Influence of tail structure on thermotropic phase behavior, stability, supramolecular organization, and vesicle properties of nonionic β-alaninol-based amphiphiles: Homologs of N-acylethanolamines.

The hydrophobic tail structure of lipids or amphiphiles plays a critical role in governing the self-assembly, structure, dynamics, and function. In the present work, β-alaninol-based amphiphiles bearing cholesterol, saturated, unsaturated, and branched fatty acid-based tails were synthesized in N-acyl and N-cholesteroyl forms and systematically investigated to elucidate how tail architecture controls physicochemical properties. Results revealed that variations in amphiphile tail structure influenced pronounced differences in phase transition behavior and supramolecular packing. Amphiphiles bearing saturated, unsaturated, or branched tails favored more tilted or less-ordered bilayer arrangements than the cholesterol-based amphiphile, which lead to lower phase transition temperatures of fatty acid-based amphiphiles than the cholesterol-based amphiphile. Thermal analysis studies revealed that N-acylation substantially enhanced thermal stability, with decomposition temperatures increased by 50-70 °C compared to the corresponding parent fatty acids; however, the cholesteroyl-based amphiphile exhibited lower enhancement than cholesterol. Laurdan and ANS (8-anilinonapthalene-1-sulphonic acid) fluorescence studies revealed a strong correlation between tail structure, membrane packing and interfacial hydration, in which unsaturation in tail lowers the gel-to-liquid-crystalline transition temperature and enhances ANS accessibility. Dynamic light scattering and field-emission scanning electron microscopy confirmed the formation of unilamellar vesicles, where tail architecture significantly influences vesicle size, polydispersity, and zeta potential. Comparison of bilayer-related properties between matched-chain saturated ethanolamine- and β-alaninol-based amphiphiles revealed only moderate effects arising from the headgroup substitution. Overall, these findings establish amphiphile tail design as a key structural parameter for controlling amphiphile packing, phase behavior, and hydration, offering molecular-level insights for tuning properties of lipid-based assemblies for various applications.