(170a) Biological Activities of Cyclometalated Half-Sandwich Complexes of Iridium(III) with Heterocyclic Scaffolds

Dihalobridged binuclear complex [{(h⁵-C₅Me₅)Ir(m-Cl)Cl}₂] undergo halide bridge cleavage reactions with multidentate N, N heterocycles namely 5'-chloro-3'-methyl-1',2-diphenyl-5-(pyridin-2-yl)-3,4-dihydro-1'H,2H-3,4'-bipyrazole (L₁) / 4-(5-chloro-3-methyl-1-phenyl-1H-pyrazol-4-yl)-6-(pyridin-2-yl)pyrimidin-2-amine (L₂) / 7-(5-chloro-3-methyl-1-phenyl-1H-pyrazol-4-yl)-5-(pyridin-2-yl)-[1,2,4]triazolo[1,5-a]pyrimidine (L₃)  forming a new half sandwich cationic mononuclear iridium(III) complex [(h⁵-C₅Me₅)Ir(k²-L)Cl]Cl. The complexes were fully characterized by various physicochemical techniques, namely, elemental analyses, spectral (ESI-MS, IR, ¹H, ¹³C NMR, UV/vis). The in vitro antibacterial activity against three gram negative and two gram positive microorganisms and in vitro antituberculosis activity against Mycobacterium tuberculosis H37Rv strain were studied for all compounds and all the complexes shows good inhibition as compared to ligands. The in vitro cytotoxicity was determined using brine shrimp bioassay and LD₅₀ value obtained in the range of 7–12 mg mL^-1. Cellular level cytotoxicity was performed using bioassay of S. pombe and it shows inevitable viability as concentration increases. The DNA binding activity was studied by absorption titration and viscosity measurements. The complexes bind to CT-DNA through intercalation mode (kb = 10⁵). DNA nuclease activity was studied by agarose gel electrophoresis method and the compounds show 70–80% cleavage.