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

Two lysine-based oligomeric surfactants 2C₁₂LyNa₂ and 3C₁₂LyNa₃ were synthesized using cyanuric chloride and N ^ε-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 (A _min), adsorption efficiency and effectiveness (pC₂₀), maximum surface excess concentration (Γ _max), and standard free energy for micellization and adsorption (ΔG _mic ^∘ , ΔG _ads ^° ). The A _min value of 2C₁₂LyNa₂ and 3C₁₂LyNa₃ is two times that of the monomeric surfactant sodium N ^ε-lauroyl-l-lysine (C₁₂LyNa). With increasing degree of oligomerization, pC ₂₀ increases, which follows the reverse order for ΔG _mic ^° and ΔG _ads ^° . 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.