Acoustic characterization and hydration number analysis of nicotinamide (Vitamin B

The ultrasonic velocity (u) and density (π) of aqueous nicotinamide (Vitamin B3) solutions were determined using an Anton Paar DSA 5000 M densimeter–sound velocity analyser at 0.1 MPa. Measurements were carried out over a molal concentration range from 0 to 1.11177 mol.kg-1 and at temperatures between 298.15 K and 323.15 K. From these experimental data, hydration number (nH), acoustic properties like apparent molar isentropic compressibility (KΦ), limiting apparent molar isentropic compressibility (KΦ0) and a semi-empirical interaction factor (SK) were evaluated. The analysis of these parameters provides insight into solute–solvent interactions, revealing whether nicotinamide acts as a structure-maker or structure-breaker in water. The results also explain the hydration phenomena, acoustic behavior, and structural modifications occurring within these binary mixtures.