Structural aspects of the metal-insulator transitions in V0.985Al0.015O2

The crystal structure of V_0.985Al_0.015O₂ has been refined from single-crystal X-ray data at four temperatures. At 373°K it has the tetragonal rutile structure. At 323°K, which is below the first metal-insulator transition, it has the monoclinic M₂ structure, where half of the vanadium atoms are paired with alternating short (2.540 Å) and long (3.261 Å) V-V separations. The other half of the vanadium atoms form equally spaced (2.935 Å) zigzag V chains. At 298°K, which is below the second electric and magnetic transition, V_0.985Al_0.015O₂ has the triclinic T structure where both vanadium chains contain V-V bonds, V(1)-V(1) = 2.547 Å and V(2)-V(2) = 2.819 Å. At 173°K the pairing of the V(1) chain remains constant: V(1)-V(1) = 2.545 Å, whereas that of the V(2) chain decreases: V(2)-V(2) = 2.747 Å. From the variation of the lattice parameters as a function of temperature it seems that these two short V-V distances will not become equal at lower temperatures. The effective charges as calculated from the bond strengths at 298 and 173°K show that a cation disproportionation has taken place between these two temperatures. About 20% of the V⁴⁺ cations of the V(1) chains have become V³⁺ and correspondingly 20% of the V⁴⁺ cations of the V(2) chains have become V⁵⁺. This disproportionation process would explain the difference between the two short V-V distances. Also it would explain why the T → M₁ transition does not take at lower temperatures.     

Crystal structure,dimensionality, and 4d electron distribution in K0.30MoO3 and Rb0.30MoO3

Single crystals of K_0.30MoO₃ and Rb_0.30MoO₃ were synthesized by electrolytic reduction of MoO₃/ A₂MoO₄ melts. The crystal structures were refined from X-ray diffraction data (3265 and 1280 independent reflections, respectively). The finalR andwR factors were 0.037 and 0.047 for the K bronze and 0.031 and 0.033 for the Rb bronze. The lattice parameters of the body-centered cells used in the present refinements were: K_0.30Mo0₃,a = 16.2311(7),b = 7.5502(4),c = 9.8614(4)A?,β = 94.895(4)^o; Rb_0.30MoO₃,a = 16.361(3),b = 7.555(1),c = 10.094(2)A?,β = 93.87(5)^o. The 4d electron distribution over the 20 Mo sites [4Mo(1), 8Mo(2), 8Mo(3)] of the unit cell are 10, 45, and 45% for K_0.30Mo0₃ and 14, 43, and 43% for Rb_0.30MoO₃, respectively. In both cases about 90% of the 4d electrons are situated on those sites which contribute to the electrical conductivity. The variations of the lattice parameters versus temperature are reported. The thermal linear-expansion coefficient is highly anisotropic. The structural dimensionality depends upon the sublattice under consideration. The K, Mo, and O sublattices are mono-, two-, and three-dimensional, respectively. The relationship between the structural dimensionality of K_0.30MoO₃ and the physical properties is discussed.     

A novel design approach for the epitaxial layer for 4H-SiC and 6H-SiC power bipolar devices

The paper evaluates the optimal design of the low-doped base region inside power diodes and other bipolar devices. It is demonstrated theoretically that a low-doped base region of P⁺N⁻N⁺ diodes can provide a high breakdown voltage and an optimal on-resistance . A simple, accurate and CPU timesaving approach is presented to extract an optimal value for the base region width, W_B, and its doping concentration, N_D. The paper details an analytical relation between W_B and N_D, and gives a method for quantifying the trade-off between their values for a given breakdown voltage and for obtaining the minimal on-resistance. Analytical results are confronted with experimental results for 4H-SiC- and 6H-SiC-based diodes.     

The First Snake Venom KTS/Disintegrins-Integrin Interactions Using Bioinformatics Approaches

Snake venom contains a number of active molecules that have been shown to possess high anti-tumor activities; disintegrins are an excellent example among these. Their ability to interact and bind with integrins suggests that they could be very valuable molecules for the development of new cancer therapeutic approaches. However, in the absence of a clear Lysine-Threonine-Serine (KTS) Disintegrins Integrin interaction model, the exact compound features behind it are still unknown. In this study, we investigated the structural characteristics of three KTS-disintegrins and the interaction mechanisms with the α1β1 integrin receptor using in silico bioinformatics approaches. Normal mode analysis showed that the flexibility of the KTSR motif and the C-terminal region play a key role and influence the KTS-Disintegrin-integrin interaction. Protein-protein docking also suggested that the interaction involving the KTSR motif is highly dependent on the residue following K21, S23 and R24. These findings contribute to a better understanding of the KTS-Disintegrin-Integrin structural differences and their interactions with α1β1 receptors, which could improve the selection process of the best active molecules for antitumor therapies.     

