Thermodynamic Study of Colorimetric Transitions in Polydiacetylene Vesicles Induced by the Solvent Effect

We report the synthesis of 10,12-pentacosadyinoic acid (PCDA) and PCDA + cholesterol (CHO) + sphingomyelin (SPH) vesicles dispersed in water and the determination of their colorimetric response induced by small amount of organic solvents. In the absence of solvent, PCDA and PCDA/CHO/SPH vesicles showed an intense blue color. The addition of CHCl3, CH2Cl2, and CCl4 caused a colorimetric transition (CT) in both structures with the following efficiency: CHCl3 > CH2Cl2 congruent to CCl4. However, CH3OH did not cause a blue-to-red transition. By microcalorimetric technique we also determined, for the first time, the enthalpy change associated with the CT process and the energy of interaction between solvent molecules and vesicle self-assembly. We observed that the chloride solvents induced a colorimetric transition, but the thermodynamic mechanism was different for each of them. CT induced by CHCl3 was enthalpically driven, while that caused by CH2Cl2 or CCl4 was entropically driven.