Molecular dynamics simulations of the supramolecular assembly between an azobenzene-containing surfactant and α-cyclodextrin: Role of photoisomerization

Control of the self-assembly and disassembly at the molecular level has become a subject of increasing activity. The supramolecular assembly between a photoswitchable azobenzene-containing surfactant, AzoC10, and α-cyclodextrin that combines photochemistry and host-guest chemistry for a stimulus-responsive vesicle has been recently reported. To clarify the role of photoisomerization in the reversible assembly and disassembly, we present in this work atomistic molecular dynamics simulations of the host-guest complexation of AzoC10 with α-cyclodextrin. The results of simulation reveal that both cis-and trans-AzoC10 form the inclusion complexes with α-CD, but the binding modes are rather different. The azobenzene moiety of trans-AzoC10 is included at the center of the cavity of α-CD, whereas one of the phenyl rings of cis-AzoC10 is exposed to water and the other is included in the cavity of α-CD. The shuttling motion of α-CD over the long alkyl chain of cis-AzoC10 is observed in the simulations. The potentials of mean force calculated for AzoC10 to pass through the cavity of α-CD show that the host-guest assembly is basically downhill for trans-AzoC10, but an energy barrier has to be overcome for cis-AzoC10 to complex with α-CD.