Quantum Chemical Calculations of Flexible Tripeptide-Ni(II) Ion-Mediated Supramolecular Fragments and Comparative Analysis of Tripeptide Complexes with Various Metal(II) Ions

An automated conformational search method was employed to efficiently determine the stable conformers and weak hydrogen bonds of a flexible tripeptide coordinated with a solitary metal-(II) ion in an aqueous environment. Quantum chemical calculations were performed to investigate the tendency of octahedral coordination formation between different metal-(II) ions and various coordination models (ammonia molecule, chelate molecule, and flexible tripeptide). The octahedral coordination was analyzed by decomposing it into tridentate, bidentate, and monodentate coordination model complexes to assess their formation propensities and conformational properties. Additionally, population analysis, including electrostatic potential mapping and natural population analysis, was performed to identify the unique properties of the Ni-(II) ion in forming octahedral coordination in crystals and to explore the potential of other metal-(II) ions for self-assembling novel coordination configurations in peptide-metal compounds. Two common hydrogen bonding interactions were examined by using artificial forces to facilitate dissociation or reinforcement.