Thermal and mechanical behavior of biodegradable polyester films containing cellulose nanofibers

Journal of Thermal Analysis and Calorimetry - Agricultural waste is a valuable source of advanced materials. Cheap nanocellulose may be obtained from plum shells agricultural residues and further...     

Leaving us with fond memories,smiles, SMILES and,alas, tears: a tribute to David Weininger, 1952–2016

David Weininger’s career, accomplishments, genius, and friendship are warmly remembered by several of his colleagues, friends, and admirers.     

Poly(ethylene glycol)/β-cyclodextrin covalent gel networks: host matrices for studying radical processes in plant extract–riboflavin systems following UV irradiation

Finding new, biocompatible matrices that allow us to model the generation of free radicals is of utmost importance for balancing the harmful and beneficial effects of the latter. In this respect, we report here the simultaneous encapsulation of the radical source and the antioxidant agent in a polyethylene glycol/β-cyclodextrin (PEG/β-CD) covalent gel network. We used electron paramagnetic resonance spectroscopy to evaluate the scavenging action of plant extracts (purple loosestrife, comfrey, milfoil, horsetail, thyme, carob, green coffee) embedded in PEG/β-CD gels. Free radicals were generated in situ by UV irradiation of riboflavin co-embedded in the gels. Prior to this, the extracts were characterized in what concerns their antioxidant activity, and their major polyphenolic constituents were quantified by liquid chromatography-electrospray ionization-tandem mass spectrometry. Purple loosestrife showed the highest antioxidant capacity, followed by comfrey and milfoil. Using the 5,5-dimethyl-1-pyrroline N-oxide spin trap, we have demonstrated that the gel-embedded extracts effectively scavenge the reactive carbon-centered free radicals generated in gel. The PEG/β-CD gels have been shown to be a valuable alternative matrix for the encapsulation of plant active principles having antioxidant activity. Moreover, co-encapsulation of the radical source transforms these gels into a controlled environment in which free radical processes can be tailored.     

Temperature effect over structure and photochemical properties of nanostructured SnO<Subscript>2</Subscript> powders

We successfully synthesized tin dioxide nanoparticles with polyhedral morphology via an ethylene glycol assisted sol-gel approach. The structural characteristics of three tin dioxide samples were investigated after being thermally treated at 400°C, 600°C and 800°C. X-ray diffraction (XRD) patterns clearly show the formation of single phase tin dioxide nanoparticles, with crystallite size of 6–20 nm, in good correlation with Fourier transform infrared (FTIR) spectra. Transmission electron microscopy (TEM) analysis confirms the formation of 6nm polyhedral nanoparticles for the 400°C sample. Ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectra suggest a high concentration of oxygen vacancies. The oxygen vacancy concentration increases with temperature, due to the combined action of the formation of V_O and the energetic O compensation. X-ray photoelectron spectroscopy (XPS) analysis also confirms the formation of single phase tin dioxide and the presence of oxygen vacancies in good agreement with UV-VIS and PL data.

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Synthesis and characterization of ZnO nanostructures obtained in mixtures of ionic liquids with organic solvents

ZnO nanoparticles were synthesized in mixtures of ionic liquids based on imidazolium cation with organic solvents (dimethyl sulfoxide and ethylene glycol) by a simple, one-step solution route at low temperature. The effect of these mixtures on the morphology, size and properties of as obtained ZnO nanopowders was investigated. The obtained nanopowders have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV-Vis absorption spectroscopy (UV-Vis) and photoluminescence (PL). The effect of the ionic liquid mixture on the photocatalytic degradation of methylene blue has been analysed. The XRD studies confirmed the hexagonal wurtzite structure of the obtained ZnO powder. The UV-Vis absorption spectra present the typical shape for ZnO, with a broad band situated in the UV region, with the maximum around 360 nm. The calculated band-gap energy is in interval 3.25–3.28 eV. The synthesized ZnO nanopowders have high photocatalytic activity against methylene blue, the best results being obtained when 1-ethyl-3-methylimidazolium tetrafluoroborate was used as the solvent.

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Kinetic studies for the esterification of acetic acid with epichlorohydrin over an anion exchange resin catalyst

The kinetics of the esterification reaction between acetic acid and epichlorohydrin catalysed by Purolite A-520E strong basic anion exchange resin was studied. The effects of certain parameters such as stirring speed, particle diameter, temperature, catalyst amount and molar ratio between reactants were experimentally determined. It was found that the overall reaction rate is intrinsically kinetically controlled. The partial orders of reaction with respect to catalyst, acetic acid and epichlorohydrin were determined. A reaction mechanism is proposed. Based on chromatographic data and taking into account the partial orders of reaction, a more detailed kinetic model is suggested.      

Ligand-based virtual screening by novelty detection with self-organizing maps

We describe a novel method for ligand-based virtual screening, based on utilizing Self-Organizing Maps (SOM) as a novelty detection device. Novelty detection (or one-class classification) refers to the attempt of identifying patterns that do not belong to the space covered by a given data set. In ligand-based virtual screening, chemical structures perceived as novel lie outside the known activity space and can therefore be discarded from further investigation. In this context, the concept of "novel structure" refers to a compound, which is unlikely to share the activity of the query structures. Compounds not perceived as "novel" are suspected to share the activity of the query structures. Nowadays, various databases contain active structures but access to compounds which have been found to be inactive in a biological assay is limited. This work addresses this problem via novelty detection, which does not require proven inactive compounds. The structures are described by spatial autocorrelation functions weighted by atomic physicochemical properties. Different methods for selecting a subset of targets from a larger set are discussed. A comparison with similarity search based on Daylight fingerprints followed by data fusion is presented. The two methods complement each other to a large extent. In a retrospective screening of the WOMBAT database novelty detection with SOM gave enrichment factors between 105 and 462-an improvement over the similarity search based on Daylight fingerprints between 25% and 100%, when the 100 top ranked structures were considered. Novelty detection with SOM is applicable (1) to improve the retrieval of potentially active compounds also in concert with other virtual screening methods; (2) as a library design tool for discarding a large number of compounds, which are unlikely to possess a given biological activity; and (3) for selecting a small number of potentially active compounds from a large data set.     

Contribution of polymeric swelling to the overall response of capacitive gas sensors

A new method for investigation of the swelling of polymers on exposure to gas or vapour has been devised and tested. It uses an optical profilometer (based on the chromatic aberration of a lens system) which is integrated into a computer-controlled gas-dosing and mixing setup. Gas and/or vapour concentration-dependent measurements have been carried out for thick layers of the polymers commonly used in gravimetric and capacitive gas sensors: poly(acrylic acid) (PAA), poly(vinyl pyrrolidone) (PVP), poly(ether urethane) (PEUT), and polydimethylsiloxane (PDMS). The thickness of PAA, PVP, and PEUT films changed significantly on exposure to humidity. These data have been used to derive the sorption isotherms of the respective polymers, which were found to be Henry or Flory–Huggins isotherms. Comparison of the geometrical (swelling) responses with capacitive responses revealed a strong correlation. The correlation, which occurs because both types of response are proportional to the water content of the polymer, is also valid for polymers with nonlinear gas responses. Finally the geometrical and electrical characteristics of the capacitive samples were used to explain the dependence of the capacitive response of different polymers on the concentration of the target gas or vapour. In this way was deduced that PDMS, which does not swell on exposure to humidity, swells in the presence of 2,3-dimethylpentane, for which no profilometer evaluations are yet available.