The 55 % Solution: A Formula for Molecular Recognition in the Liquid State

Binding of guests in self-assembled or covalently linked capsules is shown to be related to the occupancy factor or packing coefficient. Optimal binding can be expected when this value (defined as the ratio between the guest volume and the host cavity volume; right) is in the range 0.55±0.09. This is also shown to reflect the space filled in typical organic solvents. An analysis of different guests and hosts capable of reversible binding suggests a rule of general applicability as to what constitutes a good fit.