Electrostatic forces isoelectric point

On the other hand, the data in Figure 5 show that for virtually the same Mo compositions, both activity and HCHO selectivity decrease with impregnation pH. This tendency can be explained in terms of equilibrium 2. At pH values close to isoelectric point of silica (ca. 2), molybdate appears to be uniformly adsorbed by electrostatic forces, however at medium and, especially, at higher pH, crystalline M0O3 is deposited during the impregnation step. 

Dielectric Constant Magnitudes of all electrostatic interactions in a medium are determined by the dielectric constant of that medium. Thus all charge-related parameters (e.g., zeta potential, isoelectric point, electrochemical forces.) are affected by the dielectric constant (see Chapters 4-7). 

Wang et al. [607] studied the adsorption of dissolved organics from industrial effluents onto a commercial activated carbon. As illustrated in Table 20, they place emphasis on the pK, pK, or isoelectric point of the adsorbate and state that the pH effect upon the effectiveness of carbon adsorption mainly depends upon the nature of the adsorbed substance. Based on their own work and analysis of the literature, they postulate that maximum adsorption of organic acids and bases occurs around their respective pK , or pKh value, even though they acknowledge, at least as the ionic organic compounds become more complex, that electrostatic adsorption forces between the adsorbent and the ionic adsorbate appear to govern. ... 

A final point to be dealt with is the achievement of specificity with the Ti02/Pt catalyst. As was illustrated above, these particles interact selectively with MV-+ while no or very slow reaction occurs with Ru(bipy)2+. This effect is readily interpreted in terms of the positive surface charge of the particles. The Ti02 particles prepared from hydrolysis of titanium isopropoxide when charged with Pt have an isoelectric point of 3 as determined by electrophoresis technique. At pH = 1.5 employed in or experiments, the surface is positively charged (f = 28 mV). Thus the access of Ru(bipy)3+ to the particle surface is impaired by electrostatic forces which explains its astonishingly long lifetime under these conditions. 

Since electrostatic interactions are believed to be an important driving force for the formation of complexes between these classes of redox proteins, we studied, in a comparative way, the interaction between the acidic flavodoxin isolated from D. salexigens isoelectric point around 3.5) and three cytochromes C3 exibiting a wide range of isoelectric point values, purified from different SRB D. vulgaris Hildenborough (pl=9.5), D. desulfuricans ATCC 27774 (pl=7.0) and D, gigas NCIB 9334 (pl=5.5). 

The isoelectric points (iep s) of the two substrates used in this study were measured [25] by using a DELS A 440 and found to be at pH 8.2 for HFO and at pH 9,2 for HCO. Both Ni(II) and Zn(II) are completely adsorbed at pH values considerably less than either of these values (see Sec. HI, Figs. 3-51, indicating that the surface is positively charged during adsorption. Electrostatic forces, in this case, are unfavorable to adsorption, and there must be a strong specific interaction for adsorption to occur. 

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