Octanol-water coefficient

A chemical must have certain physicochemical properties to elicit an endocrine disrupting effect. For example, the ability to enter the body and to cross the cell membrane into the cellular medium requires a degree of lipophilicity. Fipophilic potentials may be compared by reference to the chemical s octanol-water coefficient (usually expressed as log K ). This property, together with molecular size and chemical structure, has an important influence on the bioacciimiilation... 

K(,(., calculated from the octanol-water coefficient (K w) solubility, and melting point data ranged from 2.93 to 3.47, and compared favorably with literature values (Karickhoff 1981). McLean et al. (1988) estimated a lower Kq . of 39, equal to a log of 1.59. More recently, a of 5,100, equal to log 3.7, has been reported (HSDB 1999). These values indicate that methyl parathion is moderately mobile to immobile in soil (Swann et al. 1983). 

K., The correlation of polymer-water and octanol-water coefficients Estimation of drug solubilities in polymers, Int. J. Pharm., 45, 1-11, 1988. 

Mirrlees, M. S., Moulton, S. J., Murphy, C. T., Taylor, P. J. Direct measurement of octanol-water coefficients by high-pressure liquid chromatography. J. Med. Chem. 1976, 19, 615-519. 

Poole, S. K., Poole, C. F. Separation methods for estimating octanol-water coefficients. J. Chromatogr. E 2003, 797, 3-19. 

MD simulations in expHcit solvents are stiU beyond the scope of the current computational power for screening of a large number of molecules. However, mining powerful quantum chemical parameters to predict log P via this approach remains a challenging task. QikProp [42] is based on a study [3] which used Monte Carlo simulations to calculate 11 parameters, including solute-solvent energies, solute dipole moment, number of solute-solvent interactions at different cutoff values, number of H-bond donors and acceptors (HBDN and HBAQ and some of their variations. These parameters made it possible to estimate a number of free energies of solvation of chemicals in hexadecane, octanol, water as well as octanol-water distribution coefficients. The equation calculated for the octanol-water coefficient is ... 

Actually, why do we need log D models Why can t we use just log P models One of the main requirements for prediction of octanol-water coefficients is to optimize bioavailability of chemical compounds. During the absorption process the... 

Absorption - desorption - N-octanol/water coefficient - Henry constant - Biodegradation and/or abiotic degr. disappearance coef. - Bioaccumulation - Aquatic Ecotox Fish 24 to 96 hours Daphnia 24 to 48 hours - Air/soil/sediment Ecotox ... 

As we have seen in (Eq. 4.40) and in Fig. 4.14, the distribution (or partition) coefficient for the (ab)sorption of a non-polar organic solute onto a solid phase can be estimated from the octanol-water coefficient Kow (see Eq. 4.42)... 

Table 4.6 Octanol-water Coefficients and Partition Coefficients of Organic Substances on Natural Soil Materials (Modified from Schwarzenbach et al., 1983)...

All PCDD/F isomers are solids with high melting points, but low vapor pressure and low solubihty in water. The high octanol-water coefficients are an indication of the observed bioaccumulative behavior in plants and animals for these compounds. Detailed environmentally important physicochemical properties can be found in the literature. All higher chlorinated compounds are very persistent in the environment with half-lives of 5-10 years photolysis with sunlight is the only degradation process in the environment. 

Li, L., Wang, L., Han, S., and Zhang. Z. Comparison of four methods of predicting newly measured octanol/water coefficients (log Ko ) for heterocyclic nitrogen compounds and the partition mechanism. Environ. Toxicol. Chem., 18(12) 2723-2728. 1999. 

Broto, P., Moreau, G., and Vandycke, C. (1984) Molecular structures perception, autocorrelation descriptor and SAR studies. System of atomic contributions for the calculation of the n-octanol/water coefficients. Eur. J. Med. Chem. 19, 61-65. 

