A Naphthalimide–Sulfonylhydrazine Conjugate as a Fluorescent Chemodosimeter for Hypochlorite

Fast and easy detection of hypochlorite by a smartphone-based fluorescent turn-on probe: Applications to water samples, zebrafish and plant imaging

We have developed a fluorescent probe DBT-Cl ((E)-2-(2-(4-(diphenylamino)benzylidene) hydrazinyl)-N,N,N-trimethyl-2-oxoethan-1-aminium chloride) for ClO- with an aggregation-induced emission (AIE) strategy depending on solvent polarity. DBT-Cl possessed a prominent solvatochromic emission property with intramolecular charge transfer (ICT) from the TPA (triphenylamine) to the amide group, which was studied by spectroscopic analysis and DFT calculations. These unique AIE properties of DBT-Cl led to the recognition of ClO- with high fluorescent selectivity. DBT-Cl quickly detected ClO- in less than 1 sec with a fluorescent color change from green to cyan. DBT-Cl had a low detection limit of 9.67 μM to ClO-. Detection mechanism of DBT-Cl toward ClO- was illustrated to be oxidative cleavage of DBT-Cl by 1H NMR titrations, ESI-mass, and DFT calculations. We established the viability for dependable detection of ClO- in actual water samples, as well as zebrafish and plant imaging. In particular, DBT-Cl was capable of easily monitoring ClO- through a smartphone application. Therefore, DBT-Cl assured a promising approach for a fast-responsive and multi-applicable ClO- probe in environmental and living organism systems.

A New Fluorene-Based Fluorescent Probe for Recognition of Hypochlorite Ions and its Applications

Oxidative stress is a trigger for many diseases and occurs with the unstable hypochlorite (ClO-), known as one of the reactive oxygen species (ROS) in organisms. Then, HOCI is acknowledged as an oxidizing species that eliminates a variety of environmental pollutants. Hence, the development of novel methodologies for the selective and precise identification of HOCl/ ClO- is considered to be of utmost importance. In this study, the design, characterization, and applications of a fluorene-based fluorescent probe (FHBP) dependent on the ESIPT mechanism with a "turn-on" response for the sensitive/selective determination of ClO- against other competing samples were reported. The experimental results indicated that the detection limit for ClO-could be quantitatively determined by the probe to be 8.2 × 10-7 M. The binding constant of the probe FHBP with ClO- was computed as 9.75 × 103 M-1. In addition, the response time of FHBP was appointed to be 30 s, indicating a rapid reaction with ClO-. It has also been demonstrated that this probe can be successfully used for the detection of ClO- on filter papers, TLC sheets, cotton swabs, and real samples.

Spectroscopic and Biological Properties of the 3-Imino-1,8-naphthalimide Derivatives as Fluorophores for Cellular Imaging

This paper presents the photophysical and biological properties of eight 3-imino-1,8-naphthalimides. The optical properties of the compounds were investigated in the solvents that differed in their polarity (dichloromethane, acetonitrile, and methanol), including three methods of sample preparation using different pre-dissolving solvents such as dimethyl sulfoxide or chloroform. In the course of the research, it was found that there are strong interactions between the tested compounds and DMSO, which was visible as a change in the maximum emission band (λem) of the neat 3-imino-1,8-naphthalimides (λem = 470-480 nm) and between the compounds and DMSO (λem = 504-514 nm). The shift of the emission maximum that was associated with the presence of a small amount of DMSO in the sample was as much as 41 nm. In addition, the susceptibility of imines to hydrolysis in the methanol/water mixture with increasing water content and in the methanol/water mixture (v/v; 1:1) in the pH range from 1 to 12 was discussed. The studies showed that the compounds are hydrolysed in the CH3OH/H2O system in an acidic environment (pH in the range of 1 to 4). In addition, it was found that partial hydrolysis occurs in systems with an increased amount of water, and its degree may depend on the type of substituent on the imine bond. The compounds tended to quench the emission (ACQ) in the aggregated state and increase the emission related to the protonation of the imine bond. Moreover, it was found that the substituent in the imine bonds influenced a compound's individual photophysical properties. Biological tests, including cytotoxicity studies and cellular localisation, were also performed for all of the molecules. All of the tested compounds exhibited green fluorescence in the MCF-7 cells and showed co-localisation in the mitochondria, endoplasmic reticulum, and lysosome. The obtained photophysical and biological results indicate the promising potential use of the tested compounds as cellular dyes.

