# Understanding How Thiolates Promote Dioxygen Chemistry

> **NIH NIH R01** · UNIVERSITY OF WASHINGTON · 2022 · $428,170

## Abstract

Project Summary
Cysteinate-ligated non-heme iron superoxo intermediates (RS-FeIII-O2•–) play a key role in the mechanisms of
isopenicillin N-synthase (IPNS) and cysteine dioxygenase (CDO). The former provides our only source of β-
lactam antibiotics, and the latter is known to prevent metastases of cancerous tumors and neurological disorders.
Very little is known about the mechanisms of these reactions, the understanding of which will facilitate the
synthesis of new anticancer drugs and antibiotics to which bacteria are not yet resistant. Very few well-
characterized FeIII-O2•– compounds have been reported, and only two include a thiolate in the coordination
sphere. Our group reported the first and only example of an RS-FeIII-O2•– capable of cleaving strong C-H bonds
on par with cysteine β-C-H bond cleaved by IPNS. The goal of the work proposed herein will be to determine
whether ligand constraints can be used to alter the reaction pathway of our RS-FeIII-O2•– from that of IPNS to that
of CDO. We will incorporate β-hydrogens into our aliphatic thiolate ligand and determine whether intramolecular
β C-H bond cleavage occurs, and β-deuteriums to see if that stabilizes the FeIII-O2•–, and if so, determine the
kinetic isotope effect to provide additional support for intramolecular β-C-H bond cleavage. We will determine
whether the trans thiolate influences the potency of our RS-FeIII-O2•– with respect to C-H bond cleavage by
exploring the O2 chemistry of our mixed alkoxide/thiolate-ligated FeII complex. We will use Mossbauer
spectroscopy and spectro-electrochemistry to provide evidence for the involvement of proton coupled electron
transfer in the conversion of our putative high valent O=(R)S-FeIV=O to the corresponding O=(R)S-FeIII-OH and
obtain the FeIIIO–H bond strength from the slope of the Pourbaix (pH vs E1/2) diagram. We will also examine the
effects of redox inactive Lewis acidic cations and protons on the ability of our crystallographically characterized
cis RS-FeIV=O to cleave strong C-H bonds, and determine how the thiolate affects this reactivity by synthesizing
the corresponding cis RO-FeIV=O compound and examining pH-dependent redox potentials using spectro-
electrochemistry and comparing the O–H bond strengths, obtained from the slope of the Pourbaix (pH vs E1/2)
diagram, for cis RO-FeIII-OH versus cis RS-FeIII-OH. We will insert a methylene group into the ligand scaffold of
our crystallographically characterized cis RS-FeIV=O to determine whether ligand constraints prevent
intramolecular oxo atom transfer. Lastly, we will determine whether the synergistic interaction between a 𝛑-
donating thiolate and 𝛑-accepting CO ligands facilitates hydrogenase (H2-ase) promoted H2 production and H2
cleavage.

## Key facts

- **NIH application ID:** 10444825
- **Project number:** 2R01GM123062-05
- **Recipient organization:** UNIVERSITY OF WASHINGTON
- **Principal Investigator:** Julia A Kovacs
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $428,170
- **Award type:** 2
- **Project period:** 2018-05-01 → 2026-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10444825

## Citation

> US National Institutes of Health, RePORTER application 10444825, Understanding How Thiolates Promote Dioxygen Chemistry (2R01GM123062-05). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10444825. Licensed CC0.

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