A simple fluorescent schiff base for sequential detection of Zn2+ and PPi based on imidazo[2,1-b]thiazole

A bicarboxaminoquinoline-based ratiometric fluorescent sensor for the sequential detection of Zn2+ and PPi

A new ratiometric fluorescent sensor (LP) based on bicarboxaminoquinoline was designed and synthesized for sequentially recognizing Zn2+ and PPi. In aqueous solution, LP exhibited the ratiometric fluorescence response towards Zn2+, along with the about 4-folds enhancement of fluorescence quantum yield. Subsequently, the LP-Zn2+ complex displayed the fluorescence recovery upon adding PPi through the displacement strategy. And the LODs of LP and its Zn2+ complex for sensing Zn2+ and PPi were found to be 15 nM and 5.5 nM, respectively. Notably, the reversibility of LP for sequentially sensing Zn2+ and PPi had been employed to construct the INHIBIT logic gate. Moreover, LP and its Zn2+ complex had been successfully utilized for the detection of Zn2+ and PPi in two real water samples and cells imaging.

A comparative study of two thienopyrimidine Schiff base probes for sequential monitoring of Ga3+ and Pd2

Two Schiff base probes (S1 and S2) were prepared and synthesized by incorporating thienopyrimidine into salicylaldehyde or 3-ethoxysalicylaldehyde individually, with the aim of detecting Ga3+ and Pd2+ sequentially. Upon chelation with Ga3+, S1 and S2 exhibited fluorescence enhancement in DMSO/H2O buffer. Both S1-Ga3+ and S2-Ga3+ were quenched by Pd2+. The limit of detection for S1 in response to Ga3+ and Pd2+ was 2.86 × 10-7 and 4.4 × 10-9 M, respectively. For S2, the limit of detection for Ga3+ and Pd2+ was 4.15 × 10-8 and 3.0 × 10-9 M, respectively. Furthermore, the complexation ratios of both S1 and S2 with Ga3+ and Pd2+ were determined to be 1:2 through Job's plots, ESI-MS analysis, and theoretical calculations. Two molecular logic gates were constructed, leveraging the response behaviors of S1 and S2. Moreover, the potential utility of S1 and S2 for monitoring Ga3+ and Pd2+ in domestic water was verified.

Synthesis of tetraphenylethylene-based small molecular sensor for the selective "turn-on" detection of pyrophosphoric acid in the aqueous solution

Pyrophosphoric acid (PPi) is a crucial indicator for monitoring adenosine triphosphate hydrolysis processes, and abnormal PPi levels in the human body seriously threaten human health. Thus the efficient detection of the concentration of PPi in the aqueous solution is important and urgent. This paper described the successful synthesis of a tetraphenylethylene (TPE) derivative, named as TPE-4B, which contained four chelate pyridinium groups exhibiting aggregation-induced emission characteristics. TPE-4B was explicitly developed for the selective and sensitive fluorescence detection of PPi in aqueous solutions, showing a fluorescence "turn-on" response, and the detection limit was 65 nM. The four chelate pyridinium moieties of TPE-4B exhibited robust electrostatic interactions and binding capacity towards PPi, leading to the formation of aggregations, which was confirmed by zeta potential, dynamic light scattering, and scanning electron microscopy. Compared with free TPE-4B in the aqueous solution, the zeta potential of aggregations decreased from 20.7 to 4.2 mV, the average diameter increased from 155 to 403 nm, and the morphology transformed from porous nanostructures into a block-like format. Leveraging these properties, TPE-4B is a promising candidate for a "turn-on" fluorescence sensor designed to detect PPi in the aqueous solution.

