A Highly Selective Chemosensor for Al(III) and Zn(II) and Its Coordination with Metal Ions

This paper reports a fluorescence chemosensor, N-(benzimidazol-2-yl)­salicylaldimine (H2L), for Zn­(II) and Al­(III) ions. H2L has high selectivity for Al­(III) in dimethyl sulfoxide (DMSO) and for Zn­(II) in N,N-dimethylformamide (DMF). In methanol, Zn­(II) and Al­(III) could also be distinguished by H2L with different excitation wavelengths. The fluorescent species [Zn­(HL)­(H2O)­(CH3OH)]+, [Zn­(HL)­(H2O)­(DMF)]+, [Al­(HL)2(OH)­(H2O)], and [Al­(HL)­(OH)2(H2O)­(DMSO)] formed in solution were established by a combination of experimental and theoretical methods, including Job’s plot, 1H NMR titration, electrospray inonization mass spectrometry (ESI-MS), and B3LYP-SCRF/6-31­(d) and TD-B3LYP-SCRF/6-31G* density functional theory methods. The results show that Zn­(II) and Al­(III) are all coordinated to the imine nitrogen atom and the hydroxyl oxygen atom from H2L, which is the same as the M2+ ions in the obtained mononuclear complexes [M­(HL)2(CH3OH)2] (where M = Cd, Ni, Co, and Mg). The detection limits of H2L for Zn­(II) were 5.98 μM in methanol and 5.76 μM in DMF, while the detection limits of H2L for Al­(III) were 3.3 μM in methanol and 5.25 μM in DMSO. Furthermore, it is also confirmed that H2L has low toxicity for HeLa cells and could be used to detect Zn­(II) and Al­(III) ions in living cells by bioimaging.