A partition coefficients

Solubilisation is usually treated in terms of the pseudophase model, in which the bulk aqueous phase is regarded as one phase and tire micellar pseudophase as another. This allows the affinity of the solubilisate for the micelle to be quantified by a partition coefficient P. Different definitions of P can be found in the literature, differing in their description of the micellar phase. Frequently P is... 

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... 

Earlier we learned that the partitioning of a solute between two phases is described by a partition coefficient. If the solute is initially in an aqueous phase and is extracted into an organic phase ... 

A weak acid, HA, with a fQ of I.O X 10, has a partition coefficient, Rp, between water and an organic solvent of I20( What restrictions on the sample s pH are necessary to ensure that a minimum of 99.9% of the weak acid is extracted in a single step from 50.0 mF of water using 50.0 mF of the organic solvent ... 

Extraction for enzyme recovery is a common process. Polyethylene glycol-dextran mixture is used to recover a-amylase from fermentation broth. Given a partition coefficient of 4.2, calculate the maximum enzyme recovery when... 

If both addition and fragmentation arc irreversible the kinetics differ little from conventional chain transfer. In the more general case, the rate constant for chain transfer is defined in terms of the rate constant for addition and a partition coefficient which defines how the adduct is partitioned between products and starting materials (eq. 19). 

Further supporting evidence for the importance of lipophilicity in bitter response is provided by the taste of isohumulone (118), the principal, bitter-tasting component of beer, and some of its derivatives. Isohumulone can exist in both cis and trans forms. Clarke and Hilderbrand reported that the cis form, having a partition coefficient of 0.78, is more bitter than... 

The previously proposed uptake models were mathematical assumptions and had no physical or chemical basis. Millard and Hedges, on the other hand, considered the chemistry of bone-uranium interactions. With the D-A model, they proposed that U was diffusing into bone as uranyl complexes, and adsorbing to the large surface area presented by the bone mineral hydroxyapatite (Millard and Hedges 1996). Laboratory experiments showed a partition coefficient between uranyl and hydroxyapatite under oxic conditions of 10" -10, demonstrating U uptake in the U state without the need for reduction by protein decay products as proposed by Rae and Ivanovich (1986). 

The permeation technique is another commonly employed method for determining the mutual diffusion coefficient of a polymer-penetrant system. This technique involves a diffusion apparatus with the polymer membrane placed between two chambers. At time zero, the reservoir chamber is filled with the penetrant at a constant activity while the receptor chamber is maintained at zero activity. Therefore, the upstream surface of the polymer membrane is maintained at a concentration of c f. It is noted that c f is the concentration within the polymer surface layer, and this concentration can be related to the bulk concentration or vapor pressure through a partition coefficient or solubility constant. The amount... 

The first of these environmentally-important parameters can be expressed as a partition coefficient. In aqueous solution many, but not all pesticide compounds exhibit strong affinity for soil organic matter or concentrate in the lipid phase of soil organisms. Some, notably the cationic group, also exhibit marked affinity for clay or other mineral surfaces. An overall partition (or distribution) coefficient (kD) can be defined ... 

It has been assumed implicitly in the preceding analyses that penetration of the substrate into the film and its exiting are fast, so that equilibrium is maintained and characterized by a partition coefficient. If this assumption is not valid, the rate of penetration (rate constant kfp) interferes with the current response, giving rise to an additional characteristic current, ifp = FSkfpCwhere kfp either represents a membrane penetration or... 

Thus, on measuring a partition coefficient of HA, it is imperative to know which species is being measured, i.e., neutral (undissociated, HA) or charged species (A ). Mathematical procedures can be used to take into account the complicating equilibria, and partition coefficients can be calculated for both the nonionized and ionized species of organic acids. The difference in partition coefficient between the two species is approximately... 

As an example of a partition coefficient, the octanol-water partition coefficient (K0Vf) is determined by similar experimental procedures as those for... 

The most common partition coefficient encountered in environmental work (Sect. 2.1.4) is the octanol water partition coefficient (K0VI) and the solid phase carbon-water partition coefficient (Koc). A partition coefficient for dissolved organic matter-water (i. e., Kd ()M) or dissolved organic carbon-water (i. e., Kd oc) occasionally appears in the literature. In the case of PCBs, Boyd and Sun [378] defined a partition coefficient for residual transformer oil and water as Kd oil, while Sun and Boyd [379] defined a coefficient for PCB dielectric fluid-water as Kd pen-These authors [378,379] identified a total partition coefficient that com-... 

In systems where only dynamic quenching occurs, then steady-state fluorescence intensities can be measured instead of lifetimes/101 103-,07) In experiments where comparisons are being made (i.e., for a comparison of different experimental conditions or types of membrane), it is important that the lifetime of the fluorophore (r0) is not affected by the experimental conditions. Fluorescence intensities can be obtained much more rapidly and without specialized instrumentation. Blatt and Sawyer(101) have employed a relationship essentially the same as Eq. (5.20) in this way. They have pointed out that since the quenching mechanism is collisional, the partition coefficient that is derived is a partition coefficient of the quencher into the immediate environment of the fluorophore and is therefore a local Kp. It is therefore possible to investigate the partition coefficient gradient across the lipid bilayer by using a series of probes, such as the anthroylstearates,(108) located at different depths. In their method, Eq. (5.20) has the form... 

