Emissive behavior, cytotoxic activity, cellular uptake, and PEGylation properties of new luminescent rhenium(I) polypyridine poly(ethylene glycol) complexes.

We report here a new class of biological reagents derived from luminescent rhenium(I) polypyridine complexes modified with a poly(ethylene glycol) (PEG) pendant. The PEG-amine complexes [Re(N(^)N)(CO)(3)(py-PEG-NH(2))](PF(6)) (py-PEG-NH(2) = 3-amino-5-(N-(2-(ω-methoxypoly(1-oxapropyl))ethyl)aminocarbonyl)pyridine, MW(PEG) = 5000 Da, PDI(PEG) < 1.08; N(^)N = 1,10-phenanthroline (phen) (1-PEG-NH(2)), 3,4,7,8-tetramethyl-1,10-phenanthroline (Me(4)-phen) (2-PEG-NH(2)), 4,7-diphenyl-1,10-phenanthroline (Ph(2)-phen) (3-PEG-NH(2))) and [Re(bpy-PEG)(CO)(3)(py-NH(2))](PF(6)) (bpy-PEG = 4-(N-(2-(ω-methoxypoly(1-oxapropyl))ethyl)aminocarbonyl)-4'-methyl-2,2'-bipyridine; py-NH(2) = 3-aminopyridine) (4-PEG-NH(2)) have been synthesized and characterized. The photophysical properties, lipophilicity, water solubility, cytotoxic activity, and cellular uptake properties of these complexes have been compared to those of their PEG-free counterparts [Re(N(^)N)(CO)(3)(py-Et-NH(2))](PF(6)) (py-Et-NH(2) = 3-amino-5-(N-(ethyl)aminocarbonyl)pyridine; N(^)N = phen (1-Et-NH(2)), Me(4)-phen (2-Et-NH(2)), Ph(2)-phen (3-Et-NH(2))) and [Re(bpy-Et)(CO)(3)(py-NH(2))](PF(6)) (bpy-Et = 4-(N-(ethyl)aminocarbonyl)-4'-methyl-2,2'-bipyridine) (4-Et-NH(2)). The PEG complexes exhibited significantly higher water solubility and lower cytotoxicity (IC(50) = 6.6 to 1152 µM) than their PEG-free counterparts (IC(50) = 3.6 to 159 µM), indicating that the covalent attachment of a PEG pendant to rhenium(I) polypyridine complexes is an effective way to increase their biocompatibility. The amine complexes 1-PEG-NH(2)-4-PEG-NH(2) have been activated with thiophosgene to yield the isothiocyanate complexes [Re(N(^)N)(CO)(3)(py-PEG-NCS)](PF(6)) (py-PEG-NCS = 3-isothiocyanato-5-(N-(2-(ω-methoxypoly(1-oxapropyl))ethyl)aminocarbonyl)pyridine; N(^)N = phen (1-PEG-NCS), Me(4)-phen (2-PEG-NCS), Ph(2)-phen (3-PEG-NCS)), and [Re(bpy-PEG)(CO)(3)(py-NCS)](PF(6)) (py-NCS = 3-isothiocyanatopyridine) (4-PEG-NCS) as a new class of luminescent PEGylation reagents. To examine their PEGylation properties, these isothiocyanate complexes have been reacted with a model substrate n-butylamine, resulting in the formation of the thiourea complexes [Re(N(^)N)(CO)(3)(py-PEG-Bu)](PF(6)) (py-PEG-Bu = 3-n-butylthioureidyl-5-(N-(2-(ω-methoxypoly(1-oxapropyl))ethyl)aminocarbonyl)pyridine; N(^)N = phen (1-PEG-Bu), Me(4)-phen (2-PEG-Bu), Ph(2)-phen (3-PEG-Bu)), and [Re(bpy-PEG)(CO)(3)(py-Bu)](PF(6)) (py-Bu = 3-n-butylthioureidylpyridine) (4-PEG-Bu). Additionally, bovine serum albumin (BSA) and poly(ethyleneimine) (PEI) have been PEGylated with the isothiocyanate complexes to yield bioconjugates 1-PEG-BSA-4-PEG-BSA and 1-PEG-PEI-4-PEG-PEI, respectively. Upon irradiation, all the PEGylated BSA and PEI conjugates exhibited intense and long-lived emission in aqueous buffer under ambient conditions. The DNA-binding and polyplex-formation properties of conjugate 3-PEG-PEI have been studied and compared with those of unmodified PEI. Furthermore, the in vivo toxicity of complex 3-PEG-NH(2) and its PEG-free counterpart 3-Et-NH(2) has been investigated using zebrafish embryos as an animal model. Embryos treated with the PEG complex at high concentrations revealed delayed hatching, which has been ascribed to hypoxia as a result of adhering of the complex to the external surface of the chorion.

Mitochondria-targeting cyclometalated iridium(III)-PEG complexes with tunable photodynamic activity.

We present a new class of phosphorescent cyclometalated iridium(III) polypyridine poly(ethylene glycol) (PEG) complexes [Ir(N(^)C)2(bpy-CONH-PEG)](PF6) (bpy-CONH-PEG = 4-(N-(2-(ω-methoxypoly-(1-oxapropyl))ethyl)aminocarbonyl)-4'-methyl-2,2'-bipyridine, number average molecular weight (Mn) = 5272.23, weight average molecular weight (Mw) = 5317.38, polydispersity index (PDI) = 1.009; HN(^)C = 2-phenylpyridine, Hppy (1a), 2-((1,1'-biphenyl)-4-yl)pyridine, Hpppy (2a), 2-phenylquinoline, Hpq (3a), 2-phenylbenzothiazole, Hbt (4a), 2-(1-naphthyl)benzothiazole, Hbsn (5a)). The photophysical, photochemical, and biological properties of these complexes have been compared with those of their PEG-free counterparts [Ir(N(^)C)2(bpy-CONH-Et)](PF6) (bpy-CONH-Et = 4-(N-ethylaminocarbonyl)-4'-methyl-2,2'-bipyridine; HN(^)C = Hppy (1b), Hpppy (2b), Hpq (3b), Hbt (4b), Hbsn (5b)). Upon irradiation, all the complexes exhibited intense and long-lived green to orange-red emission under ambient conditions. The emission was phosphorescence in nature and can be quenched by O2 with the generation of singlet oxygen ((1)O2). The quantum yields for (1)O2 production of the complexes in aerated DMSO (0.24-0.83) were found to be dependent on the excited-state lifetimes of the complexes, which can be altered using different cyclometalating ligands (N(^)C). Cell-based assays indicated that the PEG complexes were noncytotoxic in the dark (IC50 > 300 µM); however, most of them became significantly cytotoxic upon irradiation (IC50 = 3.4 - 23.2 µM). Laser-scanning confocal microscopy images revealed localization of complex 3a in the mitochondrial region of HeLa cells and the induction of rapid necrotic cell death upon light activation. Additionally, the lack of dark toxicity and potential application of the PEG complexes as a visualizing reagent have been demonstrated using zebrafish (Danio rerio) as an animal model.