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

Abstract

Two copper(II)-ACC complexes were prepared and characterized: [Cu(bpy)(ACC)(H2O)]⋅ CO4 (1) and [Cu(ACC)2]3 ⋅ 4H2O (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.

Regulation of epinasty induced by 2,4‐dichlorophenoxyacetic acid in pea and Arabidopsis plants

“…EDTA also reduced the emission of ET, probably by removing metals that participate in ET biosynthesis throughout Fenton‐type reactions involving 1‐aminocyclopropane‐1‐carboxylic acid (ACC), H 2 O 2 and Cu(II) (Ghattas et al . ).…”

“…The role played by ROS in the development of epinasty is validated through analysis of carbonyl content in wild-type and xdh Arabidopsis plants treated with 2,4-D, and the protective role of EDTA that prevents protein oxidation. EDTA also reduced the emission of ET, probably by removing metals that participate in ET biosynthesis throughout Fenton-type reactions involving 1-aminocyclopropane-1-carboxylic acid (ACC), H 2 O 2 and Cu(II) (Ghattas et al 2007).…”

Characterization of Cu(II)-reconstituted ACC Oxidase using experimental and theoretical approaches

“…Several years ago, we have reported on a series of structurally characterized Cu(II)-ACC complexes using aminopyridine-type ligands in which ACC is coordinated on the Cu(II) ion in a bidentate manner [20], [21], [22]. These complexes are able to oxidize the bound ACC into ethylene in the presence of hydrogen peroxide.…”

“…Indeed, we have observed, using EPR spectroscopy and upon addition of increasing amount of ascorbate, that the Cu(II)reconstituted ACCOs were very difficult to reduce using ascorbate, the co-substrate of ACCO in activity assays. We have previously reported that simple copper-ACC complexes (Scheme 2) were able to produce ethylene from the bound ACC moiety when reacted with hydrogen peroxide, a two electron reduced form of dioxygen [20,22,23]. For this reason, ethylene production mediated by ACCO-Cu enzymes was also evaluated using a peroxide-shunt assay.…”