Latent turn-on fluorescent probe for the detection of toxic malononitrile in water and its practical applications.

A latent turn-on fluorescent probe for the detection of malononitrile (NCCH2CN), a precursor of hydrogen cyanide (HCN) in the mammalian tissue metabolism, is developed based on reaction-based fluorophore generation for the first time. Malononitrile is utilized within a wide spectrum of academic and industrial applications, and it is a key reagent to make o-chlorobenzylidene malononitrile (CS gas; tear gas), which is used for riot control. Due to its extensive use as well as potential health risks and the environmental pollution, malononitrile monitoring method has been required. In this paper, we discovered that our key sensing platform, 6-(dimethylamino)-3-hydroxy-2-naphthaldehyde (named Mal-P1), responds sensitively and selectively towards malononitrile. The Knoevenagel condensation induced benzo [g]coumarin formation of Mal-P1 with malononitrile showed significant fluorescence turn-on response. In addition, Mal-P1 showed the malononitrile sensing ability in environmental samples (real water, CS gas) and imaging ability in biological sample (HeLa cell line) using fluorescence microscopy with low cytotoxicity. The successful demonstrations will facilitate further applications in a variety of fields.

Hydrazine-Selective Fluorescent Turn-On Probe Based on Ortho-Methoxy-Methyl-Ether (o-MOM) Assisted Retro-aza-Henry Type Reaction.

Hydrazine (N2H4) is one of the most widely used industrial chemicals that can be utilized as a precursor of pesticides, pharmaceutics, and rocket propellant. Due to its biological and environmental toxicity with potential health risks, various sensing tools have been developed. Among them, fluorescence-based molecular sensing systems have been highlighted due to its simple-operation, high selectivity and sensitivity, and biocompatibility. In our recent report, we disclosed a ratiometric type fluorescent probe, called HyP-1, for the detection of hydrazine, which is based on ortho-methoxy-methyl-ether (o-MOM) moiety assisted hydrazone-formation of the donor (D)-acceptor (A) type naphthaldehyde backbone. As our follow-up research, we disclose a turn-on type fluorescent probe, named HyP-2, as the next-generation hydrazine probe. The sensing rational of HyP-2 is based on the o-MOM assisted retro-aza-Henry type reaction. The dicyanovinyl moiety, commonly known as a molecular rotor, causes significant emission quenching of a fluorescent platform in aqueous media, and its cleavage with hydrazone-formation, which induces a significant fluorescence enhancement. The high selectivity and sensitivity of HyP-2 shows practical explicabilities, including real-time paper strip assay, vapor test, soil analysis, and real water assay. We believe its successful demonstrations suggest further applications into a wide variety of fields.