An innovative near-infrared fluorescent probe with FRET effect for the continuous detection of Zn2+ and PPi with high sensitivity and selectivity, and its application in bioimaging

As the second most abundant transition metal element in the human body, zinc ions play an important role in the normal growth and development of the human body. We have successfully synthesized a near-infrared fluorescent probe with FRET effect for the detection of Zn2+. Probe DR6G has good selectivity and anti-interference ability for Zn2+. When Zn2+ is added to the probe DR6G solution, it responds completely within seconds, releasing red fluorescence with a detection limit of 2.02 × 10-8 M. As the main product of ATP hydrolysis, PPi is indispensable in various metabolic activities in cells and the human body. Due to the strong binding ability of Zn2+ and PPi, it is easy to form ZnPPi precipitation, so we added PPi to the solution to complete the Zn2+ detection, and realized the continuous detection of PPi, and the detection limit was 2.06 × 10-8 M. Since Zn2+ and PPi play an important role in vivo, it is of great practical significance to design and synthesize a fluorescent probe that can continuously detect Zn2+ and PPi. Biological experiments have shown that the probe DR6G has low cytotoxicity and can complete the detection of exogenous Zn2+ and PPi in cells and living mice in vitro. Bacterial experiments have shown that the DR6G probe also has certain research value in the field of environmental monitoring and microbiology. Due to the constant variation of the fluorescence signals of Zn2+ and PPi during detection, we designed the logic gate program. In practical applications, the probe DR6G can quantitatively detect Zn2+ in zinc-containing oral liquids and qualitatively detect PPi in toothpaste.

Urea Hydrogen Peroxide and Ethyl Lactate, an Eco-Friendly Combo System in the Direct C(sp2)-H Bond Selenylation of Imidazo[2,1-b]thiazole and Related Structures

Herein, we describe a urea hydrogen peroxide-mediated sustainable protocol for the synthesis of selenylated imidazo[2,1-b]thiazole by using half molar equivalent diorganyl diselenides in ethyl lactate as a greener solvent. The reaction features high yields, easy performance on gram scale, metal-free conditions, as well as applicability to imidazopyridine and imidazopyrimidine.

Recent Advances in Fluorescent Probes for Zinc Ions Based on Various Response Mechanisms

Zinc is a vital metal element with extensive applications in various fields such as industry, metallurgy, agriculture, food, and healthcare. For living organisms, zinc ions are indispensable, and their deficiency can lead to physiological and metabolic abnormalities that cause multiple diseases. Hence, there is a significant need for selective recognition and effective detection of free zinc ions. As a probe method with high sensitivity, high selectivity, real-time monitoring, safety, harmlessness and ease of operation, fluorescent probes have been widely used in metal ion identification studies, and many convenient, low-cost and easy-to-operate fluorescent probes for Zn²⁺ detection have been developed. This article reviews the latest research advances in fluorescent chemosensors for Zn²⁺ detection from 2019 to 2023. In particular, sensors working through photo-induced electron transfer (PET), excited state intramolecular proton transfer (ESIPT), intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), chelation-enhanced fluorescence (CHEF), and aggregation-induced emission (AIE) mechanisms are described. We discuss the use of various recognition mechanisms in detecting zinc ions through specific cases, some of which have been validated through theoretical calculations.

Synthesis and photophysical investigation of Schiff base as a Mg2+ and Zn2+ fluorescent chemosensor and its application

In view of the fluorescent switching properties and anti-fatigue properties of diarylethene, a diarylethene fluorescent chemosensor for the immediate detection of zinc ion (Zn²⁺ ) and magnesium ion (Mg²⁺ ) in acetonitrile was synthesized in this article. The structure of 1o was determined by performing spectroscopy and elemental analysis. The presence of Zn²⁺ or Mg²⁺ made the chemosensor 1o show an obvious "turn-on" fluorescent signal (bright yellow-green for Mg²⁺ and bright cyan for Zn²⁺ ). The fluorescent change caused by the 1:1 binding of 1o and Zn²⁺ or Mg²⁺ might be due to hindering the excited-state intramolecular proton transfer (ESIPT) process, which were bolstered by Benesi-Hildebrand analysis, Job's plot curves, proton nuclear magnetic resonance (¹ H-NMR) titration and mass spectrometry. The limits of detection were acquired from the standard curve plots for Mg²⁺ at 44.6 nM and for Zn²⁺ at 14 nM. Based on the fluorescent behaviors, a logic gate was constructed with the emission intensity at 528/518 nm as output signal, the ultraviolet-visible (UV-vis) lights, Mg²⁺ /Zn²⁺ and EDTA as input signals. Exogenous Zn²⁺ and Mg²⁺ fluorescent bioimaging were performed on Hela cells with 1o, indicating its potential application in biodiagnostic analysis. In particular, 1o was manufactured into test paper, and Zn²⁺ or Mg²⁺ can be conveniently, efficiently and qualitatively identified by the fluorescent color variation of the test strips.

