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Journal: Luminescence : the journal of biological and chemical luminescence

22

Three anthracene-based Schiff base complexes, R1-R3 (R1 = (E)-N´-((anthracen-10-yl)methylene)benzohydrazide; R2 = (E)-1-((anthracen-10-yl)methylene)-4-phenylsemicarbazide; and R3 = (E)-1-((anthracen-10-yl)methylene)-4-phenylthiosemicarbazide) were synthesized from 9-anthracenecarboxaldehyde, benzohydrazide, 4-phenylsemicarbazide and 4-phenylthiosemi-carbazide respectively, and characterized by various spectral techniques. The absorption spectral characteristics of R1-R3 were bathochromically tuned to the visible region by extending the π conjugation. These target compounds were weakly fluorescent in tetrahydrofuran (THF) solution because of rapid isomerization of the C=N double bond in the excited state. However, the aqueous dispersion of R1-R3 in the THF/water mixture by the gradual addition of water up to 90% resulted in an increase in the fluorescence intensity mainly due to aggregation-induced emission enhancement (AIEE) properties. The formation of nanoaggregates of R1-R3 were confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The compounds R1-R3 are ideal probes for the fluorescence sensing of bovine serum albumin (BSA) and breast cancer cells by optical cell imaging.

Concepts: Electron, Cancer, Breast cancer, Optics, Light, Atom, Serum albumin, Scanning electron microscope

22

The present work introduces for the first time a nanoparticulate approach for ex vivo monitoring of acetylcholinesterase-catalyzed hydrolysis of endogenous acetylcholine released from nerve varicosities in mice atria. Amino-modified 20-nm size silica nanoparticles (SNs) doped by luminescent Tb(III) complexes were applied as the nanosensors. Their sensing capacity results from the decreased intensity of Tb(III)-centred luminescence due to the quenching effect of acetic acid derived from acetylcholinesterase-catalyzed hydrolysis of acetylcholine. Sensitivity of the SNs in monitoring acetylcholine hydrolysis was confirmed by in vitro experiments. Isolated atria were exposed to the nanosensors for 10 min to stain cell membranes. Acetylcholine hydrolysis was monitored optically in the atria samples by measuring quenching of Tb(III)-centred luminescence by acetic acid derived from endogenous acetylcholine due to its acetylcholinesterase-catalyzed hydrolysis. The reliability of the sensing was demonstrated by the quenching effect of exogenous acetylcholine added to the bath solution. Additionally, no luminescence quenching occurred when the atria were pre-treated with the acetylcholinesterase inhibitor paraoxon.

Concepts: Oxygen, Nanoparticle, Ethanol, Nanotechnology, Acid dissociation constant, In vitro, Acetylcholine, Acetylcholinesterase

0

Consumption of herbal teas, infusions and other plant-related products has always been popular due to the related health benefits. However, the safety of these products needs to be assessed, for example monitoring the potential presence of contaminants such as pesticides. In this paper, we report an analytical method for determining three neonicotinoid insecticides - thiacloprid, thiamethoxam, and imidacloprid - that are widely used worldwide. This method is based on quenching by analytes of the luminescence signal of terbium ions. Terbium presents a time-resolved luminescence signal at 256/545 nm/nm, which is quenched by the presence of low concentrations of the selected analytes. Detection limits of 0.1, 0.2 or 0.75 μg ml-1 were obtained for thiamethoxam, thiacloprid and imidacloprid, respectively. Recovery experiments in different teas (green tea, black tea, chamomile, peppermint) were performed at concentrations lower than the maximum residue limits established by the European Union and the Codex Alimentarius for tea samples. In all cases, satisfactory recovery yields were observed, and the results were compared with a chromatographic reference method. The proposed method therefore proved suitable for quantifying these insecticides, fulfilling the current legislation.

0

An easily performed, specific, sensitive, rapid, reliable and inexpensive procedure for the spectrofluorometric quantitation of ascorbic acid was proposed using acriflavine as a fluorescence quenching reagent. The procedure was based on the determined quenching effect of ascorbic acid on the natural fluorescence signal of acriflavine and the reaction between ascorbic acid and acriflavine in Britton-Robinson buffer solution (pH 6) to produce an ion-associated complex. The reduction in acriflavine fluorescence intensity was detected at 505 nm, while excitation occurred at 265 nm. The relationship between quenching fluorescence intensity (∆F) and concentration of ascorbic acid was linear (R2  = 0.9967) within the range 2-10 μg/ml and with a detection limit of 0.08 μg/ml. No significant interference was detected from other materials often found in pharmaceutical nutritional tablets. The obtained results were compared with those from high-performance liquid chromatography and appeared in good agreement, with no important differences in precision or accuracy. The proposed spectrofluorimetric method was used to determine the amount of ascorbic acid in a number of commercial pharmaceutical nutritional supplement tablets with a 95% confidence performance.

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Tigecycline (TIGE) is the newest tetracycline derivative antibiotic with low toxicity, it is used for management of infectious diseases caused by Gram-positive and Gram-negative bacteria. Hence, an efficient, selective and sensitive method was developed for analysis of TIGE in commercial formulations, human plasma and urine. The spectrofluorimetric technique based on the reaction of secondary amine moiety in TIGE with 4-chloro-7-nitrobenzofurazan (NBD-Cl) in slightly alkaline medium producing a highly fluorescent product measured at 540 nm (λex at 470 nm) after heating for 15 min at 75°C. The proposed strategy was upgraded and approved by ICH rules and bio-analytical validated using US-FDA recommendations. A linear relationship between fluorescence intensity and TIGE concentration was observed over the concentration range 40-500 ng mL-1 with limit of quantification (LOQ) 21.09 ng mL-1 and limit of detection (LOD) 6.96 ng mL-1 .The ultra-affectability and high selectivity of the proposed strategy permits analysis of TIGE in dosage form, human plasma and urine samples with good recovery ranged from 97.23% to 98.72% and from 99.36% to 99.80% respectively, without any interfering from matrix components. Also, the developed strategy was used to examine the stability of TIGE in human plasma and applied for pharmacokinetic investigation of TIGE.

