Membranes act as walls and doors separating the interior if all cell from the outside environment. The membranes are selectively permeable, and understanding how the membranes interact with ions and organic molecules--for example, physiological signal substances and drugs-- is fundamental to the understanding of life at a molecular level. The molecular mechanisms by which cell membranes interact with these types of molecules has become a central topic in pharmacological science. Three classes of lipids occur in the membranes; phospholipds, glycolipids and sterols. The amount of each depends upon the type of cell, but the phospholipids are the most prevalent. We will simulate the formation of phospholipid monolayers on a water surface to understand the relation between surface concentration and bulk concentration. The simulations will be used as guide for our up coming XPS experiments, where we will measure the same systems using a water jet at at synchrotron.