Protein dynamics observed by tunable mid-IR quantum cascade lasers across the time range from 10 ns to 1 s

Schultz, Bernd-Joachim; Mohrmann, Hendrik; Lórenz-Fonfrı́a, Vı́ctor A.; Heberle, Joachim

doi:10.1016/j.saa.2017.01.010

Cited by 36 publications

(70 citation statements)

References 55 publications

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“…This allows measuring single frequencies with nanosecond time resolution. 85 It can be expected that steady-state FTIR spectroscopy and QCL IR spectroscopy will help in identifying catalytically relevant redox species. Furthermore, a correlation of changes in the cofactor regime with differences in the amide region will include protein structural changes in the analysis of [FeFe]-hydrogenases.…”

Section: Discussionmentioning

confidence: 99%

[FeFe]-Hydrogenases: recent developments and future perspectives

et al. 2018

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[FeFe]-Hydrogenases are the most efficient enzymes for catalytic hydrogen turnover. Their H2 production efficiency is hitherto unrivalled. However, functional details of the catalytic machinery and possible modes of application are discussed controversially. The incorporation of synthetically modified cofactors and utilization of semi-artificial enzymes only recently allowed us to shed light on key steps of the catalytic cycle. Herein, we summarize the essential findings regarding the redox chemistry of [FeFe]-hydrogenases and discuss their catalytic hydrogen turnover. We furthermore will give an outlook on potential research activities and exploit the utilization of synthetic cofactor mimics.

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Section: Discussionmentioning

confidence: 99%

[FeFe]-Hydrogenases: recent developments and future perspectives

et al. 2018

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“…This is only valid for small absorptions and sufficient to demonstrate the characteristics of the interferometric setup within the context of this work. For a rigorous calibration, a separately recorded spectrum of I ref must be used to calculate A from I des using (5).…”

Section: Spectra Acquisition and Instrumentationmentioning

confidence: 99%

“…More recently, quantum cascade lasers (QCL) were employed successfully to replace notoriously weak thermal emitters as Mid-IR sources. In particular, external cavity (EC) QCLs proved to be an ideal match for many liquid sensing applications owing to their large spectral tuning range of typically 200 cm −1 [1][2][3][4][5][6][7][8][9]. To date, the vast majority of measurements are performed using direct absorption spectroscopy, in which the laser beam's intensity is recorded after passing through the sample or being totally reflected at its surface.…”

Section: Introductionmentioning

confidence: 99%

A quantum cascade laser-based Mach–Zehnder interferometer for chemical sensing employing molecular absorption and dispersion

et al. 2018

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We employ a novel spectroscopic setup based on an external cavity quantum cascade laser and a Mach-Zehnder interferometer to simultaneously record spectra of absorption and dispersion of liquid samples in the mid-infrared. We describe the theory underlying the interferometric measurement and discuss its implications for the experiment. The capability of simultaneously recording a refractive index and absorption spectrum is demonstrated for a sample of acetone in cyclohexane. The recording of absorption spectra is experimentally investigated in more detail to illustrate the method's capabilities as compared to direct absorption spectroscopy. We find that absorption signals are recorded with strongly suppressed background, but with smaller absolute sensitivity. A possibility of optimizing the setup's performance by unbalancing the interferometer is presented.

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“…25 Application of such approaches to [FeFe]hydrogenases is challenging due to the lack of intrinsic means to trigger and synchronize catalytic activity, but recent progress in the field is promising. [59][60][61][62] We briefly outline the key features of our model in the following. The diiron site of the oxidized H-cluster (Hox) features an open coordination site trans to µCO at Fed as opposed to the symmetrical geometry of many synthetic diiron compounds that lack a bridging carbonyl.…”

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confidence: 99%

The Molecular Proceedings of Biological Hydrogen Turnover

2018

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Over the past two decades, the bioinorganic chemistry of hydrogenases has attracted much interest from basic and applied research. Hydrogenases are highly efficient metalloenzymes that catalyze the reversible reduction of protons to molecular hydrogen (H) in all domains of life. Their iron- and nickel-based cofactors represent promising blueprints for the design of biomimetic, synthetic catalysts. In this Account, we address the molecular proceedings of hydrogen turnover with [FeFe]-hydrogenases. The active site cofactor of [FeFe]-hydrogenases ("H-cluster") comprises a unique diiron complex linked to a [4Fe-4S] cluster via a single cysteine. Since it was discovered that a synthetic analogue of the diiron site can be incorporated into apoprotein in vitro to yield active enzyme, significant progress has been made toward a comprehensive understanding of hydrogenase catalysis. The diiron site carries three to four carbon monoxide (CO) and two cyanide (CN) ligands that give rise to intense infrared (IR) absorption bands. These bands are sensitive reporters of the electron density across the H-cluster, which can be addressed by infrared spectroscopy to follow redox and protonation changes at the cofactor. Synthetic variation of the metal-bridging dithiolate ligand at the diiron site, as well as site-directed mutagenesis of amino acids, provides access to the proton pathways toward the cofactor. Quantum chemical calculations are employed to specifically assign IR bands to vibrational modes of the diatomic ligands and yield refined H-cluster geometries. Here, we provide an overview of recent research on [FeFe]-hydrogenases with emphasis on experimental and computational IR studies. We describe advances in attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR) and protein film electrochemistry, as well as density functional theory (DFT) calculations. Key cofactor species are discussed in terms of molecular geometry, redox state, and protonation. Isotope editing is introduced as a tool to evaluate the cofactor geometry beyond the limits of protein crystallography. In particular, the role of proton-coupled electron transfer (PCET) in the generation of catalytically relevant redox species is addressed. We propose that site-selective protonation of the H-cluster biases surplus electrons either to the [4Fe-4S] cluster or to the diiron site. Protonation of the [4Fe-4S] cluster prevents premature reduction at the diiron site and stabilizes a reactive, terminal hydride. The observed H-cluster species are assigned to rapid H conversion or to reactions possibly involved in activity regulation and cellular H sensing. In the catalytic cycle of [FeFe]-hydrogenases, an H-cluster geometry is preserved that features a bridging CO ligand. PCET levels the redox potential for two steps of sequential cofactor reduction. The concept of consecutive PCET at a geometrically inert cofactor with tight control of electron and proton localization may inspire the design of a novel generation of biomimetic catalysts for the pro...

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Protein dynamics observed by tunable mid-IR quantum cascade lasers across the time range from 10 ns to 1 s

Cited by 36 publications

References 55 publications

[FeFe]-Hydrogenases: recent developments and future perspectives

[FeFe]-Hydrogenases: recent developments and future perspectives

A quantum cascade laser-based Mach–Zehnder interferometer for chemical sensing employing molecular absorption and dispersion

The Molecular Proceedings of Biological Hydrogen Turnover

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