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

The host-guest interactions between ortho- (Ph), pyro- (Pp), and tripolypho sphate (Tr) anions together with ATP (At), ADP (Ad), and AMP (Am) nucleotid es and the two hexaazamacrocyclic ligands 1,15-dioxa-4,8,12, 18,22,26-hexaa zacyclooctacosane (Pn) and 1,13-dioxa-4,7,10,16,20,24-hexaazacyclohexacosan e (Op) have been investigated by potentiometric equilibrium methods. Ternar y complexes an formed in aqueous solution as a result of hydrogen bond form ation and Coulombic attraction between the host and the guest. Formation co nstants for all the species obtained are reported. The selectivity of the P n and Op ligands with regard to the different phosphate and nucleotide subs trates is discussed and illustrated with total species distribution diagram s. A comparison is also carried out, with the results obtained in this work and those obtained previously with three other closely related hexaazamacr ocyclic Ligands. This comparison manifests the importance of ligand basicit y, rigidity, and pi-stacking capability in order to understand their bindin g and selectivity.