Marc R. Knecht

Multimetallic nanoparticle catalysts present exciting opportunities to achieve sustainable chemical transformations based on their unique structure that can lead to enhanced reactivity, especially when a blend of functional metal atoms is incorporated. The fundamental science regarding the interaction between the metal types and the role of the surface ligands is developing, especially as the number of constituent atom types increases. To investigate these effects, a set of three different bimetallic nanoparticles were prepared (PdAu, AuAg, and PdAg) using the same peptide capping agent (the AuBP1 peptide). Simplified bimetallic materials were probed with a similar interfacial ligand to explore the effect of switching metal composition on catalytic activity, as well as the breadth of compositions that could be prepared using the same peptide ligand. Characterization of the stable structures indicated that bimetallic alloy nanocatalysts were generated with sizes of less than 5 nm in diameter. Catalytic analysis for the reduction of 4-nitrophenol revealed enhanced reactivity for nanoparticles prepared with PdAu and AuAg at metal/metal ratios of 3:2 and 4:1, respectively. These results demonstrate key structural and compositional effects in the materials, which could be used to design different particles of increased complexity for further reactivity enhancement.

Highly elastomeric materials are routinely found in nature that are generated from enzymatic cross-linking of proteins such as resilin. This process can be recreated on the benchtop using conventional photocatalytic approaches, which can be highly efficient; however, due to the large size of the elastomer generated via protein cross-linking, confirmation of the final structure remains elusive. Herein, we explore photocatalytic cross-linking of smaller resilin-like peptides (RLPs), taken from the resilin protein, which do not precipitate upon cross-linking. Using a [Ru(bpy)3]2+-based photocatalytic process, significant peptide degradation was observed, which dominated the reaction. Alternatively, enzymatic cross-linking of the peptides was observed to generate the anticipated product. Similar studies were conducted on a larger peptide construct where both the photocatalytic and enzymatic cross-linking process generated elastomeric materials with differing morphologies. AFM-based analysis confirmed vastly different Young’s moduli based upon the cross-linking strategy. Computational modeling was used to predict likely molecular-level structures and mechanical properties of the elastomer materials based on both the photocatalytic and enzymatic preparation processes, indicating that the case where the rate of cross-linking is greater than that of chain fragmentation is the more likely photocatalytic scenario, based on the trends in predicted Young’s modulus.

Conformationally responsive proteins are increasingly being harnessed to build stimulus‐responsive biointerfaces, yet the interconversion dynamics of proteins are routinely lost upon adsorption to inorganic surfaces. Heterogeneous protein attachment, driven by the stochastic presentation of surface‐interactive residues, can occlude active sites, mask allosteric interfaces, and diminish the dynamic properties the protein was recruited to provide. Here, we demonstrate a genetically encoded strategy to preserve conformational switching by biasing surface attachment through the modification of calmodulin (CaM) with a Au binding domain, the AuBP1 peptide, to promote a preferred adsorption geometry at aqueous Au interfaces. Quartz crystal microbalance with dissipation measurements reveal fully reversible viscoelastic changes in the adsorbed layer for CaM fused to AuBP1 across multiple Ca ²⁺ binding/release cycles with no measurable mass loss, which was absent for wild‐type CaM. Atomic force microscopy independently confirmed conformation‐dependent surface morphologies for the apo and holo states. Molecular dynamics simulations support a dominant AuBP1‐mediated binding configuration that minimizes disruptive surface contacts. These observations identify transferable design principles for switchable biointerfaces and establish that non‐covalent peptide‐mediated orientation can sustain functional protein dynamics in direct contact with a metal without reliance on covalent immobilization.

Nature provides a palette of materials with properties ranging from strong and tough to flexible and elastomeric. Resilin, a protein in insects, can generate resilient elastomers cross-linked at tyrosine residues. These elastomers rival or exceed the properties of synthetic materials, making it desirable to mimic the natural system. Herein, we demonstrate the use of biomolecules that incorporate resilin-like peptides (RLPs), identified from resilin, with Au binding domains. These sequences bind Au interfaces to preorganize RLPs for eventual cross-linking. This approach could be exploited to generate elastomers that mimic the Au structure. Through this analysis, sequence effects were identified that could optimize peptide domain ordering on Au to controllably cross-link the biomolecules, leading to elastomer formation. Furthermore, nanoparticle synthesis studies indicated that Au binding domain inclusion was critical to generate monodisperse materials (in both shape and size). Such results provide pathways for controllable peptide cross-linking on surfaces for biostructural formation.

