Chlorophyll a π‐Cation Radical as Redox Mediator in Superoxide Dismutase (SOD) Mimetics

Abstract

The extensive speciation of copper(II) chloride in organic solvents varies with concentration, temperature, pressure and oxygen content, providing the ability to switch between different chlorophyll transmetalation pathways. We found that one of them is exceptionally suitable for the formation and stabilisation of the chlorophyll π‐cation radical. This is due to unique redox cycling, which is coupled to the generation and transformation of various reactive oxygen species. In the presence of a proton donor, our system shows behavior which resembles that of superoxide dismutase (SOD). Regardless of light, chlorophyll acts as an electron transfer mediator.

Copper(II)-Assisted Degradation of Pheophytin a by Reactive Oxygen Species

“…Thus, a stable open-chain NCC-like product is formed, as evidenced by its circular dichroism features. In addition to the complex formation [9,47] and the redox cycling characteristic of Chla [17], the mechanism revealed here represents another pathway of reactions between Chls and transition metal ions, an alternative to those traditionally considered. This may also partly account for the role of heavy metallic pollutants in damaging the photosynthetic apparatus in plants.…”

“…The redox cycling is characteristic of Chla, which is alternately oxidized to a cation radical and reduced back in a reaction involving mixed Cu(I) and Cu(II) species. An important role in these reactions is played by reactive oxygen species (ROS), namely superoxide and peroxide, whose generation and scavenging are strictly correlated with the Chla redox cycling and Cu(II)/Cu(I) speciation equilibria [17].…”

Chlorophylls: A Personal Snapshot

“…Chl cation radicals are formed in the primary reaction of photosynthesis by electron transfer. Orzel et al [ 42 ] have now shown that in the presence of CuCl 2 , they can also be generated and participate in electron transfer in the dark.…”

“…A large fraction of the photosynthetic apparatus is therefore devoted to photoprotection [ 52 ], with carotenoids serving several lines of defense. The publication of Demming-Adams et al in this Special Issue is devoted to a particularly effective carotenoid, zeaxanthin [ 42 ]. The role of carotenoids is, however, multi-faceted.…”