Electrostatic salting

One way in which to probe the structural surroundings of a protein is to monitor the pH behavior of specific carbon sites of the C probes. pH-titration studies, of given resonances, had previously been used for probing of the protein structure, because they are known to provide information concerning electrostatic (salt-bridging) interactions in the protein, neighboring group-ionizations, and local environments. ... 

Electron transfer from Fe(II)cytc to ccp(ES) proceeds with a rate of 800 s at — AG° = 0.90 eV [73]. From measurements of ET rates at other driving forces, the cyt c/ccp reorganization energy was estimated to be 1.5 eV the relatively large X value may be a result of redox-dependent fluctuations of the protein-protein orientation, since the primary binding mode is electrostatic (salt bridges) [73]. 

The combination of the hydrophobic salting out and the electrostatic salting in terms explains very nicely the Class I type behavior. The data for carboxyhemoglobin and fibrinogen are well fitted by the theory (Figure 10). Also the order of decreasing molal surface tension increment generally follows the lyotropic order (7). 

Tertiary structure is due to / V I side-chain (R-group) interactions, which include hydrophobic interactions, covalent disulfide bridges, electrostatic salt bridges, and hydrogen bonds. 

Grochowski, P., and Trylska, J. (2008). Continuum molecular electrostatics, salt effects and counterion binding. A review of the Poisson-Boltzmann theory and its modifications. Biopolymers 89, 93—113. 

Sharp, K. A. (1995). Polyelectrolyte electrostatics Salt dependence, entropic and enthalpic contributions to free energy in the nonlinear Poisson-Boltzmann model. Biopolymers. 36 227-243. 

The ernes of ionic surfactants are usually depressed by tire addition of inert salts. Electrostatic repulsion between headgroups is screened by tire added electrolyte. This screening effectively makes tire surfactants more hydrophobic and tliis increased hydrophobicity induces micellization at lower concentrations. A linear free energy relationship expressing such a salt effect is given by ... 

Here (log cmc) is tire log cmc in tire absence of added electrolyte, is related to tire degree of counterion binding and electrostatic screening and c- is tire ionic strengtli (concentration) of inert electrolyte. Effects of added salt on cmc are illustrated in table C2.3.7. 

In some systems, such as lake and river waters, the suspended inorganic particles may be coated by biological polymers, termed humic substances, which prevent flocculation by either steric or electrostatic mechanisms. These can also interact with added inorganic salts (31) that can neutralize charged functional groups on these polymers. 

Collectors ndFrothers. Collectors play a critical role ia flotation (41). These are heteropolar organic molecules characterized by a polar functional group that has a high affinity for the desired mineral, and a hydrocarbon group, usually a simple 2—18 carbon atom hydrocarbon chain, that imparts hydrophobicity to the minerals surface after the molecule has adsorbed. Most collectors are weak acids or bases or their salts, and are either ionic or neutral. The mode of iateraction between the functional group and the mineral surface may iavolve a chemical reaction, for example, chemisorption, or a physical iateraction such as electrostatic attraction. 

To avoid generation of waste brines and the associated serious problem of brine disposal, the potash industry in the former FRG began converting some operations to electrostatic separation, a dry process for separating potassium salts from other soluble salts (24,25). 

Inks for continuous ink-jet printers typically comprise dyes dissolved in water or solvent having salts added to make the ink conductive for electrostatic charging. Whenever waterproof printing is required, low boiling solvent inks ate used. For printers that ate used in office environments, water is used as the ink solvent. Using water-based inks, humectants may be added to inhibit drying of ink in the sump and surfactants ate added to wet the printing surface. 

EIectrosta.tlcs. Electrostatic interactions, such as salt bridges, result from the electrostatic attraction that occurs between oppositely charged molecules. These usually involve a single cation, eg, the side chain of Lys or Arg, or the amino terminus, etc, interacting with a single anion, eg, the side chain of Glu or Asp, or the carboxyl terminus, etc. This attractive force is iaversely proportional to the distance between the charges and the dielectric constant of the solvent, as described by Coulomb s law. 

The continuum treatment of electrostatics can also model salt effects by generalizing the Poisson equation (12) to the Poisson-Boltzmann equation. The finite difference approach to solving Eq. (12) extends naturally to treating the Poisson-Boltzmann equation [21], and the boundary element method can be extended as well [19]. 

The concentration of salt in physiological systems is on the order of 150 mM, which corresponds to approximately 350 water molecules for each cation-anion pair. Eor this reason, investigations of salt effects in biological systems using detailed atomic models and molecular dynamic simulations become rapidly prohibitive, and mean-field treatments based on continuum electrostatics are advantageous. Such approximations, which were pioneered by Debye and Huckel [11], are valid at moderately low ionic concentration when core-core interactions between the mobile ions can be neglected. Briefly, the spatial density throughout the solvent is assumed to depend only on the local electrostatic poten-... 

Fabric filters can be more costly to operate and maintain than electrostatic precipitators, cyclones, and scrubbers however, fabric filters are more practicable for filtration of specific dusts. For example fabric systems are the typical control method for toxic dusts from insecticide manufacturing processes, salt fumes from heat treating, metallic fumes from metallurgical processes, and other applications. Any other control method may not be as efficient, nor economically feasible for such applications. 

Cationic samples can be adsorbed on the resin by electrostatic interaction. If the polymer is strongly cationic, a fairly high salt concentration is required to prevent ionic interactions. Figure 4.18 demonstrates the effect of increasing sodium nitrate concentration on peak shapes for a cationic polymer, DEAE-dextran. A mobile phase of 0.5 M acetic acid with 0.3 M Na2S04 can also be used. 

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