Ionogenic group

High sorption capacities with respect to protein macromolecules are observed when highly permeable macro- and heteroreticular polyelectrolytes (biosorbents) are used. In buffer solutions a typical picture of interaction between ions with opposite charges fixed on CP and counterions in solution is observed. As shown in Fig. 13, in the acid range proteins are not bonded by carboxylic CP because the ionization of their ionogenic groups is suppressed. The amount of bound protein decreases at high pH values of the solution because dipolar ions proteins are transformed into polyanions and electrostatic repulsion is operative. The sorption maximum is either near the isoelectric point of the protein or depends on the ratio of the pi of the protein to the pKa=0 5 of the carboxylic polyelectrolyte [63]. It should be noted that this picture may be profoundly affected by the mechanism of interaction between CP and dipolar ions similar to that describedby Eq. (3.7). 

Since the mechanism of interaction between proteins polyfunctional with respect to ionogenic groups and CP is complex, an approximate method of calculation of sorption selectivity constants according to the inverse form of Langmuir isoterm should be used. Hence, the approximate values of AG, AH and AS obtained from Eq. (3.5) should be applied (Table 7). 

Reactions of this type are quite popular and widely used to introduce hydrophilic and ionogenic groups into linear polymers as well as directly into polymer networks. These reactions include hydrolysis (PAAm, PAAc and their analogs from PAN, PVA from poly (vinyl acetate), oxyethylation and oxymethylation of starch and cellulose, sulfurization, and other reactions. These processes are of industrial importance, well studied and widely reviewed. 

Besides nonspecific effects, which can be explained in terms of the ionic strength, such specific phenomena as collapse or crosslinking under the action of multi harged ions are sharply pronounced. They are characterized by threshold phenomena both in the ionogenic group content and the concentration of ions... 

J Kopecek, J Vacik, D Lim. Permeability of membranes containing ionogenic groups. J Polym Sci A-l 9 2801-2815, 1971. 

These results are particularly relevant, since such constant interdistances may be related to the chemical properties of the proteins present in the sample. For example, they may be consistent with protein isoforms differing in a constant variation of the number of ionogenic groups in the molecule suggesting the presence of co- and post-translational modifications (Wilkins et al., 1997 Righetti et al., 2001 Mann and Jensen, 2003 Farriol-Mathis et al., 2004 Hamdan and Righetti, 2005). 

Although cellulose acetate is not inherently a polyelectrolyte there are reports which indicate that it contains a low concentration of weak acid, presumably carboxylic, groups (1). Water absorbed by cellulose acetate membranes might be preferentially located, to some extent, in the region of these ionogenic groups and so assist in their dissociation. 

Polyelectrolytes may be synthesized by a variety of post-functionalization techniques in which ionogenic groups are introduced into the structure of an existing nonionic polymer. For an excellent review of polymer functionalization reactions the reader is referred to the recent book by Akelah and Moet [65]. In this paper, representative examples of the major polymer modification techniques for polyelectrolyte synthesis will be presented. 

Fig. 12.2.1 Formation of ionogenic groups by the Hofmann reaction under different conditions. Full length of bar, total amount of ionogenic groups formed solid part, amount of carboxyl group on surface dotted part, amount of amine group on surface open part, amount of ionogenic groups released to water.

There are some cases where a reaction, that is, the formation or dissolution of a chemical bond, is involved along with ion exchange phenomena (Helfferich, 1983). Examples of this are acid-base neutralization, dissociation of weak electrolytes in solution or weak ionogenic groups in ion exchangers, complex formation, or combinations of these (Table 5.2). With some of these, very low apparent D in ion exchangers have been noted. 

The charge on colloidal particles may arise from several sources (i) dissociation of ionogenic groups, e.g., proteins or... 

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