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Square-wave adsorptive stripping voltammetry (SWAdSV) was used to determine iron in ethanol and biodiesel using a bismuth-film electrode (BiFE) prepared onto the surface of a glassy carbon electrode (GCE) by electrochemical deposition to promote the reduction of Fe (III) previously complexed with 1-(2-pyridylazo)-2-naphthol (PAN) directly in the electrochemical cell. The supporting electrolyte was composed by mixture of acetate buffer (0.1 mol L−1, pH 4.5) and ethanol (40/60% v/v) into which 500 µL of a 0.1 mmol L−1 stock solution of PAN was added as complexing agent. The Fe (III)-PAN complex presented a well-defined current peak at −0.7 V. For biodiesel, a treatment with tetramethylammonium hydroxide (TMAH) was proposed as an efficient mean to minimized matrix interferences. A limit of detection of 6.0 × 10−8 mol L−1 (0.06 µmol L−1) and limit of quantification of 2.0 × 10−7 mol L−1 (0.2 µmol L−1) were obtained for Fe(III). Under the optimized conditions, there were no significant interferences from Cu(II), Al(III), Mn(II), Cr(III), Cd(II), Zn(II) and Ni(II) and Pb(II) while Ni(II) interfered significantly. The analytical curves produced linear responses with equations I (µA) = (-1.315 × 10−7 ± 5.158 × 10−8) + (-0.238 ± 0.01) [Fe (III)] (µmol L−1), R2 = 0.992 and I (µA) = (-6.836 × 10−7 ± 1.124 × 10−8) + (-0.408 ± 0.013) [Fe (III)] (µmol L−1), R2=0.998 for pure ethanol and biodiesel, respectively. The method produced satisfactory results in quantifying original quantities of Fe(III) in fuel ethanol (5.65 ± 0.71 µmol L−1) and biodiesel (1.28 ± 0.25 µmol L−1) at a 95% confidence limit (n = 3).

Herbal teas and yerba mate infusions are an important part of the human diet that may contain toxic contaminants due to the industrial processing of the herbal material. The presence of the lipophilic compounds polycyclic aromatic hydrocarbons (PAHs) was investigated in dry yerba mate samples and how they transfer into the infusions. Samples were selected among eight different brands, and three types of yerba mate products (aged, green, and roasted). Synchronized fluorescence scanning (SFS) was used as primary screening method for PAHs in dried yerba mate, and high-performance liquid chromatography with fluorescence detection for the analysis of the infusions. SFS screening showed presence of PAHs in the dry herbal material, and the PAHs ratios suggest that the contamination originates from pyrogenic sources. Using an experimental setup to simulate the traditional yerba mate consumption (successive extractions with small amounts of water), the sum of the six PAHs in each infusion of yerba mate sample ranged from 4.8 to 30.2 ng g−1. Benzo [a] pyrene concentration ranged from n.d. to 1.1 ng g−1 while phenanthrene reached a maximum of 59 ng g −1 in the yerba mate samples tested. An estimated 0.11% to 0.54% of the six PAH analytes were transferred into the infusion and the SFS method can be used to screen the presence of PAHs in the dry material. The chemical profile of the most abundant PAHs found in the infusions indicate a low total equivalent exposure index.

Graphene quantum dots (GQDs) have been of high interest due to their size and optical characteristics, which improves when functional groups are added to their borders and defects. In this work, th...

A low-temperature sintering process was used to produce pellets at different temperatures using TiO2 anatase (Vetec) and P25 (Evonik) commercial powders. The initial powder was mixed with 75% acetic acid aqueous solution and pressed under 375 MPa. The temperature was applied after the pelletization in a conventional furnace for 4 hours. The best sintering temperature for anatase was 800°C, which is higher than typical cold sintering temperatures but below conventional ones. However, the optimal temperature was 450 °C for P25 due to its density and SEM results. The sintered pellets' maximum densities were 70% (anatase, 800oC) and 66% (P25, 450oC). It was not possible to measure the anatase pellets treated under 800oC because they disintegrated in water. This work studied the effects of the applied pressure, solvent concentration, particle size, and sintering temperature on the properties of sintered pellets, such as integrity, density, and presence of porous. It also evaluated the electrochemical activity measured by cyclic voltammetry (CV), which indicated that the sintered TiO2 pellets are porous with a partial capacitive response.

The result of a chemical measurement is consequence of a set of steps that begins with sample selection. The aim of this study was to evaluate the relative importance of the sampling in overall measurement uncertainty, taking as study case physicochemical measurements of diesel. The empirical method used was by duplicates, and the treatment of data sets was performed by four different statistical techniques: classic analysis of variance, robust analysis of variance and two different Range Statistics models. The choice must be backed by previous evaluation of data set in terms of normality, independence, presence of outliers and homogeneity of variance. It was found that Range Statistics produced most reliable results under different premises and for the variety of physicochemical parameters evaluated. Robust analysis of variance failed indicates proper influence of sampling even it is a test designed to work under the lack of some of the proper premises.

Mercury speciation was achieved using a nanocomposite, consisting of graphene quantum dots (GQDs) and TiO2 nanoparticles, to mediate photo-degradation of mercurial species into the Hg cold vapor detected by atomic spectrometry. Sample solution (containing Hg2+, CH3CH2Hg, and CH3Hg at hundreds of ng L−1) was placed in quartz tube containing formic acid solution (2% v/v) and microliter aliquot of GQDs/TiO2 nanocomposite dispersion (0.6 mg of nanocomposite). The tube was placed inside a photochemical reactor then, adapted to the mercury-dedicated spectrometer. Quantitative speciation was achieved taking advantage of the differences in UV photodegradation kinetics: Hg2+ (5 min), CH3CH2Hg (9 min) and CH3Hg (13 min). Gas-chromatography cold vapor atomic fluorescence spectrometry was used to confirm the evolution of the reactions over time during photo-reaction. The limits of detection were 10 ng L−1 for CH3CH2Hg and 7 ng L−1 for Hg2+ and CH3Hg.

