Activity coefficient in octanol

Bhatia, S.R. and Sandler, S.l. Temperature dependence of infinite dilution activity coefficients in octanol and octanol/water partition coefficients of some volatile halogenated organic compounds. J. Chem. Eng. Data, 40(6) 1196-1198,1995. 

PCNs are planar molecules and their volatility properties more closely resemble those of the approximately planar mono- and non-ortho PCBs than the multi-ortho PCBs [57]. In a plot of the heats of vaporization (AvapH, kjmol-1) of PCNs versus the Le Bas molar volume, the regression line fell close to the same line for mono-ortho PCBs and intermediate of multi-ortho and non-ortho PCBs. A plot of log Koa versus log p was virtually identical to one for mono- and non-ortho PCBs, and distinct from the regression line for multi-ortho PCBs. The combination of Koa and p[J allowed the activity coefficients in octanol to be estimated, which ranged from 1-7 and were negatively correlated with the Le Bas molar volume of the PCN molecule. No such correlation was found for multi-ortho PCBs. 

TABLE 3 CAS numbers, molecular weight, melting point (T ), molecular volume (v), fugacity ratio (F), solubility in octanol (Cg), activity coefficient in octanol (log yo), and octanol/water partition coefficient (log... 

The octanol-water partition coefficient Kow is widely used as a descriptor of hydrophobicity. Variation in /fow is primarily attributable to variation in activity coefficient in the aqueous phase (Miller et al. 1985) thus, the same correlations used for solubility in water are applicable to /fow. Most widely used is the Hansch-Leo compilation of data (Leo et al. 1971, Hansch and Leo 1979) and related predictive methods. Examples of Kow correlations are ... 

Lee, S.C., Hung, H., Shin, W.Y., Mackay, D. (2000) Estimations of vapor pressure and activity coefficients in water and octanol for selected aromatic chemicals at 25°C. Environ. Toxicol. Chem. 19, 2623-2630. 

Since the mole fraction-based partition coefficient of a dilute species between two liquid phases is the inverse of the ratio of its infinite dilution activity coefficients in each phase, the GCS model can also be used for such predictions. Among the many possible partition coefficients, the octanol-water partition coefficient, Aqw, is of special interest. For example, A/ow is a key parameter in determining the fate of a persistent organic pollutant... 

The —> physico-chemical properties used to derive BC(DEF) descriptors are activity coefficient in water, —> octanol-water partition coefficient, hoiling point, —> molarr activity, liquid state molar volume, and heat of vaporization. The eigenvalues and corresponding cumulative explained variances of the five principal properties (denoted by B, C, D, E, and F) are reported in Table B1. It can be noted that the first two principal properties B and C already explain 95.7% of the original variance of the six physico-chemical properties further analysis using different compounds and properties showed B and C to be independent of the data set used in their derivation, identifying them as measures of molecular bulk and cohesiveness, respectively. The other three parameters, D, E, and F, are of minor importance, however they were... 

Theoretically, the slope of the respective correlations should be -1 if the activity coefficients in water and in water-saturated 1-octanol were equal. These QSARs are in fact obviously similar in their slopes, which range between -0.9 and -1.5, but vary considerably in their intercepts, ranging between -0.2 and 2.2, depending on the class of chemicals. Practically, this corresponds to a parallel shift of the functions towards higher or lower absolute values for the different classes, which to some extent may reflect class-specific differences in the experimental procedures used to obtain the underlying data (Figure 4.5). 

FIGURE 6 Phase distribution equilibria involving pure phases with importance for describing environmental phase partitioning. Kaw, air-water partition coefficient Kow, octanol-water partition coefficient Kqa, octanol-air partition coefficient Pl, (supercooled) liquid vapor pressure Cw and Co, saturation solubility in water and octanol, respectively yw and yo, activity coefficient in water and octanol, respectively. 

Some correlations can be used to anticipate trends in SPME coating/water distribution constants for analytes. For example, a number of investigators have reported the correlation between octanol/water distribution constant and Kf . This is expected since is a very general measure of the affinity of a compormd to the organic phase. It should be remembered, howeveq that the trends are valid only for compormds within homologous series, such as aliphatic hydrocarbons, aromatic hydrocarbons, or phenols they should not be used to make comparisons between different classes of compormds, because of different analyte activity coefficients in the polymer. 

FIGURE 2 Activity coefficients (In yQ)of chlorinated aromatics, polynuclear aromatics and lipophilic dyes in 1-octanol as a function of molar volume. 

