Marine organisms, such as mussels and barnacles, are able to bond to surfaces under water using protein-based adhesives. Several physicochemical interactions contribute to the extraordinary adhesion and cohesive strength of these adhesive proteins, including oxidative crosslinking, hydrogen-bonding, metal coordination, hydrophilic interaction, π-π interaction and cation-π interaction. The cation-π interaction occurs between amino acids with an electron-rich π system (such as phenylalanine) and a cationic molecule (such as cationic ions Na<sup>+ </sup>and K<sup>+</sup> or amino acids with a cationic charge such as lysine). Cation-π interaction involves highly hydrophilic/hydrated positively-charged functional groups as the cationic partner. Hydration shells, especially those surrounding cationic species, are known to be strongly bound to their cationic center, providing strongly repulsive forces and inhibiting any possible adhesive interactions. This observation raises the important question of the role of cation hydration shells in modulating cation-π interactions. We address this question by dissecting cation-π interactions between surfaces coated with peptides bearing π-donor and cationic residues. Without changing the composition of the peptides, we modulate their hydration shells by changing systematically their sequence, while monitoring the cation-π interaction by measuring the adhesion energyusing the surface forces apparatus. Engineered peptides with short sequences of phenylalanine (F) and lysine (K) amino acids were used and demonstrated the ability of forming the most efficient cation-π interactions reported for underwater adhesive systems in the literature to date. This outstanding cation-π binding efficiency was achieved only when an isolated K amino acid is flanked by F amino acids in the peptide sequence. The results provided in this study allow to rationalize the molecular determinants necessary for strong cation-π interactions and offer new avenues for the development of strong mussel-inspired underwater adhesive materials.

Bio-inspired superadhesive peptides with enhanced cation-π interactions

ACS Spring Meeting 2021

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