Interactions of some short peptides with the osmolyte trimethylamine N-oxide in aqueous solution: Physico-chemical insights

The apparent molar volumes, V2,ϕ, apparent molar adiabatic compressibilities, KS,2,ϕ, and heats of dilution q of glycyl-glycine (gly-gly), glycyl-glycyl-glycine (gly-gly-gly), glycyl leucine (gly-leu), and glycyl-glycyl-leucine (gly-gly-leu) have been determined in aqueous trimethylamine N-oxide (TMAO) at T = 298.15 K. These data have been used to calculate the values of infinite dilution standard partial molar volume V2,m∘, standard partial molar isentropic compressibility KS,2,m∘, standard molar enthalpy of dilution ΔdilH°, and the corresponding transfer thermodynamic properties from water to aqueous TMAO solutions. The results on transfer thermodynamic properties of peptides from water to aqueous TMAO solutions have been interpreted in terms of ion–ion, ion–polar, hydrophilic–hydrophilic, hydrophilic–hydrophobic, and hydrophobic–hydrophobic group interactions. The results obtained in this work suggest strengthening of polar solute–solvent interactions in case of peptides compared to those in case of amino acids and support the experimental observations on the effect of TMAO on the thermodynamic and conformational stability of proteins.

► Thermodynamics of interaction of peptides with trimethyl N-oxide (TMAO) studied.
► Partial molar properties in aqueous osmolyte provide interaction details.
► Volumes, compressibilites, enthalpies indicate predominant polar interactions.
► Polar interactions account for marginal effect of TMAO on protein stability.
► Results provide quantitative fine details of TMAO–peptides interactions.