# Ultra-Weak Photon Emission from Crown Ethers Exposed to Fenton’s Reagent Fe2+-H2O2

## TL;DR

This study shows that compounds with ether bonds emit light when exposed to hydroxyl radicals, with the light intensity linked to the number of ether bonds.

## Contribution

The study demonstrates a correlation between the number of ether bonds in crown ethers and the intensity of ultra-weak photon emission upon exposure to hydroxyl radicals.

## Key findings

- Ultra-weak photon emission (UPE) was highest in Fe2+–EGTA–H2O2, followed by crown ethers with more ether bonds.
- UPE intensity correlated with the number of ether bonds in the compounds.
- Controls without H2O2 or Fe2+ showed no significant light emission.

## Abstract

We hypothesized that compounds containing ether linkages within their backbone structures, when exposed to hydroxyl radicals (•OH), can generate ultra-weak photon emission (UPE) as a result of the formation of triplet excited carbonyl species (3R=O*). To evaluate this hypothesis, we investigated the UPE of four compounds, each at a final concentration of 185.2 µmol/L: EGTA (ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid), a potent chelator of divalent cations, and three crown ethers—12-crown-4, 15-crown-5, and 18-crown-6—containing two, four, five, and six ether bonds, respectively. •OH was generated using a modified Fenton reagent—92.6 µmol/L Fe2+ and 2.6 mmol/L H2O2. The highest UPE was recorded for the Fe2+–EGTA–H2O2 (2863 ± 158 RLU; relative light units), followed by 18-crown-6, 15-crown-5, and 12-crown-4 (1161 ± 78, 615± 86, and 579 ± 109 RLU, respectively; p < 0.05), corresponding to the number of ether groups present. Controls lacking either H2O2 or Fe2+ exhibited no significant light emission compared to the buffer medium. These findings support the hypothesis that ether bonds, when oxidatively attacked by •OH, undergo chemical transformations resulting in the formation of 3R=O* species, the decay of which is associated with UPE. In crown ethers exposed to Fe2+-H2O2, the intensity of UPE was correlated with the number of ether bonds in their structure.