Rotaxanes with a photoresponsive macrocycle modulate the lipid bilayers of large and giant unilamellar vesicles

Rotaxanes equipped with actuators hold great potential for developing highly functional molecular machines. Such systems could significantly enhance our ability to study and manipulate biological and artificial membranes. Here, we introduce a rotaxane with a ring featuring two azobenzene photoswitches, which retain their photoreversibility and can be stochastically shuttled along the axle in solution. Studies in model bilayers, supported by molecular dynamics simulations, show how azobenzene photoswitching alters the interaction of rotaxanes with surrounding lipids, leading to changes in lipid packing. Such changes in the lipid bilayer were leveraged to induce the light-triggered release of sulforhodamine B from large unilamellar vesicles. Additionally, light activation of the rotaxanes is shown to induce reversible contraction and expansion of giant unilamellar vesicles. The results provide novel insights into the interactions and operation of rotaxanes in lipid bilayers and their impact on membrane properties. This will aid in developing systems for precise membrane manipulation for applications in biomedicine and bioengineering. (Figure presented.)