Kinetics of pyrolysis of some biomasses widely available in Brazil

Journal of Thermal Analysis and Calorimetry - Biomass conversion via thermal processes to generate energy will be an important part of the future energy landscape. The objective of this study was...     

Nanofibrous polysulfone/TiO2 nanocomposites: Surface properties and their relation with E. coli adhesion

Solution blow spinning, SBS, was used to prepare fibrous films of thermoplastic nanocomposites with potential antibacterial properties based on polysulfone, PSF, filled with well dispersed TiO₂ nanoparticles. The PSF/TiO₂ nanocomposites were produced with different nanoparticles content up to 10% by weight. A wide characterization was carried out focusing on the morphology at the nanoscale, roughness, contact angles, and surface free energy. Cell adhesion was studied by inspection by scanning electron microscopy (SEM). A uniform dispersion of the nanofiller was achieved, with the nanoparticles evenly embedded in the polymer along the fibers when they were created during the blow spinning process. TiO₂ content influenced the topography of the films, most likely due to a direct effect on the solvent evaporation rate. The results obtained pointed out that an increase of the surface hydrophobicity as a result of the increased roughness induced by the presence of TiO₂ nanoparticles was the main contribution to the reduction of DH5α Escherichia coli cells adhesion. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1575–1584     

Mercury speciation analysis in human hair by species-specific isotope-dilution using GC–ICP–MS

We optimized a mercury (Hg) speciation extraction method for human hair in combination with species-specific isotope-dilution analysis by gas chromatography–inductively coupled plasma–mass spectrometry (GC–ICP–MS). The method was validated on human hair reference material RM (IAEA-086), which is recommended for analysis of monomethylmercury (MMHg) and inorganic mercury (IHg). Three reagents, hydrochloric acid (HCl), nitric acid (HNO₃), and tetramethylammonium hydroxide (TMAH), and three extraction procedures, at ambient temperature for 12 h, microwave-assisted at 75 °C for 6 min, and oven heated at 80 °C for 2 h were tested. Extraction efficiency, recovery, and potential species transformations were evaluated for each method. The most efficient procedures, with recovery of ~90 % for each species with limited demethylation (<5 %) and methylation (0 %), were HNO₃ digestion, irrespective of temperature, and microwave-assisted TMAH extraction. Acidic extraction with HCl induces significant demethylation, with production of artifacts. To correct for potential demethylation artifacts we recommend spiking with isotopically enriched standards before the extraction step.     

Existence of seven solutions for an asymptotically linear Dirichlet problem without symmetries

In this paper, we establish sufficient conditions for an asymptotically linear elliptic boundary value problem to have at least seven solutions. We use the mountain pass theorem, Lyapunov–Schmidt reduction arguments, existence of solutions that change sign exactly once, and bifurcation properties. No symmetry is assumed on the domain or the non-linearity.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Heteronuclear 3 d/DyIII Coordination Clusters as Catalysts in a Domino Reaction

Three isoskeletal tetranuclear coordination clusters with general formula [M^II₂Dy^III₂L₄(EtOH)₆](ClO₄)₂?2 EtOH, (M=Co, 1 ; M=Ni, 2 ) and [Ni^II₂Dy^III₂L₄Cl₂(CH₃CN)₂]?2 CH₃CN ( 3 ), have been synthesized and characterized. These air‐stable compounds, and in particular 3 , display efficient homogeneous catalytic behavior in the room‐temperature synthesis of trans‐4,5‐diaminocyclopent‐2‐enones from 2‐furaldehyde and primary or secondary amines under a non‐inert atmosphere.     

Preparation and evaluation of lauryl methacrylate monoliths with embedded silver nanoparticles for capillary electrochromatography

In this article, capillary columns constituted by lauryl methacrylate monoliths with embedded silver nanoparticles (AgNPs) were developed and tested. Two incorporation approaches of AgNPs in monoliths were explored. The AgNPs were either photogenerated in situ during polymerization of the monolith by UV irradiation, or incorporated to the polymerization mixture (ex situ). The influence of the AgNP concentration on the morphological and chromatographic properties of the polymer matrix was investigated, and both the in situ and ex situ approaches were comparatively discussed. The morphology of the monoliths was characterized by electron microscopic techniques, and their electrochromatographic performance was also evaluated with test mixtures of neutral compounds (sterols, fatty acid methyl esters, tocopherols, and polyaromatic hydrocarbons).