Novel coumarin-based containing denrons selective fluorescent chemosesor for sequential recognition of Cu2+ and PPi

In this study, we have successfully synthesized a novel coumarin-based dendrons derivative CD and its chemical structure was characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. The sensor CD showed an obvious “on-off” fluorescence quenching response toward Cu²⁺ with a maximum quenching efficiency of 99.8%. The CD-Cu²⁺ complex showed an “off-on” fluorescence enhancement response toward PPi over many competitive anions. The detection limit of the sensor CD was 0.29?×?10^?6?M to Cu²⁺ and 2.39?×?10^?9?M to PPi. In addition, the sensor CD showed a 1:1 binding stoichiometry to Cu²⁺ and the sensor CD-Cu²⁺ showed a 2:1 binding stoichiometry to PPi in CH₃CN/HEPES buffer medium (9:1 v/v, pH?=?7.2). The stable pH range of sensor CD to Cu²⁺ and CD-Cu²⁺ to PPi was from 3 to 8.     

A novel naphthalimide–glutathione chemosensor for fluorescent detection of Fe3+ and Hg2+ in aqueous medium and its application

By rationally introducing glutathione functionalized 1, 8–naphthalimide, a novel fluorescent chemosensor (NG) was successfully synthesized. NG can high selectively and sensitively recognize Fe³⁺/Hg²⁺ ions through quenching of fluorescence among all kinds of common metal ions in aqueous medium. The binding stoichiometry ratio of NG–Fe³⁺ is verified as 2:1and NG–Hg²⁺ as 1:2 confirmed by Job's plot method, FT-IR, ¹H NMR and ESI–MS spectrum, and the possible sensing mechanism were also proposed. The chemosensor NG toward Fe³⁺ and Hg²⁺ displays the excellent advantages of high selectivity and sensitivity, low detection limits (7.92?×?10^?8 and 4.22?×?10^?8?M), high association constants (3.37?×?10⁸ and 8.14?×?10⁴?M^?2), instataneous response (about 10s) and wide pH response range (3.0–8.0). Importantly, the chemosensor NG was successfully applied to determine Hg²⁺ in tap water. Meanwhile, the test strips based on NG were prepared, which could conveniently and efficiently detect Fe³⁺ and Hg²⁺. Moreover, the complex of NG and Fe³⁺ (NG–Fe³⁺) showed high selectivity and sensitivity for H₂PO₄￣ over many other anions in the same medium.     

A self-assembled conjugated micelle with improved sensitivity for monitoring alkaline phosphatase activity

An amphiphilic coumarin derivative which forms a π-extended micelle conformation 1 was designed and developed. The exciton efficiently migrates throughout the coumarin aggregates of 1, showing amplified fluorescence quenching in the presence of Cu²⁺ ions. The 1-Cu²⁺ complex displays a highly sensitive response to pyrophosphate (PPi), leading to 80% fluorescence recovery. The activity of alkaline phosphatase (ALP) was monitored by a real-time assay where a solution containing 1, Cu²⁺, and PPi in aqueous solution exhibits a sensitive turn-off fluorescence response to ALP.     

A quinoline-based selective ‘turn on’ chemosensor for zinc(II) via quad-core complex,and its application in live cell imaging

An efficient quinoline-based fluorescent chemosensor (QLNPY) was successfully developed for the detection of zinc ions (Zn²⁺). This novel chemosensor displayed higher sensitivity and selectivity toward Zn²⁺ over other competitive metal ions accompanying with obvious fluorescence enhancement. The QLNPY-Zn²⁺ complex can be further used as a new fluorescent “turn-off” sensor for pyrophosphate (PPi) and sulfur ion (S^2?) via a Zn²⁺ displacement approach. The limits of detection were calculated to be 3.8 × 10^?8 M for Zn²⁺, 3.7 × 10^?7 M for PPi and 4.9 × 10^?7 M for S^2?. The binding mechanism of QLNPY and Zn²⁺ was investigated through NMR, HR-MS analysis and further studied by crystallographic analysis. Additionally, further application of QLNPY for sequential bioimaging of Zn²⁺ and PPi was studied in HepG2 cells, suggesting that the quinoline-based chemosensor possesses great potential applications for the detection of intracellular Zn²⁺ and PPi in vivo.     

A simple click generated probe for highly selective sequential recognition of Cu(II) and pyrophosphate

A click generated quinoline derivative (1) has been synthesized and used as a fluorescent probe for sequential recognition of Cu²⁺ and pyrophosphate (PPi) in DMSO/H₂O (1:1, v/v, HEPES 20 mM, pH = 7.4) solution. Probe 1 displays high selectivity to Cu²⁺ ions, and the in-situ prepared probe 1-Cu²⁺ exhibits high selectivity toward pyrophosphate (PPi) with emission recovery of probe 1. Therefore, 1-Cu²⁺ complex can be applied as a fluorescence turn-on probe for PPi with high selectivity and sensitivity.     

