Edgar Nagles

Adsorptive Stripping Voltammetric Determination of Amaranth and Tartrazine in Drinks and Gelatins Using a Screen-Printed Carbon Electrode

A fast, sensitive, and selective method for the simultaneous determination of one pair of synthetic colorants commonly found mixed in food products, Amaranth (AM) and Tartrazine (TZ), based on their adsorption and oxidation on a screen-printed electrode (SPE) is presented. The variation of peak current with pH, supporting electrolyte, adsorption time, and adsorption potential were optimized using square wave adsorptive voltammetry. The optimal conditions were found to be: pH 3.2 (PBS), Eads 0.00 V, and tads 30 s. Under these conditions, the AM and TZ signals were observed at 0.56 and 0.74 V, respectively. A linear response were found over the 0.15 to 1.20 µmol L−1 and 0.15 to 0.80 µmol L−1 concentrations, with detection limits (3σ/slope) of 26 and 70 nmol L−1 for AM and TZ, respectively. Reproducibility for 17.7 µmol L–1 AM and TZ solutions were 2.5 and 3.0% (n = 7), respectively, using three different electrodes. The method was validated by determining AM and TZ in spiked tap water and unflavored gelatin spiked with AM and TZ. Because a beverage containing both AM and TZ was not found, the method was applied to the determination of AM in a kola soft drink and TZ in an orange jelly and a soft drink powder.

Secondary Metabolite Profiling of Species of the Genus Usnea by UHPLC-ESI-OT-MS-MS

Lichens are symbiotic associations of fungi with microalgae and/or cyanobacteria, which are considered among the slowest growing organisms, with strong tolerance to adverse environmental conditions. There are about 400 genera and 1600 species of lichens and those belonging to the Usnea genus comprise about 360 of these species. Usnea lichens have been used since ancient times as dyes, cosmetics, preservatives, deodorants and folk medicines. The phytochemistry of the Usnea genus includes more than 60 compounds which belong to the following classes: depsides, depsidones, depsones, lactones, quinones, phenolics, polysaccharides, fatty acids and dibenzofurans. Due to scarce knowledge of metabolomic profiles of Usnea species (U. barbata, U. antarctica, U. rubicunda and U. subfloridana), a study based on UHPLC-ESI-OT-MS-MS was performed for a comprehensive characterization of their secondary metabolites. From the methanolic extracts of these species a total of 73 metabolites were identified for the first time using this hyphenated technique, including 34 compounds in U. barbata, 21 in U. antarctica, 38 in U. rubicunda and 37 in U. subfloridana. Besides, a total of 13 metabolites were not identified and reported so far, and could be new according to our data analysis. This study showed that this hyphenated technique is rapid, effective and accurate for phytochemical identification of lichen metabolites and the data collected could be useful for chemotaxonomic studies.

New combination between chitosan, single walled carbon nanotubes and neodymium(III) oxide found to be useful in the electrochemical determination of rutin in the presence of morin and quercetin

A glassy carbon electrode surface was modified with a new combination of chitosan, single walled carbon nanotubes (SWCNT) and neodymium(III) oxide (NdOX) and was found to be effective in the detection of rutin (RU), a natural antioxidant. The modified electrode displayed high activity toward the oxidation of RU compared to other flavonoids, such as quercetin (Q) and morin (MO). The oxidation peaks of RU, MO and Q were exhibited at +0.53, +0.42 and +0.39 V, respectively. Moreover, anodic peak currents were 37.27, 10.39 and 2.27 μA, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the electrode surface, and square wave voltammetry (SWV) was used to quantify RU. The detection limit (3σ/b) was 0.092 μmol L−1, and the RSD was 2.5%. A new sensor was used in the quantification of RU in roasted beans infusion of Coffea arabiga L. and extract of Zamia furfuracea L.f. ex Aiton with satisfactory results.

