Polymerization-induced color changes of polydiacetylene-containing liposomes and peptide amphiphile fibers

Polydiacetylenes have received much attention due to their intrinsic optical properties. Their inclination to change color in response to environmental factors has been extensively exploited in the sensing of analytes. In this study we functionalized diacetylene-containing peptide amphiphiles and phospholipids with α-bromo esters so that they could be used as initiators in atom transfer radical polymerization (ATRP) reactions. Subsequently, the supramolecular assemblies formed by these molecules upon their addition to water, namely peptide amphiphile fibers and liposomes, were stabilized by polymerizing the diacetylene moieties present in the molecules. As a result, highly colored, disassembly resistant, macro initiators were created. To investigate whether steric crowding on the surface of these assemblies could influence the color of the polydiacetylenes, we utilized the initiator functionality that had been introduced prior to assembly in ATRP. We found that the chromatic properties of the polydiacetylenes were directly related to the formation of polymer on the surface of peptide amphiphile fibers as well as liposomes. Furthermore, we were able to demonstrate that the progress of this color change could be monitored with UV-visible spectroscopy.