Characterization of Cu(II)-ACC complexes and conversion of the bound ACC into ethylene in the presence of hydrogen peroxide. Detection of a brown intermediate at low temperature

Two copper( II)-ACC complexes were prepared and characterized: [Cu(bpy)( ACC)( H2O)]center dot CO4 ( 1) and [Cu( ACC)(2)](3)center dot 4H(2)O( 2). Their crystallographic structures are described and analyzed. Spectroscopic characterizations ( UV-visible and EPR) confirm that the structure is maintained in solution. These complexes are able to produce ethylene in the presence of hydrogen peroxide in an ACC Oxidase- like reaction in water and in methanol. The conversion of ACC into ethylene depends on the amount of base, and, in methanol, 3 equivalents of NaOH are needed for optimum activity. The base is proposed to play a role in H2O2 deprotonation. The presence of an exogenic ligand ( bpy) is important for the reactivity and may stabilize a reaction intermediate. Indeed, a brown intermediate with an absorption band centered at 433 nm can be detected at low temperature when 1 is treated with 10 equivalents of H2O2. Copyright (C) 2007.