Nature Chemistry, Published online: 01 June 2026; doi:10.1038/s41557-026-02158-x Ultrathin single-crystalline 2D peptide structures are widespread in nature but challenging to construct synthetically. Now it has been shown that a metal-directed β-sheet-like assembly strategy enables the generation of free-standing ultrathin 2D peptide crystals—with programmable sequence, chirality and side-chain chemistry—that can be used to stereoselectively bind glucocorticoids and chiral pharmaceutical molecu