Acidic amino acids are

aspaic acid and glutamic acid are proton donors. At physiologic pH, the side chains of these amino acids are fully ionized, containing a negatively charged carboxylate group (-COO-). They are, therefore, called aspaate or glutamate to emphasize that these amino acids are negatively charged at physiologic pH Asparagine and Glutamine are neutral amino acids. Ref: LIPPINCOTT's Biochemistry 6th Edition Pg No. 5.