High Quality Content by WIKIPEDIA articles! Tetramethylammonium (TMA) or (Me4N+) is the simplest quaternary ammonium cation consisting of four methyl groups attached to a central nitrogen atom, and is positively charged. It must exist in association with a counter-ion, and is most commonly found in simple salts such as tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide and tetramethylammonium hydroxide. Tetramethylammonium salts are used in chemical synthesis and are widely employed in pharmacological research. They also occur as toxic natural products, although the counterions may be difficult to identify. The identity of the anion associated with the tetramethylammonium cation frequently has little or no bearing on a particular chemical or biological type of action, but this is not invariably so.