The cationic tetramethylammonium (TMA) motif is pervasive in biochemistry, particularly as the charged choline group. Choline-containing lipids are the most abundant phospholipids in biological membranes. Beyond its biological importance, choline-based ionic liquids have recently become of interest as eco-friendly and biocompatible solvents. Tetramethylammonium is also a key motif in other biological species such as betaine and lecithin, all of which play important roles in choline metabolism. In a different context, lysine methylation is a translational modification that occurs on lysine residues within a wide range of proteins.