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 V°(meas) -V°(int) and K°(meas) -K°(int). The values of V°(int) have been estimated from Vo of the uncharged amide isomers and V°cryst, the crystal molal volume. Both V°(elect) and K°(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.
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