dc Proton conductivity at low‐frequency in Nafion conductivity spectrum probed by time‐resolved SAXS measurements and impedance spectroscopy

The electric transport properties of Nafion membranes are investigated by impedance spectroscopy (IS) and correlated with small angle X‐ray scattering (SAXS). Detailed IS measurements in a wide range of temperature and frequencies (f) allowed separating contributions from different charge carriers in Nafion. At controlled relative humidity and temperature, Nafion IS spectrum exhibits at T > 160 °C two distinct frequency‐independent conductivities occurring at high f ～ 10⁶ Hz and low f < 10^?2 Hz. Such IS measurements were combined with time‐dependent SAXS measurements under applied dc electric potential, which provided compelling evidence that the low‐f dc conductivity is related to the motion of protons via ion‐hopping in hydrated Nafion membranes. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 822–828     

Magnetic composites from minerals: study of the iron phases in clay and diatomite using Mössbauer spectroscopy, magnetic measurements and XRD

Magnetic particles as matrix for enzyme immobilization have been used and due to the enzymatic derivative can be easily removed from the reaction mixture by a magnetic field. This work presents a study about the synthesis and characterization of iron phases into magnetic montmorillonite clay (mMMT) and magnetic diatomaceous earth (mDE) by ⁵⁷Fe Mössbauer spectroscopy (MS), magnetic measurements and X-ray diffraction (XRD). Also these magnetic materials were assessed as matrices for the immobilization of invertase via covalent binding. Mössbauer spectra of the magnetic composites performed at 4.2 K showed a mixture of magnetite and maghemite about equal proportion in the mMMT, and a pure magnetite phase in the sample mDE. These results were verified using XRD. The residual specific activity of the immobilized invertase on mMMT and mDE were 83 % and 92.5 %, respectively. Thus, both magnetic composites showed to be promising matrices for covalent immobilization of invertase.     

Optical and morphological properties of N-doped TiO2 thin films

Nitrogen doped titanium dioxide (TiO₂) thin films were deposited by RF magnetron sputtering onto various substrates. The films were prepared in plasma of argon, oxygen, and nitrogen, with varying the nitrogen content, from 0% up to 70%. The resulting TiOx–Ny films were found to consist of cubic TiN osbornite and tetragonal TiO₂ rutile phases. Using optical spectroscopy with large spectral range from 350 to 1000 nm, the band gap width was determined and a narrowing of the optical gap from 2.76 to 2.32 eV was observed as a function of the N-content. It was found that the optical properties of the TiOx–Ny layers are influenced by the surface morphology, roughness, surface energy and phase content. The chemical composition, the crystalline structure, the surface morphology and the surface energy were thoroughly studied by the Rutherford backscattering spectrometry (RBS), grazing-angle XRD, atomic force microscopy (AFM) and contact angle measurements (wettability), respectively.     

Impedance spectroscopy investigation of the water-in-oil microemulsions formation

In this work it was investigated the microemulsion formation using impedance spectroscopy analysis. The results indicated that the microemulsion formation is clearly observed on the impedance complex plane. The phase transition related with microemulsion formation is characterized by a time relaxation distribution. In the condition of the microemulsion formation, the impedance spectra are characterized by a single relaxation time.     

Noise-to-Harmonics Ratio as an Acoustic Measure of Voice Disorders in Boys

This prospective study assessed the efficacy of computerized noise-to-harmonics ratio (NHR) to quantify perceptual and endoscopic findings of dysphonia and/or structural lesion of the vocal fold. Fifty Brazilian boys without vocal complaints were submitted to computerized, perceptual, and endoscopic examination. Thirty boys were dysphonic--3 were classified into the grade category, 5 into breathiness, 9 into roughness, and 15 into grade/breathiness. Vocal fold lesions were observed in 25 boys (17 nodules and 8 cysts). The Mann-Whitney U test revealed that NHR was significantly higher in boys with a structural lesion (p = 0.007) and in boys with dysphonia (p < 0.0001). However, according to a logistic regression model, only the occurrence of dysphonia was explained by NHR; the risk for having dysphonia increased approximately twice (odds ratio = 1.92, 95% confidence interval = 1.3-2.9) with each increase of 0.01 in NHR. Our results suggest that noise is a useful quantitative index to confirm a perceptual diagnosis of dysphonia and to evaluate quantitative changes in a dysphonic voice over time. However, we believe that computerized analysis should be used as a complement, rather than a substitute, for perceptual evaluation. Further studies with a larger sample are required to investigate the relationship between noise and lesions of the vocal folds.     

Palladium(II) chemically bonded to silica surface applied to the separation and identification of polycyclic aromatic sulfur heterocycles in heavy oil

Separation of polycyclic aromatic sulfur heterocycles among themselves and also from interferents in petrochemical matrices is a challenging task because of their low concentration, matrix complexity, and also due to the presence of polyaromatic hydrocarbons, as they present similar physico‐chemical properties. Therefore, the objective of this work was preparation, characterization, and application of a stationary phase for separation of these compounds in a heavy gas oil sample and their identification by comprehensive two‐dimensional gas chromatography. The stationary phase was prepared by grafting mercaptopropyltrimethoxisilane onto a silica surface, followed by palladium(II) chloride immobilization. Elemental analysis, thermogravimetry, nitrogen adsorption‐desorption isotherms, infrared analysis, and scanning electron microscopy were performed to characterize this solid phase. Sulfur compounds were separated in an open column packed with the stationary phase and analyzed by comprehensive two‐dimensional gas chromatography coupled to time‐of‐flight mass spectrometric detection. The number of compounds tentatively identified was 314 and their classes were thiophenes, benzotiophenes, dibenzothiophenes, naphthothiophenes, benzonaphthothiophenes, and dinaphthothiophenes. Separation among sulfur compounds and polyaromatic hydrocarbons was successful, which is a difficult goal to achieve with the traditionally employed solid phases. Some recalcitrant compounds (dibenzothiophenes with substituents of two and four carbons) were fully separated and tentatively identified.     

Arylid-OX and Arylid-BOX derived catalysts: applications in catalytic asymmetric cyclopropanation

A novel family of chiral non-racemic monodentate oxazoline ligands known as Arylid-OXs 1a and 1b was prepared in good overall yields. These ligands were screened in bench-mark Cu(I)-catalyzed cyclopropanations and gave ees as high as 58%. Both ¹H NMR and computational studies using 1a indicated that the active catalyst was most likely to be the di-coordinated complex, Cu(I)-1a₂(MeCN)₂. Two novel ortho-substituted Arylid-BOX ligands 2a and 2b were also synthesized in very good yields. These ligands were tested in the same reaction as for 1a and 1b and, although excellent yields could be obtained with 2b, which is assumed to be due to an electron-donating effect from the ortho-methoxy group, a best ee of only 56% was obtained with 2a. In fact, both the enantioselectivities and diastereoselectivities obtained with these ortho-substituted ligands were in line with those previously obtained with the para-substituted series.     

Processing effects of nanometric rare earth-doped tin oxides on the synthesis of methyl vinyl ketone

Nanoparticle catalysts based on SnO₂ were processed by two different methods, víz.the polymeric precursor and high-energy mechanical milling. The sample morphology and catalytic performance in the aldol condensation between methanol and acetone were modified by the processing and rare earth doping. This revised version was published online in August 2006 with corrections to the Cover Date.