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.     

A novel colorimetric fluorescence sensor for Fe3+ based on quinoline Schiff base

A novel fluorescent sensor bearing a quinoline and an anisidine moiety has been developed for highly selective detection of Fe³⁺, which shows photo‐induced electron transfer (PET) behavior induced by Fe³⁺. Binding of Fe³⁺ to the sensor induced the electron of C = N group transfer from quinoline to iron, the result exhibits fluorescent enhancement. With the features of easy synthesis, simple structural skeleton and excellent sensing ability, the newly synthesized chemosensor also applied as a highly selective fluorescent probe in complex samples containing various competitive metal ions. The probe could fulfill various needs in biological and environmental fields.     

A highly selective aggregation‐induced emission fluorogen for sensitive detection of Al3+ in living cells

A Schiff's base derivative was synthesized using a condensation reaction between 8‐formyl‐7‐hydroxy‐4‐methylcoumarin and furan‐2‐carbohydrazide that produced marked aggregation‐induced emission and had excellent ability to specifically recognize aluminium ions (Al³⁺). This compound displayed faint fluorescence in the benign solvent dimethyl formamide, and exhibited obvious green fluorescence following addition of specific amounts of water. Moreover, it exhibited strong blue fluorescence after combination with Al³⁺ even in the presence of other interfering ions. These experimental results demonstrated that this derivative could be used as a fluorescence probe for Al³⁺. The advantages, including significant fluorescence change, high selectivity and sensitivity, and fast response, meant that this probe could be used both to detect Al³⁺ in water samples and for fluorescence imaging in living cells.     

Sensitive and selective detection of Cu(II) ion: A new effective 1,8‐naphthalimide‐based fluorescence ‘turn off’ sensor

The present study reports the development of a new 1,8‐naphthalimide‐based fluorescent sensor V for monitoring Cu(II) ions. The sensor exhibited pH independence over a wide pH range 2.52–9.58, and indicated its possible use for monitoring Cu(II) ions in a competitive pH medium. The sensor also showed high selectivity and sensitivity towards the Cu(II) ions over other competitive metal ions in DMSO–HEPES buffer (v/v, 1:1; pH 7.4) with a fluorescence ‘turn off’ mode of 79.79% observed. A Job plot indicated the formation of a 1:1 binding mode of the sensor with Cu(II) ions. The association constant and detection limit were 1.14 × 10⁶ M^–1 and 4.67 × 10^–8 M, respectively. The fluorescence spectrum of the sensor was quenched due to the powerful paramagnetic nature of the Cu(II) ions. Potential application of this sensor was also demonstrated when determining Cu(II) ion levels in two different water samples.     

A new Schiff base as a turn‐off fluorescent sensor for Cu2+ and its photophysical properties

A new Schiff base receptor 1 was synthesized and its photophysical properties were investigated by absorption, emission and excitation techniques. Furthermore, its chromogenic and fluorogenic sensing abilities towards various metal ions were examined. Receptor 1 selectively detects Cu²⁺ ion through fluorescence quenching and detection was not inhibited in the presence of other metal ions. From fluorescence titration, the limit of detection of receptor 1 as a fluorescent ‘turn‐off’ sensor for the analysis of Cu²⁺ was estimated to be 0.35 μM.     

A coumarin‐based fluorescent probe for Hg2+ and its application in living cells and zebrafish

Mercury (Hg) is a heavy metal with high toxicity and easy migration; it can be enriched through the food chain, and cause serious threats to the natural environment and human health. So, the development of a method that can be used to detect mercury ions (Hg²⁺) in the environment, in cells, and in organisms is very important. Here, a new 7‐hydroxycoumarin‐derived carbonothioate‐based probe ( CC‐Hg ) was designed and synthesized for detection of Hg²⁺. After addition of Hg²⁺, a large fluorescence enhancement was observed due to the formation of 7‐hydroxyl, which reinforced the intramolecular charge transfer process. The CC‐Hg probe had good water solubility and selectivity. Moreover, the probe was able to detect Hg²⁺ quantitatively over the concentration range 0–2 μM and with a detection limit of 7.9 nM. Importantly, we successfully applied the probe to detect Hg²⁺ in water samples, in living cells, and in zebrafish. The experimental results demonstrated its potential value in practical applications.     

