# Synthetic Models of the Oxygen Evolving Complex of Photosystem II

> **NIH NIH R01** · CALIFORNIA INSTITUTE OF TECHNOLOGY · 2020 · $209,434

## Abstract

Abstract
Biological dioxygen generation occurs within Photosystem II (PSII) in cyanobacteria and plants. The
active site responsible for this transformation, the Oxygen Evolving Complex (OEC), consists of a
Mn4CaOn cluster embedded in a large protein complex. This metal cluster is responsible for the
oxygenic atmosphere on Earth, and consequently for most life as we know it. Given the broad
fundamental interest and potential applications of water splitting to make dioxygen, the structure of
this cluster and the mechanism of catalysis have been the subject of many spectroscopic,
computational, synthetic, crystallographic and biochemical studies. Despite significant advances, the
mechanism of oxygen production is still not well understood. The exact Mn oxidation states along the
catalytic cycle and the site of O-O bond formation continue to be debated. The large protein matrix
has complicated direct studies of the OEC active site and the rational synthesis of accurate small-
molecule models suitable for structure-function studies has been hampered by the complexity of the
cluster.
Our goals include developing synthetic routes to MnxMOn models (x=3, 4; M=Ca, Mn, other metals) of
the OEC and its subsites and undertaking mechanistic studies that will allow a deeper understanding
of the effects different constituents (metals, ancillary and oxo ligands, protonation state) have on the
chemical and physical properties of the cluster relevant to achieving high oxidation states and
effecting O2 production. To that end, we will test hypotheses regarding electron, oxygen-atom and
proton transfers and ligand substitution in these complex systems with implications for O-O bond
formation. With few exceptions, the synthesis of predictable manganese oxide clusters has been
frustrated by the propensity of oxo ligands to bridge and form complicated oligomeric structures. Our
approach to overcoming this problem is to use relatively small, but rigid organic frameworks to support
trimanganese complexes that have been elaborated to site-differentiated metal-oxo clusters, including
close structural and functional models of the biological system. These synthetic clusters will allow for
spectroscopic benchmarking (EPR, XES, XAS) in comparison with the biological system. Our work on
synthetic complexes will complement the studies performed on the protein by allowing systematic
structure-property studies to uncover the chemical features that control the reactivity and
spectroscopy of these clusters and the mechanism of catalysis.

## Key facts

- **NIH application ID:** 9980923
- **Project number:** 5R01GM102687-07
- **Recipient organization:** CALIFORNIA INSTITUTE OF TECHNOLOGY
- **Principal Investigator:** Theodor Agapie
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $209,434
- **Award type:** 5
- **Project period:** 2013-09-01 → 2023-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9980923

## Citation

> US National Institutes of Health, RePORTER application 9980923, Synthetic Models of the Oxygen Evolving Complex of Photosystem II (5R01GM102687-07). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9980923. Licensed CC0.

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