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Research
Bioinorganic Chemistry
has developed in the last decades to become a field that attracts a broad spectrum of scientists that range from biochemists, enzymologists,
coordination chemists, spectroscopists to theoreticians. The draw for these scientists is the unique role that transition metals play in biology.
For example, they act as catalysts in
the transformation of biological molecules to mediate essential biological processes, transport small molecules and electrons, and regulate cell function.
One important goal of
bioinorganic chemistry is the determination of mechanisms of enzymatic reactions on a molecular level. Our research
evaluates the properties of metal centers in enzymes using inorganic model complexes that we investigate with
high-end spectroscopic methods to provide insight into how these metalloproteins work. In addition, we are also involved in many collaborative
projects where we study metalloproteins directly, using again a plethora of spectroscopic and theoretical methods.
In comparison,
Bioorganometallic Chemistry
is a relatively new field that is
focused on the properties of metal-carbon bonds in biology and their utilization for catalysis. The by far most
prominent example for this area is coenzyme B12 (cobalamine), which corresponds to a cobalt complex of
a highly functionalized porphyrin derivative (a 'corrin' macrocycle).
Another example are hydrogenases , which are enzymes that catalyze the
conversion of protons and electrons into hydrogen (and vice versa). The latter enzymes are of special interest in the area of alternative energies (see below). In the field of
Bioorganometallic Chemistry, we are particularly interested in
artifical metalloenzymes
that are engineered to catalyze non-biological, in our case
organometallic, reactions. Here, we use small heme proteins (especially myoglobin) as a platform, and via cofactor exchange (using porphyrin derivatives and
other, alternative cofactors), we aim at generating artificial metalloenzymes that can catalyze carbene transfer as well as C-C and C-heteroatom
bond forming reactions.
Solar energy is a viable and ubiquitously available energy source, but in order to move to an energy economy that is based on alternatives to carbon-based fuels,
large scale energy storage technology needs to be developed. In this way, solar energy could be captured during the day, and would then be
available in the evening when energy consumption spikes. One possible approach to overcome this challenge is the direct
conversion of solar energy into a chemical fuel.
Particularly attractive in this regard is the photoelectrochemical splitting of water for the generation of hydrogen. Besides energy storage,
hydrogen is also an important chemical feedstock that is used on the multi-million ton scale every year in fertilizer production and oil refining.
Large-scale hydrogen production from protons and electrons, whether directly coupled to water oxidation photoanodes or to electolyzers powered by
renewable energy sources, must inevitably be facilitated by heterogeneous catalysts to allow for application of the catalysts in large-scale flow reactors.
To this end, electrocatalysts must be designed that are inexpensive, easy to
assemble, and that can be prepared on a large scale without difficulty. Much work in this area has been inspired by the hydrogenase enzymes mentioned above.
Our work in this area is focused on the surface functionalization of light-absorbing semiconductor electrodes with
Cobalt(III)-bis(benzenedithiolate) hydrogen production catalysts
and derivatives, using reduced graphene oxide and related 2D materials as interface that allow for easy and efficient
surface-attachment of the catalysts.
More established approaches with chemical linkers are also explored.
For the investigation of both metalloenzymes and inorganic coordination compounds, a number of sophisticated spectroscopic methods are
used. However, in order to apply them to the usually quite complicated vibrational or electronic spectra of heme proteins, it is necessary
to calibrate these methods using simple metalloporphyrin complexes.
Therefore, we are carrying out high-level Spectroscopic Investigations of Metalloporhyrins
using magnetic circular dichroism and polarized resonance Raman spectroscopy on a number of compounds of type [MIII(TPP)X]
(M = Fe, Co, Mn; X = Cl-, ClO4-, SR-, etc.;
TPP2- = tetraphenylporphyrin dianion).
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