The+ amino acids exists as Zwitter ions in aqueous solution. Due to this, dipolar salt like structure amino acids have strong dipole-dipole attractions.
Thus, their melting points are higher than corresponding halo acids which do not have salt like character. Secondly, they interact strongly with $H _{ 2 }O$ due to their salt like character. As a result, polar amino acids dissolve in polar solvents like $H _{ 2 }O$. Hence, the solubility of amino acids in water is, higher than that of corresponding halo acids, which do not have any salt like character.