Deposition of gold nanoparticles on β-FeOOH nanorods for detecting melamine in aqueous solution

This study demonstrates a facile but efficient approach to deposit metallic (gold) nanoparticles on β-FeOOH nanorods to obtain Au/β-FeOOH nanocomposites without the assistance of any polymers or surfactants at ambient conditions. In this method, a strong reducing agent (NaBH(4)) can be used to extensively produce Au nanoparticles, converting β-FeOOH into Fe(3)O(4) and depositing gold particles onto magnetic Fe(3)O(4) simultaneously. The microstructure, composition, and chemical properties of the obtained nanocomposites are characterized by various advanced techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-vis spectroscopy. Moreover, the Au/β-FeOOH nanocomposite can be used to detect trace melamine using UV spectrum in the ultraviolet wavelength range (190-260 nm), in which the nanocomposites show a higher sensitivity toward melamine due to the promotion of symmetry-forbidden bands (n→π(*)) of melamine molecules and also avoid the disturbance of commercial products containing solid colloids or food colorings that distort visual spectrum during the detection of chemical sensing. The deposition mechanisms and their sensing detection toward melamine are discussed.     

ω-Thioacetylalkylphosphonium salts: Precursors for the preparation of phosphonium-functionalised gold nanoparticles

Two new ω-thioacetylalkylphosphonium salts that function as masked cationic alkanethiolate ligands for the stabilisation of gold nanoparticles have been prepared. Both (3-thioacetylpropyl)triphenylphosphonium bromide and (6-thioacetylhexyl)triphenylphosphonium bromide were shown to form water-soluble gold nanoparticles of ca. 5-10 nm in size that are stable for up to six months. The related (3-thioacetylpropyl)diphenylphosphine oxide was also prepared but did not act as a stabilising ligand in gold nanoparticle formation.     

β-Cyclodextrin functionalized gold nanoparticles: characterization and its analytical application for l-tyrosine

β-Cyclodextrin functionalized gold nanoparticles (β-CD-Au NPs) were synthesized and characterized. The interaction of β-CD-Au NPs with l-tyrosine (l-Tyr) is studied by fluorescence and absorption spectroscopy. β-CD-Au NPs was found to remarkably quench fluorescence of l-Tyr at 305 nm. Experimental conditions including media acidity, temperature and concentration of buffer were examined for the inclusion formation. Furthermore, fluorescence resonance energy transfer occurred with Föster radius 2.39 nm. Apparent binding constants and corresponding thermodynamic parameters at different temperatures were calculated by Stern–Volmer equation and thermodynamic formula, respectively. The binding constant declines with the increasing temperature illustrating static quenching exists and the binding l-Tyr on β-CD-Au NPs is a spontaneous molecular interaction process in which entropy and Gibbs free energy decreases. Hydrophobic interaction and van der Waals forces could be in dominant action in the formation of the complex. The concentration of l-Tyr is proportional to decrease of the fluorescence intensity in the range of 0.02–1.5 μM with the detection limit (S/N = 3) of 1.6 nM. There is little interference from the coexisting substances normally used as the pharmaceutical main compositions. The proposed method combined the unique physical and chemical properties of the gold core with the molecular recognition ability of β-CD and possessed high sensitivity and good selectivety. It has been successfully applied to determination of l-Tyr in compound amino acid injection.     

Acetyl-BINOL as mimic for chiral β-diketonates: a building block for new modular ligands

α-Acetyl-(S)-BINOL was prepared by ortho-lithiation and subsequent acetylation of acetal-protected (S)-BINOL. The β-hydroxyketone moiety of this compound is herein a structural mimic for a β-diketonate and forms six-membered chelates with transition metal ions. The second hydroxy-function was submitted to esterification with several carboxylic acids bearing another donor function, thus, new tridentate chiral ligands were obtained. Out of this library the l-proline-α-acetyl-(S)-BINOL-ester was identified to be most effective for the titanium-mediated addition of Et₂Zn to PhCHO yielding the respective secondary alcohol with up to 93% ee, which is better than with using (S)-BINOL itself. Besides a solvent dependency (use of MeCN is optimal), the proper choice of the counter-ion is crucial: anion exchange of bromide by trifluoroacetate gave a significant increase of enantioselectivity.     

