Molecular recognition of carbonate ion using a novel turn-on fluorescent probe.

A novel turn-on fluorescent probe 3 was synthesized by condensing salicylaldehyde and nicotinic hydrazide for the selective detection of CO in aqueous medium. Probe 3 exhibited a turn-on fluorescence response toward CO with excellent selectivity, sensitivity (DL = 2.76 μM), and good reversibility. The binding constant (K) of probe 3 with CO was calculated to be 5 × 10 M (log K 3.69). The 1:1 stoichiometry of the complex between probe 3 and CO ions was confirmed by Job's plot and ESI-MS spectra. Deprotonation and hydrogen-bonding interactions are involved in the recognition of CO ion, which was also suggested by H NMR, ESI-MS spectra, and Density Functional Theory (DFT) calculations. Moreover, an INHIBIT type molecular logic gate was constructed by using 3:CO and CHCOOH as inputs and current signal as output. Owing to the practical applications, probe 3 demonstrated its efficiency in quantifying CO ion in real water samples through standard addition method, thus showcasing its potential in real environment. Further, the MTT assay indicated very low cytotoxicity (IC = 1 mM) of probe 3 and also the cell imaging experiments demonstrated the effective sensing of CO ions with probe 3 in the biological systems.