A N‐(2‐hydroxyethyl)piperazine dangled 2,5‐diphenyl‐1,3,4‐oxadiazole‐based fluorescent sensor for selective relay recognition of Cu2+ and sulfide in water

A new 2,5‐diphenyl‐1,3,4‐oxadiazole‐based derivative (L) was synthesized and applied as a highly selective and sensitive fluorescent sensor for relay recognition of Cu²⁺ and S^2? in water (Tris–HCl 10 mM, pH = 7.0) solution. L exhibits an excellent selectivity to Cu²⁺ over other examined metal ions with a prominent fluorescence ‘turn‐off’ at 392 nm. L interacts with Cu²⁺ through a 1:2 binding stoichiometry with a detection limit of 4.8 × 10^–7 M. The on‐site formed L–2Cu²⁺ complex exhibits excellent selectivity to S^2? with a fluorescence ‘off–on’ response via a Cu²⁺ displacement approach. Copyright © 2016 John Wiley & Sons, Ltd.     

A Schiff‐based sensor with turn‐on fluorescence for selective detection of Hg2+

A simple Schiff‐base colorimetric receptor 1 was prepared. It exhibits an ‘off–on‐type’ mode with high sensitivity in the presence of Hg²⁺. The change in color is very easily observed by the naked eye in the presence of Hg²⁺, whereas other metal cations do not induce such a change. A Job plot indicated a 1 : 1 complexation stoichiometry between receptor 1 and Hg²⁺. The association constant for 1–Hg²⁺ in Tetrahydrofuran (THF) was determined to be 1.3 × 10⁹ M^‐1 using a Hill plot. Copyright © 2013 John Wiley & Sons, Ltd.     

Subchronic intravenous toxicity study of biofunctional ZnO and its application as a fluorescence probe for cell‐specific targeting

Successful development of safe and highly effective nanoprobes for targeted imaging of in vivo early cancer is a great challenge. Herein, we choose the visible‐light emitting zinc oxide non–core/shell type nanoparticle (NP) fluorophores (ZHIE) as prototypical materials. We have reported on these materials previously. The results showed that the ZHIE NPs exhibited good water solubility and good biocompatibility. This study was conducted to investigate the toxicity of ZHIE NPs when intravenously administered to mice repeatedly at the dose required for successful tumor imaging in vivo. Anti‐macrophage‐1 antigen (Mac1), a macrophage differentiation antigen, antibody‐conjugated ZHIE NPs successfully realized targeted imaging of murine macrophage cell line Raw264.7 cells. In conclusion, ZHIE NPs are not toxic in vivo and antibody‐conjugated ZHIE NPs have great potential in applications, such as single cell labeling.     

Development of highly selective fluorescent ferrocenyl-iminopyridine chemosensor for biologically relevant Fe3+

Design, synthesis, characterization, and ion detection studies of two ferrocene-appended Schiff bases namely N-(2-[ferrocenylamino]ethyl)-5-nitropyridin-2-amine ( 1 ) and ferrocenylamino-1H-imidazole-4-carboxamide ( 2 ) been reported. Both the chemosensors have been thoroughly characterized using Fourier transfer infrared, ¹H and ¹³C nuclear magnetic resonance, high resolution mass spectrometry, and ultraviolet/visible (UV/visible) and fluorescence spectral techniques. Probes 1 and 2 were designed with the aim of appending the ferrocenyl group with pyridine ring having an amine substitution (for 1 ) and imidazole ring with an amide substitution (for 2 ). Interaction of these probes with a series of cations and anions was examined through UV/vis and fluorescence spectral techniques. Probe 2 exhibited an insignificant response towards anions and loss of selectivity for cations, whereas 1 displayed highly selective detection towards biologically important Fe³⁺ in 2:1 (probe:cation) stoichiometry. Notably, none of the cations and anions could interfere the selectivity of Fe³⁺ ensured by 1 in aqueous medium. The limit of detection for Fe³⁺ detection using 1 was determined to be 0.2 ppm. The results strongly suggest that 1 could find promising future application as a chemosensor for Fe³⁺ in biological systems for quantification and qualitative analysis.     

