Vanillin-coumarin hybrid molecule as an efficient fluorescent probe for trace level determination of Hg(II) and its application in cell imaging

An efficient Hg²⁺ selective fluorescent probe (vanillin azo coumarin, VAC) was synthesized by blending vanillin with coumarin. VAC and its Hg²⁺ complex were well characterized by different spectroscopic techniques like ¹H NMR, QTOF-MS ES⁺, FTIR and elemental analysis as well. VAC could detect up to 1.25 μM Hg²⁺ in aqueous methanol solution through fluorescence enhancement. The method was linear up to 16 μM of Hg²⁺. Negative interferences from Cu²⁺, Ni²⁺, Fe³⁺, and Zn²⁺ were eliminated using EDTA as a masking agent. VAC showed a strong binding to Hg²⁺ ion as evident from its binding constant value (2.2 × 10⁵), estimated using Benesi-Hildebrand equation. Mercuration assisted restricted rotation of the vanillin moiety and inhibited photoinduced electron transfer from the O, N-donor sites to the coumarin unit are responsible for the enhancement of fluorescence upon mercuration of VAC. VAC was used for imaging the accumulation of Hg²⁺ ions in Candida albicans cells.     

A xanthone and a polyketide derivative from the leaves of Cassia obtusifolia (Leguminosae)

A new xanthone, 1,8-dihydroxy-3-methoxy-6-methylxantone and a new polyketide derivative, (4R^∗,5S^∗,6E,8Z)-ethyl-4-((E)-but-1-enyl)-5-hydroxypentdeca-6,8-dienoate, together with 20 known secondary metabolites, including 2 steroids, 4 xanthones, 10 anthraquinones, 2 triterpenoids, 1 fatty ester, and (E)-eicos-14-enoic acid, were isolated from the leaves of Cassia obtusifolia. To the best of our knowledge, the last compound was isolated from a natural source for the first time. The structures of all the compounds were elucidated on the basis of 1D and 2D NMR experiments. Some of the compounds were tested against Salmonella typhi, Staphylococcus aureus, Candida albicans ATCC 9002, and Candida tropicalis, they did not show any activity.     

Coordination to copper(II) strongly enhances the in vitro antimicrobial activity of pyridine-derived N(4)-tolyl thiosemicarbazones

Five copper(II) complexes with N(4)-ortho, N(4)-meta and N(4)-para-tolyl thiosemicarbazones derived from 2-formyl and 2-acetylpyridine were obtained and thoroughly characterized. The crystal structure of N(4)-meta-tolyl-2-acetylpyridine thiosemicarbazone (H2Ac4mT) was determined, as well as that of its copper(II) complex [Cu(2Ac4mT)Cl], which contains an anionic ligand and a chloride in the coordination sphere of the metal. The in vitro antimicrobial activities of all thiosemicarbazones and their copper(II) complexes were tested against Salmonella typhimurium and Candida albicans. Upon coordination a substantial decrease in the minimum inhibitory concentration, from 225 to 1478 μmol L⁻¹ for the thiosemicarbazones to 5–30 μmol L⁻¹ for the complexes was observe against the growth of Salmonella typhimurium and from 0.7–26 to 0.3–7 μmol L⁻¹ against the growth of C. albicans, suggesting that complexation to copper(II) could be an interesting strategy of dose reduction.     

A study on multifunctional protein fibre with UV protection,moth repellency and antibacterial properties using ESIPT core containing benzimidazole and benzothiazole based functional acid azo dyes

Water soluble fluorescent acid azo dyes with benzimidazole and benzothiazole component having excited state intramolecular proton transfer (ESIPT) core were synthesised by diazo coupling. The structure of the dyes were analysed and confirmed by Fourier Transform Infrared – spectroscopy (FT-IR), elemental analysis, ¹H NMR and ¹³C NMR analysis. Absorption and emission characteristics of the dyes were studied in different polarity solvents shown bathochromic (red) shift as solvent polarity increases. Wool and silk fabric dyed with synthesised dyes displayed high exhaustion, uniform dyeing and good wet fastness properties. The dyed substrate showed green and purple fluorescence under UV light (366 ​nm) along with UV protection. Dyed wool fabric was also assessed for antibacterial activity by calculation of bacterial reduction Staphylococcus Auerus (Gram positive), Klebsiella Pneumonia (Gram negative) bacteria. The dyed wool were also examined for the resistivity against insect pests Anthrenus Flavipies (Le Conte) by calculation of the fabric weight loss, Mortality of moth and visible assessment of fabric attacked by moth after 14 days in given conditions. Consequently, it was demonstrated that wool fabric dyed with Benzimidazole and benzothiazole based acid dyes had various functionalities, such as UV protection, antibacterial activity and mild moth repellency.     

