Physical properties and packing states of molecular assemblies of synthetic glycolipids in aqueous dispersions

Abstract

Amidic glycolipids, 1,5-bis-O-alkyl-N-maltooligonoyl-L-glutamate (1), having various lengths of two hydrocarbon chains (carbon number, m: 14, 16, 18) and maltooligotose with (glucose unit, n: 3, 5, 7) and a N-glycosidic lipid, 1,5-bis-O-octadecyl-N-maltopentaonosyl-L-glutamate (2) have been synthesized. The assembling structures were analyzed by microscopic observation, such as negatively stained TEM, cryo-TEM, and AFM. The glycolipid 1a (m,n: 14,5) showed a fiber-like structure in all the observed temperatures, while 1b (16,5) showed a fiber-like structure when the hydrating temperature was above the gel-to-liquid crystalline phase transition temperature (T_c; 45°C) and a large disk-like structure when incubated below the T_c. The glycolipid 1c (18,5) took a large disk-like structure after hydration of the powder above the T_c. The glycolipids 1d (18,3) and 1e (18,7) showed a mixture of large disks and large vesicles and a mixture of small disks and micelles, respectively. The N-glycosidic lipid, 2, with no amide linkage made a vesicular structure only. The preparation procedure using high shear stress, such as extrusion and sonication, converted the large disk of 1c to smaller assemblies, such as small disk-, cone-, and granule-like assemblies, depending on the preparation conditions. The glycolipid molecules in the planer part of the disk were packed so tightly that molecular mobility was very low even above the T_c (58°C), and the reactivity of the saccharide chain against Concanavalin A was also very low, indicating that the high reactivity probably comes from the loose packing of saccharide chains around the edge part of the assemblies.