Apparent specific volumes of some dipeptides (containing L-valine and L-leucine in aqueous alkylurea solutions)

The apparent molal volumes of nine dipeptides containing glycine, l-valine, and l-leucine have been determined in methyl, N,N′-dimethyl and ethylurea solutions from precise density measurements. Limiting partial molal volumes. 02, at various solute concentrations have also been calculated. The experimental values of 02 in water agree reasonably well with those calculated as the sum of 02 of both acids after accounting for the electrostrictive effect and loss of water. There is no correlation between the values of 02 of individual dipeptides in alkylureas which means that the intrinsic volume and the electrostrictive effect make the largest contribution to 02. The contribution from other effects is within the limit of experimental error. The volumes of transfer from water to alkylurea solutions are all positive and reflect by and large the electrostrictive effect.