Figure 17.
(A) Size illustration of various cargo molecules and (B) azobenzene stalks FRS1-MSN and EXT2-MSN. Because of the shorter stalk length, FRS1-MSN is limited to loading cargo molecules <2 nm. Hoechst 33342 and propidium iodide dyes remain excluded from FRS1-MSN as a result of their size. However, EXT2-MSN is observed to load all three of the listed fluorophores. (C) Schematic illustration of the fully assembled rotaxane nanovalve and operation. (1) After synthesis, the nanovalves are suspended in an organic solvent, which destabilizes hydrophobic interactions between the α-cyclodextrin and azobenzene moiety and allows for cargo loading. (2) Upon solvent exchange to water, rebinding of the cyclodextrin to azobenzene seals in the loaded cargo. (3) Irradiation with light induces isomerization to cis-azobenzene, forcing cyclodextrin to move to the end of the stalk, and allowing cargo to release. (4) Upon removal of the light stimulus, thermal relaxation of cis-azobenzene to its more stable trans isomer allows rebinding of the cyclodextrin and seals in the remaining cargo. Reprinted with permission from 57, copyright (2014) Nanoscale.