A fast,highly selective and sensitive dansyl-based fluorescent sensor for copper (II) ions and its imaging application in living cells

Since the copper ions (Cu²⁺) play a fatal role in many foundational physiological processes, it is important to develop a simple, highly sensitive and selective sensor for Cu²⁺ detection in living systems. Herein, an intramolecular charge transfer (ICT) and dansyl-based fluorescent chemosensor 1 was designed, synthesized and characterized for the sensitive and selective quantification of Cu²⁺. It exhibited remarkable fluorescence quenching upon addition of Cu²⁺ over other selected metal ions, attributed to the complex formation between 1 and Cu²⁺ with the association constant 6.7 × 10⁵ M^?1. The sensor 1 showed a fast and linear response towards Cu²⁺ in the concentration range from 0 to 12.5 × 10^?6 mol L^?1 with the detection limit of 2.5 × 10^?7 mol L^?1. This detection could be carried out in a wide pH range of 5.0–14. Furthermore, sensor 1 can be used for detecting Cu²⁺ in living cells.     

Solvent-dependent chromogenic sensing for Cu and fluorogenic sensing for Zn and Al: a multifunctional chemosensor with dual-mode

A new multifunctional chemosensor 1 was synthesized and characterized by spectroscopic tools along with a single crystal X-ray crystallography. It can exhibit selective recognition responses toward Cu²⁺, Zn²⁺ and Al³⁺ in different solvent systems with bimodal methods (colorimetric and fluorescence). This sensor 1 detected Cu²⁺ ions through a distinct color change from colorless to yellow in aqueous solution. Interestingly, the receptor 1 was found to be reversible by EDTA. The detection limit (11 μM) of 1 for Cu²⁺ is much lower than WHO guideline (30 μM) in drinking water. In addition, the sensor 1 showed significant fluorescence enhancements in the presence of Zn²⁺ ion and Al³⁺ ion in two different organic solvents (DMF and MeCN), respectively. The binding modes of the three complexes were determined to be a 1:1 complexation stoichiometry through Job plot, ESI-mass spectrometry analysis, and ¹H NMR titration.     

A novel on-off-on fluorescent chemosensor for relay detection of Fe3+ and PPi in aqueous solution and living cells

A novel on-off-on fluorescence chemosensor BP based on benzothiazole for the relay recognition of Fe³⁺ and PPi was designed and synthesized. The chemosensor BP exhibited a high affinity to Fe³⁺ in the presence of other competing cations. The resultant BP-Fe³⁺ showed excellent recognition ability for PPi via Fe³⁺ displacement approach. The detection limits of BP for Fe³⁺ and BP-Fe³⁺ for PPi were estimated to be 2.59 × 10^?8 M and 8.47 × 10^?8 M, respectively. The low cytotoxicity and good cell-membrane permeability of BP and BP-Fe³⁺ complex makes them capable of Fe³⁺ and PPi imaging in living Hep G2 cells.     

A highly selective coumarin-based chemosensor for the sequential detection of Fe3+ and pyrophosphate and its application in living cell imaging

A new chemosensor based on coumarin FB has been designed and synthesized for the detection of Fe³⁺ and PPi. FB displayed a high affinity to Fe³⁺ in the presence of other competing cations. The resulting FB-Fe³⁺ complex displayed highly sensitivity to PPi via Fe³⁺ displacement approach. The Fe³⁺ and PPi recognition processes is rapid and reversible, the detection limits of FB to Fe³⁺ and FB-Fe³⁺ complex to PPi were estimated to be 8.73?×?10^?8?M and 1.25?×?10^?8?M, respectively. The good biocompatibility of FB enables the investigation of fluorescent response for Fe³⁺ and PPi in living cells by confocal microscope. A B3LYP/6-31G(d,p) basis set was employed for optimization of FB and FB-Fe³⁺ complex.     

A selective colorimetric and fluorescence chemosensing sensor for Cr<Superscript>3+</Superscript> based on a rhodamine base derivative

A rhodamine-conjugated coumarin (L) was used in designing a selective fluorescence chemosensor for the determination of trace amounts of Cr³⁺ ions in acetonitrile–water (MeCN/H₂O (90:10, %v/v) solutions. The intensity of the fluoresce emission of the chemosensor is intensified upon addition of Cr³⁺ ions in MeCN/H₂O (90:10, %v/v) solutions, due to the formation of a selective 1:1 complex between L and Cr³⁺ ions. The fluorescence enhancement versus Cr³⁺ concentration has been found to be linear from 1.0?×?10^?7 to 1.8?×?10^?5 M and a detection limit of 7.5?×?10^?8 M. The proposed fluorescent probe proved to be highly selective towards Cr³⁺ ions as compared to other common metal ions and could be successfully applied to the determination of Cr³⁺ concentrations in some water and wastewater samples.     

