Electronic structure of the valence bands of SnF2 studied by ultraviolet photoelectron spectroscopy

The main features of the photoelectron spectrum of the valence bands of solid-phase SnF₂ are susccessfully interpreted in terms of linear combination of atomic orbitals-molecular orbital theory.     

Anomalous spin-orbit effects in a strained InGaAs/InP quantum well structure

There is currently a large effort to explore spin-orbit effects in semiconductor structures with the ultimate goal of manipulating electron spins with gates. A search for materials with large spin-orbit coupling is therefore important. We report results of a study of spin-orbit effects in a strained InGaAs/InP quantum well. The spin-orbit relaxation time, determined from the weak antilocalization effect, was found to depend nonmonotonically on gate voltage. The spin-orbit scattering rate had a maximum value of 5×10¹⁰ s^?1 at an electron density of n=3×10¹⁵ m^?2. The scattering rate decreased from this for both increasing and decreasing densities. The smallest measured value was approximately 10⁹ s^?1 at an electron concentration of n=6×10¹⁵ m^?2. This behavior could not be explained by either the Rashba or the bulk Dresselhaus mechanisms but is attributed to asymmetry or strain effects at dissimilar quantum well interfaces.     

Evaluation of a reversed-phase column (supelcosil LC-ABZ) under isocratic and gradient elution conditions for estimating octanol-water partition coefficients

The solvation parameter model is used to identify suitable chromatographic models for estimating the octanol-water partition coefficient for neutral compounds of varied structure by reversed-phase liquid chromatography. The stationary phase Supelcosil LC-ABZ with methanol-water mobile phases affords a series of suitable correlation models for estimating the octanol-water partition coefficient (log KOW) under isocratic and gradient elution conditions. Isocratic separations with mobile phase compositions containing from about 25 to 40% (v/v) methanol provide the most accurate results for log KOW values in the range -0.1 to 4.0. Gradient separations programmed from 5 to 100% (v/v) methanol are suitable for faster separations of compounds with large log KOW values. The standard error in the estimate for the regression models of the predicted log KOW values against literature values are 0.135 log units for the 30% (v/v) methanol-water isocratic system and 0.263 log units for the methanol-water gradient system. Isocratic retention factors predicted from two gradient separations with gradient times of 15 and 45 min afford a poorer fit for the correlation models between log KOW and the estimated retention factors than that of either the above isocratic and gradient models. Plots of the retention factor (log k) as a function of mobile phase composition are generally non-linear. Values of log kw obtained by non-linear extrapolation to a volume fraction of 0% (v/v) methanol do not afford a useful model for estimating log KOW.     

Chromatographic and spectroscopic studies of the solvent properties of a new series of room-temperature liquid tetraalkylammonium sulfonates

Fifteen tetraalkylammonium salts of the functionalized sulfonic acids N,N-bis(2-hydroxy- ethyl)-2-aminoethanesulfonic acid, 2-(cyclohexylamino)ethanesulfonic acid and 2-hydroxy-4- morpholinopropanesulfonic acid were synthesized and the eight organic salts that were liquid at room temperature were characterized by physical, spectroscopic and chromatographic methods. All liquid salts were viscous at room temperature but after dilution with a suitable cosolvent could be used as mobile phases in liquid chromatography. For this application, the rapid deterioration of silica-based column packings was more of a deterrent than the physical properties of the salts. The tetraalkylammonium sulfonates had wide liquid ranges and were stable as column packings up to 150–180°C, making them suitable for use in gas chromatography. Their solvent properties were characterized by solvatochromic parameters [E_T(30), π*, α and β] and by thermodynamic parameters determined by gas chromatography. Good agreement was found between the predictions of the two methods. The liquid salts showed strong orientation and solvent hydrogen bond acceptor capacity with weak hydrogen bond donor capacity in spite of the functionalization of the anions. The most probable reason for the weak hydrogen bond donor capacity of the anions is the unavailability of these functional groups for solute interactions owing to their preferential involvement in the formation of anion association complexes. The chemically defined structure, unique solvent properties and wide usable temperature ranges make the tetraalkylammonium sulfonates useful stationary phases for gas chromatography.     

System Maps for Retention of Small Neutral Compounds on a Superficially Porous Ethyl-Bridged,Octadecylsiloxane-Bonded Silica Stationary Phase in Reversed-Phase Liquid Chromatography

The system constants of the solvation parameter model are used to prepare system maps for the retention of small neutral compounds on an ethyl-bridged, ocatadecylsiloxane-bonded superficially porous silica stationary phase (Kinetex EVO C18) for aqueous mobile phases containing 10–70% (v/v) methanol or acetonitrile. Electrostatic interactions (cation-exchange) are important for the retention of weak bases with acetonitrile–water but not methanol–water mobile phase compositions. Compared with a superficially porous octadecylsiloxane-bonded silica stationary phase (Kinetex C18) with a similar morphology but different topology statistically significant differences in selectivity at the 95% confidence level are observed for neutral compounds that vary by size and hydrogen-bond basicity with other intermolecular interactions roughly similar. These selectivity differences are dampened with acetonitrile–water mobile phases, but are significant for methanol–water mobile phase compositions containing <30% (v/v) methanol. A comparison of a totally porous ethyl-bridged, octadecylsiloxane-bonded silica stationary phase (XBridge C18) with Kinetex EVO C18 indicated that they are effectively selectivity equivalent.