1H and 13C NMR assignments of new methoxylated furanoflavonoids from Lonchocarpus araripensis

Two new polymethoxylated flavonoids, 2',5',6'-trimethoxy-[2',3' : 3',4']furano dihydrochalcone and 2,4',4,5-tetramethoxy-[2',3' : 6,7]-furanodihydroaurone, were isolated from the root barks of Lonchocarpus araripensis, along with the known compounds 3,4,5,6-tetramethoxy-[2',3' : 7,8]-furanoflavan, 3,6-dimethoxy-1',1'-dimethylcromene-[2',3' : 7,8]-flavone, 3',4'-methylenodioxy-5,6-dimethoxy-[2',3' : 7,8]-furanoflavone, 3,5,6-trimethoxy-[2',3' : 7,8]-furanoflavanone, 3,5,6-trimethoxy-[2',3' : 7,8]-furanoflavone, and 6alpha-hydroxy-medicarpin. The complete (1)H and (13)C NMR assignments of the new furan flavonoids were performed using 1D and 2D pulse sequences, including COSY, HSQC, and HMBC experiments, and comparison with spectral data for analog compounds from the literature, particularly for the new furanodihydroaurone because of several inconsistencies on the carbonyl chemical shifts from the literature.     

Radioluminescence properties of rare earths doped SrAl2O4 nanopowders

Nanopowders of SrAl₂O₄ pure and doped with rare earths were prepared via a proteic sol-gel methodology. The prepared materials presented a single crystalline phase, confirmed by XRD measurements. AFM results indicate that the average particle size is about 53 nm for SrAl₂O₄ powders. The radioluminescence spectrum of SrAl₂O₄: Eu²⁺, Dy³⁺ is composed by two intense peaks around 520 and 570 nm followed by a weaker emission peaking at 615 nm. It was observed that the intensity of RL emission during irradiation with X-rays decreased as a function of the irradiation time, indicating the build up of radiation damage in the nanopowders. The irradiated samples exhibited a persistent radiation damage that changes the colour of the sample, and also influenced the reduction in the scintillation efficiency. The saturation level of SrAl₂O₄: Eu²⁺ is 96%, exhibiting good resistance to radiation damage.     

Lateral Casimir force beyond the proximity-force approximation

We argue that the appropriate variable to study a nontrivial geometry dependence of the Casimir force is the lateral component of the Casimir force, which we evaluate between two corrugated metallic plates outside the validity of the proximity-force approximation. The metallic plates are described by the plasma model, with arbitrary values for the plasma wavelength, the plate separation, and the corrugation period, the corrugation amplitude remaining the smallest length scale. Our analysis shows that in realistic experimental situations the proximity-force approximation overestimates the force by up to 30%.     

Optimization of the sonication extraction method of Hibiscus tiliaceus L. flowers

The influence of several experimental parameters on the ultrasonic extraction of Hibiscus tiliaceus L. flowers were investigated: extraction time, solvent polarity, sample amount, solvent volume and sample particle size. It was concluded that the most influential variables were extraction time and solvent polarity. The optimized procedure employed 5 g of ground flowers, 150 mL of methanol and 140 min of extraction. The extracts were fractionated using preparative silica columns and the resulting fractions were analyzed by GC/MS. Some saturated hydrocarbons, fatty acids, fatty acid methyl esters, phytosterols, and vitamin E were identified in the plant extracts.     

CR-39 alpha particle spectrometry for the separation of the radon decay product 214Po from the thoron decay product 212Po

In this work, it is presented an experimental assembly based on electric capture of radionuclides in order to discriminate the alpha activity of ²¹⁴Po (radon decay product) from ²¹²Po (thoron decay product) one. The alpha activity was registered with CR-39 analyzing etch pit diameters and optical density. This discrimination may allow for the estimation of the relative contribution of the alpha activity due to thoron decay products compared to the total activity due to radon decay products.     