In contrast, diffusion of MeOH measured via permeabilify measurements (assuming a partition coefficient of 1) was lower (1.3 x 10 and 6.4 x 10 cm s for Nafion 117 and BPSH 40, respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of MeOH in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 pm for Nafion 117 and BPSH 40, respectively), whereas the NMR method observes diffusion over a lengfh of approximately 4-8 pm. 

The octanol/buffer represents a partition coefficient between two bulk phases it is less affected by the structure of the analyte and therefore it cannot be used to predict the exact value of liposome membrane-to-buffer Xp, which is also affected by the geometry of the analyte (41 4). However, it is accepted and established that the octanol-to-buffer can help to predict transmembrane passive diffusion (40). In the case of liposomes such as Doxil, in which the internal aqueous phase (intraliposome aqueous phase) is different from the external liposome aqueous medium due to large differences in the composition and pH of these two aqueous phases, there are two different liposome membrane-to-aqueous phase partition coefficients this is referred to as asymmetry in the membrane-to-aqueous media partition coefficient. 

Kaneko, T., Wang, P.-W., and Sato, A. Partition coefficients for gasoline additives and their metabolites, /. Occup. Health, 42 86-87, 2000. 

Gas-liquid relationships, in the geochemical sense, should be considered liquid-solid-gas interactions in the subsurface. The subsurface gas phase is composed of a mixture of gases with various properties, usually found in the free pore spaces of the solid phase. Processes involved in the gas-liquid and gas-solid interface interactions are controlled by factors such as vapor pressure-volatilization, adsorption, solubility, pressure, and temperature. The solubility of a pure gas in a closed system containing water reaches an equilibrium concentration at a constant pressure and temperature. A gas-liquid equilibrium may be described by a partition coefficient, relative volatilization and Henry s law. 

In a sediment system, the hydrolysis rate constant of an organic contaminant is affected by its retention and release with the sohd phase. Wolfe (1989) proposed the hydrolysis mechanism shown in Fig. 13.4, where P is the organic compound, S is the sediment, P S is the compound in the sorbed phase, k and k" are the sorption and desorption rate constants, respectively, and k and k are the hydrolysis rate constants. In this proposed model, sorption of the compound to the sediment organic carbon is by a hydrophobic mechanism, described by a partition coefficient. The organic matrix can be a reactive or nonreactive sink, as a function of the hydrolytic process. Laboratory studies of kinetics (e.g., Macalady and Wolfe 1983, 1985 Burkhard and Guth 1981), using different organic compounds, show that hydrolysis is retarded in the sohd-associated phase, while alkaline and neutral hydrolysis is unaffected and acid hydrolysis is accelerated. 

The two-phase titration was first described in 1963 (19) as a means to simultaneously determine a partition coefficient and pKa. Several variations have appeared since (20-24), but none has seemed to gain favor. I like the simplified approach of Clarke (25,26) who uses the method to determine partition coefficients after separately determining (or knowing) the pKa. 

For isomorphous substitution also a partition coefficient D can be defined which takes into account the competition between the impurity and substituted ions. For cadmium D is given by ... 

When two immiscible solvents are placed in contact with each other and a non-ionizable compound is dissolved in one of the solvents, the compound distributes itself between the two solvents. This distribution is referred to as partitioning. The ratio of the concentrations of the compound in each phase is a constant for a specific set of solvents, pH, buffers, buffer concentrations, ionic strength and temperature. This ratio is referred to as a partition coefficient or distribution coefficient and is equal to the ratio of the solubilities in the two solvents. When the compound is a weak acid or base, the distribution of the compound can be shown to be given by the following equation for a monoprotic compound ... 

A neutral compound has a partition coefficient of 5 between ether and water. What percentage of the compound would be extracted from 10 ml of water if (i) 30 ml of ether were used to extract the compound or (ii) three 10 ml volumes of ether were used in succession to extract the compound ... 

A drug has a partition coefficient of 12 between chloroform and water. 

Taking as a reference the EON = 5 oligomer, which is close to optimum formulation in a system with n-heptane and water at ambient temperature, and has a partition coefficient of 0.02, it means that the EON = 3 oligomer is 6 times less hydrophilic, and the EON = 7 oligomer 8 times more hydrophilic. 

With the use of the regression models a partition coefficient for each compound and a selectivity for each pair of substances can be predicted in each composition of the extraction liquid within the factor space. Figure 7.1 demonstrates the response surfaces of the partition coefficients of two compounds i and j in a binary extraction liquid i.e. an extraction liquid composed of two solvents). The compositions where the partition coefficients of i and j are optimal are represented by O, and 0, respectively. The optimal compositions with regard to the selectivity is represented by 0 . Two situations are given. 

If the variance of a partition coefficient (which has been modelled with equation (3)) in a given mixture composition has to be estimated, the following derivation is made (y= In P) ... 

---