Partition coefficient values

It should finally be noted that the amount of the neutral and zweitterionic forms of a compound in solution is determined by its tatuomeric equilibrium constant, defined as Kz = cz/cn. Therefore, the neutral species and the zwitterion coexist around the isoelectric pH, and membrane permeation is conditioned by Kx and by the partition coefficient values of both tautomers. 

PC = partition coefficient values from Adson et at. (1995). Molecular density p 1.0 g/mL. Diffusion coefficient and molecular radius calculated by Eqs. (41) and (42). 

The solubilities in water and octanol of the pyrazino[l,2-A]quinazolones 23 (R1 =Me, R4 = H R1 = R4 = Me) with various N-2 substituents were determined. Solubility ratios and partition coefficient values were fitted to a predictive equation to evaluate the possibility of aqueous solubility estimates <1997IJP233>. 

Despite these reservations, environmental distribution values may be considered valid for the sorption process, to a first approximation. On this basis, it can be concluded that detected environmental partition coefficients show the clear affinity of surfactants to particulate material. The affinity is higher for cationic surfactants than for other surfactants, as shown by the high partition coefficient values (Table 5.4.1). Partition coefficients are also higher for the water column than for sediments (Table 5.4.1), and it is difficult to offer an explanation for this, bearing in mind the many factors affecting the partition coefficient in both natural water and sediment. 

Using predictive models for measuring environmental chemodynamics of organic pollutants in complex mixtures requires literature data on partition coefficient values. In some cases the values cited are not strictly experimental, being derived from linear free energy relations, while in others wide variations are reported in experimental values. The main problem is how one should evaluate which values are correct. Thus, Table 2 provides some basis to discriminate between reported values of partition coefficients, as well as predictive equations for partition coefficient calculations [21,62,65-85]. 

Bennett and Larter (1997) also studied the solvation of alkylphenols in crude oil-water systems at equilibrium to obtain partitioning coefficients under variable temperature, pressure, and water salinity concentration. Alkylphenol depletion from crude oil, expressed by phenol, cresols, and 3,5 dimethyl phenol, versus temperature in a range of 25-125°C, is given in terms of partition coefficient (P) values (Fig. 16.22). Partition coefficient values increase with addition of alkyl groups to the phenol nucleus. Note that the alkylphenol partition coefficient curves for different isomers tend to converge at higher temperatures and, as a consequence, differences between phenol and p-cresol decrease with increases in temperature. Similar results for oil-deionised water and oil-brine experiments show that increasing temperature leads to a decrease in partition coefficient values. 

DNB will remain in the water column and <1% will be adsorbed to suspended solid and sediment (ERA 1991b). 1,3,5-TNB with an octanol-water partition coefficient value lower than 1,3-DNB (see Table 3-2), is expected to exist almost exclusively in the water column. 

Table 2 Migration Factors and Partition Coefficient Values of Cephalosporins in Various Systems... 

There are two methods for crossing the BBB passive diffusion or active transport. Passive diffusion is the route preferred by most neuroactive drugs. Lipid solubility is a desired chemical property for a molecule to diffuse across the BBB. For a molecule to cross the BBB by passive diffusion it should have a molecular weight less than 650 g/mol and should have a logP (logarithm of the octanol-water partition coefficient) value... 

The substance with higher water partition coefficient values can penetrate... 

Click on the Compute button to calculate physiochemical properties including the number of hydrogen bond acceptors and donors, XlogP (partition coefficient) values, molecular weights, number of rotatable bond, and the Topological Polar Surface Area (TPSA) of compounds. 

Table 4.2 Partition coefficient values of the four dry building materials.

There already exists a substantial literature devoted to the estimation of various material properties with the help of additive structual increments (Reid et. al, 1987, Van Krevelen, 1990). The regular solution theory in combination with additive structural increments has a wide application for estimating the relative solubilities of organic substances in polymers and the solubility of polymers in various solvents (Barton, 1983) and will be described later in this chapter. When estimating partition coefficient values, one is quickly confronted with this method s application limits, particularly with polar and non-polar structures, for example the partitioning of substances between polyolefins and alcohol (Baner and Piringer, 1991). 

