In silico Investigation of the Thermochemistry and Photoactivity of Pyruvic Acid in an Aqueous Solution of NaCl

Abstract

The photochemistry of oxo‐carboxylic acids contributes significantly to the complex chemistry occurring in the atmosphere. In this regard, pyruvic acid undergoes photoreactions that lead to many diverse products. The presence of sodium cation near pyruvic acid in an aqueous solution, or its conjugate base in non‐acidic conditions, influences the hydration equilibrium and the photosensitivity to UV‐visible light of the oxocarboxylic acid. We performed an ab initio metadynamics simulation which serves two purposes: first, it unveils the mechanisms of the reversible hydration reaction between the keto and the diol forms, with a free‐energy difference of only 2 kJ/mol at 300 K, which shows the influence of sodium on the keto/diol ratio; second, it provides solvent‐shared ion pairing (SSIP) and contact ion pairing (CIP) structures, including Na+ coordinated to carbonyl, for the calculations of the electronic transition energies to an antibonding π* orbital, which sheds light on the photoactivity of these two forms in the actinic region.