A chemosensor with a paddle structure based on a BODIPY chromophore for sequential recognition of Cu2+ and HSO3−

In this study, a highly selective chemosensor ML based on a BODIPY fluorescent chromophore was synthesized for sequential recognition of Cu²⁺ and HSO₃⁻ in a CH₃OH/H₂O (99 : 1 v/v) system, which contained three recognition sites and its structure characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. The sensor ML showed an obvious “on–off” fluorescence quenching response toward Cu²⁺ and the ML-Cu²⁺ complex showed an “off–on” fluorescence enhancement response toward HSO₃⁻. The detection limit of the sensor ML was 0.36 μM to Cu²⁺ and 1.4 μM to HSO₃⁻. In addition, the sensor ML showed a 1 : 3 binding stoichiometry to Cu²⁺ and the recovery rate of ML-Cu²⁺ complex identifying HSO₃⁻ could be over 70%. Sensor ML showed remarkable detection ability in a pH range of 4–8.

A highly selective chemosensor based on a BODIPY chromophore for sequential recognition of Cu²⁺ and HSO₃⁻.     

An efficient and sensitive chemosensor based on salicylhydrazide for naked-eye and fluorescent detection of Zn2+

We reported here the synthesis of a diarylethene with a 2,4-dihydroxybenzoyl hydrazine moiety (1O) for Zn²⁺ recognition. The compound is easy to prepare with a high yield up to 85%. Compound 1O can act as a highly selective and specific fluorescent sensor for Zn²⁺ without interference by other common metal ions. The LOD for Zn²⁺ detection was determined to be 1.28 × 10⁻⁶ mol L⁻¹. Meanwhile, 1O can be used as a naked-eye detector for the Zn²⁺ ion with an obvious color change from colorless to olive. Based on the fluorescent properties of 1O, we constructed a logic circuit with four inputs of the combinational stimuli of UV/vis light and Zn²⁺/EDTA, and one output of fluorescence intensity.

A naked-eye and fluorescent detector for Zn²⁺ was synthesized by the combination of salicylhydrazide and diarylethene with good photochromic properties.     

A turn-on fluorescence sensor for the highly selective detection of Al3+ based on diarylethene and its application on test strips

A novel turn-on fluorescent sensor for Al³⁺ based on photochromic diarylethene with a 2-hydroxybenzhydrazide unit has been successfully designed and synthesized. The photochromic and fluorescent characteristics were studied methodically in methanol under irradiation using UV/vis light and induced by Al³⁺/EDTA. This fluorescent sensor was highly selective toward Al³⁺ with an obvious fluorescent color change from dark blue to blue. The Job''s plot and mass spectrometry (MS) analysis indicate a binding stoichiometry of 1 : 1 between the fluorescent sensor and Al³⁺. Moreover, a test strip containing this fluorescent sensor was prepared to allow for the easy detection of Al³⁺ in water. Finally, a logic circuit was designed using four input signals (In1: UV; In2: vis; In3: Al³⁺; In4: EDTA) and one output signal.

A novel fluorescent sensor, 1O, based on photochromic diarylethene with a 2-hydroxybenzhydrazide unit was designed and synthesized and can be used to recognize Al³⁺ in methanol (2.0 × 10⁻⁵ mol L⁻¹).     

A dual responsive fluorescent probe for selective detection of cysteine and bisulfite and its application in bioimaging

A coumarin-based dual responsive fluorescent probe with a simple structure was developed for the detection of Cys and HSO₃⁻. Under simulated physiological conditions, Cou-F displayed an on–off fluorescence response to Cys at 521 nm and an off–on fluorescence response to HSO₃⁻ at 500 nm. Furthermore, Cou-F had the advantages of high sensitivity, strong specificity and rapid response. The detection limits of Cou-F toward Cys and HSO₃⁻ were 0.54 μM and 0.65 μM, respectively. Cou-F enabled high selective responses to Cys and HSO₃⁻ over other biologically related species. The response times of Cou-F toward Cys and HSO₃⁻ were 80 s and 100 s. The fluorescence imaging of Cys and HSO₃⁻ was achieved in living RAW246.7 cells.

