Molecular Recognition Based on Hydrogen-bonding in the Coliposomes of Phosphatidylcholine and Amphiphiles Using Nucleobases1

A functional amphiphile, N6-myristoyl-9-[8-(l-trimethylamino)octyl] adenine bromide (MTOAB), was used to form coliposomes of phosphatidylcholine(PC), PC/thymine, and PC/TOTB using sonication. The morphologies of the coliposomes were characterized using TEM (transmission electron microscopy). The UV-Vis spectroscopic behavior of PC/MTOAB/thymine(molar ratio =5:1:1) and PC/MTOAB/TOTB(molar ratio = 5: 1: 1) of coliposomal solutions showed that as a result of base pairing, absorption intensity showed a decrease at 263 nm with increase of time. The decrease of absorption intensity is ascribed to the hypochromic effect, which is because of the formation of hydrogen bonds between adenine and thymine in the coliposomes. The same effect was also observed for the mixture of aqueous PC/MTOAB liposomes and PC/TOTB liposomes after fusion, whereas the nocomplementary coliposomes formed from PC/MTOAB and PC/TOTB did not show these spectroscopic changes. The molecular recognition through hydrogen interactions between adenine and thymine is very slow because of the possible occurrence of molecular lateral diffusion and exchange of amphiphile before recognition progresses in coliposomes. These results provide useful information for the design of supramolecular devices such as vesicles and liposomes, which can be used to mimic primitive recognition processes observed in biological systems.