Octanol/water distribution ratio

The correlation between the molar aqueous solubility of solvents log(s/mol dm"3), and the 1 -octanol/water distribution ratio, log P... 

Table 1 Octanol-water distribution ratio measured using different CCC methods.

Figure 11. Uptake rates of inorganic Hg (a) and of methylmercury (b) by a marine alga as a function of the octanol-water distribution ratio of the Hg-species under various conditions of pH and chloride concentrations. The neutral species HgCl and CH5HgClH diffuse through the membranes. Reprinted with permission from [79] Mason, R. P. et al. (1996). Uptake, toxicity, and trophic transfer in a coastal diatom , Environ. Sci Technol., 30, 1835-1845 copyright (1996) American Chemical Society...

ZZoW Apparent octanol-water distribution ratio at ... 

In contrast to air-water partitioning, the situation may be a little more complicated when dealing with organic solvent-water partitioning of organic acids and bases. As an example, Fig. 8.9 shows the pH dependence of the n-octanol-water distribution ratios, D,ow (HA, A"), of four pesticides exhibiting an acid function ... 

Figure 8.9 The pH dependence of the /z-octanol-water distribution ratio of pentachlorophenol (PCP, pKj = 4.75), 4-chloro-a-(4-chlo-rophenyl) benzene acetic acid (DDA, pKb = 3.66), 2-methyl-4,6-dinitrophenol (DNOC, pKia = 4.46), and 2,4,5-trichlorophenoxy acetic acid (2,4,5-T, pKia = 2.83). (from Jafvert et al., 1990).

Figure 8.10 Calculated octanol-water distribution ratio of 2,4-dini-tro-6-methylphenol (DNOC, p= 4.46) as a function of pH and K+ concentration (adapted from Jafvert et al. 1990).

Figure 10.14 Log octanol-water distribution ratios (log D,ow, broken lines) and log L-a-dioleylphos-phatidylcholine liposome-water distribution ratios (log Dflipsw, solid lines) of pentachlorophenol (PCP) and 2-sec-butyl-4,6-dinitrophenol (dinoseb) as a function of pH at 25°C and 100 mM ionic strength. Data from Escher et al. (2000).

Figure 10.15 Plot of log 1 /LCi50 for guppies versus (a) log octanol-water distribution ratio (log Z),ow, Eq. 10-41), and (b) log liposome-water distribution ratio (log Z),lipsw, Eq. 10-41) at pH 7 for a series of chlorinated benzenes (o) and chlorinated phenols ( ) as well as for the herbicide 2-.9ec-butyl-4.6-dinitrophenol (dinoseb) (v). The liposomes used were L-a-dimy-ristoyl-phosphatidylcholine (chlorinated benzenes) and L-a-dioleyl-phosphatidylcholine (chlorinated phenols and dinoseb). The pH dependence of D/ow and D,lipsw of pentachlorophenol (PCP) and dinoseb is shown in Fig. 10.14. Data from Saarikoski and Viluskela (1992), Gobas et al. (1988), Escher and Schwarzenbach (1996), and Gunatilleka and Poole (1999).

Using a pPLC system, log P for one unknown compound was determined in less than 1 hr. It is important to note that the excess capacity provided by the system (24 columns are available for simultaneous analysis) allows simultaneous determination of log P for six additional compounds. The same study required 5 hr using conventional HPLC, and consumed 300 mL of solvent, equivalent to 15 times the volume of solvent used for the evaluations via jtiPLC. A similar approach can be used to evaluate log D, the octanol-water distribution coefficient—a measure of the distribution ratios of all combinations (ionized and unionized) of octanol and pH-buffered water. 

Figure 12. pH-dependence of the octanol-water and liposome-water distribution ratio, (a) TBT, (b) TPT. Reprinted in part from [233], with permission from Hunziker, R. W., Escher, B. I. and Schwarzenbach, R. P. (1997). pH-dependence of the partitioning of triphenyltin between phosphatidylcholine liposomes and water , Environ. Sci. Technol., 35, 3899-3904 copyright (2001) American Chemical Society... 

For example, the ratio of the n-octanol/watcr distribution coefficient of the nondissociated species to that of the ionic species is nearly 10,000 for 3-methyl-2-nitrophenol, but only about 1000 for pentachlorophenol because of the greater significance of the hydrophobicity of the ionized form of pentachlorophenol. The logarithm of the -octanol/water distribution coefficient of pentachlorophenol as the phenolate is about 2 (determined at pH 12, and 0.1 M KC1), which indicates significant distribution of the ionized form into the n-octanol phase [8,37], Extraction of such highly hydrophobic ionogenic organic compounds can result from mixed-mode mechanisms that incorporate both the hydrophobic and ionic character of the compound. 

There are a few approaches to fadUtate the interpretation of data on the complex and variable mixtures of chlorobiphenlys in marine environmental samples. The composition of mixtures can be represented as mole percent contributions of individual CBs to their sum Duinker et al., 1980) or as molar ratios, e.g., CBx/CB153 Boon et al., 1992). This allows visual, qualitative and quantitative comparisons between samples with widely different overall compositions. Quantitative and less arbitrary comparison is possible with statistical methods such as principal component analysis Jackson, 1991). Finally, distribution patterns between the CB mixtures in solution and in suspended particles can be studied by plotting concentration ratios in these compartments Le., distribution coefficients) against known molecular properties, e.g., octanol-water distribution coefficients Schulz-BuU et al., 1998). 

Once the composition of each equiHbrium phase is known, infinite dilution activity coefficients for a third component ia each phase can then be calculated. The octanol—water partition coefficient is directly proportional to the ratio of the infinite dilution activity coefficients for a third component distributed between the water-rich and octanol-rich phases (5,24). The primary drawback to the activity coefficient approach to estimation is the difficulty of the calculations involved, particularly when the activity coefficient model is complex. 

Several models have been suggested for the estimation of the distribution ratios of nonionic solutes between water and (practically) immiscible organic solvents. One model takes 1-octanol to represent, in general, lipophilic ( fat-liking ) media, which hydrophobic ( water-fearing ) solutes would prefer over water. Such media may be oils, biological lipid membranes, and, somewhat less suitably, hydrocarbon solvents. 

Table 2.5 lists the additive values for representative fragments/and structural factors F. As an example, the infinite dilution distribution ratio of C2H5 C(0)0C2H5, ethyl propionate, between 1-octanol and water is obtained as follows. The carboxylate group contributes -1.49 to log P, each ethyl group contributes 0.89 -H 0.66 - 0.12 = 1.43 (for the methyl and methylene groups and... 

The use of distribution coefficients for the QSAR treatment of ionizable compounds has been extended to consideration of ion-pair partitioning into biolipid phases. Two experimental methods for determining ion-pair partition coefficients are described. One is a single-phase titration in water-saturated octanol, in which case (for acids) log Pj = log P + pKa - pKa. The other is a two-phase titration (octanol/water) from which the ratio (P + 1)/(Pj + 1) can be calculated. An example outcome is that the uncoupling activity of phenols can be represented by an equation in log instead of log D and pKa. 

Figure 3.3-6 The distribution ratios between [BMIMjlPFg] and water (neutral pH) for organic solutes correlate with literature partition functions of the solutes between octanol and water (log P).

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