Although such a hydrogen-based new energy scheme is appealing, its viability is dependent on highly efficient and robust catalysts for these Small Molecule Activation reactions. Recently, a variety of metal corroles have been demonstrated to be efficient in catalyzing HER, OER, and ORR. The redox-active trianionic corrole ligands can afford a rigid four-coordinated square-planar molecu...

  • energy related Small Molecule Activation reactions oxygen reduction and hydrogen and oxygen evolution reactions catalyzed by porphyrin and corrole based systems
    Chemical Reviews, 2017
    Co-Authors: Wei Zhang, Wenzhen Lai, Rui Cao
    Abstract:

    Globally increasing energy demands and environmental concerns related to the use of fossil fuels have stimulated extensive research to identify new energy systems and economies that are sustainable, clean, low cost, and environmentally benign. Hydrogen generation from solar-driven water splitting is a promising strategy to store solar energy in chemical bonds. The subsequent combustion of hydrogen in fuel cells produces electric energy, and the only exhaust is water. These two reactions compose an ideal process to provide clean and sustainable energy. In such a process, a hydrogen evolution reaction (HER), an oxygen evolution reaction (OER) during water splitting, and an oxygen reduction reaction (ORR) as a fuel cell cathodic reaction are key steps that affect the efficiency of the overall energy conversion. Catalysts play key roles in this process by improving the kinetics of these reactions. Porphyrin-based and corrole-based systems are versatile and can efficiently catalyze the ORR, OER, and HER. Becau...

Owen J. Metters - One of the best experts on this subject based on the ideXlab platform.

  • Small Molecule Activation by Intermolecular Zr(IV)-Phosphine Frustrated Lewis Pairs
    Journal of the American Chemical Society, 2016
    Co-Authors: Owen J. Metters, Sebastian J. K. Forrest, Hazel A. Sparkes, Ian Manners, Duncan F. Wass
    Abstract:

    We report intermolecular transition metal frustrated Lewis pairs (FLPs) based on zirconocene aryloxide and phosphine moieties that exhibit a broad range of Small Molecule Activation chemistry that has previously been the preserve of only intramolecular pairs. Reactions with D2, CO2, THF, and PhCCH are reported. By contrast with previous intramolecular examples, these systems allow facile access to a variety of steric and electronic characteristics at the Lewis acidic and Lewis basic components, with the three-step syntheses of 10 new intermolecular transition metal FLPs being reported. Systematic variation to the phosphine Lewis base is used to unravel steric considerations, with the surprising conclusion that phosphines with relatively Small Tolman steric parameters not only give highly reactive FLPs but are often seen to have the highest selectivity for the desired product. DOSY NMR spectroscopic studies on these systems reveal for the first time the nature of the Lewis acid/Lewis base interactions in transition metal FLPs of this type.

  • Small Molecule Activation by Intermolecular Zr(IV)-Phosphine Frustrated Lewis Pairs
    2016
    Co-Authors: Owen J. Metters, Sebastian J. K. Forrest, Hazel A. Sparkes, Ian Manners, Duncan F. Wass
    Abstract:

    We report intermolecular transition metal frustrated Lewis pairs (FLPs) based on zirconocene aryloxide and phosphine moieties that exhibit a broad range of Small Molecule Activation chemistry that has previously been the preserve of only intramolecular pairs. Reactions with D2, CO2, THF, and PhCCH are reported. By contrast with previous intramolecular examples, these systems allow facile access to a variety of steric and electronic characteristics at the Lewis acidic and Lewis basic components, with the three-step syntheses of 10 new intermolecular transition metal FLPs being reported. Systematic variation to the phosphine Lewis base is used to unravel steric considerations, with the surprising conclusion that phosphines with relatively Small Tolman steric parameters not only give highly reactive FLPs but are often seen to have the highest selectivity for the desired product. DOSY NMR spectroscopic studies on these systems reveal for the first time the nature of the Lewis acid/Lewis base interactions in transition metal FLPs of this type

Costas A. Lyssiotis - One of the best experts on this subject based on the ideXlab platform.

  • Small Molecule Activation of metabolic enzyme pyruvate kinase muscle isozyme 2, PKM2, circumvents photoreceptor apoptosis.
    Scientific reports, 2020
    Co-Authors: Thomas J. Wubben, Mercy Pawar, Eric Weh, Andrew M. Smith, Peter Sajjakulnukit, Li Zhang, Lipeng Dai, Heather Hager, Manjunath P. Pai, Costas A. Lyssiotis
    Abstract:

    Photoreceptor cell death is the ultimate cause of vision loss in many retinal disorders, and there is an unmet need for neuroprotective modalities to improve photoreceptor survival. Similar to cancer cells, photoreceptors maintain pyruvate kinase muscle isoform 2 (PKM2) expression, which is a critical regulator in aerobic glycolysis. Unlike PKM1, which has constitutively high catalytic activity, PKM2 is under complex regulation. Recently, we demonstrated that genetically reprogramming photoreceptor metabolism via PKM2-to-PKM1 substitution is a promising neuroprotective strategy. Here, we explored the neuroprotective effects of pharmacologically activating PKM2 via ML-265, a Small Molecule activator of PKM2, during acute outer retinal stress. We found that ML-265 increased PKM2 activity in 661 W cells and in vivo in rat eyes without affecting the expression of genes involved in glucose metabolism. ML-265 treatment did, however, alter metabolic intermediates of glucose metabolism and those necessary for biosynthesis in cultured cells. Long-term exposure to ML-265 did not result in decreased photoreceptor function or survival under baseline conditions. Notably, though, ML-265-treatment did reduce entrance into the apoptotic cascade in in vitro and in vivo models of outer retinal stress. These data suggest that reprogramming metabolism via Activation of PKM2 is a novel, and promising, therapeutic strategy for photoreceptor neuroprotection.

  • Small Molecule Activation of metabolic enzyme pyruvate kinase muscle isozyme 2, PKM2, provides photoreceptor neuroprotection
    2019
    Co-Authors: Thomas J. Wubben, Mercy Pawar, Eric Weh, Andrew M. Smith, Peter Sajjakulnukit, Li Zhang, Lipeng Dai, Heather Hager, Manjunath P. Pai, Costas A. Lyssiotis
    Abstract:

    Abstract Photoreceptor cell death is the ultimate cause of vision loss in many retinal disorders, and there is an unmet need for neuroprotective modalities to improve photoreceptor survival. Similar to cancer cells, photoreceptors maintain pyruvate kinase muscle isoform 2 (PKM2) expression, which is a critical regulator in aerobic glycolysis. Unlike PKM1, which has constitutively high catalytic activity, PKM2 is under complex regulation. Recently, we demonstrated that genetically reprogramming photoreceptor metabolism via PKM2-to-PKM1 substitution is a promising neuroprotective strategy. Here, we explored the neuroprotective effects of pharmacologically activating PKM2 via ML-265, a Small Molecule activator of PKM2, during acute outer retinal stress. We found that ML-265 increased PKM2 activity in 661W cells and in vivo in rat eyes without affecting the expression of genes involved in glucose metabolism. ML-265 treatment did, however, alter metabolic intermediates of glucose metabolism and those necessary for biosynthesis in cultured cells. Long-term exposure to ML-265 did not result in decreased photoreceptor function or survival under baseline conditions. Notably, though, ML-265-treatment did reduce entrance into the apoptotic cascade in in vitro and in vivo models of outer retinal stress. These data suggest that reprogramming metabolism via Activation of PKM2 is a novel, and promising, therapeutic strategy for photoreceptor neuroprotection.