Effect of the central metal ion on the cleavage of DNA by [M(TPA)Cl]ClO4 complexes (M = CoII, CuII and ZnII, TPA = tris(2-pyridylmethyl)amine): An efficient artificial nuclease for DNA cleavage

[M(TPA)Cl]ClO4 center dot nH(2)O complexes (1: M = Co-II, n = 0; 2: M = Cu-II, n = 1/2; 3: M = Zn-II, n = 0) where TPA = tris (2-pyridylmethyl) amine, were synthesized and structurally characterized. The molecular structure of [Cu(TPA)Cl]ClO4 center dot 1/2H(2)O was determined by single crystal X-ray crystallography. In aqueous solution, the complex ions [M(TPA)Cl](+) (M = Co-II or Cu-II) are hydrolyzed to the corresponding aqua species [M(TPA)(H2O)](2+). In contrast to the TBP [Cu(TPA)(H2O)](2+), the corresponding TBP cobalt(II) species showed severe distortion towards tetrahedral geometry. The interactions of the three complexes with DNA have been investigated at pH 7.0 (1.0 mM Tris-Cl buffer) and 37 degrees C. Significant DNA cleavages were obtained for complexes 1 and 2, whereas complex 3 did not show any detectable cleavage for DNA. Under pseudo Michaelis-Menten kinetic conditions, the kinetic parameters k(cat) and K-M were determined as k(cat) = 6.59 h(-1) and K-M = 2.20 x 10(-4) M for 1 and the corresponding parameters for 2 are k(cat) = 5.7 x 10(-2) h(-1) and K-M = 6.9 x 10(-5) M, and the reactivity of the complexes in promoting the cleavage of DNA decreases in the order 1 > 2 >> 3. The rate enhancements for the DNA cleavage by 1 and 2 correspond to 1.8 x 10(8) and 1.6 x 10(6), respectively, over the non-catalyzed DNA. The reactivity of the two complexes was discussed in relation to other related artificial nucleases. (C) 2011 Elsevier B. V. All rights reserved.