Hydroxide ion hydration in aqueous solutions

Hydroxide ion hydration was studied in aqueous solutions of selected alkali metal hydroxides by means of Fourier transform infrared (FTIR) spectroscopy of HDO isotopically diluted in H2O. The quantitative difference spectra procedure was applied for the first time to investigate such systems. It allowed removal of bulk water contribution and separation of the spectra of solute-affected HDO. The obtained spectral data were confronted with ab initio calculated structures of small gas-phase and polarizable continuum solvation model (PCM) solvated aqueous clusters, OH-(H2O)n, n = 1-7, to establish the structural and energetic states of hydration spheres of the hydrated hydroxide anion. This was achieved by comparison of the calculated optimal geometries with the interatomic distances derived from HDO band positions. The energetic state of water in OH- hydration shells, as revealed by solute-affected HDO spectra, is similar to that of an isoelectronic F- anion. No evidence was found for the existence of stable hydroxide dimer, H3O2-, in an aqueous solution. Spectral data do confirm, however, existence of a weak interaction with a single water molecule at the hydrogen site of OH-.     

Diastereoselective Addition of Allyl Reagents to Variously N‐Monoprotected and N,N‐Diprotected L‐Alaninals

Diastereoselective C₃‐elongation processes of N‐Boc‐, N‐Z‐, N‐Bn‐N‐Boc‐, and N‐Bn‐N‐Z‐L ‐alaninals (Boc=^tBuOCO, Z=PhCH₂OCO, Bn=PhCH₂) using various allyl reagents, such as allyl bromide in the presence of Zn/aqueous NH₄Cl solution, of SnCl₂⋅2 H₂O/NaI or of Mg/CuCl₂⋅2 H₂O, as well as allyltrichlorosilane, are described. A substantially different influence of the N‐protecting groups replacing either one or two amino protons was observed, allowing the selective synthesis of either the syn‐ or anti‐diastereoisomer as a major product.     

Two-electron valence indices from the Kohn-Sham orbitals

The recent Hartree-Fock (HF) difference approach to the chemical valence indices (ionic and covalent), formulated in the framework of the pair-density matrix, is implemented within the Kohn-Sham (KS) density functional theory (DFT). The valence numbers are quadratic in terms of displacements of the molecular spin-resolved charge-and-bond-order (CBO) matrix elements, relative to values in the separated atoms limit (SAL). It is shown that the global valence represents a generalized “distance” quantity measuring a degree of similarity between the two CBO matrices: the molecular and SAL. Numerical values for typical molecules exhibiting single and multiple bonds demonstrate that the KS orbitals give rise to these new bond valences in good agreement with both chemical and HF predictions. This KS bond multiplicity analysis is applied to the chemisorption system including the allyl radical and a model surface cluster of molybdenum oxide. It is concluded that the quadratic valence analysis represents a valuable procedure for extracting useful chemical information from standard DFT calculations. © 1997 John Wiley & Sons, Inc.     

Biodegradation of polyorganosiloxanes

Biodegradation of various polyorganosiloxanes (about 30 substances) under the influence of several biotype bacteria strain (16 types) were studied. A special procedure of biodegradation and analytical methods of evaluation the degree of degradation were applied. It was found that nearly all polysiloxanes tested are biodegradable but the degree of degradation depends on their composition and structure, as well as on the type of bacteria strain chosen.     

Coupling of benzyl halides mediated through alkali metal supramolecular complexes. A novel route to poly(p-xylylene)

Coupling of benzyl bromide giving 1,2-diphenylethane was demonstrated to proceed at room temperature in THF solution mediated by the potassium/18-crown-6 supramolecular complex. Based on this model reaction a novel method for the low temperature synthesis of poly(p-xylylene) from α,α′-dibromo-p-xylene is proposed. Experimental evidence of the polymer structure was provided by solid-state ¹³C NMR and IR spectroscopy.     

Trace analysis of hetero aromatic compounds (NSO) in water and polluted groundwater by Solid phase micro-extraction (SPME)

By using Solid Phase Micro-Extraction (SPME) and Capillary Gas Chromatography (CGC) a method was developed to analyze hetero aromatic compounds (NSO) in water. Compounds with nitrogen, sulfur, or oxygen in the aromatic ring system are found in creosotecontaminated groundwater. NSO are highly water-soluble, toxic, and have adverse organoleptic characteristics. SPME is a fast, simple, and solvent-free sample preparation technique that involves exposing a polymer coated fiber to a sample to extract contaminants. Different fiber coatings were tested, and polyacrylate was found to extract NSO in the highest amounts and to be most versatile. Extraction was strongly enhanced by salting. The optimized SPME method combined with CGC coupled to an ion trap mass spectrometer (ITMS) has detection limits of 20–40 ng/L for the semi-volatile and 1–10 μg/L for the volatile NSO, response linear with respect to concentrations over three orders of magnitude, and precision of 3–14% relative standard deviation. The method was evaluated using real creosote-contaminated groundwater samples and feasibility was demonstrated. SPME-CGC/ITMS allows an unequivocal identification and quantification at a low NSO level in environmental samples.     

