Hyperbranched polylysine: Synthesis, mechanism and preparation for NIR-absorbing gold nanoparticles

Abstract

Abstract The ring-opening polymerization (ROP) of N-(tetrafluoroboran ammonium)- l -lysine-N-carboxyanhydride (NH3BF4-Lys NCA) was initiated by triethylamine to prepare hyperbranched polylysine (HPlys) fluoroborate with narrow polydispersity at a low temperature. Both mass spectroscopy analysis and DFT computation evidenced that the resultant cyclic dimer mainly initiated ROP as a secondary species according to normal amine mechanism. The hyperbranched polylysine in aqueous solution existed in a unimolecular state at low concentrations, but transformed into spherical micellar aggregates at a high concentration of 5\u2009mg/mL, as characterized by dynamic laser scattering and transmission electron microscopy. By utilizing multivalent coordination interactions between hyperbranched polylysine and gold, the plasmonic gold nanoparticles (HPlys@Au NPs) were successfully prepared in aqueous solution, which elevated the solution by 23.1\u2009°C upon 5\u2009min of NIR laser irradiation (808\u2009nm, 2\u2009W/cm2).