Effect of Phase Structure on Sintering Behavior of Zirconia Nanopowders

Zirconia nanopowder compacts with comparable particle sizes and pore size distributions but different phase structures were prepared. The sintering behavior of monoclinic, tetragonal, and cubic zirconia nanopowders was directly compared. The densification and microstructural changes during sintering were investigated. The tetragonal and cubic nanopowders showed similar sintering behavior whereas the monoclinic nanopowder exhibited a more difficult densification and coarser microstructure compared with tetragonal and cubic powders. The differences in the densification of zirconia nanopowders resulted from significant differences in the microstructure evolution during sintering. The microstructural changes in nanopowder compacts during sintering were described and a correlation between microstructural changes and interfacial energies associated with different crystal structures was discussed.     

Detection of light-absorbing iron oxide particles using a modified single-particle soot photometer

Copyright © 2016 American Association for Aerosol Research     

Engineered Glycosidases for the Synthesis of Analogs of Human Milk Oligosaccharides

Enzymatic synthesis is an elegant biocompatible approach to complex compounds such as human milk oligosaccharides (HMOs). These compounds are vital for healthy neonatal development with a positive impact on the immune system. Although HMOs may be prepared by glycosyltransferases, this pathway is often complicated by the high price of sugar nucleotides, stringent substrate specificity, and low enzyme stability. Engineered glycosidases (EC 3.2.1) represent a good synthetic alternative, especially if variations in the substrate structure are desired. Site-directed mutagenesis can improve the synthetic process with higher yields and/or increased reaction selectivity. So far, the synthesis of human milk oligosaccharides by glycosidases has mostly been limited to analytical reactions with mass spectrometry detection. The present work reveals the potential of a library of engineered glycosidases in the preparative synthesis of three tetrasaccharides derived from lacto-N-tetraose (Galβ4GlcNAcβ3Galβ4Glc), employing sequential cascade reactions catalyzed by β3-N-acetylhexosaminidase BbhI from Bifidobacterium bifidum, β4-galactosidase BgaD-B from Bacillus circulans, β4-N-acetylgalactosaminidase from Talaromyces flavus, and β3-galactosynthase BgaC from B. circulans. The reaction products were isolated and structurally characterized. This work expands the insight into the multi-step catalysis by glycosidases and shows the path to modified derivatives of complex carbohydrates that cannot be prepared by standard glycosyltransferase methods.     

Synthesis,Characterization and Immunological Evaluation of Self‐Adjuvanting Group A Streptococcal Vaccine Candidates Bearing Various Lipidic Adjuvanting Moieties

Four group A streptococcal glycolipopeptide vaccine candidates with different lipidic adjuvanting moieties were prepared and characterized. The immunogenicity of the compounds was evaluated by macrophage and dendritic cell uptake studies and by in vivo quantification of systemic IgG antibody by ELISA. Three of the candidates showed significant induction of the IgG response.     

Antibacterial modification of nylon-6 nanofibers: structure,properties and antibacterial activity.

Antibacterial nylon 6 (PA6) nanofibers have been prepared in one-step procedure using Nanospider technology. Chlorhexidine (CHX), 1-dodecyltrimethylamonium bromide (DTAB) and benzyltrimethylamonium bromide (BTAB) have been used as antibacterial agents. Samples were characterized by a series of analytical and testing methods to investigate the surface chemistry, zeta potential, structure, morphology, phase composition, mechanical properties and antibacterial activity. Experimental characterization has been combined with molecular modeling to analyze the interaction of nanofibers with modifying molecules for better understanding the effect of nanofibers modification on their properties. Antibacterial modification of PA6 led to significant changes of zeta potential (from -31 mV for PA 6 up to -49 mV for PA6/BTAB), changes in phase composition (decrease of alpha phase content and increase of gamma phase content for PA6/BTAB and PA6/CHX) and to significant increase of fiber diameter for PA6/BTAB. Antibacterial modification resulted in the straightening of nanofibers and to higher permeability of nanofiber textile for all investigated samples. Tensile tests showed the the increase of Young modulus for all the investigated samples. All the modified samples: PA6/DTAB, PA6/BTAB and PA6/CHX exhibit good antibacterial activity.     

