A comparative study on the interaction of M³⁺(H₂O)_5-6 ions (M = Fe, Ru, and Os) with the hydroxy group

Context: The heavy metal ions are the typical carcinogenic agents. Up to now, the interaction mechanism of toxic metal ions with the biomolecules such as carbohyrate have not been elucidated and reported in the detail. In this research work, the adjacent dissociation Gibbs energy (E_AB) of M³⁺(H₂O)₅(R-OH) complexes depended significantly on the molecular volume of primary alcohols and the inductive effects of substituent R in primary alcohols (R = CH₃, CH₃CH₂, CH₃CH₂CH₂, CH₃CH₂CH₂CH₂, Cl-CH₂, F-CH₂) as well as the length of linear cellulose. The affinity of M³⁺(H₂O)₅ ions with the sixth water molecule in gas phase reduced in the order as follows: Fe³⁺ > Ru³⁺ > Os³⁺, which were determined by the E_AB values and bond lengths of M-O. The water solvent made the E_AB values of Fe³⁺(H₂O)₆ ions and Fe³⁺(H₂O)₅(CH₃OH) ions changed completely in the case of the polarizable continuum model, while the Onsager model gave the good agreement with the gas phase model.

Methods: The nature of interaction between hydrated Fe³⁺(H₂O)₅ ion and the hydroxy groups of primary alcohols were investigated using density functional theory method at the B3LYP/6-311 + G** level, the PBEPBE/6-311 + G** level. The influence of water solvent was evaluated using the Onsager model and the polarizable continuum model. The two-layer ONIOM approach and the local softness analysis were employed for the hydroxy groups of linear cellulose at the B3LYP/6-311 + G**:HF/6-31G* level. The affinity of M³⁺(H₂O)₅ ions (M = Fe, Ru, and Os) with the sixth water molecule were probed at the B3LYP/QZVPP/6-311 + G** level (QZVPP basis set for the metal atoms).