Steric desolvation enhances the effective molarities of intramolecular H-bonding interactions

CHEKMENEVA, Elena, HUNTER, Christopher A., MISURACA, Maria Cristina and TUREGA, Simon M. (2012). Steric desolvation enhances the effective molarities of intramolecular H-bonding interactions. Organic & Biomolecular Chemistry, 10 (30), 6022-6031.

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Free energy contributions due to intramolecular phosphonate diester–phenol H-bonds have been measured for 20 different supramolecular architectures in cyclohexanone 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 over 100 different zinc porphyrin–pyridine ligand complexes. These complexes have previously been characterised in toluene and in 1,1,2,2-tetrachloroethane (TCE) solution. Intramolecular ester–phenol H-bonds that were measured in these less polar solvents are too weak to be detected in cyclohexanone, which is a more competitive solvent. The stability of the intermolecular phosphonate diester–phenol H-bond in cyclohexanone is an order of magnitude lower than in TCE and two orders of magnitude lower than in toluene. As a consequence, only seven of the twenty intramolecular phosphonate diester–phenol interactions that were previously measured in toluene and TCE could be detected in cyclohexanone. The effective molarities (EM) for these intramolecular interactions are different in all three solvents. Determination of the EM accounts for solvent effects on the strengths of the individual H-bonding interactions and the zinc porphyrin–pyridine coordination bond, so the variation in EM with solvent implies that differences in the solvation shells make significant contributions to the overall stabilities of the complexes. The results suggest that steric effects lead to desolvation of bulky polar ligands. This increases the EM values measured in TCE, because ligands that fail to replace the strong interactions made with this solvent are unusually weakly bound compared with ligands that make intramolecular H-bonds.

Item Type: Article
Additional Information: First published online 11 May 2012
Research Institute, Centre or Group - Does NOT include content added after October 2018: Biomedical Research Centre
Identification Number:
Page Range: 6022-6031
Depositing User: Jamie Young
Date Deposited: 30 Jun 2015 13:14
Last Modified: 18 Mar 2021 18:45

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