Investigation of the phase behaviour of systems containing lecithin and 2-acyl lysolecithin derivatives

A series of modified phospholipids (m-PC) possessing different acyl chains in position 2, from butanoyl to hexadecanoyl, Were prepared by partial synt hesis from soybean lysolecithin, They were used with soybean lecithin to co nstruct phase diagrams containing ethanol as cosolvent, water and medium ch ain triglycerides (MCT) or isopropyl myristate (IPM) as oils. The weight ra tios lecithin:m-PC and surfactants:ethanol were kept constant at 1:1. The r esults indicate that the m-PCs have a strong effect on the microemulsion (L ) and liquid crystalline (LC) domains in the water-rich/oil-poor part of th e phase diagrams, although all diagrams correspond to a single lecithin:m-P C ratio. On decreasing the acyl chain length, and thus increasing the hydro philicity of the surfactant, there was a corresponding increase in the L ar ea, which moved towards the aqueous corner of the phase diagrams. The LC ph ase was detected only in the presence of the hexadecanoyl derivative for th e systems containing MCT, and it was not detected only in the presence of t he butanoyl derivative for the systems containing IPM. The use of a second hydrophilic surfactant to adjust the packing properties of the lecithin-alc ohol systems. and:or to increase the fluidity of the surfactant film, incre ased the region of existence of the isotropic systems. This may be of impor tance in the formulation of drug delivery systems, especially those which a re diluted by biological fluids upon administration. (C) 1999 Elsevier Scie nce B.V. All rights reserved.