Complexity of packing common bases in matroids

Mathematical Programming - One of the most intriguing unsolved questions of matroid optimization is the characterization of the existence of k disjoint common bases of two matroids. The...     

Grain boundary diffusion induced reaction layer formation in Fe/Pt thin films

The solid-state reaction in Pt(15 nm)/Fe(15 nm) and Pt(15 nm)/Ag(10 nm)/Fe(15 nm) thin films after post-annealing at 593 K and 613 K for different annealing times has been studied. The structural properties of these samples were investigated by various methods including depth profiling with secondary neutral mass spectrometry, transmission electron microscopy, and X-ray diffraction. It is shown that after annealing at the above temperatures where the bulk diffusion processes are still frozen, homogeneous reaction layers of FePt and FePt with about 10 at.% Ag, respectively, have been formed. Corresponding depth profiles of the element concentrations revealed strong evidence that the formation mechanism is based on a grain boundary diffusion induced solid-state reaction in which the reaction interfaces sweep perpendicularly to the original grain boundary. Interestingly, X-ray diffraction indicated that in both thin-film systems after the solid-state reaction the ordered L1₀ FePt phase, which is the requested phase for future magnetic data storage applications, is also present.     

Interaction of oligonucleotides with benzo[c]phenanthridine alkaloid sanguilutine

Benzo[c]phenanthridine alkaloid sanguilutine was extracted and purified from the dried roots of Sanguinaria canadensis. The interaction of the positively charged iminium form of alkaloid with double-stranded DNA oligonucleotides was studied using luminescence spectroscopy. The results showed that the interaction with various double-stranded oligonucleotides was not specific to A-T or G-C base pairs; also, no preference was found for either homogeneous or heterogeneous base composition of strands. The association constants were calculated to be in the range of (1.31–14.36) × 10⁵ M^?1. The luminescence intensity response at 610 nm to low concentrations of double-stranded DNA was found to be linear and can potentially be used for the fluorometric quantification of DNA. The limit of detection was estimated to be 120 ng mL^?1 of DNA (calculated by 3σ method).     

Development of antimicrobial packaging materials with immobilized glucose oxidase and lysozyme

Packaging based on immobilization of antimicrobial enzymes provides a promising form of active packaging systems applicable in food processing. Glucose oxidase and lysozyme were immobilized by the Ugi reaction with cyclohexyl isocyanide and glutaraldehyde on polyamide and ionomer films partially hydrolysed by hydrochloric acid. The immobilization of the enzymes on the surface of films was confirmed by FT-IR spectroscopy and the films were characterized by the specific activity of the immobilized enzymes. The enzyme migration into model solutions and the effect of pH, temperature and storage time on the activity of immobilized enzyme were also evaluated. Immobilization of lysozyme onto polyamide and ionomer films resulted in the loss of enzyme activity. The polyamide and ionomer films with immobilized glucose oxidase inhibited the growth of bacteria Escherichia coli CNCTC 6859, Pseudomonas fluorescens CNCTC 5793, Lactobacillus helveticus CH-1, Listeria ivanovii CCM 5884 and Listeria innocua CCM 4030 on agar media.      

Comparison of the efficiency and the specificity of DNA-bound and free cationic porphyrin in photodynamic virus inactivation

The risk of transmitting infections by blood transfusion has been substantially reduced. However, alternative methods for inactivation of pathogens in blood and its components are needed. Application of photoactivated cationic porphyrins can offer an approach to remove non-enveloped viruses from aqueous media. Here we tested the virus inactivation capability of meso-Tetrakis(4-N-methylpyridyl)porphyrin (TMPyP) and meso-Tri-(4-N-methylpyridyl)monophenylporphyrin (TMPyMPP) in the dark and upon irradiation. T7 bacteriophage, as a surrogate on non-enveloped viruses was selected as a test system. TMPyP and TMPyMPP reduce the viability of T7 phage already in the dark, which can be explained by their selective binding to nucleic acid. Both compounds proved to be efficient photosensitizers of virus inactivation. The binding of porphyrin to phage DNA was not a prerequisite of phage photosensitization, moreover, photoinactivation was more efficiently induced by free than by DNA bound porphyrin. As optical melting studies and agarose gel electrophoresis of T7 nucleoprotein revealed, photoreactions of TMPyP and TMPyMPP affect the structural integrity of DNA and also of viral proteins, despite their selective DNA binding.     

Quantification of methyl thiocyanate in the headspace of Pseudomonas aeruginosa cultures and in the breath of cystic fibrosis patients by selected ion flow tube mass spectrometry

Infection by Pseudomonas aeruginosa (PA) is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). Breath analysis could potentially be a useful diagnostic of such infection, and analyses of volatile organic compounds (VOCs) emitted from PA cultures are an important part of the search for volatile breath markers of PA lung infection. Our pilot experiments using solid‐phase microextraction, SPME and gas chromatography/mass spectrometric (GC/MS) analyses of volatile compounds produced by PA strains indicated a clear presence of methyl thiocyanate. This provided a motivation to develop a method for real‐time online quantification of this compound by selected ion flow tube mass spectrometry, SIFT‐MS. The kinetics of reactions of H₃O⁺, NO⁺ and O₂^+? with methyl thiocyanate at 300 K were characterized and the characteristic product ions determined (proton transfer for H₃O⁺, rate constant 4.6 × 10^–9 cm³ s^–1; association for NO⁺, 1.7 × 10^–9 cm³ s^–1 and nondissociative charge transfer for O₂^+?_, 4.3 × 10^–9 cm³ s^–1). The kinetics library was extended by a new entry for methyl thiocyanate accounting for overlaps with isotopologues of hydrated hydronium ions. Solubility of methyl thiocyanate in water (Henry's law constant) was determined using standard reference solutions and the linearity and limits of detection of both SIFT‐MS and SPME‐GC/MS methods were characterized. Thirty‐six strains of PA with distinct genotype were cultivated under identical conditions and 28 of them (all also producing HCN) were found to release methyl thiocyanate in headspace concentrations greater than 6 parts per billion by volume (ppbv). SIFT‐MS was also used to analyze the breath of 28 children with CF and the concentrations of methyl thiocyanate were found to be in the range 2–21 ppbv (median 7 ppbv). Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of various spices on acrylamide content in buckwheat ginger cakes

The aim of this work was to study the effect of various spices (cloves, cinnamon, allspice, white pepper, anise, star anise, coriander, fennel, nutmeg, cardamom, vanilla, and ginger) on acrylamide formation in buckwheat ginger cakes. The spices were characterised by their free radical scavenging activity and applied to formulation of the buckwheat ginger cakes in the same portions. After baking, the acrylamide content was determined by LC/ESI-MS-MS. The results showed a reduction in acrylamide content of up to 23 % in the buckwheat ginger cakes with the addition of nutmeg, fennel, anise, or cloves. A decrease in acrylamide content from 5 % to 11 % was found in the buckwheat ginger cakes with vanilla, cardamom, white pepper, or ginger. By contrast, the acrylamide content in the buckwheat ginger cakes with cinnamon or coriander increased by up to 29 %. No change in the acrylamide content was observed in the buckwheat ginger cakes with star anise or allspice. Only a slight correlation between the di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH^·) free radical scavenging activity of the added spices and the final acrylamide content in the buckwheat ginger cakes (0.68) was observed. The final acrylamide content was probably influenced not only by the free radical scavenging activity of the spices added, but also by their chemical composition and the reactiveness of particular constituents with synergistic/antagonistic effect in the matrix studied.