Synthesis and interfacial properties of amphiphatic cryptophanes

Abstract

The new amphiphatic cryptophanes M5 and M6 were synthesized from their precursor M4. They present interesting properties due to their long chain substituents on one of the cyclotriveratrylene moieties. M4 was synthesized from a thio-cyclotriveratrylene platform obtained from thio-vanillin, using the template method developed for the preparation of dissymmetrical cryptophanes. The tris-hexanol (M5) or tris-hexadecyl (M6) substituted cryptophanes exhibited enhanced amphiphatic properties, which were investigated through the π–A isotherms of the interfacial films obtained at the air–water interface (Langmuir monolayers). The corresponding surface elasticity coefficients of the films were determined and their stability analyzed at different surface pressures. Stable molecular films of M5 were obtained after a first compression step, suggesting a rearrangement of the molecules at the interface. This behavior matched with a reduction of the molecular area consistent with the formation of bilayers of M5 molecules. Cryptophane M6 formed stable and reversible Langmuir monolayers at higher surface pressure (π_max = 27 mN m⁻¹). This was attributed to interactions between the long alkyl chain substituents of the cryptophane, which favor the organization of the molecules on the water subphase. At higher pressure both compounds form aggregates irreversibly.