Hydration induced coordination transition and interaction mechanism of Na⁺ with adenine deoxyribonucleotide in...

The coordination behavior and non-covalent interactions in adenine deoxyribonucleotide (Adn)-Na⁺ clusters with up to five water molecules are systematically investigated. Three distinct conformations of the anhydrous Adn-Na⁺ cluster were identified. Detailed structural analysis revealed that the central conformation is the most stable, followed by the bridge conformation, and the sugar-phosphate backbone conformation. Upon the addition of water molecules, the Na⁺-Adn coordination transforms from a central geometry to a bridging configuration. At n = 4 water molecules, Na⁺ achieves a four-coordinate structure. With increasing hydration, Na⁺ gradually dissociates from Adn, cation-π interactions with the adenine ring are also weakened, as reflected by increased distances and altered angles. Energy decomposition analysis indicates that the Adn-Na⁺ interaction is predominantly governed by electrostatic forces, followed by orbital interactions. Multiple theoretical approaches consistently demonstrate that the Adn-Na⁺ interaction weakens progressively as the number of water molecules in the cluster increases.