Octanol/water partition coefficient quantitative structure-activity

There is a continuing effort to extend the long-established concept of quantitative-structure-activity-relationships (QSARs) to quantitative-structure-property relationships (QSPRs) to compute all relevant environmental physical-chemical properties (such as aqueous solubility, vapor pressure, octanol-water partition coefficient, Henry s law constant, bioconcentration factor (BCF), sorption coefficient and environmental reaction rate constants from molecular structure). 

The octanol-water partition coefficient, Kow, is the most widely used descriptor of hydrophobicity in quantitative structure activity relationships (QSAR), which are used to describe sorption to organic matter, soil, and sediments [15], bioaccumulation [104], and toxicity [105 107J. Octanol is an amphiphilic bulk solvent with a molar volume of 0.12 dm3 mol when saturated with water. In the octanol-water system, octanol contains 2.3 mol dm 3 of water (one molecule of water per four molecules of octanol) and water is saturated with 4.5 x 10-3 mol dm 3 octanol. Octanol is more suitable than any other solvent system (for) mimicking biological membranes and organic matter properties, because it contains an aliphatic alkyl chain for pure van der Waals interactions plus the alcohol group, which can act as a hydrogen donor and acceptor. 

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... 

Drug binding is enhanced by hydrophobicity in that portion of the drug that binds to the pocket toe. Quantitative structure-activity relationship (QSAR) analysis of these compounds have consistently shown that the most predictive parameter of antiviral activity is a measure of hydrophobicity, the octanol water partition coefficient (logP) [80,82,85]. These studies have also consistently shown that there is no apparent correlation between electrostatic potential or dipole moment and potency. 

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. 

Common unspecific mode of action of all organic compounds has been taken up in quantitative structure-activity relationships (QSARs see Chapter 5) as the concept of baseline toxicity and in toxicokinetics as the body burden concept (see Chapter 2). Baseline toxicity refers to the idea that a minimum toxicity expectation may be formulated for any given organic compound based on considerations of a compound s partition properties between hydrophilic and lipophilic chemicals (e.g., between water and octanol). Commonly, this is expressed in terms of the octanol-water partition coefficient (K0,J of a chemical. The partition coefficient allows estimations of a local concentration or body burden for each individual chemical in the mixture. Assuming that this produces the same toxic effect (disturbances of cell membranes), it is then possible to anticipate joint narcotic action by adding together the respective local concentrations or body burdens for each individual mixture component. 

From this log value we estimated by means of a Quantitative Structure-Activity Relationship (QSAR) of Mackay [345] a BCFw for musk xylene of about 3,800 and a BCFl of 79,200 for this compound in fish [346]. The predicted BCFw of musk ketone (log K(, = 4.20 [344]) was 760 and the BCFl 15,800 [346]. These data, the chemical structures, n-octanol/water partition coefficients (log Ko s)... 

A convenient point of departure is that of the increasingly popular quantitative structure activity relationships (QSAR) mentioned above [696,699,11], which derive adsorbate-adsorbent interaction indices from, for example, water solubility data, molecular connectivities [697], n-octanol-water partition coefficients, reversed-phase liquid chromatography capacity factors [723], or linear solvation energy relationships (LSER). 

POP) in the environment, that is, how the chemical in water will be taken up by animal and vegetable life and by soils and sediments. This coefficient is also used as an indicator of chemical hydrophobicity in most quantitative structure-activity relationship (QSAR) models for designing new drugs (Franke, 1984). Experimental values of the octanol-water partition coefficient for the hydrophobic chemicals common in the chemical industry vary... 

BR is the relative biologic activity under investigation, for example the molar EDr>o or the percent response at a given dose. Log P is the logarithm of the octanol-water partition coefficient, a is the approprite Hammett signa constant (electronic in nature), and Es is the Taft steric parameter. With the important demonstration by Hansch that the partition coefficient is often an additive constitutive property, all of the physical parameers may be obtained from the literature. A second important contribution by Hansch is the recognition that the use of statistical techniques is essential to the analysis of quantitative structure-activity relationships. To develop an equation such as that above, one feeds the... 

