MEMBRANES AND WATER - AN INTERESTING RELATIONSHIP

The relationship between membranes and interfacial water is discussed. Various interfacial properties for a number of simulated membrane/wat er systems are compared. Although the simulated membranes consist of w idely varying hydrophobic and hydrophilic components, some general pro perties emerge. A geometrical ordering principle is observed for all s urfaces, resulting in a negative surface potential for all systems. Th e induced water order decays without any previously observed long-rang e oscillations. More specific properties relate to the dipolar charge distributions of the hydrophilic surfaces, which are akin to biomembra nes. In contrast to the hydrophobic surfaces they have a broad interfa ce with a high density. Compensation of local charge density is the ma in ordering principle for water in these systems. The interplay betwee n membrane and water properties is further discussed in relation to th e hydration force. It is concluded that the non-exponential decay of t he surface molecules will lead to a more complicated decay of the hydr ation force than usually assumed, whether arising from water ordering or from surface protrusions.