Triclosan Adsorption on Chitosan: Computational Study of Molecular Interactions and Potential for Environmental Remediation

The compound triclosan (TCS) is widely found in personal hygiene products, and when present in effluents, it can cause problems to human health, such as endocrine disruption, intestinal problems, and liver tumors. A sustainable alternative for the removal of TCS is the use of adsorbent biopolymers, which are low-cost, renewable, and biodegradable. One of the most widely used biopolymers is chitosan (CHT), which has excellent adsorptive properties due to its functional groups. In this context, the present work evaluated, through computational simulations, the interaction of the TCS molecule with CHT. The frontier molecular orbitals and the molecular electrostatic potential show that different forms of interactions can occur, and thus, five complexes were shown to be stable after the optimization of the interactions. The bond lengths of the interactions ranged from 1.839 Å to 3.606 Å and were formed mainly by hydrogen bonds and H^...Cl interactions. The binding energy (∆E_Bind) allowed us to infer that adsorption occurred, ∆E_Bind < 0, and the values ranged from -4.14 kcal mol^-1 to -17.74 kcal mol^-1. The thermodynamic properties demonstrated that the process was exothermic and that two complexes were spontaneous: TCS^...CHTⁱⁱⁱ with ΔG= -3.14 kcal mol^-1 and TCS^...CHT^iv with ΔG= -2.82 kcal mol^-1. The topological parameters revealed that almost all interactions between TCS and CHT were electrostatic, and the non-covalent interaction analysis confirmed the presence of van der Waals interaction between the complexes. Thus, it can be confirmed that this study showed the efficient use of chitosan for the treatment of effluents containing the emerging contaminant triclosan.