Intramolecular aglycon delivery for (1 → 2)-β-mannosylation: towards the synthesis of phospholipomannan of Candida albicans

A high yielding method for 1,2-cis-β-D-mannosylation by intra-molecular aglycon delivery (IAD) through p-methoxy benzyl ether/acetal exchange and phenylsulfoxide donor is reported, along with its application in iterative assembly of antigenic (1 → 2)-β-pentamannoside domain of phospholipomannan (PLM) of fungal pathogen Candida albicans.     

Immuno-capture and in situ detection of Salmonella typhimurium on a novel microfluidic chip

The new method presented in this article achieved the goal of capturing Salmonella typhimurium via immunoreaction and rapid in situ detection of the CdSe/ZnS quantum dots (QDs) labeled S. typhimurium by self-assembly light-emitting diode-induced fluorescence detection (LIF) microsystem on a specially designed multichannel microfluidic chip. CdSe/ZnS QDs were used as fluorescent markers improving detection sensitivity. The microfluidic chip developed in this study was composed of 12 sample channels, 3 mixing zones, and 6 immune reaction zones, which also acted as fluorescence detection zones. QDs–IgG–primary antibody complexes were generated by mixing CdSe/ZnS QDs conjugated secondary antibody (QDs–IgG) and S. typhimurium antibody (primary antibody) in mixing zones. Then, the complexes went into immune reaction zones to label previously captured S. typhimurium in the sandwich mode. The capture rate of S. typhimurium in each detection zone was up to 70%. The enriched QDs-labeled S. typhimurium was detected using a self-assembly LIF microsystem. A good linear relationship was obtained in the range from 3.7 × 10 to 3.7 × 10⁵ cfu mL⁻¹ using the equation I = 0.1739 log (C) − 0.1889 with R² = 0.9907, and the detection limit was down to 37 cfu mL⁻¹. The proposed method of online immunolabeling with QDs for in situ fluorescence detection on the designed multichannel microfluidic chip had been successfully used to detect S. typhimurium in pork sample, and it has shown potential advantages in practice.     

Design,synthesis and antifungal activity of novel selenochroman-4-one derivatives

A series of novel selenochroman-4-one derivatives bearing semicarbazone or nitrogen heterocycle was designed, synthesized, tested antifungal activity and characterized via ¹H-NMR, ¹³C-NMR, and HRMS. The design of the compounds is based on the principle of molecule hybrid and bioisosterism. We aimed at attaching semicarbazones or nitrogen heterocycle to the selenochroman-4-one for enhancing antifungal activity. The antifungal activity of target compounds was evaluated using the microdilution broth method in vitro test. Bioassay results indicated that some of the derivatives displayed good fungistatic activity on Candida zeylanoides, Candida albicans, Cryptococcus neoformans, resistant to fluconazole strain 103 (Candida albicans), resistant to fluconazole strain 100 (Candida albicans) and strain SC5314 (Candida albicans). All the compounds exhibit antifungal activities against the tested funguses in different levels, among them, 7 compounds of antifungal activity against several funguses is better than that of the control drug fluconazole. Based on the results, preliminary structure activity relationships (SARs) were summarized to serve as a foundation for further investigation.     

One-pot synthesis of strongly fluorescent DNA-CuInS2 quantum dots for label-free and ultrasensitive detection of anthrax lethal factor DNA

Herein, high quality DNA-CuInS₂ QDs are facilely synthesized through a one-pot hydrothermal method with fluorescence quantum yield as high as 23.4%, and the strongly fluorescent DNA-CuInS₂ QDs have been utilized as a novel fluorescent biosensor for label-free and ultrasensitive detection of anthrax lethal factor DNA. L-Cysteine (L-Cys) and a specific-sequence DNA are used as co-ligands to stabilize the CuInS₂ QDs. The specific-sequence DNA consists of two domains: phosphorothiolates domain (sulfur-containing variants of the usual phosphodiester backbone) controls the nanocrystal passivation and serves as a ligand, and the functional domain (non-phosphorothioates) controls the biorecognition. The as-prepared DNA-CuInS₂ QDs have high stability, good water-solubility and low toxicity. Under the optimized conditions, a linear correlation was established between the fluorescence intensity ratio I/I₀ (I₀ is the original fluorescence intensity of DNA-CuInS₂ QDs, and I is the fluorescence intensity of DNA-CuInS₂ QDs/GO with the addition of various concentrations of anthrax lethal factor DNA) and the concentration of anthrax lethal factor DNA in the range of 0.029–0.733 nmol L⁻¹ with a detection limit of 0.013 nmol L⁻¹. The proposed method has been successfully applied to the determination of anthrax lethal factor DNA sequence in human serum samples with satisfactory results. Because of low toxicity and fine biocompatibility, DNA-CuInS₂ QDs also hold potential applications in bioimaging.     

