Bis­(tri­chloro­phosphine)­iminium salts, [Cl3P=N=PCl3]+, with transition metal halide counter‐ions

The structures of four bis­(tri­chloro­phosphine)­iminium {[Cl₃P=N=PCl₃]⁺; systematic name: tri­chloro­[(tri­chloro­phos­phor­an­yl­idene)im­in­io]phos­phor­us(V)} salts, namely bis(tri­chloro­phosphine)­iminium hexa­chloro­niobate, (Cl₆NP₂)[NbCl₆], (I), bis­(tri­chloro­phosphine)­iminium hexa­chloro­tantalate, (Cl₆NP₂)[TaCl₆], (II), bis­(tri­chloro­phosphine)­iminium tri‐μ‐chloro‐bis­[tri­chloro­titanium(IV)], (Cl₆NP₂)[Ti₂Cl₉], (III), and bis­[bis­(tri­chloro­phosphine)­iminium] di‐μ‐chloro‐bis­[tetrachloro­zirconium(IV)], (Cl₆NP₂)₂[Zr₂Cl₁₀], (IV), have been determined. The P=N distances in the discrete [Cl₃P=N=PCl₃]⁺ moieties in structures (I), (II) and (IV) range from 1.5460 (14) to 1.5554 (16) Å, and the P=N=P angles range from 136.8 (3) to 143.4 (4)°. The [Cl₃P=N=PCl₃]⁺ cation in (III) is disordered and the calculated geometries for the cation are therefore less reliable. Compounds (I) and (II) are isostructural and the metal anions have slightly distorted octahedral geometries. The anion in compound (III) consists of two distorted octahedral Ti centres linked by three μ₂‐Cl atoms, while in compound (IV), the dianion is derived from two distorted edge‐shared ZrCl₆ octahedra.     

An alternating direction scheme on a nonuniform mesh for reaction-diffusion parabolic problems

In this paper we develop a numerical method for two-dimensionaltime-dependent reaction-diffusion problems. This method, whichcan immediately be generalized to higher dimensions, is shownto be uniformly convergent with respect to the diffusion problems.This method, which can immediately be generalized to higherdimensions, is shown to be uniformly convergent with respectto the diffusion parameter.     

Melting and dissociation of ammonia at high pressure and high temperature

Raman spectroscopy and synchrotron x-ray diffraction measurements of ammonia (NH(3)) in laser-heated diamond anvil cells, at pressures up to 60 GPa and temperatures up to 2500 K, reveal that the melting line exhibits a maximum near 37 GPa and intermolecular proton fluctuations substantially increase in the fluid with pressure. We find that NH(3) is chemically unstable at high pressures, partially dissociating into N(2) and H(2). Ab initio calculations performed in this work show that this process is thermodynamically driven. The chemical reactivity dramatically increases at high temperature (in the fluid phase at T > 1700 K) almost independent of pressure. Quenched from these high temperature conditions, NH(3) exhibits structural differences from known solid phases. We argue that chemical reactivity of NH(3) competes with the theoretically predicted dynamic dissociation and ionization.     

The neuroblast and angioblast chemotaxic factor SDF-1 (CXCL12) expression is briefly up regulated by reactive astrocytes in brain following neonatal hypoxic-ischemic injury

Background  

Stromal cell-derived factor 1 (SDF-1 or CXCL12) is chemotaxic for CXCR4 expressing bone marrow-derived cells. It functions in brain embryonic development and in response to ischemic injury in helping guide neuroblast migration and vasculogenesis. In experimental adult stroke models SDF-1 is expressed perivascularly in the injured region up to 30 days after the injury, suggesting it could be a therapeutic target for tissue repair strategies. We hypothesized that SDF-1 would be expressed in similar temporal and spatial patterns following hypoxic-ischemic (HI) injury in neonatal brain.