An analytical method for the determination of 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone (INHHQ) is reported for the first time. The electrochemical method involving INHHQ was perf...

A high-performance chromatographic method was developed to determine the fungicide kresoxim-methyl. Off-line photochemical derivatization was used to induce the formation of a stable and fluorescen...

Two fluorescent D-A-D styryl-benzothiadiazole fluorophores possessing either styryl-BTD-styryl (2) or aryl-BTD-styryl (4) architectures have been synthesized using Heck reactions as key step. Compounds presented absorption in blue region and emission ranging from 531 to 560 nm with positive solvatochromism. Lippert Mattaga plots indicated a substantial effect of solvent polarity over the emission profile. As the fluorescence of the compound 4 was more sensitive to changes in the environment, this compound was evaluated as a probe to chemosensing etanol/water percentage in hydroalcoholic solutions. Good linearity was observed between fluorescence intensity and ethanol content in the range from 40% to 90%. Analyses of commercial solutions of sanitizers and cleaning products (%

Methods to determine Al and Si in both fuel oils and crude oils by X-ray fluorescence (XRF) spectrometry were developed. Since interference from the sample matrix was found critical in direct analysis of liquid samples, determinations were performed on samples as thin films deposited onto a solid substrate (filter paper). Quantification using the analytical curve, prepared with organic standards, was found to be adequate to determine the analytes in fuel oils by energy dispersive (ED) XRF, with limit of detection (LOD) of 1.6 µg g−1 (Al) and 1.2 µg g−1 (Si). In crude oils, Al and Si could only be successfully determined by EDXRF after ashing and fusion of samples with Li2B4O7 (following sample preparation reported in the ASTM D5184 ), providing samples in aqueous solutions that required matrix-matched calibration (inorganic standards in solution containing Li2B4O7 and placed onto solid substrates) for quantification, leading to LOD of 1.3 µg g−1 (Al) and 0.7 µg g−1 (Si). Direct analyzes of crude oils onto solid substrates, after only a dilution with tetrahydrofuran (THF), were only possible by wavelength dispersive (WD) XRF, which provides selectivity and sensibility enough to determine the original Al (LOD 0.5 µg g−1) and Si (LOD 0.3 µg g−1) in real samples using matrix matched standards made with white clay certified material dispersed in mineral oil diluted in THF.

Mercury speciation analysis in produced water (PW) was achieved by optical multipath cold vapor atomic absorption spectrometry. One sample aliquot was treated with SnCl2, producing Hg0 that was carried out to the optical detection cell to be determined. Another aliquot was exposed to UV, promoting oxidation of CH3Hg+ to Hg2+, and then determined after chemical reduction with SnCl2. The CH3Hg+ content was the difference of the results achieved for both aliquots. Matrix effects imposed by oil and salt were studied and although intensity of the mercury time profile was affected, quantification was successfully achieved by using matrix-matched standards containing adjusted NaCl and total oil content. Both conductivity (to estimate salt content) and turbidimetry (to estimate oil content) measurements were made for the PW samples in order to adjust sample to the matrix matched standards. Analyte addition was also used and limit of quantification was 12 ng L−1 with satisfactory recoveries for both Hg2+ and CH3Hg+.

Batch-injection analysis (BIA) with amperometric detection, using a boron-doped diamond (BDD) electrode, was developed for the determination of gentamicin sulfate (total components). System was operated at +2000 mV with acetate buffer (1.0 × 10−2 mol L−1; pH 4.40) as supporting electrolyte. Oxidation of analyte occurred right after the analyte solution plug (60 μL) reaches the surface of the electrode. Solid-phase extraction, using a cartridge packed with a kanamycin-imprinted polymer, was used to improve selectivity in determinations. The instrumental precision was

Photochemical derivatization (at 253 nm) of varenicline in alkaline medium (in NaOH 0.64 mol L−1) was successfully achieved aiming to induce strong fluorescence for quantitative purposes. The intense fluorescence from the produced photo-derivative covered a linear range of three orders of magnitude (10−8–10−6 mol L−1 range) allowing the spectrofluorimetric determination of the analyte in pharmaceutical formulations. For urine, the UV exposed sample was analyzed by high-performance liquid chromatography using borate buffer (0.01 mol L−1, pH 10.0). Separations were made using a C18 column with borate buffer (0.01 mol L−1, pH 10)/methanol (30:70% v/v) in isocratic elution. Detection limit was 2.5 × 10−7 mol L−1 for determination using HPLC. Measurement uncertainty was estimated and both methods were applied for the determination of varenicline in a pharmaceutical preparation and urine samples with acceptable recoveries using no expensive and toxic derivatization dyes.

