title: Nuclear targeting terpyridine iron(II) complexes for cellular imaging and remarkable photocytotoxicity.
abstract: Iron(II) complexes [Fe(L)(2)](2+) as perchlorate (1-3) and chloride (1a-3a) salts, where L is 4'-phenyl-2,2':6',2″-terpyridine (phtpy in 1, 1a), 4'-(9-anthracenyl)-2,2':6',2″-terpyridine (antpy in 2, 2a) and 4'-(1-pyrenyl)-2,2':6',2″-terpyridine (pytpy in 3, 3a), were prepared and their photocytotoxicity studied. The diamagnetic complexes 1-3 having an FeN(6) core showed an Fe(III)-Fe(II) redox couple near 1.0 V vs. saturated calomel electrode in MeCN-0.1 M tetrabutylammonium perchlorate. Complexes 2 and 3, in addition, displayed a quasi-reversible ligand-based redox process near 0.0 V. The redox and spectral properties are rationalized from the theoretical studies. The complexes bind to DNA in a partial intercalative mode. The pytpy complex efficiently photo-cleaves DNA in green light via superoxide and hydroxyl radical formation. The antpy and pytpy complexes exhibited a remarkable photocytotoxic effect in HeLa cancer cells (IC(50), ~9 μM) in visible light (400-700nm), while remaining essentially nontoxic in dark (IC(50), ~90 μM). Formation of reactive oxygen species (ROS) inside the HeLa cells was evidenced from the fluorescence enhancement of dichlorofluorescein upon treatment with the pytpy complex followed by photo-exposure. The antpy and pytpy complexes were used for cellular imaging. Confocal imaging and dual staining study using propidium iodide (PI) showed nuclear localization of the complexes.
authors.affiliation: Department of Inorganic and Physical Chemistry, Indian Institute of Science, Sir C V Raman Avenue, Bangalore 560012, Karnataka, India.
authors.forename: Uttara
authors.initials: U
authors.lastname: Basu
authors.forename: Imran
authors.initials: I
authors.lastname: Khan
authors.forename: Debasis
authors.initials: D
authors.lastname: Koley
authors.forename: Sounik
authors.initials: S
authors.lastname: Saha
authors.forename: Paturu
authors.initials: P
authors.lastname: Kondaiah
authors.forename: Akhil R
authors.initials: AR
authors.lastname: Chakravarty
mesh_terms: D002467:Cell Nucleus / Q000737:chemistry*; D053837:DNA Cleavage; D004563:Electrochemistry; D005296:Ferrous Compounds / Q000737:chemistry* / Q000633:toxicity; D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D011725:Pyridines / Q000737:chemistry* / Q000633:toxicity; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D005296:Ferrous Compounds; D011725:Pyridines; D017382:Reactive Oxygen Species