Water solubility coefficients

As a rule, the higher the solubility of component i in water, the lower it is in organic substance. That defines inverse correlation between Kwj and Ki vs. solubility in water CM max tmn, provides an opportunity to evaluate K, i value either from values of water solubility coefficient or from the octanol-water partition coefficient or even from the very structure of the adsorbate molecule when experimental data are absent. 

Figure 14.5 Water solubility coefficients (S) (bars) and plasticization factors (lines) of the EVOH amorphous fraction in PP/EVOH films at 25 °C and 0.98 water activity.

Two approaches to quantify/fQ, i.e., to establish a quantitative relationship between the structural features of a compoimd and its properties, are described in this section quantitative structure-property relationships (QSPR) and linear free energy relationships (LFER) cf. Section 3.4.2.2). The LFER approach is important for historical reasons because it contributed the first attempt to predict the property of a compound from an analysis of its structure. LFERs can be established only for congeneric series of compounds, i.e., sets of compounds that share the same skeleton and only have variations in the substituents attached to this skeleton. As examples of a QSPR approach, currently available methods for the prediction of the octanol/water partition coefficient, log P, and of aqueous solubility, log S, of organic compoimds are described in Section 10.1.4 and Section 10.15, respectively. 

A series of studies has been made by Yalkowsky and co-workers. The so-called general solubility equation was used for estimating the solubility of solid nonelectrolytes [17, 18]. The solubility log S (logarithm of solubility expressed as mol/L) was formulated with log P logarithm of octanol/water partition coefficient), and the melting point (MP) as shown in Eq. (11). This equation generally... 

S. W. Karickhoff and D. S. Brown, determination of Octanol Water Distribution Coefficients, Water Solubilities, and Sediment/Water Partitions Coefficientsfor Hydrophobic Organic Pollutants, EPA-600/4-79-032, report, EPA, Washington, D.C., 1979. 

Table 14. Effect of Siloxane Molecular Weight on Water Solubility and Octanol-Water Partition Coefficient...

The solubility coefficient S is used as a measure of water solubility. It is the ratio between the concentrations in water and air phases at equilibrium. Ethanol, a very soluble gas, has a solubility coefficient of 1 100 at, 37 C while the coefficient for nitrous oxide, a poorly soluble gas, is 0.1.5. 

TABLE 20.7 Conformational Coefficients for Water-Soluble Polymers in 0.05 N Sodium Nitrate with TSK-PW Columns... 

Closely related to water solubility as a polarity measure is the partition coefficient of a substance between water and an immiscible organic solvent. Most commonly the organic solvent is selected to be n-octanol, and the symbol P is given to the octanol/water partition coefficient. Then log P is a quantitative measure of hydro-phobicity and, therefore, of nonpolarity. Table 8-3 gives log P values for many of... 

It should be recognized that all plastic materials over a time period allow a certain amount of water vapor, organic gas, or liquid to permeate the thickness of the material. It is only a matter of degree of permeation between various materials used as barriers against vapors and gases. It has been found that the permeability coefficient is a function of the solubility coefficient and diffusion coefficient. The process of permeation is explained as the solution of the vapor into the incoming surface of the barrier, followed by diffusion through the barrier thickness, and evaporation on the exit side. 

The toxicological or cumulative effect of illicit drugs on the ecosystems has not been studied yet. Moreover, their fate and transport in the environment is to a big extent still unknown. Due to their physical-chemical properties (octanol-water partition coefficient, solubility, etc.) some of them, such as cannabinoids, are likely to bioaccumulate in organisms or concentrate in sediments whereas the rest, much more polar compounds, will tend to stay in aqueous environmental matrices. However, continuous exposure of aquatic organisms to low aquatic concentrations of these substances, some of them still biologically active (e.g., cocaine (CO), morphine (MOR) and MDMA) may cause undesirable effects on the biota. 

The BUSES model provides an estimate of the organic carbon/water partition coefficient (Koc) based on the octanol/water partition coefficient (Kow)- From these data, it is evident that the methyltins are less likely to partition onto organic carbon (in sediments, soils, biota) than are the butyl- and octyltin compormds due to then-lower partition coefficients and higher water solubilities. The 7/oc value can then be used to derive sohds/water partition coefficients in suspended matter, in sediment, and in soil using values of 10%, 5%, and 2% for organie carbon, representing typical organic carbon contents of suspended matter, sediment, and soil, respeetively. 

