Hollandite as a Functional and Structural Model for the Biological Water Oxidizing Complex: Manganese-Calcium Oxide Minerals as a Possible Evolutionary Origin for the CaMn₄ Cluster of the Biological Water Oxidizing Complex

Abstract

Oxygen evolution was observed upon mixing either hollandite, which has been proposed as a structural model for the biological water oxidizing complex, or hausmannite with an aqueous solution of cerium (IV) ammonium nitrate. Oxygen evolution from water during irradiation with visible light (λ > 400 nm) was also observed upon adding either hollandite or hausmannite to an aqueous solution containing tris (2,2′-bipyridyl)ruthenium(II) chloride and chloro pentaammine cobalt(III) chloride in acetate buffer. These experiments showed that hollandite is a good catalyst for oxygen evolution in presence of cerium (IV) ammonium nitrate or tris (2,2′-bipyridyl)ruthenium (III). Thus, hollandite is not only a structural but also a functional model for the biological water oxidizing complex. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental file.

Keywords:

• hausmannite
• hollandite
• oxygen evolution
• photosystem II
• water oxidizing complex

Acknowledgments

This work was supported by Institute for Advanced Studies in Basic Sciences (IASBS).