Proteins interactions with surfactants

Ejfect of pH It is obvious that in order to recover the protein from reverse micelles, the pH of the stripping solution needs to change toward the pi, which will result in a reduction of the protein interaction with the oppositely charged head groups. The extent of protein recovery from reverse micelles increases with increasing pH for anionic surfactants however, for cationic surfactants the opposite is true. 

In the case of the rather porous and flexible structure of sodium caseinate nanoparticles, the data show that the interaction with surfactants causes a tendency towards the shrinkage of the aggregates, most likely due to the enhanced cross-linking in their interior as a result of the protein-surfactant interaction. This appears most pronounced for the case of the anionic surfactants (CITREM and SSL) interacting with the sodium caseinate nanoparticles. Consistent with this same line of interpretation, a surfactant-induced contraction of gelatin molecules of almost 30% has been demonstrated as a result of interaction with the anionic surfactant a-olefin sulfonate (Abed and Bohidar, 2004). 

When a protein is interacting with surfactant micelles, the following intrinsic features of the micelles are suggested as being of general importance in relation to their influence on the character of the protein self-assembly (IFin et al., 2005) ... 

This shows that the cytochrome c extraction into an organic phase is carried out at a very low DOLPA concentration, in which reverse micelles cannot be formed. Also, the molar ratio required for the complete protein extraction was approximately 20, which corresponds to the number of cationic charged residues available for the electrostatic interaction with an anionic surfactant in one cytochrome c molecule. These results support the concept that proteins are extracted by electrostatic interactions with surfactant molecules, and that the existence of reverse micelles is not necessary for causing protein transfer, as mentioned above. 

Plasma protein interactions with polymer colloids Symmetrical Measurement of changes in particle (PS latex) size due to aggregation and adsorption of proteins effect of Pluronic surfactants on aggregation and protein adsorption [J.-T. Li and K. D. Caldwell, Colloids Surf. B Biointerfaces 7 9-22 (1996)]... 

Tn nature proteins interact with ions, lipids, and other proteins as part of the broad spectrum of necessary biological processes including membrane functionality and antigen-antibody effects. Protein functionality can be altered greatly by the interaction of proteins with surface-active agents, and the subject of protein-surfactant interaction is important in relation to food, cosmetic, and biomedical areas. 

FIGURE 14.9. As natural polyelectrolytes, proteins present special problems in that their solution characteristics can change significantly with changes in pH, in the presence of electrolytes, or npon interaction with surfactants, especially charged materials. 

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

The study of skin irritation is probably still more complex than that of eye irritation. Surfactants interact with epidermal tissues, proteins, and enzymes causing local effects. Singer and Pittz [369], Cooper and Berner [370], and Schwuger and Bartnik [371] presented excellent explanations and reviews on these interactions. 

In reality, many proteins demonstrate mixed mode interactions (e.g., additional hydrophobic or silanol interactions) with a column, or multiple structural conformations that differentially interact with the sorbent. These nonideal interactions may distribute a component over multiple gradient steps, or over a wide elution range with a linear gradient. These behaviors may be mitigated by the addition of mobile phase modifiers (e.g., organic solvent, surfactants, and denaturants), and optimization (temperature, salt, pH, sample load) of separation conditions. 

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