Revealing the Hydrolysis Mechanism of a Hg²⁺-Reactive Fluorescein Probe: Novel Insights on Thionocarbonated Dyes

Abstract

As one of the most toxic metal pollutants, mercury is the subject of extensive research to improve current detection strategies, notably to develop sensitive, selective, fast, and affordable Hg2+-responsive fluorescent probes. Comprehending the sensing mechanism of these molecules is a crucial step in their design and optimization of their performance. Herein, a new fluorescein-based thionocarbonate-appended Hg2+-sensitive probe was synthesized to study the hydrolysis reactions involved in the sensing process. Autohydrolysis was revealed as a significant component of the signal generation mechanism, occurring concurrently with Hg2+-catalyzed hydrolysis. This knowledge was used to investigate the effects of key experimental conditions (pH, temperature, chloride ions) on sensing efficiency. Overall, the chemical and physical properties of this new thionocarbonated dye and the insights into its sensing mechanism will be instrumental in designing reliable and effective portable sensing strategies for mercury and other heavy metals.

A cyanine‐based dual‐modal probe for fluorimetric detection of mercury ion and colorimetric sensing of pH

“…After reaction of probe CY with Hg 2+ ions, the base peak was observed at m/z 462.1, assignable to the fragment [M – I + Na] + , corresponding to the de‐iodine product in Scheme 2 plus sodium ion. This Hg 2+ ‐induced desulphurisation strategy has been well proved to be quite effective for design of Hg 2+ ion fluorescent probes based on thione‐containing compounds 45–47 …”

“…This Hg 2+ -induced desulphurisation strategy has been well proved to be quite effective for design of Hg 2+ ion fluorescent probes based on thione-containing compounds. [45][46][47] Practical application of probe CY to determination of Hg 2+ concentrations in different water samples was explored. Different water samples were obtained by adding different amount of Hg 2+ (5, 10 and 15 μM) to the Jingyue Lake water and tap water, respectively.…”

Metal-Enhanced Hg2+-Responsive Fluorescent Nanoprobes: From Morphological Design to Application to Natural Waters

“…Therefore, reaction with sufficient PCTF molecules can produce two thionocarbonate moieties. 43 Compared to the bare fluorescein molecule, its dithionocarbonated counterpart is nonluminescent in the visible region due to a forced spirolactone backbone preventing tautomerization and electron delocalization ( Scheme S2 ). Hence, this drastic alteration in optical properties from reactants to products allows to monitor the reaction progress by fluorimetry.…”

“… 52 − 57 As a case in point, a Hg 2+ -sensitive ″turn on″ molecular probe with an Fl backbone was recently reported, where a nonemissive fluorescein dithionocarbonate incurs a Hg 2+ -assisted hydrolysis leading to the release of Fl emissivity. 43 …”

Colorimetric and fluorometric probes for the optical detection of environmental Hg(ii) and As(iii) ions

“…Another azo based sensor 68b [124b] has been indroduced for successful colorimetric detection of Hg(II) in DMSO-water (1 A combination of the dye Pyronin and chelating agent meso-2,3-dimercaptosuccinic acid developed the sensor 69 [125] for the detection and removal of Hg 2+ . This one of the rare systems which can detect and sense Hg Thinocarbonate appended fluorescein based chemodosimeter 70 [126] was developed for turn-on fluorescent detection of Hg 2+ in a HEPES buffer solution (20 mM, pH 7.4, 1% EtOH).…”