Targeted Discovery of Tetrapeptides and Cyclic Polyketide-Peptide Hybrids from a Fungal Antagonist of Farming Termites

Herein, we report the targeted isolation and characterization of four linear nonribosomally synthesized tetrapeptides (pseudoxylaramide A–D) and two cyclic nonribosomal peptide synthetase-polyketide synthase-derived natural products (xylacremolide A and B) from the termite-associated stowaway fungus Pseudoxylaria sp. X187. The fungal strain was prioritized for further metabolic analysis based on its taxonomical position and morphological and bioassay data. Metabolic data were dereplicated based on high-resolution tandem mass spectrometry data and global molecular networking analysis. The structure of all six new natural products was elucidated based on a combination of 1D and 2D NMR analysis, Marfey's analysis and X-ray crystallography.     

Identification of chemical species created during γ-irradiation of antioxidant used in polyethylene and polyethylene-co-vinyl acetate multilayer film

With the increasing use of γ-irradiated containers made of multilayer polymeric flexible films for food and biopharmaceutical applications, the possible migration of degradation products of the polymers and their additives is becoming a topic of concern. This article aims at highly reliably identifying the degradation products generated after gamma irradiation and their origin to later on assess their potential harmfulness in single-use containers. In this study, GC–MS is used to identify by-products created by γ-irradiation of primary and secondary antioxidants usually present in polyolefin-based biotechnological single-use materials and to confirm identification relevancy based on the literature survey or standard when available. Degradation pathways are proposed to account for the formation of by-products identified during the study and to list intermediates and other by-products present in too small amounts to be detected and identified accurately in all extractable studies.     

Bioactive Polylactide Fibrous Materials Prepared by Crazing Mechanism

Bioactive suture materials made of biodegradable polymers containing biologically active substances are increasingly demanded in contemporary surgical practice. Herein, the functional fibrous materials are produced by structural modification of polylactide (PLA) fibers according to the crazing mechanism in water–ethanol solutions. The threshold of ethanol concentration, at which the breaking elongation of the polymer substantially increases (up to 600–700%), is found to be 30 wt%. The crazing mechanism is employed to fill the porous structure of PLA fibers by different antiseptic substances (brilliant green, iodine, and fuchsin). PLA loaded by 0.8 wt% of brilliant green exhibits antimicrobial activity on Escherichia coli and Candida guilliermondii. The additive is released stepwise for a prolongated time period (2.5 months). The addition of 1–6 wt% iodine dramatically accelerates the polymer degradation in sodium‐phosphate buffer solution at 37 °C. The obtained filled fibers may possess great interest for producing suture materials with prolonged action of functional components and variable degradation times.     

Asphaltenes as a tackifier for hot-melt adhesives based on the styrene-isoprene-styrene block copolymer

The use of heavy crude oil asphaltenes and resins (termed asphaltenes) as the components of hot-melt adhesives based on the styrene-isoprene triblock copolymer was considered. The rheological, thermophysical, strength, and adhesive characteristics of the mixtures containing from 10 to 40 wt% of asphaltenes were studied. The addition of 10 to 20 wt% of asphaltenes enhanced the strength and adhesive properties of the mixtures and only slightly changed their rheology. The higher concentrations of asphaltenes reduced the viscosity of the mixtures but did not lead to improved characteristics of the adhesives. The ambiguous effect of asphaltenes is probably due to their uneven distribution between the microphases of the block copolymer as well as their ability to act both plasticizers and reinforcing particles depending on temperature. A comparison of asphaltenes and conventional tackifiers based on hydrocarbon resins revealed their comparable effect on the properties of the block copolymer.     

Time-Resolved Photoluminescence in Heterostructures with InGaAs:Cr/GaAs Quantum Wells

Semiconductors - The results of studies of the time-resolved photoluminescence in semiconductor heterostructures containing two noninteracting InGaAs quantum wells in a GaAs matrix are reported....     

