Surface Tension of Glycine, Alanine, Aminobutyric Acid, Norvaline, and Norleucine in Water and in Aqueous Solutions of Strong Electrolytes at Temperatures from (293.15 to 313.15) K

Abstract

The surface tension of glycine, alanine, 2-aminobutyric acid (AABA), norvaline, and norleucine in water and in aqueous solutions of five strong electrolytes (LiCl, NaCl, KCl, (NH4)2SO4, and Na2SO4) was determined in the temperature range between 293.15 and 313.15 K with a LAUDA TVT2 tensiometer using the drop volume method. As the temperature rises, the surface tension decreases as the cohesion between molecules becomes weaker. The limiting slopes of the surface tension as a function of mole fraction of the amino acids in water show that glycine and alanine are hydrophilic solutes whereas α-aminobutyric acid, norvaline, and norleucine behave as hydrophobic solutes, and this behavior is not affected by the addition of the salts. The presence of electrolytes increases the surface tension of the α-amino acid solutions; however, it is not possible to classify the effect of the anions and cations on this property because the surfaces of the mixed solvents are different and a comparison between them is not pert...