Double-strand DNA cleavage by copper complexes of 2,2′-dipyridyl with electropositive pendants

Two highly charged cationic copper( II) complexes have been synthesized and characterized structurally and spectroscopically: [ Cu( L-1)(2)( Br)](ClO4)(5) ( 1) and [ Cu( L-2)(2)( Br)](ClO4)(5) (2) ( L-1 = 5,5' -di(1-( triethylammonio) methyl)- 2,2'- dipyridyl cation and L-2 = 5,5'- di( 1-( tributylammonio) methyl)- 2,2-dipyridyl cation bidentate ligands). X- Ray structures show that Cu( II) ions in both complexes have a trigonal- bipyramidal CuN4Br- configuration. Two nitrogen atoms of the electropositive pendants and coordinated bromine atom basically array in a straight line. Their close distances of N center dot center dot center dot Br atoms are 5.772 and 5.594 angstrom, respectively, which is comparable to that of adjacent phosphodiesters in B- form DNA ( ca. 6 angstrom). In the absence of reducing agent, supercoiled plasmid DNA cleavage by the complexes has been performed and their hydrolytic mechanisms have been investigated. The pseudo- Michaelis -Menten kinetic parameters (k(cat)), 4.15 h(-1) for 1, 0.43 h(-1) for 2 and 0.61 h(-1) for [Cu(bipy)( NO3)(2)], were obtained. This result indicates that 1 exhibits markedly higher nuclease activity than its corresponding analogues. The high ability of DNA cleavage for 1 is attributed to the effective cooperation of the metal moiety and two positive pendants since the array of linear tri- binding sites matches with one of three phosphodiester backbones of nucleic acid.