Counterion partition coefficient

Calculations usirig this value afford a partition coefficient for 5.2 of 96 and a micellar second-order rate constant of 0.21 M" s" . This partition coefficient is higher than the corresponding values for SDS micelles and CTAB micelles given in Table 5.2. This trend is in agreement with literature data, that indicate that Cu(DS)2 micelles are able to solubilize 1.5 times as much benzene as SDS micelles . Most likely this enhanced solubilisation is a result of the higher counterion binding of Cu(DS)2... 

Fluorescence quenching studies in micellar systems provide quantitative information not only on the aggregation number but also on counterion binding and on the effect of additives on the micellization process. The solubilizing process (partition coefficients between the aqueous phase and the micellar pseudo-phase, entry and exit rates of solutes) can also be characterized by fluorescence quenching. 

Because the degree of ionization is a function of the pH of the aqueous phase and the pKa of the solute, the apparent partition coefficient P fluctuates as the pH of the aqueous phase (usually a buffer solution) is changed, whereas the true (or corrected) partition coefficient (P) should remain constant. However, in reality the different buffer species may not only affect P but also P because of different degrees of ion-pair formation and the different polar nature of the counterions used. Among the different buffer species, 1-octanol-phosphate buffer appears to give the most consistent results compared with 1-octanol-water. In some publications, the apparent partition coefficient P is also described as the distribution coefficient D. 

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. 

The standard potential of transfer for an individual ion, A cp , is not amenable to thermodynamic measurement. Its value can be determined by measuring the distribution ratio of its salt, for which the Gibbs free energy of transfer of the counterion is already known. From the experimentally accessible partition coefficient of the salt, the standard Gibbs free energy of transfer of the salt, AG aI7P, from phase a to phase p is calculated as... 

The subscripts ieS and ieM refer to the ion-exchange equilibria at the solution-stationary phase and the solution-micelle interface, respectively. The [C] concentrations are the counter anion concentration in the aqueous phase, aq, including added salts, and the one on the stationary phase, s. is the micellar counterion dissociation constant, (j) is the column phase ratio, [M] is the micellar concentration and k is the anion retention fector. Equation 13.6 obtained from ion-exchange equilibria resembles the classical Armstrong-Nome equation. The Pwm Partition coefficient of eq. 13.6 can be related to the KjeM constant by [30] ... 

These are only the theoretical dependencies real behavior of actual molecule usually is significantly altered due to different types of intermolecular interactions. Molecular solvation, association, hydrogen bonding, and counterions all have a significant effect on drug ionization constant and partitioning and distribution coefficients. Detailed and comprehensive discussion of these effects could be found in the book by Avdeef [22]. 

Since electrical neutrality must be maintained in ion-exchange chromatography, the distribution of ions between the mobile and stationary phases is complicated by the need for counterions. The use of partition or distribution ratios in the usual way is therefore not entirely appropriate instead, a selectivity coefficient is used to denote the equilibrium distribution of ions. Thus for (25-1) and (25-2) the law of mass action... 

Based on the concept mentioned above, Shibukawa et al. [ref. 31] have proposed a new model regarding the distribution of ionic solutes in practical exclusion chromatography, where the distribution of sample ion is assumed to be dependent not only on its own physicochemical properties but also on those of the counterion and coion in the eluent. The background eluent ion effect on the distribution coefficients of ionic solutes on neutral hydrophilic gels can be understood on the basis of the ion partition model presented. If there is not any specific interaction such as complex formation between the sample ion s (hereafter sample ion is represented by cation, but, of course, the expressions... 

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