  In various chemical systems enthalpy-entropy compensation (EEC) is a
well-known rule of behavior, although the physical roots of it are still not
completely understood. It has been frequently questioned whether EEC is a truly
physical phenomenon or a coincidence due to trivial mathematical connections
between statistical-mechanical parameters - or even simpler: A phantom effect
resulting from the misinterpretation of experimental data. Here, we review EEC
from a new standpoint using the notion of correlation which is essential for
the method of factor analysis, but is not conventional in physics and
chemistry. We conclude that the EEC may be rationalized in terms of hidden (not
directly measurable with the help of the current experimental set-up) but
physically real factors, implying a Carnot-cycle model in which a micro-phase
transition (MPT) plays a crucial role. Examples of such MPTs underlying
physically valid EEC should be typically cooperative processes in
supramolecular aggregates, like changes of structured water at hydrophobic
surfaces, conformational transitions upon ligand-biopolymer binding, and so on,
so forth. The MPT notion could help rationalize the occurrence of EEC in
connection with hydration and folding of proteins,enzymatic reactions,
functioning of molecular motors, DNA de- and rehybridization, as well as
similar phenomena.
