Relative affinity coefficient

In this situation, it is the ratio of S to I and the relative affinity coefficients (Km and K ) that determines the extent of inhibition. 

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 ... 

If two adsorbates fill the same adsorption volume as shown by the vertical dotted line in Fig. 9.2, their adsorption potentials E and Eq will differ only because of differences in their molecular properties. Consequently, the ratio of adsorption potentials is assumed by Dubinin to be constant and he calls E/Eq the affinity coefficient which, for an adsorbate pair, is a measure of their relative affinities for a surface or their... 

One of the most important factors influencing the transfer of an anesthetic from the lungs to the arterial blood is its solubility characteristics (Table 25-2). The blood gas partition coefficient is a useful index of solubility and defines the relative affinity of an anesthetic for the blood compared with that of inspired gas. The partition coefficients for desflurane and nitrous oxide, which are relatively insoluble in blood, are extremely low. When an anesthetic with low blood solubility... 

Partition coefficient represents the equilibrium ratio of the molar concentrations of a chemical substance (the solute) in a system containing two immiscible liquids. The octanol / water partition coefficient is expressed as either Kow or P and is a descriptor of a substance s relative affinity for lipids and water. For purposes of simplification, Kow is usually reported as its common logarithm (log Kow or log P). A large log Kow value for a chemical (relative to other substances) indicates that the chemical has a greater affinity for the n-octanol phase and, hence, is more hydrophobic (lipophilic). A negative log Kow value indicates that a chemical has a greater affinity for the water phase and, hence, is more hydrophilic. 

The method can be extended to the analysis of the competition for three guests simultaneously. The results are displayed on an equilateral triangle in which each apex represents a pure guest. Various situations arise, depending on the relative affinities of the chosen host for guest A, B and C. Following Pivotar el al., [8] we may define a selectivity coefficient ... 

Adsorption equilibria are often summarized by the distribution or partition coefficient, Kd, which expresses the relative affinity for a sorbate in solution to be absorbed or desorbed (Oscarson and Hume, 1998). The distribution coefficient, Kd, is usually defined as the ratio of concentrations in the adsorbed and liquid phase, thus ... 

A number of studies have measured the activation of plasma transaminases by pyridoxal phosphate added in vitro however, it is difficult to interpret the results, because plasma transaminases arise largely accidentally, as a result of cell turnover, and the amount released will depend on tissue damage. Furthermore, there is a considerable amount of pyridoxal phosphate in plasma, largely associated with serum albumin, and the extent to which plasma transaminases are saturated will depend largely on the relative affinity of albumin and the enzyme concerned for the coenzyme, rather than reflecting the availability of pyridoxal phosphate for intracellular metabolism. Studies on erythrocyte transaminase activation coefficient are easier to interpret, because the extent to which the enzymes are saturated depends mainly on the availability of pyridoxal phosphate. 

The retention of a solute is directly proportional to the magnitude of its distribution coefficient (K) between the mobile phase (gas) and the stationary phase. The magnitude of K depends on the relative affinity of the solute for the two phases thus, the stronger the forces between the solute molecule and the molecules of the stationary phase, the larger the distribution coefficient and the more the solute is retained. It follows that the stationary phase must interact strongly with the solutes to be retained and to achieve a separation. Molecular interaction results from intermolecular forces, of which there are only two types effective in gas chromatography (GC). 

In order to avoid possible associations of the solute in the organic phase, partition coefficients should be measured at low concentrations or extrapolated to infinite dilution of the solute. They are dimensionless measures of the relative affinity of a molecule with respect to the two phases and depend on absorption, transport, and partitioning phenomena. Compounds for which F > 1 or logP > 0 are lipophilic, and compounds for which F < 1 or logF < 0 are hydrophilic. In particular, lipophilicity depends on solute bulk, polar and hydrogen-bonding effects. 

It has been shown for several systems that the partition coefficient can be approximated by the solubility of the agent in the organic phase divided by its solubility in the aqueous phase, a useful starting point for estimating relative affinities. 

A series of batch equilibrations was carried out to determine the relative affinities of selected lanthanides and actinides for niobate, zirconate, and titanate ion exchange materials as a function of pH. These affinities are expressed as distribution coefficients (l9 ), where ... 

DYNAMICS OF DISTRIBUTION The natural aqueous system is a complex multiphase system which contains dissolved chemicals as well as suspended solids. The metals present in such a system are likely to distribute themselves between the various components of the solid phase and the liquid phase. Such a distribution may attain (a) a true equilibrium or (b) follow a steady state condition. If an element in a system has attained a true equilibrium, the ratio of element concentrations in two phases (solid/liquid), in principle, must remain unchanged at any given temperature. The mathematical relation of metal concentrations in these two phases is governed by the Nernst distribution law (41) commonly called the partition coefficient (1 ) and is defined as = s) /a(l) where a(s) is the activity of metal ions associated with the solid phase and a( ) is the activity of metal ions associated with the liquid phase (dissolved). This behavior of element is a direct consequence of the dynamics of ionic distribution in a multiphase system. For dilute solution, which generally obeys Raoult s law (41) activity (a) of a metal ion can be substituted by its concentration, (c) moles L l or moles Kg i. This ratio (Kd) serves as a comparison for relative affinity of metal ions for various components-exchangeable, carbonate, oxide, organic-of the solid phase. Chemical potential which is a function of several variables controls the numerical values of Kd (41). 

It was demonstrated in Sections A and B that in spite of a few discrepancies the macroscopic parameters characterizing the distribution of ions between solution and the surface (Kd, PH50) taken from different sources are rather consistent. These coefficients can be used to compare affinities between different ions and certain surface. For example silica has higher affinity to Zn (Fig. 4.58) than to Ni (Fig. 4.57), at least at pH >6.5, and iron III (hydr) oxides have higher affinity to Se IV (Fig. 4.60) than to Se VI (Fig, 4.62). Many affinity series have been established using experimental results obtained at certain experimental conditions, but apparently the relative affinity of a surface to different ions is rather insensitive to experimental... 

These data are for classical resins of high exchange capacity. Selectivity coefficients for the resins used in modern ion chromatography are apt to be significantly different. Nevertheless, the values in Tables 5.2 and 5.3 do give some indication of the relative affinity of the resins for various ions. 

Partition coefficients are dimensionless measures of the relative affinity of a molecule with respect to the two phases and depend on absorption, transport, and partitioning phenomena. 

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