Theoretical study of hydrogen bond interactions of methanesulfonic acid with eugenol/methyleugenol

Abstract

Methanesulfonic acid (MSA) is the simplest organic sulfate molecule, and it has been considered to play an important role in new particle formation besides H2SO4. The atmospheric eugenol (EU) and methyleugenol (ME) may interact with MSA via hydrogen bond interactions to participate in new particle formation. All possible structures were optimized by DFT. There are three types of hydrogen bonds in the studied systems: S−OH···O, C−OH···O, and S−OH···π. The most stable conformer was the one where MSA interacting with EU via S−OH···OCH3 and C−OH···O to form a nine-membered ring. For ME, MSA interacts with the two OCH3 groups to form a five-membered ring. The ring formations make the two complexes to be the most stable conformers with binding energies of −45.9 and −52.0 kJ mol−1 for MSA−EU and MSA−ME, respectively. In contrast, the binding energies of the S−OH···π conformers are about −43.3 to −38.0 kJ mol−1. The Gibbs free energies of formation of the most stable conformers of MSA−EU and MSA−ME are −4.7 and −10.6 kJ mol−1, respectively. It means that the MSA−EU and MSA−ME complexes may play a certain role in new particle formation. The red shifts of the OH-stretching vibrational transitions, and atoms in molecules analysis were used to understand the nucleation of MSA with EU/ME.