Molecular Interactionand Hydration Properties ofAliphatic Biogenic Polyamines: Insights through Volumetric, Viscometricand Acoustic Investigations

In context of understanding the precise biochemical and industrial mechanisms underlying the actions of the studied aliphatic biogenic polyamines, namely, putrescine dihydrochloride, cadaverine dihydrochloride, and spermine tetrahydrochloride, the present study systematically investigates the density, speed of sound, and dynamic viscosity data over a dilute concentration range of (0.02–0.2) mol·kg^–1, a temperature range of (288.15–313.15) K and an atmospheric pressure of 1.013 × 10⁵ Pa. The physiochemical properties of the aqueous polyamine solutions were assessed through volumetric and compressibility measurements along with viscous flow parameters. The density and speed of sound data were utilized to calculate apparent molal volume and isentropic compressibility, which were further extrapolated to infinite dilution to obtain the limiting values <i>V</i>_ϕ⁰ and <i>K</i>_<i>S</i>,ϕ⁰ and the corresponding slopes <i>S</i>_<i>v</i> and <i>S</i>_<i>k</i> respectively. Thermal expansion and hydration behavior were also examined by computing the limiting apparent molal expansibility (<i>E</i>ϕ⁰) and hydration number (<i>n</i>_H). The identification of Hepler’s constant (∂²<i>V</i>_ϕ⁰/<i>∂T</i>²), <i>B</i>-coefficient, and d<i>B</i>/d<i>T</i> values highlight the structure-breaking and hydrophilic nature of the studied polyamines. The results, however, indicate that the observed hydration phenomenon cannot be attributed solely to their total charge or the electrostatic forces; hydrophobic hydration of the aliphatic chain segments also significantly contributes to the underlying mechanisms influencing their physiochemical behavior and molecular interactions with the water structure.