A betaine () in chemistry is any neutral

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one elemen ...

with a positively charged

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

ic functional group, such as a quaternary ammonium or

phosphonium In polyatomic cations with the chemical formula (where R is a hydrogen or an alkyl, aryl, or halide group). These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions. Types of phosphonium ...

cation (generally:

onium An onium (plural: onia) is a bound state of a particle and its antiparticle. These states are usually named by adding the suffix ''-onium'' to the name of one of the constituent particles (replacing an ''-on'' suffix when present), with one except ...

ions) that bears no hydrogen atom and with a negatively charged functional group such as a

carboxylate In organic chemistry, a carboxylate is the conjugate base of a carboxylic acid, (or ). It is an ion with negative charge. Carboxylate salts are salts that have the general formula , where M is a metal and ''n'' is 1, 2,...; ''carboxylat ...

group that may not be adjacent to the cationic site. Historically, the term was reserved for trimethylglycine (TMG) which is involved in

methylation In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These t ...

reactions and detoxification of homocysteine. This is a modified amino acid consisting of

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinogen ...

with three methyl groups serving as methyl donor for various metabolic pathways. 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). It is commonly pronounced ''beta-INE'' or ''BEE-tayn''. In biological systems, many naturally occurring betaines serve as organic osmolytes. These are 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 permits water retention in cells, thus protecting from the effects of dehydration. This accumulation is non-perturbing to enzyme function, protein structure, and membrane integrity. Betaine is also a

methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in man ...

donor of increasingly recognised significance in biology.

Glycine betaine

The original betaine, ''N'',''N'',''N''-trimethylglycine, was named after its discovery in

sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet (''Beta vulgaris''). Together w ...

(''Beta vulgaris'' subsp. ''vulgaris'') in the nineteenth century. It is a small ''N''-trimethylated

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

. It is a zwitterion, which cannot isomerize because there is no labile hydrogen atom attached to the nitrogen atom. This substance may be called ''glycine betaine'' to distinguish it from other betaines.

Uses

Biochemistry

Phosphonium betaines are intermediates in the Wittig reaction. The addition of betaine to

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) ...

s improves the amplification of DNA by reducing the formation of secondary structure in GC-rich regions. The addition of betaine may enhance the specificity of the polymerase chain reaction by eliminating the base pair composition dependence of DNA melting.

Food additive

In 2017, the

European Food Safety Authority The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002, ...

concluded that betaine was safe "as a novel food to be used at a maximum intake level of 6 mg/kg body weight per day in addition to the intake from the background diet."

Approved drug

prescription drug A prescription drug (also prescription medication or prescription medicine) is a pharmaceutical drug that legally requires a medical prescription to be dispensed. In contrast, over-the-counter drugs can be obtained without a prescription. The re ...

(''Cystadane'') containing betaine has limited use for oral treatment of genetic homocystinuria to lower levels of homocysteine in circulating blood.

Dietary supplement

Trimethylglycine, a betaine, is used as a dietary supplement, although there is no evidence that supplement doses are effective or safe. Common side effects of taking oral betaine include nausea and stomach upset.

Safety concern

Betaine is an irritant of eyes and skin.