Supramolecular gels based on organic diacid monoamides of cholesteryl glycinate

Three diacid monoamides of cholesteryl glycinate (1, 2, and 3) were designed and synthesized. The gelation behaviors of these compounds and their corresponding ammonium salts (1('), 2('), and 3(')) were tested in 28 solvents. It was found that 1, 2, and 3 were weak gelators, but their neutralization with ammonia enhanced their gelling ability significantly. In particular, 1(') behaves as an "ambidextrous gelator." It gelatinizes both apolar solvents and water. More interestingly, some of the alkyl alcohols and water can be gelatinized at room temperature by simply bubbling ammonia into the system, which contained a suitable amount of 1. Several techniques, such as polarizing optical microscopy and scanning electron microscopy (SEM), revealed that 1(') aggregates into spherulite microparticles in 1-pentanol, at the dilution or the gel state. Moreover, SEM monitoring studies revealed that 1(') first aggregated into microparticles and then these particles aggregated into fiber-like structures and finally into a three-dimensional (3D) network structure. Attenuated total reflection Fourier infrared transform spectroscopy and salt effect studies demonstrated respectively that hydrogen bonding formation between NH and CO and electrostatic interaction are two of the main driving forces for the formation of the gels.