Betaine

Topic

A betaine is any neutral chemical compound with a positively charged cationic functional group bearing no hydrogen atom, such as a quaternary ammonium, and a negatively charged functional group, such as a carboxylate. Historically, the term was reserved for trimethylglycine (TMG), a specific zwitterion involved in methylation reactions and the detoxification of homocysteine. Because they lack a labile hydrogen atom attached to the cationic atom, betaines are stable zwitterions that cannot isomerize.