Lysine-based oligomeric surfactants with cyanuric chloride: synthesis and micellization properties

Abstract

Two lysine-based oligomeric surfactants 2C12LyNa2 and 3C12LyNa3 were synthesized using cyanuric chloride and Ne-lauroyl-l-lysine. Their physicochemical properties of aqueous solutions were determined by surface tension and conductivity as well as dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. From the results of surface tension and conductivity measurements, the critical micelle concentration decreases by one order of magnitude with increasing degree of oligomerization. 3C12LyNa3 and 2C12LyNa2 tend to form premicellar aggregates in solution at a sufficiently low concentration. In addition, their interface behaviors such as adsorption and micellization are reflected by parameters such as the minimum surface area per molecule (Amin), adsorption efficiency and effectiveness (pC20), maximum surface excess concentration (Γmax), and standard free energy for micellization and adsorption (ΔGmic∘, ΔGads°). The Amin value of 2C12LyNa2 and 3C12LyNa3 is two times that of the monomeric surfactant sodium Ne-lauroyl-l-lysine (C12LyNa). With increasing degree of oligomerization, pC20 increases, which follows the reverse order for ΔGmic° and ΔGads°. TEM results showed that C12LyNa forms slightly entangled rod-like micelles. 2C12LyNa2 and 3C12LyNa2 can self-assemble into regular spherical assemblies; DLS showed that with increasing degree of oligomerization for 2C12LyNa2 and 3C12LyNa3, the diameters of the spherical aggregates decrease and the hydrophobic interaction and hydrogen bonding become stronger.