A novel and synthetically facile coumarin-thiophene-derived Schiff base for selective fluorescent detection of cyanide anions in aqueous solution: Synthesis,anion interactions,theoretical study and DNA-binding properties

A colorimetric and fluorescent chemosensor (chemosensor 2) for the detection of cyanide anions in aqueous solution has been designed and synthesized in high yield. The sensing mechanism of the chemosensor was verified via UV–vis, fluorimetric, and NMR titrations, and was theoretically explained using DFT and TD-DFT calculations. The chemosensor could optically discriminate the presence of fluoride ions over other anions by a color change from yellow to red with an enhancement of pink fluorescence in DMSO. However, it showed strong green fluorescence when CN^? was added to a mixture of DMSO/water (6:4 v/v). Thus, the chemosensor can be employed in selective detecting of CN^? besides other interference anions (F^?, AcO^? and H₂PO₄^?) in aqueous solution. Moreover, 2 can be used to detect CN^? at a concentration as low as 0.32?μM, which is lower than the WHO guideline (2.7?μM) for cyanide. A low quantity of CN^? (1.08?μM) can be detected and quantified using the prepared chemosensor. Moreover, the UV–vis and fluorescence spectroscopy studies of the interactions between 2 and dublex DNA revealed intercalative binding of calf thymus DNA to the chemosensor.     

Benzothiazole-based heterodipodal chemosensor for Cu2+ and CN– ions in aqueous media

A simple and selective chemosensor, A, was developed for recognizing Cu²⁺. The emission spectra of receptor A showed a fluorescence quenching response upon addition of Cu²⁺ with a low detection limit of 4.51 nM, significantly less than the WHO recommended guideline for drinking water. In addition, the formed A?Cu²⁺ complex was examined for secondary sensing of anions. The A?Cu²⁺ complex showed selectivity for CN^– via a recovering emission profile of A.     

Dual-signaling fluorescent chemosensor based on bisthiazole derivatives

A new bisthiazole chemosensor (3) with phenolic substituents at the position 2 of the thiazole rings was prepared. The chemosensor 3 acts as a potential dual-function fluorescence chemosensor with Cu²⁺ and Zn²⁺ ions causing complete quenching and ratiometric change of fluorescence, respectively. The mechanism of fluorescence was based on the cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT).     

A useful scaffold based on acenaphthene exhibiting Cu2+ induced excimer fluorescence and sensing cyanide via Cu2+ displacement approach

A new simple organic scaffold based on acenaphthene 4 was designed and synthesized. The chromogenic and fluorogenic properties of 4 toward different metal ions and anions were investigated in H₂O/MeCN (8:2, v/v) solution. The probe 4 in the presence of Cu²⁺ exhibited strong static excimer emission at 507 nm along with a decrease in monomer emission at ～400 nm ratiometrically, attributed to a complexation through aldimine and amide groups of 4. Additionally, 4 upon interaction with different anions illustrated significant fluorescence enhancement with cyanide. However, interaction of complex, 4-Cu²⁺ with CN^? revealed fluorescence quenching attributed to formation of stable [Cu(CN)_x]^1?x species in the medium. A naked-eye sensitive fluorescent green color of solution was changed to blue. The mechanism of interaction between 4 and Cu²⁺ and sensing of cyanide through Cu²⁺ displacement approach was confirmed by the change in optical behaviors and ¹H NMR and ESI-MS spectral data analysis.     

A novel rhodamine-based turn-on probe for fluorescent detection of Au3+ and colorimetric detection of Cu2+

In this work, we design and synthesize the novel probe RC through introduction the 1-aza-4,13-dithia-15-crown-5 ring into the structure of rhodamine 6G hydrazide, where the N atom of crown ring is responsible for quenching of rhodamine fluorescence. The compound obtained behaves as multifunctional cation sensor providing selective fluorescent response to Au³⁺ and selective colorimetric response to Cu²⁺ ions in aqueous acetonitrile (1/1, v/v) at pH 7.0. The use of 10^?5?M RC solution allowed reliable determination of target cations in the presence of a wide range of environmentally relevant ions with detection limits of 2?×?10^?6?M and 5?×?10^?7?M for gold and copper, respectively.     

