Unexpected products of the allyldiethylamine hydroformylation homogeneously catalyzed by rhodium complexes

Attempts to carry out the hydroformylation of allyldiethylamine homogeneously catalyzed by rhodium complexes led to unexpected formation of N,N,N,N-tetraethyl-1,4-diaminobutane and 4-(diethylamino)-1-butanole as final products. The role of the catalyst on the product formation and the reaction mechanism are briefly discussed.     

Integrated material flow and radioactivity distribution methodology within the calculation tool for evaluation of parameters for decommissioning of nuclear installations

Decommissioning of nuclear facilities becomes an important issue in all areas of nuclear technology, mainly in their energetic applications. Decommissioning process has to be planned in the safe, ecological and economic manner. It determines the requirements on appropriate evaluation of needed technologies, media, amount of solid materials released into the environment, radioactivity of effluents, amount of radioactive waste for disposal, number and exposure of personnel and finally the financial demands. A detailed evaluation of these parameters may be done by analytical calculation approach. This approach models a real process of decommissioning with its individual basic activities. The methodology of integrated material flow and radioactivity distribution within this calculation evaluation tool is applied and implemented to describe the real decommissioning activities and their mutual relations to obtain more accurate outputs.     

Structural Study of the Partially Disordered Full‐Length δ Subunit of RNA Polymerase from Bacillus subtilis

The partially disordered δ subunit of RNA polymerase was studied by various NMR techniques. The structure of the well‐folded N‐terminal domain was determined based on inter‐proton distances in NOESY spectra. The obtained structural model was compared to the previously determined structure of a truncated construct (lacking the C‐terminal domain). Only marginal differences were identified, thus indicating that the first structural model was not significantly compromised by the absence of the C‐terminal domain. Various ¹⁵N relaxation experiments were employed to describe the flexibility of both domains. The relaxation data revealed that the C‐terminal domain is more flexible, but its flexibility is not uniform. By using paramagnetic labels, transient contacts of the C‐terminal tail with the N‐terminal domain and with itself were identified. A propensity of the C‐terminal domain to form β‐type structures was obtained by chemical shift analysis. Comparison with the paramagnetic relaxation enhancement indicated a well‐balanced interplay of repulsive and attractive electrostatic interactions governing the conformational behavior of the C‐terminal domain. The results showed that the δ subunit consists of a well‐ordered N‐terminal domain and a flexible C‐terminal domain that exhibits a complex hierarchy of partial ordering.     

Determination of Heat of Adsorption on Clean Solid Surfaces

One of the basic parameters characterizing the bond between a chemisorbed atom (or molecule) and the surface is its dissociation energy. It is difficult, however, to determine the bond energy and therefore it becomes necessary to turn to some other quantity, which is sufficiently close to the bond energy and which can be determined without much difficulty. Such a quantity is the heat of adsorption. Heat of adsorption is defined as the difference between the total energy of the adsorption system prior to and after the adsorption process, i.e., it equals the sum of all energy changes connected with adsorption. Thus the experimentally determined value for the heat of adsorption is obviously closely related to the bond energy of the chemisorbed particle, though this relation is not quite simple [1,2].     

Synthesis and properties of YBa2Cu3O7-δ – Y2Ba4CuWO10.8 superconducting composites

YBa₂Cu₃O_7-δ (YBCO) is a well-known high-temperature superconductor. However, its critical current density and thus maximum trapped magnetic field can be improved significantly by introducing the secondary phases (artificial pinning centers). In this contribution, we successfully prepared YBCO single-grain bulks with Y₂Ba₄CuWO_10.8 phase serving as a source of pinning centers. This phase was prepared by solid-state reaction and further refined by milling. In the next step single-grain YBCO bulks with homogeneously distributed Y₂Ba₄CuWO_10.8 were prepared by top-seeded melt growth. Precursors as well as the final product were characterized by XRD, SEM and EDS. The phase composition of YBCO bulks containing Y₂Ba₄CuWO_10.8 was analyzed using Rietveld analysis. Thermal stability of YBCO bulk was studied by STA. Furthermore, PPMS was used to study electrical resistivity and critical current density. Bulk superconducting properties such as levitation force and trapped field ability were also measured.     