Made available in DSpace on 2021-06-25T11:21:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-10-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The layered structure of hydrotalcite-like compounds is responsible for many chemical and physical properties attractive in designing electrodes for analytical applications. Mg/Al hydrotalcite-like materials were prepared with different Mg/Al molar ratios ranging from 1.5:1 to 6:1 and electrochemically characterized before being included into epoxy-graphite to form the electrode matrix. The electrochemical response of the electrodes was evaluated by the use of potassium ferro/ferricyanide redox pair as a probe for voltammetry and impedance spectroscopy. The electm-catalytic effect on the potassium ferm/ferricyanide redox pair showed was more effective when Mg and Al is 1.5:/1 M proportion due, apparently, to the more positively charged hydrotalcite layers and more affinity for anions such as Fe(CN)(6)(3-/4-). This epoxy-graphite-hydrotalcite composite presents the lowest potential difference and lowest loading transfer resistance associated with the hydrotalcite phase, which are desirable properties for potential electroanalytical purposes. The results indicated the potential application of the epoxy-graphite-hydrotalcite electrode for ion exchange of negative-charged chemical species. Univ Havana, Dept Analyt Chem, Havana, Cuba Sao Paulo State Univ, Dept Analyt Chem, Sao Paulo, SP, Brazil Pontificia Univ Catolica Rio de Janeiro, Dept Chem, Rio De Janeiro, RJ, Brazil Univ Estado Rio De Janeiro, Dept Mech Engn & Energy, Rio De Janeiro, RJ, Brazil Sao Paulo State Univ, Dept Analyt Chem, Sao Paulo, SP, Brazil CAPES: 213/14 FAPERJ: E-26/202.912/2017 CNPq: 409090/2018-2 CNPq: 303866/2017-9

This work presents the development of a new electrochemical method for the indirect determination of atorvastatin (ATO) using Pb2+ as a probe at a potential value of -0.40 V. The square-wave voltammetric parameters such as the frequency (50 Hz), amplitude (100 mV) and step size (2 mV) were adjusted to obtain the most symmetrical and intense probe peak. The influences of pH (2.0), background electrolyte composition (HNO3), and probe concentration (250 μmol L−1) were studied in order to achieve highest signal attenuation. The signal suppression mechanism was investigated, indicating that it occurs due to the adsorption of atorvastatin and its oxidation products on the working electrode surface competing with the probe deposition. This suppression approach enhanced the analytical signal by a factor of 100 times when compared to the atorvastatin signal monitoring, leading the optimized method to a limit of quantification (LOQ) of 0.41 μmol L−1 with the linear response up to 2.85 μmol L−1. The repeatability was determined to be 2.95% (n = 10) and the method showed selectivity against other statins (rosuvastatin and pravastatin). As a proof of concept, atorvastatin was determined in a pharmaceutical formulation sample, with a satisfactory recovery of 100.3 ± 3.2%.

Flavonoids (biologically relevant hydroxyphenols) are natural antioxidants. Analytical sensing of flavonoids using quantum dots (QDs) is a result of the electron-withdrawing properties of carbonyl and hydroxyl groups in flavonoid structure that promotes effective photoluminescence quenching of QDs. In this article, the influence of a cationic surfactant organized media on interactions between five flavonoids (i.e. flavone, 3-hydroxyflavone, 5-hydroxyflavone, 7-hydroxyflavone and quercetin) and 3MPA-CdTe quantum dots (QDs) was studied. Investigation was based on results achieved by photoluminescence and electronic absorption spectroscopies, complemented by electrophoretic mobility and conductivity studies. The results showed that quercetin produces significant photoluminescence quenching of QDs in water, compared to the response in the presence of either flavone or the single-hydroxylated flavones, likely due to the increased hydrophilicity of the former. In contrast, in aqueous media containing cationic surfactant cetytrimethylammonium bromide (CTAB), interactions are modulated by solubilization of flavonoids in the microenvironments with different polarity of surfactant aggregates around the QDs. The results suggest that the photoluminescence response of 3MPA-CdTe QDs is related not only to the chemical structure of the flavonoids, but also to the nature of environment surrounding the dispersed particles.

The synthesis of a phenoxy-benzothiadiazole (BTD) derivative is reported for the first time. This derivative was employed as an intermediate in the obtention of two novel highly fluorescent aryl-phenoxy-BTD dyes. Their photophysical properties were evaluated in solution and the results indicate a strong intramolecular charge transfer (ICT) character in the excited state. The luminophore 3a, possessing a donor-BTD-phenoxide architecture, exhibits superior fluorescence quantum yield (0.67) than the designed acceptor-BTD-phenoxide dye (0.06). After electrochemical and photoluminescence characterization of thin films of 3a, an OLED with the configuration ITO/PEDOT:PSS/3a/TPBi/LiF/Al was constructed. This device displayed a green emission centered at 547 nm, with CIE coordinates of (0.40, 0.55). For comparison, an OLED using a previously reported luminescent BTD-pyridyl derivative was also constructed. The OLED made with the phenoxy-BTD derivative operated using less current density and led to higher irradiance and electrical stability, indicating the high potential of ArO-BTD dyes for future application in electroluminescent devices.

A set of samples of novel colorized zinc oxide-nanosilica composites was synthesized and analyzed. The color and optical properties are directly dependent on ZnO concentration in the composites. Visible light-driven (λ = 550 nm) catalytic activity on the degradation of pharmaceuticals was tested and indicated that the most active sample with 9 mmol of ZnO per 1 g of SiO2 was ca. 13 times (toward propanolol), 24 times (toward carbamazepine) and ca. 37 times (toward metoprolol) more effective than blank (catalyst-free photolysis) decontamination. Besides showing a typical charge transfer band on the UV–Vis spectra, all the samples demonstrated a visible light absorbance at ca. 500 nm. Due to the diminution of ZnO particles size, the sample with the minimal concentration of zinc oxide exhibited pronounced luminescence at the region of >500 nm. The microscopy confirmed the decrease of ZnO agglomerated crystalline phase with diminution of ZnO concentration over SiO2 matrix. XPS studies provided information about the chemical species contributing to the formation of nanocomposites, including the presence of some unexpected trace elements, and also the surface effects of incorporating ZnO nanoparticles into SiO2 matrix also. With the help of elemental analysis, certain impurities in ZnO were identified, which might be responsible for the outstanding optical and catalytic behavior of the samples. The toxicity results confirmed that applied process can be used for detoxification of wastewater.

