Physicochemical study of solute–solute and solute–solvent interactions of l-phenylalanine in (water + arabinose/glucose/sucrose) solutions at different temperatures

• The study reports density, ultrasonic speed and viscosity data of l-phenylalanine in aqueous-carbohydrate solutions.
• The study elucidates interactions of l-phenylalanine with carbohydrates in aqueous media.
• Correlates physicochemical properties of l-phenylalanine with its behavior in aqueous-carbohydrate solutions.
• The structure-making/breaking ability of l-phenylalanine in these aqueous-carbohydrate solutions is reported.

The values of density, ρ and ultrasonic speed, u of solutions of l-phenylalanine in aqueous-carbohydrate solvents (2.5 and 5% of arabinose/glucose/sucrose, w/w in water) at T = (293.15, 298.15, 303.15, 308.15, 313.15, and 318.15) K; and viscosities, η of these solutions at (298.15, 303.15, 308.15, 313.15, and 318.15) K and at atmospheric pressure were measured. From these experimental results, the apparent molar volume, VϕVϕ, limiting apparent molar volume, Vϕ° and the slope, Sv  , transfer volume, Vϕ,tr°, apparent molar compressibility, Ks,ϕKs,ϕ, limiting apparent molar compressibility, Ks,ϕ° and the slope, Sk  , transfer volume, Vϕ,tr°, transfer compressibility, Ks,ϕ,tr°, limiting apparent molar expansivity, Eϕ°, Hepler’s constant, (∂2Vϕ°/dT2), Falkenhagen Coefficient, A, Jones–Dole coefficient, B   and hydration number, nHnH were calculated. The Gibbs free energies of activation of viscous flow per mole of solvent, Δμ1°# and per mole of solute, Δμ2°#, entropies, ΔS°ΔS° and enthalpies, ΔH°ΔH° of activation of viscous flow were also calculated and discussed in terms of transition state theory. The structure-making/breaking ability of the amino acid has also been discussed in terms of the sign of (∂2Vϕ°/dT2) and dB/dT. The results have been interpreted in terms of solute–solvent and solute–solute interactions in these systems.