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QM/MM Studies on Ozonolysis of α-Humulene and Criegee Reactions with Acids and Waters at Air-Water/Acetonitrile Interfaces

Abstract

Herein we have employed combined CASPT2 and B3LYP electronic structure methods in the framework of quantum mechanics/molecular mechanics (QM/MM) approach to explore the ozonolysis reaction of α-humulene and subsequent Criegee reactions with acids and waters at the air-water/acetonitrile interface as a surrogate of atmospheric aqueous organic media. First, we have found that the 1,3-cycloaddition reactions of ozone on α-humulene proceed concertedly and have small barriers, less than 2.5 kcal/mol at the QM(CASPT2)/MM level. Second, the five-membered ring cleavage reactions of the generated ozonides are rate-limiting steps and have considerable barriers (more than 10.0 kcal/mol). This ring-opening reaction is also concerted, which simultaneously leads to the cleavage of the O-O and C-C bonds producing sesquiterpene Criegee intermediates at the air-water/acetonitrile interface. Third, although these Criegee intermediates can react with both waters and acids near the air-water/acetonitrile boundary, the addition reactions with acids have much smaller barriers, which range from 2.7 kcal/mol of R1-COOH to 5.6 kcal/mol of R7-COOH. By contrast, in water addition reactions, several different water-mediated reaction pathways have been disclosed. Their reaction barriers are found to decrease remarkably with increasing of water molecules involved in the reactions. Finally, we have found that in addition to low water concentration near the air-water/acetonitrile boundary, distinct reactivities of Criegee intermediates with acids and waters should also play a very important role in the determination of the fate of Criegee intermediates. Our present QM/MM work provides new mechanistic insights into ozonolysis and Criegee reactions at air-water/acetonitrile interfaces and gives important implication for new particle formation and secondary organic aerosol formation near the marine boundary.

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Publication details

The article was received on 18 Mar 2018, accepted on 15 May 2018 and first published on 15 May 2018


Article type: Paper
DOI: 10.1039/C8CP01750F
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    QM/MM Studies on Ozonolysis of α-Humulene and Criegee Reactions with Acids and Waters at Air-Water/Acetonitrile Interfaces

    P. Xiao, J. Yang, W. Fang and G. Cui, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP01750F

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