Reversible deformation–formation of a multistimuli responsive vesicle by a supramolecular peptide amphiphile

Abstract

A systematic study of the ternary complex formation process for aromatic amino acids using ucurbit[8]uril (CB[8]) and a viologen amphiphile shows that the affinity of the amino acid needs to be higher or in a comparable range to that of CB[8] for the amphiphile in order to form the ternary complex. Based on these observations, a supramolecular peptide amphiphile and its corresponding vesicle are prepared using a peptide containing an azobenzene moiety. The azobenzene group at the N-terminus of the peptide served as the second guest for CB[8]. The vesicles obtained from this peptide amphiphile show response to a number of external triggers. The trans–cis isomerization of the azobenzene group upon irradiation with UV-light of 365 nm leads to the breakdown of the ternary complex and eventually to the disruption of the vesicle. The deformation–reformation of the vesicle can be controlled by illuminating the disrupted solution with light of 420 nm as it facilitates the cis–trans isomerization. Thus, the vesicle showed a controlled and reversible response to UV-light with the ability for manipulation of the formation–deformation of the vesicle by the choice of an appropriate wavelength. The vesicle showed response to a stronger guest (1-adamantylamine) for CB[8], which displaces both the guests from the CB[8] cavity and consequently ruptures the vesicle structure. 2,6-Dihydroxynaphthalene acts as a competitive guest and thereby behaves as another external trigger for replacing the peptide from the CB[8] cavity by self-inclusion to form the ternary complex. Henceforth, it allows retaining the vesicle structure and results in the release of the peptide from the vesicle.