A colorimetric/ratiometric chemosensor based on an aggregation-induced emission strategy for tracing hypochlorite in vitro and in vivo

Excessive levels of hypochlorite (ClO^-) negatively affect environmental and biological systems. Thus, it is essential to develop sensors that can identify ClO^- in various systems such as the environment and living organisms. In this study, we report the development and evaluation of a novel aggregation-induced emission (AIE) strategy-based colorimetric and ratiometric fluorescent chemosensor 2,2'-(((1E,1'E)-[2,2'-bithiophene]- 5,5'-diylbis(methanylylidene))bis(hydrazin-1-yl-2-ylidene))bis(N,N,N-trimethyl-2-oxoethan-1-aminium) chloride (BMH-2∙Cl) for detecting ClO^-. BMH-2∙Cl enabled highly selective ClO^- detection through a color change from yellow to colorless and a fluorescence color change from turquoise to blue in a perfect aqueous solution. BMH-2∙Cl exhibited low limits of detection (2.4 ×10^-6 M for colorimetry and 2.9 ×10^-7 M for ratiometric fluorescence) for detecting ClO^- with a rapid response within 5 s. The detection mechanism for ClO^- and an AIE property change of BMH-2∙Cl were demonstrated by ¹H NMR titration, ESI-MS, variation of water fraction (f_w) and theoretical calculations. In particular, we confirmed not only the practicality of BMH-2∙Cl by using test strips, but also demonstrated the potential for efficient ClO^- detection in biological and environmental systems such as real water samples, living zebrafish and bean sprouts.

Polarity-Driven Isomerization of a Hydroxynaphthalimide-Containing Spiropyran at Room Temperature

Design of spiropyrans showing spontaneous isomerization driven by the polarity of solvents is an important consideration for the synthesis of optical sensory materials. Although some spiropyrans undergo polarity-driven isomerization, they must be heated owing to the high activation energy required for isomerization. In this study, we describe that a spiropyran containing a hydroxynaphthalimide unit (1) exhibits a polarity-driven isomerization at room temperature. It exists as a colorless spirocyclic (SP) form in less polar solvents but is isomerized to a colored merocyanine (MC) form in polar solvents. The equilibrium amount of the MC form increases with an increase in the polarity of solvents. The MC form involves two resonance structures-the quinoidal and zwitterionic forms. In polar media, the zwitterionic form dominates mainly owing to solvation by polar molecules. Solvation stabilizes the negative charge of the zwitterionic form and decreases its ground state energy, thereby enhancing SP → MC isomerization. The SP ⇌ MC isomerization terminates within barely 30 s even at room temperature because the naphthol moiety with high π-electron density lowers the activation energy for the rate-determining rotational step.

An AIE based fluorescent chemosensor for ratiometric detection of hypochlorous acid and its application

Detecting and imaging intracellular hypochlorous acid (HClO) is of great importance owning to its prominent role in numerous pathological and physiological processes. In this contribution, a novel AIE-based fluorescent chemosensor has been developed by employing a benzothiazole derivative. The synthesized probe displayed remarkable ratiometric fluorescent response to HClO with a large emission shift (139 nm), resulting in naked-eye fluorescence changes from red to blue. Under the optimal conditions, this probe was capable of quantitatively detecting HClO within 10 s, and possessed good sensitivity and high selectivity toward HClO over other biologically relevant species. Moreover, it has been successfully utilized to image the exogenous and endogenous HClO in living cells through dual channels, and conveniently detect hypochlorous acid solution on test strips with better accuracy, demonstrating its potential for monitoring HClO in biological and environment fields.

Highly Selective Recognition of Pyrophosphate by a Novel Coumarin-Iron (III) Complex and the Application in Living Cells

In this paper, a novel NL-Fe3+ ensemble was designed as a fluorescent chemosensor for highly selective detection of pyrophosphate (PPi) in DMSO/H2O (2:8/v:v, pH = 7.2) solution and living cells. NL showed a strong affinity for Fe3+ and was accompanied by obvious fluorescence quenching. Upon the addition of PPi to the generated NL-Fe3+ ensemble, the fluorescence and absorption spectra were recovered completely. Spectroscopic investigation showed that the interference provoked by common anions such as adenosine-triphosphate (ATP), adenosine diphosphate (ADP), and phosphates (Pi) can be ignored. The detection limit of NL-Fe3+ to PPi was calculated to be 1.45 × 10−8 M. Intracellular imaging showed that NL-Fe3+ has good membrane permeability and could be used for the detection of PPi in living cells. A B3LYP/6-31G(d,p) basis set was used to optimize NL and NL-Fe3+ complex.