Phosphorescent Zinc Probe for Reversible Turn-On Detection with Bathochromically Shifted Emission
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- 作者：Seung Yeon Ryu ; Mijoung Huh ; Youngmin You ; Wonwoo Nam
- 刊名：Inorganic Chemistry
- 出版年：2015
- 出版时间：October 19, 2015
- 年：2015
- 卷：54
- 期：20
- 页码：9704-9714
- 全文大小：703K
- ISSN：1520-510X
文摘
Phosphorescent molecules are attractive complements to fluorescent compounds for bioimaging. Time-gated acquisition of the long-lived phosphorescence signals provides an effective means to eliminate unwanted background noises due to short-lived autofluorescence. We have previously investigated the molecular principles governing modulation of photoinduced electron transfer in phosphorescence zinc probes that were based on biscyclometalated Ir(III) complexes (Woo, H. et al. J. Am. Chem. Soc. 2013, 135, 4771鈥?787). The studies established that phosphorescence turn-on responses would be attainable for Ir(III) complexes with high triplet-state energies. This sets an upper limit to an emission wavelength, restricting the development of red- or near-IR-phosphorescence turn-on probes. To address this challenge, we designed and synthesized a new phosphorescent probe having an electron-deficient 2-(2-pyridyl)pyrazine diimine ligand tethering a di(2-picolyl)amine (DPA) zinc receptor. This ligand control led to red phosphorescence emission (位ems = 596 nm), with an excited-state reduction potential (E*red) retained as high as 1.44 V versus standard calomel electrode (SCE). The E*red value was more positive than the ground-state oxidation potential of DPA (1.05 V vs SCE), permitting an occurrence of photoinduced electron transfer at a rate of 2 脳 107 s鈥?. Zinc binding at DPA abolished the electron transfer to produce phosphorescence turn-on signaling. The probe was capable of detecting zinc ions selectively over other competing biological metal ions in aqueous buffer solutions (pH 7.4, 20 mM piperazine-N,N鈥?bis(2-ethanesulfonic aid)) with the zinc dissociation constant of 109 pM. Finally, bioimaging utility of the probe has been successfully demonstrated by visualizing exogenously supplied zinc ions in live HeLa cells. The research described in this paper demonstrates that judicious ligand control enables retention of turn-on responses in the low-energy phosphorescence region.