Polyelectrolytes phosphated

Phosphate and polyelectrolyte AB cements are resistant to attack by boiling water, steam and mild acids and this suggests that they could be employed in technologies where these properties are important. 

Buffer salts also can exert a secondary salt effect on drug stability. From Table 5 and Fig. 5 it is clear that the rate constant for an ionizable drug is dependent on its pKa. Increasing salt concentrations, particularly from polyelectrolytes such as citrate and phosphate, can substantially affect the magnitude of the pKa, causing a change in the rate constant. (For a review of salt effects, containing many examples from the pharmaceutical literature see Ref. 116.)... 

Recently, Bartels and Arends113 studied the adsorption of poly(4-vinylpyridinium fluoride) with different hexadecyl group content on hydroxyapatite. Adsorbance decreased as the hexadecyl content, i.e. the charge density, was increased. Desorption experiments showed that the adsorption of this polyelectrolyte in water is essentially irreversible. However, the polymer partially desorbed when excess calcium ions were added. Bartels and Arends concluded that adsorption of poly(4-vinylpyridinum fluoride) occurs as a result of the uptake of fluoride ions by hydroxyapatite which releases phosphate ions into water. They also suggested that this adsorption phenomenon can be interpreted in terms of an ion-exchange mechanism. 

Figure 21.1 has been drawn to suggest that F+ > r. This inequality is generally true for nucleic acids in low to moderate salt, a phenomenon sometimes called the polyelectrolyte effect (Draper, 2008 Record and Richey, 1988). Any RNA conformational change that increases the density of phosphate charges will also increase T+ at the expense of T (Record et al., 1998). Flowever, T + may be similar to T at high salt concentrations for instance, T+ = 0.46 and T = —0.54 ions/nucleotide for DNA in 0.98 MNaBr (Strauss et al., 1967). 

Specific interactions between starch and proteins were observed as early as the beginning of the twentieth century. Berczeller996 noted that the surface tension of aqueous soap solutions did not decrease with the addition of protein (egg albumin) alone, but it did decrease when starch and protein were added. This effect was observed to increase with time. Sorption of albumin on starch is inhibited by bi- and trivalent ions and at the isoelectric point. Below the isoelectric point, bonding between starch and albumin is ionic in character, whereas nonionic interactions are expected above the isoelectric point.997 The Terayama hypothesis998 predicts the formation of protein complexes with starch, provided that starch exhibits the properties of a polyelectrolyte. Apart from chemically modified anionic starches (such as starch sulfate, starch phosphate, and various cross-linked starch derivatives bearing ionized functions), potato starch is the only variety that behaves as a polyelectrolyte. Its random phosphate ester moieties permit proteins to form complexes with it. Takeuchi et a/.999-1002 demonstrated such a possibility with various proteins and a 4% gel of potato starch. 

The negative charge density, and hence the polyelectrolyte effect, is smaller for single-stranded polynucleotides than for multistrand species (see below). Nonspecific binding of metal ions with nucleic acid phosphates exhibits negative cooperativity, because bound cations reduce the net charge of the polyanion. 

---