A systematic evaluation of molecular recognition phenomena. 1. Interactionbetween phosphates and nucleotides with hexaazamacrocyclic ligands containing m-xylylic 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 hexaazamacrocyclic ligand 3,7,11,19,23,27-hexaazatricyclo[27.3.1 .1 (13,17)]triaconta-1(32),13, 15, 17(34),29(33),30-hexaene (Bn) have been investigated by potentiometric equilibrium methods. Ternary complexes are f ormed in aqueous solution as a result of hydrogen bond formation and Coulom bic attraction between the host and the guest. Formation constants for all the species obtained are reported. The selectivity of the Bn ligand with re gard to the phosphate and nucleotide substrates is discussed and illustrate d with species distribution diagrams. A comparison of the present results w ith those obtained for the similar but smaller macrocyclic ligand 3,6,9,17, 20,23-hexaazatricyclo[23.3.3.1.1(11,15)]triaconta- 1(29),11(30),12,14,25,27 -hexaene (Bd) is also discussed. It is found that the competition of the Ed and Bn ligands for the formation of ternary species with a specific substr ate is strongly dependent on the p[H]. The crystal structure of the compoun d [(H6Bn)(H2PO4)(6)]. 2H(2)O with empirical formula C28H68N6O26P6 has been solved by means of X-ray diffraction analysis. The compound belongs to the triclinic P (1) over bar space group with Z = 1, a = 8.892(2) Angstrom, b = 9.369(4) Angstrom, c = 16.337(8) Angstrom, alpha = 73.72(4)degrees, beta = 83.01(4)degrees, and gamma = 64.81.(3)degrees. The phosphate counterions a re found to bridge adjacent layers of macrocyclic molecules through an exte nsive hydrogen-bonding network.