COBALT(III) POLYAMINE COMPLEXES AS CATALYSTS FOR THE HYDROLYSIS OF PHOSPHATE-ESTERS AND OF DNA - A MEASURABLE 10-MILLION-FOLD RATE INCREASE

Complexes between cobalt(III) and eight different 1,4,7,10-tetraazacyc lododecane (cyclen) as well as two tris(3-aminopropyl)amine (trpn) der ivatives are reported with varying numbers and structures of peralkyla mmonium groups in side chains of the ligands. The presence of addition al positive charges has small effects on hydrolysis rates of nitrophen yl- and bis(nitrophenyl)phosphate esters but leads to substantially en hanced cleavage of plasmid DNA. Increasing the number of the charged s ide groups and/or their distance to the metal ion center provides for better binding to the DNA groove, as shown also by affinity measuremen ts with calf-thymus DNA. In line with this, saturation kinetics of pla smid DNA cleavage yield a corresponding increase of efficiency in Mich aelis-Menten-type K-M values, with rather constant k(cat) parameters. A binuclear cobalt complex with two cyclen centers separated by a -(CH 2)(6)-N+(CH3)(2)-(CH2)(6)-N+(CH3)(2)-(CH2)(6)- spacer shows, with only 5 x 10(-5) M catalyst concentration, the largest known rate enhanceme nt factor of >10(7) (corresponding to >10(11) at 1 M) against DNA; inc ubation with 0.05 mM at 37 degrees C for only 2 h leads to almost comp lete cleavage without appearance of products typical for redox cleavag e. These results are in contrast to experiments with corresponding cop per(II) complexes with added hydrogen peroxide, which has no effect wi th corresponding Co, Zn, Cd, or Ni complexes.