Ultrasonic, Volumetric, and Thermodynamic Analysis of Dopamine Hydrochloride in Aqueous Solutions: Hydrogen Bonding Dynamics and Molecular Associations over <i>T</i> = (298.15 to 323.15) K

This work investigates the molecular behavior of dopamine hydrochloride (DH) in aqueous environments, aiming to support the development of effective drug delivery formulations. The study examined a wide concentration range (0.1017–1.176 mol·kg–1) and over a temperature range of T = (298.15 to 323.15) K. Volumetric, viscometric, ultrasonic, thermo-acoustic, and thermodynamic measurements were employed to understand and analyze hydrogen bonding, hydration behavior, and structural dynamics. Key parameters, including apparent and partial molar volumes, apparent and partial molar isentropic compressibility, adiabatic compressibility, intermolecular free length, and acoustic impedance, provided insights into solute–solvent and intermolecular solute–solute interactions. Viscosity analysis revealed the influence of DH on the molecular mobility and interaction-driven resistance. Internal pressure, hydration number, and thermodynamic activation parameters, such as Gibbs free energy, enthalpy of activation, and entropy of activation, highlighted the balance of order and randomness within the solutions. These results enhance the understanding of DH’s behavior in aqueous media, providing a scientific basis for improving its stability, solubility, and bioavailability in therapeutic formulations.