Synthesis and structural characterization of new 2-bromo-1,3-bis(triazol-1-ylmethyl)benzene ligands. Study of their behavior as complexing agents for determination of nickel(II) by adsorptive stripping voltammetry

Reaction of 2-bromo-1,3-bis(bromomethyl)benzene (1) with 1,2,3-triazole and benzotriazole yields 2-bromo-1,3-bis(triazol-1-ylmethyl)benzene (2) and 2-bromo-1,3-bis(benzotriazol-1-ylmethyl)benzene (3), isolated as white solids, air stable at room temperature, and characterized by elemental analysis, mass spectra, IR, and NMR (1H, 13C) spectroscopy. The molecular structure of 3 was determined by single-crystal X-ray diffraction. These ligands were evaluated for determination of ultra-trace concentrations of nickel by adsorptive stripping voltammetry. The method is based on adsorptive accumulation of the Ni(II)-L complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using square wave modulation. However, only with 2 was a signal observed at −0.81 V. Under the best experimental conditions (pH 5.5; ligand concentration 0.30 μmol L−1; adsorptive potential (E ads) −0.70 V and adsorptive time (t ads) 80 s), the peak current is proportional to the Ni(II) concentration to 15.0 μg L−1, with a 3 detection limit of 0.2 μg L−1. The proposed method was validated by determining Ni(II) in certified reference waste water (SPS–WW1) with satisfactory results.

Development of Antibacterial and Antifungal Triazole Chromium(III) and Cobalt(II) Complexes: Synthesis and Biological Activity Evaluations

In this work, six complexes (2–7) of Cr(III) and Co(II) transition metals with triazole ligands were synthesized and characterized. In addition, a new ligand, 3,5-bis(1,2,4-triazol-1-ylmethyl)toluene (1), was synthesized and full characterized. The complexes were obtained as air-stable solids and characterized by melting point, electrical conductivity, thermogravimetric analysis, and Raman, infrared and ultraviolet/visible spectroscopy. The analyses and spectral data showed that complexes 3–7 had 1:1 (M:L) stoichiometries and octahedral geometries, while 2 had a 1:2 (M:L) ratio, which was supported by DFT calculations. The complexes and their respective ligands were evaluated against bacterial and fungal strains with clinical relevance. All the complexes showed higher antibacterial and antifungal activities than the free ligands. The complexes were more active against fungi than against bacteria. The activities of the chromium complexes against Candida tropicalis are of great interest, as they showed minimum inhibitory concentration 50 (MIC50) values between 7.8 and 15.6 μg mL−1. Complexes 5 and 6 showed little effect on Vero cells, indicating that they are not cytotoxic. These results can provide an important platform for the design of new compounds with antibacterial and antifungal activities.

Speciation of morin and rutin in black tea, Cymbopogon citratus and fruit infusions by adsorption voltammetry using screen-printed carbon electrodes coated with chitosan: effect of pH on speciation

This paper presents the versatility of chitosan in the preparation of modified electrodes without the use of other substances. We present a sensitive and selective method of speciation for the determination of rutin (RT) and morin (MR) in natural products on a screen-printed carbon electrode coated with chitosan (CS-SPC). MR and RT may be adsorbed onto the surface of the SPC electrode coated with CS, increasing the intensity of the current by more than 60 and 45% for RT and MR, respectively, compared to that of the unmodified SPC. On the other hand, anodic peak currents were observed at the same potential value. This effect can impede the speciation for the detection of RT and MR in real samples. By evaluating the concentration of CS deposited on the electrode surface, a separation of 100 mV between RT and MR was achieved. Moreover, anodic peak currents for RT and MR as a function of the pH using a phosphate buffer solution (PBS) were evaluated, and the results clearly showed that in an acid medium, the MR signal is only 8.0% compared to that of the RT signal. These two parameters make speciation possible for the detection and quantification of RT and MR. Detection limits were 0.090 and 0.90 μmol L−1 for RT and MR, respectively. The relative standard derivations (RSD) were 3.5 and 4.0%, respectively. The accuracy was evaluated using a urine chemistry control spiked with known quantities of RT and MR. Finally, the usefulness of the modified electrode was evaluated to quantify RT and MR in commercial samples of black tea, as well as infusions of Cymbopogon citratus and fruits, which provided consistent results compared to previous reports.

A new and simple electroanalytical method to detect thiomersal in vaccines on a screen-printed electrode modified with chitosan

The use of a screen-printed electrode modified with chitosan (Cs) to determine thiomersal (TMS) through the oxidation of thiosalicylic acid by linear sweep anodic stripping voltammetry is reported for the first time in this work. The screen-printed electrode was coated with chitosan (Cs/SPCE) and the surface was studied with cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode presented activity towards the oxidation of thiomersal (TMS) at 0.24 V. The signal is the product of the oxidation of the thiosalicylic acid or organic part and not of the mercury in the chemical structure of thiomersal. Optimal parameters for linear sweep anodic stripping voltammetry were pH 3.2 in phosphate buffer solution (PBS), accumulation time (tACC) 90 s, accumulation potential (EACC) −1.0 V and scan rate 100.0 mV s−1; the oxidation signal was proportional to the concentration of TMS between 0.99 and 10.90 μmol L−1, with a detection limit of 0.038 μmol L−1 and the relative standard deviation (RSD) was 5.0% using seven different electrodes. The sensor was used in human urine samples spiked with thiomersal and commercial cattle vaccines with consistent results.

