Solvation rules: aromatic interactions outcompete cation-π interactions in synthetic host-guest complexes in water.

Chemical double mutant cycles were used to measure the interaction of a -methyl pyridinium cation with a π-box in a calix[4]pyrrole receptor. Although the cation-π interaction is attractive (-11 kJ mol), it is 7 kJ mol less favourable than the corresponding aromatic interaction with the isosteric but uncharged tolyl group.

Aromatic interactions with heterocycles in water.

Conformationally well-defined supramolecular complexes that can be studied in different solvents provide a platform for separating and quantifying free energy contributions due to functional group interactions and desolvation. Here 1:1 complexes formed between four different calix[4]pyrrole receptors and eleven different pyridine -oxide guests have been used to dissect the factors that govern aromatic interactions with heterocycles in water and in chloroform solution. H NMR spectroscopy shows that the three-dimensional structures of the complexes are fixed by four H-bonding interactions between the pyrrole donors at the bottom of the receptor and the -oxide acceptor on the guest, locking the geometrical arrangement of interacting functional groups in the binding pocket at the other end of the receptor.

Substituent effects on aromatic interactions in water.

Molecular recognition in water involves contributions due to polar functional group interactions, partial desolvation of polar and non-polar surfaces and changes in conformational flexibility, presenting a challenge for rational design and interpretation of supramolecular behaviour. Conformationally well-defined supramolecular complexes that can be studied in both water and non-polar solvents provide a platform for disentangling these contributions. Here 1 : 1 complexes formed between four different calix[4]pyrrole receptors and thirteen different pyridine -oxide guests have been used to dissect the factors that govern substituent effects on aromatic interactions in water.