A water‐soluble fluorescent pH probe based on perylene dyes and its application to cell imaging

A fluorescent pH probe, N,N′‐bi( l ‐phenylalanine amine)‐perylene‐3,4;9,10‐dicarboxylic diimide (PDCDA) was synthesized and used for pH sensing in living cells. A significant fluorescence intensity change was observed over a pH range from 7.0 to 4.0. Electrostatic potential maps (MEP) suggested that the electronic repulsion between PDCDAs was increased by the high negative electrostatic potential which resulted in a high water solubility of PDCDA. PDCDA was successfully applied as a high‐performance fluorochrome for living HeLa cell imaging. The results demonstrate that the probe PDCDA is a good candidate for monitoring pH fluctuations in living cells with good water solubility, low cytotoxicity, high fluorescence quantum yield and photostability. Copyright © 2015 John Wiley & Sons, Ltd.     

A highly selective and sensitive turn‐on fluorescent probe for the detection of Al3+ and its bioimaging

A novel fluorescent sensor, 1‐((2‐hydroxynaphthalen‐1‐yl)methylene)urea (ocn) has been designed and applied as a highly selective and sensitive fluorescent probe for recognition of Al³⁺ in Tris–HCl (pH = 7.20) solution. The probe ocn exhibits an excellent selectivity to Al³⁺ over other examined metal ions, anions and amino acids with a prominent fluorescence ‘turn‐on’ at 438 nm. ocn binds to Al³⁺ with a 2:1 binding stoichiometry and the detection limit was 0.3 μM. Furthermore, its capability of biological application was evaluated and the results showed that the sensor could be used to detect Al³⁺ in living cells.     

Hg2+‐selective ratiometric and colorimetric probe based on dansyl–rhodamine and its staining function in cell imaging

A new ratiometric probe composed of a dansyl–rhodamine dyad for the detection of Hg²⁺ via fluorescence resonance energy transfer was designed and synthesized. Rhodamine, dansyl chloride, and hydrazide were selected as the acceptor, donor, and reaction site, respectively. It displayed high selectivity and sensitivity to Hg²⁺ with obvious colour change and fluorescence change due to Hg²⁺‐assisted hydrolysis of rhodamine hydrazide. A good linear relationship ranging from 0 to 16 μM and 0–28 μM for the Hg²⁺ concentration was found based on absorbance and fluorescence assay, respectively. Detection limits of absorbance and fluorescence for Hg²⁺ were calculated to be 1.22 μM and 9.10 μM, respectively.     

Effect of solvents on photophysical properties and quenching of 2‐{[3‐(1H‐benzimidazole‐2‐yl) phenyl] carbonoimidoyl}phenol

The effect of solvents of varying polarity on the absorption and fluorescence emission of the Schiff base, 2‐{[3‐(1H‐benzimidazole‐2‐yl) phenyl]carbonoimidoyl}phenol, was studied using Lippert‐Mataga bulk polarity function, Reichardt's microscopic solvent polarity parameter and Kamlet's multiple linear regression approach. The spectral properties follow Reichardt's microscopic solvent polarity parameter better than Lippert‐Mataga bulk polarity parameter, indicating the presence of both general solute–solvent interactions and specific interactions. Catalan's multiple linear regression approach indicates the major role of solvent polarizability/dipolarity influence compared with solvent acidity or basicity. The solvatochromic effect was utilized to calculate the dipole moments of ground and excited states of the Schiff base using different methods. Bathochromic shift in the emission spectrum and the increase in dipole moment in the excited state signifies the intramolecular charge transfer character in the emitting singlet state. Fluorescence quenching by aniline was also studied in 1,4‐dioxane and n‐butanol, and the results were analyzed using sphere of action static quenching and finite sink approximation models. Copyright © 2014 John Wiley & Sons, Ltd.     

A naphthalene derivative as ‘turn‐on’ fluorescent chemosensor for the highly selective and sensitive detection of Al3+

A Schiff base compound derived from naphthalene has been synthesized and characterized as an Al³⁺‐selective fluorescent probe. The chemosensor ( L ) exhibits high selectively for Al³⁺ in aqueous solution, even in the presence of biologically relevant cations such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Pb²⁺ and several transition metal ions. There was no observed interference from anions like Br^?, Cl^?, HSO₃^?, SO₃^2?, S₂O₃^2?, NO₂^?, CO₃^2? and AC^?. The lowest detection limit for the chemosensor L was found to be 1.89 × 10^?8 M with a linear response towards Al³⁺ over a concentration range of 5 × 10^?6 to 4 × 10^?5 M. Furthermore, the proposed chemosensor has been used for imaging of Al³⁺ in two different types of cells with satisfying results, which further demonstrates its value for practical application in biological systems.     

