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Different Ionic Strengths (different + ionic_strength)
Selected AbstractsAnalysis of the variable charge of two organic soils by means of the NICA-Donnan modelEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2007B. Vasiliadis Summary We have tested to see if the generic set of NICA-Donnan model parameters, used to describe isolated humic substances, can also describe soil humic substances in situ. A potentiometric back-titration technique was used to determine the variable surface charge of two organic peat soils at three different ionic strengths. The non-ideal, competitive-adsorption NICA-Donnan model was used to simulate the surface charge, by assuming a bimodal distribution of H+ affinity on the soil solid phase. The model provided an excellent fit to the experimental data. The Donnan volume, VD, varied slightly with ionic strength, although the variation was less than for humic substances in solution. The values obtained for the parameters that define the affinity distributions, the intrinsic proton binding constant (log Kiint) and the heterogeneity of the site (mi), were similar to those observed for isolated soil humic acids. The abundance of carboxylic groups in the whole soil represented 30% of the typical value for isolated soil humic acids. The composition of the organic matter of the whole soils, obtained by 13C CPMAS NMR, was comparable to the characteristic composition of soil humic acids. [source] Application of ultrasonic shear rheometer to characterize rheological properties of high protein concentration solutions at microliter volumeJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2005Atul Saluja Abstract The purpose of this work was to conduct preliminary rheological analysis on high protein concentration solutions by using the technique of ultrasonic shear rheometry at megahertz frequencies. The work was aimed at establishing the viability of the technique for analyzing protein solution rheology as well as obtaining an initial understanding of the effect of solution conditions on solution rheology of a model protein. Bovine serum albumin (BSA) was used for this study, and rheological analysis was conducted at 20 ,L sample volume between pH 2.0 and 9.0 at different ionic strengths at 25°C using 5 and 10 MHz quartz crystals. Significant differences in storage modulus among solutions at pH 5.0, 7.0, and 9.0 could only be detected at 10 MHz, and the errors associated with measurements were smaller as compared to those at 5 MHz for all the solutions studied. Solutions at pH 2.0 and 3.0 showed a time-dependent change in solution rheology. For solutions at pH 5.0, 7.0, and 9.0, which did not show time dependence in solution rheology, loss modulus data at lower concentrations correlated well with the dilute solution data in the literature. At higher concentrations, pH 5.0 solutions exhibited a higher loss modulus than pH 7.0 and pH 9.0 solutions. Storage modulus decreased with increasing ionic strength, unlike loss modulus, which did not show any change, except at pI of protein when no effect was observed. The results show the potential of high frequency rheometry for analyzing subtle differences in rheology of pharmaceutically relevant protein solutions at microliter volume. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1161,1168, 2005 [source] SAXS from Four-Arm Polyelectrolyte Stars in Semi-Dilute SolutionsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2003Delphine Moinard Abstract We have performed small-angle X-ray scattering experiments on semi-dilute solutions of highly charged star polyelectrolytes. Poly(sodium acrylate) (PANa) and poly(cesium acrylate) (PACs) stars with four arms were successfully synthesized by a combination of atom transfer radical polymerization and chemical modifications. Over a wide range of polyelectrolyte concentration Cp, these two systems as well as their equivalent linear polyelectrolytes were investigated at different ionic strengths. Scattering experiments show the existence of a scattering peak denoted as qmax, which disappears with the addition of a simple electrolyte, evidencing the electrostatic character of the interactions. We have also studied the effect of the charge parameter and the nature of the counterion (Na and Cs) on the scattering properties of these star polyelectrolytes. In the case of PACs, qmax scales with the polyelectrolyte concentration as Cp1/2 over the whole range of studied concentrations, whereas it scales as Cp1/2 (for Cp,<,45 mg,·,ml,1) and Cp1/4 (for Cp,>,45 mg,·,ml,1) in the case of PANa. Variation of qmax as a function of polyelectrolyte concentration Cp for PA1Cs (,) and PA2Cs (,) stars (error bars are indicated). [source] Complexation of CH3Hg+ with chloride, sulfate and carbonate in NaClO4: construction of thermodynamic modelsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2002J. Sanz Abstract The complexation of CH3Hg+ with major ions present in sea and estuary waters (Cl,, SO42, and CO32,) was studied potentiometrically in an NaClO4 medium in the ionic strength range 0.1,3.0,mol,dm,3 at 25,°C. The potentiometric data, treated with non-linear least squares computer programs, led us to establish the formation of the species CH3HgCl in equilibrium with chloride, CH3Hg(SO4), species with sulfate and no complex with carbonate. The stoichiometric stability constants obtained at the different ionic strengths were correlated by means of the modified Bromley methodology (MBM) to determine the corresponding thermodynamic constants and interaction parameters. This study is the second of a series designed to simulate, using the MBM thermodynamic model, the behaviour of methylmercury in different conditions of sea and estuary waters. In the first study of the series, the hydrolysis equilibria of methylmercury in NaClO4 ionic media were established. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effects of Ionic Environments on Bovine Serum Albumin Fouling in a Cross-Flow Ultrafiltration SystemCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2007S. Salg Abstract The influence of electrostatic interactions on membrane fouling during the separation of bovine serum albumin (BSA) from solution was studied in a cross-flow ultrafiltration system. Experiments were carried out at different pH values between 3.78 and 7.46; and for different ionic strengths between 0.001,M and 0.1,M. The changes in permeate flux, cake layer resistance, zeta potentials of BSA and polyether sulfone (PES) membranes, and electrostatic interaction energies, were evaluated. At all of the ionic conditions studied, PES membranes are negatively charged. However, BSA molecules are either negatively or positively charged depending on the ionic environment. Whereas the cake layer resistance decreased with increasing pH and ionic strength, the permeate fluxes increased. The calculated electrostatic energy was a minimum at the isoelectric point (IEP) of BSA. However, at this point, the cake resistances corresponding to fouling at each ionic strength, were not minimized. Below the IEP of BSA, the electrostatic forces were attractive, while above the IEP, repulsive electrostatic forces were dominant. [source] | ||||||||||