# N2 Generation from Nitric Oxide Coordinated to Iron(III) Porphyrin in Acidic Glycine Buffer

## TL;DR

A new method converts nitric oxide to nitrogen gas using iron porphyrin in an acidic glycine solution.

## Contribution

A novel N–N bond formation mechanism via glycine's nucleophilic attack on iron(III) nitrosyl complexes is revealed.

## Key findings

- N2 is efficiently generated from NO in acidic glycine buffer with iron(III) porphyrin complexes.
- Glycine nucleophilic attack forms a diazo compound that hydrolyzes to release N2.
- Isotope labeling and DFT calculations confirm the proposed reaction mechanism.

## Abstract

Nitric oxide (NO) was efficiently converted to molecular
nitrogen
(N2) in an acidic aqueous solution containing iron­(III)
porphyrin encapsulated in the cyclodextrin (CD) nanocavity. The supramolecular
iron­(III) porphyrin/CD dimer complexes (hemoCD-P and hemoCD-I), where
the iron­(III) is axially coordinated by a nitrogenous ligand (pyridine
or imidazole) in the linker of the CD dimer, form stable 6-coordinated
ferric nitrosyls {FeNO}6 in acidic aqueous solution (pH
∼3). When the solution contained glycine as the buffer component,
N2 bubbles were significantly generated within several
minutes at room temperature. In this system, a new N–N bond
is formed on the iron-porphyrin due to the nucleophilic attack of
glycine on the {FeNO}6 complex. The resulting diazo compound,
ON–NH–CH2–COOH ⇄ HO–NN–CH2–COOH, was readily hydrolyzed to generate N2 along with a formation of α-hydroxyacid (HO–CH2–COOH). The reaction mechanism was evidenced by isotope-labeling
experiments using 15NO and 15N-glycine, quantitative
NMR detection of α-hydroxyacid, and theoretical calculation
by DFT. The present study will provide the possibility of N–N
bond formation promoted by the nucleophilic attack of amines to {FeNO}6 on the native heme iron.