Interactions of Peptides and Lysozyme with Aqueous Tetraethylammonium Bromide at 298.15 K

The apparent molar volumes, V _{ø, 2}, of gly-leu, gly-gly-leu and the partial specific volume ν^° of hen-egg-white lysozyme have been determined in aqueous of TEAB solutions by density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volumes V _2,m ^o for the peptides in aqueous TEAB solutions and the standard partial molar volumes of transfer Δ_tr V _2,m ^o of the peptides from water to aqueous TEAB solutions. The results on Δ_tr V _2,m ^o of peptides from water to aqueous TEAB solutions have been interpreted in terms of ion-ion, ion-polar, hydrophilic-hydrophilic and hydrophobic-hydrophobic group interactions. In order to supplement this information, enthalpies of transfer of aqueous peptides from water to TEAB solution have been determined at 298.15 K using a VP-ITC titration calorimeter. The data on partial molar volumes and enthalpies of transfer have been discussed in light of various interactions operating in the ternary system of peptides, water and TEAB. The partial specific volume of transfer of lysozyme from water to aqueous TEAB solutions also indicates the predominance of hydrophobic interactions.