(497g) Mussel-Inspired Peptoids: The Backbone's Role in Adhesive Properties

Marine mussels adhere to rocky and mineralized surfaces in wet and turbulent environments via byssal threads terminated in plaques whose surfaces are coated in several unique, intrinsically disordered proteins. Among these proteins, mussel foot protein 5 (mfp-5) exhibits the strongest adhesion to most surfaces and is heavily decorated with both the cationic amino acid, Lysine, and the catecholic amino acid, Dopa. It is suggested that a synergistic interaction between these amino acids enhances the protein’s ability to adhere to aluminosilicate surfaces and increases interprotein cohesion via cation-π bonding. Cohesion force studies on mfp-5-inspired peptides using the surface forces apparatus (SFA) were previously conducted to better understand these cation-π interactions. In this work, peptoids of identical sequences to the peptides in the previously mentioned studies have be synthesized to remove the peptide bond within the backbone while preserving the molecules’ sidechains/pendant groups. As such, the effect of the enhanced conformational freedom and the reduced hydrogen bonding capacity afforded by the peptoid backbone was directly studied. We present SFA measurements on peptoid films between mica surfaces with systematically varied hydroxylation of their aromatic amino acids (Phenylalanine, Tyrosine, or Dopa). Molecular dynamics simulations were also conducted to model the likely surface conformations of the peptoid and peptide molecules. Based on the results, we propose that the increased conformational freedom and reduced hydrogen bonding in the peptoid backbone promote a larger fraction of side chains (Lysine, Dopa, Tyrosine) in an adsorbed peptoid to bind to substrates, thus increasing adhesion to substrates at the expense of cohesion with other peptoids in the film. These results suggest that the adhesive performance of mfp-5 depends on a balance between adhesion and cohesion and imply that backbone chemistry is not to be ignored when designing wet adhesives.