0

Two new twinborn benzimidazole derivates (L and A), which bonded pyridine via the ester space on the opposite and adjacent positions of the benzene ring of benzimidazole respectively, were designed and synthesized. Compound L displayed fluorescence quenching response only towards copper(II) ions (Cu2+ ) in acetonitrile solution with high selectivity and sensitivity. However, compound A presented ‘on-off’ fluorescence response towards a wide range of metal ions to different degrees and did not have selectivity. Furthermore, compound L formed a 1:1 complex with Cu2+ and the binding constant between sensor L and Cu2+ was high at 6.02 × 104  M-1 . Job’s plot, mass spectra, IR spectra, 1 H-NMR titration and density functional theory (DFT) calculations demonstrated the formation of a 1:1 complex between L and Cu2+ . Chemosensor L displayed a low limit of detection (3.05 × 10-6  M) and fast response time (15 s) to Cu2+ . The Stern-Volmer analysis illustrated that the fluorescence quenching agreed with the static quenching mode. In addition, the obvious difference of L within HepG2 cells in the presence and absence of Cu2+ indicated L had the recognition capability for Cu2+ in living cells.

0

In this study, an up-converting phosphor technology-based lateral-flow (UPT-LF) assay was developed to detect severe fever with thrombocytopenia syndrome virus (SFTSV) total antibodies rapidly and specifically. SFTSV recombinant N protein (SFTSV-rNP) was coated on analytical membrane for sample capture, up-converting phosphor (UCP) particles were used as the reporter, the luminescence emitted by UCP particles was converted to a measurable signal by a biosensor. The performance of UPT-LF assay was evaluated by testing 302 field serum samples by ELISA (enzyme-linked immunosorbent assay), Western blotting and UPT-LF assay. UPT-LF assay exhibited a lower detection limit than ELISA, and a satisfied level of agreement was exhibited by Kappa statistics (Kappa coefficient = 0.938). Considering Western blotting as the reference for comparison, the sensitivity and specificity of UPT-LF assay could reach 98.31% and 100%. UPT-LF assay showed no specific reaction with hantavirus total serum antibodies, which avoids the misdiagnosis of SFTSV from hantavirus that could cause similar clinical symptoms. UPT-LF assay was able to achieve acceptable results within 15 min and needed only 10 μL sample for each test. As a whole, UPT-LF assay is a candidate method for on-site surveillance of SFTSV total antibodies owing to its excellent sensitivity, specificity, stability, easy operation and for being less time consuming.

0

Novel palladium(II) complexes (7a-7e) of substituted quinoline derivatives were synthesized. The complexes were characterized using various techniques such as thermogravimetric analysis (TGA), elemental analysis, conductance measurement, mass, absorption, infra-red (IR), 1 H NMR, 13 C NMR and energy-dispersive X-ray spectroscopy (EDX). Complexes for herring sperm DNA (HS DNA) binding were explored and absorption titration and the binding constant (Kb ) as well as Gibb’s free energy were evaluated. Complex 7d exhibited the highest binding constant, therefore the thermodynamic parameters of 7d at different temperatures were evaluated. To support the results of the absorption titration, fluorescence titration, viscosity measurement and molecular docking studies were performed. The fluorescence quenching data as evaluated from Stern-Volmer equation were used to calculate KSV , Kf and the number of binding sites. The results of all these studies were in good agreement with the absorption study. DNA electrophoretic mobility was performed to explore the possible application of metal complexes as artificial metallonucleases. The antibacterial activity of the complexes was accessed against different pathogenic bacteria and cytotoxicity was measured using brine shrimp and S. pombe.

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Four novel salicyloylhydrazone derivatives and their terbium(III) complexes were synthesized and characterized. The thermal analysis results showed that the terbium(III) complexes possessed good thermal stability. The fluorescence research results showed that the terbium(III) complex substituted by phenyl possessed the best fluorescence intensity among them, and its fluorescence quantum yield was also the highest. The exploration of the electrochemical properties indicated that the introduction of electron-donating groups to the ligand can increase the highest occupied molecular orbital (HOMO) energy levels and decrease the oxidation potential of the corresponding terbium(III) complexes. The introduction of electron-withdrawing groups to the ligand can reduce their HOMO energy levels and increase their oxidation potential. The results showed that the terbium(III) complexes are good candidates for luminescent material.

0

A reversible and easy assembled fluorescent sensor based on calix[4]arene and phenolphthalein (C4P) was developed for selective zinc ion (Zn2+ ) sensing in aqueous samples. The probe C4P demonstrated high selective and sensitive detection towards Zn2+ over other competitive metal ions. Interaction of Zn2+ with a solution of C4P resulted in a considerable increment in emission intensity at 440 nm (λex  = 365 nm) due to the suppression of photoinduced electron transfer (PET) process and the restriction of C=N isomerization. The binding constant (Ka ) of C4P with Zn2+ was calculated to be 4.50 × 1011  M-2 and also the limit of detection of C4P for Zn2+ was as low as 0.108 μM (at 10-7  M level). Moreover, the fluorescence imaging in the human colon cancer cells suggested that C4P had great potential to be used to examine Zn2+ in vivo.