Deprotonation of a carboxyl group gives a carboxylate anion. Betaines such as cocamidopropyl betaine have a carboxylate with the ammonium. It is a zwitterion, consisting of both a quaternary ammonium cation and a carboxylate. Other carboxylate salts form complexes; e.g., citrate and tartrate. The carboxylate group can coordinate to metal ions forming coordination complexes. The X group is typically an electronegative, such as chloride, hydroxide, or carboxylate. This is crystallized to make nylon salt, an ammonium/carboxylate mixture. Metal salts, especially copper compounds, facilitate the reaction via the intermediacy of metal carboxylate complexes. The acetate anion, [CHCOO],(or [CHO]) is one of the carboxylate family. The overall process converts the methyl groups to carboxylate and dehydrogenates the backbone. Calcium stearate is a carboxylate of calcium, classified as a calcium soap. The carboxylate group confers solubility in water. Similarly, a molecule containing a phosphonium group and a carboxylate group cannot isomerize. Metadoxine is an ion pair salt of pyridoxine and pyrrolidone carboxylate (PCA). It is chemically incompatible with paints relying on metal carboxylate curing agents.