Synthesis, crystal structures and biological evaluation of water-soluble zinc complexes of zwitterionic carboxylates

Three water-soluble zinc complexes, [Zn(Cbp)2Br2] (1) (Cbp = N-(4-carboxybenzyl)pyridinium), {[Zn(BCbpy)2(H2O)4]3Br6·2(BCbpy)·2(4,4′-bipy)} (2) (BCbpy = 1-(4-carboxybenzyl)-4,4′-bipyridinium) and {[Zn4(Bpybc)6(H2O)12](OH)8·9H2O}2n (3) (Bpybc = 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridinium), were synthesized and characterized by IR, elemental analysis and single-crystal X-ray crystallography. In complex 1, the central Zn atom adopts a distorted tetrahedral coordination geometry that is formed from two unidentate Cbp ligands and two Br atoms. For complex 2, the Zn atom in [Zn(BCbpy)2(H2O)4]2+ is strongly coordinated by four water molecules and two N atoms from two BCbpy ligands, hence forming an octahedral geometry. In complex 3, each Bpybc ligand bridges two [Zn(H2O)3]2+ units through two terminal carboxylate groups in a monodentate coordination mode, thus forming a flowerlike two-dimensional network. Agarose gel electrophoresis (GE) and ethidium bromide (EB) displacement experiments indicated that complex 3 was capable of converting pBR322 DNA into open circular (OC) and linear forms, and exhibited high binding affinity toward calf-thymus DNA. MTT assay showed that complex 3 displayed inhibitory activities toward the proliferation of lung adenocarcinoma A549 and mouse sarcoma S-180 cells, with the IC50 values being 27.3 and 48.8 μM, respectively.