Cobalt(III) Polyamine Complexes as Catalysts for the Hydrolysis of Phosphate Esters and of DNA. A Measurable 10 Million-Fold Rate Increase¹

Abstract

Complexes between cobalt(III) and eight different 1,4,7,10-tetraazacyclododecane (cyclen) as well as two tris(3-aminopropyl)amine (trpn) derivatives are reported with varying numbers and structures of peralkylammonium groups in side chains of the ligands. The presence of additional positive charges has small effects on hydrolysis rates of nitrophenyl- and bis(nitrophenyl)phosphate esters but leads to substantially enhanced cleavage of plasmid DNA. Increasing the number of the charged side groups and/or their distance to the metal ion center provides for better binding to the DNA groove, as shown also by affinity measurements with calf-thymus DNA. In line with this, saturation kinetics of plasmid DNA cleavage yield a corresponding increase of efficiency in Michaelis−Menten-type K M values, with rather constant k cat parameters. A binuclear cobalt complex with two cyclen centers separated by a −(CH2)6-N+(CH3)2-(CH2)6-N+(CH3)2-(CH2)6− spacer shows, with only 5 × 10-5 M catalyst concentration, the largest known rate enhancement factor of >107 (corresponding to >1011 at 1 M) against DNA; incubation with 0.05 mM at 37 °C for only 2 h leads to almost complete cleavage without appearance of products typical for redox cleavage. These results are in contrast to experiments with corresponding copper(II) complexes with added hydrogen peroxide, which has no effect with corresponding Co, Zn, Cd, or Ni complexes.

Hydrolysis of plasmid DNA catalyzed by Co(III) complex of cyclen attached to polystyrene

“…It has been estimated that > 10 7 -fold rate increase was achieved with CoCyc in hydrolysis of phosphodiester linkages leading to the conversion of a supercoiled DNA to the corresponding open circular form. 9 Hydrolytic nature of the DNA cleavage by the Co(III) complexes of polyamines including cyclen was evidenced by chemical or enzymatic religation 10 of the cleavage products as well as by the detection 6 of 3 0 -OH and 5…”

“…9 The cationic substituents introduced in 1b-d facilitated complexation between the catalyst and the DNA substrate, but the intrinsic reactivity of the Co center was little affected by the substituents.…”

“…PCD was synthesized by suspension copolymerization of chloromethylstyrene and divinylbenzene (2 mol% relative to chloromethylstyrene) according to a procedure reported in the literature 16 MeO PCD was carried out by following the procedure reported in the literature. 9 The content of CoCyc was estimated through measuring the amount of Co(III) ion released from the resin upon treatment with concentrated nitric acid by inductively coupled plasmaatomic emission spectroscopy. The content of guanidinium was measured by the binding experiment 15 with pnitrobenzoate.…”

“…CoCyc was synthesized as reported. 9 Plasmid pUC18 DNA (2686 base pairs) was used as the supercoiled DNA substrate. The plasmid DNA was prepared and isolated according to standard protocols.…”

The Interaction of Copper-Bipyridyl Complex with DNA and Cleavage to DNA

“…Hettich et al 9 investigated the dinucleotide TpT reacted with 5 mM EuCl3 at 70˚C for up to 14 days, which allowed the reaction to be followed up to 25% completion. The electrochemical method can modulate the redox reaction under physiological conditions.…”