Oc tanol-water partition coefficient

Best, S. A. Merz Jr., K. M. Reynolds, C. H., Free energy perturbation study of oc-tanol/water partition coefficients Comparison with continuum GB/SA calculations, J. Phys. Chem. B 1999,103, 714-726. 

Finizio, A., M. Vighi, and D. Sandroni, Determination of n-Oc-tanol/Water Partition Coefficients (Kl)W) of Pesticides Critical Review and Comparison of Methods, Chemosphere, 34, 131-161 (1997b). 

Chromosorb T shows the direct correlation of capacity with the oc-tanol-water partition coefficient expected of hydrophobic adsorbents (6). Its overall affinity for hydrophobic water contaminants is similar to that of Amberlite XAD-8 (Rohm and Haas), but it has additional affinity for humic acid and for water-soluble, cationic, aromatic dyes. Chromosorb T is more easily cleaned than the XAD resins, and it is more inert, contributing essentially no contaminants to eluates. Table IV illustrates the adsorption and recovery of a series of hydrophobic test solutes at 50 ppb in 8 L of synthetic hard water on a 50-mL bed of Chromosorb T. 

Tse, G. and Sandler, S.I. 1994. Determination of infinite dilutions activity coefficients and 1-oc-tanol/ water partition coefficients of volatile organic pollutants. J. Chem. Eng. Data 39, 354—357. 

Meylan, W.M., and P.H. Howard. 1995. Atom/Fragment Contribution Method for Estimating Oc-tanol-Water Partition Coefficients. ]. Pharm. Sci, 84, 83-92. 

Determination of Octanol/Water Partition Coefficients. Since oc-tanol/water partition coefficient data for trifluoromethanesulfonanilide (I) and its substituted derivatives have not been reported in the literature and since it was not apparent that any of the substituent tt values previously determined by Fujita et al. (11) would be directly applicable to the TFMS herbicidal system, all TFMS partition coefficients and tt values were determined experimentally. The fluoroalkanesulfonanilides are very acidic because of the electron-withdrawing power of the parent fluoro-alkanesulfonyl group (5). The parent TFMS compound (I), for example, has a pKa in water of 4.45 at 25 °C. This inherent acidity extends to all TFMS series members and requires that the usual partition coefficient measurement procedure described by Fujita et al. (11) be modified to obtain accurate values of log P and tt. 

Fig. 2. A simplified example of the general relationships between on the one hand the oc-tanol/water partition coefficient (Ko ) and on the other hand internal effect concentrations (body residues), bioconcentration and acute toxicity for narcotic organic chemicals and small freshwater fish [16], reproduced with permission...

Briggs, G.G. Theoretical and Experimental Relationships between Soil Adsorption, Oc-tanol-Water Partition Coefficients, Water Solubilities, Bioconcentration Factors, and the Parachor, J. Agric. Food Chem., 29(5) 1050-1059 (1981). 

For drugs, solubility in fat is as important as solubility in water. Since drugs must cross a lipid membrane to enter a cell, solubility in octanol, a lipophilic alcohol, is often used to estimate fat solubility (lipophilicity). is the oc-tanol-water partition coefficient and is calculated exactly as one would expect. This expression can be generalized as... 

As a unitary result, it was found that the sorbed mass increased with decreasing pH values. Protonation of the surfaces of the solids with an increased affinity to anions might be the reason for this, rather than a hydrophobic effect. The pH-values were some orders above the pk -values of the acids. There was no interaction between any soil component and the substance with the highest oc-tanol-water-partition coefficient which is 2.27 for 4-methylbenzoic acid. This result emphasizes the polar properties of the mineral soil particles in the suspension. 

An advantage of defining the problem in this manner is that the partition coefficient has become a central property in quantitative structure-activity relationships (QSAR) and a large data base of P values is available in the medicinal chemistry literature (22-24). In particular, if a correlation (Equation 15) between the polymer-water and octanol-water partition coefficients can be established for a series of solutes, it becomes possible to utilize log P (oc-tanol/water) value as a reference point from which to calculate the polymer-water value. 

Typical applications of reversed-phase chromatography are shown in Table 2. Beyond analytical apphca-tions, RP-TLC on bonded phases is also a tool for physicochemical measurements, particularly for molecular hpophilicity determination of biologically active compounds. Hydrophobicity can be measured by partition between an immiscible polar and nonpolar solvent pair, particularly in the reference system n-oc-tanol-water. The partition coefficient, P, is frequently used to interpret quantitative structure-activity relationships (QSAR studies). 

Selection of the octanol-water system is often justified in part beeause, like biological membrane components, oetanol is flexible and contains a polar head and a nonpolar tail. Hence, the tendency of a drug molecule to leave the aqueous phase and partition into oc-tanol is viewed as a measure of how efficiently a drug will partition into and diffuse across biological barriers such as the intestinal membrane. Although the octanol-water partition coefficient is, by far, most commonly used, other solvent systems such as cyclohexane-water and chloroform-water systems offer additional insight into partitioning phenomena. 

The partition coefficient is a way to measure the tendency of a molecule to dissolve in membranes, which correlates with its ability to dissolve in organic solvents. It is determined by allowing a compound to equilibrate between water and an organic phase, n-oc-tanol. The log(P) value is defined as logjo of the ratio of the concentration of a compound in n-octanol to the concentration of the compound in water. For example, if the concentration of the compound in the n-octanol phase is 100 times that in the aqueous phase, then log(P) is 2. 

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