A novel ratiometric fluorescent aptasensor accurately detects patulin contamination in fruits and fruits products

Patulin (PAT) contamination in fruit and fruit products is a significant public health concern. Here, we developed a ratiometric fluorescent aptasensor for PAT detection based on aptamer-recognition and Exonuclease III amplification. Two structure selective dyes, SYBR Green I (SGI) and N-methyl mesoporphyrin IX (NMM), were used as fluorescent probes. In the developed biosensing system, the binding of PAT to aptamer triggered the liberation of cDNA. Subsequently, amplification was mediated by Exonuclease III. S1 was released from the S1-S2 duplex by enzymatic hydrolyzation and incorporated into a stable G-quadruplex. As a result, the fluorescence of SGI decreased, whereas that of NMM increased. There was a strong linear correlation between the relative fluorescence intensity and PAT concentrations (20 to 500 ng·L^?1 range) (R² = 0.99). The biosensing system was highly sensitive, and could detect PAT concentration as low as 4.7 ng·L^?1. The sensor was also highly specific, and could differentiate PAT from several other related mycotoxins. In summary, we developed a new bioassay for the accurate detection of PAT contamination in fruits and fruit products. This research provides a new approach for developing ratiometric bioassays based on structure-selective dyes and enzymatic conversion processes.     

Inhibitory Effects of Erythrosine/Curcumin Derivatives/Nano-Titanium Dioxide-Mediated Photodynamic Therapy on Candida albicans

This study focuses on the role of photosensitizers in photodynamic therapy. The photosensitizers were prepared in combinations of 110/220 µM erythrosine and/or 10/20 µM demethoxy/bisdemethoxy curcumin with/without 10% (w/w) nano-titanium dioxide. Irradiation was performed with a dental blue light in the 395–480 nm wavelength range, with a power density of 3200 mW/cm² and yield of 72 J/cm². The production of ROS and hydroxyl radical was investigated using an electron paramagnetic resonance spectrometer for each individual photosensitizer or in photosensitizer combinations. Subsequently, a PrestoBlue^® toxicity test of the gingival fibroblast cells was performed at 6 and 24 h on the eight highest ROS-generating photosensitizers containing curcumin derivatives and erythrosine 220 µM. Finally, the antifungal ability of 22 test photosensitizers, Candida albicans (ATCC 10231), were cultured in biofilm form at 37 °C for 48 h, then the colonies were counted in colony-forming units (CFU/mL) via the drop plate technique, and then the log reduction was calculated. The results showed that at 48 h the test photosensitizers could simultaneously produce both ROS types. All test photosensitizers demonstrated no toxicity on the fibroblast cells. In total, 18 test photosensitizers were able to inhibit Candida albicans similarly to nystatin. Conclusively, 20 µM bisdemethoxy curcumin + 220 µM erythrosine + 10% (w/w) nano-titanium dioxide exerted the highest inhibitory effect on Candida albicans.     

A Three‐Component Assembly Promoted by Boronic Acids Delivers a Modular Fluorophore Platform (BASHY Dyes)

The modular assembly of boronic acids with Schiff‐base ligands enabled the construction of innovative fluorescent dyes [boronic acid salicylidenehydrazone (BASHY)] with suitable structural and photophysical properties for live cell bioimaging applications. This reaction enabled the straightforward synthesis (yields up to 99 %) of structurally diverse and photostable dyes that exhibit a polarity‐sensitive green‐to‐yellow emission with high quantum yields of up to 0.6 in nonpolar environments. These dyes displayed a high brightness (up to 54 000 m ^?1 cm^?1). The promising structural and fluorescence properties of BASHY dyes fostered the preparation of non‐cytotoxic, stable, and highly fluorescent poly(lactide‐co‐glycolide) nanoparticles that were effectively internalized by dendritic cells. The dyes were also shown to selectively stain lipid droplets in HeLa cells, without inducing any appreciable cytotoxicity or competing plasma membrane labeling; this confirmed their potential as fluorescent stains.     

