ABSTRACT
We now consider the solvation, partitioning, and transfer of molecules from one medium to another. For example, toxins dissolve in one medium, such as water, and partition or transfer into another medium, such as the oil components of fish. A central type of action in biology—the binding of a drug or metabolite to a protein—requires first desolvation, i.e., the stripping away of water molecules from the ligand and the receptor. Drugs that act on the brain must be designed not only for their ability to bind their biological targets but also for their ability to transport across an interface called the blood–brain barrier. Related to partitioning and solvation are colligative properties: vapor pressure depression by solutes, boiling temperature elevation, freezing temperature depression, and osmotic pressure. For example, salt dumped on icy roads will melt the ice. Salt added to a boiling pot of water will reduce the boiling. Reverse osmosis is a way to purify salt water to make it drinkable. In this chapter, we use the liquid mixture lattice model to illustrate, in a simple approximate way, the molecular basis for solvation and colligative processes.
