We have performed an ab initio study of aluminum(III) cation with the aspartic and glutamic amino acid residues, i.e., the carboxylate group. Density functional theory methodology was used, and the covalent and noncovalent interactions were analyzed using natural bond orbital theory. First we have investigated the smallest functional moiety of these amino acids, the carboxylate anion. Additionally, we have sequentially introduced two methyl groups to more accurately represent the aspartic and glutamic acid chains. We have compared these data with the nontoxic metal cation, e.g., magnesium(II). Our calculations demonstrate that aluminum(III) binds much more tightly to the ligands than magnesium(II) and the addition of the methyl groups leads to stronger bonds, though the effect of the second methyl group is less than that of the first.