The apparent molal volumes and adiabatic compressibilities of aqueous amino acids at 25°C

The apparent molal volumes and adiabatic compressibilities of 15 amino acids in water have been determined at 25°C from precise density and sound measurements. The electrostriction partial molal volume and compressibility of the amino acids were determined from V̄⁰(meas) - V̄⁰(int) and K̄⁰(meas) - K̄⁰(int). The values of V̄⁰(int) have been estimated from V̄⁰ of the uncharged amide isomers and V̄⁰_cryst, the crystal molal volume. Both V̄⁰(elect) and K̄⁰(elect) yield values of 4.1 ± 0.4 for the number of water molecules hydrated to the amino acids. Group contributions for the partial molal volume and adiabatic compressibilities have been determined from the amino acids. The volume results are in good agreement with the values calculated by other workers on soluble organic solutes.