Mechanistic insights into the base-catalyzed hydrolysis of PCDDs via QSAR and DFT approaches

Abstract

Polychlorinated dibenzo-p-dioxins (PCDDs) are persistent organic pollutants that pose considerable threats to ecological and human health owing to their high toxicity potential. Understanding the mechanisms for underlying the base-catalyzed hydrolysis of PCDDs in aquatic environments is essential for assessing their environmental behaviour and ecological risks. Herein, we combined quantitative structure–activity relationship (QSAR) models with density functional theory calculations to analyse the base-catalyzed hydrolysis mechanisms of PCDDs. Among the four developed QSAR models, the single-parameter QSAR model based on the lowest unoccupied molecular orbital energy (E_LUMO) demonstrated the best performance, achieving a coefficient of determination of 0.89 and a root mean square error of 0.49, indicating superior overall performance. Results indicate that the second-order rate constants for base-catalyzed hydrolysis (k_OH) of PCDDs are primarily influenced by E_LUMO, molecular polarizability (α), molecular volume (V_m), degree of chlorination (N_Cl), and chlorine position. Specifically, increases in the α and V_m values of PCDDs lead to higher log k_OH values, while an increase in the E_LUMO value results in a lower log k_OH value. This study investigates the relationship between the molecular structure and the rate of base-catalyzed hydrolysis of PCDDs, providing valuable insight into their environmental fate. Furthermore, this research offers a novel theoretical perspective on the base-catalyzed hydrolysis of PCDDs, which will aid in regulatory assessments and risk management.