Transition metal-promoted decomposition of urushiol from poison ivy

The active irritant in poison ivy, urushiol, has been extracted from native plants for the investigation into its metal-catalyzed oxidative decomposition. The decomposition of urushiol by atmospheric oxygen is promoted by complexes of Fe(III), including those of the ligands tris(2-methylpyridyl)amine (TPA) and nitriolotriacetate (NTA), and by simple Fe(III) salts. This is evidenced by the disappearance of the urushiol aromatic proton signal in the H-1-NMR spectrum, as well as by identification of some of the oxygenation products by GC-MS. Analogous reactions using Zn(II) and Ni(II) complexes and salts show that substantial amounts of unishiol remain unreacted. This suggests that reactivity similar to that of catechol-dioxygenase enzymes may be the mechanism of the oxidative decomposition, and that simple coordination to transition metals may not be the mechanism by which urushiol is inactivated, as has been previously reported. (C) 2012 Elsevier B.V. All rights reserved.