Thiomersal is employed as preservative in vaccines, cosmetic and pharmaceutical products due to its capacity to inhibit bacterial growth. Thiomersal contains 49.55% of mercury in its composition and its highly toxic ethylmercury degradation product has been linked to neurological disorders. The photo-degradation of thiomersal has been achieved by visible light using graphene quantum dots as catalysts. The generated mercury cold vapor (using adjusted experimental conditions) was detected by multipath atomic absorption spectrometry allowing the quantification of thiomersal at values as low as 20 ng L− 1 even in complex samples as aqueous effluents of pharmaceutical industry and urine. A kinetic study (pseudo-first order with k = 0.11 min− 1) and insights on the photo-degradation process are presented.

Quality of vegetable oils is affected by the presence of metals, even at low concentrations. A study was conducted to advance evaluate the degradation of canola induced by the presence of copper CuO (expected to be less reactive than Cu 2+ ). Samples were heated at 90 °C for fourteen days and the results suggested that contamination does influence not only the oxidation rate but also the extension of the degradation processes. FT-IR and Raman spectra showed the decreasing of the carbonyl absorption belonging to triglycerides during the oxidation process, which was most pronounced in the CuO contaminated oil, indicating the increasing of the hydrolysis process. Furthermore, the oxidation of the olefinic bonds also appears to be copper-mediated, since the cis C H vibration band decreases to a larger extent in the metal-containing samples. CuO exerted a greater degradation as it caused a more pronounced decrease of both the number of unsaturations and carbonyl groups of esters, besides the more effective decrease in the induction time and the higher production of secondary oxidation products.

Square-wave anodic voltammetry (SWV) was used to determine lapachol using a laboratory-made graphite-epoxy electrode. The electrolytic medium consisted of an aqueous solution containing cationic surfactant CTAB (1.2 × 10− 4 mol L− 1), buffer phosphate (4.0 × 10− 2 mol L− 1; pH 6.0) and KNO3 (1.0 mol L− 1). The cationic surfactant improved diffusion and interaction of the analyte with the electrode, producing a reversible process that improved the total current measured by SWV. Lapachol signal was measured at − 470 mV after pre-concentration at 400 mV during 140 s, using frequency of 30 Hz, pulse amplitude of 40 mV with step potential of 20 mV. The instrumental limit of detection was 0.029 mg L− 1 and the dynamic linear range covered two decades. In the presence of β-lapachone (structural isomer) selectivity was achieved by first order derivative of the SWV signal. Lapachol determination in ethanolic extract of heartwood of Tabebuia impetiginosa was accomplished after a simple thin-layer chromatographic separation of the analyte from components of the complex sample. The results agreed (at 95% confidence level) with the ones achieved by using high performance liquid chromatography with absorciometric detection.

In this work, the photoluminescence of aqueous dispersion of amino-functionalized graphene quantum dots (GQDs-amino), with average size of 28 nm, was studied in the presence of histamine when interaction was mediated by different metal ions. Stronger and selective interaction towards histamine occurred in the presence of Eu 3 + , Fe 3 + and Cu 2 + . The sensibility of the normalized photoluminescence suppression curves ( K s ) indicated a ten time stronger interaction of histamine with the surface of the GQDs in the presence of Fe 3 + . The linear response observed in the GQDs-amino-Fe 3 + (luminescence at 345/435 nm) covered the histamine concentration from 4.3 × 10 − 7 mol L − 1 (limit of quantification) to 3.2 × 10 − 5 mol L − 1 . The GQDs-amino-Fe 3 + was applied as a probe in the analysis of tuna fish samples after cationic solid phase extraction. Analytical results were statistically similar to the ones achieved with a reference HPLC-fluorescence (after chemical derivatization) based method. The proposed method for determination of histamine is simple, does not involve the use of toxic labeling reagents and can easily be adapted for routine quality control analysis of fish and related foodstuffs.

Kanamycin is an antibiotic from the aminoglycoside class used to treat a myriad of infections. Aminoglycosides enhanced the photoluminescence of the thioglycolic acid modified CdTe quantum dots (TGA-CdTe QDs) following a Langmuir binding isotherm model. Binding constants were calculated indicating strong interactions between surface of nanoparticles and aminoglycosides. For kanamycin, the equilibrium binding constant was of 5.6 × 10 7 L mol −1 . Based on this, a sensitive and selective method was developed for kanamycin determination based on the enhanced photoluminescence of TGA-CdTe QDs. Solid phase extraction with a new molecularly imprinted polymer, made using kanamycin as a template, provided high selectivity towards aminoglycosides. Under adjusted conditions, the two orders of magnitude analytical curve (linearized Langmuir binding isotherm) was constructed from 1.4 × 10 −8 mol L −1 (limit of quantification) to 1.6 × 10 −6 mol L −1 (8.1–92.8 ng mL −1 ) of kanamycin sulphate. The proposed procedure was tested for the determination of kanamycin in milk and yellow fever vaccine with recoveries between 86.6 and 93.7%. In addition, the kanamycin effect on TGA-CdTe QDs was also demonstrated under capillary electrophoresis regime, indicating another possibility for selective sensing.

