Luminescent cyclometalated iridium(lll) polypyridine indole complexes-synthesis, photophysics, electrochemistry, protein-binding properties, cytotoxicity, and cellular uptake

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

154 Scopus Citations
View graph of relations

Author(s)

  • Jason Shing-Yip Lau
  • Pui-Kei Lee
  • Keith Hing-Kit Tsang
  • Cyrus Ho-Cheong Ng

Detail(s)

Original languageEnglish
Pages (from-to)708-718
Journal / PublicationInorganic Chemistry
Volume48
Issue number2
Publication statusPublished - 19 Jan 2009

Abstract

A series of luminescent cyclometalated iridium(lll) polypyridine indole complexes, [lr(N-C)2(N-N)](PF6) (HN-C = 2-phenylpyridine (Hppy), N-N = 4-((2-(indol-3-yl)ethyl)aminocarbonyl)-4′-methyl-2,2′- bipyridine (bpy-ind) (1a), N-N = 4-((5-((2-(indol-3-yl)ethyl)aminocarbonyl) pentyl)aminocarbonyl)-4′-methyl-2,2′-bipyridine (bpy-C6-ind) (1b); HN-C = 7,8-benzoquinoline (Hbzq), N-N = bpy-ind (2a), N-N= bpy-C6-ind (2b); and HN-N = 2-phenylquinoline (Hpq), N-N = bpy-ind (3a), N-N = bpy-C6-ind (3b)), have been synthesized, characterized, and their photophysical and electrochemical properties and lipophilicity investigated. Photoexcitation of the complexes in fluid solutions at 298 K and in alcohol glass at 77 K resulted in intense and long-lived luminescence (λem = 540-616 nm, τo = 0.13-5.15 μs). The emission of the complexes has been assigned to a triplet metal-to-ligand charge-transfer (3MLCT) (dπ(lr) → π*(N-N)) excited state, probably with some mixing of triplet intraligand (3IL) (π→π*) (pq) character for complexes 3a,b. Electrochemical measurements revealed that all the complexes showed an irreversible indole oxidation wave at ca. +1.1 V versus SCE, a quasi-reversible iridium(IV/lll) couple at ca. +1.3 V, and a reversible diimine reduction couple at ca. -1.3 V. The interactions of these complexes with an indole-binding protein, bovine serum albumin (BSA), have been studied by emission titrations, and the Ka values are on the order of 10 4 M-1. Additionally, the cytotoxicity of the complexes toward human cervix epithelioid carcinoma (HeLa) cells has been examined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay. The IC50 values of the complexes ranged from 1.1 to 6.3 μM, which are significantly smaller than that of cisplatin (30.7 μM) under the same experimental conditions. Furthermore, the cellular uptake of the complexes has been investigated by flow cytometry and laser- scanning confocal microscopy. The microscopy images indicated that complex 3a was localized in the perinuclear region upon interiorization. Temperature-dependence experiments suggested that the internalization of the complex was an energy-requiring process such as endocytosis. This has been confirmed by cellular-uptake experiments involving the luminescent conjugates Ir-BSA and Ir-TF (TF = holo-transferrin), which were prepared by conjugation of the proteins with the complex [lr(pq) 2(phen-NCS)](PF6) (phen-NCS = 5-isothiocyanato-1,10- phenanthroline). © 2009 American Chemical Society.

Citation Format(s)

Luminescent cyclometalated iridium(lll) polypyridine indole complexes-synthesis, photophysics, electrochemistry, protein-binding properties, cytotoxicity, and cellular uptake. / Lau, Jason Shing-Yip; Lee, Pui-Kei; Tsang, Keith Hing-Kit; Ng, Cyrus Ho-Cheong; Lam, Yun-Wah; Cheng, Shuk-Han; Lo, Kenneth Kam-Wing.

In: Inorganic Chemistry, Vol. 48, No. 2, 19.01.2009, p. 708-718.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review