EFFECT OF ADDING ISOPROPYL MYRISTATE TO MICROEMULSIONS BASED ON SOYBEAN PHOSPHATIDYLCHOLINE AND TRIGLYCERIDES

The effect on the phase behavior and microstructure of pharmaceuticall y interesting microemulsions which is produced by adding isopropyl myr istate (IPM) to the systems is described. The microemulsions are based on water, 1-propanol, soybean phosphatidylcholine (SbPC), and two dif ferent triglycerides; a medium-chain triglyceride (C-8-C-10) and a lon g-chain triglyceride (soybean oil). When IPM was added to the triglyce ride oil phase, the spontaneous curvature of the surfactant film decre ased and the flexibility of the surfactant monolayer increased. The ch ange in spontaneous curvature was manifested by a gradual change in th e microstructure of the microemulsion, as revealed by NMR self-diffusi on data, from an oil-in-water type of structure at low concentrations of LPM to an oil continuous structure at higher IPM concentrations. At intermediate IPM concentrations, the microstructure was found to be o f a bicontinuous nature. By optimizing the amount of IPM and the 1-pro panol concentration, one-phase microemulsions containing equal amounts of water and oil can be obtained at lower surfactant concentrations a nd lower 1-propanol concentrations, compared with those for a system w ith only the triglyceride as the nonpolar phase.