FACTOID # 17: Though Rhode Island is the smallest state in total area, it has the longest official name: The State of Rhode Island and Providence Plantations.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Partition coefficient

A partition coefficient is a measure of differential solubility of a compound in two solvents. The logarithmic ratio of the concentrations of the solute in the solvent is called log P (sometimes LogP). The best known of these partition coefficients is the one based on the solvents octanol and water. The octanol-water partition coefficient is a measure of the hydrophobicity and hydrophilicity of a substance. In the context of drug-like substances, hydrophobicity is related to absorption, bioavailability, hydrophobic drug-receptor interactions, metabolism and toxicity. In the field of hydrogeology, the octanol water partition coefficient is used to predict and model the migration of dissolved hydrophobic organic compounds in soil and groundwater. A substance is soluble in a fluid if it dissolves in that fluid. ... A chemical compound is a chemical substance consisting of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition. ... A solvent is a fluid phase (liquid, gas, or plasma) that dissolves a solid, liquid, or gaseous solute, resulting in a solution. ... Logarithms to various bases: is to base e, is to base 10, and is to base 1. ... In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. ... A substance is soluble in a fluid if it dissolves in the fluid. ... Octanol is a straight chain fatty alcohol with eight carbon atoms and the formula C8H17OH and its molecular weight is 130. ... Impact of a drop of water. ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... The adjective hydrophilic describes something that likes water (from Greek hydros = water; philos = friend). ... Look up absorption in Wiktionary, the free dictionary Absorption may refer to: In physics: absorption (chemistry) - absorption of particles of gas or liquid in liquid or solid material as studied in physical chemistry absorption (optics) - absorption of photons by a material Absorption (acoustics) - absorption of sound waves by a material... In pharmacology, bioavailability is used to describe the fraction of an administered dose of medication that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. ... In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ... Metabolism (from Greek μεταβολισμός metabolismos) is the biochemical modification of chemical compounds in living organisms and cells. ... The skull and crossbones is a common symbol for toxicity. ... Hydrogeology (hydro- meaning water, and -geology meaning the study of rocks) is the part of hydrology that deals with the distribution and movement of groundwater in the soil and rocks of the Earths crust (commonly in aquifers). ...

Contents

[edit]

Application

[edit]

Shake flask (or tube) method

The classical and most reliable method of log P determination is the shake-flask method, which consists of mixing a known amount of solute in a known volume of octanol and water, then measuring the distribution of the solute in each solvent. The most common method of measuring the distribution of the solute is by UV/VIS spectroscopy. There are a number of pros and cons to this method: Ultraviolet-Visible Spectroscopy or Ultraviolet-Visible Spectrophotometry (UV/ VIS) involves the spectroscopy of photons (spectrophotometry). ...


Pros:

  • Most accurate method
  • Accurate for broadest range of solutes (neutral and charged compounds applicable)
  • Chemical structure does not have to be known beforehand.

Cons:

  • Time consuming (>30 minutes per sample)
  • Octanol and water must be premixed and equilibrated (takes at least 24 hours to equilibrate)
  • Complete solubility must be attained.
  • The concentration vs. UV-Vis response must be linear over the solute's concentration range. (See Beer-Lambert law)

As an alternative to UV/VIS spectroscopy other methods can be used to measure the distribution, one of the best is to use a carrier free radiotracer. In this method (which is well suited for the study of the extraction of metals) a known amount of a radioactive material is added to one of the phases. The two phases are then brought into contact and mixed until equilibrium has been reached. Then the two phases are separated before the radioactivity in each phase is measured. If an energy dispersive detector can be used (such as a high purity germanium detector) then it is possible to use several different radioactive metals at once, with the more simple gamma ray detectors it is only possible to use one radioactive element in the sample. In optics, the Beer-Lambert law, also known as Beers law or the Beer-Lambert-Bouguer law is an empirical relationship that relates the absorption of light to the properties of the material through which the light is travelling. ... Ultraviolet-Visible Spectroscopy or Ultraviolet-Visible Spectrophotometry (UV/ VIS) involves the spectroscopy of photons (spectrophotometry). ... A radioactive tracer, also called a radioactive label, is a substance containing a radioisotope. ... For alternative meanings see metal (disambiguation). ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles. ... Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ... General Name, Symbol, Number germanium, Ge, 32 Chemical series metalloids Group, Period, Block 14, 4, p Appearance grayish white Atomic mass 72. ...


If the volume of both of the phases are the same then the math is very simple.


For a hypothetical solute (S)


D or P = radioactivity of the organic phase / radioactivity of the aqueous phase


D or P = [Sorganic]/[Saqueous]


In such an experiment using a carrier free radioisotope the solvent loading is very small, hence the results are different to those which are obtained when the concentration of the solute is very high. A disadvantage of the carrier free radioisotope experiment is that the solute can absorb on the surfaces of the glass (or plastic) equipment or at the interface between the two phases. To guard against this the mass balance should be calculated.


