# Novel reactions of a profluorescent nitroxide probe with ozone showcase a cascade of solvent-dependent redox reactions

## TL;DR

This study shows how a chemical probe reacts with ozone, producing detectable fluorescence that could help monitor air pollution.

## Contribution

The study reveals a cascade of solvent-dependent redox reactions between a profluorescent nitroxide and ozone.

## Key findings

- BPEAnit shows a dose-dependent fluorescence increase when exposed to low ozone concentrations.
- Solvent and moisture significantly influence the reaction products and their distribution.
- Alternative solvents like ethanol and cyclohexane produce simpler reaction profiles.

## Abstract

The accurate detection of airborne pollutants remains critical for safeguarding both environmental integrity and public health. Equally important is the consideration of method stability and susceptibility to degradation by common reactive atmospheric species, such as ozone. This study examines the reactivity of ozone towards the profluorescent nitroxide (PFN) BPEAnit, a molecular probe that is used in an acellular assay for detecting reactive oxygen species (ROS) from particulate pollution. Online fluorescence measurements revealed a dose-dependent increase in fluorescence when a BPEAnit/DMSO solution was exposed to low-level ozone concentrations (0–544 ppb). Exposure to excess ozone (ca. 9.5 ppm) produced sufficient fluorescent products for LC-MS analysis, which, when combined with isotope labelling, enabled structural characterization of several products, accounting for 43.5% of the total fluorescent signal. Under similar conditions the parent fluorophore (BPEA) showed no reactivity toward ozone, confirming the specificity of BPEAnit. The primary mechanism is proposed as a single-electron transfer between BPEAnit and ozone, forming an oxoammonium cation and ozone radical anion, which react with DMSO to yield carbon- and sulfur-based adducts. Increased moisture significantly altered the product distribution, highlighting the need to consider ambient humidity in these atmospheric assays. Preliminary evaluation of alternative solvent systems, ethanol and cyclohexane, revealed simpler reaction profiles with fewer products; however factors such as solvent volatility, ozone dose-response, and product stability require further investigation. These findings support the reliability of the BPEAnit probe towards ozone, as well as demonstrating a sensitive, ozone-responsive fluorescence profile, offering potential for broader application in atmospheric monitoring.

This study explores the reactivity of the profluorescent nitroxide BPEAnit with ozone, showing a dose-dependent fluorescence response that yields multiple products influenced by solvent system and moisture content.