Internucleobase-interaction-directed self-assembly of nanofibers from homo- and heteroditopic 1,omega-nucleobase bolaamphiphiles

The complementary 1,omega -thymine, 1,omega -adenine, and 1,omega-(thymine, adenine) bolaamphiphiles, [N,N'-bis[3-(2,4-dihydroxy-5-methylpyrimidine-1- yl)propionyl]1,n-diaminoalkane [T-n-T (n = 10, 11, 12)], N,N'- bis[3-(6-ami nopurine-9-yl)propionyl] 1,n-diaminoalkane [A-n-A (n = 10, 11, 12)], and N- [3-(2,4-dihydroxy-5-methylpyrimidine-1-yl)propionyl], N'-[3-(6-aminopurine- 9-yl)propionyl] 1,n-diaminoalkane [T-n-A (n = 10, 11, 12)], respectively] h ave been synthesized. The spontaneous homo- and heteroassembly of these nuc leobase-based bolaamphiphiles has been studied by light microscopy, energy- filtering transmission electron microscopy, FT-IR, and powder X-ray diffrac tion analyses. The achiral T-10-T bolaamphiphile produced in 10% ethanolic/ aqueous solutions unprecedented double-helical ropes of 1-2 mum in widths and several hundred micrometers in length, whereas the complementary homolo gue A-10-A gave only microcrystalline solids of 1-10 mum in size. In contra st, an equimolar mixture of T-10-T and A-10-A yielded supramolecular fibers of 15-30 nm in width. H-1 NMR, CD, and UV studies of solution photoreactio ns of T-10-T suggested that under natural light the chiral rope formation i s triggered by photodimerization of trace amounts of the thymine moieties i n the T-10-T assemblies. Complementary hydrogen bond formation between the thymine-adenine heterobase pairs was found to prevent such a photoreaction and resulted in no chiral rope formation. The heteroditopic T-12-A bolaamph iphile self-assembled to form supramolecular fibers. Multilamellar organiza tion was proposed for the homo- and heteroassemblies made of T-n-T and A-n- A.