title: The cellular uptake and localization of non-emissive iridium(III) complexes as cellular reaction-based luminescence probes.
abstract: Improvement of cellular uptake and subcellular resolution remains a major obstacle in the successful and broad application of cellular optical probes. In this context, we design and synthesize seven non-emissive cyclometalated iridium(III) solvent complexes [Ir(CˆN)(2)(solv)(2)](+)L(-) (LIr2-LIr8, in which CˆN = 2-phenylpyridine (ppy) or its derivative; solv = DMSO, H(2)O or CH(3)CN; L(-) = PF(6)(-) or OTf(-)) applicable in live cell imaging to facilitate selective visualization of cellular structures. Based on the above variations (including different counter ions, solvent ligands, and CˆN ligands), structure-activity relationship analyses reveal a number of clear correlations: (1) variations in counter anions and solvent ligands of iridium(III) complexes do not affect cellular imaging behavior, and (2) length of the side carbon chain in CˆN ligands has significant effects on cellular uptake and localization/accumulation of iridium complexes in living cells. Moreover, investigation of the uptake mechanism via low-temperature and metabolism inhibitor assays reveal that [Ir(4-Meppy)(2)(CH(3)CN)(2)](+)OTf(-) (LIr5) with 2-phenylpyridine derivative with side-chain of methyl group at the 4-position as CˆN ligand permeates the outer and nuclear membranes of living cells through an energy-dependent, non-endocytic entry pathway, and translocation of the complex from the cell periphery towards the perinuclear region possibly occurs through a microtubule-dependent transport pathway. Nuclear pore complexes (NPCs) appear to selectively control the transport of iridium(III) complexes between the cytoplasm and nucleus. A generalization of trends in behavior and structure-activity relationships is presented, which should provide further insights into the design and optimization of future probes.
authors.affiliation: Department of Chemistry & State Key Laboratory of Molecular Engineering of Polymers, Fudan University, 220 Handan Road, Shanghai 200433, PR China.
authors.forename: Chunyan
authors.initials: C
authors.lastname: Li
authors.forename: Yi
authors.initials: Y
authors.lastname: Liu
authors.forename: Yongquan
authors.initials: Y
authors.lastname: Wu
authors.forename: Yun
authors.initials: Y
authors.lastname: Sun
authors.forename: Fuyou
authors.initials: F
authors.lastname: Li
mesh_terms: D003287:Contrast Media / Q000138:chemical synthesis; D006367:HeLa Cells; D006801:Humans; D007495:Iridium / Q000737:chemistry*; D008163:Luminescent Measurements / Q000379:methods*; D008856:Microscopy, Fluorescence / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D015335:Molecular Probes / Q000138:chemical synthesis*; D013347:Subcellular Fractions / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: D003287:Contrast Media; D015335:Molecular Probes; D007495:Iridium