Electron capture dissociation of oligosaccharides ionized with alkali, alkaline Earth, and transition metals

We extend the application of electron capture dissociation (ECD) (which requires at least two charges) to oligosaccharides without basic functionalities by utilizing alkali, alkaline earth, and transition metals (Na+, K+, Ca2+, Ba2+, Mg2+, Mn2+, Co2+, and Zn2+) as charge carriers in electrospray ionization. Both linear and branched oligosaccharides were examined, including maltoheptoase, p-lacto-N-hexaose, and an N-linked glycan from human alpha1-acid glycoprotein. For comparison, infrared multiphoton dissociation (IRMPD) was also applied to all oligosaccharide species. We show that, for certain metal-adducted oligosaccharides, particularly maltoheptaose, cross-ring cleavage, which can provide saccharide linkage information, is the dominant fragmentation pathway in ECD. By contrast, glycosidic cleavages dominate in IRMPD although cross-ring fragmentation was also observed to varying degrees depending on metal ion type. The branched N-linked glycan did not fragment as easily following ECD compared to the linear oligosaccharides, presumably due to intramolecular noncovalent interactions. However, this limitation was partially overcome with a combined ECD/IRMPD approach (activated ion ECD). For all metal-adducted oligosaccharides, complementary structural information was obtained with ECD as compared to IRMPD. Our results demonstrate that ECD of metal-adducted oligosaccharides is a valuable tool for structural characterization of oligosaccharides.     

Poly(aniline) nanowires in sol-gel coated ITO: a pH-responsive substrate for planar supported lipid bilayers

Facilitated ion transport across an artificial lipid bilayer coupled to a solid substrate is a function common to several types of bioelectronic devices based on supported membranes, including biomimetic fuel cells and ion channel biosensors. Described here is fabrication of a pH-sensitive transducer composed of a porous sol-gel layer derivatized with poly(aniline) (PANI) nanowires grown from an underlying planar indium-tin oxide (ITO) electrode. The upper sol-gel surface is hydrophilic, smooth, and compatible with deposition of a planar supported lipid bilayer (PSLB) formed via vesicle fusion. Conducting tip AFM was used to show that the PANI wires are connected to the ITO, which convert this electrode into a potentiometric pH sensor. The response to changes in the pH of the buffer contacting the PANI nanowire/sol-gel/ITO electrode is blocked by the very low ion permeability of the overlying fluid PSLB. The feasibility of using this assembly to monitor facilitated proton transport across the PSLB was demonstrated by doping the membrane with lipophilic ionophores that respond to a transmembrane pH gradient, which produced an apparent proton permeability several orders of magnitude greater than values measured for undoped lipid bilayers.     

Effect of high gradient magnetic fields on the anodic behaviour and localized corrosion of iron in sulphuric acid solutions

The influence of high gradient magnetic fields on the anodic dissolution of iron in sulphuric acid solutions and the localization of the corrosion attack is investigated by means of potentiodynamic and potentiostatic polarization experiments and subsequent surface profile analysis. A localization of the material loss is observed in every potential region of the anodic Fe dissolution except from the passive region. The impact of the magnetic field on the anodic current density and the localization of the corrosion attack are explained by the action of the Lorentz force and the magnetic field gradient force.     

Enzymatic (2R,4R)-Pentanediol Synthesis – “Putting a Bottle on the Table”

(2R,4R)-Pentanediol is an interesting precursor for the synthesis of chiral ligands. A ketoreductase (KRED) was employed for the asymmetric reduction of acetylacetone to this diol. Biocatalysis often suffers from low concentrations of hydrophobic substrates and low stability of the enzyme in unconventional media. Here, we present an engineered KRED variant applicable in a neat substrate system, including upscaling to the multi-liter scale and downstream processing (DSP). Our engineered KRED applied in a neat substrate system is a powerful technique for the synthesis of chiral diols yielding product concentrations of 208 g L⁻¹.     

Novel ceramic–polymer composites synthesized by compaction of polymer-encapsulated TiO2-nanoparticles

A novel processing route for producing composites from ceramic particles and a thermoplastic polymer with high ceramic content was developed. Via a radical emulsion polymerization reaction in an aqueous suspension, titanium dioxide is encapsulated by a thin layer of poly(methyl methacrylate). Subsequently, the coated particles are compacted by applying high pressure (∼1 GPa) at a temperature above the glass transition temperature of the polymer (∼160 °C). This technique enables producing dense, hard and stiff composites at low processing temperatures. Microstructural investigations of composites by scanning electron microscopy confirm successful coating of titanium dioxide particles by polymer. Compositions were estimated from thermogravimetric measurements. A maximum TiO₂ volume content of almost 70% was achieved. For characterizing mechanical properties, Vickers microhardness as well as flexural strength and elastic modulus were determined. With respect to pure PMMA, composites exhibit a 10-fold increase in microhardness. Furthermore, a strong increase in elastic modulus with TiO₂ contents, up to 40 GPa at 66 vol.% TiO₂ was observed. These moduli are among the highest found in literature for ceramic polymer composites. However, bending strength of the material is still low.     

Reconstitution effect of Mg/Ni/Al layered double hydroxide

Layered double hydroxide (LDH) having a different cation (Mg, Ni, Al) composition was successfully synthesized by the low supersaturation method. The sample was thermally decomposed and reconstituted in water and nitrate media at different temperatures. X-ray powder diffraction and X-ray fluorescence were used to investigate the differences between the obtained layered materials and those after the reconstitution process. To the best of our knowledge, there are only few studies where the influence of the third metal cation on the reconstitution process was analyzed.     

Antimicrobial nanoparticles and biodegradable polymer composites for active food packaging applications

The food industry faces numerous challenges to assure provision of tasty and convenient food that possesses extended shelf life and shows long-term high-quality preservation. Research and development of antimicrobial materials for food applications have provided active antibacterial packaging technologies that are able to meet these challenges. Furthermore, consumers expect and demand sustainable packaging materials that would reduce environmental problems associated with plastic waste. In this review, we discuss antimicrobial composite materials for active food packaging applications that combine highly efficient antibacterial nanoparticles (i.e., metal, metal oxide, mesoporous silica and graphene-based nanomaterials) with biodegradable and environmentally friendly green polymers (i.e., gelatin, alginate, cellulose, and chitosan) obtained from plants, bacteria, and animals. In addition, innovative syntheses and processing techniques used to obtain active and safe packaging are showcased. Implementation of such green active packaging can significantly reduce the risk of foodborne pathogen outbreaks, improve food safety and quality, and minimize product losses, while reducing waste and maintaining sustainability.     

Chemical-biological exploration of the limits of the Ras de- and repalmitoylating machinery

A dynamic de-/repalmitoylation cycle determines localization and activity of H- and N-Ras. This combined cellular de- and repalmitoylation machinery has been shown to be substrate tolerant--it accepts variation of amino acid sequence, structure and configuration. Here, semisynthetic Ras-proteins in which the C-terminal amino acids are replaced by peptoid residues are used to reveal the first limitations of substrate recognition by the de- and repalmitoylating machinery.