Rational design of aminoanthraquinones for colorimetric detection of heavy metal ions in aqueous solution

A family of water-soluble colorimetric chemosensors incorporating an anthraquinone signalling subunit functionalized with a polyamine chain that bears hydrophilic diethoxyphosphoryl moieties was prepared with the aim of assaying metal cations. The outstanding UV-Vis absorption properties of the 1-aminoanthraquinone chromophore allowed the efficient visual detection and quantification of copper(II) ions by chelators L-1-L-3 in buffered aqueous solution. Moreover, the visible response of L-2 is not interfered by addition of large excesses of 13 common metal ions, whereas chemosensor L-3 produces also a color change in the presence of equimolar amounts of lead(II). Considering the 134 nm gap between both absorption maxima, simultaneous colorimetric quantification of lead and copper can be envisaged. Detailed potentiometric and spectrophotometric analysis of Cu2+ complexation by L-2 and L-3, as well as Pb2+ and Cd2+ by L-3 was undertaken in order to gain a deeper insight into the pH-dependent speciation and understanding the color changing process. Furthermore, the inner coordination sphere of the [PbL3](2+) complex was probed by NMR spectroscopy.