The oxygen-evolving complex (OEC) of photosystem II catalyzes water oxidation in the presence of sunlight to furnish dioxygen, protons and electrons. The released protons and electrons can then be used to generate hydrogen (H2) which is considered as the most promising fuel of the future. Recent studies have confirmed the OEC to be a Mn4CaO5 cluster supported by six carboxylates, one imidazole and four water molecules. One of these water molecules is thought to be involved in O–O bond formation, and is finally released as O2. The Mn4CaO5 cluster consists of a Mn3CaO4 cubane core with the fourth Mn dangling away from the core via an oxido bridge. This “dangler” Mn is considered pivotal for the functionality of the OEC as it is most likely involved in the crucial O–O bond formation step. Although tremendous efforts have been spent on artificial photosynthesis systems, synthetic water oxidation catalysts that closely mimic the structure and function of OEC in PS II are very limited. One of the promising ways to assemble the Mn4CaO5 cluster is through rational design of the ligands that can offer multiple metal-binding sites within the same ligand framework. The work herein reports the design and synthesis of such ligands where the cyclam-based macrocycles of different ring-size have been used as basal platform to support multiple metal-binding units comprised of N– and O–donor atoms through the amide linker between them.

Assembling oxygen-evolving complex (OEC) of photosystem II: Design and synthesis of ligands

255th National Meeting (2018)

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