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-catalysed condensation of various benzaldehydes with different monoalkylureas. Many of these compounds form thermoreversible gels with a number of organic solvents at very low concentrations (<3 mM) and which are stable to temperatures higher than 100 °C. Electron microscopy revealed a three-dimensional (3D) network of intertwined fibres, which are several tens of micrometers 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. 1H NMR, 2D NMR, 13C NMR and 13CCP/MAS NMR techniques were used to obtain information about the aggregation and possible aggregate symmetry of geminal bis-ureas in solution, in the gel state, and in the solid state.