The self-assembly of lipophilic guanosine derivatives in solution and on solid surfaces

The self-assembly of lipophilic deoxyguanosine derivatives 1 and 2 has been studied in solution by NMR spectroscopy and ESI-MS (electrospray ionizatio n mass spectrometry). NMR data show the existence of two types of self-asse mbled, ribbonlike structures (A and B), which are connected at the guanine moieties through two different I-I-bonded networks. The first species (A), which is stable in the solid state and characterised by cyclic NH(2)-O(6) a nd NH(1)-N(7) hydrogen bonds, is detected soon after dissolving the polycry stalline powder in rigorously anhydrous CDCl3. In solution it slowly underg oes a structural transition towards a thermodynamically stable ribbon chara cterised by NH(1)-O(6) and NH(2)-N(3) cyclic hydrogen bonds (B). On the oth er hand, at surfaces, self-assembled ribbon nanostructures have been grown from solutions of derivative 1 both on mica and at the graphite-solution in terface. They have been investigated by means of tapping mode scanning forc e microscopy (SFM) and scanning tunnelling microscopy (STILI), respectively . SFM revealed dry, micrometer-long nanoribbons with a molecular cross-sect ion, while STM imaging at submolecular resolution indicates a molecular pac king of type A, like the one detected in the solid state. This indicates th at, upon adsorption at the solid - liquid interface, the guanosine moieties undergo a structural rearrangement from a B-type to an A-type ribbon.