Betaine

This article is about the group of chemical compounds. For glycine betaine, see trimethylglycine.

A betaine in chemistry is any neutral chemical compound with a positively charged cationic functional group such as an quaternary ammonium or phosphonium cation (generally: onium ions) which bears no hydrogen atom and with a negatively charged functional group such as a carboxylate group which may not be adjacent to the cationic site. A betaine thus may be a specific type of zwitterion. Historically the term was reserved for trimethylglycine only.

Phosphonium betaines are intermediates in the Wittig reaction.

In biological systems, many betaines serve as organic osmolytes, substances synthesised or taken up from the environment by cells for protection against osmotic stress, drought, high salinity or high temperature. Intracellular accumulation of betaines, non-perturbing to enzyme function, protein structure and membrane integrity, permits water retention in cells, thus protecting from the effects of dehydration. It is also a methyl donor of increasing significance.

The addition of betaine to polymerase chain reactions improves the amplification of DNA by reducing the formation of secondary structure in GC-rich regions. The addition of betaine has been reported to enhance the specificity of the polymerase chain reaction by eliminating the base pair composition dependence of DNA melting.^[1][2]

Glycine betaine

The chemical structure of trimethylglycine

Main article: Trimethylglycine

The original betaine, N,N,N-trimethylglycine, was named after its discovery in sugar beet (Beta vulgaris) in the 19th century. It is a small N-trimethylated amino acid, existing in zwitterionic form at neutral pH. This substance is now often called glycine betaine to distinguish it from other betaines that are widely distributed in microorganisms, plants and animals.

See also

• Ylide
• Cocamidopropyl betaine
• Osmoprotectants

Further reading

• IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "betaines".

References

1. ^ Rees, William A.; Yager, Thomas D.; Korte, John; Von Hippel, Peter H. (1993). "Betaine can eliminate the base pair composition dependence of DNA melting". Biochemistry 32 (1): 137–44. doi:10.1021/bi00052a019. PMID 8418834. 
2. ^ Henke, W; Herdel, K; Jung, K; Schnorr, D; Loening, SA (1997). "Betaine improves the PCR amplification of GC-rich DNA sequences". Nucleic Acids Research 25 (19): 3957–8. doi:10.1093/nar/25.19.3957. PMC 146979. PMID 9380524. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=146979.