The structure of artificial lipids possessing oligo(ethylene glycol) and their behavior in water

The synthesis of artificial lipids containing 3,5-bis- or 3,4,5-tris(dodecyloxy)benzamide and oligo(ethylene glycol) (OEG) moieties is described. The terminal group was either an alcohol or an amine, and the length of ethylene glycol unit was three, six, eight or nine. The critical micelle concentration (CMC) of these artificial lipids was determined by a fluorescent probe method using Nile red. The CMC values were lower than that of single chain OEG alkyl ether surfactants. The 3,4,5-tris(dodecyloxy)benzamide derivatives had a higher CMC (∼10−5 M) than the 3,5-bis(dodecyloxy)benzamide derivatives (∼10−6 M). The particle size distribution of aqueous dispersions of the artificial lipids was determined using a dynamic light scattering method. The particle size distributions were different depending on the length of OEG chain, the number of hydrophobic chains, and the terminal functional group. Short OEG derivatives formed insoluble aggregates even at low concentrations, and a long OEG derivative produced large water soluble aggregates.