Two fluorescent turn-on probes for detecting thiophenols in environmental water and in living cell imaging

Application of a Strong Base Anion Exchange Resin for the Removal of Thiophenol from Aqueous Solution

Thiophenol (synonyms: phenyl mercaptan, benzenethiol) may appear in the aquatic environment as a result of human activity. It is used as a raw material in organic synthesis in various industries for the production of dyes, pesticides, pharmaceuticals and polymers, such as polyphenylene sulfide (PPS). It may also enter water through contamination with petroleum substances (thiophenol may be present in crude oil). Due to the fact that thiophenol is toxic to living organisms, its removal from water can be a very important task. For the first time, this paper presents experimental studies of the sorption and desorption process of thiophenol on an ion exchange resin. Thiophenol sorption experiments on AmbeLite®IRA402 (Cl form) were tested at different pH levels (4, 7, and 9) and different ionic strengths of the aqueous solution. Its detection in water was carried out using UV spectroscopy. At pH 4, the thiophenol sorption process is basically independent of the ionic strength of the solution, but also the least effective. The sorption capacity of a thiophenol solution in distilled water is about 0.37-0.46 mg/g, for a solution with an ionic strength of 0.1 M 0.42 mg/g. At pH 7 and 9, the sorption of thiophenol from an aqueous solution is similar and definitely more effective. The sorption capacity of the thiophenol solution in distilled water is about 13.83-14.67 mg/g, and for a solution with an ionic strength of 0.1 M, it is 2.83-2.10 mg/g. The desorption efficiency of thiophenol from AmbeLite®IRA402 resin (washing with 4% HCl) at pH 7 is 90%, which is promising for the resin reuse process. Kinetic studies were performed and a pseudo-first-order and second-order kinetic model was fitted to the obtained experimental sorption data. In most cases, the simulation showed that the pseudo-second-order model gives a better fit, especially for the sorption of thiophenol from the solution with an ionic strength of 0.1 M. The fit of the Freundlich and Langmuir isotherm models to the experimental results indicates that the latter model provides better agreement. Analysis of the infrared spectra supported by quantum chemical calculations (DFT/PCM/B3LYP/6-31g**) confirms the experimental results observed during the sorption process. At pH 7 and 9, the thiophenol is sorbed in anionic form and-together with the ion exchange processes that occur between the dissociated thiol group and the quaternary ammonium group-an interaction between the aromatic structures of thiophenolate anions and IRA402 also takes place.

A Dicyanoisophorone-based Fluorescent Turn-on Probe for Rapid Detecting Thiophenol in Aqueous Medium and Living Cell Imaging

A novel colorimetric and fluorescent thiophenol probe based on dicyanoisophorone has been successfully achieved, which has low-cost, easy operation, high selectivity, sensitivity and stability. The chemosensor shows a large Stokes shift and approximately 170 nm when excited at 510 nm. ISO-DiNO2 could be utilized as "Turn-on" and a naked-eyes chemosensor to detect PhSH, which is accompanied by a distinct color shift from red to dark purple with strong red fluorescence at 365 nm UV-light. Its limit of detection was determined to be 1.15 μM. More importantly, ISO-DiNO2 can react instantaneously (<10 s) with PhS-. In addition, ISO-DiNO2 has been utilized in test paper strips, water sample together with imaging of PhS- in living Raw264.7 cells, demonstrating that ISO-DiNO2 has excellent and promising applications.

β-cyclodextrin-modulated ratiometric supramolecular BODIPY fluoroprobe for highly selective and sensitive detection of thiophenol

Thiophenol (PhSH) is an important industrial intermediate but displays significant toxicity towards environmental and biological systems. Here, we introduce a supramolecular system based on β-cyclodextrin (β-CD) and boron dipyrromethene (BODIPY) as a ratiometric fluorescence probe to discriminate PhSH in environmental water samples, cells, and in vivo. In aqueous solutions, BODIPY shows extremely weak fluorescence intensity due to its aggregation into nanometer-sized clusters, which prevents its interaction with thiols. However, within a β-CD environment, it can selectively and sensitively detect PhSH. Also, the stability of the probe was significantly improved. The mechanism studies based on stoichiometry, NMR spectroscopy, and theoretical calculation revealed distinct intermolecular interactions between β-CD and BODIPY, including host-guest interactions and hydrogen bonds. Low limit of detection (10.7 nM) and rapid response time (5 min) have been achieved, and the practicality of the supramolecular system (BODIPY@β-CD) has been verified by actual sample analysis. Furthermore, the first hydrogel-based sensing system for portable PhSH detection has been developed, facilitating rapid and on-site colorimetric visualization across both liquid and gas phases. Most importantly, using a low amount of the probe, early stages of low-dose exposure to PhSH can be visualized in living cells and zebrafish. Therefore, BODIPY@β-CD is a robust new monitoring tool for the detection of PhSH in various scenarios, indicating the promising application value of the host-guest supramolecular probe in detecting highly toxic substances.

Theoretical Investigation on the "ON-OFF" Mechanism of a Fluorescent Probe for Thiophenols: Photoinduced Electron Transfer and Intramolecular Charge Transfer

In this study, the sensing mechanism of (2E,4E)-5-(4-(dimethylamino)phenyl)-1-(2-(2,4dinitrophenoxy)phenyl)penta-2,4-dien-1-one (DAPH-DNP) towards thiophenols was investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT). The DNP group plays an important role in charge transfer excitation. Due to the typical donor-excited photo-induced electron transfer (d-PET) process, DAPH-DNP has fluorescence quenching behavior. After the thiolysis reaction between DAPH-DNP and thiophenol, the hydroxyl group is released, and DAPH is generated with the reaction showing strong fluorescence. The fluorescence enhancement of DAPH is not caused by an excited-state intramolecular proton transfer (ESIPT) process. The potential energy curves (PECs) show that DAPH-keto is less stable than DAPH-enol. The frontier molecular orbitals (FMOs) of DAPH show that the excitation process is accompanied by intramolecular charger transfer (ICT), and the corresponding character of DAPH was further confirmed by hole-electron and interfragment charge transfer (IFCT) analysis methods. Above all, the sensing mechanism of the turn-on type probe DAPH-DNP towards thiophenol is based on the PET mechanism.

Visual and quantitative monitoring of thiophenol by a novel deep-red emitting fluorescent probe in environmental and biological systems

Detection of highly toxic thiophenols in biological or environmental systems is of great importance. Therefore, fast, reliable, and sensitive probes are needed to detect thiophenols. Herein, a novel triphenylamine conjugated dicyanoisophorone-based near infrared fluorescence probe is reported to determine trace thiophenol (PhSH) levels. The probe demonstrates a distinct "turn-on" fluorescence response to thiophenol among the tested analytes and its quantum yield (Φ) increases from 0.011 to 0.142. It has low cytotoxicity with cell viability of 90-100% up to 10.0 μM of the probe, a strong anti-interference capability, a large Stokes shift (150 nm), and a fast response time (<1 min). In addition, the probe exhibits a good linear response to PhSH over the range from 0 to 15.0 μM with a detection limit of 32.3 nM (R² = 0.9978). The detection process is also confirmed through HPLC. The practical applicability of the probe is proved by a smartphone platform, TLC kit, plant tissue imaging, soil assay, tap, and lake water analysis with good recovery values (92.3-117%), and concentration-dependent live cell bioimaging PhSH from 5.0 to 15.0 μM. Therefore, the present probe is a robust candidate for monitoring PhSH levels in biological and environmental systems.