The fact that the redox potential of the couple CO₃^.-/CO₃^2-, 1.57 V, is considerably lower than that of the OH^./H₂O suggests that in many catalytic oxidation processes carbonate might be involved. Indeed results point out that the Fenton reaction in the presence of HCO₃^- proceeds via:

Fe(H₂O)₆²⁺ + HCO₃^- ⇌

                          Fe^II(CO₃)(H₂O)₃ + H₃O⁺  + 2H₂O

Fe^II(CO₃)(H₂O)₃ + OOH^- ⇌

             (CO₃)Fe^II(OOH)(H₂O)₂^- + H₂O

(CO₃)Fe^II(OOH)(H₂O)₂^- ®

                                           (CO₃)Fe^IV(OH)₃(H₂O)^-

(CO₃)Fe^IV(OH)₃(H₂O)^- ®

     Fe^III(OH)₃(H₂O) + CO₃^.-

i.e. the active ROS in physiological media and in advanced oxidation processes is CO₃^.- and not OH^..

Furthermore DFT calculations suggest that CO₃^.- is expected as the active species in photo-catalytic oxidation processes.

The observation that Cu^II(CO₃)_n^(2n-2)-, Co^II(CO₃)_n^(2n-2)-and Ni^IIL²⁺ in the presence of bicarbonate are good electro-catalysts for water oxidation is due to:

1. The carbonate ligand lowers considerably the redox potential of the central cation.
2. The carbonate ligand is a non-innocent ligand, i.e. a considerable charge transfer from the central cation to the carbonate occurs. This charge transfer is involved in the water oxidation.

Acknowledgement: This study was supported by a grant from the Pazy Foundation.

The fact that the redox potential of the couple CO₃^.-/CO₃^2-, 1.57 V, is considerably lower than that of the OH^./H₂O suggests that in many catalytic oxidation processes carbonate might be involved. Indeed results point out that the Fenton reaction in the presence of HCO₃^- proceeds via:

Fe(H₂O)₆²⁺ + HCO₃^- ⇌

                          Fe^II(CO₃)(H₂O)₃ + H₃O⁺  + 2H₂O

Fe^II(CO₃)(H₂O)₃ + OOH^- ⇌

             (CO₃)Fe^II(OOH)(H₂O)₂^- + H₂O

(CO₃)Fe^II(OOH)(H₂O)₂^- ®

                                           (CO₃)Fe^IV(OH)₃(H₂O)^-

(CO₃)Fe^IV(OH)₃(H₂O)^- ®

     Fe^III(OH)₃(H₂O) + CO₃^.-

i.e. the active ROS in physiological media and in advanced oxidation processes is CO₃^.- and not OH^..

Furthermore DFT calculations suggest that CO₃^.- is expected as the active species in photo-catalytic oxidation processes.

The observation that Cu^II(CO₃)_n^(2n-2)-, Co^II(CO₃)_n^(2n-2)-and Ni^IIL²⁺ in the presence of bicarbonate are good electro-catalysts for water oxidation is due to:

1. The carbonate ligand lowers considerably the redox potential of the central cation.
2. The carbonate ligand is a non-innocent ligand, i.e. a considerable charge transfer from the central cation to the carbonate occurs. This charge transfer is involved in the water oxidation.

Acknowledgement: This study was supported by a grant from the Pazy Foundation.

The fact that the redox potential of the couple CO₃^.-/CO₃^2-, 1.57 V, is considerably lower than that of the OH^./H₂O suggests that in many catalytic oxidation processes carbonate might be involved. Indeed results point out that the Fenton reaction in the presence of HCO₃^- proceeds via:

Fe(H₂O)₆²⁺ + HCO₃^- ⇌

                          Fe^II(CO₃)(H₂O)₃ + H₃O⁺  + 2H₂O

Fe^II(CO₃)(H₂O)₃ + OOH^- ⇌

             (CO₃)Fe^II(OOH)(H₂O)₂^- + H₂O

(CO₃)Fe^II(OOH)(H₂O)₂^- ®

                                           (CO₃)Fe^IV(OH)₃(H₂O)^-

(CO₃)Fe^IV(OH)₃(H₂O)^- ®

     Fe^III(OH)₃(H₂O) + CO₃^.-

i.e. the active ROS in physiological media and in advanced oxidation processes is CO₃^.- and not OH^..

Furthermore DFT calculations suggest that CO₃^.- is expected as the active species in photo-catalytic oxidation processes.

The observation that Cu^II(CO₃)_n^(2n-2)-, Co^II(CO₃)_n^(2n-2)-and Ni^IIL²⁺ in the presence of bicarbonate are good electro-catalysts for water oxidation is due to:

1. The carbonate ligand lowers considerably the redox potential of the central cation.
2. The carbonate ligand is a non-innocent ligand, i.e. a considerable charge transfer from the central cation to the carbonate occurs. This charge transfer is involved in the water oxidation.

Acknowledgement: This study was supported by a grant from the Pazy Foundation.

The fact that the redox potential of the couple CO₃^.-/CO₃^2-, 1.57 V, is considerably lower than that of the OH^./H₂O suggests that in many catalytic oxidation processes carbonate might be involved. Indeed results point out that the Fenton reaction in the presence of HCO₃^- proceeds via:

Fe(H₂O)₆²⁺ + HCO₃^- ⇌

                          Fe^II(CO₃)(H₂O)₃ + H₃O⁺  + 2H₂O

Fe^II(CO₃)(H₂O)₃ + OOH^- ⇌

             (CO₃)Fe^II(OOH)(H₂O)₂^- + H₂O

(CO₃)Fe^II(OOH)(H₂O)₂^- ®

                                           (CO₃)Fe^IV(OH)₃(H₂O)^-

(CO₃)Fe^IV(OH)₃(H₂O)^- ®

     Fe^III(OH)₃(H₂O) + CO₃^.-

i.e. the active ROS in physiological media and in advanced oxidation processes is CO₃^.- and not OH^..

Furthermore DFT calculations suggest that CO₃^.- is expected as the active species in photo-catalytic oxidation processes.

The observation that Cu^II(CO₃)_n^(2n-2)-, Co^II(CO₃)_n^(2n-2)-and Ni^IIL²⁺ in the presence of bicarbonate are good electro-catalysts for water oxidation is due to:

1. The carbonate ligand lowers considerably the redox potential of the central cation.
2. The carbonate ligand is a non-innocent ligand, i.e. a considerable charge transfer from the central cation to the carbonate occurs. This charge transfer is involved in the water oxidation.

Acknowledgement: This study was supported by a grant from the Pazy Foundation.