The logP value of a compound, which is the logarithm of its partition coefficient between n-octanol and water log(coctanol/cwater), is a well established measure of the compound's hydrophilicity. Low hydrophilicities and therefore high logP values cause poor absorption or permeation.
Thus a normalised organic carbon to water partition coefficient (KOC), described as the ratio between the sorption coefficient Kd, and the organic carbon content of the sorbent, in units of mass of organic carbon (OC) per mass of soil (g OC/g soil) is commonly used to assess the extent to which an organic chemical is
Lipophilicity. The most commonly used measure of lipophilicity is LogP, this is the partition coefficient of a molecule between an aqueous and lipophilic phases, usually octanol and water.
The n-octanol-water partition coefficient, Kow is a partition coefficient for the two-phase system consisting of n-octanol and water. Kow serves as a measure of the relationship between lipophilicity (fat solubility) and hydrophilicity (water solubility) of a substance.
: any of four liquid alcohols C8H17OH derived from normal octane: such as. a : the primary alcohol CH3(CH2)6CH2OH having a penetrating odor, occurring free or in the form of esters in oils from plant seeds and fruits, and used chiefly in organic synthesis and in perfumes.
a. 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. It is defined as the ratio between un-ionized drug distributed between the organic and aqueous layers at equilibrium.
The octanol-air partition coefficient (K(OA)) is useful for predicting the partitioning behavior of organic compounds between air and environmental matrices such as soil, vegetation, and aerosol particles. At present, experimentally determined K(OA) values are available for only several hundred compounds.
Chemicals with low Kow values (e.g., less than 10) may be considered relatively hydrophilic; they tend to have high water solubilities, small soil/sediment adsorption coefficients, and small bioconcentration factors for aquatic life.
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.
Linear correlations in the form of the following are obtained; log Kow = a log t + b where a = slope, t is the retention time and b = intercept. mostly widely used quantitative structure activity relationships used today.
Soil adsorption coefficient (Kd) measures the amount of chemical substance adsorbed onto soil per amount of water. It is also known as Freundlich solid-water distribution coefficients (Kf).
The unit of solubility is generally in mg/L (milligrams per liter) or ppm (parts per million).
The lipophilicity of a compound is most commonly quantified by measuring the extent of distribution between an aqueous phase and a hydrophobic phase such as 1-octanol.
Lipophilicity is an important physicochemical parameter that contributes to the absorption, distribution, metabolism, excretion, and toxicity of a drug. This, in turn, affects the solubility and permeability of a drug and contributes to its potency and selectivity.
A widely used model to access physicochemical properties of the compound is LogP (partition coefficient). LogD is more convenient for practical measurements, as it takes into account solution pH, which is important for the analysis of the drug candidate properties in various biologic media with different pH values.
Definition: Lipophilic or 'lipid-loving' molecules are attracted to lipids. A substance is lipophilic if it is able to dissolve much more easily in lipid (a class of oily organic compounds) than in water.
Lipophilicity is defined as the affinity of a drug for a lipid environment. It has become a critical parameter in the Pharmaceutical industry, which indicates the relationship of a drug with their biological, pharmacokinetic, and metabolic properties.
Bioavailability refers to the extent a substance or drug becomes completely available to its intended biological destination(s).
: having an affinity for lipids (such as fats) a lipophilic metabolite.
logD is a log of partition of a chemical compound between the lipid and aqueous phases. The most popular lipid phase is octanol. LogP is equivalent to logD for non-ionisable compounds and represents the partition of the neutral form for ionizable compounds (and, hence, is a virtual, unmeasurable, property).
A pKa, the pH at which a molecule is half-ionized, is important because most biologically active compounds are ionizable. LogP, a compound's partition coefficient between an oily and aqueous phase, is used to predict absorption and is pKa-dependent.
log P was calculated by taking the logarithm of the ratio of the HPLC peak area of each compound in octanol to the corresponding peak area in buffer. Consequently, log P values were based on analysis of both aqueous and octanol fractions.
Logarithm Rules and Properties
| Rule name | Rule |
|---|
| Logarithm quotient rule | logb(x / y) = logb(x) - logb(y) |
| Logarithm power rule | logb(x y) = y ∙ logb(x) |
| Logarithm base switch rule | logb(c) = 1 / logc(b) |
| Logarithm base change rule | logb(x) = logc(x) / logc(b) |
ChromlogD gives approximately a 2-log unit higher lipophilicity value than the octanol/water log D for compounds having three to five log D values in the octanol/water system. It provides a dynamic partition coefficient of a compound between the hydro-organic mobile phase and C-18.
a. 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. It is defined as the ratio between un-ionized drug distributed between the organic and aqueous layers at equilibrium.