The partition coefficient values in the third column of Table 4-7 were estimated using Eq. (4-101). In the last column of this table are the estimated partition coefficient values for i in a polyolefin/water system calculated by dividing the KCfW by Kc,/p to get KP/W (Eq. 4-35). 

Three different approaches have been presented for estimating the partitioning of solutes between plastics and liquids. In the context of evaluating the output from these different approaches it is also useful to define the expected experimental ranges and limits for partition coefficients based on the solutes, plastic and contacting liquid phases involved. Table 4-9 shows approximate upper and lower limits for partition coefficients one may normally encounter in plastic/food systems based on the polarities of the solutes, plastics and foods. The table also gives approximate ranges of partition coefficient values for various solutes between typical food contact plastics and liquid phases. 

Table 4-9tu Approximate partition coefficient values for various plastic/food package systems.

To further illustrate the possible experimental ranges of partition coefficients, examples of experimentally determined partition coefficient ranges are given below. In Table 4-10 data for BHT partitioned between polypropylene and different food and food simulants at 40 °C and in Table 4-11 for d-limonene partitioned between LDPE and various foods and food simulants are shown. The partition coefficient values in these tables are representative examples of the ranges one can expect with polyolefins which are the most common food contact plastics. 

Handbooks. Tabulations of traditional properties of chemicals (Tb, Tm, p, Saq) are often available in publications by fine-chemical manufacturers (e.g., Fisher Scientific, Web page www.fishersci.com). Other collections of these parameters, surface tension, the specialized partition coefficient values, and kinetics of transformations include Winholz et al.,54 Howard et al.,55 Dean,56 Lide,57 Mackay et al.,58 Howard and Meylan,59 Tomlin,60 Yaws,61 and Verschueren.62... 

Table II gives binding constants and partition coefficient values (P) calculated by the NLLSQ program using reported capacity factors for solutes bound to micelles. These values were determined on two different LC columns. One to one equations were used to obtain the binding constants (Equation 1). This table shows the ability of this particular NLLSQ routine to perform linear least square approximations. NLLSQ programs usually are less accurate at this. The mobile phase in this study was composed of solutions of sodium dodecylsufate (SDS). These binding constants were converted to partition coefficients by Equation 4.

Partition Coefficients. Values for log P are given in a number of monographs. Where the pH of the aqueous phase is stated, the values given are apparent coefficients at that pH (not ion-corrected). Where no pH is stated for the aqueous phase, it can be assumed that log P is for the neutral form of the substance even though it is potentially ionisable. The values given are approximate only but they serve to indicate the characteristics of the substance when it is submitted to an extraction process. 

Because of the wide range of partitioning coefficient values, in most cases the decimal logarithm of K i, is used, and it is denoted as LogP ... 

Extensive efforts have been made to develop quantitative structure/activity relationships (QSARs) that predict membrane transport (16, 17). Particularly extensive use has been made of log P (log solvent/water partition coefficient values) and the Hansch equation (Equation 14.3) ... 

The partition coefficient is a measure of the quality of a fuzzy partition. The closer C(P) is to 1, the better the fuzzy partition P will be. The outputs of a fuzzy clustering algorithm for several different values of n may be compared by means of the partition coefficient. The best partition (and the best n) is that associated with the highest partition coefficient value. 

It is widely accepted that the two most important physicochemical parameters that determine a molecule s skin permeability are a) its lipophilicity, with a log (octanol/water partition coefficient) value of 2 being quite favorable, and b) its molecular size— smaller compounds permeating better than big ones. " Thus, it is no surprise that the passive transdermal delivery of peptides and proteins, which are typically either very polar (or charged) and/or of high molecular weight (>1000 Da), is extremely inefficient and rarely results in fluxes, which would elicit significant therapeutic effect. 

Partition coefficients values for different vegetable oils vary considerably and are affected by the purity of the oil see Table 1V.< ... 

---