A coumarin-based dual responsive fluorescent probe with a simple structure was developed for the detection of Cys and HSO₃⁻.     

A highly selective fluorescence “turn-on” sensor for Ca2+ based on diarylethene with a triazozoyl hydrazine unit

A new photochromic diarylethene derivative with a triazozoyl hydrazine unit has been designed and synthesized. Its photochromism and photoswitchable fluorescence behaviors were studied systematically by the stimuli of lights and chemical substances in acetonitrile solution. With the addition of Ca²⁺, the emission intensity enhanced 6.7 fold, accompanied by an obvious fluorescent color change from dark to light blue. The complexation between the derivative and Ca²⁺ is reversible with the 1 : 1 stoichiometry, which was verified by Job''s plot and MS. The limit of detection (LOD) for Ca²⁺ was determined to be 2.49 × 10⁻⁸ mol L⁻¹. Based on this unimolecular platform, a logic circuit was designed with fluorescence intensity at 482 nm as the output and the combined stimuli of UV/vis and Ca²⁺/EDTA as four inputs.

A new photochromic diarylethene derivative with a triazozoyl hydrazine unit has been designed and synthesized.     

A highly selective multi-responsive fluorescence sensor for Zn2+ based on a diarylethene with a 4,6-dimethylpyrimidine unit

A novel turn-on mode fluorescent diarylethene containing a 4,6-dimethylpyrimidine unit was developed to fluorescently sense Zn²⁺. Its multiple-responsive properties induced by Zn²⁺/EDTA and ultraviolet/visible light have been systematically studied. The fluorescence sensor could efficiently detect Zn²⁺ with a 10 times enhancement of emission intensity and fluorescence color change (dark-green). In addition, the sensor showed clear discrimination from Cd²⁺. The limit of detection of the sensor was measured to be 8.48 × 10⁻⁸ mol L⁻¹ for Zn²⁺. Finally, a molecular logic circuit was fabricated with the emission at 528 nm as the output signal and light and chemical stimuli as input signals.

A novel multi-responsive fluorescence sensor based on a diarylethene derivative with a 4,6-dimethylpyrimidine unit was developed for Zn²⁺ detection.     

A new class of fluorogenic thiazolo[2,3-b]quinazolinone receptor: selective detection towards mercury and hydrogen bisulfate ions in aqueous medium

A series of fluorophoric and structurally diverse thiazoloquinazoline derivatives were synthesized in a one-pot multicomponent cascade reaction using a microwave irradiation technique. The unique structural arrangement of the synthesized compounds encouraged us to design a new type of bioactive molecular receptor. This receptor interacts with HSO₄⁻ in 1 : 1 and Hg²⁺ in 1 : 2 binding stoichiometric ratios resulting in a change in fluorescence as well as absorption spectra in aqueous medium. The ion bonded receptor complex possibly enhances the fluorescence signal of the receptor via H-bonded complex formation with HSO₄⁻ ions and co-ordinate complex formation with Hg²⁺ ions.

Fluorophoric thiazoloquinazoline derivatives were synthesized under microwave assisted one-pot three-component cascade reaction. Owing to their unique structural arrangement, a new bioactive molecular receptor was developed for HSO⁴⁻ and Hg²⁺ ions.     

Phenothiazine and semi-cyanine based colorimetric and fluorescent probes for detection of sulfites in solutions and in living cells

