Isoniazid-sensing Behavior of a Hybrid Silsesquioxane and Cobalt Pentacyanonitrosylferrate-based Nanocomposite

A novel silsesquioxane and cobalt nitroprusside compound was prepared from octa(aminopropyl)silsesquioxane, resulting in a nanocomposite (ACCoN), which was then characterized by different spectroscopic techniques. The cyclic voltammograms of the ACCoN-modified graphite paste electrode indicated a redox pair with a formal potential (E^θ′)=0.38 V, assigned to the Co^(II)Fe^(II)(CN)₅NO/Co^(II)Fe^(III)(CN)₅NO redox couple. The ACCoN-modified graphite paste electrode was sensitive to isoniazid concentrations, presenting a linear response at a concentration range from 6.0×10⁻⁷ to 1.0×10⁻⁵ mol L⁻¹, with limit of detection and amperometric sensitivity of 5.53×10⁻⁷ mol L⁻¹ and 0.17 A/mol L⁻¹, respectively.     

CeCl3-mediated addition of acetylenic bis-lithium salts to aldehydes and ketones: An efficient route to bis-substituted alkyne diols

An efficient, chemoselective protocol to access propargylic diols via a CeCl₃-mediated addition reaction is reported. Propargylic alcohols were transformed into the corresponding acetylenic bis-lithium salt intermediates, which react with aldehydes and ketones in the presence of dry CeCl₃ to furnish the corresponding bis-substituted alkyne diols. This protocol does not involve protection-deprotection or transmetallation steps, and allows the use of poorly reactive or highly enolizable substrates.     

Characterization,thermal properties and phase transitions of amazonian vegetable oils

Thermal profiles of buriti pulp oil (Mauritia flexuosa Mart.), tucumã pulp and kernel oils (Astrocarium vulgare Mart.), rubber seed oil (Hevea brasiliensis), passion fruit oil (Passiflora edulis) and ucuúba butter (Virola surinamensis) were analyzed by thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC). Gas chromatography and calculated iodine values were performed to determine the fatty acid profile and to measure the degree of unsaturation in these oils, respectively. The TG curves showed three steps of mass loss, which can be attributed to the degradation of polyunsaturated, monounsaturated and saturated fatty acids. The DSC crystallization and melting curves are reported and depended on the fatty acid composition. Usually, oil samples with a high degree of saturation showed crystallization and melting profiles at higher temperatures than the oils with a high degree of unsaturation. The data obtained by physicochemical analysis of oil samples were analyzed by principal component analysis and hierarchical cluster analysis to increase understanding of the data set, examining the presence or absence of natural groupings between samples.     

Multiscale Creep Compliance of Epoxy Networks at Elevated Temperatures

Epoxy networks are thermoset polymers for which an important structural length scale, molecular weight between crosslinks (M _c), influences physical and mechanical properties. In the present work, creep compliance was measured for three aliphatic epoxy networks of differing M _c using both macroscale torsion and microscale depth-sensing indentation at temperatures of 25 and 55°C. Analytical relations were used to compute creep compliance (J(t)) for each approach; similar results were observed for the two techniques at 25°C, but not at 55°C. Although creep compliance measurement differed at elevated temperatures, there were clear correlations between M _c, glass transition temperature, T _g, and the observed time-dependent mechanical behavior via both techniques at 55°C, but these correlations could not be seen at 25°C. This work demonstrates the capacity of depth-sensing indentation to differentiate among epoxy networks of differing structural configurations via J(t) for small material volumes at elevated temperatures.     

Use of elemental and molecular-mass spectrometry to assess the toxicological effects of inorganic mercury in the mouse Mus musculus

The biochemical response of mice (Mus musculus) to acute subcutaneous inorganic-mercury exposure was assessed over a 14-day period by analyzing cytosolic extracts of the liver, the kidneys, and blood plasma. Integrated metallomic and metabolomic approaches using elemental and molecular-mass spectrometry were used to obtain comprehensive insight into the toxicological effects of mercury regarding its distribution and possible perturbation of metabolic pathways. The metallomic approach involved the use of size-exclusion chromatography (SEC) coupled with multiaffinity chromatography inductively coupled plasma-mass spectrometry (ICP-MS) and isotopic-dilution analysis. The metabolomic approach involved the direct infusion of polar and lipophilic tissue extracts into a mass spectrometer (DIMS) in the positive and negative acquisition mode (ESI+and ESI?). The use of SEC–ICP-MS enabled us to detect changes in the metalloproteome in the liver and the kidneys during the exposure period, and revealed that interactions between Hg and endogenous Cu and Zn adversely affected the homeostasis of these essential metals. The detection of an Hg–Se detoxification product in mouse plasma substantiated the known interaction between Hg and Se in mammals. Use of DIMS in conjunction with partial-least-squares discriminant analysis (PLS-DA) uncovered time-dependent changes of endogenous metabolites over time, corroborated by histopathology investigation of specific mouse tissues. The perturbations of endogenous metabolic profiles were explained in terms of the adverse effect of mercury on energy metabolism (e.g. glycolysis, Krebs cycle), the degradation of membrane phospholipids (apoptosis), and increased levels of specific lipids in plasma. In summary, use of an SEC–ICP-MS-based metallomics approach in conjunction with molecular-mass-spectrometry-based metabolomics is revealed as a promising strategy to more comprehensively investigate the toxicological effects of harmful environmental pollutants and xenobiotics. ?      

