GLC theory yields the expression for K./O K,,0 = CORT nART P (Vx + V+ VW P (5) where n. is the number of moles of solute x in the octanol (saturated with water), V,, V0 and Vw are the volumes of solute, octanol and water, in the octanol phase, respec- using diluted tissue homogenates with a classic partition coefficient [lipid/water partition coefficient or in vivo tissue/plasma ratio (K p)] and lipid partitioning solely responsible for drug . 3.2.3 Octanol-water partition coefficients As mentioned above, the physicochemical constant log k oct is used to describe the lipophilicity of the penetrant. true false . the ratio of the concentration of the drug in two immiscible phases: a nonpolar liquid (representing membrane) and an aqueous buffer (representing . Further, if it is assumed that muscle contains 5% lipid with the remainder water and that fat is 80% lipid then: P lw = [lipid]/[water] P ow; k = [partition coefficient residues in fat:blood]/[partition coefficient of residues in muscle:blood]; ow muscle . If one were asked to name the most important among these factors that will influence it, one would have to name the lipid-water partition coefficient, which is determined by the pKa of the drug and the pH of the body fluids. Partition Coefficient (Definition 1) The higher the P value is, the better the hydrophobic (lipophilic) property the drug may have. Octanol-water partition coefficient (Kow) is a very valuable parameter with numerous environmental applications, where it is used as a primary characterizing parameter since it represents a measure of the tendency of a compound to move from the aqueous phase into lipids. The typical quantitative descriptor of lipophilicity is the partition coefficient P . The lipid/water partition coefficient denotes the ratio of the concentration of a drug in two immiscible or slightly miscible phases.
The partition coefficient generally refers to the concentration ratio of un-ionized species of compound, whereas the distribution coefficient refers to the concentration ratio of all species of the compound . Although trivial, it is not uncommon that this relevant detail is overlooked, and different partition constants are . Lipid-water partition coefficient. Although the use of a partition coefficient of drugs between drug car-riers and water is thus desirable, such studies have not been reported previously. Following intravenous administration, drugs are distributed fastest to: Drug movement into, within and out of the body, which includes absorption, distribution, and elimination: Term. 9. The logarithm of the ratio of the concentrations of the un-ionized solute in the solvents is . 1) Shake flask method 2) Chromatographic method 3) Spectroscopy method Phenobarbitone has a high lipid/water partition coefficient of 5. Definition. The lipid-to-water partition coefficient describes the distribution (ratio) of a drug (concentration) in a lipid compared with water media. c. Lipid partition coefficient. The common definition of nonspecific binding is the condition in which D f in eq. Little Pro on 2016-01-13 88072 n-Octanol/Water Partition Coefficient ( Kow) is defined as the ratio of the concentration of a chemical in n-octanol and water at equilibrium at a specified temperature. Partition coefficient and log P. The partition coefficient is a ratio of concentrations of un-ionized compound between the two solutions. The developed innovative ion pair, tetracycline docusate, was characterized in terms of its thermal stability, water solubility, octanol-water, and liposome-water partition coefficients, using UV . mental animals according to this definition (Reivich . The drug penetration rate into CSF, similar to other tissue cells, is determined mainly by the extent of protein binding, degree of ionization, and lipid-water partition coefficient of the drug. e. Concentration gradient . Lipids are classically defined as biological materials that are insoluble in water but soluble in organic solvents such as methylene chloride/methanol. This ratio is therefore a comparison of the solubilities of the solute in these two liquids. Passive transport (down hill movement) Most important Mechanism for most of the Drugs Majority of drugs diffuses across the membrane in the direction of concentration gradient No active role of the membrane Proportional to lipid : water partition coefficient Lipid soluble drugs diffuse by dissolving in the lipoidal matrix of the membrane . The distribution coefficient also takes into account ionization. 