Diode Structures Based on (In,Fe)Sb/GaAs Magnetic Heterojunctions

Technical Physics Letters - The current–voltage characteristics of light-emitting diodes based on InGaAs/GaAs heterostructures with an injector made of (In, Fe)Sb diluted magnetic...     

Natural deep eutectic solvents (NADES) based on citric acid and sucrose as a potential green technology: a comprehensive study of water inclusion and its effect on thermal,physical and rheological properties

In this work, NADES based on sucrose and citric acid was synthesised and evaluated. Physical properties such as density, viscosity and thermal profile were evaluated at different temperatures and water contents. Viscosity and density were inversely affected by temperature and water content. Increases in the sucrose fraction resulted in higher viscosity, but no differences in density were observed. The rheological model of Ostwald-de-Waele indicated three distinct rheological behaviours at different temperatures, water content and sucrose fractions. The Arrhenius model showed a good fit for the temperature effect on the apparent viscosity of all NADESs. The NADES decomposition temperature was approximately 393 K. The thermal characterisation revealed that all NADESs presented glass transitions at temperatures below 204.59 K, confirming their formation and stability. Based on these results, the NADES proposed appears as potential green solvent to be used in industrial processes such as extraction, separation and biochemical technology.     

N‐ICE plasmids for generating N‐terminal 3 × FLAG tagged genes that allow inducible,constitutive or endogenous expression in Saccharomyces cerevisiae

PCR‐mediated homologous recombination is a powerful approach to introduce epitope tags into the chromosomal loci at the N‐terminus or the C‐terminus of targeted genes. Although strategies of C‐terminal epitope tagging of target genes at their loci are simple and widely used in yeast, C‐terminal epitope tagging is not practical for all proteins. For example, a C‐terminal tag may affect protein function or a protein may get cleaved or processed, resulting in the loss of the epitope tag. Therefore, N‐terminal epitope tagging may be necessary to resolve these problems. In some cases, an epitope tagging strategy is used to introduce a heterologous promoter with the epitope tag at the N‐terminus of a gene of interest. The potential issue with this strategy is that the tagged gene is not expressed at the endogenous level. Another strategy after integration is to excise the selection marker, using the Cre‐LoxP system, leaving the epitope tagged gene expressed from the endogenous promoter. However, N‐terminal epitope tagging of essential genes using this strategy requires a diploid strain followed by tetrad dissection. Here we present 14 new plasmids for N‐terminal tagging, which combines two previous strategies for epitope tagging in a haploid strain. These ‘N‐ICE’ plasmids were constructed so that non‐essential and essential genes can be N‐terminally 3 × FLAG tagged and expressed from an inducible promoter (GAL1), constitutive promoters (CYC1 or PYK1) or the endogenous promoter. We have validated the N‐ICE plasmid system by N‐terminal tagging two non‐essential genes (SET1 and SET2) and two essential genes (ERG11 and PKC1). Copyright © 2016 John Wiley & Sons, Ltd.     

Chitosan‐g‐Polyester Microspheres: Effect of Length and Composition of Grafted Chains

Hydrophobic segments made of oligo(l,l ‐ or d,l ‐lactides) or poly(l,l ‐lactide) are grafted onto chitosan backbone in order to use their amphiphilic behavior to prepare degradable microcarriers intended to be used for tissue engineering. Hydrophilic–lipophilic balance of these copolymers is adjusted playing on the respective length of their hydrophilic and hydrophobic moieties. Thanks to their self‐emulsifying properties, these graft copolymers are processed into microspheres in the absence of hydrophilic emulsifier commonly added in the aqueous phase of the oil/water emulsion. The copolymers containing amorphous oligolactide segments of medium length are demonstrated to be the most effective ones for microparticle fabrication. The microparticles are characterized using SEM, EDX, and FTIR. The reactivity of amine group is demonstrated using fluorescein isothiocyanate staining. The resulting microspheres disclose a porous core and a shell enriched by the hydrophilic polysaccharide moieties. Stabilization of the oil/water interface during the microsphere fabrication, total yield, size distribution, and microparticle surface morphology are mainly affected by the macromolecular features of the copolymers.