Exploring New Molecular Architectures for Anion Recognition: Synthesis and ATP Binding Properties of New Cyclam-Based Ditopic Polyammonium Receptors

Synthesis and characterization of three new polyamine receptors, composed of a cyclam unit (cyclam=1,4,8,11-tetraazacyclotetradecane) linked by a 2,6-dimethylpyridinyl spacer to the linear polyamines 1,4,8,11-tetraazaundecane (L1py), 1,4,7-triazaheptane (L2py), and to a quaternary ammonium group (L3py(+)), are reported. All receptors form highly charged polyammonium cations at neutral pH, suitable for anion recognition studies. ATP recognition was analyzed by using potentiometric, calorimetric, H-1 and P-31 NMR measurements in aqueous solution. All receptors form 1:1 adducts with ATP in aqueous solution, stabilized by charge-charge and hydrogen-bonding interactions between their ammonium groups and the anionic triphosphate chain of ATP. The binding ability of the three receptors for ATP increases in the order of L3py(+) < L2py < L1py. These adducts are stabilized by largely favourable entropic contributions, probably due to the large desolvation of the host and guest species upon complexation. The sequence observed for the binding affinity is explained in terms of the different ability of the three receptors to wrap around the phosphate chain of ATP.