Gold nanorod separation and characterization by asymmetric-flow field flow fractionation with UV–Vis detection

The application of asymmetric-flow field flow fractionation (A4F) for low aspect ratio gold nanorod (GNR) fractionation and characterization was comprehensively investigated. We report on two novel aspects of this application. The first addresses the analytical challenge involved in the fractionation of positively charged nanoparticles by A4F, due to the interaction that exists between the negatively charged native membrane and the analyte. We show that the mobile phase composition is a critical parameter for controlling fractionation and mitigating the membrane-analyte interaction. A mixture of ammonium nitrate and cetyl trimethyl ammonium bromide at different molar ratios enables separation of GNRs with high recovery. The second aspect is the demonstration of shape-based separation of GNRs in A4F normal mode elution (i.e., Brownian mode). We show that the elution of GNRs is due both to aspect ratio and a steric-entropic contribution for GNRs with the same diameter. This latter effect can be explained by their orientation vector inside the A4F channel. Our experimental results demonstrate the relevance of the theory described by Beckett and Giddings for non-spherical fractionation (Beckett and Giddings, J Colloid and Interface Sci 186(1):53–59, 1997). However, it is shown that this theory has its limit in the case of complex GNR mixtures, and that shape (i.e., aspect ratio) is the principal material parameter controlling elution of GNRs in A4F; the apparent translational diffusion coefficient of GNRs increases with aspect ratio. Finally, the performance of the methodology developed in this work is evaluated by the fractionation and characterization of individual components from a mixture of GNR aspect ratios.     

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.     

Formation of cooperative amidoaminocalixresorcinarene – methotrexate nanosized aggregates in an aqueous solution and on the surface of gold nanoparticles

Cooperative nanoscale associates of amido(dimethylamino) calixresorcinarenes with pentyl (C5) and undecyl (C11) substituents on lower rim with antitumor drug-methotrexate (MTX) in aqueous solution and on the surface of gold nanoparticles C5@Au and C11@Au were formed. The formation of nanoparticles was investigated by ¹H NMR, NMR FT-PGSE, 2D NOESY, DLS, TEM, spectrophotometry, fluorimetry. It was found that during the interaction of C5 or C11 macrocycles with MTX in aqueous solution, the latter generates dissociation of macrocycles self-associates with formation of cooperative macrocycle–MTX associates of smaller size due to multiple non-covalent interactions, which leads to increase in fluorescence intensity of MTX. In contrast, binding of MTX by macrocyclic associates preorganized as bilayer on surface of gold nanoparticles through electrostatic interactions induces aggregation of C5@Au-MTX or C11@Au-MTX associates, which results in quenching of MTX fluorescence in solution. Such particles have possible potential in the field of binding and delivery of antitumor drugs.     

Modification of composites of block copolymers–gold nanoparticles with enzymes and their characterization by electrochemical techniques

In this work, the poly(styrene-vynil pyridine) block copolymer was used as a porous pattern to study the electrodeposition of gold inside the pores, as a new method to obtain gold nanoparticles. The porous pattern left by the copolymer film onto a conductive glass surface was characterized by atomic force microscopy (AFM), evidencing pores of 30 nm diameter. After the electrodeposition, 30 nm diameter gold nanoparticles were obtained and they were characterized by cyclic voltammetry (CV) and AFM, and then used to study the adsorption of glucose oxidase enzyme. The adsorption process of glucose oxidase on gold nanowires was investigated by CV and electrochemical impedance spectroscopy. The morphological and capacitance results indicate that the block copolymer–gold nanoparticle composite seems to be a good candidate to design biosensors and immunosensors.     

Inclusion complexes of Sulconazole with β-cyclodextrin and hydroxypropyl β-cyclodextrin: characterization in aqueous solution and in solid state

Complexation between sulconazole (SULC), an imidazole derivative with in vitro antifungal and antiyeast activity, and β-cyclodextrins (β-CD and HP-β-CD) was studied in solution and in solid states. Complexation in solution was evaluated using solubility studies and nuclear magnetic resonance spectroscopy (¹H-NMR). In the solid state, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and RX diffraction studies were used. Solubility studies suggested the existence of inclusion complex between SULC and β-CD or HP-β-CD. ¹H-NMR spectroscopy studies showed that the complex formed occurs by complexation of imidazole ring into inner cavity. DSC studies showed the existence of a complex of SULC with β-CD. The TGA and RX studies confirmed the DSC results of the complex. Solubility of SULC in solid complexes was studied by the dissolution method and it was found to be much more soluble than the uncomplexed drug.     