Anti-lipid peroxidation and induction of apoptosis in the erythroleukaemic cell line K562 by extracts from (Tunisian) Rhamnus alaternus L. (Rhamnaceae)

Total oligomer flavonoids (TOF) enriched and ethyl acetate (EA) extracts from Rhamnus alaternus induce apoptotic death in human chronic myelogenous leukaemia K562 cell line, as demonstrated by gel electrophoresis, which demonstrates the characteristic ladder patterns of DNA fragmentation and the proteolytic cleavage of poly(ADP ribose) polymerase (PARP). The effect of R. alaternus extract in reducing oxidative stress was evaluated by anti-lipid peroxidation which was monitored by measuring malondialdehyde level in K562 cultured cells. The TOF and EA extracts were found to be effective to protect against lipid peroxidation. Their IC?? values were 196 and 273?μg?mL?1, respectively. These findings suggest that R. alaternus extracts exhibit potential antioxidant and proapoptotic properties.     

Aqueous Extract of Crataegus azarolus Protects Against DNA Damage in Human Lymphoblast Cell K562 and Enhances Antioxidant Activity

The present study was carried out to characterize the cellular antioxidant effect of the aqueous extract of Crataegus azarolus and its antigenotoxic potential using human myelogenous cells, K562. The antioxidant capacity of this extract was evaluated by determining its cellular antioxidant activity (CAA) in K562 cells. Also, preceding antigenotoxicity assessment, its eventual genotoxicity property was investigated by evaluating its capacity to induce the DNA degradation of treated cell nuclei. As no genotoxicity was detected at different exposure times, its ability to protect cell DNA against H₂O₂ oxidative effect was investigated, using the “comet assay.” It appears that 800 μg/mL of extract inhibited the genotoxicity induced by H₂O₂ with a rate of 41.30 %, after 4 h of incubation. In addition, this extract revealed a significant cellular antioxidant capacity against the reactive oxygen species in K562 cells.     

Structure cristalline d'un conducteur métallique bidimensionnel: Le bronze violet de potassium et molybdene K0.9Mo6O17

Single crystals of the purple bronze K_0.9Mo₆O₁₇ have been grown by a electrolytic reduction technique. Measurements of the electrical resistivity show that this compound is a quasi two-dimensional metal. A crystal structure determination is used to explain the strongly anisotropic resistivity. K_0.9Mo₆O₁₇ is found to be trigonal with lattice parameters: a = 5.538 Å and c = 13.656 Å; Z = 1. The space group is $\text{P}\text{3}$. The K cations are surrounded by 12 oxygen anions which form icosahedral sites. One third of the Mo cations (Mo(1)) occupy tetrahedral sites, while the Mo(2) and Mo(3) cations have octahedral surroundings. The structure can be described as slabs of ReO₃-type connected by KO₁₂ icosahedra. Each slab is built up of 4 layers, parallel to the (001) plane, of Mo(2) and Mo(3) octahedra sharing corners. Two slabs are connected by K icosahedra which share 2 faces with the upper and lower neighboring Mo(3) octahedra. Each K icosahedron is edge linked to 3 upper and 3 lower Mo(1) tetrahedra. Each Mo(1) tetrahedron is itself corner linked to 3 Mo(3) octahedra of the neighboring layer. The deformations of the occupied polyhedra are a good illustration of the Pauling's third rule. There is no Mo(1)OMo(1) bonding, so that the MoOMo bonding, infinite in the a and b directions, is disrupted in the c direction. The Zachariasen's bond length-bond strength relation has been applied to the MoO bonds. The computed effective mean Mo valences are +6 for Mo(1) on tetrahedral sites and about 5.1 and 5.8, respectively, for Mo(2) and Mo(3) on octahedral sites. The 4d electrons of Mo atoms are so located in the two-dimensional infinite slabs of octahedra. The conduction band is expected to be an antibonding π1 band resulting from the hybridization of the Mo 4dt_2g and oxygen p_π states. Thus, the structural properties should lead to a very anisotropic Fermi surface and thus, to a quasi two-dimensional electrical conductivity.