Preparation and study of photoswitchable fluorescence nanoparticles based on spirobenzopyran

The preparation and performance characterization of〈50 nm spirobenzopyran-based photochromic nanocomposites with photoswitchable fluorescence are presented.The nanocomposites were fabricated by means of a modifed miniemulsion polymerization process,in which the hydrophobic spirobenzopyran was covalently attached to the polymer chains and the matched fluorescent dyes were noncovalently embedded in the nanoscale cross-linked polymeric matrix,respectively.The obtained nanocomposites with a high relative fluorescence quantum yield（Q）exhibited superior fluorescent photoswitchable performance due to the effective photo-induced intermolecular energy transfer.The stability of photomerocyanine was also improved.     

The first total synthesis of (±)-4-methoxydecanoic acid: a novel antifungal fatty acid

The hitherto unknown (±)-4-methoxydecanoic acid was synthesized in six steps and in 25% overall yield starting from commercially available 4-penten-1-ol. The title compound demonstrated 17-fold higher antifungal activity (MIC = 1.5 mM) against Candida albicans ATCC 60193 and Cryptococcus neoformans ATCC 66031 when compared to unsubstituted n-decanoic acid. Our results demonstrate that mid-chain methoxylation appears to be a viable strategy for increasing the fungitoxicity of fatty acids.     

Synthesis of new fluorescent building blocks via the microwave-assisted annulation reaction of 1,1,2-trimethyl-1H-benzo[e]indole with acrylic acid and its derivatives

The reaction of 1,1,2-trimethyl-1H-benzo[e]indole with acrylic acid and its derivatives was employed for the preparation of novel fluorescent building blocks. Treatment of 1,1,2-trimethyl-1H-benzo[e]indole with acrylic acid, acrylamide or tert-butyl acrylate in an autoclave or a microwave reactor at 180–200 °C afforded benzo[e]pyrido[1,2-a]indole derivatives. Various chemical transformations of the latter compounds have been performed to yield functionalized benzo[e]indole scaffolds. The structure assignments were based on data from ¹H and ¹³C NMR spectroscopy and single crystal X-ray analyses. The optical properties of the obtained benzo[e]indoline derivatives were studied by UV–vis and fluorescence spectroscopy.     

Spectrofluorimetric determination of trace nitrite in food products with a new fluorescent probe 1,3,5,7-tetramethyl-2,6-dicarbethoxy-8-(3',4'-diaminophenyl)-difluoroboradiaza-s-indacene

A new fluorescent probe 1,3,5,7-tetramethyl-2,6-dicarbethoxy-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s-indacene (TMDCDABODIPY) has been developed to detect nitrite in meat products and vegetables. The fluorescence of TMDCDABODIPY is very weak, but when it reacts with nitrite, a strong fluorescent triazole forms in aqueous medium at room temperature, which offers the advantage of specificity and sensitivity for the determination of nitrite. The fluorescence intensity was linear over a nitrite concentration of 9-300 nmol l⁻¹ with a detection limit of 0.21 nmol l⁻¹ (S/N = 3). The proposed method has been used for the determination of trace nitrite in food products with the recoveries of 94.62-105.48%.     

Novel water-soluble fluorescent polymer containing recognition units: Synthesis and interactions with PC12 cell

New water-soluble fluorescent poly(N-vinylpyrrolidone) (PVP) containing carbonylhydrazide recognition units was synthesized by free radical polymerization of N-vinylpyrrolidone in the presence of mercaptoacetic acid as chain transfer agent and then being modified by 1-pyrenebutyric acid hydrazide. FT-IR, ¹H NMR, gel permeation chromatography-multi-angle laser light scattering and fluorescence spectroscopy were used to characterize these polymers. Results of fluorescence measurements show that these polymers have a good affinity for deoxyribonucleic acid (DNA). The interactions with PC12 cell results indicated that the polymer with suitable molecular weight could penetrate into PC12 cell and emit fluorescence. This water-soluble polymer with recognition units and high luminescence can be used as a promising fluorescent probe for measurements of biomacromolecules and cells.     