1C and . the body. verse fashion, to the amount of lipid and myelin present (Randall, 1938; Katzman and Pappius, 1973). The greater the solubility of a substance, the higher its partition coefficient, and the higher the partition coefficient, the higher the permeability of the membrane to that particular substance. Phenobarbitone has a high lipid/water partition coefficient of 5.9. Based on quantitative information obtained by EPR measurements for drug concentration in each phase (oil, micelle, aqueous), partition coefficients used in simulations of the impact of ingested food lipids ("Definition of Partition Coefficient, K") were estimated. Materials and Methods We conducted potentiometric titration experiments to determine lipid membrane-water partition coefficients of four . It measures relative solubility of a chemical with water (a polar molecule) and compared with octanol (a non-polar molecule similar to biological phospholipids found in cell walls/membranes). Based upon the outcome of the present study, lipid (bio)chemicals with a log K ow up to 7-8 appear amenable to the three assays. 2. Thiopentone sodium has a chloroform/water partition coefficient of about 100, so it is highly . It is defined as the ratio between un-ionized drug distributed between the organic and aqueous layers at equilibrium. Kow = Concentration in Octanol/ Concentration in water 1C and . definition of the standard free energy is based on the mole fraction partition coefficient K x : in which n b, n f, n L and n w are the moles of bound peptide, free peptide, lipid and water molecules, respectively . The free energy profiles through a DOPC membrane of solutes with different logarithm of octanol-water partition coefficients, logP OW, and their solvent accessibility are presented in Fig. 100/100 or 0.01/0.01 logP become . Lipophilicity is the tendency of a compound to partition into a non-polar organic phase versus an aqueous phase. DEFINITION: The ability of a chemical compound to elicit a pharmacological/ therapeutic effect is related to the influence of various physical and chemical (physicochemical) .
KR/W is the air/water (saturated with octanol) partition coefficient. Blood-gas partition coefficient, also known as Ostwald coefficient for blood-gas, is a term used in pharmacology to describe the solubility of inhaled general anesthetics in blood. hand and water on the other hand, that is, on the fat/water partition coefficient."1 This was interpreted as favoring lip-ids as the primary targets of anesthetics and a single non-specific theory to explain anesthesia. Purpose Potentiometric lipid membrane-water partition coefficient studies neglect electrostatic interactions to date; this leads to incorrect results. in bioconcentration studies for different tissues (e.g., whole fish, edible, and nonedible) on a whole weight basis and lipid weight basis, when available. It is a measure of how well substance partitions between lipid and water. Integrating eq. This process can be studied in pure lipid membranes, although it is acknowledged that the properties of even relatively pure lipid patches in native . Pharmacodynamics: . However, solubility . The partition coefficient is a simple ratio between two concentrations, and it doesn't matter what concentration units you are using as long as they are the same for both solutions.
Passive diffusion is the transport of a molecule across a lipid bilayer membrane according to its electrochemical potential gradient without the assistance of additional transporter molecules. i is the molar volume of water, i=W, or lipid, i=L. We herein show how to account properly for such interactions in potentiometric data analysis. It is defined as the ratio of unionised drug distributed between the organic and aqueous phases at equilibrium. It is a purely theoretical volume, which can substantially exceed the total body volume, or potentially . 1. Partition Coefficient. This coefficient provides an indication of the degree to which a pollutant accumulates into fatty tissues and any organic phase. The partition. Specifically, the pH and pKa of the drug will influence the lipid-water partition coefficient of a drug. Partition coefficient and log P. The partition coefficient is the ratio of concentrations of un-ionized compound between the two solutions. Log [Drug]octanol (lipid)/ [Drug] water. Regardless of the partition coefficient definition thought as most adequate to describe the partition equilibrium between the two phases, the concentration of the solute . d. Density of transporters. For molecules of equal solubility, smaller ones penetrate . Lipid Lipid/water partition coefficients, The simplest way to predict the lipid/ water partition coefficient, Kiw, of a drug is based on measurements of the surface pressure, ttd, of the drug as a function of its concentration in the aqueous subphase (Gibbs adsorption isotherm).The Gibbs adsorption isotherm provides the air/water partition coefficient, Kaw, and the cross-sectional area, Ad of . The lipid-water partition coefficient (K LW) is essential for understanding and modeling bioconcentration. To measure the partition coefficient of ionizable solutes, the pH of the