Novel cyclic azobenzene-containing vesicles: photo/reductant responsiveness and potential applications in colon disease treatment

Abstract

A cyclic azobenzene was chosen as a pendant in the hydrophobic segments of amphiphilic copolymers, and novel nanoparticles were constructed with dual photo and reductant responsiveness. To investigate the topological effects of the cyclic azobenzene architecture on the properties, an analogue of the amphiphilic copolymer with linear azobenzene units was also synthesized. Two kinds of amphiphilic copolymers with cyclic azobenzene (PEG₄₅-b-PCAzo₁₇) and linear azobenzene pendants (PEG₄₅-b-PLAzo₁₉) assembled into stable vesicles in PB solution (pH = 7.4) and also show unique dual sensitivities to ultraviolet radiation and dithionate derivatives. We have investigated the differences of the vesicles obtained from the two kinds of copolymers in the encapsulation and release of Nile Red (NR) or doxorubicin (DOX). The vesicles formed by PEG₄₅-b-PCAzo₁₇ exhibited higher drug loading content and better reversibility of NR fluorescence variation under alternating irradiation with UV/Vis light than those formed by PEG₄₅-b-PLAzo₁₉; meanwhile, neither disruption of the vesicles nor leakage of Nile Red molecules was detected. Moreover, the CAzo-containing vesicles showed a higher release rate and larger release amount of DOX molecules from the membrane under the reduction of Na₂S₂O₄. Because dithionites can act as a mimic of azoreductase, the amphiphilic copolymer with cyclic azobenzene revealed competitive performance as a drug carrier for colon disease treatment.