A Synthetic Model of the Mn ₃ Ca Subsite of the Oxygen-Evolving Complex in Photosystem II

Abstract

A model compound sheds light on the puzzling role of calcium in the metal cluster that oxidizes water during photosynthesis.

Synthetic model of the asymmetric [Mn 3 CaO 4 ] cubane core of the oxygen-evolving complex of photosystem II

“…The above points make 1 distinctly different from the recently reported [Mn 3 CaO 4 ðO 2 CMeÞ 3 L] (2) complex (16), where L is an O 3 , N 3 hexadentate platform group providing pyridyl and alkoxo ligands to each of the three Mn IV ions. Complex 2 contains a [Mn 3 CaO 4 ] cubane without an external metal ion, and as a result it closely approaches threefold symmetry with Mn⋯Mn and Ca⋯Mn distances in the 2.8301(7)-2.8385(7) and 3.2245(9)-3.2376(9) Å ranges, respectively.…”

“…Although biochemical studies had previously shown Ca to be essential for OEC activity, and X-ray spectroscopy had established the presence of an oxo-bridged Mn 4 Ca heteronuclear cluster, these crystallographic data reenergized efforts to achieve the synthesis of the OEC in the laboratory. Several Mn∕Ca compounds are now known (12)(13)(14)(15), but there is only one complex that has approached the cubane moiety of the OEC structure (16). We here report the development of methodology for synthesizing in the absence of a protein milieu the [Mn 3 CaO 4 ] cubane with an external metal attached to it.…”

Oxygen Atom Transfer and Oxidative Water Incorporation in Cuboidal Mn3MOn Complexes Based on Synthetic, Isotopic Labeling, and Computational Studies

“…Improving upon the published procedure, [15] in the glovebox, a roundbottom flask equipped with a stir bar was charged with 1 (1.00 g, 0.835 mmol) and Ca(OTf) 2 (0.310 g, 0.917 mmol, 1.1 equiv). THF (130 mL) was added, and the yellow heterogeneous mixture was stirred at room temperature for 5 min.…”

Nano-size layered manganese–calcium oxide as an efficient and biomimetic catalyst for water oxidation under acidic conditions: comparable to platinum

“…14 For example, Agapie et al have reported a potential role for calcium in facilitating high oxidation states at a calcium-manganese multinuclear complex. 15 In conclusion, the layered manganese-calcium oxide powder has relatively good kinetics for the oxygen evolution reaction under acidic conditions, but significantly slower under neutral and basic conditions. We verified these results using two different experimental techniques, one where the layered manganese-calcium oxide powder was cast onto a GC electrode and another where the catalytic activity was measured directly using a convective-suspension-collision technique.…”