Theoretical insights into seawater metal ion binding on β-d-ribose: site selectivity, thermodynamics, and electronic...

Metal ion contamination of seawater poses growing environmental and public health challenges, driving demand for sustainable, selective adsorbents. Here, we employ density functional theory (DFT) at the (M06-2X/6-311++G(d,p) level with implicit aqueous solvation (PCM) to investigate the adsorption of seawater metal ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe²⁺, Zn²⁺) onto β-d-ribose. Among six evaluated coordination sites, Site 5 consistently exhibited the strongest binding for all cations, attributable to its highly nucleophilic oxygen atoms. The binding affinity follows the order Fe²⁺>> Zn²⁺ > Mg²⁺ >> Ca²⁺ > K⁺ ≥ Na⁺, consistent with the cation charge density and M-O bond lengths. NBO second-order perturbation energies E ⁽²⁾ (kcal mol^-1) further reflect this trend: Fe²⁺ (120.30) > Zn²⁺ (87.27) > Mg²⁺ (64.94) > Ca²⁺ (24.84) > Na⁺ (19.38) > K⁺ (5.39). Divalent cations, particularly Fe²⁺, exhibit significantly stronger interactions and greater charge-transfer stabilization compared to monovalent ions, as corroborated by AIM analysis showing the highest electron density at the bond critical point (ρ) for the Fe²⁺⋯Ri complex. Global reactivity descriptors further confirm the electronic stability and relative softness of the resulting complexes. Overall, β-d-ribose shows promise as a bio-based scaffold for selective ion capture with potential applications in desalination and environmental remediation.