Potassium hydride — the new initiator for anionic polymerization of oxiranes

Potassium hydride with 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) was used in the anionic polymerization of (butoxymethyl)oxirane. Polymers with low ratio of mass- to number-average molar masses (M̄_w/M̄_n < 1.1) were obtained, each macromolecule being terminated (after hydrolysis) with a hydroxyl group on both of its ends. Chain transfer reactions to the monomer were not observed to operate in this system.     

Stability of model membranes in the presence of organotin compounds

The influence of tri‐ and di‐alkyltins (TATs and DATs) as well as di‐ and triphenyltin compounds (DPhTs and TPhTs) on haemolysis of red blood cells (RBCs) and stability of planar lipid membranes (PLMs) has been studied. The results obtained show that the efficiency of TATs (trimethyl‐, triethyl‐, tri‐n‐propyl‐ and tributyl‐tin chlorides) in destroying PLMs did not differ greatly when the compounds were studied in solutions of physiological pH (phosphate buffer, pH 7.4). A decrease in pH to 5.0 caused small changes in the efficiency of the three largest TAT molecules and a significant decrease in the efficiency of trimethyltin chloride. Both haemolytic and PLM experiments showed that the most active TAT was tri‐n‐propyltin chloride. The destructive action of DAT (dimethyl‐ and dibutyltin) and DPhT dichlorides was somewhat more differentiated. Dimethyltin dichloride (DMT) interaction with model membranes was a little weaker than that of DPhT and dibutyltin dichlorides and all these compounds influenced the model membranes to a lesser extent than TATs or TPhT. To bring about comparable haemolysis effects the dichlorides had to be used at much greater concentrations than the chlorides. The haemolytic properties of the dichlorides, especially of that of DMT, significantly increased in solution at pH 5.0. TPhT chloride interacted with model membranes similarly to TAT chlorides. Also, no great difference in efficiency of this compound was found for the two buffer solutions used. Copyright © 2000 John Wiley & Sons, Ltd.     

Crystal Structure and Vibrational Spectra of Erbium Trisodium Bis(Cyclotriphosphate) Nonahydrate,ErNa<Subscript>3</Subscript>(P<Subscript>3</Subscript>O<Subscript>9</Subscript>)<Subscript>2</Subscript> · 9H<Subscript>2</Subscript>O

Abstract The cyclotriphosphate salt, ErNa₃(P₃O₉)₂ · 9H₂O, has been characterized by single-crystal X-ray diffraction [hexagonal, space group , with unit cell parameters of a = b = 30.8451(14), c = 12.8063(8) ?; Z = 18]. The structure consists of alternating layers of [P₃O₉]³⁻ groups, ErO₈ dodecahedra, Na(1)O₆ and Na(2)O₇ polyhedra linked together by water molecules. The P₃O₉ rings are grouped along the c-axis in a P₃O₉–ErO₈ arrangement thereby producing broad, hexagonal channels of diameter of 6.65 ? with a side dimension of 3.907 ?. The absence of coincidences for the majority of the IR and Raman bands observed for the cyclotriphosphate salt is in accord with the centrosymmetric structure of the material. The vibrational spectra have been interpreted on the basis of factor group effects. Graphical abstract We report the crystal structure and vibrational spectra of erbium trisodium bis(cyclotriphosphate)nanohydrate salt ErNa ₃ (P ₃ O ₉ ) ₂ · 9H ₂ O H. Assaaoudi, M. Ijjaali, A. Ennaciri, I. S. Butler* and J. A. Kozinski Crystal structure and vibrational spectra of erbium trisodium bis(cyclotriphosphate) nonahydrate,ErNa₃(P₃O₉)₂ · 9H₂O. Projection of the coordination polyhedra of ErNa₃(P₃O₉)₂ · 9H₂O down the c axis     

Study of the effects of the prefilled-plasma parameters on theoperation of a short-conduction plasma opening switch

Spectroscopic methods are used to determine the density, the temperature, the composition, the injection velocity, and the azimuthal uniformity of the flashboard-produced prefilled plasma in an 85-ns, 200-kA plasma opening switch (POS). The electron density is found to be an order of magnitude higher than that obtained by charge collectors, which are commonly used to determine the density in such POSs, suggesting that the density in short conduction POS's is significantly higher than is usually assumed. We also find that the plasma is mainly composed of protons. The spectroscopically measured plasma parameters are used here to calculate the conduction currents at the time of the opening predicted by various theoretical models for the POS operation. Comparison of these calculated currents to the measured currents indicates that the plasma behavior during conduction is governed either by plasma pushing or by magnetic-field penetration and less by sheath widening near the cathode, as described by existing models. Also, the conduction current mainly depends an the prefilled electron density and less on the plasma flux, which is inconsistent with the predictions of the erosion (four-phase) model for the switch operation. Another finding is that a better azimuthal uniformity of the prefilled plasma density shortens the load-current rise time