Supramolecular Self-Assembly of EF-Hand Modular Peptides for Aqueous Separation of Rare Earth Elements.

Efficient and green separation of rare earth elements (REE) remains a critical challenge, with conventional solvent extraction relying heavily on toxic organic solvents. Herein, three biomimetic peptides (NF-H1, NF-H2, and NF-H3) integrating the Nap-FF hydrophobic assembly motif with EF-hand-derived REE-recognition sequences were designed for fully aqueous REE separation. The peptides form stable, preassembled β-sheet scaffolds via Nap-FF-mediated hydrophobic interactions and intermolecular hydrogen bonding, within which specific coordination of RE3+ with EF-hand side-chain carboxyl groups neutralizes surface charges and drives supramolecular aggregation, triggering macroscopic aqueous-phase separation. A synergistic binding mechanism, that is, specific coordination interaction and noncovalent binding, yields an adsorption stoichiometry of 1:1.2 (peptide:RE3+), surpassing the canonical EF-hand capacity. The system achieves selective separation of light RE3+ (La3+, Ce3+, Pr3+, and Nd3+) under mild, solvent-free conditions, with adsorption efficiency exceeding 80% over five adsorption-desorption cycles, demonstrating excellent recyclability. This work provides a green, recyclable peptide self-assembly platform for efficient aqueous REE enrichment and recovery.