Alzheimer's and Parkinson's diseases share similar amyloidogenic mechanisms, in which metal ions might play an important role. In this last neuropathy, misfolding and aggregation of α-synuclein (α-Syn) are crucial pathological events. A moderate metal-binding compound, namely, 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone (INHHQ), which was previously reported as a potential ‘Metal-Protein Attenuating Compound’ for Alzheimer's treatment, is well-tolerated by healthy Wistar rats and does not alter their major organ weights, as well as the tissues' reduced glutathione and biometal levels, at a concentration of 200 mg kg− 1. INHHQ definitively crosses the blood-brain barrier and can be detected in the brain of rats so late as 24 h after intraperitoneal administration. After 48 h, brain clearance is complete. INHHQ is able to disrupt, in vitro, anomalous copper-α-Syn interactions, through a mechanism probably involving metal ions sequestering. This compound is non-toxic to H4 (human neuroglioma) cells and partially inhibits intracellular α-Syn oligomerization. INHHQ, thus, shows definite potential as a therapeutic agent against Parkinson's as well. Fil: Cukierman, Daphne Schneider. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: Pinheiro, Ana Beatriz. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: Castiñeiras-Filho, Sergio L.P.. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: da Silva, Anastácia Sá P.. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: Miotto, Marco César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario. Universidad Nacional de Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario; Argentina Fil: De Falco, Anna. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: de P. Ribeiro, Thales. Universidade Federal do Rio de Janeiro; Brasil Fil: Maisonette, Silvia. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: da Cunha, Alessandra L.M.C.. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: Hauser-Davis, Rachel A.. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: Fernandez, Claudio Oscar. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: Aucélio, Ricardo Q.. Pontifícia Universidade Católica do Rio de Janeiro; Brasil Fil: Outeiro, Tiago F.. Universität Göttingen; Alemania Fil: Pereira, Marcos D.. Universidade Federal do Rio de Janeiro; Brasil Fil: Fernandez, Claudio Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario. Universidad Nacional de Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario; Argentina Fil: Rey, Nicolás A.. Pontifícia Universidade Católica do Rio de Janeiro; Brasil

Two nonsymmetrical π-extended 2,1,3-benzothiadiazoles (BTDs) bearing a 4-pyridyl moiety (BTD-4pyr and BTD-Et4pyr) were synthesized by sequential cross coupling reactions. The structural difference between the two dyes is the presence of a triple bond between the BTD core and the 4-pyridyl moiety in BTD-Et4pyr. The compounds architecture is similar to previously described selective mitochondrial biomarkers. Both compounds exhibit large Stokes shifts (93–137 nm), high fluorescence quantum yields and linear fluorescence response in the nanomolar range. The existence of the triple bond decreased in about 35% the fluorescence measured from BTD-Et4pyr in respect to BTD-4pyr. Solid-state fluorescence of the dyes were measured, producing considerable smaller Stokes shifts than the ones observed in solutions (74 nm for BTD-4pyr and 66 nm for BTD-Et4pyr). X-ray crystallography analysis of BTD-4pyr indicated a quinoid character for the BTD ring and a nonplanar relation between the BTD core and the aryl/heteroaryl groups. DFT calculations pointed out that the LUMO electron density is concentrated over the BTD core. In relation to HOMO, the electron density is distributed mainly at the methoxyphenyl group, in the hydrocarbon fraction of the BTD core and in ethynyl group for BTD-Et4pyr.

•Thioglycolic acid modified CdTe QDs were used to determine histamine.•The method was applied in the determination of histamine in tuna fish.•Selectivity was improved by using cationic solid phase extraction.•Mechanism of interaction between histamine and QDs was studied.

The determination of captopril was performed by measuring the photoluminescence quenching of pH sensitive mercaptopropanoic acid capped CdTe quantum dots. Under optimum conditions, the calibration model (log F0/F as a function of the concentration of captopril) was linear up to 8 × 10–6 mol/L (1.7 μg/mL) and the limit of detection (xb – 3sb) was 2.7 × 10–7 mol/L (18 ng/mL). A possible mechanism for quenching is proposed. The method was applied in the determination of captopril in two commercial pharmaceutical formulations, indicating that it can be used for simple and fast quantitative control of commercial medicines or pharmaceutical preparations.

In this work, it is shown the development and validation of innovative analytical methodology based on solid-phase extraction (SPE) with molecularly imprinted polymers (MIP) as a sorbent associated to UV–Vis spectroscopy to isolate and quantify, respectively, rosuvastatin (RSV) in water samples. For this purpose, porogenic solvent in MIP synthesis and SPE extraction parameters for MIP and non-imprinted polymers (NIP) were evaluated univariately for comparison purposes. The sorptive capacity and characterization studies by infrared spectroscopy and atomic force microscopy showed difference between MIP and NIP. The selectivity study of the MIP–RSV against other statins (simvastatin and atorvastatin) showed that the synthesized MIP can also be applied as a solid phase for isolation and quantitative pre-concentration of RSV and atorvastatin. The conjugation of SPE and UV–Vis spectroscopy in the determination of RSV in aqueous matrices led to large factor of pre-concentration (125 times), limit of detection (LOD) of 3 μg L−1, limit of quantification (LOQ) of 10 μg L−1, precision of 2.87% (n = 10), and accuracy of 83.1% (n = 4).

