Synthesis and chemosensory studies of a heterocyclic thiosemicarbazone as a new tributyltin optical chemosensor

Thiosemicarbazones are a versatile type of organic compounds known by their coordination ability with different types of analytes, due to the presence of sulfur and nitrogen heteroatoms. Therefore, the functionalization of thiosemicarbazones with heterocyclic moieties can be a promising route to develop new optical chemosensors. Tributyltin (TBT) is an antifouling component of paints which is acutely toxic to aquatic environments, being quickly absorbed by microorganisms and causing problems such as imposex. Herein, we report the synthesis of a novel heterocyclic thiosemicarbazone, functionalized with a quinoline moiety, in order to assess the potential of this recognition moiety for TBT optical chemosensing.

The new thiosemicarbazone was synthesized by a condensation reaction between quinoline aldehyde precursor and N-phenylhydrazinecarbothioamide, and the compound was then submitted to chemosensory studies in the presence of TBT in acetonitrile solution. A preliminary chemosensory study was performed showing that 50 equivalents of TBT were needed in order to induce a change of color from colorless to yellow. Spectrophotometric titration was performed to assess the concentration of TBT necessary for a maximum optical signal, revealing that 100 equivalents of TBT were necessary to reach maximum absorbance, although it was able to respond with a detectable color change to a TBT concentration as low as 10 uM.