Substituent effect on fluorescence signaling of the naphthalene carbohydrazone based chemosensor: Its implication in the detection of Zn(II) ions and secondary sensing PPi

Abstract

A series of naphthalene carbohydrazone based fluorescent chemosensors L1-L4 were developed for the detection of Zn2+ by significant fluorescence enhancement. The binding ratio of the L1-Zn2+ complex was determined by a Job’s plot to be 1:1 and confirmed by ESI–MS studies. The corresponding of the L1-Zn2+ ensemble was elucidated through X-ray crystallography along with spectroscopic studies. Furthermore, the LX-Zn2+ (X = 1–2) complexes can specifically detect pyrophosphate (PPi) in HEPES buffer solution through fluorescence quenching. The detection limit of LX-Zn2+ (X = 1–2) for PPi sensing were calculated to be as low as 2.54 ppb and 0.94 ppb, respectively. In addition, due to their good cell membrane permeability and low cytotoxicity, L1-L4 have been applied to sequentially detect Zn2+ and PPi in living cells. More importantly, the electronic effect of substitute groups on fluorescence signaling have been studied by substituent properties ranging from electron-donating to electron-withdrawing, which sets up a promising strategy for the rational design of fluorescent sensors.