Gold nanoparticles (AuNPs), produced using sodium borohydride in water (AuNPs-H), also in the presence of the surfactants cetyltrimethylammonium bromide (AuNPs-CTAB) and didecyldimethylammonium bromide (AuNPs-D10AB), were characterized and investigated in terms of their optical localized surface plasmon resonance (LSPR) response. The automation of the syntheses improved reproducibility of AuNPs. CTAB was chosen as a model one-tail surfactant capping agent for AuNPs and D10AB (two-tail surfactant) was employed for the first time, as a capping agent for AuNPs. Thus, it was possible to carry out a comparative study for the production of AuNPs, varying the surfactant concentration levels from 1.0 × 10−2 to 1 × 10-4 mol L-1. The LSPR profiles were monitored in function of the time, taking into account storage conditions (at 4 °C and at 27 °C). A more unstable behavior was observed for the AuNPs produced in the presence of D10AB at 1.0 × 10-4 mol L-1, which suggested the disassembling of AuNPs over time. The catalytic activity of the AuNPs was evaluated in the presence of 4-nitrophenol, and the most effective kinetics were observed for systems containing the one-tail surfactant CTAB, at 1.0 × 10−2 mol L-1 (8 min), and for AuNPs-H, which has no organic coating, (6 min). Finally, the evaluation of the optical response from AuNPs was conducted with four aminoglycosides (AMG), indicating that these surfactants prevent interaction between AMG and the surface of the nanoparticles since at higher concentrations of CTAB or D10AB there is no significant variation in the LSPR spectral band in presence of AMG. In contrast, strong interaction, observed as variation of LSPR band, was found for the AuNPs-H-AMG systems.

The determination of captopril is proposed using graphene quantum dots produced by the pyrolysis of citric acid and glutathione (GSH-GQDs). Captopril induces both quenching and spectral red-shifting in the photoluminescence from aqueous dispersions of GSH-GQDs. By employing Fe 3+ as mediator (that enables signal quenching of GSH-GQDs), the presence of captopril restored the photoluminescence of quantum dots. Under optimized experimental conditions, the signal quenching from the GSH-GQDs as function of the concentration of captopril showed a linear response range covering three orders of magnitude (10 −6 to 10 −4 mol L −1 ). The proposed approaches were tested by determining captopril in simulated samples and in commercial pharmaceutical formulations. The measurement of either the spectral shifting observed of the GSH-GQDs probe or the photoluminescence switch on/off using GQDs-GSH-Fe 3+ resulted in satisfactory recoveries of captopril, showing the quantitative sensing potential.

Carbazoles, quinolines, indoles, pyrroles, anilines and acridines are nitrogen-containing polycyclic aromatic compounds (NPAC) that contribute to deteriorate fuels affecting storage stability, causing problems to motor engines and poisoning automotive catalysts. Carbazole, 3-ethylcarbazole, 9-ethylcarbazole, 9-methylcarbazole, quinoline, benzo[ h ]quinoline, indole, 3-methylindole, acridine and N,N-dimethylaniline were separated and quantified in diesel and gas oil by reverse-phase high performance liquid chromatography with fluorimetric detection and molecular absorption photometric detection using introduction of fuel samples as detergentless microemulsion (DME). The DME is composed by ethanol, propan-2-ol, water and iso-octane in specific proportions to stabilize the organic samples. The introduction of sample in the DME simplifies the procedure since it avoids extraction of the analytes and enables the determination of basic and neutral NPAC altogether. The limits of quantification for the analytes in the DME were in μg L −1 order (ng range for 10 μL of injected volume). Satisfactory analyte recoveries were achieved (between 89.5% and 108.7%). Results were found to be comparable using or not using 7-methylindole and N-methylpyrrole as internal standards (since these were not found in the analyzed samples). Studies showed homogeneity of the analytes in the DME after mechanical stirring (at 7200 rpm for 5 min). Stability studies indicated results with coefficients of variation below 3%. The method is adequate for a rapid screening of NPACs in petroleum samples.

Creatinine levels in blood and urine can be used as an important biomarker for the diagnosis of renal, thyroid, and muscle malfunctions. In this work, a square-wave voltammetric method for creatinine was developed using a gold electrode modified with a film composed by Nafion mixed with a graphene quantum dots dispersion prepared in the presence of Cu2+. Such Au/Nafion-GQDs-Cu electrode relies on the interactions of creatinine with Cu2+ released from the oxidation of Cu thus decreasing the characteristic Cu/Cu2+ anodic peak at +350 mV. A linear response was obtained for the analyte in the concentration range from 1.0 × 10−6 mol L−1 (0.11 mg L−1) to 4.5 × 10−4 mol L−1 (50.9 mg L−1). The proposed sensor was simple to prepare and the method was successfully applied for creatinine determination in urine samples.

A series of luminescent aryloxy-benzothiadiazole derivatives with architectures ArO-BTD-Ar’ and ArO-BTD-NAr’ were synthetized. The aim was to achieve a molecular design based on restriction of intramolecular rotation of the ArO- group associated to the presence of bulky aryl or N-aryl groups, which can avoid detrimental π-π stacking and favor radiative decays in the aggregated/solid state. In solution, these compounds showed fluorescence emission located in the blue to red regions with relative high fluorescence quantum yields (φFL = 0.27–0.74). For all ArO-BTD-Ar’ derivatives, emission enhancement was observed upon aggregation. The essential role of the ArO- group in the AIEEgenic ability was confirmed by comparing with Ar’-BTD-Ar’ analogs. Some solid ArO-BTD-Ar’ compounds displayed higher φFL than when in solution. Their aggregation-induced enhanced emission (AIEE) were corroborated by studies in water/acetone systems (I/I0 emission rations up to 7.7). Monocrystal X-ray analysis of selected compounds confirmed the twisted nature and absence of detrimental π-π stacking. The more emissive compound (φFL = 0.83) was applied as emitting material in a green OLED structure, presenting turn-on voltage around 3.5 V and luminance up to 1200 cd m−2, with a maximum current efficiency of 5.6 × 10−1 cd A−1 at 6.5 V.

