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

Cation−π interactions play important roles in various biological systems. Recently, cation−π 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−π interactions. Here, we designed mussel-inspired model peptides to characterize the amine–catechol pair effect on cation−π interactions. We used nanomechanics to measure the interaction directly and probed cation−π 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−π 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.