Properties of various phosphatidylcholines as emulsifiers or dispersing agents in microparticle preparations for drug carriers.

We investigated characteristics of various phosphatidylcholines (PCs) used as dispersing agents and emulsifiers. Six PCs with different lengths of acyl hydrocarbon chains and different degrees of unsaturated acyl hydrocarbon chains were selected to examine influences of a lipophillic part of phosphatidylcholines in emulsion and dispersion systems. Vesicles and oil-in-water emulsions were prepared by sonication under several ambient temperature conditions. Mean diameters of vesicles and oil droplets in emulsions were measured by a submicron particle sizer. In vesicles that are generated by hydration of the PCs and have a bilayer form, particle size was influenced by length and degree of unsaturation of acyl hydrocarbon chains of a PC. PCs with shorter acyl hydrocarbon chains or unsaturated bonds are considered more potent dispersing agents. Preparation temperature of the PC is also a factor affecting potency of dispersion. In O/W emulsions in which PCs were absorbed at water-oil interfaces and which have a single layer form or liquid-crystal layer form, particle size was also influenced by length and degree of unsaturation of acyl hydrocarbon chains of a PC. PCs with shorter and saturated acyl hydrocarbon chains are considered more potent emulsifiers. Unsaturation of acyl hydrocarbon chains weaken the ability of emulsification due to vulnerable double bonds. For stable emulsions, it is considered beneficial for PCs to form small oil droplets and lamellae liquid-crystal phase. From this perspective, saturated PCs with short hydrocarbon chains, i.e., DLPC and DMPC, may have advantages in preparing a stable emulsion not only by giving a smaller droplet size but also by forming lamellae liquid-crystal phase. When considering characteristics of PCs as emulsifiers, their characteristics as dispersing agents is also useful information.