Glycoprotein adsorption into bilirubin/cholesterol mixed monolayers at the air-water interface

The adsorption of alpha(1)-acid glycoprotein into bilirubin/cholesterol mixed monolayers with various component molar ratios is investigated using surface pressure-area (pi-A) isotherms and (d pi/dA)-A curves. The results showed that the surface area per molecule increased after the adsorption/insertion of glycoprotein molecules into the monolayers. The compressibility of mixed monolayers increased as a result of hydrogen bonding between bilirubin and glycoprotein molecules, while the interactions between bilirubin and cholesterol are weakened. The adsorption of glycoprotein into a monolayer induced changes in molecular surface area depending on the surface pressure and molar fraction of bilirubin. The transmission electron microscopy of mixed monolayers confirmed the insertion of glycoprotein particles of spherical shape with an average diameter of about 80 nm into the monolayer.