As with water solubility data, there is eonsiderable uncertainty associated with some of the log Wqw values reported in the lUCLID data sets, with impurities in the substances possibly contributing to increased water solubility and, hence, a lower than expeeted partition coefficient. 

As most organotins decompose, boiling points of 250 °C were assumed in the absence of a "true boiling point. The values for Henry s law constant and organic carbon/water partition coefficient were all derived from EUSES unless otherwise indicated. The chlorides were chosen as soluble salts in this table toxicity is independent of salt (see section 8), and soluble salts maximize likely environmental exposure, giving worst case in modelling environmental fate. 

Swann R, Laskowski D, McCAll P, et al. 1983. A rapid method for the estimation of the environmental parameters octanol/water partition coefficient, soil sorption constant, water to air ratio, and water solubility. Residue Rev 85 18-28. 

R is the gas constant Dq and activation energy Eu are constants derived from an Arrhenius plot for diffusion coefficients applying at different temperatures, and solubility coefficient was obtained from a separate permeation test at TiK. Suitable testing using a specially constmcted permeation cell water-cooled at one end provided good validation data. 

An important factor in determining the course of uptake, transport, and distribution of xenobiotics is their polarity. Compounds of low polarity tend to be lipophilic and of low water solubility. Compounds of high polarity tend to be hydrophilic and of low fat solubility. The balance between the lipophilicity and hydrophilicity of any compound is indicated by its octanol-water partition coefficient (K J, a value determined when equilibrium is reached between the two adjoining phases ... 

It is poorly soluble in acetone, 2-butanone, ethyl acetate, acetonitrile, and DMF, and insoluble in alcohols, petroleum ether, and diethyl ether. The partition coefficients of a number of solutes between PCL and water have been measured and correlated with octanol-water partition coefficients (Fig. 9) (58,59). The linear correlation (Eq. 2) when combined with the water solubility of the solutes serves as a method of estimating the solubility of drugs in PCL from first principles. ... 

The penetration of ions from the subphase into the shell of spread particles is a general phenomenon and can be used to modify and functionalize the particle surface. For example, metal ions, such as Ba and Fe, or cationic polyelectrolytes, such as the polycation of polyallylamine, can be adsorbed at anionic particles, while anionic water-soluble dyes, such as phthalocyanine tetrasulfonic acid and 1.4-diketo-3.6-diphenylpyrrolo[3.4-c]pyrrole-4, 4 -disulfonic acid (DPPS) [157], can be adsorbed at cationic particles. However, since only a monolayer of the dye is adsorbed, a deep coloration of the particles is not obtained unless a dye with very high absorption coefficient is used [156],... 

In 1868 two Scottish scientists, Crum Brown and Fraser [4] recognized that a relation exists between the physiological action of a substance and its chemical composition and constitution. That recognition was in effect the birth of the science that has come to be known as quantitative structure-activity relationship (QSAR) studies a QSAR is a mathematical equation that relates a biological or other property to structural and/or physicochemical properties of a series of (usually) related compounds. Shortly afterwards, Richardson [5] showed that the narcotic effect of primary aliphatic alcohols varied with their molecular weight, and in 1893 Richet [6] observed that the toxicities of a variety of simple polar chemicals such as alcohols, ethers, and ketones were inversely correlated with their aqueous solubilities. Probably the best known of the very early work in the field was that of Overton [7] and Meyer [8], who found that the narcotic effect of simple chemicals increased with their oil-water partition coefficient and postulated that this reflected the partitioning of a chemical between the aqueous exobiophase and a lipophilic receptor. This, as it turned out, was most prescient, for about 70% of published QSARs contain a term relating to partition coefficient [9]. 

Despite the work of Overton and Meyer, it was to be many years before structure-activity relationships were explored further. In 1939 Ferguson [10] postulated that the toxic dose of a chemical is a constant fraction of its aqueous solubility hence toxicity should increase as aqueous solubility decreases. Because aqueous solubility and oil-water partition coefficient are inversely related, it follows that toxicity should increase with partition coefficient. Although this has been found to be true up to a point, it does not continue ad infinitum. Toxicity (and indeed, any biological response) generally increases initially with partition coefficient, but then tends to fall again. This can be explained simply as a reluctance of very hydrophobic chemicals to leave a lipid phase and enter the next aqueous biophase [11]. An example of this is shown by a QSAR that models toxicity of barbiturates to the mouse [12] ... 

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