Polypeptide-based amphiphilic brush copolymers as unimolecular micelles: synthesis, characterisation, and encapsulation study

Polypeptide-based amphiphilic brush copolymers PLL-g-(PBLG-b-PEG) and PLL-g-(PZLL-b-PEG) with a poly(L-lysine) (PLL) backbone and amphiphilic oligo(-benzyl-L-glutamate)-b-poly(ethylene glycol) (PBLG-b-PEG) or oligo(epsilon-benzyloxycarbonyl-L-lysine)-b-poly(ethylene glycol) (PZLL-b-PEG) side chains were synthesised, characterised, and evaluated as unimolecular nanocontainers to encapsulate hydrophobic guest molecules. The structure of these brush polymers was modulated by tuning the length of the PLL, PBLG/PZLL, and PEG segments. The final products were characterised with H-1 nuclear magnetic resonance and gel permeation chromatography. The morphology and aggregation behaviours of brush copolymers were examined by using a transmission electron microscope and dynamic light scattering. It was revealed that these water-soluble brush copolymers resembled unimolecular micelles in an aqueous solution. An encapsulation study was performed using pyrene and oil red O as the model compounds, and the results showed that hydrophobic molecules could be solubilised in these unimolecular micelles with high loading capacities. The synthesised polypeptide-based amphiphilic brush copolymers could serve as promising unimolecular nanocarriers for the delivery of hydrophobic drugs.