Judging on host-guest binding mode uniqueness: Association entropy as an indicator in enantioselection

Supramolecular enantiodifferentiation was studied by isothermal titration calorimetry in an effort to address the order - disorder distinction in the diastereomeric complexes formed from a chiral macrocyclic host and enantiomeric carboxylates. As a result, the association entropy component T Delta S emerged as an indicator in the enantioselection of tartrate 14 and aspartate 15 by the macrocycle 13 containing two guanidinium anchor groups connected to each other by four urea units. The parent monotopic guanidinium compounds 1 or 2 did not show any enantioselection for chiral carboxylates.