Partition coefficient

The n- octanol - water partition coefficient Kow (even spellings such as octanol / water partition coefficient commonly and correctly ) is a dimensionless partition coefficient, which is the ratio of the concentrations of a chemical in a biphasic system consisting of 1 -octanol and water. If, however, a chemical in the octanol-water system in several species before, so each species is assigned a separate Kow.

Especially in the English literature of the Kow value is also referred to as P- value.

Closely related to the Kow value is the D- value always indicates only the concentration ratio of the chemical waiving distinguishing different species.

Applications

The Kow value is a Modellmaß for the relationship between lipophilicity ( fat solubility ) and hydrophilic (water solubility ) of a substance. The expectation is to estimate the distribution coefficient of this substance in other systems with an aqueous and a lipophilic phase with the aid of the octanol - water partition coefficient. Kow is greater than one, when a fat-like substance in solvents such as n-octanol is more soluble, less than unity when it is more soluble in water. According Log P is positive for lipophilic and negative for hydrophilic substances.

So Kow values ​​are used among other things to assess the environmental fate of persistent organic pollutants. Chemicals with high coefficient example, are more likely to accumulate in the fatty tissues of organisms (depot effect). Closely linked to this is the so-called bioconcentration factor BCF. It is the ratio of the concentrations of a substance in biota (biomass) and in water. BCF and Kow can be equated to a first approximation.

Additionally, the parameter plays an important role in pharmacology ( Rule of Five ) and in toxicology. Ernst Overton and Hans Meyer independently discovered already in 1900 that anesthetics showed an even higher efficacy, the greater its log P value was ( Meyer- Overton rule). Furthermore, Kow values ​​very well suited to estimate how a substance is distributed between the lipophilic biomembranes and the aqueous cytosol within a cell.

Appraisal

Since it can not be measured for all chemicals of Kow, there are various models for the prediction, eg by quantitative structure -activity relationships (QSAR ) or by Linear Free Energy Relationships ( LFER ).

Also from the UNIFAC model, there is a variant for the estimation of octanol - water partition coefficient.

Equations

  • Definition of the Kow - or P- value
  • Concentration of species i of a chemical in the octanol -rich phase
  • Concentration of species i of a chemical in the water-rich phase
  • Definition of the D- value
  • Concentration of a chemical in the oktanolreichen phase
  • Concentration of a chemical in the water-rich phase

Sample Data

The values ​​listed are sorted by the size of the partition coefficient. Acetamide is hydrophilic, 2,2 ', 4,4' ,5- Pentachlorobiphenyl lipophilic.

Phase (matter) 1-Octanol Bioaccumulation Biota (ecology) Quantitative structure–activity relationship Hexamethylbenzene Dortmund Data Bank Digital Object Identifier
487248
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