Several N-cholyl amino acid alkyl esters were found to act as novel, potent organogelators for aromatic solvents and cyclohexene. These novel organogelators afford stable, transparent, and thermoreversible gels. Modification of the molecular structure and IR measurements show that gelation takes place by means of a hydrogen-bonded network and involves at least the amide bond and several hydroxy groups of the cholic acid component. The chiral center of the amino

Cholic acid was coupled to an alkyl tail via three different connecting groups, amide, urea, and ester group, and the gelation capabilities of these compounds in different solvents were compared. Both amide and urea derivatives form one-component gels. They give transparent and stable gels in aromatic solvents through a hydrogen bonded network of monomolecular fibers. Structural variations give information about the molecular requirements for gelation. A new kind of two-component gel was found for the ester derivatives with two carbohydrates, isomannide and isosorbide. Formation of wormlike, inverted micelles causes gelation of apolar solvents. The optimal stoichiometry of the co-gelators lies close to 1:1.

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Small-angle neutron scattering measurements were performed on some cholic acid-based gel systems in order to gain detailed information about the network structure. The presence of thin fibers with a radius of about 10-20 A was found for various gelators. Two types of interaction between different sorts of fibers were demonstrated, depending on the molecular structure of the gelator. The first type involves the presence of microcrystalline knots with a dimension of about 100-200 A between the fibers. Upon heating, this network gradually disintegrates. The second type involves loose entanglements between flattened fibers. The occurrence of these types of interaction is related to the length of the alkyl tail attached to cholic acid.