PH and ionic strength, effect

Cabaniss, S.E. (1990) pH and ionic strength effects on nickel-fulvic acid dissociation kinetics. Environ. Sci. Technol., 24, 583-588. 

The theoretical background to classical electrostatics is first reviewed, beginning with the physical basis for the electrostatic response of a protein/solvent system to a charge distribution, and ways of modelling this response. Consistent classical electrostatic frameworks for describing a protein/solvent system are then described. In addition the methods must be able to model temperature, pH and ionic strength effects if these affect the property of interest. Of particular importance is the way one may extract experimentally observable properties from such models. 

Yang, A. and B. Honig. (1994). Structural origins of pH and ionic strength effects on protein stability. Acid denaturation of sperm whale apomyoglobin. J. Mol. Biol. 237 602-14. 

Tsapikouni, T.S. and Missirlis. Y.R, pH and ionic strength effect on single fibrinogen molecule adsorption on mica studied with AFM, Colloids Surf. B. SI, 89, 2007. 

Braghetta A., DiGiano F.A., Ball W.P. (1997), Nanofiltration of natural organic matter pH and ionic strength effects. Journal of Environmental Engineering, 123, 7, 628-641. 

M. Arunyanart and L.J. Cline-Love, Influence of Micelles on Partitioning Equilibria of lonizable Species in LC pH and Ionic Strength Effects, Anal. Chem., 57 2837 (1985). 

A.-S. Yang and B. Honig, /. Mol. Biol., 237, 602 (1994). Structural Origins of pH and Ionic Strength Effects on Protein Stability. Acid Denaturation of Sperm WTiale Apomyoglobin. 

Hemolysis in hypotonic phosphate buffer pH and ionic strength effects Hemolysis in low ionic strength alkaline buffer density gradient centrifugation Homogenization gradient centrifugation... 

Most of the Langmuir films we have discussed are made up of charged amphiphiles such as the fatty acids in Chapter IV and the lipids in Sections XV-4 and 5. Depending on the pH and ionic strength of the subphase, electrostatic effects can become quite important. Here we develop the theoretical foundation for charged films with the Donnan relationship. Then we mention the influence of subphase pH on film behavior. 

An effective experimental design is to measure the pseudo-first-order rate constant k at constant pH and ionic strength as a function of total buffer concentration 6,. Very often the buffer substance is the catalyst. Let B represent the conjugate base form of the buffer. Because pH is constant, the ratio (B]/[BH ] is constant, and the concentrations of both species increase directly with 6 where B, = [B] -t-[BH"]. 

The kinetics of decarboxylation of 4-aminosalicylic acid in some buffer solutions at 50 °C were studied. The first-order rate coefficients increased with increasing buffer concentration, though the pH and ionic strength were held constant (Table 217). This was not a salt effect since the rate change produced by substituting potassium chloride for the buffer salt was shown to be much smaller. It follows from the change in the first-order rate coefficients (kx) with... 

Vukov6 has developed equations based on experimental data that predict the effect of temperature, pH, and ionic strength on rate constants of sucrose decomposition in acid and alkaline medium. Other workers61 report that Vukov s equation generally agrees with their experimental rate data. 

Chrambach this indicates that the effective protein size for gel filtration is larger than the effective size for gel electrophoresis. They concluded that this could not be accounted for by gel swelling, pH, or ionic strength effects. Biefer and Mason [36] found the constant a in Eq. (93) to be 0.93. They measured the conductance of cellulose acetate filter pads with porosities from 0.5 to 0.9 in solutions of 10 M KCl. 

In the presence of polyethylene oxide MW 300,000 at a concentration of 0.025 g liter , variations in pH and ionic strength have no effect on elution volumes and a single calibration curve is obtained as shown in Figure 4 and Table II. This behavior presumably also results from modification of the glass surface by the polyethylene oxide surfactant, but in this case charge effects appear to be completely suppressed and the effective pore diameter and volume reduced. Such an interpretation is also in accord with the fact that the elution voliomes are lower with polyethylene oxide than with Tergitol, since Tergitol is a much smaller molecule than the polyethylene oxide. 

The release of non-Brownian particles (diameter s 5 pm) from surfaces has been studied. The influence of several variables such as flow rate, particle size and material, surface roughness, electrolyte composition, and particle surface charge has been considered. Experiments have been performed in a physically and chemically well-characterized system in which it has been observed that for certain particle sizes there exists a critical flow rate at which the particles are released from surfaces. This critical flow rate has been found to be a function of the particle size and composition. In addition, it has been determined that the solution pH and ionic strength has an effect on the release velocity. 

If a reaction is reversible and if one has assumed a rate function that does not take the reverse reaction into account, one observes a downward curvature. As equilibrium is approached, the slope of this curve approaches zero. Another cause of curvature is a change in temperature during the course of the experiment. An increase in temperature causes an increase in the reaction rate, leading to an upward curvature. Bunnett (3) has discussed a number of other sources of curvature, including changes in pH and ionic strength, impurity effects, autocatalysis, and side reactions. 

In the case of dissociating or ionizing organic chemicals such as organic acids and bases, e.g., phenols, carboxylic acids and amines, it is desirable to calculate the concentrations of ionic and non-ionic species, and correct for this effect. A number of authors have discussed and reviewed the effect of pH and ionic strength on the distribution of these chemicals in the environment, including Westall et al. (1985), Schwarzenbach et al. (1988), Jafvert et al. (1990), Johnson and Westall (1990) and the text by Schwarzenbach, Gschwend and Imboden (1993). 

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