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  • Hildebrandt, P.  (668)
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  • 1
    Language: English
    In: Science (New York, N.Y.), 19 December 2014, Vol.346(6216), pp.1456-7
    Description: How do electric fields affect enzymatic processes? Binding and crystallographic studies have shown that electrostatic interactions are important in the substrate-binding step that initiates enzyme catalysis. However, for the subsequent steps, experimental data have been limited....
    Keywords: Static Electricity ; Ketosteroids -- Metabolism ; Steroid Isomerases -- Chemistry
    ISSN: 00368075
    E-ISSN: 1095-9203
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  • 2
    In: Physical Chemistry Chemical Physics, 2015, Vol.17(28), pp.18222-18237
    Description: Spectroscopic techniques play a major role in the elucidation of structurefunction relationships of biological macromolecules. Here we describe an integrated approach for bio-molecular spectroscopy that takes into account the special characteristics of such compounds. The underlying fundamental concepts will be exemplarily illustrated by means of selected case studies on biocatalysts, namely hydrogenase and superoxide reductase. The treatise will be concluded with an overview of challenges and future prospects, laying emphasis on functional dynamics, in vivo studies, and computational spectroscopy.
    Keywords: Hydrogenase -- Chemistry ; Oxidoreductases -- Chemistry;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 3
    Language: English
    In: Journal of the American Chemical Society, 12 September 2012, Vol.134(36)
    Description: High-valent copper-nitrene intermediates have long been proposed to play a role in copper-catalyzed aziridination and amination reactions. However, such intermediates have eluded detection for decades, preventing the unambiguous assignments of mechanisms. Moreover, the electronic structure of the proposed copper-nitrene intermediates has also been controversially discussed in the literature. These mechanistic questions and controversy have provided tremendous motivation to probe the accessibility and reactivity of Cu(III)-NR/Cu(II)N(•)R species. In this paper, we report a breakthrough in this field that was achieved by trapping a transient copper-tosylnitrene species, 3-Sc, in the presence of scandium triflate. The sufficient stability of 3-Sc at -90 °C enabled its characterization with optical, resonance Raman, NMR, and X-ray absorption near-edge spectroscopies, which helped to establish its electronic structure as Cu(II)N(•)Ts (Ts = tosyl group) and not Cu(III)NTs. 3-Sc can initiate tosylamination of cyclohexane, thereby suggesting Cu(II)N(•)Ts cores as viable reactants in oxidation catalysis.
    Keywords: Chemistry
    ISSN: 0002-7863
    E-ISSN: 1520-5126
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  • 4
    Article
    Article
    Language: English
    In: Angewandte Chemie International Edition, 21 June 2010, Vol.49(27), pp.4540-4541
    Description: : A novel application of Raman microscopy takes advantage of a spectral window to map the uptake and distribution of metal‐carbonyl‐based drugs in single cells. The approach provides information on cell structure and molecular structure simultaneously and may have significant impact on drug screening and on the analysis of cellular processes in general.
    Keywords: Antitumor Agents ; Carbonyl Ligands ; Cells ; Molecular Imaging ; Raman Microscopy
    ISSN: 1433-7851
    E-ISSN: 1521-3773
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  • 5
    Language: English
    In: Journal of the American Chemical Society, 16 July 2014, Vol.136(28), pp.9870-3
    Description: [NiFe] hydrogenases catalyze the reversible cleavage of hydrogen and, thus, represent model systems for the investigation and exploitation of emission-free energy conversion processes. Valuable information on the underlying molecular mechanisms can be obtained by spectroscopic techniques that monitor individual catalytic intermediates. Here, we employed resonance Raman spectroscopy and extended it to the entire binuclear active site of an oxygen-tolerant [NiFe] hydrogenase by probing the metal-ligand modes of both the Fe and, for the first time, the Ni ion. Supported by theoretical methods, this approach allowed for monitoring H-transfer from the active site and revealed novel insights into the so far unknown structure and electronic configuration of the hydrogen-binding intermediate of the catalytic cycle, thereby providing key information about catalytic intermediates and reactions of biological hydrogen activation.
    Keywords: Hydrogenase -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 6
    Language: English
    In: Journal of the American Chemical Society, 25 February 2015, Vol.137(7), pp.2555-64
    Description: Oxygen-tolerant [NiFe] hydrogenases are metalloenzymes that represent valuable model systems for sustainable H2 oxidation and production. The soluble NAD(+)-reducing [NiFe] hydrogenase (SH) from Ralstonia eutropha couples the reversible cleavage of H2 with the reduction of NAD(+) and displays a unique O2 tolerance. Here we performed IR spectroscopic investigations on purified SH in various redox states in combination with density functional theory to provide structural insights into the catalytic [NiFe] center. These studies revealed a standard-like coordination of the active site with diatomic CO and cyanide ligands. The long-lasting discrepancy between spectroscopic data obtained in vitro and in vivo could be solved on the basis of reversible cysteine oxygenation in the fully oxidized state of the [NiFe] site. The data are consistent with a model in which the SH detoxifies O2 catalytically by means of an NADH-dependent (per)oxidase reaction involving the intermediary formation of stable cysteine sulfenates. The occurrence of two catalytic activities, hydrogen conversion and oxygen reduction, at the same cofactor may inspire the design of novel biomimetic catalysts performing H2-conversion even in the presence of O2.
