Imidazolium based gemini amphiphiles derived from L-valine. Structural elements and surfactant properties

Abstract

Imidazolium amphiphiles often display excellent surfactants properties, while amide functionalities and chirality can implement self-assembly. The introduction of these functionalities in imidazolium gemini amphiphiles is expected to allow tuning their aggregation, achieving a higher emulsifying capacity of interest for practical applications. l-valine-derived gemini surfactants have been prepared and their aggregation investigated using NMR, UV-CD, fluorescence, LS or microscopy. The imidazolium gemini amphiphiles synthetized, presented excellent surfactant properties. The aromatic substitution pattern defines additional geometric constrains facilitating a fine tune of their properties, displaying the para-substituted compound best properties. This can be associated to facilitating the required conformational organization of polar and apolar fragments, while reducing coulombic repulsions between imizadolium rings. Two critical aggregation concentrations (CACs) were observed by fluorescence in aqueous media, with the formation of well-defined vesicles in the second step. Dynamic equilibria between aggregates of different sizes seem to be present. These gemini surfactants revealed of interest as emulsifiers for oil/water systems and for controlled fragrance delivery using (R)-limonene as a benchmark volatile compound.