Reflections on the construction of anion receptors: Is there a sign to resign from design?

The principles and conceptual basis of the design of molecular hosts for anions is examined. Starting from general considerations on the fundamentals of supramolecular binding and selectivity the role of the underlying model is illuminated. Turning to an agenda to be followed in the construction of concrete anion hosts the aspects of function, the guest to be bound, the competition situation and the strategic feasibility are discussed. Finally, arguments to include various facets of association entropy are presented that were unraveled by recent experimental studies. As a conclusion, the necessity to consider entropic influences in host design is emphasized. Although this adds to the complexity of the design task an optimistic prospect for success is voiced in view of recent progress in computational prediction and the support from experimental entropy data.