Zinc is an essential trace element involved in many biological activities; however, its functions are not fully understood. To elucidate the role of endogenous labile Zn2+, we developed a novel ratiometric fluorescence probe, 5-(4-methoxyphenyl)-4-(methylsulfanyl)-[2,2′-bipyridin]-6-amine (6 (rBpyZ)) based on the 6-amino-2,2′-bipyridine scaffold, which acts as both the chelating agent for Zn2+ and the fluorescent moiety. The methoxy group acted as an electron donor, enabling the intramolecular charge transfer state of 6 (rBpyZ), and a ratiometric fluorescence response consisting of a decrease at the emission wavelength of 438 nm and a corresponding increase at the emission wavelength of 465 nm was observed. The ratiometric probe 6 (rBpyZ) exhibited a nanomolar-level dissociation constant (Kd = 0.77 nM), a large Stokes shift (139 nm), and an excellent detection limit (0.10 nM) under physiological conditions. Moreover, fluorescence imaging using A549 human lung adenocarcinoma cells revealed that 6 (rBpyZ) had good cell membrane permeability and could clearly visualize endogenous labile Zn2+. These results suggest that the ratiometric fluorescence probe 6 (rBpyZ) has considerable potential as a valuable tool for understanding the role of Zn2+ in living systems.

中文翻译：

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基于6-氨基-2,2'-联吡啶支架的内源性Zn2+高亲和力比率荧光探针及其在活细胞中的应用

锌是参与许多生物活动的必需微量元素；然而，它的功能还没有被完全理解。为了阐明内源性不稳定 Zn2+ 的作用，我们开发了一种基于 5-(4-methoxyphenyl)-4-(methylsulfanyl)-[2,2'-bipyridin]-6-amine (6 (rBpyZ)) 的新型比率荧光探针在 6-amino-2,2'-bipyridine 支架上，它作为 Zn2+ 的螯合剂和荧光部分。甲氧基充当电子供体，使分子内电荷转移状态为 6 (rBpyZ)，并观察到由 438 nm 发射波长处的降低和 465 nm 发射波长处的相应增加组成的比率荧光响应. 比率探针 6 (rBpyZ) 表现出纳摩尔级解离常数 (Kd = 0.77 nM)、大斯托克斯位移 (139 nm)、在生理条件下具有出色的检测限 (0.10 nM)。此外，使用 A549 人肺腺癌细胞的荧光成像显示 6 (rBpyZ) 具有良好的细胞膜通透性，可以清楚地显示内源性不稳定的 Zn2+。这些结果表明，比率荧光探针 6 (rBpyZ) 作为了解 Zn2+ 在生命系统中的作用的有价值工具具有相当大的潜力。