Formation of nucleotide base-pairs at the interface of a polydiacetylene cytosine derivatized monolayer

Langmuir monolayers of diacetylene lipids with a cytosinyl head-group (PDC), mixed with an alcohol derivative of the same lipid (PDOH), were formed on water and on guanosine solution, and were UV polymerized in situ. Brewster angle microscopy (BAM), atomic force microscopy (AFM) and visible light absorption spectroscopy were performed on the monolayers. It was found that the optimal ratio for the lipid mixtures is approximately 2:1 PDC/PDOH. For lipid mixtures with different ratios, the film decomposes into phases of the preferred composition and a second phase enriched with the excess compound. The stable mixed phase exhibits a distinct striated appearance along the polymer linear direction. Films formed on guanosine-containing subphase have similar phases; however, the stable striated phase appears more developed in the direction perpendicular to the polymer chains. A specific base-pair formation at the air–solution interface between the diacetylene monolayer and the free complementary nucleoside in the solution is suggested.