Four hemicyanine probes for selectively detecting sulfites (HSO₃⁻/SO₃²⁻) have been constructed by the condensation reaction of 7-substituted (CN, Br, H and OH) phenothiazine aldehyde with 1-ethyl-2,3,3-trimethylindolium iodide. All four probes show a fast and sensitive response to HSO₃⁻/SO₃²⁻via a Michael addition, with a detection limit lower than 40 nM based on monitoring their UV/vis absorption changes. Although all four probes display an increase in fluorescence when responding to HSO₃⁻/SO₃²⁻, the increment is larger for the probe with an electron-withdrawing group than the probe with an electron-donating group, except for Br. Thus, among four probes the 7-cyano probe (PI-CN) possesses the largest fluorescent response to HSO₃⁻/SO₃²⁻, and the lowest detection limit (7.5 nM). More expediently and easily, a film and a test paper with PI-CN have been prepared to detect HSO₃⁻/SO₃²⁻ in a sample aqueous solution selectively. Finally, the detection of HSO₃⁻/SO₃²⁻ by PI-CN in biological environments has been demonstrated by cell imaging.

Four 7-substituted phenothiazine hemicyanines display a substituent effect on the fluorescence response toward sulfites. The CN-substituted probe exhibits the best sensing behavior.     

A bifunctional sensor based on diarylethene for the colorimetric recognition of Cu2+ and fluorescence detection of Cd2+

A novel bifunctional sensor based on diarylethene with a benzyl carbazate unit was synthesized successfully. It not only served as a colorimetric sensor for the recognition of Cu²⁺ by showing changes in absorption spectra and solution color, but also acted as a fluorescent sensor for the detection of Cd²⁺ through obvious emission intensity enhancement and fluorescence color change. The sensor exhibited excellent selectivity and sensitivity towards Cu²⁺ and Cd²⁺, and the limits of detection for Cu²⁺ and Cd²⁺ were 8.36 × 10⁻⁸ mol L⁻¹ and 1.71 × 10⁻⁷ mol L⁻¹, respectively, which were much lower than those reported by the WHO and EPA in drinking water. Furthermore, its application in practical samples demonstrated that the sensor can be effectively applied for the detection of Cu²⁺ and Cd²⁺ in practical water samples.

A bifunctional sensor for colorimetric recognition of Cu²⁺ and fluorescent detection of Cd²⁺ was synthesized. It not only showed high selectivity and sensitivity to Cu²⁺ and Cd²⁺, but also could be used in practical water samples with high accuracy.     

A colorimetric and fluorescent chemosensor for Hg2+ based on a photochromic diarylethene with a quinoline unit

A new colorimetric and fluorescent ‘on–off’ chemosensor, 1O, based on a photochromic diarylethene with a quinoline unit was designed and synthesized. The chemosensor 1O demonstrated selective and sensitive detection of Hg²⁺ ions in the presence of other competitive metal ions in acetonitrile. The stoichiometric ratio of the sensor 1O for Hg²⁺ was determined to be 1 : 1, and the limit of detection of the probe 1O was calculated to be 56.3 nM for Hg²⁺. In addition, a molecular logic circuit with four inputs and one output was successfully constructed with UV/vis light and metal-responsive behavior. ESI-MS spectroscopy, Job''s plot analysis, and ¹H NMR titration experiments confirm the binding behavior between 1O and Hg²⁺.

A new colorimetric and fluorescent ‘on–off’ chemosensor, 1O, based on a photochromic diarylethene with a quinoline unit was designed and synthesized.     

A mitochondrion-targeted dual-site fluorescent probe for the discriminative detection of SO32− and HSO3− in living HepG-2 cells

Sulfur dioxide, known as an environmental pollutant, produced during industrial productions is also a common food additive that is permitted worldwide. In living organisms, sulfur dioxide forms hydrates of sulfite (SO₂·H₂O), bisulfite (HSO₃⁻) and sulfite (SO₃²⁻) under physiological pH conditions; these three exist in a dynamic balance and play a role in maintaining redox balance, further participating in a wide range of physiological and pathological processes. On the basis of the differences in nucleophilicity between SO₃²⁻ and HSO₃⁻, for the first time, we built a mitochondrion-targeted dual-site fluorescent probe (Mito-CDTH-CHO) based on benzopyran for the highly specific detection of SO₃²⁻ and HSO₃⁻ with two diverse emission channels. Mito-CDTH-CHO can discriminatively respond to the levels of HSO₃⁻ and SO₃²⁻. Besides, its advantages of low cytotoxicity, superior biocompatibility and excellent mitochondrial enrichment ability contribute to the detection and observation of the distribution of sulfur dioxide derivatives in living organisms as well as allowing further studies on the physiological functions of sulfur dioxide.

