Dibromo and diiodo derivatives of [4.4]dibenzo-24-crown-8 as novel efficient sorbents of elements from mineral acid solutions

The sorption behavior of novel functionalized endoreceptors, halogen (Br, I) derivatives of [4.4]dibenzo-24-crown-8, with respect to sorption of 34 elements from 1–5 M HNO₃ solurions and 29 elements from 1–5 M HCl solutions were studied. The receptors poorly extract elements from nitric acid solutions but are strong sorbents of some elements from concentrated hydrochloric acid solutions. The highest distribution ratios of elements (D, cm³/g) for sorption from 5 M HCl were observed for 4′,4″,5″[4.4]dibromodibenzo-24-crown-8: Au (D = 880) > Ga (469) > Sb (70) > Fe (55) > Sn (14.3) > Mo (10.3) > Re (2.9) > Cd (1.4) > Ge (0.61) > In (0.33) ≈ Zn (0.32) ≈ Ni (0.31) > Zr (0.29) ≈ Cr (0.28) > Sr, Tl (0.25) > Be (0.24) > Mn (0.22) ≈ La (0.21) ≈ Ba (0.20) > Ca, K, Mg, Si (< 0.1). A new way for increasing the sorption properties of dibenzocrown ethers by introducing bromine substituents into the polyether benzene rings was established. The sorption of elements from concentrated hydrochloric acid solutions follows an anion exchange mechanism by analogy with extraction of these elements.     

A Simple Homemade Reaction Station for use in Parallel Solution-Phase Synthesis. Optimization of a Regioselective One-Step Deprotective o-formylation Reaction Mediated by the Vilsmeier-Haack Reagent POCl3⋅DMF

Summary We report herein the fabrication of a simple and price-affordable portable reaction station for use in parallel solution-phase synthesis. This homemade device uses currently available laboratory components and equipment. Specifically designed to fit standard magnetic hotplates/stirrers, it can simultaneously hold up to 24 heated and magnetically stirred glass reactors of both 10 and 50 mL capacities. Glass reactors are connected by flexible 16-gauge metal needles to a central gas manifold equipped with an inlet/outlet for vacuum and inert gases. Reaction temperatures can be optimally varied from −78 ^∘C to 150 ^∘C. Using a statistical screening DOE method, this parallel array reactor station has been successfully operated to optimize the one-step deprotective O-formylation of a sterically hindered bis-O-tert-butyldiphenylsilyl (O-TBDPS) aromatic diol. The latter transformation was mediated by the Vilsmeier-Haack reagent POCl₃⋅DMF using a range of Lewis acid and metal salt promoters, including their binary combinations.     

Anomalously Large Burgers Vectors of Screw Dislocations in Gallium Nitride Nanowires

Crystallography Reports - The results of structural studies of GaN nanowires containing screw dislocations are presented. It is found that the length of the Burgers vector of dislocations may reach...     

Structure of Dibenzocrown Ethers and their H-Bonded Adducts.1. [1.5]Dibenzo-18-Crown-6 and Biphenyl-20-Crown-6: Complexes with Amidosulfuric Acid

The interaction of the amidosulfuric acid NH ₃ SO ₃ with 15 distal and proximal dibenzocrown ethers, including diphenyloxide, diphenylsulfide and biphenyl ones leads to the stable (1:1) complexes only in the case of [2.4]- and [1.5]dibenzo-18-crown-6 and biphenyl-20-crown-6. According to the data of the X-ray analysis, in the two last adducts the amidosulfuric acid coordinates to hexadentate crown ethers in a zwitterion form through a near-ideal ‘tripod’ arrangement to alternate crown oxygen atoms. The conformations of crown molecules are different in complexes and in initial macrocyclic ligands.This revised version was published online in July 2005 with a corrected issue number.     

Surface phases and nanostructures on silicon surface

The paper gives definitions of conventional terms related to silicon surface science, such as surface, surfaced phase, adatoms, “in phase” and “on phase” atoms. The formation methods of surface phases are illustrated as well as their role in physical processes on the surface. The influence of surface phases on diffusion, desorption, adsorption, and phase interface formation at the silicon surface is described.     

Electron-stimulated nitridation of Si(100) in pure ammonia

We present the results of an AES study of the Si(100) electron-stimulated nitridation at RT by ammonia gas. The influence of the gas pressure and electron beam density on the nitridation rate have been determined within the ranges 10⁻⁶–10⁻⁹ Torr and 5 × 10⁻³–5 × 10⁻² A/cm², respectively. The silicon nitride growth rate has been found to be proportional to the electron flux and is enhanced with increased ammonia pressure in the range 10⁻⁹–10⁻⁷ Torr. Beyond 10⁻⁷ Torr the Si nitride growth rate is constant and independent of ammonia pressure. A phenomenological model of electron-stimulated nitridation process is suggested, which is in good agreement with the experimental data. The rate of electron-stimulated nitridation has been deduced.     

Studying Evolution of the Ensemble of Micropores in a SiC/Si Structure during Its Growth by the Method of Atom Substitution

Physics of the Solid State - The time evolution of the ensemble of micropores formed in the near-surface region of silicon during the growth of thin films of silicon carbide is studied by the...