"Off-On" based fluorescent chemosensor for Cu2+ in aqueous media and living cells

A novel Cu²⁺-specific “off-on” fluorescent chemosensor of naphthalimide modified rhodamine B (naphthalimide modified rhodamine B chemosensor, NRC) was designed and synthesized, based on the equilibrium between the spirolactam (non-fluorescence) and the ring-opened amide (fluorescence). The chemosensor NRC showed high Cu²⁺-selective fluorescence enhancement over commonly coexistent metal ions or anions in neutral aqueous media. The limit of detection (LOD) based on 3 × δ_blank/k was obtained as low as 0.18 μM of Cu²⁺, as well as an excellent linearity of 0.05-4.5 μM (R = 0.999), indicating the chemosensor of high sensitivity and wide quantitation range. And also the coordination mode with 1:1 stoichiometry was proposed between NRC and Cu²⁺. In addition, the effects of pH, co-existing metal ions and anions, and the reversibility were investigated in detail. It was also demonstrated that the NRC could be used as an excellent “off-on” fluorescent chemosensor for the measurement of Cu²⁺ in living cells with satisfying results, which further displayed its valuable applications in biological systems.     

A highly sensitive and selective fluorescent probe for Fe3+ containing two rhodamine B and thiocarbonyl moieties and its application to live cell imaging

A novel turn-on rhodamine B-based fluorescent chemosensor (RBCS) was designed and synthesized by reacting N-(rhodamine B)lactam-1,2-ethylenediamine and carbon disulfide. Upon addition of Fe³⁺ in EtOH/H₂O solution (2:1, v/v, HEPES buffer, 0.6?mM, pH 7.20), the RBCS displayed a significant fluorescence enhancement at 582?nm and a dramatic color change from colorless to pink, which can be detected by the naked eye. Significantly, the RBCS exhibited a highly selective and sensitive ability toward Fe³⁺. The detection limit of the probe was 2.05?×?10^?7?M. Job's plot indicated the formation of 1:1 complex between the RBCS and Fe³⁺. Moreover, the practical use of the RBCS is demonstrated by its application in the detection of Fe³⁺ in HeLa cells.     

Naphthalene-derived Al3+-selective fluorescent chemosensor based on PET and ESIPT in aqueous solution

A simple fluorescent chemosensor HL based on naphthalene with high selectivity and sensitivity towards Al³⁺ over other commonly coexisting metal cations in fully aqueous solution to enhance the potential applications of the fluorescent chemosensor was developed. HL exhibited a significant fluorescence enhancement at 475?nm in the presence of Al³⁺ over other competitive metal ions with a low detection limit of 0.43?μM due to the inhibition of the photo induced electron transfer (PET) and the excited-state intramolecular proton transfer (ESIPT). The 1:1 binding stoichiometry between HL and Al³⁺ was corroborated by the Job plot and the ESI-MS spectrum. Importantly, the reversible recognition process of HL to Al³⁺ will make HL could be used circularly and repeatedly in practical applications by addition of Na₂EDTA. In addition, the binding behavior and sensing mechanism of HL to Al³⁺ were illustrated in detail by the ¹H NMR titration experiment.     

Selective Chemosensor of Fe3+ Based on Fluorescence Quenching by 2,2′‐Bisbenzimidazole Derivative in Aqueous Media

2,2′‐Bisbenzimidazole derivative ( L ) was designed as a fluorescent chemosensor for Fe³⁺. This structurally simple chemosensor displays significant fluorescence quenching with increasing concentrations of Fe³⁺. L exhibited high selectivity and antidisturbance for Fe³⁺ among environmentally relevant metal ions in aqueous media. The method of Job's plot indicated the formation of 1:2 complex between L and Fe³⁺, and the possible binding mode of the system was also proposed. In addition, further study demonstrates the detection limit on fluorescence response of the sensor to Fe³⁺ is down to 10^?7 mol·L^?1 range. The binding mode was investigated by fluorescence spectra, ESI‐MS, IR data, ¹H NMR, ¹³C NMR and crystal data.     

A simple colorimetric chemosensor for relay detection of Cu2+ and S2− in aqueous solution

A simple colorimetric chemosensor 1 was developed for the sequential detection of Cu²⁺ and S^2?. Sensor 1 could rapidly detect Cu²⁺ by an obvious color change from colorless to yellow. The binding mode of 1 to Cu²⁺ was determined to be a 1:1 complexation stoichiometry through Job plot and ESI-mass spectrometry analyses. The sensing mechanism of Cu²⁺ by 1 was proposed by theoretical calculations. Importantly, the detection limit for Cu²⁺ was found to be 0.12 μM, which was much lower than the recommended value (31.5 μM) of the World Health Organization (WHO). Additionally, 1 could detect and quantify Cu²⁺ in real water samples. Moreover, the resulting 1-Cu²⁺ complex could be used as a highly selective colorimetric sensor for S^2? in the presence of various anions without any interference. The detection limit for S^2? was determined to be 1.66 μM, which was much lower than the guideline (14.8 μM) recommended by WHO in fresh water.