EFFECT OF PHOTOPOLYMERIZATION ON THE MORPHOLOGY OF HELICAL SUPRAMOLECULAR ASSEMBLIES

A photosensitive chiral lipid was synthesized by introducing 2,4-hexadienoyl groups into a L-glutamate derivative. The lipid in water spontaneously formed single-walled helical aggregates at either 15 or 70-degrees-C (T(c) = 51-degrees-C). The lipid assemblies at 15-degrees-C showed a typical blue shift in the absorption of the 2,4-hexadienoyl groups and extremely strong exciton coupling of the absorption (e.g., [theta]1246 = -1.5 X 10(6) deg cm2 dmol-1). These results show that the 2,4-hexadienoyl groups strongly interact in the bilayer interior at temperatures below T(c). Photoirradiation (254 nm) decreased the absorption of 2,4-hexadienoyl groups, and induced a morphological transition from helical lamellar to tubular aggregates at temperatures below T(c) and to twisted fibrous aggregates above T(c). The aggregates produced by photoirradiation at 70-degrees-C showed significant stability to temperature change. Binding of methyl orange to the bilayer assembly showed that the morphological transition induced by irradiation at 15-degrees-C occurs with a change of physical states.