FIGURE 3 The expected behaviour of the activity coefficient (In y)of chemically related compounds in water (W), 1-octanol (O) and lipid tissues of organisms (I) versus molar volume, v. 

Many additional consistency tests can be derived from phase equiUbrium constraints. From thermodynamics, the activity coefficient is known to be the fundamental basis of many properties and parameters of engineering interest. Therefore, data for such quantities as Henry s constant, octanol—water partition coefficient, aqueous solubiUty, and solubiUty of water in chemicals are related to solution activity coefficients and other properties through fundamental equiUbrium relationships (10,23,24). Accurate, consistent data should be expected to satisfy these and other thermodynamic requirements. Furthermore, equiUbrium models may permit a missing property value to be calculated from those values that are known (2). 

Aqueous solutions are not suitable solvents for esterifications and transesterifications, and these reactions are carried out in organic solvents of low polarity [9-12]. However, enzymes are surrounded by a hydration shell or bound water that is required for the retention of structure and catalytic activity [13]. Polar hydrophilic solvents such as DMF, DMSO, acetone, and alcohols (log P<0, where P is the partition coefficient between octanol and water) are incompatible and lead to rapid denaturation. Common solvents for esterifications and transesterifications include alkanes (hexane/log P=3.5), aromatics (toluene/2.5, benzene/2), haloalkanes (CHCI3/2, CH2CI2/I.4), and ethers (diisopropyl ether/1.9, terf-butylmethyl ether/ 0.94, diethyl ether/0.85). Exceptionally stable enzymes such as Candida antarctica lipase B (CAL-B) have been used in more polar solvents (tetrahydrofuran/0.49, acetonitrile/—0.33). Room-temperature ionic liquids [14—17] and supercritical fluids [18] are also good media for a wide range of biotransformations. 

There are apparently two sources of this effect. The molar volume of water changes relatively little as a result of the presence of a small quantity of dissolved octanol, however the quantity of dissolved water in the octanol is considerable, causing a reduction in molar volume of the octanol phase. The result is that even if activity coefficients are unaffected, log S0/Sw will be about 0.1 units less than that of log KoW. Effectively, the octanol phase swells as a result of the presence of water, and the concentration is reduced. In addition, when log KqW exceeds 4.0 there is an apparent effect on the activity coefficients which causes log (SQ/SW) to increase. This increase can amount to about one log unit when log Kow is about 8. A relatively simple correlation based on the analysis by Beyer et al. (2002) (but differing from their correlation) is that... 

The octanol-water partition coefficient appears to correlate better with biological activity than partition coefficients in other solvent-water mixtures as, for example, hexane water, because the amphiphilic nature of octanol can accommodate a greater variety of more or less hydrophobic molecules. 

Octanol/water partition coefficients, Pow, which measure the relative solubilities of solutes in octanol and in water, are widely used as descriptors in quantitative structure-activity relationships (QSAR), for example in pharmacological and toxicological applications.49 Since experimental values of these are not always available, a number of procedures for predicting them have been proposed (see references in Brinck et al.).50... 

The LFER that results when correlating partitioning in the octanol-water system and the humic substances-water system Implies that the thermodynamics of these two systems are related. Hence, much can be learned about humic substances-water partitioning by first considering partitioning In the simpler octanol-water system. The thermodynamic derivation that follows is based largely on the approach developed by Chlou and coworkers (18-20), Miller et al. (21), and of Karickhoff (J, 22). In the subsequent discussion, we will adopt the pure liquid as the standard state and, therefore, use the Lewls-Randall convention for activity coefficients, l.e., y = 1 if the mole fraction x 1. 

C.V where C is the molar concentration and Vg is the molar volume of the solvent. Hence we can write Equation 5 in terms of the molar concentrations and obtain an expression for the octanol/water partition coefficient, KQW = CQ/CW in terms of the activity coefficient and the molar volumes of octanol and water (19) ... 

The most important factor in determining KQW is the aqueous-phase activity coefficient (aqueous solubility) of the organic solute. The observed partition coefficients are less than the ideal partition coefficients (K w) as result from 1) the incompatibility of the solute in water-saturated octanol and, to a lesser degree,... 

Yonezawa, Y. and Umshigawa, Y. Chemical-biological interactions in biological pnrification systems. V. Relation between biodegradation rate constants of aliphatic alcohols by activated slndge and their partition coefficients in a 1 -octanol-water system, Chemosphere, 8(3) 139-142, 1979. 

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