Chromogenic and fluorogenic chemodosimeter derived from Meldrum's acid detects cyanide and sulfide in aqueous medium

The detection of anionic analytes is of extreme importance since many of these species are toxic and they play a variety of roles in biological, environmental and industrial processes. However, the techniques currently used for their detection are costly and highly complex and thus the search for new detection methods for these analytes is a growing area of scientific research. In this regard, techniques involving the use of molecular and supramolecular devices are being developed, which offer simplicity, precision, reliability and low cost, in both quantitative and qualitative analyses. Herein, a novel compound was synthesized through the Knoevenagel condensation reaction between Meldrum's acid and pyrene–1–carbaldehyde. The final product, 2,2–dimethyl–5–(pyren–1–ylmethylene)–1,3–dioxane–4,6–dione (1), was completely characterized. The performance of compound 1 as a chemodosimeter for the detection of CN− and sulfide was verified. The compound was shown to be simultaneously a selective chromogenic (on–off) and fluorogenic (off–on) chemodosimeter for CN− and sulfide in an organic–aqueous system, with a 1:1 anion:compound stoichiometry. To make the system selective only for CN−, Pb(NO3)2 was added so that all of the sulfide present in the sample precipitated and became unavailable to interact with the chemodosimeter, leaving only the CN− available to react with the system. In all cases the limits of detection were below those established by WHO, with the analytical tests carried out by means of the fluorescence technique allowing the detection of CN− at 10−8 mol L−1. Finally, the system could be used for the detection of CN− spiked in tap water samples.