Rational design and sensing mechanism of a dual-site fluorescence probe for HSO₃⁻ and SO₃²⁻.     

Recognition of trace organic pollutant and toxic metal ions via a tailored fluorescent metal–organic coordination polymer in water environment

A novel fluorescence material H₂Sr₂(bqdc)₃(phen)₂ (1) for trace recognition of organic pollutant and toxic metal ions is designed and prepared by two weak fluorescent ligands and Sr²⁺. The latter was selected although it played no role in the modulation process of luminescence and despite low-cost, alkaline earth, metal–organic coordination polymers lacking competitive functionality. The strong fluorescence of the fluorescence material was based on the propeller configuration of the metal–organic coordination polymer, which was characterized by X-ray single crystal diffraction showing that the N active sites inside the crystal channels can interact with external guests. Convenient fluorescence detection of 3-AT can be realized using an ultraviolet lamp and test strip and the determination of Cd²⁺ showed good reusability with a detection limit of 1 × 10⁻⁹ mol L⁻¹, which is lower than the standard stipulated by the Environmental Protection Agency. Detailed experiments results revealed that the material was a promising candidate for specifically recognizing amitrole and Cd²⁺ because of its selective fluorescence quenching and sensitive detection in water.

Complexes with strong fluorescence can conveniently detect the trace organic pollutant amitrole and repeatedly recognize toxic Cd²⁺with a low detection limit.     

A simple fluorescent probe for detection of Ag+ and Cd2+ and its Cd2+ complex for sequential recognition of S2−

In this study, we designed and synthesized a simple probe 2-(8-((8-methoxyquinolin-2-yl)methoxy)quinolin-2-yl)benzo[d]thiazole (DQT) for detection of Ag⁺ and Cd²⁺ in a CH₃OH/HEPES (9 : 1 v/v, pH = 7.30) buffer system. Its structure was characterized by NMR, ESI-HR-MS and DFT calculations, and its fluorescence performance was also investigated. Probe DQT showed fluorescence quenching in response to Ag⁺ and Cd²⁺ with low detection limits of 0.42 μM and 0.26 μM, respectively. Importantly, the complexation of the probe with Cd²⁺ resulted in a red shift from blue to green, making it possible to detect Ag⁺ and Cd²⁺ by the naked eye under an ultraviolet lamp. The DQT-Cd²⁺ complex could be used for sequential recognition of S²⁻. The recovery response could be repeated 3 times by alternate addition of Cd²⁺ and S²⁻. A filter paper strip test further demonstrated the potential of probe DQT as a convenient and rapid assay.

A fluorescent probe for detection of Ag⁺ and Cd²⁺ and its Cd²⁺ complex for sequential recognition of S²⁻.     

A new ratiometric fluorescence assay based on resonance energy transfer between biomass quantum dots and organic dye for the detection of sulfur dioxide derivatives

Sulfur dioxide (SO₂) is considered as the fourth gas signal molecule after nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S). It plays important roles in several physiological processes. Therefore, the design and synthesis of nanoprobes for the detection of SO₂ derivatives in cells is of great significance. Herein, we report a new ratiometric fluorescence nanoprobe based on resonance energy transfer (RET) between biomass quantum dots (BQDs) and organic dye (DMI) for the detection of SO₂ derivatives. The proposed ratiometric fluorescence assay allows the determination of HSO₃⁻ in the range of 1.0 to 225 μM with a detection limit of 0.5 μM. Importantly, the proposed ratiometric fluorescence nanoprobe exhibits a high photostability and good selectivity for HSO₃⁻ over other chemical species including H₂S and biological mercaptans. Quantitation of HSO₃⁻ in cell lysates by using the nanoprobe is demonstrated.

