Thermal induced structural and magnetic transformations in Fe73.5−xCex=0,3,5,7Si13.5B9Nb3Cu1 amorphous alloy

Structural and magnetic properties of amorphous and partly crystallized Fe_73.5?xCe_x=0,3,5,7Si_13.5B₉Nb₃Cu₁ alloys, were analysed in the temperature ranging from RT to 800 °C with scanning calorimetry and magnetometry. The Fe(Si) and Fe(B) structures were identified and characterised with set of crystallization temperatures and activation energies. Also, Curie temperatures for amorphous and for crystalline structures were determined and analysed as functions of Ce content.     

A Simple Synthesis of 2′,5′-Disubstituted-Spiro [Dihydroacridine 9(10H), 4′-Thiazolines] by the Reaction of Corresponding 3-(Acridin-9-Yl)-Thioureas with Methyl Bromoacetate and Bromoacetonitrile

A convenient method has been devised for the preparation of the spirodihydro-acridinethiazolines 5a-j by the treatment of thioureas 3a-e with methyl bromoacetate and bromoacetonitrile via non-isolable isothioureas 4a-j and their subsequent cyclization with methanolic sodium methoxide.     

Activity and regenerability of dealuminated zeolite Y in liquid phase alkylation of benzene with 1-alkene

HY-zeolite and its deep-bed dealuminated and EFAL-extracted forms were tested in liquid phase alkylation of benzene with 1-hexadecene in a batch reactor at 120°C. Deep-bed dealumination of the HY-sample at 560 °C followed by careful selective extraction of extra-framework aluminium by hydrochloric acid increased the catalytic activity as well as oxidative regenerability of Y-zeolite.     

Adsorption of cesium and strontium on natrified bentonites

The influence of chemical activation–natrification of bentonites on adsorption of Cs and Sr was studied with regards to utilization of bentonites for depositing high-level radioactive waste and spent nuclear fuel. Bentonite samples from three Slovak deposits in three different grain-size (15, 45 and 250 μm), natural and natrified forms (Na-bentonites); under various experimental conditions, such as contact time, adsorbent and adsorbate concentration have been studied. When comparing the Na-bentonites and their natural analogues, the highest adsorbed Cs and Sr amounts were reached on the natrified samples. After the Sr adsorption a drop in the pH equilibrium value was observed together with the increase of the initial Sr concentration. A disadvantage of the natrified bentonite forms is formation of colloid particles. After 2 h of phase mixing a gentle turbidity was observed as well as formation of a gel-like form. The above findings were confirmed by observing the particle distribution in dry and wet dispersion and centrifugation at two different speeds. Natrification as a technological process of bentonite quality improvement cannot be applied when constructing a long-term repository for high-level radioactive waste and spent nuclear fuel. The main problem of natrification is a technological process which leads to a significant pH increase. Alkaline environment in combination with the K presence and increased temperature in the vicinity of radio-active waste can lead to a rapid illitization of smectite and loss of the original adsorption qualities. Moreover, sodium additions are a significant point of uncertainty since it is not possible to state what amount of Na enters the interlayer space and what amount stays in the inter-partition space.     

Study of gramicidin A--phospholipid interactions in Langmuir monolayers: analysis of their mechanical, thermodynamical, and electrical properties

The mechanisms of interactions between gramicidin A (gA) and dimyristoylphosphatidylcholine (DMPC) in monolayers formed at the air-water interface were studied by analyzing their mechanical, thermodynamical, and electrical properties evaluated from measurements of pressure-area isotherms and of Maxwell displacement currents (MDC). A contactless method of recording MDC enabled us to monitor changes in the charge state of the monolayer-constituting molecules and to find the relation between a phase state of the monolayer and structural transitions of gA. The peptide-lipid interactions were quantified in terms of the excess of Gibbs free energy, excess entropy, as well as the molecular dipole moments at various gA/DMPC molar ratios, at various temperatures (in the gel phase and also in the liquid-crystalline phase of DMPC molecule), and at various surface pressures. It was found that the strongest interactions between gA and DMPC took place at the gA/DMPC molar ratio at around 0.25. At this monolayer composition, the phospholipids, via their carbonyl moieties, dominantly interact with the single helical gA, which mostly stands upright on the surface and is anchored by its C-terminus to the water surface, and prevent the formation of the intertwined helical gA dimers. The optimum ratio was confirmed also by anomalous electrical behavior of electrical dipole moments derived from MDC measurements.     

