Thermodynamic aspects of dicarboxylate recognition by simple artificial receptors

B. R. Linton, M. Scott Goodman, E. Fan, S. A. Van Arman, A. D. Hamilton

Research output: Contribution to journalArticle

Abstract

Recognition of dicarboxylates by bis-functional hydrogen-bonding receptors displays divergent thermodynamics in different solvent systems. NMR titration and isothermal titration calorimetry indicated that neutral bis-urea and bis-thiourea receptors form exothermic complexes with dicarboxylates in DMSO, with a near zero entropic contribution to binding. The increased binding strength of bis-guanidinium receptors precluded quantitative measurement of binding constants in DMSO, but titration calorimetry offered a qualitative picture of the association. Formation of these 1:1 complexes was also exothermic, but additional endothermic events occurred at both lower and higher host-guest ratios. These events indicated multiple binding equilibria but did not always occur at a discrete 2:1 or 1:2 host-guest molar ratio, suggesting higher aggregates. With increasing amounts of methanol as solvent, bis-guanidinium receptors form more endothermic complexes with dicarboxylates, with a favorable entropy of association. This switch from association driven by enthalpy to one driven by entropy may reflect a change from complexation involving the formation of hydrogen bonds to that promoted by solvent liberation from binding sites.

Original languageEnglish (US)
Pages (from-to)7313-7319
Number of pages7
JournalJournal of Organic Chemistry
Volume66
Issue number22
DOIs
StatePublished - Nov 2 2001

ASJC Scopus subject areas

  • Organic Chemistry

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