A new ratiometric fluorescence assay has been developed for the detection of sulfur dioxide derivatives with repeatability and selectivity. The assay was applied to quantitate HSO₃⁻ in cell lysates with accurate results.     

A monomolecular platform with varying gated photochromism

In the development of modern high-performance photoelectric materials, the gated photochromic materials have attracted wide attention. However, the integration of varying signal regulations into gated photochromism to construct efficient photochromic materials is still an urgent necessity. Herein, we designed and synthesized a new gated photoswitching DTEP based on a Schiff base with a diarylethene core. The photochromic properties of compound DTEP can be regulated to different degrees by multiple stimuli, including UV/visible light, Cu²⁺ and Ni²⁺. The compound DTEP showed different response abilities to Cu²⁺ and Ni²⁺, due to the diverse complexation modes between DTEP and Cu²⁺ as well as Ni²⁺. The photochromic properties of compound DTEP could be inhibited completely by the introduction of Cu²⁺ to form a 1 : 1 complexation, while the weak gated photochromism could be found from the DTEP–Ni²⁺ complex in a 1 : 2 stoichiometry. Relying on such varying degrees of gated photochromic properties, a new molecular logic circuit was constructed to undertake complicated logical operations.

A strategy to realize varying degrees of gated photochromic properties by coordinating with different metal ions within one unimolecular system was devised to achieve the construction of a logic circuit for multi-functional molecular switching.     

A theoretical study on the formation and oxidation mechanism of hydroxyalkylsulfonate in the atmospheric aqueous phase

Hydroxymethanesulfonate (HMS) is an important organosulfur compound in the atmosphere. In this work, we studied the formation mechanism of HMS via the reaction of formaldehyde with dissolved SO₂ using the quantum chemistry calculations. The results show that the barrier (9.7 kcal mol⁻¹) of the HCHO + HSO₃⁻ reaction is higher than that (1.6 kcal mol⁻¹) of the HCHO + SO₃²⁻ reaction, indicating that the HCHO + SO₃²⁻ reaction is easier to occur. For comparison, the reaction of acetaldehyde with dissolved SO₂ also was discussed. The barriers for the CH₃CHO + HSO₃⁻ reaction and CH₃CHO + SO₃²⁻ reaction are 16.6 kcal mol⁻¹, 2.5 kcal mol⁻¹, respectively. This result suggests that the reactivity of HCHO with dissolved SO₂ is higher than that of CH₃CHO. The further oxidation of CH₂(OH)SO₃⁻ and CH₃CH(OH)SO₃⁻ by an OH radical and O₂ shows that the SO₅˙⁻ radical can be produced.

We report the formation of an important organosulfur compound HMS and its oxidation using theoretical calculation.     

A novel diarylethene-based fluorescent “turn-on” sensor for the selective detection of Mg2+

A new photochromic diarylethene derivative with a 4-methylphenol unit has been designed and synthesized. It displayed distinct photochromism and fluorescent ‘‘turn on’’ features to Mg²⁺ in acetonitrile solution. With the addition of Mg²⁺, there was an obvious increase of fluorescent emission intensity at 552 nm, accompanied by a clear change of fluorescent color from dark purple to green. Meantime, the 1 : 1 stoichiometry between the derivative and Mg²⁺ was verified by Job''s plot and HRMS. Furthermore, the sensor was successfully applied in the detection of Mg²⁺ in practical samples. Moreover, based on the multiple-responsive fluorescence switching behaviors, it also could be used to construct a molecular logic circuit with UV/vis lights and Mg²⁺/EDTA as input signals and the emission at 552 nm as the output signal.

A new photochromic diarylethene derivative with a 4-methylphenol unit has been designed and synthesized.     

