Recognition promoted by Zn2+ between phenanthroline bridging polyaza ligands and nucleotides -: Zn2+ acts as 'messenger' between the receptor and substrate

The stability constants of the supramolecular complexes formed between L-(a,L-b,L-c,L-d) or their Zn2+ complexes, and adenosine 5'-triphosphate (ATP) in aqueous solution were determined by potentiometric titrations (25degreesC, I = 0.1 mol dm(-3) KNO3). The results show that protonated aliphatic-substituted La,d and aromatic-substituted L-b,L-c ligands and/or Zn(11) ion can efficiently recognition the substrate, ATP. All of the equilibrium studies, H-1 and P-31 nuclear magnetic resonance spectra indicate that multiple interactions, including coordination, pi-stacking, ion-pairing, H-bonding, and possible ion-pi-donor, hydrophobic and even van der Waals interactions exist in the Zn(II)-L-ATP systems. On the other hand, the recognition of the substrates by the protonated ligands was significantly promoted by the addition of Zn(H), which leads to coordination competition between the mixed ligands, L and nucleotide. In Zn(II)/L/ATP systems the tendency for phosphate chain to receive proton and metal ion increases, facilitating the cleavage of the phosphate chain of the nucleotide. Copyright (C) 2003 John Wiley Sons, Ltd.