Quaternary ammonium compounds are any of a group of ammonium salts in which organic radicals have been substituted for all four hydrogens of the original ammonium cation. They has a central nitrogen atom which is joined to four organic radicals and one acid radical. The organic radicals may be alkyl, aryl, or aralkyl, and the nitrogen can be part of a ring system. They are prepared by treatment of an amine with an alkylating agent. They show a variety of physical, chemical, and biological properties and most compounds are soluble in water and strong electrolytes. In addition to their tendency of locating at the interface of two phases (liquid–liquid or solid–liquid) to introduces continuity between the two different phase, they have properties of disrupting micro-organisms' cell processes.