Infrared study of helix strandedness in the poly A-poly U system

Abstract

We designed and synthesized a uracil-appended cholesterol gelator (1) in order to control the gel stability and the gel morphology by addition of the complementary and non-complementary nucleobase derivatives. Compound 1 forms columnar stacks in cyclohexane due to the van der Waals interaction (cholesterol–cholesterol interaction) and the intergelator hydrogen bonding between uracil moieties. Addition of a ‘monomeric’ adenosine (3) into the gel only decreases the stability with increasing the concentration. The destabilization is ascribed to a lack of intergelator hydrogen bonding accompanied with forming the complementary base pairs between 1 and 3. In contrast, addition of adenine-appended cholesterol (7) induces a different behavior; with increasing 7 concentration the mixed gel is initially stabilized and then destabilized, giving rise to a maximum at the ratio of 1/7=1:1 for the Tgel plot. One may consider, therefore, that when the additive has a common, column-forming cholesterol moiety, the cholesterol–cholesterol interaction can operate cooperatively with the complementary base pairing. In addition, the gel fiber structure is clearly changed by the addition of 7. Taking the fact that there is no report for such an additive effect inducing a structural change with maintaining the gel stability into consideration, our attempt combining cholesterol columnar stacks with the nucleobase additives provides a new methodology to control the stability and the morphology of organogels.