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 CHCl(3), CH(2)Cl(2), and CCl(4) caused a colorimetric transition (CT) in both structures with the following efficiency: CHCl(3) > CH(2)Cl(2) ≅ CCl(4). However, CH(3)OH 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 CHCl(3) was enthalpically driven, while that caused by CH(2)Cl(2) or CCl(4) was entropically driven.