Fluorescent Sensors For Zn～(2+) Based On Bis(2-picolyl)amine

Analysis and detection of Zn2+ in cells is very significant as it has multiple and important roles in living process. But many normal analysis techniques, for examples. UV-Vis spectrum, NMR and EPR cannot be used to detect the special metal ions in living things. The fluorescence method is not only simple but also excellent in real space, real time, high sensitivity and selectivity. There is important significance to understand the multiple roles of zinc with availability of fluorescent probe systems permitting quantitative determination and imaging of zinc fluxes and levels over a broad concentration range.Based on carbonic anhydrase (CA)-sulfonamide inhibition, three fluorescent probes Dl, D2 and D3 were designed and synthesized. Under physiological conditions, the emission maximum wavelength of D2 was blue shifted from 540nm to 520nm upon addition of Zn2+, and the fluorescence intensity enhanced nearly 4-fold. The apparent dissociation constant (Kd) is in the sub-nM range, and its fluorescence was not induced by other biologically important cations such as Ca2+ and Mg2+ under physiological conditions.Three compounds Nl, N2 and N3 based on 4-amino-l,8-Naphthalimide were designed and synthesized. In tris-HCl neutral buffers, both the absorption and emission maximum wavelength of N2 are in the visible range. Upon addition Zn2+, the fluorescence enhancement is 5-fold and K4 is 0.8nM. Using fluorescence microscopy, the probe is shown to be capable of imaging intracellular Zn2+ changes.A series of fluorescent probes N4, N5 and N6 based on PET were designed and synthesized with imide as reaction position of 1,8-Naphthalimide. In pH 7.4 aqueous solution, both quantum yields of N4 and N5 are 0.004. Upon addition of saturating Zn2+, the quantum yields increased 43 and 23-fold, respectively. At pH 5, they are 30 and 10-fold, respectively. So, compared to H+, the fluorescence intensity can be enhanced selectively by Zn2+. Theoretical calculations show that intramolecular hydrogen bonding can inhibit the fluorescence intensity, which provides a new idea to avoid the affects of H+ for PET fluorescent probes.A PET fluorescence probe Bl for Zn2+ that utilizes 1,3,5,7-tetramethyl-8-phenyl-boron dipyrromethene as a reporting group and di(2-picolyl)amine as a chelater for Zn2+ was synthesized and characterized.Molecular model of intermediate 2 gives a planar conformation of the boron dipyrromethene moiety, while that of Bl exhibits a curved conformation. Upon addition of saturating Zn2+, the quantum yield of Bl increased 11-fold, and up to 0.857. With pK'a of 2.1, up to now, Bl has the lowest pK'a in all the Zn2+probes. The fluorescence intensity of Bl-Zn2+ complex is pH-independent in the range of pH 3-10. Using fluorescence microscopy, the probe is shown to be capable of penetrating into living cells and imaging intracellular Zn2+ distribution.