Co-operative electrostatics for understanding crown ether hydration patterns

A prototype problem in supramolecular chemistry is: Would it be possible to understand qualitative trends in hydration preocess of crown ether from simple considerations at the molecular levels? An answer is offered for the hydration of 18-crown-6 in terms of co-operative electrostatic effects. These effects are monitored by mapping the molecular electrostatic potential topography of 18-crown-6 as well as various interemediate hydrated species, followed by electrostatic modelling. All model calculations have been done at ab-initio HF/6-31G** level. The trends of these hydration patterns are in good agreement with the corresponding fully optimized ab-initio ones. Final structure of 18C6·4H 2 O is quite similar to the corresponding experimental crystal structure. Such an electrostatics-based method seems to be an excellent general tool for understanding weak interactions in supramolecular chemistry.