K8Gd3Si12O32Cl · 2H2O,a new member of the family of porous silicates with K and RE elements

Crystals of K₈Gd₃Si₁₂O₃₂Cl · 2H₂O (space group $P\bar 1$ ), a new member of the family of porous silicates containing rare earths, are obtained under hydrothermal conditions. The structure retains the main features of the family in which original one-story layers of Si-tetrahedra formed by 6-membered rings of two types and large-in-diameter 8-membered and 12-membered rings are bound by Gd-octahedra to form a framework. Large pores in the interlayer space of the mixed framework are filled with K⁺ ions. The penetration of Cl^? ions from a concentrated mineralizing solution into the centers of the eight-membered rings of the layer corroborates the ion-exchanging properties of the crystals of this structural type. The filling of rings and pores of different types in different members of the family by K⁺ and Cl^? ions, hydroxyl groups, and water molecules is analyzed.     

Simulation of chemical metabolism for fate and hazard assessment. V. Mammalian hazard assessment

Animals and humans are exposed to a wide array of xenobiotics and have developed complex enzymatic mechanisms to detoxify these chemicals. Detoxification pathways involve a number of biotransformations, such as oxidation, reduction, hydrolysis and conjugation reactions. The intermediate substances created during the detoxification process can be extremely toxic compared with the original toxins, hence metabolism should be accounted for when hazard effects of chemicals are assessed. Alternatively, metabolic transformations could detoxify chemicals that are toxic as parents. The aim of the present paper is to describe specificity of eukaryotic metabolism and its simulation and incorporation in models for predicting skin sensitization, mutagenicity, chromosomal aberration, micronuclei formation and estrogen receptor binding affinity implemented in the TIMES software platform. The current progress in model refinement, data used to parameterize models, logic of simulating metabolism, applicability domain and interpretation of predictions are discussed. Examples illustrating the model predictions are also provided.     

Partial automorphisms and injective partial endomorphisms of a finite undirected path

Semigroup Forum - In this paper, we study partial automorphisms and, more generally, injective partial endomorphisms of a finite undirected path from Semigroup Theory perspective. Our main...     

Novel K/Mn phosphate hydrates,K2Mn3(H2O)2[P2O7]2 and KMn(H2O)2[Al2(PO4)3]: hydrothermal synthesis and crystal chemistry

Two novel K/Mn phosphate hydrates, namely, dipotassium trimanganese dipyrophosphate dihydrate, K₂Mn₃(H₂O)₂[P₂O₇]₂, (I), and potassium manganese dialuminium triphosphate dihydrate, KMn(H₂O)₂[Al₂(PO₄)₃], (II), were obtained in the form of single crystals during a single hydrothermal synthesis experiment. Their crystal structures were studied by X‐ray diffraction. Both new compounds are members of the morphotropic series of phosphates with the following formulae: A₂M₃(H₂O)₂[P₂O₇]₂, where A = K, NH₄, Rb or Na and M = Mn, Fe, Co or Ni, and AM²⁺(H₂O)₂[M³⁺₂(PO₄)₃], where A = Cs, Rb, K, NH₄ or (H₃O); M²⁺ = Mn, Fe, Co or Ni; and M³⁺ = Al, Ga or Fe. A detailed crystal chemical analysis revealed correlations between the unit‐cell parameters of the members of the series, their structural features and the sizes of the cations. It has been shown that a mixed type anionic framework is formed in (II) by aluminophosphate [(AlO₂)₂(PO₄)₂]_∞ layers, with a cationic topology similar to the Si/Al‐topology of the crystal structures of feldspars. A study of the magnetic susceptibility of (II) demonstrates a paramagnetic behaviour of the compound.     

Characterization of rice husks and the products of its thermal degradation in air or nitrogen atmosphere

Rice husk is a by-product of rice milling process and are a major waste product of the agricultural industry. They have now become a great source as a raw biomass material for manufacturing value-added silicon composite products, including silicon carbide, silicon nitride, silicon tetrachloride, pure silicon, zeolite, fillers of rubber and plastic composites, adsorbent and support of catalysts. The bulk and true densities of raw rice husk with different moisture and sizes were determined. The rice husk was subjected to pyrolysis in fluidized-bed reactor in air or nitrogen atmosphere. The products obtained were characterized by thermogravimetric and X-ray powder analysis, IR-spectroscopy, scanning electron microscopy and nitrogen adsorption at 77 K. The specific surface area of the products is comparable with this of γ-Al₂O₃. The kinetics of H₂SeO₃ adsorption out of aqueous solutions at 298 K was studied. The adsorption capacity of white rice husks ash was found to be higher than that of black rice husk ash and the adsorption kinetics obeyed the second order kinetic equation.     

Geometrically designed,variable knot regression splines

A new method of Geometrically Designed least squares (LS) splines with variable knots, named GeDS, is proposed. It is based on the property that the spline regression function, viewed as a parametric curve, has a control polygon and, due to the shape preserving and convex hull properties, it closely follows the shape of this control polygon. The latter has vertices whose x-coordinates are certain knot averages and whose y-coordinates are the regression coefficients. Thus, manipulation of the position of the control polygon may be interpreted as estimation of the spline curve knots and coefficients. These geometric ideas are implemented in the two stages of the GeDS estimation method. In stage A, a linear LS spline fit to the data is constructed, and viewed as the initial position of the control polygon of a higher order (\(n>2\)) smooth spline curve. In stage B, the optimal set of knots of this higher order spline curve is found, so that its control polygon is as close to the initial polygon of stage A as possible and finally, the LS estimates of the regression coefficients of this curve are found. The GeDS method produces simultaneously linear, quadratic, cubic (and possibly higher order) spline fits with one and the same number of B-spline coefficients. Numerical examples are provided and further supplemental materials are available online.     

Hydrogen-bonded complexes of nitrous and nitric acids with ethene Ab initio and DFT studies

The complexes formed by ethene with nitric and nitrous (trans and cis) acids have been investigated by ab initio (SCF and MP2) and B3LYP calculations with 6-311++G(d,p) basis set. Full geometry optimisation has been performed for the complexes studied. The most stable structures of the complexes are established. Bearing in mind the corrected values of the dissociation energy the studied hydrogen-bonded complexes can be ordered as follows: C(2)H(4)...HONO(2)>C(2)H(4)...HONO-trans>C(2)H(4)...HONO-cis. In the complexes the acids act as proton donors forming the pi-type of hydrogen bond with ethene. The predicted changes in the vibrational characteristics (vibrational frequencies and infrared intensities) arising from the hydrogen bonding are in good agreement with the experimentally measured. The predicted frequency shift of the stretching OH vibration in the nitric acid is largest (-210 cm(-1)), followed by the shifts in the trans-HONO (-141 cm(-1)) and cis-HONO (-109 cm(-1)). The calculations predict an increase of the IR intensity of the stretching O-H vibration in the complexes from 6 to 10 times.