Colloidal transport of uranium in soil: Size fractionation and characterization by field-flow fractionation–multi-detection

The aim of this study was to characterize colloids associated with uranium by using an on-line fractionation/multi-detection technique based on asymmetrical flow field-flow fractionation (As-Fl-FFF) hyphenated with UV detector, multi angle laser light scattering (MALLS) and inductively coupling plasma-mass spectrometry (ICP-MS). Moreover, thanks to the As-Fl-FFF, the different colloidal fractions were collected and characterized by a total organic carbon analyzer (TOC). Thus it is possible to determine the nature (organic or inorganic colloids), molar mass, size (gyration and hydrodynamic radii) and quantitative uranium distribution over the whole colloidal phase. In the case of the site studied, two populations are highlighted. The first population corresponds to humic-like substances with a molar mass of (1500 ± 300) g mol⁻¹ and a hydrodynamic diameter of (2.0 ± 0.2) nm. The second one has been identified as a mix of carbonated nanoparticles or clays with organic particles (aggregates and/or coating of the inorganic particles) with a size range hydrodynamic diameter between 30 and 450 nm. Each population is implied in the colloidal transport of uranium: maximum 1% of the uranium content in soil leachate is transported by the colloids in the site studied, according to the depth in the soil. Indeed, humic substances are the main responsible of this transport in sub-surface conditions whereas nanoparticles drive the phenomenon in depth conditions.     

Transformations of methyl orange dimers in aqueous–acid solutions,according to UV–Vis spectroscopy data

The effect acidity has on the UV–Vis absorption spectra of azo dye methyl orange (MOD) in aqueous solutions of hydrochloric acid in the pH range of 1.7 to 7 and sulfuric acid in the 0.24 to 18 mol/L range of concentrations is investigated. The spectral transformations of MOD solutions are compared to the corresponding spectral transformations of solutions of dimethylaminoazobenzene (DAB), which is an azo dye akin to MOD. A close resemblance between the spectral transformations of MOD and dimers DAB₂ is revealed. It is concluded that the ground state of MOD, like the ground state of DAB, consists of not individual molecules but of supramolecular dimers MOD₂. It is found that dimers MOD₂ in aqueous low-acidic solutions are reversibly protonated with the formation of di- and triprotonated forms, which reversibly dissociate into diprotonated monomers upon an increase in acidity. The structural formulas of the chromogenic groups responsible for the spectral transformations, and the mechanisms of their reversible transformations, are given.     

Colorimetric detection of cadmium in water using L-cysteine Functionalized gold–silver nanoparticles

Abstract

A new simple colorimetric assay was developed for the selective and sensitive detection of cadmium (II) in water samples using L-cysteine functionalized gold–silver nanoparticles. The gold–silver nanoparticles were synthesized by reducing HAuCl₄ and AgNO₃ in aqueous medium and were further functionalized with L-cysteine. The formation of homogeneous gold–silver nanoparticles was characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, particle size distribution, and ultraviolet–visible absorption methods. In the presence of cadmium (II), the aggregation of functionalized gold–silver nanoparticles caused by the interaction between cadmium (II) and L-cysteine resulted in a naked-eye visible color change of L-cysteine functionalized gold–silver nanoparticles from orange–yellow to green, which can be monitored by a simple ultraviolet–visible spectrophotometer. Under the optimal conditions, the absorbance ratio at 600–435?nm (A₆₀₀/A₄₃₅) was linear to the concentration of cadmium (II) from 0.4 to 38.6?μM, and the limit of detection of cadmium (II) was 44?nM. Interference measurements showed that the method exhibited good selectivity. The proposed method was successfully applied to the determination of cadmium (II) in environmental water samples. The results indicated that this simple, selective, and sensitive sensing system has good potential for practical applications.     

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.     

