Intermolecular Correlations in Liquid Lactic Acid Based on ab initio Molecular Dynamics Simulations Combined with High-Energy X-ray Diffraction Measurements

Abstract

The structural and bonding properties of liquid L-lactic acid were investigated through ab initio molecular dynamics simulations, leveraging on the agreement between the static structure factors obtained from high-energy X-ray diffraction (HEXRD) measurements. It has been demonstrated that predominant intermolecular interactions arise from hydrogen bonding. Hydrogen atoms in two hydroxy groups tend to form hydrogen bonds with two of the three oxygen atoms in neighboring molecules. This results in the presence of an oxygen atom in the hydroxy group of the carboxy group that does not significantly contribute to hydrogen bond formation with neighboring hydrogen atoms. This is consistent with the behavior observed in the crystalline phase. However, in the liquid state, four types of intermolecular hydrogen bonds are primarily formed, whereas in the crystal, only two types are observed. We show that the directionality of hydrogen bonds determines the intermolecular orientation. We thoroughly studied the structural properties and covalent bonding between atoms and charged states of atoms.