Automated Determination of Cu(II), Pb(II), Cd(II) and Zn(II) in Environmental Samples by Square Wave Voltammetry Exploiting Sequential Injection Analysis and Screen Printed Electrodes

This paper describes the development of a methodology for quantification of Cu(II), Pb(II), Cd(II) and Zn(II) in waters and sediments by anodic stripping voltammetry (ASV) automated by Sequential Injection Analysis (SIA) using a graphite screen printed sensor modified with mercury. Determinations were made by standard addition automated by the SIA system. The limits of detection and quantification were, respectively, 1.3 and 4.3 µg L^?1 for Cu(II), 1.4 and 4.6 µg L^?1 for Pb(II), 0.6 and 1.8 µg L^?1 for Cd(II) and 4.2 and 14 µg L^?1 for Zn(II). These limits were obtained for a sample volume of 1000 µL, flow rate of 10 µL s^?1 (during the deposition step), and utilizing 3 flow reversals (volume of reversion=950 µL), totalizing a deposition time of 315 s. The potentiostat worked synchronically with the SIA system applying the conditioning potential of ?0.1 V vs. pseudo reference of Ag (100 s), deposition potential of ?1.0 V for Cu(II), Pb(II) and Cd(II) or ?1,3 V for Zn(II), square wave frequency of 100 Hz, potential step of 6 mV and pulse height of 40 mV. For quantification of Zn(II) in sediment extracts, deposition of Ga⁰ on the working electrode was necessary to avoid the formation of intermetallic between Zn⁰ and Cu⁰. The accuracy of the method was assessed by spike and recovery experiments in water samples which resulted recovery rates near 100 % of the spiked concentrations. Recoveries of concentrations in the certified sediment sample CRM‐701 undergoing the three steps sequential extraction procedure of BCR varied from 71.7 % for Zn(II) in the acetic acid extract to 112.4 % for Cu(II) in the oxidisable fraction, confirming that the standard addition approach corrected the matrix effects in the complex samples of sediment extracts.     

Obtaining nanocomposites of polyamide 6 and cellulose whiskers via extrusion and injection molding

Nanocomposites of polyamides with cellulose whiskers are difficult to obtain by conventional processing of extrusion and injection molding because of the low thermal stability of the cellulosic nanostructures and the relatively high processing temperature of polyamides, which is higher than the temperature of thermal degradation of cellulose whiskers. Thus, in this study cellulose whiskers were coated with polyamide 6 (PA6) in order to increase their thermal stability and prevent the formation of agglomerates. This coating on cellulose whiskers allows their application to obtain nanocomposites with polyamides, whose processing temperatures are relatively high, around 250 °C. Cellulose whiskers (CWs) were obtained from cotton fibers by acid hydrolysis. The freeze-dried CWs were coated with PA6 by dispersing them in formic acid; PA6 was solubilized in this suspension. The cellulose-coated whiskers (CCWs) were characterized by X-ray diffraction, differential scanning calorimetry (DSC), thermogravimetry (TG), scanning electron microscopy (SEM-FEG) and infrared spectroscopy. SEM-FEG and TG results showed that the PA6 coating on CWs prevented high agglomeration of dried CWs and promoted an increase in their thermal stability from 180 to 280 °C, allowing the use of CCWs to obtain nanocomposites with PA6 using conventional processing routes, such as extrusion and injection molding, at appropriate processing temperatures. In this way, 1 wt% CCWs was used to prepare nanocomposites with PA6. The PA6 + 1CW nanocomposites were compared to neat PA6 without CWs. The samples were characterized by tensile tests and DSC, and the results showed that the PA6 coating on CWs was effective in raising the thermal stability of CWs, improving the dispersion of CWs in the matrix of PA6, resulting in a 45 % increase in the elastic modulus of the nanocomposite with only 1 wt% of coated cellulose whiskers in comparison to neat PA6.     

Thermal behavior and the compensation effect of vegetal fibers

The thermal degradation behavior and the Arrhenius parameter of curaua, kenaf, and jute vegetal fibers were studied using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and thermogravimetry analysis. XRD showed that the crystallite sizes in the (200) plane were in the order: curaua < jute < kenaf, and similar results were obtained for basal spacing. FTIR spectroscopy corroborated the XRD results. The thermal behavior of the fibers was analyzed by identifying the cellulose and hemicellulose content using independent parallel first-order models. The results were not very consistent with the kinetic degradation models of Kissinger, Friedman, and Flynn–Wall–Ozawa (taking into account the standard errors), which were used to determine the apparent activation energy of the fibers. In addition, the frequency factor (pre-exponential parameter) was observed to be independent of the heating rate. The fibers exhibited a compensation effect; i.e., higher apparent activation energies led to higher frequency factors. Finally, the solid-state degradation mechanism of all fibers was found to comprise diffusion and random nucleation followed by instantaneous growth of nuclei.