Development of artificial receptors for colorimetric recognition of metal ions is a vibrant area of present day investigation due to the widespread applicability in the field of biochemistry and environmental science.1 Among the various metal ions, copper(II) is the third most plentiful transition metal ion in human body and implicated in several physiological responses.2 Thus far, numerous technologies have been developed for the detection of copper(II) ion at trace quantity levels including atomic absorption spectroscopy, inductively coupled plasma emission or mass spectrometry, X-ray photoelectron spectroscopy, surface-plasmon resonance detector and voltammetry. However, these methods are usually complicated, time-consuming and costly as a consequence of need for highly sophisticated instrumentation.3 To overcome the previous drawbacks, we have developed a novel colorimetric azo-imine receptor (L), based on the combination of 2,6-pyridinedicarbohydrazide and azo-coupled salicylaldehyde scaffold. The devised receptor was found to exhibit a remarkable selectivity and sensitivity to Cu2+ as evidenced by an immediate color change in aqueous media. Importantly, the new copper(II) complex has been elucidated by spectroscopic methods (IR and UV-Vis) as well as elemental analysis and MALDI-TOF mass analysis. Successfully, the current receptor can detect Cu2+ ions even at 0.47 μM level, which is much lower than the World Health Organization (WHO) permissible level (30 μM) in drinking water.