A new π-acidity scale for several N-donor heterocycles as ligands in neutral gold(III) complexes

A computational DFT approach for the comparison of the π-acceptor character of some N-donor heterocycles L {L = pyridines (py), pyrimidines (pm), imidazoles (im), pyrazoles (pz) and isoxazoles (io)} in neutral AuCl₃L complexes is reported. The electronic properties of these ligands have been tuned by adding methyl and/or trifluoromethyl groups in various positions. Linear relationships between the Mulliken charge of the AuCl₃ fragment in AuCl₃L and the computed proton affinity (PA) of the heterocycle were obtained for all the considered ligands. The different slopes found on changing the N-donor type represent a measure of the π-acidity of these nitrogen ligands once coordinated to AuCl₃, and as a consequence the π-acceptor ability scale pyridines ≈ pyrimidines < imidazoles < pyrazoles ≈ isoxazoles has been derived. Moreover, on the basis of the metal fragment charge variation, a minimum proton affinity value for a meaningful interaction between the ligands and the AuCl₃ fragment has been estimated.     

A highly sensitive and specific enzyme immunoassay for detection of β-amanitin in biological fluids

Polyclonal antisera to -amanitin were generated in sheep and used to construct a competitive ELISA for measurement of the toxin in human serum and urine. The assay had a detection limit of about 80 pg mL^–1, a dynamic range of 80–2,000 pg mL^–1, a cross reactivity of 22% with -amanitin, and no cross reactivities with cyclic peptides from algal sources. Assay responses in buffer, serum, and urine were remarkably similar. Coupling of the toxin to carrier proteins was carried out by previously unreported methods. The key step that allowed the construction of the highly sensitive assay was the introduction of a novel heterologous hapten derivative made of -amanitin-cyanuric chloride derivative. The new derivative overcame the problems of bridge binding that was, in this case, particularly serious with the homologous hapten derivative. The study demonstrated that the developed antiserum and ELISA procedure can be used to detect -amanitin and related toxins from Amanita phalloides in human serum and urine samples from suspected poison cases and enable early treatment to be administered.     

Flow field-flow fractionation: a versatile approach for size characterization of α-tocopherol-induced enlargement of gold nanoparticles

Flow field-flow fractionation (FlFFF) was used for size characterization of gold nanoparticles. The measured particle sizes obtained from FlFFF for the commercial 10 nm gold nanoparticle standard and the gold nanoparticles synthesized in the laboratory were in good agreement with those measured by transmission electron microscopy (TEM). Further, the capability of α-tocopherol to induce enlargement of gold nanoparticles by catalysis of the reduction of AuCl₄⁻ by citrate was observed by monitoring the changes in particle size of gold nanoparticles using FlFFF. The effects of α-tocopherol and incubation time on enlargement of the gold nanoparticles were examined. Higher concentrations of α-tocopherol resulted in larger nanoparticles. At fixed α-tocopherol concentration, larger nanoparticles were formed at longer incubation times.     

An aptamer based assay for the β-adrenergic agonist ractopamine based on aggregation of gold nanoparticles in combination with a molecularly imprinted polymer

A sensitive visual aptamer-based assay is presented for the determination of ractopamine (RAC) in animal feed beef. In the absence of RAC, the aptamer binds to gold nanoparticles (AuNPs) and this prevents the AuNPs to undergo salt-induced aggregation which usually is accompanied by a color change from red to blue. If however, RAC is present, it will bind to the aptamer while the AuNPs remain uncoated so that aggregation and a color change will occur due to salt-induced aggregation. This can be monitored by spectrophotometer or even with bare eyes. Under optimal conditions, the aptasensor exhibits a linear range that covers the 10 to 400 ng.mL￣¹ RAC concentration range. The limit of detection is as low as 10 ng.mL￣¹. In order to further improve selectivity, a RAC-selective molecularly imprinted membrane was prepared and used to pre-extract RAC from complex samples. The combined method (molecularly imprinted membrane and aptasensor) was applied to the determination of RAC in spiked animal feed and beef and gave recoveries that ranged from 72.7 % to 87.3 % for complete feed and from 78.2 % to 86.5 % for beef, respectively.

