A thermodynamic and spectrophotometric study of anion binding with a multifunctional dipyridine-based macrobicyclic receptor

Synthesis and characterisation of a new macrobicycle containing two dipyridine units (L) is reported. Protonated forms of L are efficient receptors for inorganic phosphate and nucleotide anions. The binding properties of L toward these substrates have been investigated in aqueous solution by means of potentiometric, microcalorimetric and 1H NMR measurements. Only 1:1 receptor–anion complexes have been found in solution. The stability of the adducts with inorganic phosphates anions is higher than that found for the nucleotides complexes. The complexation reactions are endothermic, and promoted by invariably favourable entropic contributions, indicating that these pairing processes are mostly determined by the desolvation of the interacting species that occurs upon charge neutralisation.