Geminal bis-ureas as gelators for organic solvents: Gelation properties and structural studies in solution and in the gel state

Several geminal bis-urea compounds were synthesised by means of an acid-cat alysed condensation of various benzaldehydes with different monoalkylureas. Many of these compounds form thermoreversible gels with a number of organi c solvents at very low concentrations (< 3 mM) and which are stable to temp eratures higher than 100 degrees C. Electron microscopy revealed a three-di mensional (3D) network of intertwined fibres, which are several tens of mic rometers long and have a width ranging from approximately 30 to 300 nm. The possible aggregate forms and aggregate symmetries were evaluated by means of molecular mechanics calculations. H-1 NMR, 2D NMR, C-13 NMR and C-13-CP/ MAS NMR techniques were used to obtain information about the aggregation an d possible aggregate symmetry of geminal bis-ureas in solution, in the gel state, and in the solid state.