Ionic mobility and ionic association of singly charged ions in glycerol

Experimental molar conductivity data for KCl, NaCl and LiCl in glycerol at 298.15?K were analysed by least-square fitting in the concentration range 0.5–100?mol?m^?3in order to compute the values of the molar conductivity at infinite dilution Λ⁰and the Onsager constant S. Using previously measured transference numbers and assuming the Kohlrausch infinite dilution law, the limiting ionic mobilities were deduced. The results obtained show that the transport mechanisms in this solvent and other similar hydrogen-bonded solvents such as water and ethylene glycol are the same. The data were also interpreted in terms of ion–ion and ion–solvent interactions using the Fuoss paired ion model in the concentration range 0.5–100?mol?m^?3. The fitting of Fuoss’ equation of 1978 to these data led us to an estimate of the ionic association by computing the conductimetric pairing constants. The latter were further analysed by Gilkerson's equation to yield the difference between the solvation energy of the free ions and the ion pairs. The computed values allow an estimation of whether the electrolyte is a structure maker or a structure breaker.     

Separation of alkylbenzyl quaternary ammonium compounds by capillary zone electrophoresis with sample stacking injection

Summary A systematic investigation of operational buffer systems, sample preparation and instrument parameters for achieving the best possible performance for determinating an homologous series of N-benzyl-N-alkyl-N,N-dimethylammonium chloride compounds by capillary zone electrophoresis with direct UV detection. The most effective separation was achieved within 3.5 min with the addition of acetonitrile (40%) in a phosphate buffer (20 mM pH 5.2) using a 40 cm fused-silica capillary operating at 25 KV and 20°C. Degassing of all electrolyte solutions and samples was very important. The linearity and repeatability for each compounds were satisfactory. To improve detection limits, on-column sample preconcentration, sample stacking, was investigated achieving a tenfold enrichment factor and quantitation limits about 10⁻⁷M.     

Temperature measurements of shock heated materials using multispectral pyrometry: Application to bismuth

A new device for temperature measurements of shock heated materials has been developed in order to refine their equations of state. We present temperature measurements for bismuth samples in contact with a lithium fluoride window. The shock pressure of these experiments ranges from 18 to 97 GPa. Received 2 June 1997 / Accepted 26 January 1998     

Synthesis of 2-methylidene-1-silacyclohexanes by intramolecular hydrosilylation

The preparation of various (hex-5-ynyl)silanes was achieved following two different synthetic approaches from readily available materials such as 4-bromobutene, 6-iodohexyne and chlorosilanes. Different reaction conditions for intramolecular hydrosilylation were tested to prepare the corresponding 2-methylidene-1-silacyclohexanes. Notably, the use of Speier’s catalyst allowed the regioselective formation of the desired products in moderate yields.     

Control of crystalline phases in magnetic Fe nanoparticles inserted inside a matrix of porous carbon

Two magnetic composites made up of Fe nanoparticles (Fe-NPs) embedded in a porous amorphous carbon matrix are presented. One of the samples, Fe-S-AC, was obtained with the aid of sucrose and the other, Fe-AC, in the absence of this substance. The XRD patterns show Bragg diffraction peaks associated with α-Fe and γ-Fe crystalline phases in the Fe-AC sample, while only peaks corresponding to the α-Fe phase are observed for Fe-S-AC powders. The Fe-NPs exhibit broad particle-size distributions for both samples, 5–50 nm for Fe-AC, whereas two populations (2–8 and 10–70 nm) for the Fe-S-AC composite are found. This fact gives rise to poorly defined blocking temperatures, as it can be deduced from the broad maxima observed in M_ZFC(T) variations. In addition, M(H) curves for both Fe-AC and Fe-S-AC samples reveal the existence of exchange-bias effect for T<60 K, probably due to a magnetic coupling within a core/shell structure of the Fe-NPs, although this effect was observed to be less significant for Fe-S-AC.     

Cooperativity in multiple unusual weak bonds

This review covers two aspects concerning cooperativity in multiple weak bonds: a summary of literature results and a theoretical study of a complete series of model complexes. All the 15 combination of five weak bonds were explored: hydrogen bonds, hydric bonds, dihydrogen bonds, halogen bonds and ion–π interactions. Since in several cases there were no examples reported, a systematic exploration has been carried out on simple models at the MP2/aug-cc-pVTZ level. The results thus obtained have been analyzed using the atoms in molecules methodology.     

Simultaneous determination of metal ions. Catalytic oxidation of cobalt by metal ions when extracted with quinolin-8-ol

The catalytic effect of various ions on the aerial oxidation of Co(II) when extracted from weakly acidic solutions with quinolin-8-ol in chlorofom was studied. Oxidation is complete only in the presence of Fe(III) or V(V). Mixtures of Al(III), Cu(II), Fe(III) and Ni(II) with Co(II) at concentrations in the range 1–8 μg ml^?1 were analysed by using a multi-component analysis program involving first-order derivative spectra. Because of the metal ion interaction, a multivariate calibration process is required. The recovery factors achieved ranged from 93 to 111%.     

Long-Distance Transmission at Zero Dispersion: Exact Expressions for One-Time Statistical Properties

We study the transmission of a signal through a dispersionless fiber with in-line amplifiers. The nonlinearities of the fiber and the noise generated at each amplifier are taken into account. Exact analytical expressions are obtained for the field averages. From these results we obtain the distributed amplification approximation, and study the conditions under which this approximation is valid.