Aqueous phases, partitioning

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. 

Glowa, G.A. and Wren, J.C. Aqueous-phase partitioning and hydrolysis or organic halides. Can. J. Chem., 81(3) 230-243, 2003. 

The Henry s Law Constant Effect of Temperature on Air-Water Partitioning Effect of Solution Composition on Air-Water Partitioning Illustrative Example 6.2 Evaluating the Direction of Air-Water Gas Exchange at Different Temperatures Illustrative Example 6.3 Assessing the Effect of Solution Composition on Air-Aqueous Phase Partitioning Availability of Experimental Data Estimation of Air-Water Partition Constants... 

Assessing the Effect of Solution Composition on Air-Aqueous/Phase Partitioning... 

At the SMC The change in membrane polarity as well as removal of the aqueous layer limiting step are effects which, undoubtedly, must also be produced by the surfactant molecules. These effects are apparently masked by micelle solubilization governed by micelle-aqueous phase partitioning (P ). According to the Col-lander equation [31], two partition coefficients found in two related systems can be expressed as follows ... 

Thus, if K%f is the oil aqueous phase partition coefficient and Ca the total aqueous concentration, then, as in Eq. (9),... 

Some examples for PAH compounds suggest that decreased solubility and non-aqueous-phase partitioning and sorption processes are restrictive toward microbial degradation. Wodzinski and Bertolini (16) and Wodzinski and Coyle (17) concluded that bacteria utilize naphthalene, biphenyl, and phenanthrene as dissolved solutes, with the rate of biodegradation independent of the total amount of solid-phase hydrocarbon. Stucki and Alexander (18) found that the dissolution rate of phenanthrene may limit the biodegradation rate. 

The totality of micelles represents a colloidal phase, into which a substance is dissolved in the aqueous phase partitions. The capacity of the micellar phase to solubilize a solute can therefore be expressed as a partition coefficient A n,. Hence, a linear relationship can be expected between the concentration of substance solubilized by micelles and the concentration of the surfactant Cs in the system. Because only micelles contribute to the solubilizing effect but not the monomeric surfactant molecules, the critical micelle concentration Ccmc must be subtracted from the total of the surfactant concentration. The resulting total concentration of solute in the micellar solution is then ... 

Equations (11) and (12) show that devolatilization is strongly affected by the thermodynamic equilibria of the VOCs between different phases. High values of the polymer partides/aqueous-phase partition coefficient imply that the concentration in the aqueous phase will be low and hence it will be difficult to remove the VOC from the particles. Similarly, a low value of the Henry s law constant means that the concentration of VOCs in the gas phase is low and hence, devolatilization will be difficult. Figure 18.7 shows the kinetics of devolatilization of vinyl acetate, acetaldehyde, and n-butanol in a VAc/BA/AA latex, and that of BA in a BA/S/AA latex by stripping in laboratory-scale equipment, under equilibrium conditions. It can be seen that the devolatilization of BA was slow due to the high affinity (high feS,) of BA to the polymer particles. The removal of n-butanol was also very slow because of its high solubility in the aqueous phase and low vapor pressure (a low value of the Henry s law constant). 

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