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Artificial Metalloproteins Containing Co4O4 Cubane Active Sites
journal contribution
posted on 2018-02-05, 00:00 authored by Lisa Olshansky, Raúl Huerta-Lavorie, Andy I. Nguyen, Jaicy Vallapurackal, Ariel Furst, T. Don Tilley, A. S. BorovikArtificial
metalloproteins (ArMs) containing Co4O4 cubane
active sites were constructed via biotin–streptavidin
technology. Stabilized by hydrogen bonds (H-bonds), terminal and cofacial
CoIII–OH2 moieties are observed crystallographically
in a series of immobilized cubane sites. Solution electrochemistry
provided correlations of oxidation potential and pH. For variants
containing Ser and Phe adjacent to the metallocofactor, 1e–/1H+ chemistry predominates until pH 8, above which the
oxidation becomes pH-independent. Installation of Tyr proximal to
the Co4O4 active site provided a single H-bond
to one of a set of cofacial CoIII–OH2 groups. With this variant, multi-e–/multi-H+ chemistry is observed, along with a change in mechanism at
pH 9.5 that is consistent with Tyr deprotonation. With structural
similarities to both the oxygen-evolving complex of photosystem II
(H-bonded Tyr) and to thin film water oxidation catalysts (Co4O4 core), these findings bridge synthetic and biological
systems for water oxidation, highlighting the importance of secondary
sphere interactions in mediating multi-e–/multi-H+ reactivity.