Preparation and characterization of supported bimetallic gold–iron nanoparticles,and its potential for heterogeneous catalysis

Research on Chemical Intermediates - Bimetallic gold–iron catalysts supported on ZrO2 and TiO2 were prepared by under potential deposition. The characterization of the catalysts was performed...     

Inclusion complexes of 5-flucytosine with β-cyclodextrin and hydroxypropyl-β-cyclodextrin: characterization in aqueous solution and in solid state

Complexation between 5-flucytosine (5-FC), a cytosine analogue with in vitro antifungal and antiyeast activity, and β-cyclodextrins (β-cyclodextrin and hydroxypropyl-β-cyclodextrin) was studied in solution and in solid states. Complexation in solution was evaluated using solubility studies, UV–vis and ¹H-NMR. In the solid state, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), FT-IR and X-ray diffraction studies were used. UV–vis, FT-IR and ¹H-NMR spectroscopy studies showed that the complex formed occurs by complexation of piridinique base analogue into inner cavity. DSC studies showed the existence of a complex of 5-FC with β-CDs. X-ray studies confirmed the DSC results of the complex existence. Solubility studies showed that the complexed drug is forty times more soluble than free 5-FC, indicating the obtained systems as future, promising drug carriers.     

Rapid and sensitive method for the determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with UV–Vis detection

A high-performance liquid chromatography (HPLC) method for the determination of acetaldehyde in fuel ethanol was developed. Acetaldehyde was derivatized with 0.900 mL 2,4-dinitrophenylhydrazine (DNPHi) reagent and 50 L phosphoric acid 1 mol L^–1 at a controlled room temperature of 15°C for 20 min. The separation of acetaldehyde-DNPH (ADNPH) was carried out on a Shimadzu Shim-pack C₁₈ column, using methanol/LiCl_(aq) 1.0 mM (80/20, v/v) as a mobile phase under isocratic elution and UV–Vis detection at 365 nm. The standard curve of ADNPH was linear in the range 3–300 mg L^–1 per injection (20 L) and the limit of detection (LOD) for acetaldehyde was 2.03 g L^–1, with a correlation coefficient greater than 0.999 and a precision (relative standard deviation, RSD) of 5.6% (n=5). Recovery studies were performed by fortifying fuel samples with acetaldehyde at various concentrations and the results were in the range 98.7–102%, with a coefficient of variation (CV) from 0.2% to 7.2%. Several fuel samples collected from various gas stations were analyzed and the method was successfully applied to the analysis of acetaldehyde in fuel ethanol samples.     

Solvothermal preparation,and characterization,of Cu–Ag nanoparticles

Cu–Ag nanoparticles have been successfully synthesized by one-pot solvothermal treatment of a mixture of AgNO₃ and Cu(OAc)₂·H₂O in ethylene glycol solution at 180 °C for 10 h. The samples were characterized by UV–visible absorption, X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). The results showed that Cu–Ag nanoparticles and a small amount of phase-separated Cu–Ag alloy nanoparticles with an average diameter of 100 ± 30 nm were synthesized by the solvothermal treatment procedure. The mechanism of formation is discussed.     

Electrodeposition of polypyrrole–Au nanoparticles composite from one solution containing gold salt and monomer

An easy method of preparation of polymer/metal–nanoparticle composites is reported. KAu(CN)₂ and pyrrole do not react (redox reaction) in solutions of moderate pH. The gold complex, due to its inertness, is stable in the presence of 10 μM CN^? for weeks. Therefore the electrodeposition of controlled amounts of polypyrrole and Au nanoparticles on the graphite surface can be done in one solution by applying a sequence of 0.75 and ? 1.6 V potentials. Pulse deposition of both components leads to substantial improvement of the layer smoothness and homogenous distribution of Au nanocrystallites.     

4-Aminothiophenol functionalized gold nanoparticles as colorimetric sensors for the detection of cobalt using UV–Visible spectrometry

The 4-aminothiophenol functionalized gold nanoparticles (4-ATP-Au NPs) were used as colorimetric sensors for the detection of Co²⁺ in aqueous solution by using UV–Visible spectrometry. The 4-ATP-Au NPs were characterized by UV–Visible, FT-IR, TEM and dynamic light scattering (DLS) which confirmed their higher binding affinity towards Co²⁺ through coordinate covalent interactions that can be observed with the naked eye. The absorbance ratio (A₅₇₀/A₅₂₃) was linear with Co²⁺ concentration in the range of 15 × 10^?3 to 1 × 10^?3 M with a correlation coefficient of (R ²) 0.994, and the limit of detection was 5.79 × 10^?5 M.     

