Research on the degradation mechanism and products of 2,4,6-tribromophenol in the water environment and the mechanism of competition between T4 and TTR binding.

2,4,6-Tribromophenol (TBP), a widely used chemical intermediate, poses a significant health risk due to its ubiquity in food and the environmental matrices. Owing to its structural similarity to thyroxine (T4), TBP may interfere with thyroid function. It competes for binding sites on transthyretin (TTR), the primary transport protein for T4. This study investigated the photodegradation of TBP induced by hydroxyl radical (•OH). Degradation intermediates were identified using liquid chromatography-mass spectrometry (LC-MS), and degradation pathways were proposeed based on density functional theory (DFT) calculations. The toxicity of these intermediates was evaluated with ECOSAR and TEST. The interaction between TBP and TTR was examined by fluorescence and Fourier transform infrared (FTIR) spectroscopy, which revealed static quenching and alterations in TTR's secondary structure. Molecular docking and molecular dynamics simulations confirmed that TBP and its degradation products form stable bindinds at the T4 site on TTR. Notably, some degradation products exhibited high binding affinity, suggesting that TTR may co-transport them alongside T4 to target organs. These findings reveal a mechanism through which TBP and its degradation products may disrupt thyroid hormone transport by competitive binding and co-transport.