Three major approaches to the prediction of aqueous solubility of organic chemicals using Quantitative Structure Activity Relationship (QSAR) techniques arc reviewed. The rationale behind six QSAR models derived from these three approaches, and the quality of their fit to the experimental data are summarized. Their utility and predictive ability are examined and compared on a common basis. Three of the models employed octanol-water partition coefficient as the primary descriptor, while two others used the solvatochromic parameters. The sixth model utilized a combination of connectivity indexes and a modified polarizability parameter. Considering the case of usage, predictive ability, and the range of applicability, the model derived from the connectivity- polarizability approach appears to have greater utility value. 

The octanol/water partition coefficient is one of the most frequently used descriptors in biological quantitative structure activity relationships. It is considered to reflect the hydrophobicity of a molecule and therefore to be relevant both for correlating the transport properties and the receptor binding of biologically active molecules. Since pharmacological and toxicological research often concerns poorly characterized or not yet synthesized molecules, there is a... 

In recent years there has been a notable increase in research on structure-activity relationships (SARs), also called quantitative structure-activity relationships (QSARs), used to assess the toxicity of substances for which there are few experimental data. This approach involves establishing mathematical relationships derived from computer modeling, based on known toxicity data of similar (or dissimilar) types of compounds, octanol-water partition coefficients, molar connectivity index values, and other parameters. A detailed discussion on this subject is beyond the scope of this book. 

Offshore oil production requires many chemicals for well drilling, for the treatment of the produced oil, for the treatment of gas, and for the stimulation and workover of the wells [100,101]. Altogether,25 classes of chemicals are used in offshore oil production [102]. The chemicals are undergoing increasingly detailed testing. As in other Quantitative Structure-Activity Relationships (QSAR), the octanol/water partition coefficient (Kq, ) is a crucial factor determining the environmental behavior and toxicity of the chemicals [103]. Toxicity... 

In qualitative and quantitative structure activity relationship studies, the lipophilic character of a compound is usually modelled by the logarithm of the octanol water partition coefficient, i.e., log P. 

The use of computer techniques in the correlation of biological activity with substrate physical-chemical properties has received much attention in the area of medicinal chemistry. The use of these techniques, denoted Quantitative Structure Activity Relationships (QSAR), were developed mostly by Hansch and his coworkers eind have been reviewed by Tute te), Purcell et. al. (9) and Dunn (10). These techniques were utilized by Greenberg (1 l) ln the correlation of odor threshold and suprathreshold data with Log P, the log (n-octanol/water partition coefficient). In the same study it was reported that steric and polar effects as measured by the Taft Steric and Polar Constants poorly correlated with odor intensity data. 

The bioaccumulation of a substance into an organism is not an adverse effect hazard in itself. Bioconcentration and bioaccumulation may lead to an increase in body burden which may cause toxic effects due to direct and/or indirect exposure. Bioaccumulative substances characterized by high persistence and toxicity, negligible metabolism and a log ATow between 5 and 8 may represent a concern when widely dispersed in the environment. The potential of a substance to bioaccumulate is primarily related to its lipophilicity. A surrogate measure of this quality is the n-octanol - water partition coefficient (/fow), which is correlated with bioconcentration potential. Therefore, /fow values are normally used as predictors in quantitative structure - activity relationships (QSARs) for bioconcentration factors (BCFs) of organic non-polar substances. 

The octanol-water partition coefficient scale may not be the best tool for hydrophobicity evaluation. The ability of MLC for hydrophobicity measurement and some studies on quantitative structure retention activity relationships (QSAR) are described in Chapter 9. Chapters 10 and 11 contain selected examples of applications in the analysis of a variety of samples, especially pharmaceutical preparations and physiological fluids, some of them are taken from the authors own experience. Details on the nature of the sample, stationary phase, mobile phase composition, detection wavelength, and figures of merit, are tabulated at the end of each of these... 

Mono-substituted benzene, di-substituted benzene, functional groups, acute toxicity. Photobacterium phosphoreum, quantitative structure-activity relationships, octanol/water partition coefficient. 

Quantitative structure-activity relationships, fathead minnow, Pimephales promelas, Taft sigma constants, octanol/water partition coefficients, ketones, nitriles, alcohols, esters. 

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