A facile and robust synthesis of carbon dots (CDs) emitting blue-light in water without activation and stabilization has been developed by pyrolysis of citric acid (CA) adsorbed in silica gel (SiO2) pores. Effect of the host pore size on luminescent properties of SiO2@CDs nanocomposite as well as water suspension of CDs has been studied. The synthesis conditions such as concentration of the precursor, duration of synthesis also have been investigated. It has been demonstrated that upon the thermal treatment of silica gels saturated with CA (60% of maximum loading) at 170 °C for 5–600 min, luminescent CDs are shaped inside the nanoreactor pores. These SiO2@CDs emit photoluminescence centered at 450 nm. Silica-immobilized CDs can be separated from the source molecules and side-products by centrifugation, which allows avoiding the dialysis of the resulted mixture and so improve the scaling of the synthesis. The CDs can be easily released from SiO2@CDs by washing it with water. Water-eluted CDs demonstrate photoluminescence at 447 nm. The smaller pore size of the host and longer time of thermal treatment promote the formation of the CDs with better photoluminescent peak symmetry and higher quantum yield up to 10.1%.

The determination of kanamycin sulfate was made indirectly by measuring its effect on photoluminescent amino functionalized graphene quantum dots (GQDs-amino) associated with gold nanoparticles (AuNPs) that were produced by the reduction of AuCl4 with NaBH4 in an aqueous dispersion of GQDs-amino (obtained by the pyrolysis of citric acid and glutathione) also containing the cationic surfactant CTAB. The AuNPs-GQDs-amino-CTAB system presents a suppressed photoluminescence that is amplified in the presence of kanamycin. Under optimized experimental conditions, the photoluminescence amplification of the nanomaterial system showed a linear response as a function of kanamycin concentration, covering three orders of magnitude (10−7 to 10−5 mol L−1). The use of solid phase extraction with a cartridge packed with aminoglycoside selective molecularly imprinted polymer ensured selectivity in determinations made on yellow-fever vaccine and veterinary pharmaceutical formulations. The analytical results were statistically similar to those obtained with an HPLC-based fluorescence method (after chemical derivatization). The proposed method is a simple, sensitive and selective approach that does not involve the use of toxic reagents employed for chemical derivatization of aminoglycoside antibiotics.

A series of triphenylamino (TPA)-chalcones and triphenylamino-β-arylchalcones, displaying either D-π-D or D-π-A architecture, were synthesized through aldol condensations and Heck reactions. The chalcone derivatives display intense absorption bands ranging from 389 to 432 nm and molar extinction coefficients of ca. 105 L mol-1 cm-1 corresponding to π-π* electronic transitions. The photoluminescence emissions are peaked between 470 and 563 nm with large Stokes shifts (80-131 nm), attributed to charge transfer in the excited state. The dyes present low fluorescence quantum yields, which is attributed to radiationless excited state deactivation related to aryl rings rotation. Spectroscopic and electrochemical methods were used to determine the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. Both optical and electrochemical properties of the TPA-chalcone derivatives are considerably affected by the substitution pattern of the chalcones aryl rings and also by the β-arylation of the olefin moiety.

Ligand-free carbynoid-encapsulated gold nanocomposites (Au@Carbynoid NCs) with blue-shifted localized surface plasmon resonance (LSPR) have been synthesized by CO2 recycling induced by pulsed laser ablation (PLA) of a solid gold target in aqueous solution with NaOH at pH 7.0. High Resolution Transmission Electron Microscopy (HRTEM) images at not destructive acceleration voltage of 80 kV revealed carbynoid nanocrystals around the gold core, associated to the intense bond length alternation (BLA) Raman mode of the carbon atomic wires (CAWs), centered at 2124 cm−1, observed in the Surface Enhanced Raman Scattering (SERS) spectra. It was verified that interlinking process with sp to sp2 conversion of the CAWs is induced both by high acceleration voltage in HRTEM and high irradiance of the excitation beam used in SERS measurements. Post synthesis mixing of Pluronic-F127 copolymer with pre-synthesized Au@Carbynoid NCs allows the formation of a fully biocompatible colloidal solution of Au@Carbynoid/Copolymer NCs. SERS investigation highlights that the Raman band of the BLA mode can be used as efficient Raman tag to monitor the functionalization of the NCs with the copolymer. The biocompatibility of the NCs was demonstrated performing a study of cytotoxicity using human skin fibroblasts. As proof of principle, it was demonstrated that the photodynamic activity of the bifunctional Au@Carbynoid/PF127 NCs in the presence of chlorin e6 (Ce6) drug can be enhanced inducing the aggregation state of the colloidal suspension. The stability of the colloidal dispersions of Au@Carbynoid NCs functionalized with Pluronic-F127 is verified after centrifugation in PBS (0.15 mol L−1 NaCl) solutions, confirming the possibility to use the green carbynoid based NCs as drug-carrier in biological applications.

