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Antonie J. W. G. Visser - One of the best experts on this subject based on the ideXlab platform.

  • The stacked Flavin Adenine Dinucleotide conformation in water is fluorescent on picosecond timescale
    Chemical Physics Letters, 2003
    Co-Authors: Haik Chosrowjan, Fumio Tanaka, Seiji Taniguchi, Noboru Mataga, Antonie J. W. G. Visser
    Abstract:

    The fluorescence upconversion technique has been applied to examine the picosecond fluorescence decay kinetics of Flavin Adenine Dinucleotide (FAD) in aqueous solution. In the observation range of 30 ps three fluorescent lifetimes can be distinguished. The shortest-lived component (∼1 ps) arises from water relaxation around the excited Flavin. The 9-ps component originates from the intramolecular complex between Flavin and Adenine, whereas the nanosecond decay is attributed to the unstacked form of FAD. The spectra of the three forms are derived from global analysis of decay curves at different emission wavelengths and time regimes using a triple exponential function. It is assumed that the amplitude belonging to the nanosecond fluorescence component reflects the steady-state fluorescence spectrum. Fluorescence anisotropy to its maximum value of 0.4 is instantaneously created.

Norbert Sewald - One of the best experts on this subject based on the ideXlab platform.

  • Straightforward Regeneration of Reduced Flavin Adenine Dinucleotide Required for Enzymatic Tryptophan Halogenation.
    ACS catalysis, 2019
    Co-Authors: Mohamed F. Ismail, Lea Schroeder, Marcel Frese, Tilman Kottke, Frank Hollmann, Caroline E. Paul, Norbert Sewald
    Abstract:

    Flavin-dependent halogenases are known to regioselectively introduce halide substituents into aromatic moieties, for example, the indole ring of tryptophan. The process requires halide salts and oxygen instead of molecular halogen in the chemical halogenation. However, the reduced cofactor Flavin Adenine Dinucleotide (FADH2) has to be regenerated using a Flavin reductase. Consequently, coupled biocatalytic steps are usually applied for cofactor regeneration. Nicotinamide Adenine Dinucleotide (NADH) mimics can be employed stoichiometrically to replace enzymatic cofactor regeneration in biocatalytic halogenation. Chlorination of l-tryptophan is successfully performed using such NADH mimics. The efficiency of this approach has been compared to the previously established enzymatic regeneration system using the two auxiliary enzymes Flavin reductase (PrnF) and alcohol dehydrogenase (ADH). The reaction rates of some of the tested mimics were found to exceed that of the enzymatic system. Continuous enzymatic halogenation reaction for reaction scale-up is also possible.

  • Straightforward Regeneration of Reduced Flavin Adenine Dinucleotide Required for Enzymatic Tryptophan Halogenation
    2019
    Co-Authors: Mohamed Ismail, Lea Schroeder, Marcel Frese, Tilman Kottke, Frank Hollmann, Caroline E. Paul, Norbert Sewald
    Abstract:

    Flavin-dependent halogenases are known to regioselectively introduce halide substituents into aromatic moieties, for example, the indole ring of tryptophan. The process requires halide salts and oxygen instead of molecular halogen in the chemical halogenation. However, the reduced cofactor Flavin Adenine Dinucleotide (FADH2) has to be regenerated using a Flavin reductase. Consequently, coupled biocatalytic steps are usually applied for cofactor regeneration. Nicotinamide Adenine Dinucleotide (NADH) mimics can be employed stoichiometrically to replace enzymatic cofactor regeneration in biocatalytic halogenation. Chlorination of l-tryptophan is successfully performed using such NADH mimics. The efficiency of this approach has been compared to the previously established enzymatic regeneration system using the two auxiliary enzymes Flavin reductase (PrnF) and alcohol dehydrogenase (ADH). The reaction rates of some of the tested mimics were found to exceed that of the enzymatic system. Continuous enzymatic halogenation reaction for reaction scale-up is also possible

Mark H. Stockett - One of the best experts on this subject based on the ideXlab platform.

  • Absorption and luminescence spectroscopy of mass-selected Flavin Adenine Dinucleotide mono-anions.
    The Journal of chemical physics, 2018
    Co-Authors: L. Giacomozzi, Christina Kjær, J. Langeland Knudsen, Lars H. Andersen, S. Brøndsted Nielsen, Mark H. Stockett
    Abstract:

    We report the absorption profile of isolated Flavin Adenine Dinucleotide (FAD) mono-anions recorded using photo-induced dissociation action spectroscopy. In this charge state, one of the phosphoric acid groups is deprotonated and the chromophore itself is in its neutral oxidized state. These measurements cover the first four optical transitions of FAD with excitation energies from 2.3 to 6.0 eV (210–550 nm). The S0 → S2 transition is strongly blue shifted relative to aqueous solution, supporting the view that this transition has a significant charge-transfer character. The remaining bands are close to their solution-phase positions. This confirms that the large discrepancy between quantum chemical calculations of vertical transition energies and solution-phase band maxima cannot be explained by solvent effects. We also report the luminescence spectrum of FAD mono-anions in vacuo. The gas-phase Stokes shift for S1 is 3000 cm−1, which is considerably larger than any previously reported for other molecular ions and consistent with a significant displacement of the ground and excited state potential energy surfaces. Consideration of the vibronic structure is thus essential for simulating the absorption and luminescence spectra of Flavins.We report the absorption profile of isolated Flavin Adenine Dinucleotide (FAD) mono-anions recorded using photo-induced dissociation action spectroscopy. In this charge state, one of the phosphoric acid groups is deprotonated and the chromophore itself is in its neutral oxidized state. These measurements cover the first four optical transitions of FAD with excitation energies from 2.3 to 6.0 eV (210–550 nm). The S0 → S2 transition is strongly blue shifted relative to aqueous solution, supporting the view that this transition has a significant charge-transfer character. The remaining bands are close to their solution-phase positions. This confirms that the large discrepancy between quantum chemical calculations of vertical transition energies and solution-phase band maxima cannot be explained by solvent effects. We also report the luminescence spectrum of FAD mono-anions in vacuo. The gas-phase Stokes shift for S1 is 3000 cm−1, which is considerably larger than any previously reported for other molecular i...

