A betaine (/ -, - /,) in chemistry is any neutral chemical compound with a positively charged cationic functional group such as a quaternary ammonium or phosphonium cation (generally: onium ions) that bears no hydrogen atom and with a negatively charged functional group such as a carboxylate group that may not be adjacent to the cationic site. A betaine thus may be a specific type of zwitterion. Historically, the term was reserved for TMG (trimethylglycine) only. Biologically, TMG is involved in methylation reactions and detoxification of homocysteine.
The pronunciation of the compound reflects its origin and first isolation from sugar beets (Beta vulgaris subsp. vulgaris), and does not derive from the Greek letter beta (β), however, it often is pronounced beta-INE or BEE-tayn.
In biological systems, many naturally occurring betaines serve as organic osmolytes, substances synthesized 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 increasingly recognised significance in biology.
The original betaine, N,N,N-trimethylglycine, was named after its discovery in sugar beet (Beta vulgaris subsp. vulgaris) in the nineteenth century. It is a small N-trimethylated amino acid, existing in zwitterionic form at neutral pH. In the 21st century, this substance is called glycine betaine to distinguish it from other betaines that are widely distributed in microorganisms, plants, and animals.
Phosphonium betaines are intermediates in the Wittig reaction.
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.
- Alex Nickon and Ernest F. Silversmith (1987). Organic Chemistry, the Name Game: Modern Coined Terms and Their Origins. Pergamon. ISBN 978-0080344812.
- DNA Methylation and Complex Human Disease, Michel Neidhart
- 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.
- 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.