Phenanthroline-containing macrocycles as multifunctional receptors for nucleotide anions. A thermodynamic and NMR study

The synthesis of the phenanthroline-containing macrocycle 2,6,10,14-tetraaza[15](2,9)cyclo(1,10)phenanthrolinophane (L1) is reported. L1 contains a tetraamine chain connecting the 2,9-positions of a phenanthroline unit. Protonation of L1 has been studied by means of potentiometric and H-1 and C-13 NMR techniques, allowing the determination of the basicity constants and of the stepwise protonation sites. The protonation features of L1 are compared with those of macrocycle 2,5,8,11-tetraaza[12](2,9)cyclophenanthrolinophane (L2), in which the amine groups are linked by ethylenic chains. Considering the [H(4)L1](4+) and the [H(4)L2](4+) species, the acidic protons are located on the aliphatic nitrogens, while phenanthroline is not involved in protonation. Binding of diphosphate, triphosphate, ATP and ADP has been studied by means of potentiometry and H-1 and P-31 NMR. Both L1 and L2 behave as multifunctional receptors for the nucleotide anions at neutral or slight acidic pHs, giving 1:1 complexes. Charge-charge and hydrogen bonding interactions take place between the polyphosphate chain of nucleotides and the polyammonium groups of L1 and L2, while the adenine moiety gives charge-dipole interactions with the ammonium groups and pi-stacking with the phenanthroline unit of the receptors. The high upfield displacements in the H-1 NMR spectra exhibited by the adenine protons upon complexation by L1 suggest a partial inclusion of nucleotides inside the macrocyclic cavity.