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·nH2O complexes (1: M = CoII, n = 0; 2: M = CuII, n = ½; 3: M = ZnII, n = 0) where TPA = tris(2-pyridylmethyl)amine, were synthesized and structurally characterized. The molecular structure of [Cu(TPA)Cl]ClO4·½H2O was determined by single crystal X-ray crystallography. In aqueous solution, the complex ions [M(TPA)Cl]+ (M = CoII or CuII) 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 °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 kcat and KM were determined as kcat = 6.59 h−1 and KM = 2.20 × 10−4 M for 1 and the corresponding parameters for 2 are kcat = 5.7 × 10−2 h−1 and KM = 6.9 × 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 × 108 and 1.6 × 106, respectively, over the non-catalyzed DNA. The reactivity of the two complexes was discussed in relation to other related artificial nucleases.