Microheterogeneity of Singlet Oxygen Distributions in Irradiated Humic Acid Solutions

TLDR

Singlet oxygen is a highly reactive species generated by solar irradiation of organic matter in environmental waters and is implicated in many reactions, yet its spatial distribution in natural waters remains difficult to quantify. The study assessed the microheterogeneous distribution of singlet oxygen in irradiated chromophoric dissolved organic matter solutions. This assessment employed molecular probes of varying hydrophobicity. Using hydrophobic trap‑and‑trigger chemiluminescent probes, the study found that apparent singlet‑oxygen concentrations were orders of magnitude higher than with the hydrophilic furfuryl alcohol probe, revealing a steep gradient between CDOM macromolecules and the aqueous phase and enabling a kinetic model that predicts probabilistic distributions under varying solvent conditions.

Abstract

Singlet oxygen ( 1 O 2 ) is a highly reactive species formed through solar irradiation of organic matter in environmental waters. Implicated in a range of reactions, it has proven difficult to quantify its spatial distribution in natural waters. We assessed the microheterogeneous distribution of 1 O 2 in irradiated solutions containing chromophoric dissolved organic matter (CDOM) by using molecular probes of varying hydrophobicity. The apparent 1 O 2 concentrations ([ 1 O 2 ] app ), measured by recently developed hydrophobic trap-and-trigger chemiluminescent probe molecules, were orders of magnitude higher than those measured by the conventional hydrophilic probe molecule furfuryl alcohol. The differential [ 1 O 2 ] app values measured by these probes reflect a steep concentration gradient between the CDOM macromolecules and the aqueous phase. A detailed kinetic model based on the data predicts probabilistic 1 O 2 distributions under different solvent conditions.