  This review focuses on the striking recent progress in solving for
hydrophobic interactions between small inert molecules. We discuss several new
understandings. Firstly, the _inverse _temperature phenomenology of hydrophobic
interactions, _i.e., strengthening of hydrophobic bonds with increasing
temperature, is decisively exhibited by hydrophobic interactions between
atomic-scale hard sphere solutes in water. Secondly, inclusion of attractive
interactions associated with atomic-size hydrophobic reference cases leads to
substantial, non-trivial corrections to reference results for purely repulsive
solutes. Hydrophobic bonds are _weakened by adding solute dispersion forces to
treatment of reference cases. The classic statistical mechanical theory for
those corrections is not accurate in this application, but molecular
quasi-chemical theory shows promise. Finally, because of the masking roles of
excluded volume and attractive interactions, comparisons that do not
discriminate the different possibilities face an interpretive danger.
