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

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 (lambda > 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.