Defect Structure of Alkaline-Earth,Cadmium, and Lead Titanates

X-ray powder diffraction, scanning electron microscopy, and x-ray microanalysis data indicate that Ba, Ca, Sr, Cd, and Pb titanates contain defect structures associated with crystallographic shear. Spatially periodic shear gives rise to modulated displacements of the Ti and O atoms across the shear plane, resulting in long-period structures. The parameters of such structures depend on the nature of the sample (single crystal, ceramic, or powder), its microstructure, and the crystal chemistry of the titanate.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 573–584.Original Russian Text Copyright © 2005 by Reznichenko, Shilkina, S. Titov, Razumovskaya, V. Titov, Shevtsov.     

Conjugates of Methylene Blue with Cycloalkaneindoles as New Multifunctional Agents for Potential Treatment of Neurodegenerative Disease

The development of multi-target-directed ligands (MTDLs) would provide effective therapy of neurodegenerative diseases (ND) with complex and nonclear pathogenesis. A promising method to create such potential drugs is combining neuroactive pharmacophoric groups acting on different biotargets involved in the pathogenesis of ND. We developed a synthetic algorithm for the conjugation of indole derivatives and methylene blue (MB), which are pharmacophoric ligands that act on the key stages of pathogenesis. We synthesized hybrid structures and performed a comprehensive screening for a specific set of biotargets participating in the pathogenesis of ND (i.e., cholinesterases, NMDA receptor, mitochondria, and microtubules assembly). The results of the screening study enabled us to find two lead compounds (4h and 4i) which effectively inhibited cholinesterases and bound to the AChE PAS, possessed antioxidant activity, and stimulated the assembly of microtubules. One of them (4i) exhibited activity as a ligand for the ifenprodil-specific site of the NMDA receptor. In addition, this lead compound was able to bypass the inhibition of complex I and prevent calcium-induced mitochondrial depolarization, suggesting a neuroprotective property that was confirmed using a cellular calcium overload model of neurodegeneration. Thus, these new MB-cycloalkaneindole conjugates constitute a promising class of compounds for the development of multitarget neuroprotective drugs which simultaneously act on several targets, thereby providing cognitive stimulating, neuroprotective, and disease-modifying effects.     

Competing topological phases in few-layer graphene

We investigate the effect of spin-orbit coupling on the band structure of graphene-based two-dimensional Dirac fermion gases in the quantum Hall regime. Taking monolayer graphene as our first candidate, we show that a quantum phase transition between two distinct topological states—the quantum Hall and the quantum spin Hall phases—can be driven by simply tuning the Fermi level with a gate voltage. This transition is characterized by the existence of a chiral spin-polarized edge state propagating along the interface separating the two topological phases. We then apply our analysis to the more difficult case of bilayer graphene. Unlike in monolayer graphene, spin-orbit coupling by itself has indeed been predicted to be unsuccessful in driving bilayer graphene into a topological phase, due to the existence of an even number of pairs of spin-polarized edge states. While we show that this remains the case in the quantum Hall regime, we point out that by additionally breaking the layer inversion symmetry, a non-trivial quantum spin Hall phase can re-emerge in bilayer graphene at low energy. We consider two different symmetry-breaking mechanisms: inducing spin-orbit coupling only in the upper layer, and applying a perpendicular electric field. In both cases, the presence at low energy of an odd number of pairs of edge states can be driven by an exchange field. The related situation in trilayer graphene is also discussed.     

Structure of ceramics produced through high-temperature nitridation of hafnium foil

The high-temperature hafnium nitridation process, with HfN_x formation, comprises two stages. With increasing nitridation temperature and time, the lattice parameter of the nitride decreases. The observed discrete nucleation of nitride microcrystals on the surface is a consequence of metal diffusion through an amorphous carboxynitride. No structural defects were detected by high-resolution transmission electron microscopy in selected areas.