Polyelectrolyte complexes polyion protein

Polyelectrolyte complexes formed by polyion pairing are of special interest, including protein-polyelectrolyte interactions such as protein-DNA complexes. A special case of polyelectrolyte complexes are polyelectrolyte multilayers (PEM) on surfaces formed by ion pairing, van der Waals interactions and counterion release of oppositely charged polyelectrolytes [2, 3]. 

Polyanions and polycations can co-react in aqueous solution to form polyelectrolyte complexes via a process closely linked to self-assembly processes [47]. Despite progresses in the field of (inter-) polyelectrolyte complexes [47] (IPEC from Gohy et al. [48], block ionomer complexes BIC from Kabanov et al. [49], polyion complex PIC from Kataoka and colleagues [50, 51], and complex coacervate core micelles C3M from Cohen Stuart and colleagues [52], understanding of more complex structures such as polyplexes (polyelectrolyte complexes of DNA and polycations) [53] is rather limited [54]. It has also to be considered that the behavior of cationic polymers in the presence of DNA and their complexes can be unpredictable, particularly in physiological environments due to the presence of other polyelectrolytes (i.e., proteins and enzymes) and variations in pH, etc. 

Polyanion-polycation-complexes are known for a long time on an empirical basis from the mutual precipitation of proteins. Already at the end of the previous century Kossel [1] recognized the electrostatic interaction between the oppositely charged polyions as the driving force for precipitation. Willstaetter [2] also introduced the term symplexes for polyelectrolyte complexes. 

It may be deduced from these results that one polyelectrolyte molecule forms a complex with many of the protein molecules until all of the polyion charges are stoichiometrically neutralized with the opposite charges of the proteins. An outline of such a situation is given by the schematic illustration shown in Fig. 18.12, in which the complex consists of a number of inflexible and global protein... 

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