Influence of Urea on Shifting Hydrophilic to Hydrophobic Interactions of Pr(NO3)3, Sm(NO3)3, and Gd(NO3)3 with BSA in Aqueous Citric Acid: A Volumetric, Viscometric, and Surface Tension Study

Density, surface tension, and viscosity for hexahydrate nitrate salts of praseodymium, samarium, and gadolinium from (0.023 to 0.150) mol·kg–1 in aqueous solutions of: (a) citric acid (1.11 mol·kg–1), (b) citric acid + urea, (c) citric acid + bovine serum albumin, and (d) citric acid + urea + bovine serum albumin at 298.15 K and atmospheric pressure are reported. By using densities and viscosities, the apparent molar volumes, limiting apparent molar volumes, apparent molar transfer volumes, and viscosity B-coefficients have been calculated. The varying trends of aforesaid physicochemical parameters have been interpreted in light of the solute–solvent and solute–solute interactions. An attempt has thus been made to investigate the influence of urea on the interacting activities of lanthanide nitrate with citric acid and the critical role being played by bovine serum albumin in decoding the dominance of hydrophilic–hydrophobic interactions.