Multi-site probe for selective turn-on fluorescent detection of Al(III) in aqueous solution: synthesis, cation...

An easy to make organic probe (hereafter called as R) possessing multiple ligating sites have been synthesized and characterized using spectral techniques. The probe exhibits selective and sensitive turn-on fluorescence response with Al(III) in aqueous dimethylformamide (DMF) (1:1 v/v) solution. Fluorescence titration experiment shows that the probe binds with Al(III) with a 1:1 stoichiometry and a binding constant of 6.6 × 10⁴ M^-1.The mode of coordination of R with Al(III) has been established suing ²⁷Al and ¹H NMR studies and the results suggest formation of an octahedral complex been them. The suggested point of attachment of R with Al(III) corroborates well with Density Functional Theory (DFT) optimized structure and Mulliken charges computed. Chelation-enhanced fluorescence (CHEF) is proposed as the mechanism of enhancement of fluorescence upon addition of Al(III) to R. The probe detects Al(III) in aqueous solution with a detection limit of 0.2 μM, which is much lower than the permissible limit of Al(III) set by the World Health Organization (WHO).The probe works in a wide pH range (4-11) and thus makes it a suitable candidate for environmental and biological applications. The fluorescence signals of R were used to construct an INHIBIT molecular logic gate. The confocal fluorescence microscope experiments show that R could be employed as a fluorescent probe for detecting Al(III) in living cells.