The obtaining of NiCr2O4 nanoparticles by unconventional synthesis methods

This paper presents a study regarding the obtaining of NiCr₂O₄ by two new unconventional synthesis methods: (i) the first method is based on the formation of Cr(III) and Ni(II) carboxylate-type precursors in the redox reaction between the nitrate ion and 1,3-propanediol. The thermal decomposition of these complex combinations, at ~300 °C, leads to an oxide mixture of Cr₂O_3+x and NiO, with advanced homogeneity, small particles and high reactivity. On heating this mixture at 500 °C, Cr₂O₃ reacts with NiO to form NiCr₂O₄, which was evidenced by FT-IR and X-ray diffractometry (XRD) analysis; (ii) the second method starts from a mechanical mixture of (NH₄)₂Cr₂O₇ and Ni(NO₃)₂·6H₂O. On heating this mixture, a violent decomposition at 240 °C with formation of an oxides mixture (Cr₂O₃ + CrO₃) and NiO takes place. On thermal treatment up to 500 °C, an intermediary phase NiCrO₄ is formed, which by decomposition at ~700 °C leads to NiCr₂O₄, evidenced by FT-IR and XRD analysis. NiCr₂O₄ is formed, in both cases, starting with a temperature higher than 400 °C, when the non-stoichiometric chromium oxide (Cr₂O_3+x ) loses the oxygen excess and turns to stoichiometric chromium oxide (Cr₂O₃), which further reacts with NiO.     

Gold internal standard correction for elemental imaging of soft tissue sections by LA-ICP-MS: element distribution in eye microstructures

Laser ablation coupled to inductively coupled plasma mass spectrometry has been developed for the elemental imaging of Mg, Fe and Cu distribution in histological tissue sections of fixed eyes, embedded in paraffin, from human donors (cadavers). This work presents the development of a novel internal standard correction methodology based on the deposition of a homogeneous thin gold film on the tissue surface and the use of the ¹⁹⁷Au⁺ signal as internal standard. Sample preparation (tissue section thickness) and laser conditions were carefully optimized, and internal normalisation using ¹⁹⁷Au⁺ was compared with ¹³C⁺ correction for imaging applications. ²⁴Mg⁺, ⁵⁶Fe⁺ and ⁶³Cu⁺ distributions were investigated in histological sections of the anterior segment of the eye (including the iris, ciliary body, cornea and trabecular meshwork) and were shown to be heterogeneously distributed along those tissue structures. Reproducibility was assessed by imaging different human eye sections from the same donor and from ten different eyes from adult normal donors, which showed that similar spatial maps were obtained and therefore demonstrate the analytical potential of using ¹⁹⁷Au⁺ as internal standard. The proposed analytical approach could offer a robust tool with great practical interest for clinical studies, e.g. to investigate trace element distribution of metals and their alterations in ocular diseases.

Development of a nanocomposite system and its application in biosensors construction

The present work describes the development of a nanocomposite system and its application in construction of a new amperometric biosensor applied in the determination of total polyphenolic content from propolis extracts. The nanocomposite system was based on covalent immobilization of laccase on functionalized indium tin oxide nanoparticles and it was morphologically and structural characterized. The casting of the developed nanocomposite system on the surface of a screen-printed electrode was used for biosensor fabrication. The analytical performance characteristics of the settled biosensor were determined for rosmarinic acid, caffeic acid and catechol (as laccase specific substrate). The linearity was obtained in the range of 1.06×10^?6 ? 1.50×10^?5 mol L^?1 for rosmarinic acid, 1.90×10^?7 ? 2.80×10^?6 mol L^?1 for caffeic acid and 1.66×10^?6 ? 7.00×10^?6 mol L^?1 for catechol. A good sensitivity of amperometric biosensor 141.15 nA µmol^?1 L^?1 and fair detection limit 7.08×10^?8 mol L^?1 were obtained for caffeic acid. The results obtained for polyphenolic content of propolis extracts were compared with the chromatographic data obtained by liquid-chromatography with diode array detection.      