Adaptable chromatic number of graph products

A colouring of the vertices of a graph (or hypergraph) G is adapted to a given colouring of the edges of G if no edge has the same colour as both (or all) its vertices. The adaptable chromatic number of G is the smallest integer k such that each edge-colouring of G by colours 1,2,…,k admits an adapted vertex-colouring of G by the same colours 1,2,…,k. (The adaptable chromatic number is just one more than a previously investigated notion of chromatic capacity.) The adaptable chromatic number of a graph G is smaller than or equal to the ordinary chromatic number of G. While the ordinary chromatic number of all (categorical) powers G^k of G remains the same as that of G, the adaptable chromatic number of G^k may increase with k. We conjecture that for all sufficiently large k the adaptable chromatic number of G^k equals the chromatic number of G. When G is complete, we prove this conjecture with k≥4, and offer additional evidence suggesting it may hold with k≥2. We also discuss other products and propose several open problems.     

Stereodivergent synthesis of cyclic γ-aminobutyric acid – GABA analogues

A novel synthetic route towards two series of enantiomerically pure cyclic analogues of 2,3-cis- and 2,3-trans-γ-aminobutyric acid (GABA) was developed. The route is based on the elongation and stereodivergent manipulation of a readily accessible enantiomerically pure γ-substituted α-aminolactone. The five-step route towards the 2,3-cis-substituted GABA analogues was achieved via straightforward carbon chain extension of the lactone using a non-classical Wittig reaction followed by chemoselective reduction and a protecting group switch. The five-step route towards the 2,3-trans-substituted GABA analogues employed elongation of the same aminolactone using a Horner-Wadsworth-Emmons reaction and highly stereoselective intramolecular oxa-Michael addition as the key synthetic manipulations. Altogether this chemistry has allowed the stereodivergent preparation of a novel class of GABA analogues in two diastereomeric series.     

Effects of geometrical frustration on ferromagnetism in the Hubbard model on the generalised Shastry-Sutherland lattice

The small-cluster exact-diagonalization calculations and the projector quantum Monte Carlo method are used to examine the competing effects of geometrical frustration and interaction on ferromagnetism in the Hubbard model on the generalised Shastry-Sutherland lattice. It is shown that the geometrical frustration stabilizes the ferromagnetic state at high electron concentrations (n ? 7∕4), where strong correlations between ferromagnetism and the shape of the noninteracting density of states are observed. In particular, it is found that ferromagnetism is stabilized for these values of frustration parameters, which lead to the single-peaked noninterating density of states at the band edge. Once, two or more peaks appear in the noninteracting density of states at the band edge the ferromagnetic state is suppressed. This opens a new route towards the understanding of ferromagnetism in strongly correlated systems.     

2D MXenes as Perspective Immobilization Platforms for Design of Electrochemical Nanobiosensors

MXenes are a new group of 2D nanomaterials with fascinating properties including high electrical conductivity, hydrophilic nature, easily tunable structure and high surface area. This is why MXene modified interfaces are extremely promising for the preparation of sensitive electrochemical biosensors. While there are numerous reports on MXene‐based enzymatic biosensors for detection of a wide range of analytes, application of MXene for construction of affinity biosensors is in its infancy. The review article summarizes current state‐of the‐art in the field with a focus on MXene modifications needed for construction of robust and high performance MXene electrochemical biosensors.