Preparation and Enantioselectivity Binding Studies of a New Chiral Cobalt(II)porphyrin‐Tröger's Base Conjugate

A new bis[cobalt(II)porphyrin]‐Tröger's base conjugate was studied as a potential receptor for methyl esters of several amino acids. The conjugate was prepared as racemate, and then resolved via preparative high‐performance liquid chromatography (HPLC) on a chiral column. The high affinity to lysine, histidine, and proline methyl esters was found by complexation studies followed by UV‐Vis spectroscopy. The studies of pure enantiomers, followed by UV‐Vis and electronic circular dichroism spectroscopy, revealed the highest enantioselectivity for lysine methyl ester. Chirality 26:361–367, 2014. © 2014 Wiley Periodicals, Inc.     

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.     

Enantioseparation of Tröger's Base Derivatives by Capillary Electrophoresis Using Cyclodextrins as Chiral Selectors

The enantioseparation of seven Tröger's base derivatives (TBs) was carried out by capillary electrophoresis using α‐, β‐, and γ‐cyclodextrins as chiral selectors and phosphate at 20 mmol/l concentration, pH 2.5, as background electrolyte. The method was optimized with respect to the concentration of chosen chiral selectors (0–50 mmol/l) and the amount of organic solvent (acetonitrile, 0–25 % (v/v)) in the electrolyte. The results indicate that all the studied variables, i.e., type of chiral selector, its concentration, and the amount of the added organic solvent, have a significant impact on the enantioseparation of the studied TBs. The best results for the majority of the separated TBs were obtained utilizing β‐cyclodextrin at 5 mmol/l concentration and with various amounts of acetonitrile added ranging from 5 to 15% (v/v) in the background electrolyte. For the two smallest studied TBs, γ‐cyclodextrin with 10% (v/v) acetonitrile also provided good resolution. Chirality 25:379–383, 2013. © 2013 Wiley Periodicals, Inc.     

A coumarin‐based fluorescent turn‐on probe for detection of biothiols in vitro

A novel fluorescent probe (CA‐N) was designed and synthesized for detection of biothiols. CA‐N displayed a strong fluorescence in the presence of biothiols with high sensitivity, and the mechanism for detection biothiols was based on the Michael addition reaction of a thiol group to α,β‐unsaturated ketones. CA‐N showed low detection limit for cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), which were calculated as 3.16, 0.19 and 5.15 μM, respectively. At the same time, CA‐N exhibited high selectivity toward biothiols compared with other biological amino acids. In vitro cell experiments proved that CA‐N had no cytotoxicity, high cell permeability and could be employed in living cell imaging for biothiols. Copyright © 2015 John Wiley & Sons, Ltd.     

A simple rhodamine hydrazide‐based turn‐on fluorescent probe for HOCl detection

Hypochlorous acid (HOCl) plays a crucial role in daily life and mediates a variety of physiological processes, however, abnormal levels of HOCl have been associated with numerous human diseases. It is therefore of significant interest to establish a simple, selective, rapid and sensitive fluorogenic method for the detection of HOCl in environmental and biological samples. A hydrazide‐containing fluorescent probe based on a rhodamine scaffold was facilely developed that could selectively detect HOCl over other biologically relevant reactive oxygen species, reactive nitrogen species and most common metal ions in vitro. Via an irreversible oxidation–hydrolysis mechanism, and upon HOCl‐triggered opening of the intramolecular spirocyclic ring during detection, the rhodamine hydrazide‐based probe exhibited large fluorescence enhancement in the emission spectra with a fast response, low detection limit and comparatively wide pH detection range in aqueous media. The probe was further successfully applied to monitoring trace HOCl in tap water and imaging both exogenous and endogenous HOCl within living cells. It is anticipated that this simple and useful probe might be an efficient tool with which to facilitate more HOCl‐related chemical and biological research. Copyright © 2015 John Wiley & Sons, Ltd.     

Nonaqueous Capillary Electrophoretic Enantioseparation of Water Insoluble Tröger's Base Derivatives Using β‐Cyclodextrin as Chiral Selector

Racemic mixtures of six Tröger's base derivatives were separated by chiral nonaqueous capillary electrophoresis. The separation protocol was optimized first for suitable solvents. Then the applicability of various salts dissolved in organic solvents and their mixtures was evaluated. As chiral selectors β‐cyclodextrin and heptakis(2,6‐di‐O‐methyl)‐β‐cyclodextrin at various concentrations were used. The best enantioselectivity for the studied analytes was obtained utilizing formamide as organic nonaqueous solvent containing a mixture of sodium citrate and tris(hydroxymethyl)aminomethane acetate as electrolytes, and β‐cyclodextrin as chiral additive. The experimental results demonstrated the feasibility of nonaqueous capillary electrophoresis for enantioseparation of Tröger's base derivatives. This technique represents a suitable alternative to more commonly used capillary electrophoresis in aqueous environment. Chirality 25:810–813, 2013. © 2013 Wiley Periodicals, Inc.     

