Predicting the Adsorption of Amoxicillin and Ibuprofen on Chitosan and Graphene Oxide Materials: A Density Functional Theory Study

Abstract

The occurrence, persistence, and accumulation of antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) represent a new environmental problem due to their harmful effects on human and aquatic life. A suitable absorbent for a particular type of pollutant does not necessarily absorb other types of compounds, so knowing the compatibility between a particular pollutant and a potential absorbent before experimentation seems to be fundamental. In this work, the molecular interactions between some pharmaceuticals (amoxicillin, ibuprofen, and tetracycline derivatives) with two potential absorbers, chitosan and graphene oxide models (pyrene, GO-1, and coronene, GO-2), were studied using the ωB97X-D/6-311G(2d,p) level of theory. The energetic interaction order found was amoxicillin/chitosan > amoxicillin/GO-1 > amoxicillin/GO-2 > ibuprofen/chitosan > ibuprofen/GO-2 > ibuprofen/GO-1, the negative sign for the interaction energy in all complex formations confirms good compatibility, while the size of E_int between 24-34 kcal/mol indicates physisorption processes. Moreover, the free energies of complex formation were negative, confirming the spontaneity of the processes. The larger interaction of amoxicillin Gos, compared to ibuprofen Gos, is consistent with previously reported experimental results, demonstrating the exceptional predictability of these methods. The second-order perturbation theory analysis shows that the amoxicillin complexes are mainly driven by hydrogen bonds, while van der Waals interactions with chitosan and hydrophobic interactions with graphene oxides are modelled for the ibuprofen complexes. Energy decomposition analysis (EDA) shows that electrostatic energy is a major contributor to the stabilization energy in all cases. The results obtained in this work promote the use of graphene oxides and chitosan as potential adsorbents for the removal of these emerging pollutants from water.

Keywords: absorption; density functional theory; emergent pollutants; natural bond orbital; pharmaceuticals.

Figure 1

Left: minimum energy structures at ωB97X-D/6-311G(2d,p) level of theory. (A) amoxicillin; (B) ibuprofen; (C) graphene oxide (pyrene, GO-1); (D) graphene oxide (coronene, GO-2); and (E) chitosan. On the right, electrostatic potential (ESP) surface; scale in kcal/mol.

Figure 2

Frontier molecular orbitals for compounds studied in this work. HOMO: Highest occupied molecular orbital; LUMO: lowest unoccupied molecular Orbital obtained at wB97X-D/6311G(2d,p) theory level. AMOX = amoxicillin; IBU = ibuprofen; CS = chitosan; GO-1 = pyrene-based graphene; GO-2 = coronene-based graphene.

Figure 3

Optimized structures at ωB97X-D/6-311G(2d.p) level of theory for all complexes studied in this work. (A) amoxicillin-chitosan; (B) ibuprofen-chitosan; (C) amoxicillin-GO-1; (D) amoxicillin-GO-2; (E) ibuprofen-GO-1; (F) ibuprofen-GO-2. The dashed line suggests an important molecular interaction.