Partition coefficient definition

Solubilisation is usually treated in terms of the pseudophase model, in which the bulk aqueous phase is regarded as one phase and tire micellar pseudophase as another. This allows the affinity of the solubilisate for the micelle to be quantified by a partition coefficient P. Different definitions of P can be found in the literature, differing in their description of the micellar phase. Frequently P is... 

The constant is not a tme partition coefficient because of difference, — V, includes the soflds and the fluid associated with the gel or stationary phase. By definition, IV represents only the fluid inside the stationary-phase particles and does not include the volume occupied by the soflds which make up the gel. Thus is a property of the gel, and like it defines solute behavior independently of the bed dimensions. The ratio of to should be a constant for a given gel packed in a specific column (34). 

A problem of all such linear QSPR models is the fact that, by definition, they cannot account for the nonlinear behavior of a property. Therefore, they are much less successful for log S as they are for all kinds of logarithmic partition coefficients. 

A general definition of log P and log D, in its simplest form, can be given as the logarithm of the ratio (P or D) of the concentration of species of interest (the drug in a pharmaceutical context) in each phase, assuming the phases are immiscible and well separated prior to analysis. P is defined as the partition coefficient, whereas D is the distribution coefficient. However, the simplest form does not reveal some of the intricacies of the determination and use of these parameters, and further explanation is necessary. 

Moreover, as the ratio uf/uf is by definition the partition coefficient of I, P , this parameter can be defined by putting into evidence the ratio of the ion activities in the Nernst equation ... 

If chemical equilibrium between the melt and the solid is assumed throughout the melting column, the definition of the partition coefficient (D) ... 

In whole tissue or cell monolayer experiments, transcellular membrane resistance (Rm = Pm1) lumps mucosal to serosal compartment elements in series with aqueous resistance (R = P ). The operational definition of Lm depends on the experimental procedure for solute transport measurement (see Section VII), but its magnitude can be considered relatively constant within any given experimental system. Since the Kp range dwarfs the range of Dm, solute differences in partition coefficient dominate solute differences in transcellular membrane transport. The lumped precellular resistance and lumped membrane resistance add in series to define an effective resistance to solute transport ... 

Equilibrium. Equilibrium between compartments can be expressed either as partition coefficients K.. (i.e. concentration ratio at equilibrium) or in the fugacity models as fugacity capacities and Z. such that K.. is Z./Z., the relationships being depicted in Figur 1. Z is dellned as tfte ratio of concentration C (mol/m3) to fugacity f (Pa), definitions being given in Table I. 

Figure 1. Relationships between fugacity capacities and partition coefficients. See Table 1 for symbol definitions.

The correlation (or lack of correlation) of other physiochemical characteristics has not yet been established. For instance, are all surfactants irritants Can one classify severity by the size of the molecule Can octanol water partition coefficients predict irritation potential does a propensity to partition out of the ocular fluid mean that a compound presents more of an irritation hazard than one which is more water soluble Theoretically, these data should reflect the ability of a compound to penetrate the eye and cause an irreversible lesion. However, until definitive data are available, physical and chemical parameters will probably have limited utility in an overall assessment of irritation. 

K generally varies only by factors of three to five for a given solute (12). K typically correlates well with physico-chemical properties of the sorbate, such as aqueous solubility (S) or the octanol-water partition coefficient (K ), again suggesting that hydrophobic interaction predominates. The correlation of Koc with K has led to the definition of linear free-energy relationships (LFER) of the form... 

Although this equation reduces to an identity whenever solute-solvent interactions are embodied in the definition of the Henry s law standard state (cf section 10.2), it must be noted that K[ is the molar ratio of trace element i in the two phases and not the weight concentration ratio usually adopted in trace element geochemistry. As we will see later in this section, this double conversion (from activity ratio to molar ratio, and from molar ratio to weight concentration ratio) complicates the interpretation of natural evidence in some cases. To avoid ambiguity, we define here as conventional partition coefficients (with the same symbol K ) all mass concentration ratios, to distinguish them from molar ratios and equilibrium constants. 

For quantitative extraction of two solutes i and j, both P, and Pj should be maximised. If the ratio of the two partition coefficient is more important then the individual partition coefficients, a,j should be used as optimisation criterion (by definition indices of the partition coefficient are attached as such that is always smaller or equal to 1). Optimal values for a,j are those values which are equal to or which approximate unity ( ,v= I). 

In Eq. (MM), F (from /liter-associated material) is the concentration of the SOC in air that is in the particle phase, in ng m 3, A (from the use of an adsorbent to collect the gas) is the gas-phase concentration in ng m 3, and TSP is the concentration of total suspended / articles, in pg m 3. (Note that this is the definition in common usage today however, some earlier papers (e.g., Yamasaki et al., 1982 Pankow, 1987) defined Kp as the inverse, i.e., as equal to /((TSP) F.) Because measurements of F, TSP, and A are difficult to make in an artifact-free manner and because equilibrium may not always hold in the atmosphere (see later), the quantity (F TSP) A is often referred to as the measured partition coefficient, in contrast to the true, ther-... 

Distribution constant. KQ(K). The ratio of the concentration of a sample component in a single definite form in the stationary phase to its concentration in the mobile phase at equilibrium. Both concentrations should be calculated per unit volume of the phase. IUPAC recommends this term rather than partition coefficient. 

Nonreceptor-Mediated Drug Action. At least one important class of drugs, the general anesthetics, has been assumed not to owe its therapeutic activities to a specific receptor process. Anesthetic potency shows an excellent linear correlation with partition coefficient and this has been extrapolated to a definition of action at a lipid site. The phospholipids of cell membranes, particularly nerve cells, have been considered as principal targets for general anesthetic action. It has been hypothesized... 

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