A turn‐on luminescence probe for highly selective detection of an anthrax biomarker

Highly selective detection of Bacillus anthrax spores has attracted worldwide attention because Bacillus anthrax spores not only are harmful to the health of human beings and animals, but also can be used as biological warfare agents. Here, we report a simple platform by mixing EuCl₃·6H₂O and sodium polyacrylate in aqueous solution and further investigate its luminescence response towards Bacillus anthrax biomarker dipicolinic acid (DPA) as a turn‐on luminescence probe. Importantly, our probe has good sensitivity, lower detection limit, excellent selectivity as well as great anti‐interference ability due to the great luminescence enhancement of Eu³⁺. Moreover, a test paper is constructed to realize the purpose of portable detection. These results indicate that our probe is an excellent candidate for sensing DPA.     

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.     

Enzyme‐triggered fluorescence turn‐off/turn‐on of carbon dots for monitoring β‐glucosidase and its inhibitor in living cells

Energy transfer engineering based on fluorescent probes for directly sensing enzyme activities are in great demand as enzyme‐mediated transformations, which are central to all biological processes. Here, a fluorescence carbon dot (CD)‐based assay exhibiting selective responses to the quantitation of β‐glucosidase and the effect of its inhibitor was developed. The most common substrate, para‐nitrophenyl‐β‐d ‐glucopyranoside (pNPG) was hydrolyzed by β‐glucosidase to release p‐nitrophenol (pNP), which can efficiently quench fluorescence of CDs via an inner filter effect and electron transfer. However, in the presence of inhibitors of β‐glucosidase, the fluorescence intensity gradually recovered as the concentration of inhibitors increased. Therefore, the enzyme‐triggered fluorescence turn‐off/turn‐on of specific CDs successfully achieved sensitive detection of β‐glucosidase and monitored the effect of its inhibitors. This new strategy was applied to detect β‐glucosidase and monitor β‐glucosidase inhibitor in hepatoma cells using cell imaging. All results suggest that the new method is sensitive and promising for use in cancer diagnosis and treatment.     

Characterization of a highly Al3+‐selective fluorescence probe based on naphthalimide‐Schiff base and its application to practical water samples

A new fluorescent Al³⁺‐probe, N‐allyl‐4‐[3,3′‐((2‐aminoethyl)azanediyl)‐bis(N´‐(2‐hydroxybenzylidene)propanehy‐drazide)]‐1,8‐naphthalimide ( L ), was designed and synthesized based on 1,8‐naphthalimide. The probe L contains 1,8‐naphthalimide moiety as the fluorophore and a Schiff base as the recognition group. The structure of L was determined by single crystal X‐ray. L emission at 526 nm increased on addition of Al³⁺ under excitation wavelength at 350 nm. L exhibited high selectivity and sensitivity fluorescence emission towards to Al³⁺ in ethanol/Tris–HCl buffer solution (1:1, v/v, pH = 7.2) as compared with other tested metal ions. A good linearity with a correlation coefficient (R²) of 0.99 was observed in the concentration range 2–10 μM. The binding constant and the detection limit of L for Al³⁺ were calculated to 2.6 × 10⁴ M^?1 and 0.34 μM, respectively. The results of experiments that including Job plot, ultraviolet–visible (UV–Vis) light titration, fluorescence titration, ESI‐MS and ¹H NMR titration, indicated a 1:1 stoichiometric complex between L and Al³⁺. L was highly effective in monitoring Al³⁺ in real‐life Yellow River and tap water samples.     

A red‐emitting indolium fluorescence probe for membranes ‐ flavonoids interactions

The red‐emitting indolium derivative compound (E)‐2‐(4‐(diphenylamino)styryl)‐1,3,3‐trimethyl‐3H‐indol‐1‐ium iodide (H3) was demonstrated as a sensitive membrane fluorescence probe. The probe located at the interface of liposomes when mixed showed much fluorescence enhancement by inhibiting the twisted intramolecular charge transfer state. After ultrasonic treatment, it penetrated into lipid bilayers with the emissions leveling off and a rather large encapsulation efficiency (71.4%) in liposomes. The ζ‐potential and particle size measurement confirmed that the charged indolium group was embedded deeply into lipid bilayers. The probe was then used to monitor the affinities of antioxidant flavonoids for membranes. It was verified that quercetin easily interacted with liposomes and dissociated the probe from the internal lipid within 60 s under the condition of simply mixing. The assessment of binding affinities of six flavonoids and the coincident results with their antioxidation activities indicated that it was a promising membrane probe for the study of drug bio‐affinities.     

