title: Luminescent dendritic cyclometalated iridium(III) polypyridine complexes: synthesis, emission behavior, and biological properties.
abstract: Luminescent dendritic cyclometalated iridium(III) polypyridine complexes [{Ir(N--C)(2)}(n)(bpy-n)](PF(6))(n) (HN--C = 2-phenylpyridine, Hppy, n = 8 (ppy-8), 4 (ppy-4), 3 (ppy-3); HN--C = 2-phenylquinoline, Hpq, n = 8 (pq-8), 4 (pq-4), 3 (pq-3)) have been designed and synthesized. The properties of these dendrimers have been compared to those of their monomeric counterparts [Ir(N--C)(2)(bpy-1)](PF(6)) (HN--C = Hppy (ppy-1), Hpq (pq-1)). Cyclic voltammetric studies revealed that the iridium(IV/III) oxidation and bpy-based reduction occurred at about +1.24 to +1.29 V and -1.21 to -1.27 V versus SCE, respectively, for all the complexes. The molar absorptivity of the dendritic iridium(III) complexes is approximately proportional to the number of [Ir(N--C)(2)(N--N)] moieties in one complex molecule. However, the emission lifetimes and quantum yields are relatively independent of the number of [Ir(N--C)(2)(N--N)] units, suggesting negligible electronic communications between these units. Upon photoexcitation, the complexes displayed triplet metal-to-ligand charge-transfer ((3)MLCT) (dpi(Ir) --> pi*(bpy-n)) emission. The interaction of these complexes with plasmid DNA has been investigated by agarose gel retardation assays. The results showed that the dendritic iridium(III) complexes, unlike their monomeric counterparts, bound to the plasmid, and the interaction was electrostatic in nature. The lipophilicity of all the complexes has been determined by reversed-phase high-performance liquid chromatography (HPLC). Additionally, the cellular uptake of the complexes by the human cervix epithelioid carcinoma (HeLa) cell line has been examined by inductively coupled plasma mass spectrometry (ICP-MS), laser-scanning confocal microscopy, and flow cytometry. Upon internalization, all the complexes were localized in the perinuclear region, forming very sharp luminescent rings surrounding the nuclei. Interestingly, in addition to these rings, HeLa cells treated with the dendritic iridium(III) complexes showed specific labeled compartments, which have been identified to be the Golgi apparatus. Furthermore, the cytotoxicity of these iridium(III) complexes has been evaluated by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, People's Republic of China.
authors.forename: Kenneth Yin
authors.initials: KY
authors.lastname: Zhang
authors.forename: Hua-Wei
authors.initials: HW
authors.lastname: Liu
authors.forename: Tommy Tsz-Him
authors.initials: TT
authors.lastname: Fong
authors.forename: Xian-Guang
authors.initials: XG
authors.lastname: Chen
authors.forename: Kenneth Kam-Wing
authors.initials: KK
authors.lastname: Lo
mesh_terms: D049109:Cell Proliferation / Q000187:drug effects; D004247:DNA / Q000187:drug effects; D003712:Dendrites / Q000737:chemistry*; D004354:Drug Screening Assays, Antitumor; D006056:Golgi Apparatus / Q000737:chemistry; D006367:HeLa Cells; D006801:Humans; D007495:Iridium / Q000737:chemistry*; D049449:Luminescence; D015388:Organelles / Q000187:drug effects; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D010957:Plasmids / Q000187:drug effects; D011108:Polymers / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry*; D013329:Structure-Activity Relationship
chemical_list: D009942:Organometallic Compounds; D011108:Polymers; D011725:Pyridines; D007495:Iridium; D004247:DNA