Mechanism of Aqueous NCA-ROPISA: Self-Generated Nanoreactors, Peptide Folding and Self-Assembly.

Aqueous ring-opening polymerization-induced self-assembly of N-carboxyanhydrides (NCA-ROPISA) provides a powerful route to peptide-based nanomaterials, yet how polymerization outcompetes hydrolysis in water while driving self-assembly remains unclear. Here, time-resolved SAXS/WAXS reveals the mechanism of aqueous NCA-ROPISA during γ-benzyl-l-glutamate N-carboxyanhydride polymerization. Early nucleation of PEG-stabilized micelles creates nanoconfined reaction environments that favor polymerization by concentrating soluble monomers and maintaining reactive amino chain ends despite progressive acidification. Concurrently, β-sheet formation emerges at the onset of self-assembly, stabilizing nascent nuclei and directing anisotropic nanoparticle growth. These findings establish how nanoconfinement and secondary-structure formation cooperatively govern polymerization, self-assembly, and morphology development. Reminiscent of the ribosomal peptidyl transferase center, these self-generated nanoreactors exploit confinement to promote peptide-bond formation in water, identifying nanoconfinement as a general strategy for coupling polymerization, molecular folding, and self-assembly in biomimetic materials.