Octanol-water partition coefficient
The n-octanol-water partition coefficient, Kow is a partition coefficient for the two-phase system consisting of n-octanol and water.[1] Kow is also frequently referred to by the symbol P, especially in the English literature. It is also called n-octanol-water partition ratio.[2][3][4]
Kow serves as a measure of the relationship between lipophilicity (fat solubility) and hydrophilicity (water solubility) of a substance. 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.[citation needed]
If a substance is present as several
History
In 1899,
Applications
Kow values are used, among others, to assess the environmental fate of
Furthermore, the parameter plays an important role in drug research (Rule of Five) and toxicology. Ernst Overton and Hans Meyer discovered as early as 1900 that the efficacy of an anaesthetic increased with increasing Kow value (the so-called Meyer-Overton rule).[8]
Kow values also provide a good estimate of how a substance is distributed within a cell between the lipophilic biomembranes and the aqueous cytosol.[citation needed]
Estimation
Since it is not possible to measure Kow for all substances, various models have been developed to allow for their prediction, e.g. Quantitative structure–activity relationships (QSAR) or linear free energy relationships (LFER)[9][10] such as the Hammett equation.[9]
A variant of the UNIFAC system can also be used to estimate octanol-water partition coefficients.[11]
Equations
- Definition of the Kow or P-value
- The Kow or P-value always only refers to a single species or substance:
- with:
- concentration of species i of a substance in the octanol-rich phase
- concentration of species i of a substance in the water-rich phase
- If different species occur in the octanol-water system by dissociation or association, several P-values and one D-value exist for the system. If, on the other hand, the substance is only present in a single species, the P and D values are identical.
- P is usually expressed as a common logarithm, i.e. Log P (also Log Pow or, less frequently, Log pOW):
- Log P is positive for lipophilic and negative for hydrophilic substances or species.
- Definition of the D-value
- The P-value only correctly refers to the concentration ratio of a single substance distributed between the octanol and water phases. In the case of a substance that occurs as multiple species, it can therefore be calculated by summing the concentrations of all n species in the octanol phase and the concentrations of all n species in the aqueous phase:
- with:
- concentration of the substance in the octanol-rich phase
- concentration of the substance in the water-rich phase
- D values are also usually given in the form of the common logarithm as Log D:
- Like Log P, Log D is positive for lipophilic and negative for hydrophilic substances. While P values are largely independent of the pH value of the aqueous phase due to their restriction to only one species, D values are often strongly dependent on the pH value of the aqueous phase.
Example values
Values for log Kow typically range between -3 (very hydrophilic) and +10 (extremely lipophilic/hydrophobic).[12]
The values listed here[13] are sorted by the partition coefficient. Acetamide is hydrophilic, and 2,2′,4,4′,5-Pentachlorobiphenyl is lipophilic.
Substance | log KOW | T | Reference |
---|---|---|---|
Acetamide | −1.155 | 25 °C | |
Methanol | −0.824 | 19 °C | |
Formic acid | −0.413 | 25 °C | |
Diethyl ether | 0.833 | 20 °C | |
p-Dichlorobenzene | 3.370 | 25 °C | |
Hexamethylbenzene | 4.610 | 25 °C | |
2,2′,4,4′,5- Pentachlorobiphenyl
|
6.410 | Ambient |
See also
References
- OCLC 36430034.
- OCLC 1182869019.)
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: CS1 maint: location missing publisher (link - .
- S2CID 25971836.
- .
- S2CID 1399290.
- ^ Stockholm Convention on Persistent Organic Pollutents (POPs) (PDF). Geneva: United Nations Environment Programme. 2018. pp. Annex D.
{{cite book}}
:|work=
ignored (help) - ISBN 978-0-7817-8763-5.
- ^ PMID 3905374.
- PMID 10960181.
- ISBN 978-0-08-047228-7.
- PMID 31457869.
- ^ "Dortmund Data Bank (DDB)". Dortmund Data Bank Software & Separation Technology (DDBST) GmbH. Retrieved 2020-05-20.
Further reading
- Goss KU (July 2003). "Der Oktanol/Wasser Verteilungskoeffizient — Das Allheilmittel der Umweltchemie?" [The octanol / water partition coefficient - the panacea for environmental chemistry?]. Umweltwissenschaften und Schadstoff-Forschung (in German). 15 (4): 273–279. S2CID 102406251.</ref>
- Heuel-Fabianek B. Partition Coefficients (Kd) for the Modelling of Transport Processes of Radionuclides in Groundwater (PDF). JÜL-Berichte, Forschungszentrum Jülich, Nr. 4375, 2014 (Report). ISSN 0944-2952.
External links
- Virtual Computational Chemistry Laboratory interactive calculation and interactive comparison of several methods
- LogP-Berechnungssoftware von ACD (commercial)
- Directory of reference works and databases with octanol-water partition coefficients
- Comprehensive free database of evaluated octanol-water partition coefficients from Sangster Research Laboratories Archived 2009-02-09 at the Wayback Machine