Molecular Conformation and Orientation and Adsorption Kinetics Models of Phospholipid at the Air/Water Interface
|School||East China University of Science and Technology|
|Keywords||Pulmonary Surfactant conformation orientation Adsorption kinetics model Surfactant Protein C|
Conformation and orientation changes of pure phospholipid molecules at the air/water interface during compressing were investigated in this paper. Based on energy conservation law and surface pressure isotherms, the initial conformations and single point energy of phospholipid molecules were simulated by Gaussian 98 software, and the plots of conformation energy change vs. dihedral angle were established. One possible tack of conformation change was also proposed. According to the determined molecular conformations at different states, molecular orientations were also developed, and the compressing process was divided into three stages:angle changing stage, molecular overlapping stage and monolayer bending stage.Adsorption kinetics of phospholipids into SP-C-containing monolayers was studied. A two-step assumption was proposed to describe the mechanism of phospholipids adsorption:1) diffusing of the lipid vesicles from the bulk to the subsurface,2) forming the lipid-protein aggregations by interaction between phospholipids and SP-C and spreading at the surface. On the basis of the characteristic of surface pressure (π)～time (t) isotherms, the whole adsorption process was divided into induction stage, fast raise stage and meso-equilibrium stage, and the corresponding kinetics model at each stage was developed. The correlation results showed that the kinetics models at three stages can be described by growth model, diffusion model, and the pseudo-second-order model, respectively.Surfactant protein C (SP-C) was separated by gel chromatography from lung lavage of adult pigs. By using a film balance,π-t isotherms of SP-C-containing monolayers at different temperatures were measured. Comparisons between the experimental data and the model regression at each stage showed that the kinetic models at three stages could describe the adsorption of phospholipids into SP-C-containing monolayers.