A new chromone functionalized isoqunoline derived chemosensor with fluorogenic switching effect for selective detection of Zn2+ in real water samples and living cells

In this work, a selective chemosensor, (E)-N'-((4-oxo-4H-chromen-3-yl)methylene)isoquinoline-1-carbohydrazide (ENO), was rationally developed for colorimetric and fluorogenic detection of Zn²⁺ ions. It was readily synthesized from 4-oxo-4H-chromene-3-carbaldehyde and isoquinoline-1-carbohydrazide via one-step Schiff reaction. ENO exhibited excellent fluorescent response performances toward Zn²⁺ over a wide pH range in EtOH/H₂O media, including a distinguished color change from colorless to gold, a low limit of detection (LOD) value (34 nM), strong complexation ability (1.36 × 10⁵ M^-1) and rapid identification (2 min). The sensing mechanism of ENO toward Zn²⁺ was proposed on the basis of the chelation-enhanced fluorescence (CHEF) process, which was further supported by IR studies and the density functional theory (DFT) calculation. Moreover, ENO presented here demonstrated outstanding capability in monitoring trace level of Zn²⁺ ions in real water samples, living cells as well as the on-site assay kit.

Novel selective "on-off" fluorescence sensor based on julolidine hydrazone-Al3+ complex for Cu2+ ion: DFT study

A hydrazone (T1) was synthesized by reacting 8-hydroxyjulolidine-9-carboxaldehyde with 2-furoic hydrazide and then modified with Al³⁺ ion to form a novel hydrazone Al³⁺ complex (T1-Al³⁺) in an aqueous solution (8% propylene glycol in 10 mM HEPES pH 5.5). The T1-Al³⁺ complex was studied as a Cu²⁺ selective sensor due to its highly efficient capacibility of paramagnetic quenching. The results showed that the T1-Al³⁺ complexed sensor possesses remarkable sensitivity and selectivity for Cu²⁺ ion in 8% propylene glycol in 10 mM HEPES pH 5.5 as compared with other tested analytes. Notably, this sensor has a broad linear detection range of 10-110 µM for Cu²⁺ ion and a detection limit level of 0.62 µM, which is lower than the Cu²⁺ concentration threshold in drinking water designated by the United States Environmental Protection Agency (EPA). Additionally, it was detectable for the presence of Cu²⁺ ion in mineral water and tap water samples. The selectivity of T1-Al³⁺ complexed sensor with Cu²⁺ ion could be explained by the basis of computation with Gaussian software complied with the basis sets of B3LYP/6-31 G(d,p)/LANL2DZ. Furthermore, only T1 exhibited anticancer efficacy against HeLa and U251 cells with MTT assay.

Exploring the Photophysics of a Zn2+ Fluorescence Sensor and Its Sensing Mechanism

Sensor X is a turn-on sensor, which is applied in the fluorescence detection of Zn²⁺ ions. Its photophysical process is comprehensively investigated to clarify its weak fluorescence. With the aid of density functional theory (DFT) and time-dependent density functional theory (TDDFT), the potential energy surfaces (PES) of X on both ground and first excited states are studied. Excited-state intramolecular proton transfer (EPT) processes as well as molecule twisting motion are observed, which induces several minima on the excited-state PES. Transition states as well as rate constants for these dynamic processes are obtained to evaluate their occurrences. The twisting motion of the sensor is an ultrafast process, which is initiated by a specific EPT process and leads to a nonemissive twisted intramolecular charge transfer (TICT) state. The fluorescence of the sensor is barely observable because of the easily attainable TICT state on the excited PES. This mechanism is trustworthy and intrinsically different from the previously proposed mechanism. After clarifying the photophysical process of the sensor, the Zn²⁺ sensing mechanism is uncovered. Also, the selectivity against Cd²⁺ and Hg²⁺ is fully discussed.

