Preparation and morphology of polydiacetylene from self-assembly of diacetylene lipids

Abstract

Self–assembly of polydiacetylenes derived from vesicles of 10,12-pentacosadiynoic acid (PCDA) and its amide derivatives were investigated by using dynamic light scattering (DLS), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The condensation reaction of PCDA with 5 and 0.5 equivalents, ethylenediamine yielded the corresponding monoamide (AEPCDA) and diamide (EBPCDA). The purpose of this investigation was to find the optimum conditions by varying conditions such as pH, ionic strength (NaCl) and concentration of lipids in Milli Q water. The optimum pH for preparing the nanovesicles (<200 nm) was pH 5-7 for poly(PCDA) and pH 3 for poly(AEPCDA). For ionic strength, there was no significant difference of effect of various NaCl concentration in poly(PCDA) and its amide derivatives, so the required NaCl concentration for biomembrane preparation would be in a range of 0.1 mM – 1 mM NaCl. The various conditions for poly(EBPCDA) were ineffective because the stable and closed pack structure of poly(EBPCDA) to the external perturbations was tolerant. The study of thermochromism properties were also investigated by colorimetric method using a temperature controlled UV-Vis spectrometer. Accordingly the results indicate that the particle size had a close relation to the transition temperature. In poly(PCDA) at initial pH 5-7 nanovesicles had lower transition temperature than others. In contrast, poly(AEPCDA) at pH 3 nanovesicle had higher transition temperature than other, probably due to the effect of charged at headgroup that was protonated or deprotonated in difference environment of each monomer. Moreover, the color transition of poly(EBPCDA) exhibited excellent reversibility at initial pH 5-7 while those of poly(PCDA) and poly(AEPCDA) were irreversible. Those optimum conditions would become the useful applicational source for biosensors and thermochromic devices.