Densities (rho) and speeds of sound (u) of homologous serious of five amino acids: glycine, L-alanine, DL-alpha-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 (V-2,V-phi), apparent molar compressibility (K-S,K-2,K-phi) were calculated from the density and speed of sound data at T 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 (V-2,m(0)) and partial molar compressibility (K-S,2,m(0)) and standard enthalpy of dilution (DtrDdilH0) were determined. The contribution of zwitterionic and hydrophobic groups of amino acids to V-2,m(0) were also calculated from linear regression fitting of V-2,V-phi 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. (C) 2013 Elsevier Ltd. All rights reserved.