Thermodynamic studies on supramolecular interactions of metal ions with nucleotides/tripods ligands

Four closely related polyamino tripodal ligands 1,3,5-tri(n-2', 5'-diaminohexane)-benzene (L1), 1,3,5-tri(n-2,5'-diaminoheptane)benzene (L2), 1,3,5-tri(n-2',5-diaminooetane)-benzene (L3) and 1, 3,5-tri(n-2', 5'-diaminononane)-benzene (L4) were synthesized and characterized. Each tripodal ligand forms six protonated species in solution. The binding of these tripodal ligands to the nucleotide anions ATP, ADP and AMP are described in detail, with equilibrium constants given for each species formed. The strength of binding increases with the number of protons, corresponding to an increase in the number of hydrogen bonds and to an increase in the coulombic attractive forces. Moreover, the existence of a benzene spacer takes pi-stacking interactions with the nucleobase residue of the nucleotides. At the same time, the coordination properties of the ternary complexes formed from the above tripods and Zn(II) and ATP were studied. The metal complexes of tripods recognize the nucleotides via multiple interactions that are similar to those occurring in the center of enzymes. (C) 2002 Elsevier Science Ltd. All rights reserved.