Hydrogen-Bond-Regulated Distinct Functional-Group Display at the Inner and Outer Wall of Vesicles

Abstract

A unique supramolecular strategy enables the unidirectional assembly of two bola-shaped unsymmetric π-amphiphiles, NDI-1 and NDI-2, which feature a naphthalene–diimide chromophore connected to nonionic and anionic head groups on opposite arms. The amphiphiles differ only in the location of a hydrazide group, which is placed either on the nonionic or on the anionic arm of NDI-1 and NDI-2, respectively. The formation of hydrogen bonds between the hydrazides, which compensates for electrostatic and steric factors, promotes unidirectional alignment and the formation of monolayer vesicles. The zeta potentials and cation-assisted quantitative precipitation reveal negatively charged and nonionic outer surfaces for NDI-1 and NDI-2, respectively, indicating that hydrogen bonding also dictates the directionality of the monolayer curvature, ensuring that in both cases, the hydrazides remain at the inner wall to benefit from stronger hydrogen bonding where they are in closer proximity. This is reflected in their different abilities to inhibit α-chymotrypsin, which possesses a positively charged surface: NDI-1 induced an inhibition of 80 % whereas hardly any inhibition was observed with NDI-2.