Crystal Structures of Two Molecular Complexes between Cationic Surfactants and Hydroquinone Showing a Melanogenesis Inhibitory Effect

Abstract

Abstract Hydroquinone, showing a melanogenesis inhibitory effect, formed crystalline molecular complexes with two cationic surfactants of benzyl(hexadecyl)dimethylammonium chloride and ethyl(hexadecyl)dimethylammonium bromide from an methanol solution at low temperatures, lower than 15 °C. The crystal structures were analyzed by X-rays at 223 K. There are two crystallographically independent hydroquinone molecules and one surfactant molecule in each crystal. One of the hydroquinone molecules is sandwiched by the surfactant molecules and makes a “common packing pattern,” which has been observed in complex crystals between aromatic compounds and surfactant molecules. Another hydroquinone occupies an inversion center surrounded by the benzyldimethylammonium or ethyldimethylammonium moiety of the surfactant molecule. Such a close packing makes hydroquinone in the molecular complex stable in open air at room temperature.