Experimental approaches to membrane thermodynamics

Thermodynamics describes a system on the macroscopic scale, yet it is becoming an important tool for the elucidation of many specific molecular aspects of membrane properties. In this note we discuss this application of thermodynamics, and give a number of examples on how thermodynamic measurements have contributed to the understanding of specific membrane phenomena. We mainly focus on non-specific interactions of bilayers and small molecules (water and solutes) in the surrounding solvent, and the changes in membrane properties they bring about. Differences between thermodynamic and stoichiometric (structural) definitions of non-specific binding or partitioning are emphasized, and it is concluded that this distinction is important for weak, but not for strong, interactions.