Molecular recognition - Allosterism generated by weak host-guest interactions in molecular rectangles

Two metal-based molecular rectangles that bear two identical binding sites form 1:2 host-guest adducts with a pair of analogous planar Pt2+ complexes. The larger of the two guests shows no binding allosterisin with either of the two rectangles, but substantial positive allosterism is observed when the smaller guest binds to the rectangles. It is proposed that the smaller guest is better accommodated in the binding sites of the receptor and that this leads to allosterism. Various experiments, including H-1 NOESY spectroscopy, support the supposition that the smaller guest is better incarcerated in the receptors. (c) Wiley-VCH Verlag GmbH & Co.