Sorption isotherms of metal ions onto an N-(2-sulfoethyl)chitosan-based material from single- and multi-component solutions

The scope of work is to study the mutual influence of metal ions during their sorption by sulfoethylated chitosan. The sorption isotherms of metal ions from single- and multi-component solutions are obtained. The sorption capacity of the sorbent towards Ag(I) and Cu(II) is revealed to be 1.63 and 1.41 mmol/g in single-, and 1.40 and 0.85 mmol/g in five-component solution. By comparing the affinity parameter and capacity of sulfoethylated chitosan towards ions in single- and multi-component solutions, it is concluded that Ag(I) and Cu(II) ions suppress the sorption of cobalt(II), nickel(II), zinc(II), cadmium(II), magnesium(II), calcium(II), strontium(II), barium(II), manganese(II) and lead(II).     

Crosslinking during radical polymerization of dodecyl methacrylate

A much more efficient formation of crosslinks was observed in the free‐radical polymerization of dodecyl methacrylate with respect to the amount of decomposed peroxide than it would correspond to the additional peroxide crosslinking of formed poly(dodecyl methacrylate). Polymer crosslinking also proceeds after using 2,2´‐azoisobutyronitrile as initiator of the polymerization of dodecyl methacrylate, although with a substantially lower efficiency compared to the initiation by peroxide under comparable conditions. The efficient formation of crosslinked structures can be explained by branching and copolymerization of monomer with multifunctional dead polymer. Multifunctionality of the formed macromolecules is a result of transfer and addition reactions of the present free radicals with the formed polymer. The difference in the influence of the initiator follows from the higher reactivity of oxy radicals in transfer reactions with monomer dodecyl methacrylate which results in a greater number of polymerizable double bonds built in the polymer chain.     

Mapping of gene controlling thiamine transport in Saccharomyces cerevisiae

A recessive mutation leading to complete loss of thiamine uptake in Saccharomyces cerevisiae was mapped on the left arm of chromosome VII, approximately 56cM centromere-distal to trp5. As the analysed locus is relatively distant from its centromere and from the markers used, its attachment to chromosome VII was confirmed by chromosome loss methods.     

Pyrrole‐Assisted and Easy Oxidation of Cyclic α‐Amino Acid‐ Derived Diketopiperazines under Mild Conditions

A new procedure for the aerobic oxidation of α‐amino acids acylated by pyrrole‐carboxylic acid with triplet dioxygen is introduced. The reaction is general for a variety of pyrrole‐amino acid derivatives and represents a very practical and controllable method for the selective preparation of α‐hydroperoxy‐ or α‐hydroxy‐α‐amino acid diketopiperazines with molecular dioxygen. Furthermore, the non‐catalyzed direct oxidation of amino acid derivatives at the α‐position with molecular dioxygen represents a fundamental question.     

Determination of in vitro isoflavone degradation in rumen fluid

The aim of this study was to determine the degradation of dietary isoflavones in rumen fluid under 2 feeding regimens. The experiments were performed in vitro using a rumen fluid buffer system. The rumen fluid was taken from cows fed either a hay diet or a concentrate-rich diet (the diet consisted of 34.6% maize silage, 17.6% haylage, 12.8% alfalfa hay, and 35.0% supplemental mixture on a dry matter basis). As a source of isoflavones, 40% soybean extract (Biomedica, Prague, Czech Republic) at levels of 5, 25, 50, and 75 mg per 40 mL of rumen fluid was used. Samples of soybean extract were incubated in triplicate at 39°C for 0, 3.0, 6.0, 12.0, and 24.0 h in incubation solution. The metabolism of daidzein and genistein was faster under concentrate-rich diet conditions. In general, production of equol started after 3 to 6 h of incubation and reached the highest rate after approximately 12 h of incubation regardless of the type of diet or concentration of extract. In most of the experiments, production of equol continued after 24 h of incubation. Generally, equol production was greater under the hay diet conditions. Furthermore, experiments with higher amounts of added soybean extract revealed possible inhibitory effects of high levels of isoflavones on the rumen microflora.     

An experimental setup for investigating prebreakdown phenomena on a vacuum surface of a ceramic insulator

A setup for investigating prebreakdown phenomena on the surfaces of cathode insulators in vacuum is described. The setup reproduces the conditions under which an insulator is during operation of an actual vacuum device. The results from studying the effect of charged-particle fluxes and X-ray or optical radiations in a vacuum chamber under a stepped increase in the applied voltage to 150 kV are presented. In order to predict the development of a high-voltage breakdown, the following parameters are simultaneously recorded during measurements: the pressure in the vacuum chamber, the gas composition, and the leakage currents over the insulator surface and through the vacuum gap. The data are recorded automatically, and the collected information is stored on the hard disk of a computer.     

Activated anionic ring-opening polymerization of ε-caprolactam with magnesium di(ε-caprolactamate) as initiator: effect of magnesium halides

The activated anionic ring-opening polymerization of ε-caprolactam initiated by 0.35 mol% of combined initiator, i.e., equimolar mixture of magnesium di(ε-caprolactamate) (CL₂Mg) with magnesium halides (MgCl₂, MgBr₂, and MgI₂) as well as of ε-caprolactam magnesium bromide (CLMgBr) in the presence of 0.35 mol% of N-acetyl-ε-caprolactam as an activator has been investigated in the temperature range 140–200 °C. It was found that the reaction rate increased while the apparent activation energy decreased in the following series: CL₂Mg/MgCl₂ < CL₂Mg/MgBr₂ ~ CLMgBr < CL₂Mg/MgI₂. In addition, the poly(ε-caprolactam)s prepared with CL₂Mg/MgX₂ (MgX₂ = MgCl₂, MgBr₂, and MgI₂) are characterized by slightly higher thermal stability than polymers obtained with CLMgBr as initiator. These observations were explained in terms of the coordination of Lewis acids (MgX₂, where X = Cl, Br, and I) with imide carbonyl of N-acyllactam end groups leading to the increase of their reactivity and stability.     

Polymer nanosieve membranes for CO2-capture applications

Microporous organic polymers (MOPs) are of potential significance for gas storage, gas separation and low-dielectric applications. Among many approaches for obtaining such materials, solution-processable MOPs derived from rigid and contorted macromolecular structures are promising because of their excellent mass transport and mass exchange capability. Here we show a class of amorphous MOP, prepared by [2+3] cycloaddition modification of a polymer containing an aromatic nitrile group with an azide compound, showing super-permeable characteristics and outstanding CO(2) separation performance, even under polymer plasticization conditions such as CO(2)/light gas mixtures. This unprecedented result arises from the introduction of tetrazole groups into highly microporous polymeric frameworks, leading to more favourable CO(2) sorption with superior affinity in gas mixtures, and selective CO(2) transport by presorbed CO(2) molecules that limit access by other light gas molecules. This strategy provides a direction in the design of MOP membrane materials for economic CO(2) capture processes.