Sensing and Imaging of PPi in vivo using Lanthanide-based Second Near-infrared Luminescent Probes

pathological changes. Here, we reported a luminescent nanoprobe for the detection and imaging of PPi in vivo based on a lanthanide nanoparticle with luminescence at the second near-infrared window modified...

An AIRE-active far-red ratiometric fluorescent chemosensor for specifically sensing Zn2+ and resultant Zn2+ complex for subsequent pyrophosphate detection in almost pure aqueous media

A simple Schiff-base fluorescent chemosensor (1) was synthesized by the reaction of 3-amino-pyrazine-2-carbohydrazide and 7-diethylamino-3-formylcoumarin; the sensor 1 displayed a notable green emission at 524 nm in DMSO and an aggregation-induced ratiometric emission (AIRE) at 555 nm in an almost buffered aqueous media (0.5% DMSO content). The AIRE of 1 was quenched following binding to Zn²⁺ ions, while the fluorescence emission in the far-red region was evidently enhanced at 628 nm. Notably, the ratiometric signal output could be utilized to specifically distinguish Zn²⁺ among various metal ions. Moreover, the 1-Zn²⁺ complex was effectively employed as a fluorescent ratiometric chemosensor for pyrophosphate (PPi) detection. The detection limit was 3.52 μM and 2.45 μM for Zn²⁺ and PPi, respectively. The binding mechanism was evaluated by ¹H NMR, ESI-MS, single-crystal X-ray diffraction, TEM, time-resolved fluorescence spectrophotometry, and density functional theory studies. Overall, owing to its sensitive fluorescence behavior, cell imaging studies demonstrated that this sensor is capable of sensing Zn²⁺ and PPi in living cells.

A novel reversible fluorescent probe based on naphthalimide for sequential detection of aluminum (Al3+) and fluoride (F-) ions and its applications

A new Schiff base fluorescent probe NBP derived from the one-step condensation strategy of 2-butyl-6-hydroxy-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline-5-carbaldehyde and N-(2-(hydrazinecarbonyl)phenyl)benzamide was synthesized and characterized. NBP exhibited high selectivity toward Al³⁺ along with naked-eye color changes and prominent fluorescence enhancement. The limit of detection (LOD) of NBP toward Al³⁺ was detected to be 80 nM. The binding ratio of NBP with Al³⁺ ions was obtained as 1 : 2 on the basis of Job's plot with the association constant K_a value of 4.22 × 10¹⁰ M^-1/2. The plausible complexation mechanism of NBP toward Al³⁺ ions was validated by the density functional theory (DFT) and IR spectrum. In addition, in situ formed "NBP + Al³⁺" could be utilized as the second sensor for selective recognition of F^-via fluorescence quenching with a low detection limit (44 nM). Furthermore, the cell imaging experiments of probe NBP in HeLa cells have successfully demonstrated that NBP could serve as an indicator for monitoring Al³⁺ ions in living cells. On top of that, NBP could be used to prepare simple test paper strips for quickly and qualitatively detecting a trace amount of Al³⁺ ions in a visible manner.

Selective sensing of PPi by fluorogenic Al(III)-probe complex in aqueous medium

A newly designed Schiff base probe JN has been synthesized. It is highly selective and sensitive towards Al³⁺ in nearly 100% aqueous medium by exhibiting a dramatic "turn-on" fluorescence response at 495 nm (λ_ex = 450 nm). The sensing mechanism of JN towards Al³⁺ ions was proposed as the combination of PET, ICT, ESIPT, and CHEF processes according to spectra studies and theory calculations. The in situ generated mononuclear Al(III) complex JN-Al³⁺ could sequentially detect PPi ions by turn-off fluorescence response. The selectivity and sensitivity of the JN-Al³⁺ complex towards PPi ions are based on demetalization process. Interestingly, the fact that Al³⁺ can bind with 1, 2, or 3 PPi has been revealed by HRMS study. The probes JN and JN-Al³⁺ complexes were able to capture Al³⁺ and PPi ions, respectively, as demonstrated by fluorescence imaging of the adult zebrafish and onion inner epidermal cells samples.

