Hydrolytic cleavage of DNA promoted by cobalt(III)-tetraamine complexes: Synthesis and characterization of carbonatobis[2-(2-pyridylethyl)]-(2-pyridylmethyl)aminecobalt(III) perchlorate

cis-Aquahydroxo-tetraamine-cobalt(III) complexes of the general formula [Co(N-4)(OH)(H2O)](2+) have been prepared (pH similar to 7) from their corresponding well characterized carbonato or dichloro compounds, where N-4 = TPA (tris(2-pyridy[methyl)amine), 1; pmap {bis[2-(2-pyridylethyl)]-(2-pyridylmethyl)amine}, 2; 2,2,2-tet (triethylenetetraamine), 3: 3,2,3-tet {4,7-diaza-1,10-decanediamine}, 4; tren (tris(2-aminoethyl)amine), 5; and abap {N-(2-aminoethyl)-N,N-bis(3-aminopropyl)amine}, 6. The carbonato complex [Co(pmap)(CO3)]ClO4 was structurally characterized by X-ray crystal analysis. The interactions of the complexes 1-6 with DNA have been investigated (pH 7.0,1 = 0.1 M, 37 degrees C). The complexes 4-6 did not show any detectable hydrolytic cleavage for DNA, whereas significant cleavages were obtained with the rest of the studied complexes (1-3). Under pseudo-Michaelis-Menten kinetic conditions, the reactivity of the complexes in promoting the hydrolytic cleavage of DNA decreases in the order 1 > 3 >> 2 (rates were compared at the saturation levels, i.e. V-max') and the kinetic parameters k(cat)' and K-M were determined: k(cat)' = 3.49 x 10(-4)s(-1) and K-M = 159 mu M for 1 and k(cat)'' = 5.08 x 10(-5)s(-1) and K-M = 296 mu M for 3. The calculated values of k(cat)'' correspond to an enhancement of 3.5 x 10(7) and 5.1 x 10(6) for 1 and 3, respectively, over the uncatalyzed DNA. The DNA cleavage with these two complexes was also monitored under 'true' Michaelis-Menten kinetic conditions using constant catalyst concentration (Co(III)) and varying substrate concentrations (DNA) but no kinetic fits were observed between k(obs) and [DNA] and hence the parameters k(cat) and K-M were not calculated in this case. The reactivity of the complexes is discussed based on the structural skeletons of the tetraamine blocking ligands. (C) 2009 Elsevier Ltd. All rights reserved.