Octanol-water coefficient materials

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

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. 

Octanol/Water Coefficient 59000 34000 (Calculated). Log P = 4.68. Chemical Fate Information Bioconcentration Factor = 490 (calculated). Other Information Aerobic Biodegradation 50% after 2.9 hours. Rapid degradation via hydrolysis 93% after 24 hours at pH 7.0 and 25°C. Tests indicate this material will not bioaccumulate or persist in the environment. 

The data presented here indicates that the extent of binding for a particular compound is related to the octanol/water partition coefficient for that compound. This is very similar to the sorption of compounds from water to sediment. Compounds with log Kow values less than four (such as Lindane) will probably not be bound to an appreciable extent in the environment. Compounds with very high log Kow values (DDT and DEHP) may be bound to a significant extent. The extent of binding will depend on both the concentration of humic material and on the nature of the humic material. The humic materials used in this research showed dramatically different affinities for DDT. The reasons for this are poorly understood and deserve further study. 

The Rvalues are partition coefficients. The assumption that these are real constants Is seldom completely true, of course, because equilibrium Is rarely achieved and because the equilibrium ratios generally are not the same for all concentration levels. Moreover, It Is difficult to find the needed Information, and one must often accept a single literature value as typical of a given Intermedia transfer. When the organic content of the soli Is known or can be accurately estimated, one can usually derive Kgw from a compound s aqueous solubility, S, or Its octanol/water partition coefficient, KQW (14) Values of Kpa, namely "bloconcentratlon factors" between feed and meat animals (15,16), can also be derived from S or KQW. Bloconcentratlon factors between water and fish are well documented (14) A considerable weakness exists In our perception of the proper estimates to use for partition coefficients between soli and edible crop materials. Thus, at one time, two of the present authors used a default value of Kgp = 1 for munitions compounds that are neither very soluble In water nor very Insoluble (4) at another time, a value of was assumed for compounds with very low values of Ksw, l.e., polybromoblphenyls (6). 

Partition constant tor the distribution of various aromatic substances (mono-, di-, tri-, and tetramethyl, and chlorobenzenes) between water and an aquifer material (0.15 % organic carbon) as a function of the octanol-water partition coefficient, K<,w. The values of log Kp have been adjusted to be correct for a sorbent of 100 % organic carbon. Kow is defined for the partition of a substance A between octanol water Kow = [A0Ct]/[A(aq)]. 

Many bixxer compounds contain both hydrophobic and hydrophilic sites which can alter cell membranes through penetration. There is a correlation between bitter intensity and hydrophobicity-solubility indexes such as fee octanol/water partition coefficient, lo (7). Penetration may directly affect cAMP phosphodiesterase as part of fee transduction process (see below). A bitter receptor protein may be involved wife certain bitters, such as specific structural requirements wife fee bitter tasting dipeptides and denatonium salts (27). The latter is used in some consumer products to avoid accidental ingestion. A receptor mechanism is also supported by fee existence of a genetic "taste blindness" for some bitter materials (see below). 

Octanol/Water Partition Coefficient (Kow) — the equilibrium ratio of the concentrations of material partitioned between octanol and water. This coefficient is considered to be an index of the potential of a chemical to be bioaccumulated. Higher values of K, are associated with greater bioaccumulative potential. 

The exchange of chemical compounds from the gas phase to a surface, e.g. atmospheric particles, soil, water, vegetation or other surfaces, is controlled by the affinity of the compound to this surface. The ratio of vapour pressure to water solubility can be used as indicator between levels in the atmosphere and water surface (Henry s law H constant). In many model calculations, the ratio between POP levels in octanol and water, the octanol-water partitioning coefficient (Kow), is used as reference for the distribution of POP in organic material [14]. Consequently, the expression ///RT (Cair/Cwalcr) and Kow (Coctanoi/Cwater) provide the octanol-air partitioning coefficient (Koa) ... 

