Strong viscoelastic glycerol solutions formed from phenylalanine-based amine oxide surfactants

Abstract

Forming giant aggregates with surfactants in nonaqueous solvents is typically challenging due to weak solvophobic interactions. In this study, a series of phenylalanine-based surfactants—alkyl phenylalanine amide oxides (Cn-Phe-AO, n = 12, 14, and 16)—were synthesized. These surfactants independently induced gelation of glycerol at remarkably low concentrations of 22.5, 12.7, and 10 mM, respectively, compared with other glycerol systems. The zero-shear viscosity of a 10 mM C16-Phe-AO glycerol solution reached 10 501 Pa s. Cryogenic transmission electron microscopy (cryo-TEM) and circular dichroism (CD) confirmed the formation of left-handed helical structures, which account for the pronounced viscoelasticity of the glycerol solutions. The phenylalanine residue promotes regular molecular packing within the aggregates, enabling the formation of robust helical assemblies in glycerol that maintain a densely entangled network. Comparative analysis of aggregation in glycerol and 1,3-propanediol revealed that the hydrogen-bonding capability of the solvent is the primary driving force for the development of elongated micellar aggregates. This study establishes a model system for gelled glycerol solutions with minimal surfactants and offers new insights into molecular self-assembly in nonaqueous media.