Tuning Selectivity and Sensitivity of Mixed‐polymeric Tetraruthenated Metalloporphyrins Modified Electrodes as Voltammetric Sensors of Chloramphenicol

Mixed Ni?Co tetraruthenated porphyrin films were successfully electropolymerized on glassy carbon electrodes in alkaline solutions (pH=13) of NiTRP and CoTRP, giving excellent electrocatalytic responses for determination of the antibiotic drug chloramphenicol. Electrodes with four different compositions were obtained by varying the ratio of NiTRP and CoTRP in the deposition solution. For the characterization of these materials, SEM, ICP‐MS, EIS and CV were explored. The porphyrin modified glassy carbon electrodes presented two oxidation peaks for chloramphenicol (except for Ni‐25). The potential shifted to lower values as the percentage of CoTRP increased decreasing its oxidation potential in more than 200 mV for Ni‐50 as compared to Ni‐100. Interestingly, the materials with cobalt content larger than 50 % did not show the typical catalytic response of the Ni^IIIOOH species, but rather showed an increase in current at potentials larger than 0.4 V, demonstrating the key role played by nickel in this type of materials. The composition of polymeric mixed porphyrin materials influenced the oxidation current response of both redox waves, resulting in different sensitivities on the calibration curves.     

Rapid method for simultaneous determination of ascorbic acid and zinc in effervescent tablets by capillary zone electrophoresis with contactless conductivity detection

Ascorbic acid and zinc are essential nutrients that play important roles in nutrition, immune support, and maintenance of health. For this reason, both compounds are widely used as ingredients in dietary supplements. We report, for the first time, an analytical method for fast simultaneous determination of ascorbic acid and zinc. A single analysis run is possible every 80 s (45 injections/h). The method is based on capillary electrophoresis with capacitively coupled contactless conductivity detection using a fused silica capillary with 50 cm length (effective length of 10 cm). The separation was achieved by using a background electrolyte composed by 30 mmol/L of 2‐(morpholin‐4‐yl)ethane‐1‐sulfonic acid and 30 mmol/L of histidine, pH 6.1. The detection limits were 10 and 20 μmol/L and recovery values for spiked samples were 101 and 100% for zinc and ascorbic acid, respectively. The results obtained with the developed procedure were compared to those obtained by titration (ascorbic acid) and flame atomic absorption spectroscopy (zinc), and no statistically significant differences were observed (95% confidence level).     

Synthesis and electrochemical properties of vanadyl phosphate di-hydrate/polyaniline derivatives hybrid films

Vanadyl phosphate and its hybrid compounds have proven to undergo electrochemical intercalation and de-intercalation of lithium ions, which enables its use as cathode material for Li ion rechargeable batteries. In this context, vanadyl phosphate di-hydrate/polyaniline derivatives hybrid films were synthesized via the exfoliation and reconstruction approach in order to evaluate their potential use as cathode in ion lithium batteries. X-ray diffraction patterns indicate that the lamellar structure of the inorganic matrix is maintained, consistent with the topotactic process. In the scanning electron micrographs, hybrid films exhibit rough surface consisting of warped and cracked crystallites, quite different from vanadyl phosphate di-hydrate square platelets crystallites. Electrochemical evaluation using cyclic voltammetry and charge–discharge galvanostatic techniques shows small differences between the charge and the discharge curves, indicating an irreversibility of the hybrid systems.     

Hyperchaos and quasiperiodicity from a four-dimensional system based on the Lorenz system

This paper reports on numerically computed parameter plane plots for a dynamical system modeled by a set of five-parameter, four autonomous first-order nonlinear ordinary differential equations. The dynamical behavior of each point, in each parameter plane, is characterized by Lyapunov exponents spectra. Each of these diagrams indicates parameter values for which hyperchaos, chaos, quasiperiodicity, and periodicity may be found. In fact, each diagram shows delimited regions where each of these behaviors happens. Moreover, it is shown that some of these parameter planes display organized periodic structures embedded in quasiperiodic and chaotic regions.