Ammonium partition coefficients

For ammonium surfactants there is evidence for the existence of an additional specific interaction between the headgroups of the surfactant and the aromatic solubilisate . This is in line with the observation that partition coefficients for benzene in CTAB solutions are much higher than those for... 

Fig. 13. Thermo dynamic partitioning coefficient for ammonium chloride (8).

Lower molecular-weight quaternary ammonium halides, which partition across the two-phase system, transfer anions in measurable concentrations from the aqueous to the organic phase but, in contrast, many of the higher-molecular-weight quaternary ammonium halides with more than ca. 30 carbon atoms are virtually insoluble in aqueous media and their partition coefficients between aqueous and organic phases preclude the transfer of anions efficiently across the interface by the extraction process and yet catalysts, such as Aliquat 336 and Adogen 464, are extremely effective catalysts. 

The role of the ammonium salt anion is not the loading of the amphipathic weak base per se, but rather to control the stability of loading and the profile and rate of release of the amphipathic weak base from the liposome to the external aqueous phase. Two major factors that differentiate the different anions are, firstly, their ability to induce precipitation/crystallization/ gelation in the intraliposome aqueous phase (1,12), and secondly, their effect on the membrane/buffer and octanol/buffer partition coefficient of the amphipathic weak base (1). Regarding the precipitation, the higher the amount of precipitated amphipathic weak base, the more stable is the loading and the slower is its release rate (10-12,18,33,35) and (Wasserman et al.). There are also some risks involved in the precipitation which in some cases reduce the mechanical stability of the liposomes and change liposome shape (36). 

Absorption of some highly ionized compounds (e.g., sulfonic acids and quaternary ammonium compounds) from the gastrointestinal tract cannot be explained in terms of the transport mechanisms discussed earUer. These compounds are known to penetrate the Upid membrane despite their low Upid-water partition coefficients. It is postulated that these highly lipophobic drugs combine reversibly with such endogenous compounds as mucin in the gastrointestinal lumen, forming neutral ion pair complexes it is this neutral complex that penetrates the Upid membrane by passive diffusion. 

Porous silica particles can be used to support alkylphenyl chains substituted by sulfonated groups or quaternary ammonium groups using covalent bonding (silica — R — NR3)+OH . This approach is similar to that used to obtain the bonded silica phases used in HPLC. Certain phases compound the particularities of each technique. In such cases, separation depends on ionic coefficients as well as the partition coefficient. 

As further evidence of the importance of hydrophobic interactions in these systems, we examined the partition coefficient of methyl orange in the presence of water structure-forming and water structure-breaking salts above and below the transition temperature [70], Methyl orange is an easily detected, hydro-phobic dye which has been sulfonated to improve water solubility. Water structure-breaking salts like tetraethylammonium chloride (TEAC) are known to minimize hydrophobic interactions while water structure-forming salts like ammonium sulfate are known to increase hydrophobic interactions [165, 166]. 

Some ionised drug molecules can traverse the lipophilic gut membrane by combining with an ion of opposite charge (a counter ion) to form an ion pair. The ion pair, although composed of two ionic species, behaves as a neutral molecule with a high partition coefficient and can cross biomembranes effectively Quaternary ammonium compounds, which are charged at all values of pH, may be absorbed into the body in this way ... 

Similar results are reported using cationic surfactants. The partition coefficient of a-chymotrypsin in Aliquat solutions decreased with increasing NaCl concentration (36). However, in order to interpret these results it is necessary to take into account that alkylmethyl ammonium salts are known to be involved in anion exchanges. Assuming an exchange equilibrium between the protein and chloride counterion, an increase of the chloride ion concentration should disfavor the extraction of the protein, following a mechanism of mass action law. 

A number of factors can influence the amount of exchangeable ammonium in soils. Soil porosity, clay mineral structure, presence of other cations, and organic matter content are a few examples. The cation concentration of freshwater wetlands is generally lower than that of coastal wetlands and would result in higher partition coefficients in freshwater wetlands relative to coastal wetlands. 

Under wet soil (anaerobic) conditions, accumulation of reduced cations such as iron (II) and manganese (II) in mineral soils can potentially occupy much of the cation exchange sites (Figure 8.28). This can result in displacement of ammonium from the exchange complex. The partition coefficients for ammonium are generally lower in anaerobic soils than in drained or aerobic soils. 

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