Polyelectrolyte cationic protein precipitation

Protein purification by selective phase separation with anionic and cationic polyelectrolytes has been widely discussed by Dubin et al. [187]. The driving force of such a process is the intermolecular association with the participation of Coulomb interactions, hydrogen bonds and hydrophobic forces. Phase separation with polyampholytes has been described [188,189]. Due to the self-precipitation of polyampholytes at their own lEP in the absence of proteins, they can be used for protein extraction and purification. 

These phenomena obviously provide means of separating proteins based on the addition of appropriate surfactants, at the appropriate pH, with control of electrolyte concentration, and so on, and will not be elaborated upon here (see, however. Chapter 4, Section II.D and III.E). Subsequent to the above work by protein chemists it was found that similar precipitation reactions occur between cationic surfactants and a variety of anionic polyelectrolytes, those investigated being generally anionic polysaccharides (114-116). Scott (115), for example, found for anionic polysaccharides with weak acidic groups (hyaluronic acid, alginic acid, etc.) that precipitation with CTAB could be inhibited as a result of deionization of their carboxyl groups. With carbohydrate monoester sulfates, such as dex-tran sulfate, no such inhibition was observed. He also reported that the flocculation endpoint observed for this polyelectrolyte with CTAB corresponds to the formation of a stoichiometric salt. 

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