Synthesis, Structure, and Phosphatase-Like Activity of a New Trinuclear Gd Complex with the Unsymmetrical Ligand H3L As a Model for Nucleases

The new trinuclear gadolinium complex [Gd3L2(NO3)(2)(H2O)(4)]NO3 center dot 8H(2)O (1) with the unsymmetrical ligand 2-[N-bis-(2-pyridylmethyl)aminomethyl]-4-methyl-6-[N-bis(2-hydroxy-2-oxoethyl)aminomethyl] phenol (H3L) was synthesized and characterized. The new ligand H3L was obtained in good yield. Complex I crystallizes in an orthorhombic cell, space group Pcab. Kinetic studies show that complex 1 is highly active in the hydrolysis of the substrate 2,4-bis(dinitrophenyl)phosphate (K-m = 4.09 mM, V-max = 2.68 x 10(-2) mM s(-1), and k(cat) = V-max/[1] = 0.67 s(-1)). Through a potentiometric study and determination of the kinetic behavior of 1 in acetonitrile/water solution, the species present in solution could be identified, and a trinuclear monohydroxo species appears to be the most prominent catalyst under mild conditions. Complex 1 displays high efficiency in DNA hydrolytic cleavage, and complete kinetic studies were carried out (K-m = 4.57 x 10(-4) M, K-cat' = 3.42 h(-1), and k(cat)'/K-m = 7.48 x 10(3) M-1 h(-1)). Studies with a radical scavenger (dimethyl sulfoxide, DMSO) showed that it did not inhibit the activity, indicating the hydrolytic action of 1 in the cleavage of DNA, and studies on the incubation of distamycin with plasmid DNA suggest that 1 is regio-specific, interacting with the minor groove of DNA.