Partition coefficients composite properties

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]. 

Surfactant Properties. Hydrophyllic-lipophyllic balance (HLB) was calculated from equation 2 (3) Molecular weights and chemical compositions were obtained from the literature or from the manufacturers. The partition coefficients and HLB values were not... 

The composition of the extraction liquid is very important for the magnitude of the partition coefficient of a solute. Several quantities have been studied to describe solvent properties. Snyder [20,21] grouped the relative selectivity of solvents into solvent selectivity classification groups, each group formed according to proton donating, proton accepting and dipole interaction properties. 

The study of the coprecipitation of Mg2+ in calcite has been an active area of research, frequently marked by controversy over experimental results and their applicability to natural systems. The literature on this topic is prolific, and we will not attempt to review all of it (for a general review see Mackenzie et al 1983). The literature is divided into studies where direct measurement of the solids formed from solutions have been made, studies where properties of the solids have been inferred from their interactions with solutions (e.g., Schoonmaker et al 1982), and papers where authors have estimated values of the partition coefficient by deduction (e.g., Lahann and Seibert, 1982 Given and Wilkinson, 1985a). Here the discussion will be confined to the experimental studies where the compositions of the solids have been directly determined. 

Further analysis of the physical nature of the partition coefficient reveals that it is a composite property depending on size, shape, dipole moment, and hydrogen-bonding ability. Although many researchers have attempted to replace logP with other simple parameters, only limited success has been achieved for some, but not all, molecules. It appears that for entirely new complex molecules, it still would be necessary to measure the partition coefficient, preferably validated by the conventional shake-flask method. 

Aqueous two-phase systems are characterized by a high water content, which makes them compatible with the biological material. The distribution of biomolecules between the phases is determined mainly by their surface properties and the composition of the phase system, and is denoted by partition coefficient, Kpart, defined as the ratio of its concentration in the top and bottom phase, respectively. The partitioning is independent of the absolute concentration of the substance over a fairly wide range. Any substance prefers a phase where a maximum number of interactions are possible these could be related to electrical, hydrophilic, hydrophobic and conformational forces. Reports in the literature have shown that different characteristics of the system can be manipulated in order to achieve the... 

Enantiomers have identical chemical properties in relation to their reactions with achiral reagents. Their physical properties are identical (e.g. solubility, partition coefficients, boiling points, etc.) So why the interest in enantiomer composition This arises from the fact that in a chiral environment enantiomers behave as different compounds. The natural world is constructed of chiral systems that employ structure recognition mechanisms as a regulatory function [1,4,8], The single enantiomers of racemic drugs exhibit differences in their bioavailability, distribution, metabolism, and excretion. It is often the case that one enantiomer is the more active isomer for a given... 

Partition coefficients describe not the ion exchange but the distribution of only one of them between the media. It does not accoxmt for the effect of solutions composition and properties. Because of this the partition coefficient is not suitable for evaluating ion exchange. Nevertheless, it may be associated with the selectivity and exchange coefficients. Weight concentrations in equation (2.164) may be expressed through molar or equivalent fractions of exchange capacity and molar concentrations in the solution ... 

The HPLC technique has certain advantages that allow partition coefficients to be determined relatively rapidly in comparison to the conventional shaking-flask method. The elution process also makes it feasible to run mixture of solutes and yield results relatively free of solute-solute or solute-impurity interactions with a column giving good separation. Basically, the precision of the method depends on whether the value of yw/7o solute in the octanol-water system [Eq. (5)] can be effectively simulated by the column composition. It is therefore important that efforts be expanded to ensure that the properties of the column environment accurately reflect the bulk solvent-water (e.g., octanol-water) characteristics. If the solute can truly be equilibrated between mobile and stationary phases during elution, its retention time is determined by the ratio of the activity coefficients (i.e., partition constant) in the mobile and stationary phases. When octanol and... 

Recent studies demonstrate that both the partition coefficient and the enthalpy associated with the introduction of octanol into bilayers depend on the composition (and physical properties) of the bilayers. From the data depicted in Table 8, it appears that the variation of the enthalpy is relatively small and that no obvious correlation can be defined between the partition coefficient and A/7Sc oi- More data are needed to gain an understanding of this process and its dependence on factors such as lipid acyl chain unsaturation. 

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