The octanol/water coefficient (log P) is the standard molecular descriptor used to provide the chemical property of the hydrophobicity of a molecule. Compounds with high partition coefficients usually have very low aqueous solubility. This will decrease the chance of attack by hydroxyl radicals and lead to a lower rate constant. Nevertheless, the linear relationships with log P do not reproduce similar trends of several chemical classes such as alkane and phenol. They could be either positive or negative linear relationships. Alkene (R2 < 0.67), benzene (R2 < 0.78), carboxylic acid (R2 < 0.74), and halide (R2 < 0.55) classes do not provide significant correlations. 

The octanol-air partition coefficient was calculated initially as the quotient of the octanol-water coefficient (Kow) and air-water partition coefficient (KAW) (Paterson et al., 1991a). Recently, direct measurements obtained by passing purified air over an octanol solution of the chemical have become available (Harner and Mackay, 1995 Harner and Bidleman, 1996 Harner and Bidleman, 1997 Komp and McLachlan, 1997a), and an interpolation method based on GC retention times has been proposed (Zhang et al., 1999). The measurements indicate that the calculated values may underestimate the true KqA values. It has been postulated that this is because the octanol-water partition coefficient does not represent partitioning between pure octanol and pure water, but rather between octanol saturated with water and water saturated with octanol (Hamer and Mackay, 1995). 

Patil, G.S. (1994) Prediction of aqueous solubility and octanol-water coefficient for pesticides based on their molecular structure. J. Hazard. Materials 36, 35—43. 

Geyer H, Politzki G, Freitag D. 1984. Prediction of ecotoxicological behavior of chemicals relationship between n-octanol/water coefficient and bioaccumulation of organic chemicals by alga Chlorella. Chemosphere 13(2) 269-284. 

Once the pesticides of interest have been determined, it is then necessary to examine the type of application, the likely weather conditions, the nature of the soil and water sources, and the chemical nature of the pesticide (i.e. stability, octanol-water coefficient, binding, water solubility and, where appropriate, binding capacity to soil organic matter), to determine the risk that the chemical will reach water sources. This is discussed in Section 5 of Chapter 5,... 

Abraham and co-workers 48,75-77 modified the LSER model to predict the ti-octanol-water coefficient, log P. The model appears useful also in the case of logA-derived from reversed-phase liquid chromatography ... 

Anthracene is a solid white to yellow crystal, has a weak aromatic odor, and sinks in water. Its characteristics are boiling point, 342°C melting point, 218°C molecular weight, 178.22 density/specific gravity, 1.25 at 27 and 4°C octanol-water coefficient, 4.45. It is soluble in absolute alcohol and organic solvents. Maximum absorption occurs at 218 nm. 

Solution of equations 5-1 and 5-2 requires site-specific values as well as chemical-specific values. Critical chemical-specific properties in the above equations are the Henry s law constant (H), the organic carbon/water partition coefficient (Koc), and the effective diffusion coefficient through soil (Deff). Henry s law constants are estimated using solubility and vapor pressure values obtained from data compilations. The Koc is estimated from the octanol-water coefficient (Kow) and is commonly estimated from the Hansch and Leo (1979) fragment constant approach (TPHCWG 1997b) ... 

QSARs are used routinely in predicting aquatic toxicity quickly. The USEPA has developed QSARs for all new commercial chemicals evaluated since 1981 and has about 300 QSARs for some 100 classes of compounds, most of which are based on octanol-water coefficient (Kow) and molecular weight data (USEPA, 1994). 

Yoon et al. [61] reported a comprehensive investigation of activated carbon adsorption for the removal of 17P-estradiol, 17a-ethynyl estradiol, and bisphe-nol A (a common plasticizer). They found a range of capacities when several activated carbons were tested for removal of these compounds, and the ease of removal of the three compounds corresponded quite well to their octanol— water coefficients. Table 26.2 shows some of these results, which also suggest quite a strong effect of water quality, with water 2 having almost twice the concentration of DOC as water 1. The important conclusion for water authorities was that these compounds could be successfully removed by activated carbon. 

Figure 2 Metabolic activity (based on total product formation) as a function of the density-independent (mole-fraction based) octanol-water coefficients of the solvent. (Adapted from Ref. 45.)...

Calculated from octanol/water coefficient logKgg = 2.99... 

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