Unipolar Fatigue Behavior of BCTZ Lead‐Free Piezoelectric Ceramics

(Ba,Ca)(Ti,Zr)O₃ lead‐free piezoelectric ceramics have been considered to be one of the most potential lead‐free alternatives for PZT in the room‐temperature range. The stability of the piezoelectric performance during unipolar cycling is investigated in this study. It is found that the unipolar fatigue behavior is similar to soft PZT. Developments of bias field, offset polarization, asymmetry in strain, and dielectric hysteresis loops are observed during bipolar measurements. The changes are mainly contributed to the migration of charge carriers to the grain boundaries driven by the unscreened depolarization field. Redistribution of the accumulated charge carriers by bipolar electric cycling or thermal annealing can significantly recover the unipolar fatigued state. The unipolar strain response stabilized after 1000 cycles at 0.053% for an electric field of 0.6 kV/mm (d₃₃*= 883 pm/V), which is a good characteristic for actuator applications.     

Remendable polymers via reversible Diels–Alder cycloaddition of anthracene‐containing copolymers with fullerenes

Poly(lauryl methacrylate)s with anthracene moieties in the side chain were converted with C₆₀‐fullerene and phenyl‐C₆₁‐butyric acid methyl ester (PCBM), resulting in new remendable (self‐healing) polymeric materials. The utilization of differently substituted anthracene monomers enabled the tuning of the reactivity and the resulting mechanical properties. Copolymers with different contents of the anthracene moieties were synthesized and characterized using size exclusion chromatography, ¹H nuclear magnetic resonance (NMR) spectroscopy as well as differential scanning calorimetry (DSC). ¹H NMR spectroscopic studies were utilized in order to investigate the reversibility of the Diels–Alder reaction between copolymers with C₆₀‐fullerene and PCBM, respectively, in solution. In order to investigate the conversion of the polymers with C₆₀‐fullerene and PCBM in bulk, additionally, DSC, nanoindentation, rheology, atomic force microscopy (AFM), 3D microscopy, simultaneous thermal analysis (STA) and FT‐Raman investigations were performed. The fullerene‐containing copolymers could be healed in a temperature range of 40–80 °C. Consequently, a new generation of low temperature remendable polymers could be established. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45916.     

Influence of the Multivalency of Ultrashort Arg‐Trp‐Based Antimicrobial Peptides (AMP) on Their Antibacterial Activity

Peptide dendrimers are a class of molecules of high interest in the search for new antibiotics. We used microwave‐assisted, copper(I)‐catalyzed alkyne–azide cycloaddition (CuAAC; “click” chemistry) for the simple and versatile synthesis of a new class of multivalent antimicrobial peptides (AMPs) containing solely arginine and tryptophan residues. To investigate the influence of multivalency on antibacterial activity, short solid‐phase‐ synthesized azide‐modified Arg‐Trp‐containing peptides were “clicked” to three different alkyne‐modified benzene scaffolds to access scaffolds with one, two, or three peptides. The antibacterial activity of 15 new AMPs was investigated by minimal inhibitory concentration (MIC) assays on five different bacterial strains, including a multidrug‐resistant Staphylococcus aureus (MRSA) strain. With ultrashort (2–3 residues) peptides, a clear synergistic effect of the trivalent display was observed, whereas this effect was not apparent with longer peptides. The best candidates showed activities in the low‐micromolar range against Gram‐positive MRSA. Surprisingly, the best activity against Gram‐negative Acinetobacter baumannii was observed with an ultrashort dipeptide on the trivalent scaffold (MIC: 7.5 μM ). The hemolytic activity was explored for the three most active peptides. At concentrations ten times the MIC values, <1 % hemolysis of red blood cells was observed.     

Airborne and laboratory studies of an IAGOS instrumentation package containing a modified CAPS particle extinction monitor

An evaluation of the operation and performance of a Cavity Attenuated Phase-Shift Particle Extinction Monitor (CAPS PM_ex) was performed for use on board commercial aircraft as part of the research infrastructure IAGOS (In-service Aircraft for a Global Observing System, www.iagos.org). After extensive laboratory testing, a new flow system, using mass flow controllers, was installed to maintain constant purge and sample flows under low and varying pressure conditions. The instrument was then tested for pressures as low as 200 hPa and evaluated against particle-free compressed air and CO₂. Extinction coefficients for the studied gases were in close agreement with literature values with differences between 2.2% and 8%, proving that the CAPS technology works at low pressures. The instrument's limit of detection, with respect to 3 times the variability of the background signal for the full pressure range, was 0.2 Mm^?1 for 60s integration time. During its first research aircraft operations, the IAGOS instrument prototype, composed of one CAPS PMex and one OPC, showed excellent results regarding the stability of the instruments and the potential for characterizing different aerosol types and for estimating the contribution of sub- and super-μm sized particles to aerosol light extinction.

