Hydrogen-Bond-Mediated Molecular Interactions of Curcumin in DMSO Solution Probed by Volumetric, Acoustic, Thermodynamic, Spectroscopy, and DFT-QTAIM Studies

Abstract

Volumetric, acoustic, thermo-acoustic, and thermodynamic properties of curcumin in dimethyl sulfoxide (DMSO) solutions were investigated over the molality range 0–0.18101 mol·kg–1 at temperatures from 298.15 to 323.15 K. Density, ultrasonic velocity, and viscosity measurements were used to derive key parameters such as apparent and limiting apparent molar volumes, isentropic compressibility, and related acoustic functions to probe solute–solvent interactions. The temperature dependence of viscosity was analyzed using an activated-flow model to determine the Gibbs free energy, enthalpy, and entropy of activation. DFT (B3LYP-D3/6–311++G(d, p)) single-point calculations with the IEFPCM model were performed to evaluate hydrogen-bonding strength. FT-IR spectra show a red shift of the DMSO S═O bond, confirming hydrogen bonding with curcumin, while QTAIM analysis identifies distinct bond critical points, indicating strong intermolecular H-bonding with an interacting energy of 78.8 kJ·mol–1. The lower HOMO–LUMO gap of curcumin indicates higher chemical reactivity and a greater tendency to form hydrogen bonds, while DMSO acts as an electron-rich acceptor. The results confirm significant hydrogen-bond-driven interactions, increased solvation at low temperatures, and gradual weakening of the solvent network at elevated temperatures. These findings enhance the molecular understanding of solution interactions, supporting drug delivery and pharmaceutical applications.