    Keywords: Catalytic Domain ; Hydrogenase -- Chemistry ; Nad -- Metabolism ; Oxygen -- Metabolism
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 7
    Language: English
    In: Biochemistry, 14 January 2014, Vol.53(1), pp.20-9
    Description: Phytochromes constitute a class of photoreceptors that can be photoconverted between two stable states. The tetrapyrrole chromophore absorbs in the red spectral region and displays fluorescence maxima above 700 nm, albeit with low quantum yields. Because this wavelength region is particularly advantageous for fluorescence-based deep tissue imaging, there is a strong interest to engineer phytochrome variants with increased fluorescence yields. Such targeted design efforts would substantially benefit from a deeper understanding of those structural parameters that control the photophysical properties of the protein-bound chromophore. Here we have employed resonance Raman (RR) spectroscopy and molecular dynamics simulations for elucidating the chromophore structural changes in a fluorescence-optimized mutant (iRFP) derived from the PAS-GAF domain of the bacteriophytochrome RpBphP2 from Rhodopseudomas palustris . Both methods consistently reveal the structural consequences of the amino acid substitutions in the vicinity of the biliverdin chromophore that may account for lowering the propability of nonradiative excited state decays. First, compared to the wild-type protein, the tilt angle of the terminal ring D with respect to ring C is increased in iRFP, accompanied by the loss of hydrogen bond interactions of the ring D carbonyl function and the reduction of the number of water molecules in that part of the chromophore pocket. Second, the overall flexibility of the chromophore is significantly reduced, particularly in the region of rings D and A, thereby reducing the conformational heterogeneity of the methine bridge between rings A and B and the ring A carbonyl group, as concluded from the RR spectra of the wild-type proteins.
    Keywords: Phytochrome -- Chemistry
    ISSN: 00062960
    E-ISSN: 1520-4995
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  • 8
    Language: English
    In: Biochemistry, 11 September 2012, Vol.51(36), pp.7040-2
    Description: Activation of the corrinoid [Fe-S] protein (CoFeSP), involved in reductive CO(2) conversion, requires the reduction of the Co(II) center by the [Fe-S] protein RACo, which according to the reduction potentials of the two proteins would correspond to an uphill electron transfer. In our resonance Raman spectroscopic work, we demonstrate that, as a conformational gate for the corrinoid reduction, complex formation of Co(II)FeSP and RACo specifically alters the structure of the corrinoid cofactor by modifying the interactions of the Co(II) center with the axial ligand. On the basis of various deletion mutants, the potential interaction domains on the partner proteins can be predicted.
    Keywords: Corrinoids -- Chemistry ; Iron-Sulfur Proteins -- Chemistry
    ISSN: 00062960
    E-ISSN: 1520-4995
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  • 9
    Language: English
    In: The journal of physical chemistry. B, 25 June 2015, Vol.119(25), pp.7968-74
    Description: Metal-respiring bacteria are microorganisms capable of oxidizing organic pollutants present in wastewater and transferring the liberated electrons to an electrode. This ability has led to their application as catalysts in bioelectrochemical systems (BESs), a sustainable technology coupling bioremediation to electricity production. Crucial for the functioning of these BESs is a complex protein architecture consisting of several surface-exposed multiheme proteins, called outer membrane cytochromes, wiring the cell metabolism to the electrode. Although the role of these proteins has been increasingly understood, little is known about the protein-electrode interactions and their impact on the performance of BESs. In this study, we used surface-enhanced resonance Raman spectroscopy in combination with electrochemical techniques to unravel the nature of the protein-electrode interaction for the outer membrane cytochrome OmcB from Desulfuromonas acetoxidans (Dace). Comparing the spectroelectrochemical properties of OmcB bound directly to the electrode surface with those of the same protein embedded inside an electroactive biofilm, we have shown that the surface-exposed cytochromes of Dace biofilms are in direct contact with the electrode surface. Even if direct binding causes protein denaturation, the biofilm possesses the ability to minimize the extent of the damage maximizing the amount of cells in direct electrical communication with the electrode.
    Keywords: Bioelectric Energy Sources ; Biofilms ; Electrodes ; Bacterial Outer Membrane Proteins -- Metabolism ; Cytochromes -- Metabolism ; Desulfuromonas -- Physiology
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 10
    In: Physical Chemistry Chemical Physics, 2011, Vol.13(36), pp.16146-16149
    Description: Structural models for the Ni-B state of the wild-type and C81S protein variant of the membrane-bound [NiFe] hydrogenase from Ralstonia eutropha H16 were derived by applying the homology model technique combined with molecular simulations and a hybrid quantum mechanical/molecular mechanical approach. The active site structure was assessed by comparing calculated and experimental IR spectra, confirming the view that the active site structure is very similar to those of anaerobic standard hydrogenases. In addition, the data suggest the presence of a water molecule in the second coordination sphere of the active centre.
    Keywords: Chemistry;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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