C3-symmetric triaminoguanidine based colorimetric and fluorometric chemosensor: Sequential detection of Zn2+/PPi, its RGB performance for detection of Zn2+ ion and construction of IMPLICATION logic gate

In this work, new ethyl(E)-2-cyano-3-(1H-pyrrol-2-yl)acrylate appended C₃-symmetric star-shape triaminoguanidine based Schiff base (LH₃) was designed and synthesized from simple synthons. New probe, LH₃ was completely analyzed by ¹H NMR, ¹³C NMR and mass spectrum. In the present probe LH₃, effective π-conjugated ethyl(E)-2-cyano-acrylate unit was introduced on the periphery of the pyrrole-triaminoquanidine conjugates by using carefully chosen building units. The probe LH₃ shows high selectivity and sensitivity towards Zn²⁺ ion via colorimetric and fluorometric changes. The yellowish orange color of LH₃ solution turned to wine red color upon addition of Zn²⁺ solution, along with red shifted absorption maxima from 450 nm to 550 nm, this indicates the formation of LH₃-Zn²⁺ species. Job's plot and mass spectrum analysis confirms the formation of 1:3 stoichiometric complex between the LH₃ and Zn²⁺ ions. Further this ensemble shows selective detection towards PPi anion over the other anions based on displacement metal ion approach. Hence, reversible colorimetric/emission response of LH₃ towards Zn²⁺ and PPi ions via "on-off-on" manner could allow the construction of IMPLICATION logic gate functions. The practical efficacy of the probe LH₃ was established by utilization of the probe for the detection of Zn²⁺ ions in real water sample analysis. Further, the significant noticeable colorimetric changes of the probe LH₃ upon addition of Zn²⁺ ion have been successfully integrated with a smartphone app RGB color value to construct a real-time analysis of Zn²⁺ ions.

A novel fluorescent chemosensor based on coumarin and quinolinyl-benzothiazole for sequential recognition of Cu2+ and PPi and its applicability in live cell imaging

In this study, a highly selective fluorescent sensor (E)-2-((2-(benzo[d]thiazol-2-yl)quinolin-8-yl)oxy)-N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)acetohydrazide (TQC) was synthesized from 2-methylquinolin-8-ol and 4-(diethylamino)-2-hydroxybenzaldehyde and its structure was characterized by ¹H NMR, ¹³C NMR, ESI-HR-MS and density functional theory (DFT) calculation. Sensor TQC showed an obvious "on-off-on" fluorescence response to Cu²⁺ and PPi in a DMSO/HEPES (3:2 v/v, pH = 7.4) buffer system. The detection limits of sensor TQC were 0.06 μM to Cu²⁺ and 0.01 μM to PPi. In addition, sensor TQC showed a 1:1 binding stoichiometry to Cu²⁺ and TQC-Cu²⁺ complex showed a 2:1 binding stoichiometry to PPi. The optimum pH range of sensor TQC and TQC-Cu²⁺ was 3-8. Further studies demonstrated that sensor TQC could be made into test paper strips for the qualitative of Cu²⁺ and PPi and showed sequentially "on-off-on" fluorescent bio-imaging of Cu²⁺ and PPi in HeLa cells.

A fluorescence probe based on 6-phenylimidazo[2,1-b]thiazole and salicylaldehyde for the relay discerning of In3+ and Cr3+

A new fluorescence probe, (E)-N′-(2-hydroxybenzylidene)-6-phenylimidazo[2,1-b]thiazole-3-carbohydrazide (LB1), based on 6-phenylimidazo[2,1-b]thiazole and salicylaldehyde was designed and synthesized.

Double Schiff base from thiophene-2,5-dicarboxylic acid as an “off–on–off” fluorescence sensor for the sequential detection of In3+ and PPi

A double Schiff base T as acceptor for metal ions derived from thiophene-2,5-dicarboxylic acid was designed and synthesized, and showed a high selectivity for In³⁺ in a DMF/H₂O buffer solution.