Amino-naphthoquinone and its metal chelates for selective sensing of fluoride ions

The fluoride ion sensing ability of 2-(2-(dimethylamino)ethylamino)-3-chloronaphthalene-1,4-dione (R1) and its metal chelates viz. [Cu(R1)Cl-2], [Co(R1)Cl-2]center dot 3H(2)O, [Zn(R1)Cl-2] and [Ni(R1)Cl-2] was studied through visual detection experiment, UV-Vis, fluorescence and H-1 NMR titrations. The receptors were highly selective and sensitive for distinguishing fluoride ions from other common anions through a conspicuous change of UV-Vis and fluorescence spectra. The sensing mechanism, as confirmed by 1H NMR titration, involves formation of H-bond between the N-H moiety and F-ions. The coordination of metal ions was found to increase the H-bond donor ability of the receptor unit (N-H). The binding constant for the [Zn(R1)Cl-2] + F- complex was found to be 6.2 x 10(4) M-1 which is 15 times higher than that of R1 + F- complex. The sensing mechanism was further supported by electro chemical studies and DFT calculations using Gaussian 03 program. The detection limits of the probes in the determination of F- ions were found to 0.05-0.4 mu M, which are lower than the World Health Organization (WHO) permissible level (1.5 mg L-1).The test strips prepared using [Zn(R1)Cl-2] was found to impart striking colour change instantaneously with F-ions in water. (C) 2015 Elsevier B.V. All rights reserved.