Nitrito complexes of nickel(II), copper(II) and cobalt(II) with tridentate pyrazole based planer ligand: Structure, spectroscopy, thermal properties and imitative nuclease activity

Abstract

Functional documentation of metal complexes are essential for various aspects including gene function/regulation and drug design for lethal diseases like cancer (Sigel and Martin (1982), Peters et al. (1997), Martin and Mascharak (2000), Hazra et al. (2007), Zhang et al. (2002), Patra et al. (2003)). Therefore, we have synthesized three new nitrite bound coordination complexes with the ligand 2,6-bis (3,4,5-trimethylpyrazole) pyridine (btmpp), [Ni(btmpp)(ONO)(2)] (1), [Cu(btmpp)(ONO)(2)] (2) and [Co(btmpp)(ONO)(2)] (3) and complexes were characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction analysis. Thermal stabilities of these complexes were studied by thermogravimetric (TG) and differential thermal analyses (DTA). The single crystal X-ray analyses showed that the geometry around the Ni atom was distorted octahedral with NiN3O3 coordination sphere. One of the nitrites in complex 1 is terminally bonded to the metal centre through the oxygen atom, whereas the other one is chelated as a bidentate through both oxygen atoms. In complex 2, the coordination around the Cu atom is a distorted square-pyramid (tau = 0.083) involving three N atoms from btmpp and two oxygen atoms from nitrites. Both nitrite groups are terminally bonded to the metal. DNA interaction properties of the compounds were also analyzed by agarose gel electrophoresis. The results indicated that all of the complexes converted supercoiled plasmid DNA (pET21a) into its nicked-circular form without addition of any external agents at physiological conditions. Complex 2 was the most effective on the cleavage of DNA, and its activity was observed as a conversion of double stranded DNA into nicked and linear form.