# Functional LnFe-NxHy Models of Biological N2 Fixation

> **NIH NIH R01** · CALIFORNIA INSTITUTE OF TECHNOLOGY · 2020 · $327,439

## Abstract

Project Summary - Functional LnFe-NxHy Models of Biological N2 Fixation
Nitrogenase (N2-ase) metalloenzymes mediate biological nitrogen fixation and as such are essential to life. Their
study correspondingly attracts intense interest from the biology and chemistry communities. Nonetheless, the
mechanism by which nitrogenase enzymes promote the biological reduction of nitrogen under ambient
conditions remains enigmatic. The broad questions that motivate our NIH-supported research program are as
follows: Can a single iron site mediate the critical bond-making and breaking steps relevant to catalytic N2
fixation in a synthetic model system and, by extension, in biology? If so, what are the key intermediates and
pathways that are accessible? How can a secondary metal center and/or secondary sphere interactions impact
such reactivity? This renewal application builds on extensive progress made in the last grant period, reported
via 21 primary literature publications. We propose to continue to design and study Fe-NxHy model complexes
to address the questions highlighted above. Our approach stresses functionally, rather than structurally, faithful
models of the iron-molybdenum cofactor (FeMoco). Low molecular weight Fe-NxHy complexes will be
developed to explore iron sites in low coordinate geometries that accommodate N2 and more reduced NxHy.
Two limiting single-site mechanisms for biological nitrogen fixation have been emphasized: the first is an
alternating mechanism, where successive H-atom transfers (via H+/e- steps) occur at the distal and proximal N-
atoms of an Fe-N≡N subunit in an alternating fashion (e.g., Fe-N=NH → Fe-NH=NH → Fe-NH-NH2→ Fe-NH2-
NH2 → Fe-NH2 + NH3); the second is a distal mechanism, where three H-atom transfers at the distal N-atom to
liberate an NH3 equivalent (e.g., Fe-N2 + 3 e- + 3 H+ → Fe≡N + NH3) precede H-atom transfers to the proximal N-
atom. We also explore a hybrid cross-over mechanism that interweaves both paths. Our synthetic model studies
are used to test the viability of each of these pathways, and to understand how the local geometry and electronic
structure of Fe-NxHy species controls their reactivity patterns, with the goal of developing increasingly efficient
Fe-mediated N2-to-NH3 conversion catalysts. Regardless of the precise mechanism/s of nitrogen reduction, the
assignment of enzymatic intermediates relies upon the availability of well-defined spectroscopic parameters for
Fe-NxHy models. We will continue to collect such data, and to collaborate with researchers that specialize in
spectroscopic studies, including within nitrogenase enzymes, to enable useful comparisons to be made. In sum,
the functional Fe-NxHy model chemistry proposed herein will continue to play a critical role alongside current
biochemical, spectroscopic, and theoretical model studies aimed at unraveling the chemical mechanism/s of
biological nitrogen fixation.

## Key facts

- **NIH application ID:** 10051289
- **Project number:** 2R01GM070757-16
- **Recipient organization:** CALIFORNIA INSTITUTE OF TECHNOLOGY
- **Principal Investigator:** Jonas C Peters
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $327,439
- **Award type:** 2
- **Project period:** 2005-02-01 → 2024-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10051289

## Citation

> US National Institutes of Health, RePORTER application 10051289, Functional LnFe-NxHy Models of Biological N2 Fixation (2R01GM070757-16). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10051289. Licensed CC0.

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