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Issue 30, 2012
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Steric desolvation enhances the effective molarities of intramolecular H-bonding interactions

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Abstract

Free energy contributions due to intramolecular phosphonate diesterphenol 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 porphyrinpyridine ligand complexes. These complexes have previously been characterised in toluene and in 1,1,2,2-tetrachloroethane (TCE) solution. Intramolecular esterphenol 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 diesterphenol 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 diesterphenol 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 porphyrinpyridine 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.

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

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Publication details

The article was received on 21 Feb 2012, accepted on 27 Mar 2012, published on 11 May 2012 and first published online on 11 May 2012


Article type: Paper
DOI: 10.1039/C2OB25372K
Citation: Org. Biomol. Chem., 2012,10, 6022-6031
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    Steric desolvation enhances the effective molarities of intramolecular H-bonding interactions

    E. Chekmeneva, C. A. Hunter, M. C. Misuraca and S. M. Turega, Org. Biomol. Chem., 2012, 10, 6022
    DOI: 10.1039/C2OB25372K

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