Wax esters solubility in triacylglycerols: Molecular dynamics study of liquid state interactions and conformations

Abstract

The dissolution of wax esters (WEs) in liquid oils plays a central role in the bulk solution thermodynamic characteristics, yet the molecular origins of their solubility remain poorly understood. In the current study, the fluid organization of WEs in medium-chain triacylglycerol (TAG) was explored using molecular dynamics simulations. Three WEs differing in their total carbon number, and having equal asymmetry between the lengths of their alkyl chains, were examined as pure systems and at 10 mol. % mixed in a model TAG. Excess volumes and excess enthalpies were calculated to evaluate deviations from ideal mixing, while molecular conformations, radial distribution functions, Kirkwood–Buff integrals, and aggregate statistics were evaluated. The simulations revealed ideal mixing for CN30ΔCN2 and CN34ΔCN2, whereas CN46ΔCN2 exhibited significant positive excess volume and excess enthalpy, indicating reduced compatibility with the TAG. Analysis of molecular conformations showed that shorter WEs possess alkyl chain end-to-end distance distributions closer to those of the TAG fatty acids, resulting in greater conformational compatibility. Structural analysis demonstrated that local organizations in these fluids are primarily governed by interactions between the central polar ester moieties rather than by alkyl-chain packing. The longest WE exhibited reduced local density fluctuations, explaining its larger deviation from ideality. Aggregate analysis showed that shorter WEs form fewer but larger and more interconnected transient clusters, whereas longer WEs form smaller organizations. These findings provide a molecular-level framework linking molecular conformations, local fluid structure, and non-ideal mixing in WE–TAG mixtures, offering fundamental insight into the structure–thermodynamics relation of complex organic fluids.