# Ion Valency as a Molecular Switch for Salt‐Resistant Underwater Adhesion

## TL;DR

This paper shows how different ions can control underwater adhesion in peptide systems, with multivalent ions like Y3+ enabling strong adhesion even in salty environments.

## Contribution

The study reveals that ion valency can act as a molecular switch to modulate adhesion in cation-π-based systems under saline conditions.

## Key findings

- Multivalent ions like Mg2+ and Y3+ enhance underwater adhesion by forming stable π-cation-π networks.
- Y3+ ions show superior adhesion enhancement due to multidentate bridging capabilities.
- Monovalent K+ ions disrupt adhesion by forming weak K+-π complexes.

## Abstract

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.

Monovalent K+ ions weaken adhesion by forming K+‐π complexes with weak bridging capacity. In contrast, multivalent cations like Y3+ enhance adhesion by forming stable π‐cation‐π bridging networks, which are resistant to salt and capable of compensating for the loss of native π–π and NH3
+‐π interactions. Through these contrasting effects, K+ and Y3+ function as molecular switches that regulate adhesion in cation‐π‐based adhesive systems.