| Abstract: | Phospholipids, of which phosphoryl cholines are a specific example, are the most common lipid components of cell membranes. Synthetic acetylenic phospholipids form closed model membranes, vesicles, or liposomes when dispersed in water. Below the temperature at which lipid chain crystallization occurs irradiation of vesicles causes polymerization of the diacetylene groups. In chloroform solution the spectrum of the polymer is independent of temperature. However, when the polymer is dissolved in methanol or dispersed in water with another lipid spectral changes occur. As solution or dispersion is cooled a second peak appears on the long wavelength side of the original absorption and gradually increases in intensity. Evidence that suggests that this peak is associated with aggregated polymer chains is presented. It appears that within the aggregates exciton coupling splits the excited state into two new levels and only transitions to the level of lowest energy are allowed. |
