Hydrogen’s dual nature helps reveal hidden catalytic processes

Microorganisms have long used hydrogen as an energy source. To do this, they rely on hydrogenases that contain metals in their catalytic centers. In order to use these biocatalysts for hydrogen conversion, researchers are working to understand the catalytic process.

A team from three Max Planck Institutes (MPI), the Center for Neurodegenerative Imaging (BIN) at the University Medical Center Göttingen (UMG), the University of Kiel, and FACCTs GmbH exploits the chemical properties of hydrogen to amplify signals. I did. A type of magnetic resonance spectroscopy. In this way, scientists were able to visualize a previously unknown intermediate step in hydrogen conversion. The study is published in Nature Catalysis.

As a replacement for fossil fuels, energy sources, or catalysts in chemical processes, hydrogen is considered a strong candidate for a sustainable energy economy. On Earth, this element exists primarily in bound form, in water, as hydrogen gas, or in fossil raw materials such as natural gas and crude oil. To obtain hydrogen in its pure form, energy must be used to separate it from its compounds.

Currently, the most common method of producing hydrogen is steam methane reforming of natural gas. But it also produces carbon dioxide (CO₂), which has a negative impact on the climate. Up until now, electrodes made of the precious metal platinum have been mainly used for catalytic hydrogen production from water. This makes catalytic hydrogen production relatively expensive.

Many microorganisms are one step ahead of these production processes. To separate hydrogen and produce energy, we use three types of hydrogenases that work without precious metals and do not release CO2: (NiFe) hydrogenases from archaea and bacteria; (FeFe) bacteria; Hydrogenases from some algae and some anaerobic archaea. The same is true for (Fe) hydrogenases, which are found only in archaea.

The latter plays an important role in methanogenesis, where CO2 is reduced to methane (CH4). Homodimeric (Fe) hydrogenases contain one redox-inactive iron (Fe) per subunit, bound to a guanylylpyridinol cofactor.

Although the catalytic cycle intermediates of (NiFe) and (FeFe) hydrogenases have already been well studied, the catalytic intermediates of (Fe) hydrogenases have not been observed so far. For the first time, the research team has successfully detected an intermediate in the (Fe)-hydrogenase catalytic cycle.

The team consists of Stefan Glöggler from the Max Planck Institute for Multidisciplinary Sciences (MPI-NAT) and the Center for Imaging of Neurodegenerative Structures (BIN) at the University Medical Center Göttingen (UMG), and Lukas Kaltschnee from UMG (MPI-NAT and BIN). led by. , currently at Darmstadt University of Technology), Christian Griesinger (MPI-NAT), Seigo Shima (MPI-Terrestrial Microbiology), and colleagues from MPI für Kohlenforschung, Kiel University, and FAccTs GmbH.

The researchers took advantage of the fact that hydrogen occurs as so-called para-hydrogen and ortho-hydrogen, depending on its nuclear spin. Using nuclear magnetic resonance spectroscopy, the researchers showed that when (Fe)hydrogenase reacts with parahydrogen, the signal is amplified. This so-called parahydrogen-induced polarization (PHIP) made it possible to identify reaction intermediates and visualize how (Fe) hydrogenases combine with hydrogen during catalysis.

Scientists’ data shows that hydrides are formed at the iron center during catalysis. New methods have also made it possible to study binding kinetics. Due to its high sensitivity, PHIP is particularly promising for applications in living cells and for studying hydrogen metabolism in vivo. The results could help in the future to develop (bio)catalysts for hydrogen conversion with higher productivity.