Behavior of sulfatide/cholesterol mixed monolayers at the air/water interface.

The monolayer properties of sulfatide and cholesterol binary system have been investigated with surface pressure-mean molecular area isotherms measurements and atomic force microscopy (AFM). The thermodynamic analysis indicates that the obtained negative deviation of the excess molecular area (DeltaA((ex))) and surface excess Gibbs energy (DeltaG((ex))) from the ideal behavior at various molar ratios, suggesting an attractive interaction between sulfatide and cholesterol in the monolayers as compared with the pure components monolayers. Meanwhile, the compression modulus (C(s)(-1)) vs. surface pressure (pi) and activity coefficients (f(1) and f(2)) of mixed films dependencies for mixed monolayers are drawn at different mole fractions. The AFM images for the mixed sulfatide/cholesterol monolayers deposited on the mica at 15 and 30mNm(-1) show the stronger molecular attractive force to form condensed structure. The behavior of sulfatide is thought to be involved in lateral domain formation in biological membranes. Therefore, the interaction between sulfatide and cholesterol becomes more important in mimicking "lipid rafts" domains.