Synthesis and properties of fullerene (C70) complexes of 2,6-bis(porphyrin)-substituted pyrazine derivatives bound to a Pd(II) ion

2,6-Bis(porphyrin)-substituted 3,5-dimethylpyrazine and its zinc complex bound C₇₀ to yield 1:1 inclusion complexes, which were characterised by ESI-MS, UV–vis, fluorescence and NMR spectroscopies. Association constants of the C₇₀ complexes were determined by fluorescence and NMR spectral analyses. A decrease in absorbance of the Soret band of the pyrazine derivative by the effect of C₇₀ was observed, suggesting the existence of a charge transfer interaction between C₇₀ and porphyrin. Experimentally reliable values for the association constants were obtained by the NMR method and were about six times larger than those of the corresponding C₆₀ complexes. Palladium complexation of the porphyrin–pyrazine ligand was found to enhance the association with fullerene. The association constant of 2,6-bis(porphyrin-Zn)-substituted 3,5-dimethylpyrazine-Pd(II) complex with C₇₀ was determined to be 8400 ± 900 M^? 1. From the comparison of the association constants, it was found that inclusion room for C₇₀ in the Pd(II) complex was maintained, juxtaposed between porphyrins attached to the opposite sides of the pyrazine ligands.

     

Evaluation of radioactivity induced in the accelerator building and its application to decontamination work

For decommissioning of the cyclotron and electron synchrotron facilities, the residual radioactivity in surface and core samples of concrete, collected from various parts of buildings, was determined by gamma-ray spectrometry. It was found that the concrete samples were activated mainly by neutrons and that the major radioisotopes were ¹⁵²Eu, ⁶⁰Co, ¹³⁴Cs, ²²Na and ⁵⁴Mn. The maximum activity induced by thermal neutron capture was observed at the depth of 10 cm in the concrete wall near the deflector of the cyclotron. Tritium was also produced by the neutron reaction, because its concentration was proportional to the activities of ¹⁵²Eu and ⁶⁰Co. The surface dose rates inside the accelerator room were also monitored to define the decontamination area. The surface dose rate was proportional to the residual radioactivity, such as ⁶⁰Co. A careful evaluation was very useful in order to minimize the radioactive waste during decontamination.     

The fundamental groups of one-dimensional wild spaces and the Hawaiian earring

Let be a one-dimensional space which contains a copy of a circle and let it not be semi-locally simply connected at any point on Then the fundamental group of cannot be embeddable into a free -product of n-slender groups, for instance, the fundamental group of the Hawaiian earring. Consequently, any one of the fundamental groups of the Sierpinski gasket, the Sierpinski curve, and the Menger curve is not embeddable into the fundamental group of the Hawaiian earring.

     

On the Singular Homology of One Class of Simply-connected Cell-like Spaces

In our earlier papers we constructed examples of 2-dimensional nonaspherical simply-connected cell-like Peano continua, called Snake space. In the sequel we introduced the functor SC(−,−) defined on the category of all spaces with base points and continuous mappings. For the circle S ¹, the space SC(S¹, _*){SC(S^1, {_{*}})} is a Snake space. In the present paper we study the higher-dimensional homology and homotopy properties of the spaces SC(Z, _*){SC(Z, {_{*}})} for any path-connected compact spaces Z.     

Optical absorption in surface space-charge layers of anisotropic and tilted valley systems

In n-channel accumulation and inversion layers on the (110) and (111) surface of Si, inter-subband optical transitions can be induced by infrared light incident normal to the surface. The resonance screening and exciton-like effect depend strongly on the nature of the valley degeneracy in this configuration. Examples of numerical calculation of the absorption spectrum are presented.     

Effect of annealing temperature on some physical properties of MgB2 by using the Hall probe ac-susceptibility method

A commercially available powder of MgB₂ is used as starting material for the examination of the influence of the annealing temperature on the properties of this intermediate-T_c superconductor. We performed scanning electron microscopy (SEM) and Hall ac-susceptibility measurements as a function of temperature and ac-field amplitude on samples annealed at 650, 750, 850 and 950 °C. The imaginary part of ac-susceptibility measurements is used to calculate both the inter-granular critical current density, J_c(T_p) and density of pinning force, α_j(0). It was observed that all T_c, J_c(T_p) and α_j(0) exhibit a non-monotonic behavior on the annealing temperature range studied in this work. T_c is measured to be 39.85±0.02 K and J_c(T_p) is estimated to be as high as 60 A/cm² at 39.2 K for the sample annealed at 850 °C. The peak temperature, T_p, in the imaginary part of the ac-susceptibility curves shifts to lower temperatures with both decreasing the annealing temperature and increasing the amplitude of the ac-magnetic fields. A comparison of the experimental ac-susceptibility data with theoretical critical-state models that are currently available is performed. SEM investigations showed that the grain size increases, and the grain connectivity improves when the annealing temperature increases up to 850 °C. The possible reasons for the observed changes in transport, microstructure and magnetic properties due to annealing temperature are discussed.     

Nonracemic 3 degrees-carbamines from the asymmetric allylboration of N-trimethylsilyl ketimines with B-allyl-10-phenyl-9-borabicyclo[3.3.2]decanes

The simple and efficient asymmetric synthesis of 3 degrees -carbamines 7 from N-TMS enamines (3) and either enantiomeric form of beta-allyl-10-(phenyl)-9-borabicyclo[3.3.2]decane (1) is reported. The high reactivity (<1 h, -78 degrees C) and enantioselectivity (60-98% ee) of these substrates can be attributed to the fact that the complexation of 3 with 1 facilitates its isomerization to the corresponding syn-N-TMS ketimine complex from which allylation can occur. In addition to providing the homoallylic amines 7 with predictable stereochemistry, the procedure also permits the efficient recovery of the chiral boron moiety (50-65%) as air-stable crystalline pseudoephedrine complexes 8, which are directly converted back to 1 with allylmagnesium bromide in ether (98%).     

The non-isothermal kinetics of mullite formation in mechanically activated kaolinite–alumina ceramic system

The non-isothermal kinetics of mullite formation from both non-activated and mechanically activated kaolinite?+?alumina ceramic system have been studied by differential thermal analysis (DTA). The mixture of kaolinite and alumina was activated mechanically in a planetary mill, while amorphization in the kaolinite and alumina structure was studied by X-ray diffraction analysis. The activation energies depending on the conversion for mullite formation have been calculated from the DTA curves by using the non-isothermal method of Coats and Redfern at heating rates of 5, 10, 15, and 20?°C?min^?1. The mechanical activation of the kaolinite and alumina mixture resulted in the decrease in activation energy values for mullite formation.     

Charge density of divalent metal cations determines RNA stability

RNA molecules are exquisitely sensitive to the properties of counterions. The folding equilibrium of the Tetrahymena ribozyme is measured by nondenaturing gel electrophoresis in the presence of divalent group IIA metal cations. The stability of the folded ribozyme increases with the charge density (zeta) of the cation. Similar scaling is found when the free energy of the RNA folded in small and large metal cations is measured by urea denaturation. Brownian dynamics simulations of a polyelectrolyte show that the experimental observations can be explained by nonspecific ion-RNA interactions in the absence of site-specific metal chelation. The experimental and simulation results establish that RNA stability is largely determined by a combination of counterion charge and the packing efficiency of condensed cations that depends on the excluded volume of the cations.     

Moments of the support weight distribution of linear codes

In this work, we give the expectation and the covariance formulas for the support weight distributions of linear codes.