Spectroscopic study of cyclen-based ¹⁹F NMR probe for detection of hydrogen sulfide

A cyclen-based ¹⁹F NMR probe (F-cyclen) for hydrogen sulfide (H₂S) has been prepared and evaluated for its complex formation ability with Cu²⁺ ions and responsivity to H₂S. F-Cyclen was readily synthesized by reacting cyclen with 4-(trifluoromethyl)benzyl bromide. Visible absorption spectrophotometry showed that, same as the original cyclen, F-cyclen formed a 1:1 complex with Cu²⁺ ions. The ¹⁹F NMR signal of F-cyclen at 16.5 ppm gradually decreased in intensity with increasing CuCl₂ concentration, with trifluoromethane sulfonic acid sodium salt (TFMSNa) used as an internal standard (0 ppm). When the Cu²⁺-F-cyclen complex was subjected to an increasing concentration of Na₂S (as H₂S donor), its corresponding ¹⁹F NMR signal of F-cyclen at 16.5 ppm gradually increased in intensity. The regression curve between the ¹⁹F NMR signal intensity ratio of F-cyclen to TFMSNa and Na₂S concentration showed good linearity (r = 0.986) over the Na₂S concentration range of 25-150 μM.