It should be the case that


radioactivity of the organic phase + radioactivity of the aqueous phase = initial radioactivity of the phase bearing the radiotracer


For nonradioactive metals, it is possible in some cases to use ICP-MS or ICP-AES. Sadly ICP methods often suffer from many interferences which do not apply to gamma spectrscopy so hence the use of radiotracers (counted by gamma ray spectrscopy) is often more straightforward. ICP-MS (Inductively Coupled Plasma Mass Spectrometry) is a type of mass spectrometry that is highly sensitive and capable of analysis of a range of metals and several non-metals at below one part in 1012. ... ICP-AES (Inductively Coupled Plasma - Atomic Emission Spectrometer) uses ICP (inductively coupled plasma) to produce excited atoms that emit radiation at a wavelength characteristic of a particular element. ...

[edit]

HPLC determination

A faster method of log P determination makes use of high-performance liquid chromatography. The log P of a solute can be determined by correlating its retention time with similar compounds with known log P values. Chromatography is a family of analytical chemistry techniques for the separation of mixtures. ... Linear correlations between 1000 pairs of numbers. ...


Pros:

  • Fast method of determination (5-20 minutes per sample)

Cons:

  • The solute's chemical structure must be known beforehand.
  • Since the value of log P is determined by linear regression, several compounds with similar structures must have known log P values.
  • Different chemical classes will have different correlation coefficients, between-class comparisons are not significant.
[edit]

Chemical structure refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... In probability theory and statistics, correlation, also called correlation coefficient, is a numeric measure of the strength of linear relationship between two random variables. ...

Electrochemical methods

In the recent past some experiments using polarised liquid interfaces have been used to examine the thermodynamics and kinetics of the transfer of charged species from one phase to another. Two main methods exist.

  • ITIES, Interfaces between two immiscible electrolyte solutions which for example has been used at Ecole Polytechnique Fédérale de Lausanne. [1]
  • Droplet experiments which have been used by Alan Bond, Frank Marken[2] and also by the team at the Ecole Polytechnique Fédérale de Lausanne. Here a reaction at a triple interface between a conductive solid, droplets of a redox active liquid phase and an electrolyte solution have been used to determine the energy required to transfer a charged species across the interface.
[edit]

Prediction

QSAR algorithms calculate a log P in several different ways: QSAR (Quantitative Structure-Activity Relationship, sometimes the A stands also for Affinity=reactivity) is the quantitative correlation of the biological (ecological, toxicological or pharmacological) activity to the structure of chemical compounds, which allows the prediction of the so-called drug efficacy of a structurally related compound. ...

  • Fragment based prediction (group contribution)
It has been shown that the log P of a compound can be determined by the sum of its fragments. Fragmentary log P values have been determined statistically. This method gives mixed results and is generally not trusted to have accuracy of more than ±0.1 units.
  • Data mining prediction
A typical data mining based prediction uses e.g. support vector machines, decision trees, neural networks are usually very successful for calculating log P values when trained with compounds that have similar chemical structures and known log P values.
  • Molecule mining prediction
Molecule mining approaches apply a similarity matrix based prediction or an automatic fragmentation scheme into molecular substructures. Furthermore there exist also approaches using maximum common subgraph searches or graph kernels.
[edit]

It has been suggested that Data farming be merged into this article or section. ... Support vector machines (SVMs) are a set of related supervised learning methods used for classification and regression. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... A neural network is an interconnected group of neurons. ... This page describes mining for molecules. ... In complexity theory, Maximum Common Subgraph-Isomorphism (MCS) is a decision problem that is known to be NP-complete. ...

Limitations

LogP is not an accurate determinant of solubility for ionizable drugs as if the drug is in an acidic form it will be poor at passing through lipid membranes. In these cases the distribution coefficient (D) should be used.

[edit]

See also

[edit]

Cheminformatics is the use of computer and informational techniques, applied to a range of problems in the field of chemistry. ... QSAR (Quantitative Structure-Activity Relationship, sometimes the A stands also for Affinity=reactivity) is the quantitative correlation of the biological (ecological, toxicological or pharmacological) activity to the structure of chemical compounds, which allows the prediction of the so-called drug efficacy of a structurally related compound. ... ADME is an acronym in pharmacokinetics and pharmacology for Absorption, Distribution, Metabolism, and Excretion, and describes the disposition of a pharmaceutical compound within an organism. ... This page describes mining for molecules. ...

LogP calculators

[edit]

The Chemistry Development Kit is an open source Java library for Chemoinformatics and Bioinformatics. ... JOELib is a freeware chemical expert system mainly used for converting chemical file formats. ...

External links

[edit]

Online services for LogP prediction


  Results from FactBites:
 
Partition coefficient - Wikipedia, the free encyclopedia (846 words)
A partition coefficient is a measure of differential solubility of a compound in two solvents.
The best known of these partition coefficients is the one based on the solvents octanol and water.
The octanol-water partition coefficient is a measure of the hydrophobicity and hydrophilicity of a substance.
Diffusion of solute in soil media, D.L. Nofziger (1069 words)
is the partition coefficient of the chemical on the soil.
Organic carbon partition coefficient: Organic carbon partition coefficient is the partition coefficient in a soil divided by the organic carbon content of the soil.
Partition coefficient: Partition coefficient is the ratio of the concentration of a chemical species adsorbed on a soil to the concentration of the species in the soil solution.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m