Theoretical study of the oxidation reactions of sulfurous acid/sulfite with ozone to produce sulfuric acid/sulfate with atmospheric implications

Herein, theoretical studies were performed on the atmospheric oxidation of sulfurous acid (H₂SO₃) and sulfite ions (HSO₃⁻) by ozone (O₃) to produce sulfuric acid and hydrosulfate ions. The most favorable path for the H₂SO₃ + O₃ reaction has been found to be initiated from concerted H-abstraction and oxygen addition, with an overall energy barrier of 18.3 kcal mol⁻¹. On the other hand, the most favorable path for the HSO₃⁻ + O₃ reaction is initiated from oxygen addition, with an overall energy barrier of only 0.3 kcal mol⁻¹. Kinetic simulations were performed to estimate the significance of these reactions in the formation of atmospheric sulfate and destruction of the ozone layer. The results provide new insight into the missing source of atmospheric sulfate and particulate matter.

Herein, theoretical studies were performed on the atmospheric oxidation of sulfurous acid (H₂SO₃) and sulfite ions (HSO₃⁻) by ozone (O₃) to produce sulfuric acid and hydrosulfate ions.     

Highly sensitive determination of lead(ii) and cadmium(ii) by a large surface area mesoporous alumina modified carbon paste electrode

Nanosized mesoporous γ-alumina (M-γ-Al₂O₃) was first prepared and then modified into a carbon paste to fabricate a novel modified carbon paste electrode. The prepared alumina has pores with an amorphous wall and large surface area. The electrochemical behavior of the modified carbon paste electrode was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. The modified carbon paste electrode was employed to determine Pb²⁺ and Cd²⁺ simultaneously by a differential pulse voltammetry (DPV) method. Amperometric determination was carried out in 0.1 mol L⁻¹ NaAc–HAc buffer solution (pH 6.0) after enriching for 360 s at −1.0 V. The oxidation peak currents of Pb²⁺ and Cd²⁺ were proportional to their concentration in the range of 0.001–10 μmol L⁻¹ and 0.01–10 μmol L⁻¹, respectively. The detection limits of Pb²⁺ and Cd²⁺ were 0.20 nmol L⁻¹ and 2.0 nmol L⁻¹ (S/N = 3), respectively. The modified carbon paste electrode shows good stability, repeatability and sensitivity. The proposed method was applied to the determination of Pb²⁺ and Cd²⁺ in water samples with satisfactory results.

Nanosized mesoporous γ-alumina (M-γ-Al₂O₃) was first prepared and then modified into a carbon paste to fabricate a novel modified carbon paste electrode.     

A multi-colorimetric probe to discriminate between heavy metal cations and anions in DMSO–H2O with high selectivity for Cu2+ and CN−: study of logic functions and its application in real samples

A ditopic multi-colorimetric probe based on the phenylpridyl-thioic moiety (EN) was synthesized via a Schiff base reaction mechanism and characterized using ¹H NMR and UV-vis spectroscopy. The colorimetric analyses carried out revealed that EN was capable of discriminating between a number of heavy metal cations via coordination induced charge transfer, as well as between anions through hydrogen bonding induced charge transfer, in DMSO–H₂O (9 : 1). In particular, the ditopic probe could spectrally and colorimetrically recognize the most toxic heavy metal cations of Cd²⁺, Pb²⁺ and Hg²⁺, among others, in DMSO–H₂O. Additionally, EN was selective and sensitive to the presence of CN⁻, F⁻, AcO⁻ and H₂PO₄⁻ in the same solvent system as cations. The reversibility and reproducibility studies showed that EN exhibited complementary IMP/INH logic functions, based on colour and spectral switching (ON/OFF), modulated by F⁻/Al³⁺. The real time application of the probe was tested on food grade products to detect the presence of F⁻ in toothpastes and mouthwash dissolved in water, as well as cations in underground water (normally saline), which displayed substantial responses. Thus, EN displayed an excellent scope of response and can thus be developed for real time sensing kits, which could be used instantly in on-field analysis. Theoretical studies were conducted to complement the experimental work.

A ditopic multi-colorimetric probe based on the phenylpridyl-thioic moiety (EN) was synthesized via a Schiff base reaction mechanism and characterized using ¹H NMR and UV-vis spectroscopy.