Computer-Simulationen von Hydrationskräften zwischen Phospholipid Doppelschichten
Final Report Abstract
Our computer simulation studies within the framework of this project were an extension of our previous work where we had undertaken, for the first time, a direct computer simulation of forces operating between phospholipid membranes in water. The previous studies was extended in three directions. First, we investigated the temperature dependence of short-range interbilayer repulsion. The simulation results for PE bilayers predicted a slight decrease of the interbilayer pressure with temperature, which provided futher support in favor of our previous conclusion that the water-mediated pressure between PE bilayers is dominated by its hydration component. Second, we extended our previous simulations of fluid-state bilayers to the gel state. The simulation correctly predicted, for PE bilayers, an increase in the equilibrium interbilayer separation on going from the fluid to the gel state. Also, it was found that the mechanism of interbilayer repulsion in the two states is basically the same, while the quantitative differences in the individual pressure components can be explained in terms of the higher areal density of the gel-state bilayers. Third, we performed comparative computer simulations of PE and PC fluid-phase bilayers to understand the substantial differences in their hydration behavior and pressuredistance dependence. We found that the mechanism of interbilayer repulsion in the two types of phospholipids was cardinally different. In the PE bilayers, the repulsion originated from the hydration pressure, while the direct bilayer-bilayer interaction was attractive. By contrast, in the PC bilayers the hydration contribution was insignificant, and the repulsion originated from the direct interbilayer interaction, mainly from its electrostatic component.
