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An Enaminone Derivative of Dehydroacetic Acid as an Effective Anion Receptor in Methanol and Acetonitrile Solutions

The field of anion binding and recognition has been evolving rapidly in the past decade, with a rising number of highly diverse anion receptors reported and their binding properties studied in detail.1, 2 One of the most abundant type of the anion binders is the group of polyamine receptors. In order to develop polyamine receptors with desired properties, it is important to understand the factors that define the stability of the anion complexes in the solution. This is achieved by investigating the influence of anion geometry and basicity, number and arrangement of the binding moieties in the ligand structure, as well as solvent properties on the stability constants of the complexes formed. In the studies of binding properties of triamine derivative of dehydroacetic acid reported recently, it was found that only the protonated form of the ligand is active as an anion receptor.3, 4 The protonation properties and stability constants of a number of anion complexes with this receptor were determined. In this work we present an extensive study of anion binding and protonation properties of its tetramine analogue L (scheme 1) in methanol. Several experimental techniques (spectrophotometry, potentiometry, NMR-spectroscopy, microcalorimetry) were used and it was found that the additional NH binding group enabled binding of anions with different geometries (Cl−, NO3−, ClO4−) in the neutral, deprotonated form. As expected, the protonation of the receptor enhanced its binding properties. Further on, the binding of the anions was studied in acetonitrile and the influence of the solvent properties on the binding affinity of L was discussed.

supramolecular chemistry ; anion receptor ; stability constant ; protonation ; spectrophotometry

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