Rational metalloprotein design for energy conversion applications

Continuing and increasing reliance on fossil fuels to satisfy our population’s energy demands has encouraged the search for renewable carbon-free and carbon-neutral sources, such as hydrogen gas or CO2 reduction products. Inspired by nature, one of the objectives of this dissertation was to develop protein-based strategies that can be applied in the production of green fuels. The first project of this dissertation aimed at developing a controllable strategy to incorporate domains with different functions (e. g. catalytic sites, electron transfer modules, light absorbing subunits) into a single multicomponent system. This was accomplished through the rational design of 2,2’-bipyridine modified dimeric peptides that allowed their metal-directed oligomerization by forming tris(bipyridine) complexes, thus resulting in the formation of a hexameric assembly.

Additionally, two different approaches to incorporate non-natural organometallic catalysts into protein matrix are discussed. First, cobalt protoporphyrin IX was incorporated into cytochrome b562 to produce a water-soluble proton and CO2 reduction catalyst that is active upon irradiation in the presence of a photosensitizer. The effect of the porphyrin axial ligands provided by the protein environment has been investigated by introducing mutations into the native scaffold, indicating that catalytic activity of proton reduction is dependent on axial coordination to the porphyrin. It is also shown that effects of the protein environment are not directly transferred when applied to other reactions, such as CO2 reduction.

Inspired by the active site of [FeFe]-hydrogenases, the second approach is based on the stereoselective preparation of a novel amino acid bearing a 1,2-benzenedithiol side chain. This moiety can serve as an anchoring point for the introduction of metal complexes into protein matrices. By doing so, this strategy enables the study of protein interactions with non-natural cofactors and the effects that it may have on catalysis. The work developed herein lays a foundation for furthering the study of the use of proteins as suitable environments for tuning the activity of organometallic catalysts in aqueous conditions, and interfacing these systems with other supporting units into supramolecular assemblies.