A systematic evaluation of molecular recognition phenomena. 2. Interaction between phosphates and nucleotides with hexaazamacrocyclic ligands containing diethylic ether spacers.

The host-guest interactions between ortho- (Ph), pyro- (Pp), and tripolyphosphate (Tr) anions together with ATP (At), ADP (Ad), and AMP (Am) nucleotides and the two hexaazamacrocyclic ligands 1,15-dioxa-4,8,12,18,22,26-hexaazacyclooctacosane (Pn) and 1,13-dioxa-4,7,10,16,20,24-hexaazacyclohexacosane (Op) have been investigated by potentiometric equilibrium methods. Ternary complexes are formed in aqueous solution as a result of hydrogen bond formation and Coulombic attraction between the host and the guest. Formation constants for all the species obtained are reported. The selectivity of the Pn and Op ligands with regard to the different phosphate and nucleotide substrates is discussed and illustrated with total species distribution diagrams. A comparison is also carried out, with the results obtained in this work and those obtained previously with three other closely related hexaazamacrocyclic ligands. This comparison manifests the importance of ligand basicity, rigidity, and pi-stacking capability in order to understand their binding and selectivity.