Ion Valency as a Molecular Switch for Salt-Resistant Underwater Adhesion

Achieving underwater adhesion remains challenging due to the disruption of interfacial interactions by hydration layers and the ionic environment. This study shows how high adhesion in a saline environment can be achieved in adhesive peptide systems relying on π-π and cation-π interactions using multivalent ions. Monovalent ions (K⁺) disrupt native peptide-peptide interactions, drastically reducing adhesion strength. Conversely, multivalent ions (Mg²⁺ and Y³⁺) enable robust interfacial adhesion by forming stable π-cation-π networks, effectively compensating for disrupted native pairings. The adhesion enhancement by Y³⁺ is particularly pronounced, highlighting its unique capability for multidentate bridging. Molecular dynamics simulations and quantum mechanical analyses confirm that Y³⁺ ions stabilize extended interfacial interactions, enabling stronger stress dissipation during tensile deformation. Additionally, NMR spectroscopy supports these observations by demonstrating significant cation-dependent perturbations of aromatic (Phe) and cationic (Lys) peptide residues. A thermodynamic model further elucidates the competitive binding dynamics underpinning adhesion modulation and capturing all experimental trends. This work provides detailed molecular insights into ion valency effects on cation-π mediated underwater adhesion, guiding the development of bio-inspired materials with tailored ionic responsiveness suitable for biomedical and technological applications in saline environments.