Protease Inhibition—An Established Strategy to Combat Infectious Diseases

Therapeutic agents with novel mechanisms of action are urgently needed to counter the emergence of drug-resistant infections. Several decades of research into proteases of disease agents have revealed enzymes well suited for target-based drug development. Among them are the three recently validated proteolytic targets: proteasomes of the malarial parasite Plasmodium falciparum, aspartyl proteases of P. falciparum (plasmepsins) and the Sars-CoV-2 viral proteases. Despite some unfulfilled expectations over previous decades, the three reviewed targets clearly demonstrate that selective protease inhibitors provide effective therapeutic solutions for the two most impacting infectious diseases nowadays—malaria and COVID-19.     

Hydrogen desorption from alloys Mg–Cu(–KCl): Cu catalysis in detail

Effect of chemical composition of Mg-xCu based alloys (x = 9.94–58.00 wt %) modified by KCl upon their hydrogen storage performance was studied. Kinetic curves and pressure-concentration isotherms were measured in the ranges up to 60 bar and 388 °C, respectively. It was observed that desorption rate dc/dt is not significantly influenced by the composition. Unknown Cu-rich phase was detected that has shown a catalytic effect on desorption from a mixture with other phases. Activation energy of hydrogen desorption decreased with increasing x from 180 kJ/mol down to 98 kJ/mol. Average hydride dissociation enthalpy, ΔH, for the lowest plateau was 75 kJ/mol which is equal to literature value for pure Mg. Slightly lover average value, 67 kJ/mol was obtained for the second plateau and ΔH for the third one decreased from 70 kJ/mol for the lowest to 49 kJ/mol for the highest x.     

The properties of free-standing epoxy polymer multi-mode optical waveguides

The paper reports on the fabrication and characterisation of free-standing multimode optical epoxy polymer waveguides consisting of a core made of EpoCore and EpoClad polymer cladding and cover protection layers. The 50 × 50 μm² rectangular waveguides are intended for short-reach optical interconnection and optimised for an operating wavelength of 850 nm. The waveguides of the proposed shapes were fabricated by a standard photolithography process on a silicon substrate provided with a Poly(vinyl alcohol) thin layer. The free-standing structure was then achieved by peeling the deposited EpoClad/EpoCore/EpoClad structures of that substrate. The optical scattering losses of the created planar waveguides, measured by the fibre probe technique at 632.8 and 964 nm, were 0.30 dB cm⁻¹ at 632.8 nm and 0.17 dB cm⁻¹ at 964 nm. Propagation optical loss measurements for rectangular waveguides were performed by the cut-back method and the best samples had optical losses below 0.55 dB cm⁻¹ at 850 and 1310 nm.

     

Pillared MWW zeolites MCM-36 prepared by swelling MCM-22P in concentrated surfactant solutions

Lamellar zeolite forms like layered MCM-22 precursor, MCM-22P, offer unprecedented opportunities for creating diversity of more open zeolite structures prepared post-synthesis by expanding and modifying the interlamellar space. This is a relatively unexplored area with regard to procedures ensuring easy, least destructive and most efficient expansion of layered zeolites. Herein we explore concentrated surfactant solutions with high pH for their ability to provide swollen MCM-22 that can be converted to the pillared MCM-36. High pH of the swelling solutions was obtained by addition of tetrapropylammonium hydroxide and by partial conversion of the surfactant chloride into hydroxide by ion exchange. The products were evaluated based on their X-ray diffraction characteristics, sorption properties, scanning electron microscopy and IR spectra as indicators of catalytic potential. The swelling/pillaring efficiency was judged based on BET surface area and depended on swelling conditions, especially the apparent basicity. There was an overall decrease in acid site concentration due to incorporation of inert silica pillars. The MCM-36 zeolite with the highest BET showed increased uptake of 2,6-di-tert-butyl-pyridine by 75% compared to the parent MCM-22 suggesting enhanced accessibility of acid sites for bulky probe molecules. We conclude that concentrated surfactant solutions can be effective in swelling MCM-22P even at room temperature but an optimal approach must balance many factors including yield and activity of the final product.