Lecithin bridging by hydrogen bonds in the organogel

A series of polar solvents have been studied in order to reveal those capable of producing the thickening effect on hydrocarbon solutions of lecithin. It has been established that glycerol, formamide and ethylene glycol, in addition to water (previously known), have the ability to induce organogel formation. The IR results show that molecules of both the gel-forming solvents and non-gel-forming ones are attached to the lecithin phosphate group via hydrogen bonds. The latter influence the mobility of the choline residue. The ability to promote thickening of lecithin solutions has correlated with the polarity of molecules. The correlation is particularly pronounced in the series of such structurally related compounds as glycerol, ethylene glycol and 1,3-propanediol. It has been inferred from the results that the difference between gel-forming and non-gel-forming polar solvents is caused by their orientation and localization in the polar moiety of a lecithin molecule. In a proposed model of the organogel, the solvent molecules bridge phosphate groups of neighbouring lipid molecules, thus allowing their association into tubular aggregates through an extensive ribbon-like hydrogen bonding network.