A simple and sensitive turn‐on fluorescence probe for detection of cetyltrimethylammonium bromide in aqueous samples

The interaction of acid (PTCA) with cetyltrimethylammonium bromide (CTAB) has been studied by fluorescence spectroscopy. The fluorescence of PTCA can be greatly enhanced by the addition of CTAB, due to the formation a fluorescent supramolecular compound. Under optimum conditions, the enhancement intensity of fluorescence was proportional to the concentration of CTAB over a range of 0–4.5 µmol L^?1. Its detection limit was 0.057 µmol L^?1, which was lower than reported previously. Compared with other methods that have been reported to determine CTAB, this method has high sensitivity, stability and wide linear range and it can be used satisfactorily for the determination of CTAB in aqueous samples. Copyright © 2014 John Wiley & Sons, Ltd.     

A new fluorescent pH probe for imaging lysosomes in living cells

A new rhodamine B-based pH fluorescent probe has been synthesized and characterized. The probe responds to acidic pH with short response time, high selectivity and sensitivity, and exhibits a more than 20-fold increase in fluorescence intensity within the pH range of 7.5–4.1 with the pK_a value of 5.72, which is valuable to study acidic organelles in living cells. Also, it has been successfully applied to HeLa cells, for its low cytotoxicity, brilliant photostability, good membrane permeability and no ‘alkalizing effect’ on lysosomes. The results demonstrate that this probe is a lysosome-specific probe, which can selectively stain lysosomes and monitor lysosomal pH changes in living cells.     

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 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 dual-function fluorescent probe for the detection of pH values and formaldehyde

A dual-function fluorescent probe (Probe 1) was developed in this work for the separate detection of pH value and formaldehyde (HCHO). Probe 1 could recognize HCHO and the pH value from the amino group. The colour of the probe solution was changed from grey blue to light blue with the increase in the pH value, and luminous intensity became larger with the increase in formaldehyde concentration. The curve function relationship between fluorescence intensity and the pH value was also determined. A smartphone containing a colour detector for imaging was used to record the values of the three primary colours (R value, G value, and B value) for the probe solution in formaldehyde. Importantly, there was a linear functional relationship between the B*R/G value with HCHO concentration. Therefore, the probe could be used as a rapid tool for the detection of formaldehyde. More importantly, Probe 1 was successfully used to detect formaldehyde in an actual distilled liquor sample.     

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.     

A colorimetric and fluorescent probe for fluoride ions based on 6‐acetyl‐2‐naphthol

A colorimetric and turn‐on fluorescent probe for fluoride ions, tert‐butyldimethylsilane 6‐acetyl‐2‐naphtholate, was readily synthesized from 6‐acetyl‐2‐naphthol and tert‐butyldimethylchlorosilane (TBSCl). The probe exhibits high sensitivity and good selectivity for fluoride ions in acetonitrile. The inherent mechanism involves the cleavage of the Si–O bond in the probe, which induced yellow color formation and prominent fluorescence enhancement. Copyright © 2013 John Wiley & Sons, Ltd.     

A turn‐on indole‐based sensor for hydrogen sulfate ion

A simple indole‐based receptor 1 was prepared by a simple Schiff‐base reaction of 1H‐indole‐3‐carbaldehyde with ethane 1,2‐diamine and its fluoroionophoric properties toward anions were investigated. Indole‐based receptor 1 acts as a selective turn‐on fluorescent sensor for HSO₄^? in methanol among a series of tested anions. Fluorescence spectroscopy, ultraviolet and nuclear magnetic resonance imaging support that the HSO₄^– indeed interacted with imine nitrogen and the proton of nitrogen in indole ring. Copyright © 2013 John Wiley & Sons, Ltd.     

Terbium (III) coordination polymer–copper (II) compound as fluorescent probe for time‐resolved fluorescence ‘turn‐on’ detection of hydrogen sulfide

With recognition of the biological importance of hydrogen sulfide (H₂S), we present a simple and effective fluorescent probe for H₂S using a Tb³⁺ coordination polymer–Cu²⁺ compound (DPA/Tb/G–Cu²⁺). Dipicolinic acid (DPA) and guanosine (G) can coordinate with Tb³⁺ to form a macromolecular coordination polymer (DPA/Tb/G). DPA/Tb/G specifically binds to Cu²⁺ in the presence of coexisting cations, and obvious fluorescence quenching is observed. The quenched fluorescence can be exclusively recovered upon the addition of sulfide, which is measured in the mode of time‐resolved fluorescence. The fluorescence intensities of the DPA/Tb/G–Cu²⁺ compound enhance linearly with increasing sulfide concentrations from 1 to 30 μM. The detection limit for sulfide in aqueous solution is estimated to be 0.3 μM (at 3σ). The DPA/Tb/G–Cu²⁺ compound was successfully applied to sense H₂S in human serum samples and exhibited a satisfactory result. It displays some desirable properties, such as fast detection procedure, high selectivity and excellent sensitivity. This method is very promising to be utilized for practical detection of H₂S in biological and environmental samples.