Reaction of salicylaldehyde-2-picolinylhydrazone (HL) Schiff base ligand with precursor compounds [{(p-cymene)RuCl2}2] 1, [{(C6H6)RuCl2}2] 2, [{Cp*RhCl2}2] 3 and [{Cp*IrCl2}2] 4 yielded the corresponding neutral mononuclear compounds 5-8, respectively. The in vitro antitumor evaluation of the compounds 1-8 against Dalton's ascites lymphoma (DL) cells by fluorescence-based apoptosis study and by their half-maximal inhibitory concentration (IC50) values revealed the high antitumor activity of compounds 3, 4, 5 and 6. Compounds 1-8 render comparatively lower apoptotic effect than that of cisplatin on model non-tumor cells, i.e., peripheral blood mononuclear cells (PBMC). The antibacterial evaluation of compounds 5-8 by agar well-diffusion method revealed that compound 6 is significantly effective against all the eight bacterial species considered with zone of inhibition up to 35 mm. Fluorescence imaging study of compounds 5-8 with plasmid circular DNA (pcDNA) and HeLa RNA demonstrated their fluorescence imaging property upon binding with nucleic acids. The docking study with some key enzymes associated with the propagation of cancer such as ribonucleotide reductase, thymidylate synthase, thymidylate phosphorylase and topoisomerase II revealed strong interactions between proteins and compounds 5-8. Conformational analysis by density functional theory (DFT) study has corroborated our experimental observation of the N, N binding mode of ligand. Compounds 5-8 exhibited a HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) energy gap 2.99-3.04 eV. Half-sandwich ruthenium, rhodium and iridium compounds were obtained by treatment of metal precursors with salicylaldehyde-2-picolinylhydrazone (HL) by in situ metal-mediated deprotonation of the ligand. Compounds under investigation have shown potential antitumor, antibacterial and fluorescence imaging properties. Arene ruthenium compounds exhibited higher activity compared to that of Cp*Rh/Cp*Ir in inhibiting the cancer cells growth and pathogenic bacteria. At a concentration 100 µg/mL, the apoptosis activity of arene ruthenium compounds, 5 and 6 (~30 %) is double to that of Cp*Rh/Cp*Ir compounds, 7 and 8 (~12 %). Among the four new compounds 5-8, the benzene ruthenium compound, i.e., compound 6 is significantly effective against the pathogenic bacteria under investigation.

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The three-dimensional (3-D) cryptand-like normal and doubly-N-confused calixbenzophyrins embedded with phenyl rings in the macrocyclic skeleton are successfully synthesized from single starting materials. These structural isomers are characterized by spectral studies and unambiguously confirmed by crystal analyses.

Neutral and cationic half-sandwich arene ruthenium, Cp*Rh and Cp*Ir oximato and oxime complexes: Synthesis, structural, DFT and biological studies.

Half-sandwich ruthenium, rhodium and iridium complexes (1-12) were synthesized with aldoxime (L1), ketoxime (L2) and amidoxime (L3) ligands. Ligands have the general formula [PyC(R)NOH], where R = H (L1), R = CH 3 (L2) and R = NH 2 (L3). Reaction of [{(arene)MCl 2 } 2 ] (arene = p-cymene, benzene, Cp*; M = Ru, Rh, Ir) with ligands L1-L3 in 1:2 metal precursor-to-ligand ratio yielded complexes such as [{(arene)MLκ 2 (N∩N) Cl}]PF 6 . All the ligands act as bidentate chelating nitrogen donors in κ 2 (N∩N) fashion while forming complexes. In vitro anti-tumour activity of complexes 2 and 10 against HT-29 (human colorectal cancer), BE (human colorectal cancer) and MIA PaCa-2 (human pancreatic cancer) cell lines and non-cancer cell line ARPE-19 (human retinal epithelial cells) revealed a comparable activity although complex 2 demonstrated greater selectivity for MIA PaCa-2 cells than cisplatin. Further studies demonstrated that complexes 3, 6, 9 and 12 induced significant apoptosis in Dalton's ascites lymphoma (DL) cells. In vivo anti-tumour activity of complex 2 on DL-bearing mice revealed a statistically significant antitumour activity (P = 0.0052). Complexes 1-12 exhibit HOMO-LUMO energy gaps from 3.31 to 3.68 eV. Time-dependent density functional theory calculations explain the nature of electronic transitions and were in good agreement with experiments.