Transfer enthalpies of amino acids and glycine peptides from water to aqueous solutions of trimethylamine N-oxide at 298.15 K

Abstract

• Enthalpies of solution have been measured by calorimetry at 298.15 K. • The heterogeneous enthalpic interaction coefficients were calculated. • The results are discussed in terms of solute–solute and solute–solvent interactions. • The structure of amino acid has a more important effect on the interaction. Enthalpies of solution of glycine, l -alanine, l -serine, l -threonine, l -valine, diglycine and triglycine in aqueous solutions of trimethylamine N -oxide (TMAO) have been measured by calorimetry at 298.15 K. The results obtained were used to calculate the heterogeneous enthalpic interaction coefficients ( h AT ) between the amino acids or glycine peptides and the molecule of TMAO in water and the transfer enthalpies Δ tr H m of the amino acids or glycine peptides from water to aqueous solutions of TMAO. It has been observed that the transfer enthalpies of the amino acids and glycine peptides from water to aqueous solutions of TMAO are monotonically positive over the investigated concentration ranges. The relative order of h AT and Δ tr H m for amino acids are all l -serine > l -threonine > glycine > l -alanine > l -valine, whereas the sequence of glycine peptides is triglycine > diglycine > glycine. The results are discussed in terms of solute–solute and solute–solvent interactions.