Highly selective and sensitive colorimetric probe for Al3+ and Fe3+ metal ions based on 2-aminoquinolin-3-yl phenyl hydrazone Schiff base

A novel colorimetric probe based on 2-aminoquinolin-3-yl phenyl hydrazone Schiff base ligand (SBL) derivatives for the detection of metal ions viz. Al3+ and Fe3+ in ethanol solution was designed and synthesized. The SBL displayed quick response to Al3+ with red shift of 34 nm at 427 nm in visible region and at 420 nm for Fe3+ over the other metal ions. SBL when titrated with Fe3+ from 0 to 100 equivalent, at 233 nm and 402 nm isosbestic points are observed with increasing concentration of Fe3+ with binding constant 3.81 x 10(5) M-1. This clearly shows the affinity of SBL towards Fe3+. Similar titration was carried out for Al3+ and binding constant value was found to be 8.15 x 10(5) M-1 by Benesi Hildebrand method. Moreover, electrochemical studies by using cyclic voltammetry were also performed to know the reversibility of complex. SBL-Fe3+ was found to be reversible after addition of EDTA, thus SBL can be effectively used as switch chemosensor for detection of Fe3+. Job's plot method shows 1:1 stoichiometry for SBL-Al3+ complex and 2:1 for SBL-Fe3+ complex. In addition, H-1 NMR titration experiments of SBL with Al3+ confirms the binding mechanism as 1:1 host guest complex.