Conformational analysis of alkali metal complexes of anionic species of aspartic acid, their interconversion and deprotonation: A DFT investigation

Gas-phase geometry-optimized structures of aspartate complexes of anionic species (Hasp−) with lithium, sodium and potassium metal cations and transition-state structures for their interconversions were obtained using the density functional theory computations at the B3LYP/6-311++G(d,p) level of theory. The metal ion affinities of Hasp− species and deprotonation energies of [Hasp-M] complexes, M = Li+, Na+ and K+, and their conformers were obtained. Relative energies of the [Hasp-M] complex conformers, reaction energies, thermodynamic properties, rate and equilibrium constants of their complexation are reported. Binding energies of the most stable complexes with Li+, Na+ and K+ are −168.53, −133.34 and −117.68 kcal/mol, respectively. The most stable complex conformer as a tri-coordinated form for aspartate complex with Li+ and bi-coordinated form for aspartate complexes with Na+ and K+ were found.