Exploring the hydrogen-bonded interactions of vanillic acid with atmospheric bases: a DFT study

Hydrogen-bonded interactions of organic acids play crucial role in many chemical and biochemical processes vital for life’s maintenance. They are important as well in the context of secondary aerosol formation in the atmosphere. In the present work, we study the nature of hydrogen-bonded acid–base interactions present in the binary clusters of vanillic acid, a natural phenolic compound found in various plants and also observed in Amazonian aerosol, with common atmospheric bases such as ammonia and methylamines (mono-, di-, and tri-methylamine). Detailed and systematic quantum-chemical DFT calculations have been performed to analyze the structural, energetic, electrical, and spectroscopic properties of the clusters. The presence of strong intermolecular hydrogen-bonds and large binding electronic energies indicates that vanillic acid interacts strongly with atmospheric molecules. Scattering intensities of radiation (Rayleigh activities) are found to increase with cluster formation. The changes in binding free energy and enthalpy of formation of the vanillic acid-ammonia/amine binary clusters at lower temperatures demonstrate increased thermodynamical stability.