Peptide-gold nanozymes as catalysts for green chemistry applications ranging from cascade catalysis to carbon capture

Abstract

Protecting the environment and remediating it from the consequences of anthropogenic activities has become an important challenge in today’s world. Advancements in the field of catalysis, as an integral part of sustainable and green chemistry, play a major role in the development of new environmentally benign technologies to achieve this. In this regard, the field of nanotechnology opened up new possibilities for the design and synthesis of robust enzyme mimics (nanozymes) that fulfill the criteria of a green catalyst. In particular, gold nanoparticles (Au-NPs) functionalized with catalytically active peptides (Pep-Au-NPs) have proven to be a promising strategy towards the creation of artificial enzymes with remarkable properties in molecular recognition and catalysis. However, the field is still in its infancy. To extent the contemporary insights into the field of Pep-Au-NPs and establish first design rules, one part of the research conducted in this thesis deals with the systematic study of design principles of Pep-Au-NPs. More specifically, research was focused to systematically elucidate the effect the position of the catalytic center along the peptide sequence has on the catalytic properties of the corresponding Pep-Au-NP assemblies. A correlation was found between the hydrophobic nature of the employed substrate and the region in which catalysis takes place within the generated peptide-monolayer. The other two studies included in this work were directed to broaden the application scope of these conjugates. First, Pep-Au-NP were studied in their ability to act as a multifunctional cascade catalyst that performs two sequential reactions on a given substrate. By utilizing the hybridity of the system, a peptide-monolayer was established that catalyzed ester hydrolysis, while the Au-NP surface functioned as an efficient hydrogenation catalyst. The reaction was performed as a one-pot reaction in aqueous solution. Second, a Pep-Au-NP was designed to function as an artificial carbonic anhydrase (CA) mimic for the conversion of CO2 to HCO3- in water. The artificial CA was able to catalyze CO2-hydration and showed superior catalytic activity over the unconjugated peptide variant. Recycling of the Pep-Au-NP was possible without significant loss in activity even after treatment at elevated temperatures. The results of this work, on the one hand, contribute to the rational design and synthesis of Pep-Au-NPs as artificial nano-enzymes; on the other hand, provide proof-of-concepts that Pep-Au-NPs are able to perform reactions applied in environmental-friendly processes.