Insights into the Ozonation of Antiviral Purine Derivatives by the Basic Structures’ Kinetics and Ozone Consumption Ratios

Abstract

Adenine and guanine derivatives are widely applied as antiviral agents. Due to their incomplete removal in conventional wastewater treatment, these substances were detected in the aquatic environment. Ozonation as an additional treatment step is known to degrade the antiviral compounds. However, oxidation mechanisms are still poorly examined. This study focused on the basic structures of the large group of antiviral nucleobase analogues, purine, adenine, and guanine. Their reaction with ozone allows prognoses of the ozonation of structurally related micropollutants. Therefore, these structures and the two antivirals acyclovir and penciclovir are investigated regarding their kinetics and degradation. Both characteristics are the basis for further research regarding the comprehensive understanding of the purines’ ozonation. Results show differences for the basic structures but similarities between guanine derivatives. Overall, the fundamental examinations exhibit a strong pH-dependency. Investigation of kinetics and ozone consumption ratios at pH 7 indicates ozone attack at nitrogen sites for purine (k < 8 × 10–2 M–1 s–1) and adenine (k = 100 M–1 s–1) with a slight shift to a C-C double bond at a higher pH for adenine. In guanine analogues (k = 3 × 104 M–1 s–1), the attack occurs mostly at carbon. Altogether, knowledge transfer to structurally related micropollutants is possible in the absence of additional strong electron-withdrawing or electron-donating substituents.