The interactions between some N-acetyl-N′-methyl-l-α-amino acid amides and urea in water at 298.15 K

The enthalpies of solution of N-acetyl-N′-methylglycinamide, N-acetyl-N′-methyl-l-α-alaninamide, N-acetyl-N′-methyl-l-α-leucinamide and N-acetyl-N′-methyl-l-α-serinamide have been measured in water and in aqueous urea solutions with molalities from 0.25 to 3.0 mol kg−1 at 298.15 K. From these data the standard dissolution enthalpies of amides in aqueous urea solutions have been determined. The results have been treated according to McMillan–Mayerʹs theory in order to obtain the enthalpic coefficients of the interactions between amino acid derivatives and urea molecules. The obtained parameters were compared with the hydrophobic scale for the amino acid side chains.