Lithium-selective supramolecular assembly and capture by tripeptide gelators

We report a simple design strategy to introduce lithium-responsiveness into N-capped peptide low-molecular-weight gelators by incorporating the FFD tripeptide motif (FF extended with Asp). Asp adds an oxygen-rich carboxylate residue that enables cation-mediated assembly. In high pH aqueous solutions, 2NapFFD shows a pronounced cation selectivity. Li⁺ generates highly viscous, shear-thinning solutions with birefringent textures, while other Group 1 metals and bulky organic counterions result in low-viscosity and weakly ordered solutions. SAXS and SANS reveal that the addition of Li⁺ produces substantially extended micellar structures consistent with long cylindrical assemblies, whereas other monovalent cations lead to the formation of short cylindrical objects. The Li⁺ selectivity is intrinsic to the FFD sequence, with other aromatic caps tuning packing and mesoscale order. Finally, dialysis-driven Li⁺ exchange induces gelation and enables us to quantify the Li⁺ uptake by ICP-OES, illustrating potential for selective lithium capture.