Gel formation properties of a uracil-appended cholesterol gelator and cooperative effects of the complementary nucleobases

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 T gel 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.