Partition coefficients immiscible solvents

O ince partitioning between immiscible solvents is an equilibrium process, it should be possible to calculate partition coefficients for any solute between any two given solvents if we had a measure of the solvation forces involved. At present these forces are not that well characterized, and the reverse approach can be more enlightening—i.e., a study of how the partition coefficient varies between the systems can yield valuable insight into the types and relative magnitude of the forces involved. 

The two solvent components have thus far been assumed to be non-interactive, that is, to form ideal solutions. Since these are equivalent to those comprised of immiscible liquids, Laub and Purnell christened such systems as "diachoric" (partitioned volume) (20). That is, diachoric solutions are defined 21S those for which the solvent-solvent activity coefficients Y are unity and, hence, for which plots of solute partition coefficients against solvent composition must regress linearly. 

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... 

This experiment requires that the solvents 0 and S be immiscible then the ratio cs/co is the partition coefficient. The experiment should be carried out at sufficiently low concentrations that solute-solute interactions are negligible in both solvents. 

HSCCC is attracting attention based on its high separation scale, 100% recovery of sample, and mild operating conditions. It is a chromatographic separation process based on the partition coefficients of different analytes in two immiscible solvent systems (mobile phase and stationary phase) subjected to a centrifugal acceleration field. 

Lipophilicity is a molecular property expressing the relative affinity of solutes for an aqueous phase and an organic, water-immiscible solvent. As such, lipophilicity encodes most of the intermolecular forces that can take place between a solute and a solvent, and represents the affinity of a molecule for a lipophilic environment. This parameter is commonly measured by its distribution behavior in a biphasic system, described by the partition coefficient of the species X, P. Thermodynamically, is defined as a constant relating the activity of a solute in two immiscible phases at equilibrium [111,112]. By convention, P is given with the organic phase as numerator, so that a positive value for log P reflects a preference for the lipid phase ... 

The partition coefficient of a substance between several Immiscible solvent pairs can be combined with retention time data to confirm the identity of a substance when a pure standard is available [706]. Devised by Bowman and Beroza, the substance specific partition coefficient ("p-value") was defined as the fractional amount of substance partitioning into the less polar phase of an equal-volume, two-phase system. Only nanogram quantities of sample are required for the measurement and p-values are often sufficiently characteristic to distinguish between closely related substances. 

If a substance is soluble in both water and the organic solvent, the result of the extraction depends on the ratio of solubilities if the partition coefficient , e.g. the ratio of the solubility in water to that in ether, is large, correspondingly more ether must be used or the number of extractions must be increased. For this coefficient determines how a substance soluble in two immiscible solvents will distribute itself between them. Whether an aqueous solution should be extracted with a certain amount of ether in one portion or whether it is better to extract several times with smaller portions is... 

Based on the appropriate partition coefficient of an immiscible solvent pair it is possible to calculate the effectiveness of an extraction . 

Following the publication of the first example of fluorous biphase catalysis by Horvath and Rabai in 1994 [1], the immediate focus was to develop catalysts that would exhibit very biased partition coefficients with respect to fluorous and organic solvents. Such liquids are normally immiscible at room temperature. This was done by attaching ponytails of the formula (CH2)m(CF2) -iCF3 (abbreviated (CH2)mRf )> including arrays emanating from silicon atoms [2]. Catalysis was then effected at elevated temperatures, where fluorous and organic solvents are commonly miscible, with prod-uct/catalysis separation at the low-temperature two-phase limit. 

Liquid-hquid extraction (LLE) is widely used in many aspects of organic chemistry to purify materials. It rehes on the compounds to be separated having different partition coefficients between two immiscible solvents, such that the compound of interest preferentially partitions into one layer relative to the other component. When separating a very polar compound from a very non-polar one, this can yield extremely efficient separation. In less favourable circumstances, only a partial pre-concentration is achieved. Sometimes repetitive extractions can provide the desired pre-concentration, but with compounded losses and thus reduced sensitivity. 

Partition Coefficients of nonvl-phenyl-poly-(ethoxy)-ethanol (NPE) Surfactants. The solubility of surfactants in water and hydrophobic solvents is well documented (11,12,22), but only a few attempts at measuring partition coefficients between immiscible liquids have been reported (2,4,9,10). Partition coefficients of surfactants are of theoretical interest because of their relation to observed surfactant properties such as emulsification, wetting and detergency. Partition coefficients (K ) may be also of considerable practical value for predicting surfactant recov and recycling in industrial processes. For example, in the cold water extraction of tar sand, an effective surfactant with a high Kp could be efficiently recycled in the process water and would not follow the bitumen into the upgrading stream. 

When two immiscible solvents are placed in contact with each other and a non-ionizable compound is dissolved in one of the solvents, the compound distributes itself between the two solvents. This distribution is referred to as partitioning. The ratio of the concentrations of the compound in each phase is a constant for a specific set of solvents, pH, buffers, buffer concentrations, ionic strength and temperature. This ratio is referred to as a partition coefficient or distribution coefficient and is equal to the ratio of the solubilities in the two solvents. When the compound is a weak acid or base, the distribution of the compound can be shown to be given by the following equation for a monoprotic compound ... 

