Molecular Interactions Investigation of L-Histidine in Water and in Aqueous Citric Acid at Different Temperatures Using Volumetric and Acoustic Methods.

Densities, <italic>ρ</italic> and ultrasonic speeds, u of L-histidine (0.02–0.12 mol·kg⁻¹) in water and 0.1 mol·kg⁻¹ aqueous citric acid solutions were measured over the temperature range (298.15–313.15) K with interval of 5 K at atmospheric pressure. From these experimental data apparent molar volume Φ_{<italic>V</italic>}, limiting apparent molar volume Φ_{<italic>V</italic>}^{<italic>O</italic>} and the slope <italic>S_V</italic>, partial molar expansibilities Φ_{<italic>E</italic>}^{<italic>O</italic>}, Hepler’s constant, adiabatic compressibility <italic>β</italic>, transfer volume Φ_{<italic>V, tr</italic>}^{<italic>O</italic>}, intermolecular free length (<italic>L_f</italic>), specific acoustic impedance (<italic>Z</italic>) and molar compressibility (<italic>W</italic>) were calculated. The results are interpreted in terms of solute–solute and solute–solvent interactions in these systems. It has also been observed that L-histidine act as structure maker in water and aqueous citric acid. [ABSTRACT FROM AUTHOR]