Voltammetric behavior of rutin at a boron-doped diamond electrode. Its electroanalytical determination in a pharmaceutical formulation

This paper examined for the first time, the possibilities of the usage of a boron-doped diamond electrode for the redox behavior of rutin using cyclic and adsorptive stripping voltammetry. The cyclic voltammograms showed a pair of redox peaks at lower potentials followed by an irreversible oxidation peak at higher positive potential. Using square-wave adsorptive stripping voltammetry, the compound yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 4.0 at +0.48 V (vs. Ag/AgCl) (after 60 s accumulations at a fixed potential of 0.2 V). The calibration curve was linear in the concentration range from 0.01 µg mL^?1 to 0.1 µg mL^?1 (1.64×10^?8 M ? 1.64×10^?7 M). A detection limit of 0.0017 µg mL^?1 (2.78×10^?9 M) was observed without any chemical modifications and electrochemical surface pretreatments. As an example, the practical applicability of boron-doped diamond electrode was tested with the measurement of rutin in dietary supplement products.      

Stereoconvergent Generation of a Contrasteric syn‐Bicyclopropylidene (=syn‐Cyclopropylidenecyclopropane) by Stille‐Like Coupling

Stereoisomerically pure endo‐ and exo‐7‐halo‐7‐(trimethylstannyl)benzonorcar‐3‐enes (=endo‐ and exo‐(1‐halo‐1a,2,7,7a‐tetrahydro‐1H‐cyclopropa[b]naphthalen‐1‐yl)trimethylstannane) 4 and 6 were selectively obtained by lithium? tin or magnesium? tin transmetalation in good yields (Scheme 2 and 3). The reaction of these compounds with copper(I) thiophene‐2‐carboxylate (CuTC) produced in both cases the corresponding C_S‐symmetric bicyclopropylidene (=cyclopropylidenecyclopropane) syn‐ 1 , a single diastereoisomer (Schemes 5 and 6). The structure of syn‐ 1 was undoubtedly elucidated by X‐ray single crystal diffraction. The coupling mechanism of the carbenoid cyclopropane is discussed (Scheme 7).     

Magnesium Bromide and Magnesium Chloride Hexahydrate Catalyzed One‐Pot Synthesis of Dihydropyrimidines via Biginelli Reaction under Solvent‐Free Conditions

Biologically important 12 new important 3,4‐dihydropyrimidin‐2‐(1H)‐ones (‐thiones) were synthesized with in one‐pot three‐component Biginelli reaction from the corresponding aromatic aldehydes (5‐methyl‐2‐thiophenecarboxaldehyde and 2‐chloro‐5‐nitrobenzaldehyde), β‐keto esters (ethylacetoacetate, allylacetoacetate, and t‐butylacetoacetate), and urea/thiourea in the presence of catalytic amount of magnesium bromide and magnesium chloride hexahydrate as nontoxic, inexpensive, and easily available catalysts under solvent‐free conditions at 80 and 100°C. Compared with the catalyst‐free three‐component Biginelli reaction conditions, this method consistently has the advantage of short reaction time (45–100 min) and good to excellent yields (75–91%).     

4-hydroxy-2H-1,2-benzothiazine-3-carbohydrazide 1,1-dioxide-oxalohydrazide (1:1): X-ray structure and DFT calculations

The title compound, 4-hydroxy-2H-1,2-benzothiazine-3-carbohydrazide 1,1-dioxide-oxalohydrazide (1:1), is determined using X-ray diffraction techniques and the molecular structure is also optimized at the B3LYP/6-31G(d,p) level using density functional theory (DFT). The asymmetric unit consists of four independent molecules. The oxalohydrazide molecules have the centre of symmetry at the mid-point of the central C-C bond. Each thiazine ring adopts a half-chair conformation. Intermolecular C-H...O, N-H...O and N-H...N hydrogen bonds produce R ₂ ² (10), R ₂ ² (13), R ₃ ³ (12) and R ₃ ³ (15) rings, which lead to one-dimensional polymeric chains. An extensive three-dimensional supramolecular network of N-H...N, N-H...O, C-H...O and O-H...O hydrogen bonds is responsible for crystal structure stabilization.     

