Ratiometric Signaling of Hypochlorite by the Oxidative Cleavage of Sulfonhydrazide-Based Rhodamine–Dansyl Dyad

A reaction-based probe <b>1</b> for hypochlorite signaling was designed by the conjugation of two fluorophores, rhodamine and dansyl moieties, by the reaction of rhodamine B base with dansylhydrazine. Probe <b>1</b> exhibited pronounced hypochlorite-selective chromogenic and fluorescent signaling behavior over other oxidants used in practical applications, such as hydrogen peroxide, peracetic acid, and ammonium persulfate, as well as commonly encountered metal ions and anions. Signaling was attributed to the hypochlorite-induced oxidative cleavage of the sulfonhydrazide linkage of the probe. In particular, favorable ratiometric fluorescence signaling was possible by utilizing the emissions of the two fluorophores. A detection limit of 1.13 × 10^–6 M (0.058 ppm) was estimated for the determination of hypochlorite. A paper-based test strip was prepared and was used as a semiquantitative indicator for the presence of hypochlorite in aqueous solutions. The probe was also successfully applied for the determination of hypochlorite in practical tap water samples

Colorimetric and Fluorescent Signaling of Au³⁺ by Desulfurization of Thiocoumarin

We investigated the chemosignaling of Au³⁺ by the selective desulfurization of thiocoumarin. In the presence of a heavy metal ion chelator <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetrakis-(2-pyridylmethyl)­ethylenediamine, thiocoumarin was selectively converted to its oxo analogue by reaction with Au³⁺, resulting in a pronounced chromogenic and fluorescent signaling. Selective signaling of Au³⁺ was possible in the presence of common alkali, alkaline earth, and transition metal ions, as well as Au⁺ in a mixed aqueous environment. The colorimetric determination of Au³⁺ was possible by the color change from pink to yellowish green of the designed probe. The detection limit for the determination of Au³⁺ in 50% aqueous acetonitrile was 1.1 × 10^–7 M

Fluorescence Signaling of Zr⁴⁺ by Hydrogen Peroxide Assisted Selective Desulfurization of Thioamide

Thioamide derivative with a pyrene fluorophore was smoothly transformed to its corresponding amide by Zr⁴⁺ ions in the presence of hydrogen peroxide. The transformation was evidenced by ¹H NMR spectroscopy and the signaling was completed within 10 min after sample preparation. Interference from Ag⁺ and Hg²⁺ ions in Zr⁴⁺-selective fluorescence signaling was readily suppressed with the use of Sn²⁺ as a reducing additive. Discrimination of Zr⁴⁺ from closely related hafnium, which is a frequent contaminant in commercial zirconium, was not possible. Prominent Zr⁴⁺-selective turn-on type fluorescence signaling was possible with a detection limit of 4.6 × 10^–6 M in an aqueous 99% ethanol solution

Modulation of Quinone PCET Reaction by Ca²⁺ Ion Captured by Calix[4]quinone in Water

Calix­[4]­arene-triacid-monoquinone (CTAQ), a quinone-containing water-soluble ionophore, was utilized to investigate how proton-coupled electron transfer (PCET) reactions of quinones were influenced by redox-inactive metal ions in aqueous environment. This ionophoric quinone derivative captured a Ca²⁺ ion that drastically altered the voltammetric behavior of quinone, showing a characteristic response to pH and unique redox wave separation. Spectroelectrochemistry verified significant stabilization of the semiquinone, and electrocatalytic currents were observed in the presence of Ca²⁺-free CTAQ. Using digital simulation of cyclic voltammograms to clarify how the thermodynamic properties of quinones were altered, a simple scheme was proposed that successfully accounted for all the observations. The change induced by Ca²⁺ complexation was explained on the basis of the combined effects of the electrostatic influence of the captured metal ion and hydrogen bonding of water molecules with the support of DFT calculation