A theoretical study on hydrated sodium ion-tyrosine clusters Na⁺(Tyr)(H₂O)n (n = 0–6; Tyr = tyrosine)

To elucidate how hydration modulates cation-π interactions, we investigate Na⁺(Tyr)(H₂O)n (n = 0–6) using density-functional calculations, energy-decomposition analysis, and ab initio molecular dynamics. Optimized structures show a switch between tetra- and penta-dentate coordination upon hydration, while the cation-π contact to the phenolic ring persists. Na⁺ retains most of the positive charge; hydration stepwise lowers the water binding enthalpy, electron affinity, and ionization potentials. At higher hydration, electrostatics dominates the attractive interaction, whereas orbital donations from the carboxyl, amino and phenolic groups, together with water lone pairs, remain important. AIM topology and Mayer indices indicate weak, closed-shell Na-X contacts. AIMD at 300 K confirms the dynamical stability of the n = 6 cluster and a tendency toward a more aligned cation-π orientation. These results provide quantitative insight into hydration-controlled ion-aromatic recognition relevant to protein environments.