Copyright © 2017 American Association for Aerosol Research     

Application of β-Sitosterol + γ-Oryzanol-Structured Organogel as Migration Barrier in Filled Chocolate Products

Oil migration in filled pralines is a phenomenon that is highly correlated with the occurrence of chocolate bloom. In this study the potential to suppress or prevent oil migration by incorporation of sterol/sterolster-structured organogels was evaluated. Different quantities, 2.5 or 14% (w/w), of gel with structurant levels of either 10 or 25% (w/w) were studied in a layered model system. The gel was either a part of the nougat or of the chocolate phase, or as a separate layer. Samples were monitored regularly for a period of 24 weeks at storage temperatures of 10, 18 and 28 °C. The amount of migrated oil was determined via DSC analysis of a surface sample. The results indicate that, despite the additional oil brought into the system via the oleogel, the level of oil found in the chocolate layer is reduced through the presence of the gel. In particular, the three-layer system and gelled chocolate appear to be promising routes to either suppress oil migration or improve nutritional profiles by incorporation of liquid oils.     

Novel Type II Fatty Acid Biosynthesis (FAS II) Inhibitors as Multistage Antimalarial Agents

Malaria is a potentially fatal disease caused by Plasmodium parasites and poses a major medical risk in large parts of the world. The development of new, affordable antimalarial drugs is of vital importance as there are increasing reports of resistance to the currently available therapeutics. In addition, most of the current drugs used for chemoprophylaxis merely act on parasites already replicating in the blood. At this point, a patient might already be suffering from the symptoms associated with the disease and could additionally be infectious to an Anopheles mosquito. These insects act as a vector, subsequently spreading the disease to other humans. In order to cure not only malaria but prevent transmission as well, a drug must target both the blood‐ and pre‐erythrocytic liver stages of the parasite. P. falciparum (Pf) enoyl acyl carrier protein (ACP) reductase (ENR) is a key enzyme of plasmodial type II fatty acid biosynthesis (FAS II). It has been shown to be essential for liver‐stage development of Plasmodium berghei and is therefore qualified as a target for true causal chemoprophylaxis. Using virtual screening based on two crystal structures of PfENR, we identified a structurally novel class of FAS inhibitors. Subsequent chemical optimization yielded two compounds that are effective against multiple stages of the malaria parasite. These two most promising derivatives were found to inhibit blood‐stage parasite growth with IC₅₀ values of 1.7 and 3.0 μM and lead to a more prominent developmental attenuation of liver‐stage parasites than the gold‐standard drug, primaquine.     

Influence of residual solvent on physical and chemical properties of amorphous glassy polymer films

One of the most important areas of current research is the study of the influence of the prehistory of samples of amorphous glassy polymers on their physical and chemical properties. The study of structural changes by high temperature IR spectroscopy compared with of quantum chemical calculations allows for an understanding of the mechanism and nature of such processes. The changes in the structure of the polymer chain depending on the type of solvent used in the formation of the films are demonstrated using the examples of several different classes of polymers. In turn, the impact of such changes in the structure on the physical and chemical properties of the polymer films is demonstrated. © 2013 Society of Chemical Industry     

Influence of precursors on the formation of 3‐MCPD and glycidyl esters in a model oil under simulated deodorization conditions

To find new ways for reducing the potential of palm oil to form 3‐monochloropropane‐1,2‐diol (3‐MCPD) and glycidyl esters during refining it is helpful to know more about the influence of different precursors like diacylglycerols (DAGs) and monoacylglycerols (MAGs), lecithin, and chlorine containing compounds. After adding increasing amounts of the different precursors to a model oil obtained by removal of polar compounds from crude palm oil and heating the mixture under standardized conditions to 240°C for 2 h the contents of 3‐MCPD and glycidyl esters were analyzed according to the standard procedure of DGF C‐VI 18 (10). DAGs and MAGs were found to increase the potential of palm oil to form 3‐MCPD and glycidyl esters, but refined lecithin showed no influence. Sodium chloride as well as tetra‐n‐butylammoniumchloride (TBAC) led to higher contents of the esters. Whereas the addition of TBAC raised the amount of glycidyl esters as well as 3‐MCPD esters, sodium chloride largely raised the amount of 3‐MCPD esters. An addition of 5 mmol of sodium carbonate/kg model oil spiked with sodium chloride reduced the amount of glycidyl esters almost completely; the 3‐MCPD esters were reduced by 50%. About 1 mmol sodium hydrogen carbonate/kg oil reduced both 3‐MCPD and glycidyl esters almost completely. Practical applications : For the mitigation of the formation of 3‐MCPD esters and related compounds in refined edible oils, it is helpful to know more about the effect of different possible precursors. Using a broader data basis, it is possible to adopt the oil processing but especially the choice of the raw material to the demands of the market for lower contents of the esters in the refined products.     

The Importance of Crosslinking and Glass Transition Temperature for the Mechanical Strength of Nanofibers Obtained by Green Electrospinning

Crosslinked particles containing butyl acrylate, methyl methacrylate, and allyl methacrylate are prepared by free‐radical emulsion polymerization. The glass transition temperatures of the polymers are varied by the crosslinking densities in the latex particles. Aqueous acrylate dispersions with polymers of different glass transition temperatures are electrospun with PVA as the matrix polymer. The effects of crosslinking density and T_g on the structure and mechanical properties of the fibers are studied. Crosslinking of unreacted allyl groups is induced by UV irradiation to stabilize the fibers by interparticle crosslinking. Both the ability to undergo interparticle crosslinking and the E modulus depend on the merging of the particles during the electrospinning process.