Molecular Modeling of Fatty Acid Triglyceride Dimers and Their Aqueous Complexes by DFT: Thermodynamic Association Analysis

In this work, the B3LYP/6-31 + G (d) /wB97XD/6-311 + (d, p) density functional method was used to construct molecular models and calculate the thermodynamics of the association of dimers of three fatty acid triglycerides, namely, triacetin, tributyrin, and tricaprylin, as well as their most probable mono- and dihydrates. The hypothesis was confirmed that, along with the formation of a single strong hydrogen bond with a water molecule and a carbonyl group of a triglyceride, a weaker double hydrogen bond is formed between a water molecule and carbonyl groups of two different triglycerides. Estimation of the enthalpy for each of the two hydrogen bonds gives values approximately three times smaller than that for a strong single bond. The values of the enthalpies of association H₀^0 of triglycerides during the formation of dimeric structures increase with the increase in the length of the acyl chain from –47. 2 kJ/mol for triacetin to –65. 9 kJ/mol for tricaprylin, since the contribution of van der Waals forces increases. The increase in the equilibrium constants Ka with increasing number of acyl chains is associated with a decrease in the entropic contribution.