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Graphical abstract A sensitive visual aptamer-based assay based on aggregation of gold nanoparticles in combination with a molecularly imprinted polymer was developed for the determination of ractopamine (RAC) in animal feed and beef.

     

Effect of pH on phenolphthalein immobilized gold nanoparticles/nanostructures for pH sensing evaluations: sol–gel method

Journal of Sol-Gel Science and Technology - Sol–gel-based phenolphthalein immobilized AuNPs (phph-AuNPs) of different shapes such as spherical, dendrites, and flower are observed by varying...     

Propane Phosphonic Acid Anhydride: A Mild Reagent for β-Lactam Synthesis

The use of propane phosphonic acid anhydride (T3P) as an acid activating reagent was demonstrated in the syntheses of cis β-lactams from the reactions of a glycine Dane salt and various imines.     

Sensitive immunoassay for the β-agonist ractopamine based on glassy carbon electrode modified with gold nanoparticles and multi-walled carbon nanotubes in a film of poly-arginine

We are presenting an electrochemical immunosensor for the determination of the β-agonist and food additive ractopamine. A glassy carbon electrode (GCE) was modified with gold nanoparticles and a film of a composite made from poly(arginine) and multi-walled carbon nanotubes. Antibody against ractopamine was immobilized on the surface of the modified GCE which then was blocked with bovine serum albumin. The assembly of the immunosensor was followed by electrochemical impedance spectroscopy. Results demonstrated that the semicircle diameter increases, indicating that the film formed on the surface hinders electron transfer due to formation of the antibody-antigen complex on the modified electrode. Under optimal conditions, the peak current obtained by differential pulse voltammetry decreases linearly with increasing ractopamine concentrations in the 0.1 nmol•L⁻¹ to 1 μmol•L⁻¹ concentration range. The lower detection limit is 0.1 nmol•L⁻¹. The sensor displays good stability and reproducibility. The method was applied to the analysis of spiked swine feed samples and gave satisfactory results.

Immunoassay for ractopamine based on glassy carbon electrode modified with gold nanoparticles and a film of a composite made from poly (arginine) and multi-walled carbon nanotubes was proposed. Under optimal conditions, the peak currents obtained by differential pulse voltammetry decreases linearly with increasing ractopamine concentrations in the 0.1 nmol•L⁻¹ to 1 μmol•L⁻¹ concentration range. The detection limit is 0.1 nmol•L⁻¹.

     

A model for the enzyme-catalyzed,coenzyme B12-dependent interconversion of β-methylaspartate with glutamate

A novel rearrangement promoted by vitamin B_12s of diethyl 1-keto-2-bromomethyl-2-methylsuccinate 10 to diethyl 4-methyl-2-ketoglutarate 11 has been discovered. This can serve as a partial model for the coenzyme B₁₂ dependent enzyme catalyzed interconversion of β-methylaspartate and glutamate. The Schiff base corresponding to 10 does not react with vitamin B_12s , but it does rearrange readily under free radical conditions when treated with tri-n-butyltin hydride.     

Novel aerosol detection platform for SARS‑CoV‑2: Based on specific magnetic nanoparticles adsorption sampling and digital droplet PCR detection

The SARS?CoV?2 virus is released from an infectious source (such as a sick person) and adsorbed on aerosols, which can form pathogenic microorganism aerosols, which can affect human health through airborne transmission. Efficient sampling and accurate detection of microorganisms in aerosols are the premise and basis for studying their properties and evaluating their hazard. In this study, we built a set of sub-micron aerosol detection platform, and carried out a simulation experiment on the SARS?CoV?2 aerosol in the air by wet-wall cyclone combined with immunomagnetic nanoparticle adsorption sampling and ddPCR. The feasibility of the system in aerosol detection was verified, and the influencing factors in the detection process were experimentally tested. As a result, the sampling efficiency was 29.77%, and extraction efficiency was 98.57%. The minimum detection limit per unit volume of aerosols was 250 copies (10² copies/mL, concentration factor 2.5).     

