Supramolecular Chemistry, 62. Ligand and Cosubstrate Effects on the Hydrolysis of Phosphate Esters and DNA with Lanthanoids

Attempts are described to enhance the catalytic activity of lanthanide ions by providing cosubstrates with an increasing number of nucleophilic groups or by attaching corresponding polyols covalently to stronger metal‐binding centers like diazacrown ethers. Although the kinetic effects on the hydrolysis of bis(4‐nitrophenyl) phosphate ( BNPP ) and of super‐coiled plasmid DNA are only moderate, their dependence on cosubstrate structure and polyol configuration unambiguously demonstrates that these are involved in the slow step of the reactions. Thus, addition of gluconic acid to a LaCl 3 solution leads to a marked increase of DNA cleavage from 20 to 71%. Naphthyl units covalently bound to the diazacrown show little effect on BNPP hydrolysis, but enhance DNA hydrolysis again from e.g. 38% (RF II) to 60%. Preliminary affinity measurements with calf thymus DNA, using a fluorimetric assay with ethidium bromide, show for polyamines a dependence on the number of ligand charges as observed earlier. The naphthyl compound is characterized by a high affinity; preliminary NMR data indicate that the naphthyl units intercalate into DNA.