New organogelators bearing both sugar and cholesterol units: an approach toward molecular design of universal gelators

The gelators of organic solvents are classified into two categories on the basis of their basic intermolecular forces: hydrogen-bonded or nonhydrogen-bonded. To utilize these two interactions cooperatively for organogel formation we newly synthesized seven gelators (1-7) and two reference compounds (8 and 9) which have both a cholesterol moiety and a saccharide moiety within one molecule. The solubility of 1-7 changed drastically from totally insoluble one to very soluble one depending on the saccharide absolute configuration. In general, the gelator became very insoluble when it includes many equatorial OH groups, whereas it became very soluble when it includes many axial OH groups. Gelators 2 and 5 bearing two equatorial OH groups and one axial OH group acted as good gelators and in several cases the sol-gel phase-transition temperatures (measured in a sealed tube) were higher than the boiling points. The SEM observations of the xerogels established that the stable gels contain the entangled fibrous network. These results indicate that a very stable organogel can be designed by a cooperative coagulative effect of a cholesterol-cholesterol interaction and a saccharide-saccharide interaction.