Dissolution Behavior of Monoacylglycerol in Ethanol and Suppression of Crystallization by Addition of Solbitan Laurate in the Solution

Attempt was made to stabilize the supersaturation of (or prevent the precipitation of) glyceryl monopalmitate (GMP) which has poor solubility in ethanol at low temperature. To increase the solubility of GMP, solbitan laurate (SL-10), a nonionic surfactant, was added to an ethanol solution of GMP. Solubility was increased from 3 to 10 times as much due to SL-10. GMP prepicitated at 0.015 mol/kg GMP in ethanol, but at 0.083 mol/kg GMP in ethanol containing 0.1 mol/kg SL-10 at -5°C. The molar ratio of GMP TO SL-10 in the precipitates was 1 : 0.21 : 0.5. Precipitation time of GMP with or without SL-10 was determined at various conditions of GMP and/or SL-10 at -10+25°C. Longer precipitation time indicated greater stabilization of supersaturation of GMP. With increase in SL-10, precipitation time increased and in the GMP solution, on precipitation occurred at low temperature. At SL -10/GMP=0.4, the lowest temperature at which GMP solution supersaturation was maintained was 78°C less that of the solution containing only GMP. The mechanism for GMP supersaturation stabilization is discussed with consideration to hydrogen bonding between the OH groups of SL-10 and ester groups of GMP, and hydrophobic interactions between the hydrocarbon chains of SL-10 and GMP.