sodium-bromide and cesium-bromide

The molar electric conductivities Lambda of NaBr, KBr, and CsBr were measured in liquid ethanol at temperatures from 60 to 220 degrees C along the liquid-vapor coexistence curve. The limiting molar electrolyte conductivities Lambda(o) and the molar association constants K(A) were determined by the analysis of the concentration dependence of Lambda. The friction coefficients zeta for the Na(+), K(+), Cs(+), and Br(-) ions were estimated from Lambda(o) by an assumption that the cationic transference number of KBr is independent of temperature and density. The density dependences of zeta thus obtained together with literature values at higher densities (lower temperatures) were examined. zeta increases with decreasing density at densities above 2.0rho(c), where rho(c)=0.276 g cm(-3) is the critical density. At lower densities, the density dependences of zeta depend on ion. The relative contribution of the nonviscous effect in zeta was estimated by Deltazeta/zeta, where Deltazeta was the difference between zeta and the Stokes friction coefficient. At densities above 2.7rho(c), Deltazeta/zeta slightly decreases with decreasing density except for the Cs(+) ion. At densities below 2.7rho(c), Deltazeta/zeta increases with decreasing density and the density dependence is larger for larger ion. The results at densities above 2.2rho(c) were well explained by the Hubbard-Onsager (HO) dielectric friction theory [J. Hubbard, J. Chem. Phys. 68, 1649 (1978)] based on the sphere-in-continuum model. Below 2.2rho(c), however, experimental Deltazeta/zeta tends to be larger than the prediction of the HO theory. The lower limit density of the validity range of the HO theory is slightly higher in ethanol than in methanol.

Topics: Bromides; Cesium; Electric Conductivity; Electrolytes; Ethanol; Phase Transition; Potassium Compounds; Sodium Compounds; Temperature

Solutions consisting of protein and small molecule mixtures have been subjected to electrospray ionization to study the influence of small molecule/cation components at high concentrations on the electrospray responses of proteins. Emphasis was placed on solutions consisting of equal parts methanol and water and containing 1 vol % acetic acid. The results, therefore, are relevant to low pH solutions with significant organic content, a commonly used set of conditions in electrospray ionization mass spectrometry that tends to denature proteins. A variety of small cations/molecules were selected to sample a range of chemical characteristics. For example, sodium and cesium cations were studied to represent metal ions, tetrabutylammonium and tetramethylammonium cations were studied to represent quaternary ammonium compounds with different surface activities, and octadecylamine and glycine were studied to represent species that compete for protons but have different surface activities. A methodology for measuring relative ion suppression efficiencies was developed and applied for protein ions derived from bovine cytochrome c. The form of the small cation (i.e., metal ion, quaternary ammonium ion, or protonated molecule) did not appear to be a factor in determining the efficiency with which protein ion signals were suppressed. The extent to which ions are expected to concentrate on the surface, however, was the major factor in determining the ion suppression efficiency. Itwas found that the ion suppression efficiency of the most surface active species in this study was comparable to that of a protein on another protein after normalization by charge. These results are particularly relevant to the development of mixture analysis strategies based on ionization and tandem mass spectrometry applied to mixtures of whole proteins.

Topics: Algorithms; Amines; Animals; Bromides; Cations; Cattle; Cesium; Cytochromes c; Hydrogen-Ion Concentration; Iodides; Myoglobin; Proteins; Quaternary Ammonium Compounds; Sodium Compounds; Spectrometry, Mass, Electrospray Ionization; Ubiquitin