Deaggregation of long chain alkyl β-naphthoic acid ester with β-CD and α-CD: A mimic way to remove excessive fat from fatty liver

The deaggregating ability of β-CD and α-CD against the aggregated n-hexadecyl β-naphthoate (A16) and n-dodecyl β-naphthoate (A12) depended not only on the aggregating tendency of A16 and A12 but also on the initial concentration of the aggregated A16 or A12. The inclusive ability of β-CD with the substrates is greater than that of α-CD under hydrophobic lipophilie interaction.     

Sulfinates as Nucleophiles for the Ring-Opening of Epoxides: A Convenient Route to β-Hydroxysulfones

It has been found that the nucleophilic ring-opening of epoxides by arenesulfinates, in the presence of magnesium nitrate as a Lewis acid catalyst, provides a preparatively useful, convenient route to β-hydroxysulfones.     

Carbon nanotubes-supported palladium nanoparticles for the Suzuki reaction in supercritical carbon dioxide: A facile method for the synthesis of tetrasubstituted olefins

A facile and efficient method for the synthesis of tetrasubstituted olefins in supercritical carbon dioxide was developed by using carbon nanotubes-supported palladium nanoparticles (Pd/CNTs) as the catalyst. Compared with common Pd/C, Pd/CNTs could more effectively catalyze the reaction of dibromo-substituted olefins with boronic acids, affording the corresponding tetrasubstituted olefins with moderate to good yields. This environmentally benign route with an easy-to-handle catalyst provides an appealing alternative to the currently available methods.     

A new strategy for the preparation of heterocyclic β-amino esters: orthogonally protected β-amino esters with a piperidine skeleton

A simple strategy is presented for the introduction of a nitrogen atom into the carbocycle of an aminocyclopentenecarboxylic ester via dihydroxylation of the olefinic bond, followed by NaIO₄-mediated cleavage of the diol intermediate and ring expansion, resulting in new regioisomeric 3-amino-4-piperidinecarboxylic acid derivatives. This method permits the preparation of amino esters with a piperidine skeleton in enantiomerically pure form.     

Microfluidic device generating stable concentration gradients for long term cell culture: application to Wnt3a regulation of β-catenin signaling

In developing tissues, proteins and signaling molecules present themselves in the form of concentration gradients, which determine the fate specification and behavior of the sensing cells. To mimic these conditions in vitro, we developed a microfluidic device designed to generate stable concentration gradients at low hydrodynamic shear and allowing long term culture of adhering cells. The gradient forms in a culture space between two parallel laminar flow streams of culture medium at two different concentrations of a given morphogen. The exact algorithm for defining the concentration gradients was established with the aid of mathematical modeling of flow and mass transport. Wnt3a regulation of β-catenin signaling was chosen as a case study. The highly conserved Wnt-activated β-catenin pathway plays major roles in embryonic development, stem cell proliferation and differentiation. Wnt3a stimulates the activity of β-catenin pathway, leading to translocation of β-catenin to the nucleus where it activates a series of target genes. We cultured A375 cells stably expressing a Wnt/β-catenin reporter driving the expression of Venus, pBARVS, inside the microfluidic device. The extent to which the β-catenin pathway was activated in response to a gradient of Wnt3a was assessed in real time using the BARVS reporter gene. On a single cell level, the β-catenin signaling was proportionate to the concentration gradient of Wnt3a; we thus propose that the modulation of Wnt3a gradients in real time can provide new insights into the dynamics of β-catenin pathway, under conditions that replicate some aspects of the actual cell-tissue milieu. Our device thus offers a highly controllable platform for exploring the effects of concentration gradients on cultured cells.