Two Faces of Amine-Catechol Pair Synergy in Underwater Cation-π Interactions

Cation-pi interactions play important roles in various biological systems. Recently, cation-pi interactions have been suggested to have considerable roles in mussel adhesion, which is the most well-known biological model for underwater adhesion. Although amine-catechol pair synergy in mussel adhesion has been well studied for surface adhesion in the aqueous phase, little is known about its effect on cohesion, particularly in intermolecular cation-pi interactions. Here, we designed mussel-inspired model peptides to characterize the amine-catechol pair effect on cation-pi interactions. We used nanomechanics to measure the interaction directly and probed cation-pi interactions with nuclear magnetic resonance and Raman spectroscopy. Moreover, we established the origins of these effects through intensive Raman spectra analysis. We discovered that amine-catechol pairs have antisynergetic effects on intermolecular cation-pi interactions, and this finding may provide the insight that the amine-catechol pair synergy may not always work on the positive side in underwater adhesion.