Interaction of Sodium Dodecyl Sulfate with Poly(ethyleneimine) in Bulk Solution and at the Air-Solution Interface

Interaction of sodium dodecyl sulfate (SDS) with the cationic polyelectrolyte poly(ethyleneimine) (PEI) was investigated in this study. Turbidity measurements were performed in order to analyze the interaction and complex formation in bulk solution as a function of polymer concentration and pH. Surface tension measurements were made to investigate the properties of SDS/PEI/water mixtures at air/solution interface. Results revealed that SDS/PEI complexes form in solution depending on the surfactant and polymer concentration. A decrease was observed in surface tension values in the presence of SDS/PEI mixtures compared to the values of pure SDS solutions. Both solution and interfacial properties exhibited pH dependent behavior. A shift was seen in the critical micelle concentration of SDS solutions as a function of PEI concentration and solution pH. Monovalent and divalent salt additions showed some influence on the interfacial properties of SDS solutions in the presence of PEI.     

Cloud point extraction of aluminum (III) in water samples and determination by electrothermal atomic absorption spectrometry,flame atomic absorption spectrometry and UV-visible spectrophotometry

Cloud point extraction was applied as a preconcentration step for the determination of trace level of Al(III) in water samples with electrothermal atomic absorption spectrometry (ETAAS), flame atomic absorption spectrometry (FAAS) and UV-visible spectrophotometry. The aluminum was extracted as aluminum-Eriochrome Cyanine R (ECR) complex, at pH 6 by micelles of the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114). The investigations showed that the same CPE procedure can be used for different detection techniques. The results obtained from these techniques were evaluated. Under the optimal conditions, limit of detection obtained with ETAAS, FAAS and UV-visible spectrophotometry were 0.03 ng mL^?1, 0.06 µg mL^?1 and 0.01 µg mL^?1, respectively. The accuracy of the procedure was tested by analysing certified reference material. The method was successfully applied to determination of aluminum in water samples and dialysis fluid.     

Selective back-extraction and preconcentration of zinc(II) from metal-1,3,5-triketone extracts prior to its determination by flame atomic absorption spectrometry

A simple back-extraction method was developed for the separation and preconcentration of trace levels of zinc from different matrices. Ethyl-2-(4-methoxybenzoyl)-3-(4-methoxyphenyl)-3-oxopropanoylcarbamate (EMPC) was used as a new complexing agent for the extraction of zinc(II) from the aqueous sample phase to the methyl isobutyl ketone (MIBK) phase as Zn(EMPC)₂ complexes. The Zn(II) can be selectively stripped with 1?mL of 0.5?mol?L^?1 HCl from Mⁿ⁺(EMPC)_n complexes [Ag(I), Al(III), Cd(II), Cr(III), Cu(II), Fe(II), Fe(III), Mn(II), Ni(II), Pb(II) and Pd(II)] which dissolved in MIBK phase. Some experimental parameters, which are important for the whole extraction process, including pH, sample volume, shaking time, amount of the EMPC reagent, amount of MIBK, ionic strength, and type of back-extractant were investigated. The recovery for Zn(II) was greater than 95%. The detection limit of the method was found to be 0.2?µg?L ^{? 1} and the relative standard deviation as 6.4%. The concentrations of Zn(II) in the certified reference materials (LGC6019 river water and NIST-1547 peach leaves) by the presented method were in good agreement with the certified values. The proposed method was succesfully applied to the determination of zinc in some natural waters, rice, hair, soil, and tea samples.