Various countercurrent chromatographic techniques have been successfully employed for the separation of flavonoids. Countercurrent chromatography is a separation technique that relies on the partition of a sample between two immiscible solvents, the relative proportions of solute passing into each of the two phases determined by the partition coefficients of the components of the solute. It is an all-liquid method that is characterized by the absence of a solid support, and thus has the following advantages over other chromatographic techniques ... 

In such systems, biotransformations are generally carried out in a reaction medium composed of an aqueous phase containing the biocatalyst and a water-immiscible organic solvent which may be the substrate itself to be converted [21] or may serve as a reservoir for substrates and products [22] (Fig. 24.2). In these conditions, a constant substrate feeding in the aqueous phase is obtained owing to the partition coefficient. The substrate is used by the biocatalyst to be converted into the product of interest, which is then continuously extracted into the organic phase. 

The partition coefficient is defined as the ratio of the concentration of a substance in the aqueous phase to the concentration of the substance in a water-immiscible solvent (usually n-octanol) as the neutral molecule. Partition coefficients are often quoted as logio values. Thus, a substance with a partition coefficient of 1000 would have a log P value of 3. This latter point on neutrality is very important. 

Centrifugal partition chromatography (CPC) relies on centrifugal force rather than gravitation for the retention of the stationary phase and solvents can be pumped at higher speeds through the instruments. In addition, no need for droplets formation is required. This allows shorter separation times, without loss of resolution, and an infinite choice of solvents with the only requirement of forming two immiscible phases, stable with the time. Chloroform-based systems have been mostly used for the separation of saponins due to their favourable partition coefficient towards such solvents. [116, 119, 120]. 

B. Partition Chromatography or Liquid-Liquid Chromatography. This method is based on the following phenomenon. When a soln of a substance is shaken with an immiscible solvent, the solute would distribute itself betw two phases and when equilibrium is reached, the relation betw concn in the 1st solvent and concn in the 2nd solvent wovid be a constant, known as "partition coefficient . As various substances have different coefficients, it is possible to effect separation of components of a mixt by means of a solvent-solvent extraction, as was described in Ref 8,p 91 and Ref 35a. Martin SyngefRef 8,p 1358) found,however, that a... 

A second physicochemical parameter influencing chemical penetration through membranes is the relative lipid solubility of the potential toxicant that can be ascertained from its known partition coefficient. The partition coefficient is a measure of the ability of a chemical to separate between two immiscible phases. The phases consist of an organic phase (e.g., octanol or heptane) and an aqueous phase (e.g., water). The lipid solvent used for measurement is usually octanol because it best mimics the carbon chain of phospholipids, but many other systems have been reported (chloroform/water, ether/water, olive oil/water). The lipid solubility and the water solubility characteristics of the chemical will allow it to proportionately partition between the organic and water phase. The partition coefficients can be calculated using the following equation ... 

The second rule of Lipinski introduces the concept of lipophilicity. Lipophilicity describes the solubility of a compound in a nonpolar solvent. Lipophilic compounds dissolve readily in nonpolar solvents such as alkanes, benzene, and fats, while nonlipo-philic compounds do not. One method for quantifying lipophilicity is to measure the equilibration of a molecule between two immiscible solvents, one polar and the other nonpolar. The ratio of the concentrations of a drug in each of the two solvents represents a partition coefficient (P) (Equation 3.1). 

Hansch and Toshio Fujita, a postdoctoral researcher in Hansch s group, designed a parameter, ttr, to estimate the lipophilicity of an R-group.3 Hansch s parameter relies on partition coefficients to measure lipophilicity. Partition coefficients, P, are equilibrium constants describing the degree to which a molecule distributes into a biphasic mixture of two immiscible solvents. Hansch used 1-octanol and water as the model solvents because these were known to simulate the lipid membrane-cytosol interface. The partition coefficient of a molecule is defined as the ratio of a molecule s concentration in an octanol layer to its concentration in an aqueous layer (Equation 12.12). 

The partitioning of a substance between two immiscible solvents is an important property of a molecule. If the two solvents are polar and non-polar, the ratio of the concentrations (when measured at equilibrium and below saturation in either solvent) is considered to describe the hydrophobicity of a compound. The partition coefficient (Kow or P) may therefore be defined as ... 

The partition coefficient (k/sw) is the ratio of concentrations of a specific compound in an immiscible solvent and water at equilibrium. Solvents with high partition coefficients can sequester the target compound, thus limiting its availability for the enzyme action in the aqueous phase [129], The partition coefficient for anthracene was determined in 15 solvents from different nature mineral oils, vegetable oils, alcohols, hydrocarbons, and others. The values of log K w obtained ranged from 3.7 (silicone oil) to 5.2 (undecanone). Among the solvents evaluated, two were selected for a further study the solvent with the lowest partition coefficient (silicone oil, log Ksw 3.7) and a solvent with an intermediate value (dodecane, log Ksw 4.5) [53],... 

The partition coefficient (P) is defined as the ratio of the equilibrium concentrations of a dissolved substance in a two-phase system consisting of two largely immiscible solvents. In the case of n-octanol and water ... 

The Partition Coefficient itself is a constant. It is defined as the ratio of concentration of compound in aqueous phase to the concentration in an immiscible solvent, as the neutral molecule. The partition coefficient (P) therefore is the quotient of two concentrations and is usually given in the form of its logarithm to base 10 (log P). The Log P will vary according to the conditions under which it is measured and the choice of partitioning solvent. 

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