Self-Assembled Ionophores. An Isoguanosine-K+ Octamer

Abstract

The mononucleoside, 5‘-(tert-butyldimethylsilyl)-2‘,3‘-O-isopropylidene isoguanosine (isoG) 2, has a strong affinity for alkali metal cations. Previously, it was shown that isoG 2 self-assembles via hydrogen bonds to give a stable tetramer, (isoG)4 4, in organic solvents (Davis et al. J. Org. Chem. 1995, 60, 4167−4176). The isoG tetramer 4 can then coordinate metal cations. In this present study, vapor phase osmometry and further 1H NMR experiments confirmed that isoG 2 self-assembles via complementary hydrogen bonds to form tetramer 4. Molecular models obtained from molecular dynamics and MM2 energy minimization indicate that the isoG tetramer 4 is bowl-shaped, with four C2 oxygens located on the tetramer's convex surface. It is likely that these four oxygens on the tetramer's convex face coordinate cations. Potassium picrate was used to determine the stoichiometry of the isoG-K+ complex and its K+ binding affinity. Both 1H NMR and UV−vis spectroscopic analysis demonstrated that isoG 2 forms an octamer, ...