Control of Self-Assembly by Acid-Base Chemistry

Recent progress in the field of molecular recognition has led to the introduction of self- assembling systems of varying complexity. A simple system in which two identical subunits are held together by hydrogen bonds has previously been developed.[1] Since then, two similar capsule-forming compounds have been synthesized (figure 1).[2] These are based on p-N,N-dimethylaminophenyl- or carbethoxysubstituted glycolurils which are readily available from the corresponding benzil and dihydroxytartaric acid (disodium salt) respectively by condensation with urea. By using other alcohols for the esterification such as isoamyl alcohol or cyclohexanol, soluble glycolurils (e.g. in pyridine or dioxane) are obtained which are promising candidates for the synthesis of more complex self-assembling systems. Alkylation of the glycolurils la and lb with 1,2,4,5-tetrakisbromomethylbenzene gave the new self-complementary compounds 2a and 2b, both showing enhanced solubility in organic solvents. As expected, both compounds can encapsulate methane, ethane, and ethylene as evidenced by 1H-NMR.