Physiochemical Investigation of Different Interactions of Some Essential Amino Acids Prevailing in Aqueous Media of a Biologically Potent Drug Molecule at Various Temperature Optimized by DFT

The comparative molecular interaction between a biologically potent drug molecule, dyphylline, and two essential amino acids, l-proline and l-valine, has been studied in an aqueous medium using physicochemical methodologies at 303.15, 308.15, and 313.15 K at 0.1 MPa atmospheric pressure. The methodologies engaged herein (density, refractive index, viscosity, and surface tension) recognized the presence of the molecular interaction of dyphylline with the amino acids. Different parameters like “apparent molar volumes” (ϕ_v), “partial molar volumes at infinite dilution” (ϕ_v⁰), “limiting apparent molar expansibilities” (ϕ_E⁰), transfer properties (Δ_trφ_v⁰), “isobaric thermal expansion coefficient” (α), viscosity B-coefficients, hydration number (n_H), and thermodynamic parameters (Δμ₁^0≠, Δμ₂^0≠, TΔS₂^0≠, and ΔH₂^0≠) of viscous flow obtained from density and viscosity measurements are also used for molecular interaction determination. ¹H and ¹³C NMR spectroscopic study shows significant evidence for the presence of the solute–cosolvent interaction in solution. The interaction between the molecules has been discussed in the context of the structure-breaking/structure-making ability of the molecules in solution. The thermodynamic background of their interaction in aqueous solution has also been explored with the help of density and viscosity measurements. DFT studies construct the theoretical basis of the interaction between the components in solution.