  • absorption and luminescence spectroscopy of mass selected Flavin Adenine Dinucleotide mono anions
    arXiv: Chemical Physics, 2018
    Co-Authors: L. Giacomozzi, Christina Kjær, Lars H. Andersen, Langeland J Knudsen, Brondsted S Nielsen, Mark H. Stockett
    Abstract:

    We report the absorption profile of isolated Flavin Adenine Dinucleotide (FAD) mono-anions recorded using Photo-Induced Dissociation action spectroscopy. In this charge state, one of the phosphoric acid groups is deprotonated and the chromophore itself is in its neutral oxidized state. These measurements cover the first four optical transitions of FAD with excitation energies from 2.3 to 6.0~eV (210--550~nm). The $S_0\rightarrow S_2$ transition is strongly blue-shifted relative to aqueous solution, supporting the view that this transition has significant charge-transfer character. The remaining bands are close to their solution-phase positions. This confirms that the large discrepancy between quantum chemical calculations of vertical transition energies and solution-phase band maxima can not be explained by solvent effects. We also report the luminescence spectrum of FAD mono-anions \textit{in vacuo}. The gas-phase Stokes shift for $S_1$ is 3000~cm$^{-1}$, which is considerably larger than any previously reported for other molecular ions and consistent with a significant displacement of the ground and excited state potential energy surfaces. Consideration of vibronic structure is thus essential for simulating the absorption and luminescence spectra of Flavins.

  • Photo-induced proton-coupled electron transfer and dissociation of isolated Flavin Adenine Dinucleotide mono-anions.
    Physical chemistry chemical physics : PCCP, 2017
    Co-Authors: Mark H. Stockett
    Abstract:

    The intrinsic optical absorption spectrum and photo-dissociation pathways of Flavin Adenine Dinucleotide (FAD) mono-anions isolated in vacuo are probed using photo-induced dissociation (PID) action spectroscopy. The main photo-products are lumichrome and formylmethylFlavin. Evidence is presented that the dissociation pathway leading to these products is non-statistical i.e. occurs during the excited state lifetime. This suggests that the stacking of the Adenine and alloxazine chromophores, which enables ultra-fast quenching of the Flavin excited state by photo-induced electron transfer in aqueous solution, is inhibited in vacuo. These results provide firm experimental confirmation that lumichrome formation from Flavins proceeds via photo-induced, intra-molecular proton-coupled electron transfer.

Haik Chosrowjan - One of the best experts on this subject based on the ideXlab platform.

  • The stacked Flavin Adenine Dinucleotide conformation in water is fluorescent on picosecond timescale
    Chemical Physics Letters, 2003
    Co-Authors: Haik Chosrowjan, Fumio Tanaka, Seiji Taniguchi, Noboru Mataga, Antonie J. W. G. Visser
    Abstract:

    The fluorescence upconversion technique has been applied to examine the picosecond fluorescence decay kinetics of Flavin Adenine Dinucleotide (FAD) in aqueous solution. In the observation range of 30 ps three fluorescent lifetimes can be distinguished. The shortest-lived component (∼1 ps) arises from water relaxation around the excited Flavin. The 9-ps component originates from the intramolecular complex between Flavin and Adenine, whereas the nanosecond decay is attributed to the unstacked form of FAD. The spectra of the three forms are derived from global analysis of decay curves at different emission wavelengths and time regimes using a triple exponential function. It is assumed that the amplitude belonging to the nanosecond fluorescence component reflects the steady-state fluorescence spectrum. Fluorescence anisotropy to its maximum value of 0.4 is instantaneously created.

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

  • In situ ftir thin-layer reflectance spectroscopy of Flavin Adenine Dinucleotide at a mercury/gold electrode
    Electrochimica Acta, 1994
    Co-Authors: Viola Birss, A. S. Hinman, C. E. Mcgarvey, J. Segal
    Abstract:

    In this work, in situ FTIR thin-layer spectroelectrochemistry has been employed at a flat mercury-based electrode to obtain, uniquely, the spectrum of the reduced form of Flavin Adenine Dinucleotide (FAD) in neutral (pH 7) solutions. The flat mercury surface was achieved by the open-circuit amalgamation of gold and it was found to display the advantageous electrochemical properties, including the high hydrogen overpotential, of mercury. This electrode facilitated the determination of the difference in infrared absorbance resulting from the reduction of a solution of FAD. The spectrum of reduced FAD was recovered from the difference spectrum by adding to it the conventionally determined solution spectrum of the stable oxidized form of the redox couple. The observed shifts in band frequencies for the reduced vs. oxidised forms of FAD are consistent with the prior band assignments by normal coordinate analysis and with the previously proposed sites of the redox chemistry of FAD.