Early stages of growth of gold layers sputter deposited on glass and silicon substrates

Extremely thin gold layers were sputter deposited on glass and silicon substrates, and their thickness and morphology were studied by Rutherford backscattering (RBS) and atomic force microscopy (AFM) methods. The deposited layers change from discontinuous to continuous ones for longer deposition times. While the deposition rate on the silicon substrate is constant, nearly independent on the layer thickness, the rate on the glass substrate increases with increasing layer thickness. The observed dependence can be explained by a simple kinetic model, taking into account different sticking probabilities of gold atoms on a bare glass substrate and regions with gold coverage. Detailed analysis of the shape of the RBS gold signal shows that in the initial stages of the deposition, the gold layers on the glass substrate consist of gold islands with significantly different thicknesses. These findings were confirmed by AFM measurements, too. Gold coverage of the silicon substrate is rather homogeneous, consisting of tiny gold grains, but a pronounced worm-like structure is formed for the layer thickness at electrical continuity threshold. On the glass substrate, the gold clusters of different sizes are clearly observed. For later deposition stages, a clear tendency of the gold atoms to aggregate into larger clusters of approximately the same size is observed. At later deposition stages, gold clusters of up to 100 nm in diameter are formed.     

NMR study on reaction processes from aluminum chloride hydroxides to alpha alumina powders

Starting from gelatinous aluminum chloride hydroxide, the transformation process toward α-Al₂O₃ was examined using ²⁷Al NMR, both in the liquid and solid states, as a main analytical tool. By increasing the hydrolysis ratio (h, defined as [OH⁻]/[Al³⁺]) of the starting aqueous precursor up to h = 2.5, the transition temperature to the final product, α-Al₂O₃, decreased to as low as 500°C. In this case, the structural change from amorphous alumina to α-Al₂O₃ took place without intermediate transition Al₂O₃ phases. Examining the process of networking during the transition from aqueous sol–through the state of xerogel–to final anhydrous oxide by nuclear magnetic resonance (NMR) revealed the presence of highly polymeric species mainly ascribed to δ-[Al₂O₈Al₂₈(OH)₅₆(H₂O)₂₄]¹⁸⁺ (δ-Al₃₀). δ-Al₃₀ species were found in the solution phase and became predominant after drying. We conclude that the lower temperature synthesis of α-Al₂O₃ became possible due to preformation of polymerized AlO₆ construction units in the precursor, reducing the energy barrier for the nucleation of the final α-Al₂O₃ phase.     

Melectin: a novel antimicrobial peptide from the venom of the cleptoparasitic bee Melecta albifrons

A novel antimicrobial peptide designated melectin was isolated from the venom of the cleptoparasitic bee Melecta albifrons. Its primary sequence was established as H-Gly-Phe-Leu-Ser-Ile-Leu-Lys-Lys-Val-Leu-Pro-Lys-Val-Met-Ala-His-Met-Lys-NH(2) by Edman degradation and ESI-QTOF mass spectrometry. Synthetic melectin exhibited antimicrobial activity against both gram-positive and -negative bacteria and it degranulated rat peritoneal mast cells, but its hemolytic activity was low. The CD spectra of melectin measured in the presence of trifluoroethanol and sodium dodecyl sulfate showed a high content alpha-helices, which indicates that melectin can adopt an amphipathic alpha-helical secondary structure in an anisotropic environment such as the bacterial cell membrane. To envisage the role of the proline residue located in the middle of the peptide chain on biological activity and secondary structure, we prepared several melectin analogues in which the Pro11 residue was either replaced by other amino acid residues or was omitted. The results of biological testing suggest that a Pro kink in the alpha-helical structure of melectin plays an important role in selectivity for bacterial cells. In addition, a series of N- and C-terminal-shortened analogues was synthesized to examine which region of the peptide is related to antimicrobial activity.