The bioconcentration factor (BCF) is an expensive and difficult test and can be replaced by an estimation of relative lipophilicity of the material, the partition coefficient (log P). This physico-chemical parameter (log P) is determined by measuring the distribution ratio of the material between octanol and water (Droy, 1993 McKim et al., 1985). The logarithm of this ratio is the partition coefficient (log P) however, materials with a log P of <1 or > 6 or 7 are not expected to bioconcentrate. Graphic representation of the relationship between the octanol-water partition coefficient, log P, and predicted bioconcentration, log BCF, has the... 

Apart from the hydrophobic interactions provided by the alkyl part of the molecule, octanol has also hydrogen-bond acceptor and donor functions like lipid membranes have. This property of n-octanol made the octanol-water distribution coefficient that widely used. However, n-octanol or reversed phase materials cannot mimic the interfacial character of the bilayer structure. The ionic interactions between membrane phospholipids and solute are also not represented in the properties of octanol or reversed phase materials. To overcome this issue, alternative stationary phases... 

Materials that are solubilized in polyethylene glycol can be solubilized in the polyoxyethylene chains on the surface of a nonionic micelle. Ismail, Gouda, and Motawi found that the micellar partition coefficients of barbiturates in polysorbates 20, 40, 60, and 80 is a function of the solute substituents and is proportional to the octanol-water partition coefficient of the barbiturate. Similarly, Ikeda, Kato, and Tukamoto showed that the solubilization of alkyl barbiturates by polyoxyethylene lauryl ether is not dependent upon the number of carbons in the substituents. Since the different polysorbates contain different aliphatic groups, the rather small dependence of solubilization upon polysorbate number (i.e., upon alkyl chain length) suggests that the barbiturates are not solubilized primarily in the hydrocarbon portion of the micelle. Gouda, Ismail, and Motawi showed that the solubilization of barbiturates in polyoxyethylene stearates is proportional to the number of polyoxyethylene units in the surfactant. 

Figure 9.28. The distribution of nonpolar organic substances between aquatic solids and water (as given by the distribution coefficient Kp) is dependent upon the lipophilicity of the compound and the organic C content of the adsorbing material (foe = weight fraction). The solid phases considered here are coastal sea and lake sediments, river sediments, solids from aquifers and biomass (activated sludge). The octanol/water distribution coefficients are, respectively 500, 2400, 11,200 and 52,000 for chlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene and 1,2,4,5-tetrachlorobenzene. (Modified from Schwarzenbach and Westall, 1980).

The IPAH model incorporated a number of factors that can modify the toxicity of the sediment-borne PAHs. Equilibrium partitioning was used to estimate the concentration of each PAH in the pore water of the sediment. The assumption was that the pore water material is the fraction that is bioavail-able. QSAR was also used to estimate the interstitial water concentration based on the octanol-water partition coefficient of several PAHs. Amphipods were used as the test organism to represent environmental toxicity. A toxic unit (TU) approach was used and the toxicity is assumed to be additive. The assumption of additivity is justified since each of the PAHs has a similar mode of action. Finally, a concentration-response model was formulated using existing toxicity data to estimate the probability of toxicity. 

Rasmussen etal. (1979) attempted to measure by gas chromatography the n-octanol-water partition coefficients of the major kava lactones and found that these compounds could not be detected in the aqueous phase. Since the bulk of the earlier pharmacological work had concentrated on the water-soluble lactones, Buckley etal. (1979) investigated the biological activity of the water-soluble fiactions of kava obtained by steam distillation. They found that the fractions so obtained contained biologically active materials that were relatively free of any lactones. These materials suppressed spontaneous activity in... 

Analogous partition data are available for solvents other than octanol, e.g. olive oil, and these may be more pertinent in certain situations. However, log P values based on octanol/water partition are easily accessible for thousands of substances and, for most of the compounds found in perfumery, may be estimated reasonably well using one of the mathematical prediction models described in the literature [the two most well known are those due to Rekker (1977), and to Leo et al. (1971)]. Additionally, it is often true that for many materials partition coefficients determined in different solvent-water systems often correlate strongly with one another. 

By their Code of Ethics ETAD member companies are required to provide a Material Safety Data Sheet (MSDS) that contains parameters relevant to the ecotoxicity (LCjo, EC50, elimination, COD, BOD for some categories of dyes the partition coefficient n-octanol/water is available). 

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