Synthesis and DNA photocleaving activities of ancillary ligand-containing zinc complexes of quaternized carboxylates

Abstract

Three zinc complexes, that is, {[Zn2(Cbp)2(BDC)2(H2O)2]·4H2O·MeOH}n (1) (Cbp=N-(4-carboxybenzyl)pyridinium, BDC=1,4-benzenedicarboxylate), [Zn(BCbpy)2(H2O)4]2(BDC)2·13H2O (2) (BCbpy=1-(4-carboxybenzyl)-4,4′-bipyridinium) and {[Zn2(Bpybc)3(BDC)2]·4H2O}n (3) (Bpybc=1,1′-bis(4-carboxybenzyl)-4,4′-bipyridinium), were synthesized and characterized on the basis of IR, elemental analysis and single-crystal X-ray crystallography data. Complexes 1 and 3 possess polynuclear structures, whereas complex 2 has a mononuclear structure. Agarose gel electrophoresis studies indicated that, under the irradiation of UV-A at 365nm, complex 2 showed negligible DNA-cleaving activity, whereas complexes 1 and 3 were capable of efficiently converting pBR322 DNA into OC forms, most probably via an oxidative mechanism. Kinetic assay on complexes 1 and 3 afforded the catalytic efficiency (kmax/KM) of 0.63 and 10.8h−1mM−1, respectively. The higher cleaving efficacy of complex 3 is a likely consequence of its polynuclear structure and one more quaternary ammonium center.