Fluorescent Zinc Sensor with Minimized Proton-Induced Interferences: Photophysical Mechanism for Fluorescence Turn-On Response and Detection of Endogenous Free Zinc Ions

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• 作者：Ji Eon Kwon ; Sumin Lee ; Youngmin You ; Kyung-Hwa Baek ; Kei Ohkubo ; Jaeheung Cho ; Shunichi Fukuzumi ; Injae Shin ; Soo Young Park ; Wonwoo Nam
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：August 20, 2012
• 年：2012
• 卷：51
• 期：16
• 页码：8760-8774
• 全文大小：840K
• 年卷期：v.51,no.16(August 20, 2012)
• ISSN：1520-510X

文摘

A new fluorescent zinc sensor (HNBO鈥揇PA) consisting of 2-(2鈥?hydroxy-3鈥?naphthyl)benzoxazole (HNBO) chromophore and a di(2-picolyl)amine (DPA) metal chelator has been prepared and examined for zinc bioimaging. The probe exhibits zinc-induced fluorescence turn-on without any spectral shifts. Its crystal structure reveals that HNBO鈥揇PA binds a zinc ion in a pentacoordinative fashion through the DPA and HNBO moieties. Steady-state photophysical studies establish zinc-induced deprotonation of the HNBO group. Nanosecond and femtosecond laser flash photolysis and electrochemical measurements provide evidence for zinc-induced modulation of photoinduced electron transfer (PeT) from DPA to HNBO. Thus, the zinc-responsive fluorescence turn-on is attributed to suppression of PeT exerted by deprotonation of HNBO and occupation of the electron pair of DPA, a conclusion that is further supported by density functional theory and time-dependent density functional theory (DFT/TD-DFT) calculations. Under physiological conditions (pH 7.0), the probe displays a 44-fold fluorescence turn-on in response to zinc ions with a K_d value of 12 pM. The fluorescent response of the probe to zinc ions is conserved over a broad pH range with its excellent selectivity for zinc ions among biologically relevant metal ions. In particular, its sensing ability is not altered by divalent transition metal ions such as Fe(II), Cu(II), Cd(II), and Hg(II). Cell experiments using HNBO鈥揇PA show its suitability for monitoring intracellular zinc ions. We have also demonstrated applicability of the probe to visualize intact zinc ions released from cells that undergo apoptosis. More interestingly, zinc-rich pools in zebrafish embryos are traced with HNBO鈥揇PA during early developmental stages. The results obtained from the in vitro and in vivo imaging studies demonstrate the practical usefulness of the probe to detect zinc ions.