Theoretical Calculation Study On The Photochemical Degradation Process Of Antidepressant Drugs Sertraline And Citalopram In Water Environmen

Antidepressants are drugs specifically used to treat depression and other related disorders.In recent years,the gradual increase in patients with depression has led to an increase in the demand for such drugs.The widespread use of antidepressants worldwide will lead to their entry into the surrounding environment,which will cause a series of environmental impact problems.Photochemical degradation is an important degradation pathway of antidepressants in aquatic environment,so it is of great significance to study the photolysis process of antidepressants in water for their environmental behavior and ecological risk.At the same time,there are many active oxygen species such as hydroxyl radicals（·OH）and singlet oxygen（¹O₂）in environmental waters,which can promote the photolysis of antidepressants in the water.In this paper,the typical antidepressant drugs sertraline（SER）and citalopram（CIT）were selected as the research objects,and the quantum chemical calculation method was used to explore the photodegradation process of SER and CIT in water.In this study,density functional theory（DFT）and time-density functional theory（TDDFT）were used to investigate the principles of photolysis reactions of SER and CIT and to predict the main degradation pathways and products.The research content is divided into two parts:（1）DFT/TDDFT method was used to study the direct and indirect photolysis of SER in water;and the TDDFT method was used to calculate the UV absorption spectra of SER in the aqueous environment.The calculation results show that in the indirect photolysis process,the reaction of SER with·OH is carried out through the addition reaction of hydroxyl radicals and the substitution reaction of chlorine,and the hydroxyl addition and chlorine substitution in all pathways are exothermic reactions.The reaction of ¹O₂ with SER is carried out by substitution for chlorine on the benzene ring.The direct photolysis of SER includes dechlorination and cleavage of C8–C9/C7–N/C17–N bond.The cleavage of the carbon-chlorine bond was found in the geometry of the SER optimized by first excited triplet state.However,the higher reaction activation energy（E_a）and chemical reaction enthalpy（ΔH）indicated that the cleavage of C8–C9/C17–N bond and the substitution of oxygen for chlorine were not the main photolysis pathways.The addition product of·OH,the substitution product of·OH for chlorine,the cleavage product of the C7–N bond and the dechlorination product in the direct photolysis process are the main products in the photolysis process of SER.（2）The photolysis process of CIT in water was studied by quantum chemical calculation method.The results of indirect photolysis calculation show that:the reaction between CIT and·OH is carried out by hydroxyl addition reaction and fluorine substitution reaction,and all addition and substitution reactions are exothermic reactions.The reaction of ¹O₂ with CIT includes the substitution of ¹O₂ for F and the addition reaction at the C14 site.The UV absorption spectra of CIT in water environment were calculated by TDDFT during direct photolysis process.The results of direct photolysis calculations indicate that the cleavage of C–C/C–N/C–F bonds occurred.Through the analysis of E_a andΔH values revealed that addition reactions of hydroxyl groups,fluorine substitution reactions,¹O₂ to F substitution reactions and C14 site addition reaction,and C6–F/C7–C16/C17–C18/C18–N/C19–N/C20–N bond cleavage reactions were the main pathways of CIT photolysis.