Stability of Terpenoid-Derived Secondary Ozonides in Aqueous Organic Media

1,2,4-Trioxolanes, known as secondary ozonides (SOZs), are key products of ozonolysis of biogenic terpenoids. Functionalized terpenoid-derived SOZs are readily taken up into atmospheric aerosols; however, their condensed-phase fates remain unknown. Here, we report the results of a time-dependent mass spectrometric investigation into the liquid-phase fates of C₁₀ and C₁₃ SOZs synthesized by ozonolysis of a C₁₀ monoterpene alcohol (α-terpineol) in water:acetone (1:1 = vol:vol) mixtures. Isomerization of Criegee intermediates and bimolecular reaction of Criegee intermediates with acetone produced C₁₀ and C₁₃ SOZs, respectively, which were detected as their Na⁺-adducts by positive-ion electrospray mass spectrometry. Use of CD₃COCD₃, D₂O, and H₂¹⁸O solvents enabled identification of three types of C₁₃ SOZs (aldehyde, ketone, and lactol) and other products. These SOZs were surprisingly stable in water:acetone (1:1) mixtures at T = 298 K, with some persisting for at least a week. Theoretical calculations supported the high stability of the lactol-type C₁₃ SOZ formed from the aldehyde-type C₁₃ SOZ via intramolecular rearrangement. The present results suggest that terpenoid-derived SOZs can persist in atmospheric condensed phases, potentially until they are delivered to the epithelial lining fluid of the pulmonary alveoli via inhaled particulate matter, where they may exert hitherto unrecognized adverse health effects.