Amphiphilic properties of synthetic glycolipids based on amide linkages. I. Electron microscopic studies on aqueous gels

Amphiphiles with one or two amide linkages have been prepared by the reaction (A) of D-gluconic acid lactone with aliphatic amines (C₆-C₁₀) and (C) of N′-gluconoyl-ethylenediamine with alkanoic acids (C₆)-(C₁₀). Gel formation was found to occur on cooling the aqueous solutions at concentrations as low as 1–2%. Electron microscopy revealed that the gels of type A are composed of highly ordered ropes with right-handed twist, especially well developed with N-octylgluconamide. Type c substances with two amide linkages of opposite direction form gels consisting of smooth ribbons devoid of twisting. N-Methylation of the amide bond (type B and D substances) leads to a considerable increase in solubility. Gels are only formed from samples containing decanoic acid. These gels also consist of right-handed fibrillar ropes, only partially ordered with one N-methylated amide linkage (B), regularly aligned side-by-side with one N-methylated and one non-methylated amide bond (D). Gel formation and the typical morphology of the gels are discussed as arising mainly from strong intermolecular hydrogen bonds between amide linkages holding the molecules together and the influence of chiral centers of the carbohydrate chain which might be responsible for helical aggregates to be formed.