Bio-inspired strategies have emerged as potential approaches to prepare and employ technologically important nanomaterials as catalysts that use eco-friendly and energy efficient reaction conditions. As a result, sustainable and efficient catalytic methods may be developed using these techniques. Peptide-based fabrication strategies have become unique examples of synthetic approaches as the sequences are composition specific, are able to generate nanoparticles of <20 nm, and result in final structures which are highly active. However, the source of this activity is not understood. Principal Investigator Marc Knecht through the University of Kentucky Research Foundation believes a unique surface architecture is established leading to the activity. He intends to elucidate atomic-level structural information concerning the peptide surface ligands of biomimetic Pd nanoparticulate catalysts to isolate the motifs responsible for their enhanced catalytic reactivity for carbon-coupling reactions in water at room temperature. Unfortunately, little information is presently known about how the peptides coordinate to the surface of the catalyst particle, as it is this interaction which is likely responsible for the enhanced reactivity of the materials. The PI believes that the sequence binds in such a manner that it exposes a significant fraction of the metallic surface, from which reactivity occurs. By understanding this surface structure, the PI will be able to explore the catalytic mechanism for C-coupling, which could subsequently be exploited to expand the reactivity spectrum of these efficient catalyst materials. By understanding the surface structure and mode of sequence interactions, the rational design of peptides and other ligands could be possible to develop further enhanced nanocatalytic architectures. This is the broader technical impact of the project. The work has immediate potential to impact energy efficient and environmentally friendly catalytic schemes for use in delivering "green" chemical synthetic methods.
The broader outreach impact of the proposal employs the very visual nature of the catalytic research as a mechanism to increase interest in STEM disciplines in rural Kentucky students. The PI proposes to use the visual and colorful aspects of this research as a mechanism to grasp and maintain student interest in hopes of increasing their future educational development. From this topic, student exposure to eco-friendly/energy efficient catalysis, nanotechnology, and organic chemistry/molecules can occur.
In this project, we employed strategies inspired by biologiy to fabricate highly reactive biomolecule-stabilized Pd nanoparticle catalysts that operate under green conditions. To that end, we have used a peptide containing 12 amino acids, termed Pd4 (sequence = TSNAVHPTLRHL), which specifically binds to the surface of Pd nanoparticles via the highlighted histidine residues. This peptide binds to the nanoparticle surface in such a manner that the particles remain stable in solution while maximizing the exposure of the metal surface to drive catalytic reactions to form new carbon-carbon (C-C) bonds. We hypothesized that the peptide-binding event at the Pd surface controlled the functionality of the materials where modifications to this surface structure could be used to maximize and enhance the reactivity. This has been demonstrated for C-C coupling reactions, namely Stille and Suzuki coupling, where the reaction occurs in water, at room temperature, using very low amounts of the catalytic materials. The intellectual merit of this research focused on the combination of high-resolution characterization techniques with catalytic analysis of the materials for reactions to elucidate structure/function relationships of the bio-based nanocatalysts. We are striving to discover the optimal peptide sequence/binding abilities that direct the activation of the catalyst with optimized reactivity under energy neutral conditions, meaning no input of energy to drive the chemical process. By having materials that are most efficient under biological conditions, the quantity of energy required to drive the process may be diminished, which is critical in light of the global energy state. The broader impacts of the research program focused on using nanocatalysis as a tool to encourage middle and high school students to pursue science as a college major. This engagement activity focused specifically on underrepresented groups that come from financially strained backgrounds, where students from this population typically do not pursue higher education or research-based careers. By reaching these students at a critical age where long-term interests are developed, it is envisioned that a lasting curiosity in the physical sciences and engineering disciplines could be achieved, which could be translated to a new and engaged research work force for the future continuity of scientific development.
