Thermally induced chemical evolution in polyimide films investigated by X‐ray photoelectron spectroscopy

Thermally modified polyimide films based on 1,4‐Phenylene diamine (p‐PDA) and 3,3′,4,4′ – Benzophenone tetracarboxylic dianhydride (BTDA) were prepared and their chemical structure transformation after thermal treatment at 350 °C–500 °C was investigated. X‐ray diffraction results revealed an increase in the polymer chain order for all treated PI samples as a consequence of the thermal treatment and chain interaction. TGA analysis showed that the heat treatment promoted different thermal degradation profiles. Electron spin resonance evidenced a large population of free radicals as a result of homogeneous bond cleavage when the thermal treatment was performed at 500 °C. X‐ray photoelectron spectroscopy analysis indicated that the chemical structure transformation not only occurs on the outer surface but also in the sub‐surface layer. These results show that controlled fast thermal treatment can produce materials with specific characteristics and may serve as a general strategy for changing both structural and chemical properties of the polymers. POLYM. ENG. SCI., 58:943–951, 2018. © 2017 Society of Plastics Engineers     

Complex Analysis of Antioxidant Activity,Abscisic Acid Level,and Accumulation of Osmotica in Apple and Cherry In Vitro Cultures under Osmotic Stress

Plant response to osmotic stress is a complex issue and includes a wide range of physiological and biochemical processes. Extensive studies of known cultivars and their reaction to drought or salinity stress are very important for future breeding of new and tolerant cultivars. Our study focused on the antioxidant activity, accumulations of osmotica, and the content of abscisic acid in apple (cv. “Malinové holovouské”, “Fragrance”, “Rubinstep”, “Idared”, “Car Alexander”) and cherry (cv. “Regina”, “Napoleonova”, “Kaštánka”, “Sunburst”, “P-HL-C”) cultivated in vitro on media containing different levels of polyethylene glycol PEG-6000. Our results indicated that the studied genotypes responded differently to osmotic stress manifested as reduction in the leaf relative water content (RWC) and increment in the activities of antioxidant enzymes, proline, sugars, and abscisic acid content. Overall, cherry cultivars showed a smaller decrease in percentage RWC and enzymatic activities, but enhanced proline content compared to the apple plants cultivars. Cultivars “Rubinstep”, “Napoleonova”, and “Kaštánka” exhibited higher antioxidant capacity and accumulation of osmoprotectants like proline and sorbitol that can be associated with the drought-tolerance system.     

Multi-microbial metabolites in fonio millet (acha) and sesame seeds in Plateau State, Nigeria

We investigated 16 fonio millet and 17 sesame samples by LC/ESI–MS/MS for the spectrum of microbial metabolites contaminating these seeds. Forty-eight fungal and four bacterial metabolites were detected in fonio, while 28 fungal and two bacterial metabolites were found in sesame. Altogether, 55 metabolites were identified in both grains, 18 of which are reported for the first time to naturally occur in cereals and oil seeds. The metabolite concentrations reached 7,280 μg/kg in fonio for aurofusarin and 64,600 μg/kg in sesame for kojic acid. Aflatoxin contaminated 81 % of fonio samples at concentrations less than the 4 μg/kg maximum allowable limit (MAL) set by European Union (EU). In contrast, aflatoxin was not detected in sesame. Zearalenone levels exceeded the EU MAL (75 μg/kg) in one sample of fonio (987 μg/kg). About 62.5 % (30 out of 48) of the metabolites without regulations occurred in more than 50 % of samples of one or both seeds, while 3-nitropropionic acid, beauvericin, brevianamid F, curvularin, emodin, equisetin, macrosporin A, monocerin and tenuazonic acid were the most prevalent, occurring in all samples of either fonio, sesame or both. This is the first study reporting mycotoxin contamination in sesame in Nigeria and the broad range of microbial metabolites in millet and sesame.     

Fungal and bacterial metabolites in commercial poultry feed from Nigeria

Metabolites of toxigenic fungi and bacteria occur as natural contaminants (e.g. mycotoxins) in feedstuffs making them unsafe to animals. The multi-toxin profiles in 58 commercial poultry feed samples collected from 19 districts in 17 states of Nigeria were determined by LC/ESI-MS/MS with a single extraction step and no clean-up. Sixty-three (56 fungal and seven bacterial) metabolites were detected with concentrations ranging up to 10,200?μg?kg(-1) in the case of aurofusarin. Fusarium toxins were the most prevalent group of fungal metabolites, whereas valinomycin occurred in more than 50% of the samples. Twelve non-regulatory fungal and seven bacterial metabolites detected and quantified in this study have never been reported previously in naturally contaminated stored grains or finished feed. Among the regulatory toxins in poultry feed, aflatoxin concentrations in 62% of samples were above 20?μg?kg(-1), demonstrating high prevalence of unsafe levels of aflatoxins in Nigeria. Deoxynivalenol concentrations exceeded 1000?μg?kg(-1) in 10.3% of samples. Actions are required to reduce the consequences from regulatory mycotoxins and understand the risks of the single or co-occurrence of non-regulatory metabolites for the benefit of the poultry industry.     

