Transformation of micelles into supramolecular vesicles triggered by the formation of [4]pseudorotaxanes

Abstract

Spontaneous formation of supramolecular vesicles which are triggered by the formation of [4]pseudorotaxane B was demonstrated, whereas both Guest and [2]pseudorotaxane A, the precursors of [4]pseudorotaxane B, only assemble into micelles in DMF/water solution. The remarkable transformation of Guest from micelles to supramolecular vesicles was confirmed through DLS, TEM, and Cryo-TEM experiments. The cumulative release of a model drug, 5-carboxyfluorescein (CF), was used to determine the permeability of the supramolecular vesicles. No leakage of entrapped CF was observed within 48h by fluorescence measurement, indicating the high stability of supramolecular vesicles. The formation mechanism of supramolecular vesicles self-assembled by [4]pseudorotaxane B was also discussed. In [4]pseudorotaxane B, CB[6] is used to increase the hydrophobic property of site β, which acts as hydrophobic “tail.” Meanwhile, CB[7] plays the role of increasing “head area” of site α, which acts as hydrophilic “head.” The synergistic effect of CB[6] and CB[7] induces the formation of supramolecular vesicles. Moreover, the effect of DMF content was investigated by TEM observations. It was found that the [4]pseudorotaxane B can self-assemble into regular supramolecular vesicles when the DMF content is in the range of 50–70%.