Preparation and characterization of acrylic polymer–nanogold nanocomposites from 3-mercaptopropyltrimethoxysilane encapsulated gold nanoparticles

In this study, acrylic polymer–nanogold nanocomposites and their cast films were prepared from an acrylic copolymer and 3-mercaptopropyltrimethoxysilane (MPS) stabilized gold nanoparticles by a sol–gel reaction. The acrylic copolymer was synthesized from methyl methacrylate (MMA) and 3-(trimethoxysilyl)propyl methacrylate (MSMA). The Si–OMe groups of MPS on the surface of gold nanoparticles (MPS–Au) provided the further reaction with the same groups of MSMA, hence the covalent bonds between polymers and MPS–Au nanoparticles were formed. FE-SEM images show MPS–Au nanoparticles are dispersed well in the prepared nanocomposites, and no large aggregation is occurred. TGA results indicate that the decomposed temperatures (T_d) of low Au-content (0.1 wt.%) nanocomposites are higher than these of the acrylic copolymer and high Au-content (1.0 wt.%) nanocomposites. The temperature of maximum decomposed rate (T_p) of each prepared nanocomposite is higher than that of the acrylic copolymer. The hardness of the cast film increases with increasing the Au content. The results show the improved thermal stability and application potentials of the prepared acrylic polymer–nanogold nanocomposites.     

Cross-linking mechanisms of arginine and lysine with α,β-dicarbonyl compounds in aqueous solution

Cross-linking in proteins by α,β-dicarbonyl compounds is one of the most damaging consequences of reactive carbonyl species in vivo and in foodstuffs. In this article we investigate computationally the cross-linking of glyoxal and methylglyoxal with lysine and arginine residues using density functional theory and the wB97XD dispersion-corrected functional. Five pathways, A-E, have been characterized. In pathways A and B, the reaction proceeds via formation of the Schiff base, aldimine, followed by addition of arginine. In contrast, in pathways C-E, direct addition of arginine to the dicarbonyl compounds occurs first, leading to a dihydroxyimidazolidine intermediate, which then reacts with lysine after dehydration and proton transfer reactions. The results reveal that pathways A, C, and E are competitive whereas reactions via pathways B and D are much less favorable. Inclusion of up to five explicit water molecules in the proton transfer and dehydration steps is found to lower the energy barriers in the feasible pathways by about 5-20 kcal/mol. Comparison of the mechanisms of methylglyoxal-derived imidazolium cross-linking (MODIC) and glyoxal-derived imidazolium cross-linking (GODIC) shows that the activation barriers are lower for GODIC than MODIC, in agreement with experimental observations.     

Micro-funnel magnetic stirring-assisted liquid–liquid microextraction technique combined with UV–Vis spectrophotometry for determination of thorium in aqueous samples with the aid of experimental design

Journal of Radioanalytical and Nuclear Chemistry - In this study, trace amounts of thorium ions were extracted using a highly sensitive, selective, rapid and simple micro-funnel magnetic...     

Thermodynamics of interaction of L-α-phenylalanine with urea and dimethylformamide in aqueous solution

The thermal effects of solution of L-phenylalanine in aqueous solutions of urea and dimethylformamide (DMF) at 25°C were determined. The solubility of L-phenylalanine in water and aqueous DMF solutions was measured. The standard enthalpies, free energies, and entropies of solution of the amino acid in aqueous solutions of amides were calculated. The parameters of pair and ternary amino acid-amide interactions were determined within the framework of the McMillan-Mayer theory. The amino acid-amide pair interaction is accompanied by a decrease in the Gibbs free energy, controlled by the entropy term with DMF and by the enthalpy term with urea. The interaction of L-phenylalanine with two amide molecules is repulsive, which in the case of DMF leads to an increase in the standard free energies of solution of the amino acid at the amide mole fraction X ₂ > 0.05.