Hosting anions in solution: Tales about shiny models and their clash with experimental reality

I&EC 66

Martin Valik, Manal Haj-Zaroubi, and Franz P. Schmidtchen. Department of Chemistry, Munich Institute of Technology, Lichtenbergstrasse 4, D-85747 Garching, Germany
Generations of chemists have accepted the simple hard-body docking of host and guest (lock-and-key principle) as the prime guide to selectivity in molecular recognition. In most cases then the selectivity is read from equilibrium binding as expressed by conditional association constants. Due to the enthalpy-entropy compensation phenomenon haunting the weak energetic interactions, however, all attempts to evaluate and comprehend supramolecular relationships resting on the evaluation of free energy changes DGo only ( i.e. the binding affinity Kass) are bound to fail.

Using well characterized examples from the molecular recognition of anions by calixpyrroles 1 and bicyclic guanidinium salts 2 the current problems in the rationalisation of molecular recognition are illustrated. We shall present and expand on the experimental facts obtained by thorough trend analysis within series of closely related host compounds. As a corollary a revision of the classical (lock-and-key) model concepts is required mandating stronger attention to the design of solvation features to cope with the goals of high affinity and selectivity.

 

Molecular Hosts for Anion Binding (sponsored by Separation Science & Technology Subdivision)
1:30 PM-4:55 PM, Monday, March 29, 2004 Marriott -- Orange County 1, Oral

Division of Industrial and Engineering Chemistry

The 227th ACS National Meeting, Anaheim, CA, March 28-April 1, 2004