Decorin—An Antagonist of TGF-β in Astrocytes of the Optic Nerve

During the pathogenesis of glaucoma, optic nerve (ON) axons become continuously damaged at the optic nerve head (ONH). This often is associated with reactive astrocytes and increased transforming growth factor (TGF-β) 2 levels. In this study we tested the hypothesis if the presence or absence of decorin (DCN), a small leucine-rich proteoglycan and a natural inhibitor of several members of the TGF family, would affect the expression of the TGF-βs and connective tissue growth factor (CTGF/CCN2) in human ONH astrocytes and murine ON astrocytes. We found that DCN is present in the mouse ON and is expressed by human ONH and murine ON astrocytes. DCN expression and synthesis was significantly reduced after 24 h treatment with 3 nM CTGF/CCN2, while treatment with 4 pM TGF-β2 only reduced expression of DCN significantly. Conversely, DCN treatment significantly reduced the expression of TGF-β1, TGF-β2 and CTGF/CCN2 vis-a-vis untreated controls. Furthermore, DCN treatment significantly reduced expression of fibronectin (FN) and collagen IV (COL IV). Notably, combined treatment with DCN and triciribine, a small molecule inhibitor of protein kinase B (AKT), attenuated effects of DCN on CTGF/CCN2, TGF-β1, and TGF-β2 mRNA expression. We conclude (1) that DCN is an important regulator of TGF-β and CTGF/CCN2 expression in astrocytes of the ON and ONH, (2) that DCN thereby regulates the expression of extracellular matrix (ECM) components and (3) that DCN executes its negative regulatory effects on TGF-β and CTGF/CCN2 via the pAKT/AKT signaling pathway in ON astrocytes.     

Linear sensing actuators of polypyrrole nanofiber scaffolds

In the search for renewable materials for linear actuators, polypyrrole (PPy) glucose-glycerin nanofiber scaffolds were used here to provide the actuator with a basic fibrillary structure, mimicking natural muscles. Each nanofiber was coated with a chemically synthesized PPy film, getting conductive nanofiber scaffolds (CNS), used then as electrodes to attain a second polypyrrole doped with dodecylbenzensulfonate (PPyDBS) coat forming PPyDBS-CNS material structure. PPyDBS bulk films obtained by electropolymerization on stainless steel under the same condition were used to compare the linear actuation properties of both materials. Cyclic voltammetry, square potential waves, and square potential currents, in combination with linear actuation measurements, studied the samples. Three different potential ranges (PRs) were selected for those methodologies: 1.0 to −0.55 V (PR1), 0.8 to −0.4 V (PR2), and 0.65 to −0.55 V (PR3), revealing that PPyDBS-CNS has anion-driven actuation independent of the applied PR1–3, while in comparison PPyDBS films had in PR3 mixed ion actuation. The best strain from PPyDBS, 24.6%, was attained at PR1, and from PPyDBS-CSN, 17.5% strain in the same PR. Further characterizations are conducted, such as scanning electron microscopy, Fourier transform infrared spectroscopy, and element determination using energy dispersive x-ray spectroscopy.     

Semiconductor Diode Lasers for Terahertz Technology

We discuss different concepts for generating terahertz (THz) radiation with semiconductor diode lasers. Photomixing enables the generation of continuous wave THz radiation by difference frequency generation of two lasers or of two-colour lasers. Pulsed THz radiation for time domain THz spectroscopy is generated with modelocked diode laser systems including amplification and chirp compression. Finally, we analyse the concept of quasi time domain spectroscopy based on broadband diode laser systems.     

Study of initial stages of thin film growth by means of atomistic computer simulation and image analysis

Nucleation and initial stages of three-dimensional film growth were studied by a computer experiment. The experiment consisted of two parts - preparation of simulated thin-film structures and computational analysis of their images. The simulated structures were generated by a model combining the molecular dynamics and Monte Carlo approaches. The analysis of the obtained structures was based on the ’Quadrat Counts’ method, which proved to be one of the most promising algorithms of image processing. The results obtained by image analysis of simulated thin films were discussed and the most suitable algorithms were suggested for the analysis of experimentally prepared films.