Interaction between ganglioside G M1 and diosgenin in langmuir monolayers at the air/water interface

Summary The interaction between ganglioside G M1 (GM1) and diosgenin (Dios) in mixed monolayers was investigated using surface pressure measurements and atomic force microscopy (AFM). The miscibility and stability of the mixed monolayer was evaluated both in a qualitative and quantitative way in terms of the excess mean molecular area (Δ A ex ), excess Gibbs energy (Δ G ex ). The Δ A ex of mixed GM1/Dios monolayer was found to have positive deviations from ideality at low Dios mole fractions ( X Dios  = 0.2). Above X Dios  = 0.2, there was a marked negative deviation from ideal mixing, indicating attractive interaction between GM1 and Dios. According to the values of excess Gibbs energy of mixing monolayers, the more stable monolayers assayed was: X Dios  = 0.6. The compressibility coefficient was assessed at various surface pressures. The monolayer of Dios was more elasticity or rigid than GM1. The AFM images for the mixed monolayers at 30 mN/m indicated there was obvious phase separation in the mixed monolayers. These findings will provide useful information for understanding the interaction between drug and lipids. SCANNING 36:218–223, 2014. © 2013 Wiley Periodicals, Inc.