aqueous phase is adjusted such that the predominant form of the compound is un-ionized. When the two liquid phases are completely immiscible; 2. The organism-water partition coefficient (K BW) is determined by the body composition of the organism (i.e., lipid, NLOM, and water) and the K OW of the chemical. The distribution law is exact only for ideal solutions under the following conditions: 1. The value is greater than one if a substance is more soluble in fat-like solvents such as n-octanol, and less than one if it is more soluble in water. The octanol/water system mimics the lipid membrane/water systems found in. 1 over the length of the . We herein show how to account properly for such interactions in potentiometric data analysis. The partition coefficient, P, of a drug is given by where [drug] octan-1-ol = concentration of drug in octan-1-ol [drug] water = concentration of drug in water The Partition co-efficient, P is dimensionless and its logarithm, log P is widely used as the measure of lipophilicity. It is assumed that the partitioning of the chemical between lipid and water is directly related to the octanol-water partition coefficient. According to Henry's law, the ratio of the concentration in blood to the concentration in gas that is in contact with that blood, when the partial pressure in both compartments is equal, is nearly constant at . The lipophilicity of an organic compound is usually described in terms of what? The appeal of a single unified mechanism to explain anesthesia was (and remains) intellectually appealing. The penetration rate into the brain is slow for highly protein-bound drugs and nearly nonexistent for the ionized form of weak acids and bases. Kow is a shorthand term for the octanol-water partition coefficient. The partition coefficient is determined by the shake flask method using two immiscible solvents, the most common hydrophilic solvent is water or phosphate buffer of pH 7.4, and for oil phase is octanol. Octanol-water partition coefficient (K OW). P = [Drug]lipid / [Drug]water (NOT RIGHT ONE) Log P =. 4 is very small and thus negligible in relation to . Other articles where partition coefficient is discussed: cell: Permeation: unit of measure called the partition coefficient. The human body is made from water and lipids. The lipid solubility of a drug is measured by a parameter called as log P where P is oil/water partition coefficient (Ko/w or simply P) value of the drug. To measure the partition coefficient of ionizable solutes, the pH of the aqueous phase is adjusted such that the predominant form of the compound is un-ionized. The partition coefficient (K) of a substance, also called the partition coefficient (P), is the quotient of dividing the concentrations of a substance into two phases; made up of the mixture of two solvents that are immiscible due to their different densities and natures. Drug distribution is a necessary component of models to predict human pharmacokinetics. Partition coefficient (oil/ water) is an indicator of drug lipophilicity. Partition Coefficient The partition coefficient is the measure of the lipophilicity of a drug and an indication of its ability to cross the cell membrane. 7 8. Explanations of these values are available in the OPPTS . corresponds to a 0.14 micron aqueous layer separating the well-stirred blood from the adipose lipid . Similarly to K OC, K LW is lower than would be expected based on the conventional correlation assumption that K LW equals K OW (Table 3). The penetration rate into the brain is slow for highly protein-bound drugs and nearly nonexistent for the ionized form of weak acids and bases. For log K OW, the log of the octanol-water partition coefficient is a base 10 logarithm. Octanol/water partition coefficient is very important index in Biological,toxicological and environmental area. The total blood concentration C B can be related to the free water concentration (c B) using the blood/water partition coefficient (C B = K bld-wat c B). Dyslipidemia is strongly associated with cardiovascular diseases [1,2,3], insulin resistance and diabetes [4,5].Commonly used clinical lipid measurements such as low density lipoprotein-cholesterol (LDL-C), high density lipoprotein-cholesterol (HDL-C) or triacylglycerols, provide only limited information as they fail to measure the individual lipid species that make up the . Conclusion: The permeability of molecules through a cell membrane can be well described as a linear function of the partition coefficient with slope dependent on molecule size. k oct is the octanol-water partition coefficient, defined as ratio of the equilibrium concentrations of the penetrant in a two-phase system consisting of two immiscible solvents, (octanol . The resulting K p values were . The drug penetration rate into CSF, similar to other tissue cells, is determined mainly by