Effect of lecithin on organogel formation of 12-hydroxystearic acid

Optically active 12-D-hydroxystearic acid (12-HSA) gives a thermally reversible organogel in several organic solvents. When a small amount of lecithin coexists with 12-HSA in organic solvents, the mechanical strength of the organogel is remarkably reduced. Interaction of lecithin with 12-HSA was studied by using infrared (IR) spcctrometry, nuclear magnetic resonance (NMR) spectrometry, and scanning electron microscopy (SEM). Incorporating lecithin into 12-HSA reduced the absorbance in IR spectra, derived from hydrogen bonding between the hydroxyl groups and the carboxyl groups of 12-HSA molecules. Based on NMR measurements, the polar head groups of lecithin associate with the carboxyl groups of 12-HSA in a 1:1 molar ratio. SEM showed that the shape of the fibrous aggregates varied from a helically extended form to a spherical form. These results suggest that intermolecular 1:1 complexes were formed between lecithin and 12-HSA, which caused a structural change in the fibrous network in the 12-HSA organogel and consequently induced gel deformation.