Crude oil samples contain several types of contaminants including metalorganic compounds, sulfur containing compounds and sediments. Energy dispersive X-ray fluorescence spectrometry was used for the direct determination of S, Ca, Fe, Ni and V in crude oils, enabling a fast and reliable method that avoids complex sample preparation. Crude oil samples were homogenized and 20 μL of a diluted sample (1/1 v/v oil/toluene) were placed in the center of a 10 mm diameter filter paper that was sandwiched between two polypropylene film foils and attached to the instrument cell for measurements. For the purpose of matrix corrections, fixed amounts of H, N and O were introduced in the calibration model with C (achieved through elemental analysis) used to balance the matrix content. Quantification was made by fundamental parameters method using ASTM proficiency test samples to perform mathematical adjustment of the analytical model. The results for metals were statistically comparable to the ones obtained by flame atomic absorption spectrometry while the ones for S were in accordance to the results achieved in ASTM proficiency programs and achieved by elemental analysis. Ca, Fe, Ni and V were directly determined in the oil at concentrations as low as 1 μg g −1 and for S, the value was 0.002% w/w, showing the potential of the proposed method to screen for samples with higher amounts of these critical contaminants.

This article reports and compares the performance of two new electrochemical methods for the determination of picoxystrobin (a strobilurin-class fungicide). The methods were square-wave voltammetry (SWV) and batch-injection analysis (BIA) with multiple-pulse amperometric detection, both employing boron-doped diamond (BDD) electrode, which was cathodically treated to enhance the electrochemical activity for picoxystrobin. The SWV method presented higher sensitivity with lower detection (LOD of 0.2 μmol L − 1 or 0.07 mg L − 1 ) and quantification limits (LOQ of 0.7 μmol L − 1 or 0.25 mg L − 1 ) in comparison with the BIA amperometric method (LOD of 1.6 μmol L − 1 or 0.6 mg L − 1 and LOQ of 5.3 μmol L − 1 or 2.0 mg L − 1 ). However, the BIA-amperometric method provided wider linear range (from 5.3 to 100.0 μmol L − 1 ) in comparison with the SWV method (from 0.7 to 20.0 μmol L − 1 ) and higher analytical frequency rate (108 measurements h − 1 ). Interference of other strobilurin compounds was evaluated and the presence of trifluoxystrobin and fluoxystrobin (up to 3-fold excess) affected the SWV determination of picoxystrobin. The amperometric method undergoes interference from the all of the tested strobilurins but a simple approach, based on multiple-pulse amperometry, can indicate the presence of some of the potential interfering species. Hence, either SWV or BIA-multiple pulse amperometry can be applied for picoxystrobin depending on analyte concentration, presence of interfering species, and required analytical frequency.

A simple method based on micellar liquid chromatography (MLC) was developed to enable the simultaneous determination of norharmane, harmane, harmol, harmalol, harmine, and harmaline in phytotherapic samples of Passiflora incarnata L., Passiflora alata Dryander and urine with virtually no sample preparation. Chromatographic separation was performed under 30 min using a C18 HPLC column and isocratic elution with an aqueous micellar mobile phase (phosphate buffer pH 8.0 containing 220 mmol L−1 of sodium dodecyl sulfate and 0.5% of triethylamine) containing only 3% (v/v) of acetonitrile. Fluorescence detection allowed limits of quantification below 4.5 ng g−1. Recoveries in controlled samples were close to 100% and the sample analysis enabled the quantification of harmol as the principal β-carboline found in the phytotherapic samples, whereas another three were detected. In urine samples, the determination of harmol was made after 8 hours of drug ingestion. Both repeatability and intermediary precision, for a...

Gentamicin is an antibiotic indicated to treat mastitis in dairy cattle and for the treatment of bacterial resistance in the context of hospital infections. The effect caused by gentamicin on the optical properties of gold nanoparticles aqueous dispersions were used to develop quantitative methods to determine this antibiotic. Two different aqueous dispersions, one containing spherical Au nanoparticles (AuNPs) and the other containing Au nanorods (AuNRs), had their conditions adjusted to enable a stable and sensitive response towards gentamicin. The use of AuNPs, with measurement at 681 nm of the rising coupling plasmon band, enabled a limit of detection (LOD) of 0.4 ng mL − 1 (0.02 ng absolute LOD), ten times lower than the one achieved by measuring the decreasing of the longitudinal surface plasmon resonance band (at 662 nm). The linear analytical response of AuNPs measured at 681 nm did not require rationing of signal values to correct for linearity. Stability of the analytical response resulted in intermediary precision below 2%. No significant interference was imposed by excipients traditionally present in injectable solutions for veterinary use. Percent recoveries obtained in such formulations were between 94.5 and 98.2% regardless the existence of any difference in the proportion of the compounds known as gentamicin (C 1 , C 1a and C 2 ) in standard and in the samples. The method requires no derivatization with toxic reagents as usually is required in other spectroscopic approaches.

The determination of l -thyroxine is proposed based on the photoluminescence quenching effect caused on the l -cysteine modified ZnS quantum dots ( l -cysteine ZnS QDs) aqueous dispersion. Under optimum conditions, the analytical response followed a Stern–Volmer model and the experimental conditions were adjusted to enable a robust and reproducible photoluminescence signal. The linear response observed in the quantum dots aqueous dispersion covered the l -thyroxine concentration from the LOQ (2.0×10−8 mol L−1) to 4.0×10−6 mol L−1. The approach was tested in the determination of l -thyroxine in pharmaceutical formulations used to treat patients with thyroid gland disorder. The percent recoveries in controlled samples were between 93.3 and 103%. Analyte fortified saliva was also evaluated as a possible sample for l -thyroxine monitoring of a patient under treatment. It was identified a static type of photoluminescence quenching caused by l -thyroxine.