Development of an iron-selective antioxidant probe with protective effects on neuronal function

Iron accumulation, oxidative stress and calcium signaling dysregulation are common pathognomonic signs of several neurodegenerative diseases, including Parkinson´s and Alzheimer’s diseases, Friedreich ataxia and Huntington’s disease. Given their therapeutic potential, the identification of multifunctional compounds that suppress these damaging features is highly desirable. Here, we report the synthesis and characterization of N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetamide, named CT51, which exhibited potent free radical neutralizing activity both in vitro and in cells. CT51 bound Fe2+ with high selectivity and Fe3+ with somewhat lower affinity. Cyclic voltammetric analysis revealed irreversible binding of Fe3+ to CT51, an important finding since stopping Fe2+/Fe3+ cycling in cells should prevent hydroxyl radical production resulting from the Fenton-Haber-Weiss cycle. When added to human neuroblastoma cells, CT51 freely permeated the cell membrane and distributed to both mitochondria and cytoplasm. Intracellularly, CT51 bound iron reversibly and protected against lipid peroxidation. Treatment of primary hippocampal neurons with CT51 reduced the sustained calcium release induced by an agonist of ryanodine receptor-calcium channels. These protective properties of CT51 on cellular function highlight its possible therapeutic use in diseases with significant oxidative, iron and calcium dysregulation.

Metabolomic Analysis of Two Parmotrema Lichens: P. robustum (Degel.) Hale and P. andinum (Mull. rg.) Hale Using UHPLC-ESI-OT-MS-MS

Lichens are symbiotic associations of fungi with microalgae and/or cyanobacteria. Lichens belonging to the Parmeliaceae family comprise 2700 species of lichens, including the Parmotrema genus which is composed of 300 species. The metabolites of this genus include depsides, depsidones, phenolics, polysaccharides, lipids, diphenylethers and dibenzofurans, which are responsible for the biological activities reported including antidiabetic, antihelmintic, anticancer, antioxidant, antibacterial, anti-inflammatory, antimitotic, antitumoral, antifungal, and antioxidant enzyme inhibitory. Due to scarce knowledge of metabolomic profiles of Parmotrema species (P. andinum and P. robustum), a full metabolome study based on ultra-high performance liquid chromatography- diode array detector-electrospray ionization-quadrupole-orbitrap-mass-spectrometry (UHPLC-DAD-ESI-Q-orbitrap MS) was performed for a comprehensive characterization of their substances. From the methanolic extracts of these species, a total of 54 metabolites were identified for the first time using this hyphenated technique, including thirty compounds in P. andinum, and thirty-seven in P. robustum. Moreover, two compounds were not identified as known compounds, and could be new structures, according to our data. This report shows that this technique is effective and accurate for rapid chemical identification of lichen substances and the compounds identified could serve as chemotaxonomic markers to differentiate these ruffle lichens.

Electrocomposite Developed with Chitosan and Ionic Liquids Using Screen-Printed Carbon Electrodes Useful to Detect Rutin in Tropical Fruits

This work reports the development of a composite of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BP4) and chitosan (CS) described in previous reports through a new method using cyclic voltammetry with 10 cycles at a scan rate of 50.0 mV s−1. This method is different from usual methods such as casting, deposition, and constant potential, and it allows the development of an electroactive surface toward the oxidation of rutin by stripping voltammetry applied to the detection in tropical fruits such as orange, lemon, and agraz (Vaccinium meridionale Swartz), with results similar to those reported in previous studies. In addition, the surface was characterized by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and Raman spectroscopy. The limit of detection was 0.07 µmol L−1 and the relative standard deviation (RSD) of 10 measurements using the same modified electrode was 0.86%. Moreover, the stability of the sensor was studied for six days using the same modified electrode, where the variation of the signal using a known concentration of rutin (RT) was found to be less than 5.0%. The method was validated using a urine chemistry control spiked with known amounts of RT and possible interference was studied using ten substances including organic and biological compounds, metal ions, and dyes. The results obtained in this study demonstrated that this electrodeveloped composite was sensitive, selective, and stable.