Colorimetric recognition of multiple first-row transition metals: A single water-soluble chemosensor in acidic and basic conditions

A new tripodal chemosensor named PoPAP for colorimetric-enhancing detection of four metal ions from first-row transition series by combining pyridyl and phenolic binding sites with a highly conjugated pyridinyl-1,3,4-oxadiazolyl-phenyl moiety was designed, synthetized, and structurally analyzed. The chemosensor PoPAP is highly water soluble, it gives a selective fast colorimetric response to cations of iron, vanadium, copper and cobalt, depending on pH conditions, and it can discriminate among different oxidation states. PoPAP sensing ability was explored by absorbance spectroscopic studies, “naked-eye” perception, and UV–visible titration. The chemosensor-metal ions binding constants (Ka) and stoichiometry of host-guest complex in aqueous media were determined by classical analytical methods based on UV–visible data. The coordination geometry of PoPAP copper (II) complex was elucidated by crystal structure analysis and used as starting point for ab-initio calculations to analyze the interaction between ligand and metal.