Catalytic Water Oxidation by Iridium-Modified Carbonic Anhydrase

Area of Science:

• Biochemistry
• Bioinorganic Chemistry
• Catalysis

Background:

• Carbonic anhydrase (CA) is a zinc metalloenzyme.
• Metalloenzymes utilize metal cofactors for biological functions.
• Iridium (Ir) complexes are known catalysts.

Purpose of the Study:

• To investigate the water-oxidizing activity of an iridium-bound carbonic anhydrase.
• To explore the use of carbonic anhydrase as a scaffold for transition metal catalysts.
• To assess the thermodynamic feasibility and catalytic performance of the CA-Ir complex.

Main Methods:

• Removal of the native zinc cofactor from carbonic anhydrase.
• Coordination of iridium to the carbonic anhydrase apoprotein.
• Assay of water-oxidizing activity under mild, neutral conditions.
• Thermodynamic analysis of iridium binding.

Main Results:

• The resulting carbonic anhydrase-iridium complex (CA[Ir]) exhibited significant water-oxidizing activity (TOF of 39.8 min⁻¹).
• Iridium binding to the CA apoprotein was thermodynamically favorable (ΔH = -10.8 kcal/mol).
• Catalytic activity was dependent on the presence of iridium bound to the CA scaffold.

Conclusions:

• Carbonic anhydrase can serve as an effective biological scaffold to activate iridium for water oxidation catalysis.
• The histidine imidazoles in the CA active site can be utilized as ligands for various transition metals.
• This approach offers a pathway to develop novel bio-inspired catalysts with unique biochemical activities.