The gas-phase geometry optimizations of mono and dinuclear complexes of dianionic species of aspartic acid, asp 2− with lithium, sodium and potassium cations were carried out using density functional calculation at the B3LYP/6-311++G(d,p) level. The metal ion affinities (MIAs) of asp 2− species and its complexes [asp-M] − , M=Li + , Na + and K + were determined using the vibrational frequency calculations at the same level of theory. The most stable complex conformer for aspartate complexes with Li + , Na + and K + alkali cations were found as a tri-coordinated form. All complexations of [asp-M] − and [asp-M 2 ] complexes were found to be exothermic reactions. Relative bond distances between the alkali metal cation M + and the binding atoms of aspartate ion in [asp-M] − and [asp-M 2 ] complexes are in decreasing order: K + >Na + >Li + .