The amino acids exist as zwitter ions, \(\mathrm{H}_3 \mathrm{~N}^{+}-\mathrm{CHR}-\mathrm{COO}^{-}\) Due to this dipolar salt like character, they have strong dipole-dipole attractions. Therefore, their melting points are higher than corresponding haloacids which do not have salt like character.
Due to salt like character, amino acids interact strongly with water. As a result, their solubility in water is higher than corresponding haloacids which do not have salt like character.