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, asp2− 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 asp2− 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-M2] 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-M2] complexes are in decreasing order: K+ > Na+ > Li+.