Conformational analysis of alkali metal complexes of aspartate dianion and their interactions in gas phase

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(+).