Interaction of homologous series of amino acids with sarcosine in presence of denaturant: Volumetric and calorimetric approach

• The interactions of five amino acids studied with osmolytes sarcosine and urea.
• The results indicate predominance of ionic–ionic and hydrophilic–ionic group interactions.
• The hydration number of amino acids increases with increase in the hydrophobicity of amino acids.
• Transfer properties suggested both amino acids–sarcosine and urea–sarcosine interactions.
• Fine details of interactions presented quantitatively.

Densities (ρ) and speeds of sound (u) of homologous serious of five amino acids: glycine, l-alanine, dl-α-amino-n-butyric acid, l-valine, and l-leucine were measured in aqueous 1.0 mol · dm−3 sarcosine and (1.0 mol · dm−3 sarcosine + 1.0 mol · dm−3 urea) solutions. The values of corresponding apparent molar volume (V2,ϕV2,ϕ), apparent molar compressibility (KS,2,ϕKS,2,ϕ) were calculated from the density and speed of sound data at T=298.15T=298.15 K. Enthalpies of dilution (q) of amino acids from water to 1.0 mol · dm−3 sarcosine and (1.0 mol · dm−3 sarcosine + 1.0 mol · dm−3 urea) solution were also measured. By linear regression fitting, the values of standard partial molar volume (V2,m0) and partial molar compressibility (KS,2,m0) and standard enthalpy of dilution (ΔtrΔdilH0ΔtrΔdilH0) were determined. The contribution of zwitterionic and hydrophobic groups of amino acids to V2,m0 were also calculated from linear regression fitting of V2,ϕV2,ϕ values. The different cosolvent interactions were interpreted on the basis of cosphere overlap model. The results suggest the dominance of ionic–ionic and hydrophilic–ionic group interactions over hydrophobic–hydrophilic and ionic–hydrophobic interactions.

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