Isotope labeling

from Wikipedia, the free encyclopedia

The method of isotope labeling (also method of isotopically labeled compounds or tracer technique ) describes the systematic insertion of defined isotopes into organic compounds. By exchanging isotopes, two labeled molecules or atoms can be distinguished in the course of chemical reactions . The information obtained can be used to clarify reaction mechanisms.

properties

In a chemical reaction, only the starting materials and the products are usually recognizable. The role of two differently bound atoms in the course of the reaction can be investigated with isotope labeling. The advantage of isotope labeling is that it does not require the addition of interfering substances. The isotope used for labeling can be detected in the product and its corresponding binding situation after the reaction by means of analytical methods such as NMR technology or mass spectrometry .

Example of an isotope-labeled compound

Since the labeled compounds are usually expensive substances, a labeled compound is diluted with an excess of unlabeled compound. Examples of an exchange of isotopes are the replacement of H by heavy hydrogen such as D ( deuterium ) or T ( tritium ), 12 C by 13 C, 14 C or 16 O by 17 O, 18 O.

Applications

Melvin Calvin applied isotopic labeling in discovering the Calvin cycle . The Meselson-Stahl experiment is another well-known example of the application of isotope labeling; the experiment demonstrated the semiconservative replication of DNA.

Elucidation of reaction mechanisms

An example of the use of isotope labeling as an elucidation method in organic chemistry results, according to Roberts and Urey, with ester formation . The elucidation of the associated mechanism initially raised the question of whether the alkyl-bonded hydroxide oxygen atom of the alcohol is present in the ester or in the water formed after the reaction has ended. By using an alcohol labeled with 18 O (shown in blue below), it was possible to show that the 18 O isotope can only be detected in the ester, i.e. only the upper reaction path ( A ) takes place (only one direction of the reaction is considered, where the usually bound oxygen is the 16 O isotope):

Example of the motivation of isotope labeling based on an esterification reaction

The instability of the carbonyl group of the carboxylic acid in the course of ester formation could also be determined using isotope labeling .

Biotechnological method - metabolic marking

Targeted isotope-labeled compounds such as drugs , active ingredients in pesticides or proteins are produced in order to be able to examine the metabolism of these substances in a targeted manner. By means of isotope-labeled active substances, the breakdown of these substances in the body, their excretion (e.g. via the urine) and their fate in the environment can be studied. This is achieved, for example, with the method of metabolic labeling , in which certain cell cultures can be enriched in special nutrient media with, among other things, isotopically labeled compounds (for example 35 S) in order to be able to subsequently examine their fate in the metabolism of organisms.

SILAC method

The process of metabolic labeling is used, for example, in the context of the SILAC method (for example in the form of a 15 N labeling).

Use in other methods

A chemical variant of isotope labeling is dimethyl labeling ( ICAT ).

The isotope labeling is also used in the form of isobar labeling .

Possible production of an isotope-labeled compound

As an example, 13 C-labeled carbon dioxide can be produced starting from 13 C-labeled barium carbonate ( 1 ) by adding sulfuric acid . The labeled carbon dioxide can then be converted into carboxylic acid ( 2 ) with a 13 C-labeled carbonyl group via a Grignard reaction with butyl magnesium bromide .

Exemplary synthesis of a 13C-labeled carboxylic acid

Individual evidence

  1. ↑ a b c d e f g h i j k l m Ivan Ernest: Binding, structure and reaction mechanisms in organic chemistry. Springer-Verlag, Vienna, 1972, pp. 72-74, ISBN 978-3-211-81365-2 , doi: 10.1007 / 978-3-7091-8437-0 .
  2. ^ Hans Rudolf Christen, Günther Baars: Chemistry. 1st edition, Verlag Sauerländer; Aarau and Diesterweg Verlag; Frankfurt am Main, 1997, p. 35, ISBN 3-7941-3768-X (Sauerländer), ISBN 3-425-05393-0 (Diesterweg).
  3. ↑ a b c d Jürgen Falbe, Manfred Regitz (Ed.): RÖMPP. Dictionary. Chemistry H – L. 10th edition, Georg Thieme Verlag, Stuttgart, 1997, pp. 2015-2016, ISBN 3-13-734810-2 .
  4. ^ Richard E. Dickerson, Harry B. Gray, Marcetta Y. Darensbourg, Donald J. Darensbourg: Principles of Chemistry. 2nd edition, Walter de Gruyter, Berlin, New York, 1988, p. 747, ISBN 3-11-009969-1 .
  5. ^ Matthew Meselson, Franklin W. Stahl: The replication of DNA in Escherichia coli. In: Proceedings of the National Academy of Sciences . Volume 44, No. 7, 1958, pp. 671-682, doi: 10.1073 / pnas.44.7.671 .
  6. ↑ a b Kurt E. Geckeler, Heiner Eckstein (Ed.): Bioanalytical and biochemical laboratory methods. Springer-Verlag, Wiesbaden, 2013, pp. 457–458, ISBN 978-3-642-63745-2 , doi: 10.1007 / 978-3-642-58820-4 .
  7. ↑ Shao-En Ong, Blagoy Blagoev, Irina Kratchmarova, Dan Bach Kristensen, Hanno Steen, Akhilesh Pandey, Matthias Mann: Stable Isotope Labeling by Amino Acids in Cell Culture, SILAC, as a Simple and Accurate Approach to Expression Proteomics. In: Molecular & Cellular Proteomics. Volume 1, 2002, pp. 376-386, doi: 10.1074 / mcp.M200025-MCP200 .
  8. ↑ Steven P. Gygi, Beate Rist, Scott A. Gerber, Frantisek Turecek, Michael H. Gelb, Rudolf Hans Aebersold | Ruedi Aebersold: Quantitative analysis of complex protein mixtures using isotope-coded affinity tags. In: Nature Biotechnology. Volume 17, No. 10, 1999, pp. 994-999, doi: 10.1038 / 13690 .
  9. ↑ Thompson A, Schäfer J, Kuhn K et al. : Tandem mass tags: a novel quantification strategy for comparative analysis of complex protein mixtures by MS / MS . In: Anal. Chem. . 75, No. 8, 2003, pp. 1895-904. doi : 10.1021 / ac0262560 . PMID 12713048 .
  10. ↑ Ross PL, Huang YN, Marchese JN, Williamson B, Parker K, Hattan S, Khainovski N, Pillai S, Dey S, Daniels S, Purkayastha S, Juhasz P, Martin S, Bartlet-Jones M, He F, Jacobson A. , Pappin DJ: Multiplexed protein quantitation in Saccharomyces cerevisiae using amine-reactive isobaric tagging reagents . In: Mol. Cell. Proteomics . 3, No. 12, 2004, pp. 1154-1169. doi : 10.1074 / mcp.M400129-MCP200 . PMID 15385600 .
  11. ↑ Barium carbonate- 13 C as a raw material in the Sigma-Aldrich / Merck catalog. Website of the raw material manufacturer Sigma-Aldrich / Merck. Retrieved November 10, 2017.
  12. ^ Nils Wiberg, Egon Wiberg, Arnold Frederik Holleman: Inorganic Chemistry - Basics and Main Group Elements. Volume 1, 103rd edition, Walter de Gruyter GmbH, Berlin / Boston, 2016, pp. 235-237 & p. 1031, ISBN 978-3-11-026932-1 .
  13. ^ Captain Siegfried: Organic Chemistry. 1st edition, Verlag Harri Deutsch, Thun, Frankfurt am Main, 1985, p. 400, ISBN 3-87144-902-4 .