l-Histidine Salt-Bridged Monomer Preassembly and Polymerization-Induced Electrostatic Self-Assembly

Salt bridges are predominant in protein constructionand stabilization,yet largely unexplored for polymer nanoparticle synthesis. We hereinreport the use of l-histidine salt bridges to drive monomerpreassembly and two-dimensional electrostatic self-assembly in aqueousphoto-RAFT polymerization. l-histidine salt bridges drivethe monomer clustering nucleation, complex coacervation, and Coulombicstabilization, leading to the 2 nm ultrasmall clusters and coacervatedroplets. Homopolymerization leads to a precision two-dimensionalelectrostatic self-assembly via a droplet-monolayer-multilayer transition,i.e., salt-bridged homo-polymerization-induced self-assembly (PISA).Block copolymerization does not disturb the "salt-bridged homo-PISA"mechanism. Enhanced Coulombic repulsion via seeded polymerizationof charged monomers using as-achieved multilayer lamellae (seeds)yields supercharged 5 nm ultrathin monolayer lamellae with high colloidalstability upon dilution, salting, and long-term storage, urgentlyneeded for bioapplications. This work opens up a new avenue to useamino acid salt bridges for PISA synthesis of biologically important,yet hitherto inaccessible, salt-resistant ultrathin polyelectrolytecomplex nanomaterials.