A highly selective turn-on fluorescent chemosensor for detecting zinc ions in living cells using symmetrical pyrene system

This manuscript presents a very simple receptor based on the combination of pyrene and malonohydrazide groups for the sensitive and selective detection of Zn2+. The sensor PYMH {N1',N3'-bis(pyren-1-yl)ethylene) malonohydrazide} was synthesized in two simple steps involving synthesis of malonohydrazide followed by the synthesis of symmetrical pyrene malonohydrazide with two pyrene units on either side of the molecule. The synthesized PYMH was confirmed by FT-IR, H-1 NMR, C-13 NMR and Mass spectroanalytical techniques. The sensor was able to exhibit 'turn-on' fluorescence in the presence of Zn2+ with no significant response from other relevant ions including Na+, K+, Ca2+, Mg2+, Cd2+, Cu2+, Co2+, Ni2+, Mn2+, Hg2+, Pb2+, Fe2+, Al3+, Fe3+ and Cr3+. Moreover, the sensor was capable of selectively detecting Zn2+ in the presence of its most common interferent Cd2+. The mechanism of fluorescent enhancement was proposed based on DFT calculations and it was established to be photoinduced electron transfer (PET). H-1 NMR titrations revealed that the Zn2+ binding sites to be imine NH group, besides FT-IR spectra confirmed the coordination of C = O with Zn2+. The sensor PYMH showed the LOD of 5.1 nM (3 sigma/S), which is well below the permitted drinking water level of 76 mu M as recommended by WHO. Further, the probe PYMH is capable of detecting distribution of intracellular Zn2+ in HeLa cells.