New dicholesteryl-based gelators: gelling ability and selective gelation of organic solvents from their mixtures with water at room temperature

Four new diacid amides of dicholesteryl L-phenylalaninate were designed and prepared. The compounds with spacers containing three, four, five, or six carbon atoms are denoted as 1-4, respectively. Gelation tests showed that the four compounds are versatile organogelators, and a subtle change in the length of the spacer can produce a dramatic change in the gelation behaviors of the compounds, as well as the micro-structures of the gel networks as revealed by SEM and XRD measurements. Within the 77 gel systems studied, at least seven of them, including 2/kerosene, 2/toluene, 2/xylene, 3/kerosene, 3/1-pentanol, 3/1-hexanol and 3/1-heptanol, gel spontaneously at room temperature. Furthermore, 2 and 3 can be used for the selective gelation of xylene or kerosene from their mixtures with water. Importantly, heating and cooling cycle or addition of a co-solvent is not necessary for the selective gelation. Furthermore, the gels of 2/xylene are mechanically strong enough for separation, and thereby it is believed that 2 is a strong candidate for the practical separation of xylene from its mixture with water. FT-IR and temperature-dependent H-1 NMR measurements demonstrated that inter-molecular hydrogen bonding plays an important role for the formation and maintenance of the gel networks.