Optics and Spectroscopy. Laser Physics

Hydrogen bonding in saturated acids triglyceride monohydrates: MD and DFT modeling

K. V. Berezin^a, E. Yu. Stepanovich^b, K. N. Dvoretsky^c, E. M. Antonova^d, A. M. Likhter^b, I. Yu. Yanina<sup>ae

a</sup> Saratov State University
^b Astrakhan State University
^c Saratov State Medical University named after V. I. Razumovsky
^d Astrakhan State Medical University
^e National Research Tomsk State University

Abstract: Background and Objectives: Triglycerides, as the primary components of fats and oils, play a crucial role in various scientific and industrial fields, including food production, energy, and pharmaceuticals. Their interaction with water molecules is particularly significant, yet many aspects of these interactions remain poorly understood. This study aims to investigate hydrogen bonding in monohydrates of saturated fatty acid triglycerides using molecular dynamics (MD) and density functional theory (DFT) simulations. The objectives include determining the thermodynamic parameters of association, analyzing the influence of hydrocarbon chain length on hydration, and identifying the most stable hydration configurations. Materials and Methods: The study employed classical molecular dynamics (GROMACS) with the AMBER-03 force field and DFT calculations (B3LYP/6-31+G(d) and wB97XD/6-311+G(d,p)) to model hydrogen bonds in monohydrates of triglycerides ranging from triacetin to tristearin (chain lengths of 0 to 16 methylene groups). The MD simulations involved a 4 $\times$ 4 $\times$ 4 nm periodic boundary cell with a triglyceride molecule surrounded by water, run for 500 ps at 300 K and 1 bar. Hydrogen bonds were identified using geometric criteria (distance $\leq$ 3.5 Å, angle $\leq$ 30$^\circ$). DFT calculations optimized molecular structures and calculated thermodynamic parameters, including association energies, enthalpies, and equilibrium constants. Results: The results have revealed that carbonyl groups of the central ester chain are the primary sites for hydrogen bond formation. Monohydrates involving the central chain (Type 1) have exhibited a greater stability than those involving side chains (Type 2). The association energy for Type 1 monohydrates has saturated starting from tricaprylin (chain length of 6). A linear relationship has been observed between the thermodynamic parameter T$\Delta$S and the equilibrium constant K$_\alpha$ for Type 1 monohydrates, attributed to the loss of conformational entropy upon hydration. Non-classical hydrogen bonds (C-H$\cdots\cdots\cdots$O) have also contributed to the stability of monohydrates, influencing their spatial structure. The study has found that hydration of longer chains requires higher energy to overcome entropy losses. Conclusion: The study has demonstrated that the central carbonyl group of triglycerides is the primary hydration site, with Type 1 monohydrates being more stable than Type 2. The association energy and enthalpy reach saturation for chains longer than tricaprylin, while linear dependencies of T$\Delta$S and K$_\alpha$ on chain length highlight the role of conformational entropy in hydration. These findings enhance the understanding of triglyceridewater interactions, providing insights relevant to food science, pharmaceuticals, and the development of lipid-based delivery systems. The combined use of MD and DFT has proved effective for analyzing these complex molecular interactions.

Keywords: triglycerides, hydrogen bonds, molecular dynamics, density functional theory, hydration, thermodynamics.

UDC: 544.18:577.32

Received: 30.06.2025
Revised: 28.11.2025
Accepted: 10.09.2025

DOI: 10.18500/1817-3020-2025-25-4-425-437