Comparative analysis of the influence of H-bond strength and solvent on chelate cooperativity in H-bonded supramolecular complexes

Free energy contributions due to intramolecular ether-phenol H-bonds were measured for 24 different complexes in 1,1,2,2-tetrachloroethane solution. High throughput UV/Vis titrations were used in combination with chemical double mutant cycles to dissect out the contributions of different functional group interactions to the stabilities of 120 different zinc porphyrin-pyridine ligand complexes. The effective molarities for intramolecular ether-phenol interactions in TCE range from 70 mM to 400 mM depending on the complementarity of the binding partners. The values are practically identical to the corresponding effective molarities measured for the same ether-phenol interactions in toluene. The ether ligands were compared with analogous ligands, which have a phosphonate diester oxygen H-bond acceptor located at the same site on the ligand framework as the ether oxygen. The effective molarities for the ether-phenol interactions measured in TCE are practically identical to the corresponding values measured for phosphonate diester-phenol H-bonds embedded in the same supramolecular architecture. The experiments contradict the previous results obtained for the phosphonate diester complexes and suggest that effective molarity is a property of the molecular framework and is independent of the solvent.