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Roger A Sheldon – One of the best experts on this subject based on the ideXlab platform.

  • selenium catalysed Oxidations with aqueous hydrogen peroxide part 3 Oxidation of carbonyl compounds under mono bi triphasic conditions
    Tetrahedron, 2002
    Co-Authors: Gerdjan Ten Brink, Isabel W C E Arends, Roger A Sheldon
    Abstract:

    The total synthesis of 3,5-bis(perfluorooctyl)phenyl butylselenide (1), a recyclable catalyst for Oxidation reactions with hydrogen peroxide, is described. The catalyst can be used for Oxidation of aldehydes and ketones under monophasic, but also fluorous biphasic or fluorous triphasic conditions.

  • efficient and selective aerobic Oxidation of alcohols into aldehydes and ketones using ruthenium tempo as the catalytic system
    Journal of the American Chemical Society, 2001
    Co-Authors: Arne Dijksman, Arturo Marinogonzalez, Antoni Mairata I Payeras, And Isabel W C E Arends, Roger A Sheldon
    Abstract:

    The combination of RuCl2(PPh3)3 and TEMPO affords an efficient catalytic system for the aerobic Oxidation of a variety of primary and secondary alcohols, giving the corresponding aldehydes and ketones, in >99% selectivity in all cases. The Ru/TEMPO system displayed a preference for primary vs secondary alcohols. Results from Hammett correlation studies (ρ = −0.58) and the primary kinetic isotisotopeect (kH/kD = 5.1) for the catalytic aerobic benzyl alcohol Oxidations are inconsistent with either an oxoruthenium (ORu) or an oxoammonium based mechanism. We postulate a hydridometal mechanism, involving a “RuH2(PPh3)3” species as the active catalyst. TEMPO acts as a hydrogen transfer mediator and is either regenerated by oxygen, under catalytic aerobic conditions, or converted to TEMPH under stoichiometric anaerobic conditions.

Martin Newcomb – One of the best experts on this subject based on the ideXlab platform.

  • spectra and kinetic studies of the compound i derivative of cytochrome p450 119
    Journal of the American Chemical Society, 2008
    Co-Authors: Xin Sheng, John H Horner, Martin Newcomb
    Abstract:

    The Compound I derivative of cytochrome P450 119 (CYP119) was produced by laser flash photolysis of the corresponding Compound II derivative, which was first prepared by reaction of the resting enzyme with peroxynitrite. The UV−vis spectrum of the Compound I species contained an asymmetric Soret band that could be resolved into overlapping transitions centered at ∼367 and ∼416 nm and a Q band with λmax ≈ 650 nm. Reactions of the Compound I derivative with organic substrates gave epoxidized (alkene Oxidation) and hydroxylated (C−H Oxidation) products, as demonstrated by product studies and oxygen-18 labeling studies. The kinetics of Oxidations by CYP119 Compound I were measured directly; the reactions included hydroxylations of benzyl alcohol, ethylbenzene, Tris buffer, lauric acid, and methyl laurate and epOxidations of styrene and 10-undecenoic acid. Apparent second-order rate constants, equal to the product of the equilibrium binding constant (Kbind) and the first-order Oxidation rate constant (kox), we…

  • laser flash photolysis generation of high valent transition metal oxo species insights from kinetic studies in real time
    Accounts of Chemical Research, 2008
    Co-Authors: Rui Zhang, Martin Newcomb
    Abstract:

    High-valenttransition metal−oxo species are active oxidizing species in many metal-catalyzed Oxidation reactions in both Nature and the laboratory. In homogeneous catalytic Oxidations, a transition metametal catalyst is oxidized to a metal−oxo species by a sacrificial oxidant, and the activated transition metal−oxo intermediate oxidizes substrates. Mechanistic studies of these oxidizing species can provide insights for understanding commercially important catalytic Oxidations and the oxidants in cytochrome P450 enzymes. In many cases, however, the transition metal oxidants are so reactive that they do not accumulate to detectable levels in mixing experiments, which have millisecond mixing times, and successful generation and direct spectroscopic characterization of these highly reactive transients remain a considerable challenge. Our strategy for understanding homogeneous catalysis intermediates employs photochemical generation of the transients with spectroscopic detection on time scales as short as nanoseco…

  • laser flash photolysis generation and kinetic studies of porphyrin manganese oxo intermediates rate constants for Oxidations effected by porphyrin mnv oxo species and apparent disproportionation equilibrium constants for porphyrin mniv oxo species
    Journal of the American Chemical Society, 2005
    Co-Authors: Rui Zhang, John H Horner, Martin Newcomb
    Abstract:

    Porphyrinmanganese(V)−oxo and porphyrinmanganese(IV)−oxo species were produced in organic solvents by laser flash photolysis (LFP) of the corresponding porphyrinmanganese(III) perchlorate and chlorate complexes, respectively, permitting direct kinetic studies. The porphyrin systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPFPP), and 5,10,15,20-tetrakis(4-methylpyridinium)porphyrin (TMPyP). The order of reactivity for (porphyrin)MnV(O) derivatives in self-decay reactions in acetonitrile and in Oxidations of substrates was (TPFPP) > (TMPyP) > (TPP). Representative rate constants for reaction of (TPFPP)MnV(O) in acetonitrile are k = 6.1 × 105 M-1 s-1 for cis-stilbene and k = 1.4 × 105 M-1 s-1 for diphenylmethane, and the kinetic isotisotopeect in Oxidation of ethylbenzene and ethylbenzene-d10 is kH/kD = 2.3. Competitive Oxidation reactions conducted under catalytic conditions display approximately the same relative rate constants as were found i…

John M Woodley – One of the best experts on this subject based on the ideXlab platform.

  • automated determination of oxygen dependent enzyme kinetics in a tube in tube flow reactor
    Chemcatchem, 2017
    Co-Authors: Rolf Hoffmeyer Ringborg, Asbjorn Toftgaard Pedersen, John M Woodley
    Abstract:

    Enzyme-mediated Oxidation is of particular interest to synthetic organic chemists. However, the implementation of such systems demands knowledge of enzyme kinetics. Conventional wisdom holds that collecting kinetic data for biocatalytic Oxidations is fraught with difficulties such as limited oxygen supply and low oxygen solubility in water. We present here a novel method for the collection of such kinetic data using a pressurized tube-in-tube reactor, operated in the low-dispersed flow regime to generate time-series data. Experimental development and validation of the instrument reveal not only the high accuracy of the kinetic data obtained, but also the necessity of making measurements in this way to enable the accurate evaluation of high K_MO enzyme systems, with minimal material consumption. For the first time this paves the way to integrate kinetic data into the protein engineering cycle.