# Understanding the Selectivity of Oxygen Activation by Model Iron-Porphyrin Catalysts

> **NIH NIH F32** · YALE UNIVERSITY · 2020 · $15,416

## Abstract

PROJECT SUMMARY
 Heme-containing proteins are among the most abundant metalloproteins in nature. A significant subset of
these catalysts perform reactions utilizing dioxygen (O2), including cytochrome c oxidase (CcO) which reduces
dioxygen to water, and cytochrome P450 (CYP) which activates dioxygen in order to oxidize organic
substrates. The functions of CYP and CcO rely on their abilities to reduce O2 to water. In an “uncoupled”
process, some equivalents of reductant are wasted and reactive oxygen species (ROS) such as H2O2 are
released. ROS are known to lead to oxidative stress and a variety of diseases in the human body, so
developing an understanding of this uncoupling is important. It is hypothesized that a catalytic Fe–OOH
intermediate is the site of bifurcation between H2O and H2O2 formation. This hydroperoxy intermediate is
ubiquitous in heme-containing enzymes including cytochrome c peroxidase, heme oxygenase, and
prostaglandin H synthase. In all cases, proper proton delivery is necessary for O–O bond cleavage.
 Mutagenesis studies of P450cam have made it clear that the role of protons and H-bonding are important
in understanding selectivity, but there is debate as to how the conserved residues prevent uncoupling.
Additionally, the canonical mechanism involves one proton addition to either the proximal or distal oxygen atom
of the Fe–OOH intermediate to yield H2O2 or H2O, respectively, but there is no direct evidence of this
stoichiometry. Our preliminary data suggests that the desired distal protonation may involve a higher
dependence on protons. Therefore our goal is to study what governs the selectivity between formation of H2O
or release of H2O2 from this critical Fe–OOH intermediate.
 Our work in this proposal seeks to understand the selectivity of H2O and H2O2 formation from heme
enzymes utilizing a simple model system. Synthetic analogues provide the advantage of allowing us to
systematically vary and control structural entities, enter the catalytic cycle in new places, and independently
synthesize intermediates. Therefore, we propose to study the selectivity of O2 activation by Fe-porphyrin
catalysts proceeding through the same Fe–OOH intermediate. First, we will explore how various reaction
conditions (concentration, pKa, and structure of the acid) affect selectivity in the catalytic oxygen reduction
reaction (ORR). Secondly, we will study a variety of catalysts with varied H-bonding motifs to better understand
how the residues in an active site may influence selectivity. Additionally, we will explore the non-catalytic
reactivity of the Fe–OOH intermediate to gain independent measures of the relative rates of H2O and H2O2
formation under varied conditions. Ultimately, our goal is to understand how the reaction conditions and H-
bonding networks affect H2O versus H2O2 selectivity in a model system. This understanding will provide insight
into how enzymes can control the reactivity of the critical Fe-hydroperoxy intermediate to m...

## Key facts

- **NIH application ID:** 9927487
- **Project number:** 5F32GM129890-02
- **Recipient organization:** YALE UNIVERSITY
- **Principal Investigator:** Anna Brezny
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $15,416
- **Award type:** 5
- **Project period:** 2019-05-01 → 2020-07-05

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9927487

## Citation

> US National Institutes of Health, RePORTER application 9927487, Understanding the Selectivity of Oxygen Activation by Model Iron-Porphyrin Catalysts (5F32GM129890-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9927487. Licensed CC0.

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