Zinc(II)‐selective ratiometric fluorescent probe based on perylene bisimide derivative

A fluorescent probe of N,N′‐biscyclohexyl‐1,7‐di(3‐pyridoxy)‐perylene‐3,4:9,10‐tetracarboxylic acid diimide has been synthesized, and exhibited excellent selectivity and sensitivity for Zn²⁺ over other competing biological cations. The Zn²⁺‐selective fluorescence blue‐shift and enhancing property in conjunction with a visible colorimetric change from orange to green could be observed. With favorable photophysical properties in the visible region, the perylene bisimide derivatives remarkably improved the performance of the probe. Copyright © 2010 John Wiley & Sons, Ltd.     

A real‐time fluorescence assay for protease activity and inhibitor screening based on the aggregation‐caused quenching of a perylene probe

We have established a real‐time and label‐free fluorescence turn‐on strategy for protease activity detection and inhibitor screening via peptide‐induced aggregation‐caused quenching of a perylene probe. Because of electrostatic interactions and high hydrophilicity, poly‐l ‐glutamic acid sodium salt (PGA; a negatively charged peptide) could induce aggregation of a positively charged perylene probe (probe 1) and the monomer fluorescence of probe 1 was effectively quenched. After a protease was added, PGA was enzymatically hydrolyzed into small fragments and probe 1 disaggregated. The fluorescence recovery of probe 1 was found to be proportional to the concentration of protease in the range from 0 to 1 mU/ml. The detection limit was down to 0.1 mU/ml. In the presence of a protease inhibitor, protease activity was inhibited and fluorescence recovery reduced. Moreover, we demonstrated the potential application of our method in a complex mixture sample including 1% human serum. Our method is simple, fast and cost effective.     

A turn‐off fluorescence probe based on terpyridine for pH monitoring

A new pH‐dependent fluorescence probe 2,8‐bis((E)‐4‐([2,2′:6′,2″‐terpyridin]‐4′‐yl)styryl)‐6H,12H‐5,11‐methanodibenzo[b,f][1,5]diazocine (TBPTP) based on Tröger's base (TB) bound to terpyridine was designed and synthesized. Photophysical properties and titration experiments of TBPTP were investigated by absorption and fluorescence spectroscopy. TBPTP exhibited high sensitivity in an acidic environment with the working pH range 7.2–2.5, especially having a good liner response to pH changes in the range 2.5–4.3, which suggested that TBPTP is a good candidate for pH monitoring.     

Investigations on the interactions between naphthalimide‐based anti‐tumor drugs and human serum albumin by spectroscopic and molecular modeling methods

The interactions between the three kinds of naphthalimide‐based anti‐tumor drugs (NADA, NADB, NADC) and human serum albumin (HSA) under simulated physiological conditions were investigated by fluorescence spectroscopy, circular dichroism spectroscopy and molecular modeling. The results of the fluorescence quenching spectroscopy showed that the quenching mechanisms for different drugs were static and their affinity was in a descending order of NADA > NADB > NADC. The relative thermodynamic parameters indicated that hydrophobic force was the predominant intermolecular force in the binding of NAD to HSA, while van der Waals interactions and hydrogen bonds could not be ignored. The results of site marker competitive experiment confirmed that the binding site of HSA primarily took place in site I. Furthermore, the molecular modeling study was consistent with these results. The study of circular dichroism spectra demonstrated that the presence of NADs decreased the α‐helical content of HSA and induced the change of the secondary structure of HSA. Copyright © 2015 John Wiley & Sons, Ltd.     

Pyrazolone as a recognition site: Rhodamine 6G‐based fluorescent probe for the selective recognition of Fe3+ in acetonitrile–aqueous solution

Two novel Rhodamine–pyrazolone‐based colorimetric off–on fluorescent chemosensors for Fe³⁺ ions were designed and synthesized using pyrazolone as the recognition moiety and Rhodamine 6G as the signalling moiety. The photophysical properties and Fe³⁺‐binding properties of sensors L¹ and L² in acetonitrile–aqueous solution were also investigated. Both sensors successfully exhibit a remarkably ‘turn‐on’ response, toward Fe³⁺, which was attributed to 1: 2 complex formation between Fe³⁺ and L¹/L². The fluorescent and colorimetric response to Fe³⁺ can be detected by the naked eye, which provides a facile method for the visual detection of Fe³⁺. Copyright © 2014 John Wiley & Sons, Ltd.