β-Cyclodextrin derived full-spectrum fluorescent carbon dots: The formation process investigation and biological applications

Carbon dots (CDs), a new building unit, have been revolutionizing the fields of biomedicine, bioimaging, and optoelectronics with their excellent physical, chemical, and biological properties. However, the difficulty of preparing excitation-dependent full-spectrum fluorescent CDs has seriously hindered their further research in fluorescence emission mechanisms and biomedicine. Here, we report full-spectrum fluorescent CDs that exhibit controlled emission changes from purple (380 nm) to red (613 nm) at room temperature by changing the excitation wavelength, and the excitation dependence was closely related to the regulation of sp² and sp³ hybrid carbon structures by β-cyclodextrin-related groups. In addition, by regulating the content of β-cyclodextrin, the optimal quantum yields of full-spectrum fluorescent CDs were 8.97%, 8.35%, 7.90%, 9.69% and 17.4% at the excitation wavelengths of 340, 350, 390, 410 and 540 nm, respectively. Due to their excellent biocompatibility and color tunability, full-spectrum fluorescent CDs emitted bright and steady purple, blue, green, yellow, and red fluorescence in MCF-7 cells. Moreover, we optimized the imaging conditions of CDs and mitochondrial-specific dyes; and realized the mitochondrial-targeted co-localization imaging of purple, blue and green fluorescence. After that, we also explored the effect of full-spectrum fluorescent CDs in vivo fluorescence imaging through the intratumorally, subcutaneously, and caudal vein, and found that full-spectrum fluorescent CDs had good fluorescence imaging ability in vivo.     

Novel long alkyl side chain benzo[a]phenoxazinium chlorides: synthesis, photophysical behaviour and DNA interaction

Several fluorescent benzo[a]phenoxazinium chlorides possessing a propyl-, octyl-, decyl-, dodecyl- or tetradecylamino at the 5-position of the heterocyclic moiety were efficiently synthesised. The absorption and emission maxima of all compounds lie in the range 627-638 nm and 654-678 nm, respectively, with good fluorescence quantum yields. Studies of their photophysical properties in ethanol allowed for the estimation of the acid-base dissociation constant, K_a, revealing an enhancement with the increase in the alkyl side-chain length. It is in the aqueous medium only that the acid form is observed as coexisting with H-aggregates. The solubility markedly decreased when the chain length increased. The residual ethanol (0.2% v/v) used to facilitate the solubilisation of the benzo[a]phenoxazinium dyes allow for the existence of the basic form in an aqueous solution, possibly through preferential solvation. Photophysical studies in the presence of DNA revealed that the compounds with an alkyl side chain of up to eight carbon atoms could intercalate between DNA nucleotides. Moreover, other forms of DNA binding were found to be operative, involving also the basic form of benzo[a]phenoxazinium dyes.     

FTIR characterization of Candida species: a study on some reference strains and pathogenic C. albicans isolates from HIV+ patients

ATR–FTIR has been used together with principal components analysis to study some reference strains belonging to five different Candida species and 20 Candida albicans isolates from three HIV⁺ patients under different fluconazole regimens. The five reference strains were easily differentiated by using first derivative spectra of the carbohydrate region comprising the spectral range 900–1200 cm⁻¹. For the C. albicans clinical isolates, classification obtained by Fourier-transform infrared (FTIR) spectroscopy was compared with data from the genotypic method, PFGE. Results show a good correlation between the two methods for one patient who presented a partially conserved immune system with no previous fluconazole treatment, where all C. albicans strains isolated were susceptible to this antifungal agent. Divergences in the two methods appear for the two immuno-compromised patients receiving long-term fluconazole treatment. It is very probable that such iterative antifungal treatment can cause strong alterations in the yeast cell wall membrane and that the mismatch of the two techniques highlights the complex situation of strain-level identification and differentiation of clinical isolates originating from patients under prolonged treatment.     

Quinolin-2(1H)-one-triazole derived Schiff bases and their Cu(II) and Zn(II) complexes: Possible new therapeutic agents

The condensation of 4-amino-1,2,4-triazole with N-substituted-3-formyl-4-hydroxyquinolin-2-(1H)-one derivatives has lead to the synthesis of a new series of quinolin-2(1H)-one-triazole derived Schiff base ligands (1–3). Cu(II) and Zn(II) complexes (1a–3a and 1b–3b, respectively) of these ligands were also prepared. The complexes were characterised by standard techniques and for two of the complexes X-ray crystallography confirmed that the geometry at the metal centre was octahedral in both cases and that the Schiff base acted as a bidentate ligand coordinating to the metal(II) ion through the deprotonated oxygen and azomethine nitrogen atoms. All of the compounds were investigated for their antimicrobial activities against a fungal strain, Candida albicans, and against Gram-positive and Gram-negative bacteria. The compounds were found to be active against C. albicans but inactive against Staphylococcusaureus and Escherichia coli.