Bimetallic nanoparticles have attracted increasing scientific and technological interest as modules for creating nanoscale materials with unique magnetic, electronic, and chemical properties.

Resilin protein-based elastomers could provide pathways to synthetic materials with increased mechanical resilience; however, it remains challenging to replicate their properties when they are made in the lab. This is because Tyr-based cross-linking is necessary, which may require preorganized configurations of resilin in its natural environment. In previous work, the P1 graphene-binding peptide was conjugated with resilin-like peptides (RLPs) to produce P1/RLP conjugates. The binding of these peptides to the graphene surface was studied using QCM analysis and atomic force microscopy as an initial step toward preorganization for eventual cross-linking. Herein, the adsorption studies of RLPs (R1 and R2) and their conjugates with the P1 graphene-binding peptide are studied on hexagonal boron nitride (h-BN) using QCM analysis and molecular modeling. The results are compared with those of previous work based on the graphene surface. The binding affinity of P1/RLPs to h-BN is found to be similar to that of graphene, with notable changes that can be attributed to the variations in the surface composition. In addition, molecular simulations of the surface-adsorbed P1/RLP structures on h-BN indicate substantial differences compared to those on the graphene surface, with the RLP domain dominating the binding on h-BN. Moreover, the parent RLP peptides demonstrated increased binding to h-BN, which was not observed with graphene, thus indicating that h-BN is likely to be a poorer surface for peptide preorganization for eventual cross-linking for the controlled preparation of resilient elastomers.

The controlled binding of proteins on nanoparticle surfaces remains a grand challenge required for many applications ranging from biomedical to energy storage. The difficulty in achieving this ability arises from the different functional groups of the biomolecule that can adsorb on the nanoparticle surface. While most proteins can only adopt a single structure, metamorphic proteins can access at least two different conformations, which presents intriguing opportunities to exploit such structural variations for binding to nanoparticles. Such effects are examined using calmodulin, a sensing messenger protein, that can adopt two conformations based on Ca²⁺ binding. The affinity of the apo and holo forms of the protein for Au is examined using a highly integrated set of experimental and computation studies, which demonstrated significantly enhanced binding for the holo protein as compared to the apo. Such effects are proposed to arise from changes in the protein structure, which lead to substantially varied biomolecular surfaces that facilitate both Au adsorption and protein‐protein assembly once adsorbed. Such studies provide critical information for protein structural design to control nanoparticle adsorption for wide‐ranging applications.

Elastomers based on the resilin protein confer exceptional mechanical resilience in nature, but it remains elusive to recover the remarkable properties of these materials when they are made in the laboratory. This is possibly due to preorganized conformations of resilin in its natural setting, facilitating Tyr-based cross-linking. Here, resilin-like peptides (RLPs) are conjugated with a graphene-binding peptide, P1, to produce P1/RLP conjugates, in which the P1 domain may provide favorable preorganization on a graphene surface. Experiments using quartz crystal microbalance analysis and atomic force microscopy identified that the parent RLPs demonstrate negligible graphene binding; however, integration of the P1 with the RLPs resulted in the formation of dense, patterned bioligand overlayers on graphene. To complement this, molecular simulations revealed a notable difference in binding mode of the conjugates compared with typical materials binding peptides. Specifically, the adsorption of the P1/RLP conjugates did not focus on a few strongly bound "anchor" residues, but instead supported a more diffuse mode of binding, with many more participating residues featuring moderate contact. Analysis of the number of available Tyr residues (i.e., those not adsorbed at the surface) indicate that the RLP2-based conjugates will provide greater opportunity for cross-linking when adsorbed on graphene, providing a framework to generate patterned elastomeric materials.