the extent of protein binding, degree of ionization, and lipid-water partition coefficient of the drug. of drug is less than one it is less lipophilic. The ration of the concentration of a substance in the n-octanol phase to its concentration in the aqueous phase in an equilibrated two-phase octanol-water system. Put simply, in solution the weak acids and bases will be present in some combination of ionised and non-ionised forms. Kow serves as a measure of the relationship between lipophilicity (fat solubility) and hydrophilicity (water solubility) of a substance. D is a diffusion coefficient which is influenced by solution temperature, viscosity of the fluid, and the size of the molecules. A mechanistic tissue composition model incorporating passive and active transport for the prediction of steadystate tissue:plasma partition coefficients (Kt:pl) of chemicals in multiple mammalian species was used to assess interindividual and interspecies variability. A simple measure of the hydrophobicity of chemicals, originating from pharmacology, is the octanol-water partition coefficient, abbreviated as K ow (and sometimes also called P ow or P oct ): this is the ratio of concentrations of a chemical in n-octanol and in water, after establishment of an equilibrium between the two phases (Figure 4). Diffusion through lipid and aqueous solutions will be slightly different, depending on drug properties. For molecules of equal size, the one with greater solubility in lipids will pass more quickly into the cell. Lipids in organ tissue are predominantly present in the form of phospholipid membranes. (However, only two were correctly predicted as 'negative' in the murine Local Lymph Node Assay.) Ko/w is accepted as a good reference parameter for solute hydrophobicity. 6. The most needed liquid- liquid partition coefficient is the octanol-water partition coefficient. Partition coefficient Definition: Partition coefficient is a measure of a drugs lipophilicity and an indication of its ability to cross the cell membrane. The n-octanol/water partition ratio or coefficient (log Kow) and n-octanol/water distribution coefficient (log D) are key parameters in environmental risk assessment of chemicals as they are often used to estimate the environmental fate and bioavailability and thus exposure and toxicity of a . The KOW measures this partitioning. This definition thus encompasses a diverse group such as fatty acids, triglycerides, phospholipids, steroids, terpenes, waxes, and even fat-soluble vitamins. Octanol-water partition coefficient: A simple measure of the hydrophobicity of chemicals, originating from pharmacology, is the octanol-water partition coefficient, abbreviated as K ow (and sometimes also called P ow or P oct): this is the ratio of concentrations of a chemical in n-octanol and in water, after establishment of an equilibrium between the two phases (Figure 4). Octanol-water partition ratio is the most common way of expressing the lipophilicity of a compound, and it is defined as the ratio of the concentration of a solute in a water-saturated octanolic phase to its concentration in an octanol-saturated aqueous phase. Hydrophobic pollutants such as PCBs often partition into lipid rather than into water. In the physical sciences, a partition coefficient ( P) or distribution coefficient ( D) is the ratio of concentrations of a compound in a mixture of two immiscible solvents at equilibrium. To keep the numbers simple, the log of the partition coefficient is usually stated. Purpose Potentiometric lipid membrane-water partition coefficient studies neglect electrostatic interactions to date; this leads to incorrect results. Drugs with low oil:water partition coefficients undergo lipid diffusion more rapidly than drugs with high oil:water partition coefficients.
This coefficient provides an indication of the degree to which a pollutant accumulates into fatty tissues and any organic phase. partition coefficient. This approach predicts Kt:pl using chemical lipophilicity, pKa, phospholipid membrane binding, and the unbound plasma . In addition, the applicability of the interfacial barrier-limited model to . Drugs must be sufficiently lipid soluble (lipophilic) to pass through some level of cell membrane lipid bilayer to reach most drug receptors. Because under most experimental conditions, n b << n L and n f << n w, K x can be approximated as: 0G x can be . . If you know the distribution ratio of the chemicals to the octanol, you can estiamte bio accumulations. For example, the water solubility of hydroxyl, carboxyl, and amino . Diffusion through lipid and aqueous solutions will be slightly different, depending on drug properties. Indeed, Ko/w can be rapidly estimated using capillary electrophoresis with a micellar or micro emulsion solution and/or RPLC
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