Phase behavior and spherical hollow particle formation by dipeptide-based two-headed amphiphiles in a mixed solvent of dimethyl sulfoxide and water

Dipeptide-based two-headed amphiphiles ([(Val)l(Val)l]2C10) in aqueous media transform from rod-like micelles to fibrous structures via vesicle-like intermediates on exposure to acid vapor. A similar phase behavior is present when the molecule is dissolved in DMSO followed by the addition of water (a poor solvent). On the basis of SLS, FT-IR, and FE-SEM measurements, spherical colloids are formed at a small DMSO content (20%) and fibrous structures are formed at a moderate DMSO content (40–60%). This phase behavior is influenced by the chirality of the amphiphiles. A mixed system composed of [(Val)l(Val)l]2C10 and [(Val)d(Val)d]2C10, and a system of [(Val)l(Val)d]2C10 immediately form crystals without formation of spherical colloids or fibrous structures. By optimizing the mixing ratio of the solvents and concentration of the solute, stable micrometer-sized hollow spheres composed of [(Val)l(Val)l]2C10 stabilized by non-covalent bonds are easily prepared.