Effect of metal ions in Baijiu on cluster formation of water, ethanol, acetic acid and ethyl acetate molecules: Molecular dynamics and density functional theory studies

Abstract

Metal ions in Baijiu play an important role in the formation of liquor flavor, but their molecular mechanism has not been studied yet. In this study, molecular dynamics was used to calculate the radial distribution function (RDF), coordination number, and mean square displacement (MSD) of K⁺, Ca²⁺, and Fe²⁺ in water, ethanol, acetic acid, and ethyl acetate systems. Density functional theory was used to determine the binding energy, geometric configuration, and charge distribution of different clusters. The results of the MSD and RDF indicate that Ca²⁺ and Fe²⁺ are easily encapsulated by water or ethanol molecules in the system, resulting in weaker diffusion ability than K⁺. The interaction energy between K⁺, Ca²⁺, and Fe²⁺ and each molecule in the system increases sequentially, especially for Fe²⁺, which significantly changes the charge of molecules in the cluster. There are hydrogen bonds between molecules in clusters formed with K⁺ as the core, but there are no hydrogen bonds between molecules in clusters formed with Ca²⁺ and Fe²⁺ as the core. The cohesion of clusters formed with K⁺, Ca²⁺, and Fe²⁺ as the core increased in that order. The results of this study lay a theoretical foundation for understanding the molecular mechanism of metal ions in Baijiu.