Polymersome-Based Modular Nanoreactors with Size-Selective Transmembrane Permeability.

Polymersome nanoreactors encapsulating the enzymes or particulate catalysts attract interest because of their potential use as modular reactors to synthesize complex compounds via a cascade of chemical reactions in a single batch. To achieve these goals, a key requirement is the tunable permeability of the polymersome membrane, which allows the size-selective transportation of reagents and products while protecting the encapsulated catalysts during the chemical reaction. We report here a stimuli-responsive route for controlling the permeability of the polymersomes of the binary blend of poly(ethylene glycol)--polystyrene (PEG--PS) and poly(ethylene glycol)--poly(acrylbenzylborate) (PEG--PABB). The presence of HO (1 mM) in the medium (0.1 M PBS, pH 7.4) triggers the oxidation of benzyl borate pendants of PABB to form poly(acrylic acid) (PAA). This transformation results in the perforation of the compartmentalizing membrane of polymersomes by the dissolution of PEG--PAA domains embedded in the inert PEG--PS matrix. By controlling the composition of the stimuli-responsive block copolymer, the polymersomes of the binary blend exhibit size-selective permeability without losing the structural integrity. Release of fluorescent guests with different sizes (fluorescein, PEG2k-, PEG5k-Rho) can be controlled by tuning the composition (PEG--PS/PEG--PABB = 100/0-80/20) of blended polymersomes. Selective permeability of the membrane provides protection of the encapsulated enzymes from external proteases present in the medium, resulting in the one-pot synthesis of small molecules via cascades of chemical reactions. The nanoparticular catalysts are also encapsulated within the permeable polymersomes, serving as modular reactors for the conversion of organic compounds via a cascade of reactions.