Structural manipulation of pyrochlores: Thermal evolution of metastable Gd2(Ti1−yZry)2O7 powders prepared by mechanical milling

The structural and microstructural characteristics of metastable Gd₂(Ti_1−yZr_y)₂O₇ powders prepared by mechanical milling have been studied by a combination of XRD and Raman spectroscopy. Irrespective of their Zr content, as-prepared powder phases present an anion-deficient fluorite-type of structure as opposed to the pyrochlore equilibrium configuration obtained for the same solid solution by other synthetic routes. These fluorites are stable versus thermal activation, at least up to temperatures of 800 °C. For the Ti-rich compositions, thermal treatments at higher temperatures facilitate the rearrangement of the cation and anion substructures and the relaxation of mechanochemically induced defects whereas for compositions with high Zr content, the fluorite crystal structure is retained even at temperatures as high as 1200 °C. Interestingly enough, transient pyrochlores showing a very unusual cation distribution were observed during the thermally induced defect-recovery process.     

Front roughening in three-dimensional imbibition

We investigate the structure and dynamics of the interface between two immiscible liquids in a three-dimensional disordered porous medium. We apply a phase-field model that includes explicitly disorder and discuss both spontaneous and forced imbibition. The structure of the interface is dominated by a length scale ξ_× which arises from liquid conservation. We further show that disorder in the capillary and permeability act on different length scales and give rise to different scalings and structures of the interface properties. We conclude with a range of applications.     

Kinetics of the solution polymerization of dioxolane in the presence of water

Water acts as a cocatalyst in the polymerization of dioxolane initiated by the ion pair ～Si^⊕HSO₄^?. The dependence of the reaction rate on the water concentration exhibits a maximum, the width of which strongly depends on the concentration of dioxolane. The change of the coordinates of the maximum and its shape with the decrease of the monomer concentration causes the reaction rate to decrease with increasing conversion. The point at which the slope of the conversion curve changes is a function of initial concentration of water. There is a very fast decrease of the concentration of free water in the polymerizing system. The consumption of water is associated with some peculiarities. The amount of free water which remains in the system is a function of the concentration of the original initiator. The ratio [H₂O]_∞/[initiator] is constant over a rather broad range of initial concentration of water.     

Simulation of aerated lagoon using artificial neural networks and multivariate regression techniques

The aim of this study was to develop an empirical model that provides accurate predictions of the biochemical oxygen demand of the output stream from the aerated lagoon at International Paper of Brazil, one of the major pulp and paper plants in Brazil. Predictive models were calculated from functional link neural networks (FLNNs), multiple linear regression, principal components regression, and partial least-squares regression (PLSR). Improvement in FLNN modeling capability was observed when the data were preprocessed using the PLSR technique. PLSR also proved to be a powerful linear regression technique for this problem, which presents operational data limitations.     

Room-temperature synthesis and conductivity of the pyrochlore type Dy2(Ti1−yZry)2O7 (0?y?1) solid solution

Different compositions in a solid solution of general formula Dy₂(Ti_1−yZr_y)₂O₇, showing high oxygen ion conductivity, have been successfully prepared at room temperature via mechanochemical synthesis. Stoichiometric mixtures of the constituent oxides were dry milled together in a planetary ball mill by using zirconia vials and balls. Chemical changes in the powder mixtures as a function of composition and milling time were followed by X-ray diffraction and revealed that, in all cases and after milling for 19 h, the powder mixtures consisted of a single phase. Electrical properties were measured on sintered pellets as a function of frequency, temperature and zirconium content, revealing an increase in conductivity of more than one order of magnitude for y?0.4, which, as observed in the similar Y₂(Ti_1−yZr_y)₂O₇, has been related with the onset of disordering of the anion sublattice. Despite increasing structural disorder with increasing Zr content, conductivity remains almost constant for y>0.6, reaching a maximum value of ∼5×10⁻³ for Dy₂Zr₂O₇ at 900 °C.     

Rearrangement of spiro-benzimidazolines: preparation of N-alkenyl- and N-alkyl-benzimidazol-2-ones

A synthetically useful protocol has been developed for the preparation of highly functionalized N-alkenyl-benzimidazol-2-ones. Reaction of commercially available o-phenylenediamines with variously substituted cyclic ketones provides spiro-benzimidazolines. Treatment of these spiro-benzimidazolines with triphosgene in the presence of potassium carbonate results in rapid rearrangement and formation of N-alkenyl-benzimidazol-2-ones in modest to excellent yield for the two-step sequence. Extension of this methodology toward the preparation of a μ opiate receptor antagonist and droperidol, a potent antiemetic and antipsychotic agent, currently a marketed pharmaceutical is also described. Upon treatment of spiro-benzimidazolines with triphosgene in the presence of sodium triacetoxyborohydride, N-alkyl-benzimidazol-2-ones were formed.     

A more convenient and general procedure for O-monobenzylation of diols via stannylenes: a critical reevaluation of the Bu2SnO method

A more consistent, straightforward, and economical protocol for generation of stannylene species and their reaction with BnBr leading to products of O-monobenzylation of diols has been set. It has shown to be specially indicated for substrates bearing vicinal trans 1,2-diol moieties on cyclohexane backbones, which are more resistant to these transformations. Such protocol has been successfully applied to myo-inositol derivatives and acyclic diols.     

Effect of brain lesions on [3H]ohmefentanyl binding site densities in the rat striatum and substantia nigra.

We have recently demonstrated that [3H]ohmefentanyl, a non-peptidergic opioid ligand which was suggested to cross the blood brain barrier in contrast to other peptidergic opioid ligands, bound not only to mu opioid receptor sites but also to sigma sites. In order to examine whether [3H]ohmefentanyl can be used as a marker for mu sites, we investigated the effects of brain lesions on [3H]ohmefentanyl binding site densities, as compared with [3H][D-Ala2, MePhe4, Gly-ol5]enkephalin ([3H]DAGO), a selective mu ligand. These binding site densities were measured by quantitative autoradiography in the rat striatum and substantia nigra, two brain structures known to contain a high density of mu receptors, following lesions of the nigro-striatal dopaminergic pathway and striatal intrinsic neurons. Following unilateral nigral lesion with 6-hydroxydopamine, [3H]ohmefentanyl binding site densities were decreased in the patches (-35%) and matrix (-20%) of the ipsilateral striatum and in the lesioned substantia nigra pars compacta (-49%). Unilateral striatal lesion with quinolinic acid induced 72%, 61% and 50% decreases in [3H]ohmefentanyl binding in the patches and matrix of the lesioned striatum and in the ipsilateral substantia nigra pars reticulata, respectively. Similar results were obtained in the binding of [3H]DAGO. Indeed, a significant linear correlation was observed between [3H]ohmefentanyl and [3H]DAGO binding site densities. Therefore, mu opioid receptors may be mainly located on intrinsic neurons in the striatum, dopaminergic cell bodies in the substantia nigra pars compacta and nerve terminals of striatal efferents in the substantia nigra pars reticulata.(ABSTRACT TRUNCATED AT 250 WORDS)     

High-throughput chemistry toward complex carbohydrates and carbohydrate-like compounds

In the area of peptide and nucleic acid chemistry and biology, high-throughput synthesis has played an important role in providing useful small-molecule-based chemical probes in understanding the structure and function relationships. The past several years, there has been a constant rise in interest toward understanding the biological roles and functions of another important class of biomolecules, i.e., carbohydrates and carbohydrate conjugates. Although at early stages, in recent years, several groups have developed high-throughput synthetic methods to obtain complex carbohydrates or carbohydrate-like small-molecules. The present review article summarizes some of these developments.