Evaluation of Oxidative Potential of Pyrenequinone Isomers by the Dithiothreitol (DTT) Assay

Atmospheric quinoid polycyclic aromatic hydrocarbons (PAHQs) have adverse health effects as redox-active species in particulate matter (PM). Several PAHQs are known to be very reactive in the dithiothreitol (DTT) assay; however, it is unclear if pyrenequinones, their parent pyrene is one of the most abundant polycyclic aromatic hydrocarbons (PAHs) in the atmosphere, contribute to the loss of DTT in PM extracts. Herein, by employing the DTT assay, we evaluated oxidative potentials of three pyrenequinone isomers (4, 5-pyrenequinone [4, 5-PyQ] and a mixture of 1, 6-/1, 8-pyrenequinones [1, 6-/1, 8-PyQ]), along with 9, 10-phenanthrenequinone (PQN), 1, 2-naphthoquinone (1, 2-NQ), and 1, 4-naphthoquinone (1, 4-NQ), of which DTT loss rates were examined previously. Our results demonstrate that the DTT consumption by ortho-type PAHQs is fast, particularly by 4, 5-PyQ. The order of DTT loss rate by the PAHQs tested in this study was as follows: 4, 5-PyQ ∼ PQN > 1, 2-NQ > 1, 4-NQ ∼ 1, 6-/1, 8-PyQ. 4, 5-PyQ was confirmed to be active in the DTT assay for the first time in this study. The DTT consumption rate by 4, 5-PyQ is 14.6 ± 0.8 mol/min/PAHQ-mol, which is comparable to that of PQN (14.4 ± 0.1 mol/min/PAHQ-mol) known as the most active PAHQs by the DTT assay so far.