A molecular level insight into adsorption of β-lactam antibiotics on vermiculite surface

The adsorption processes of β-lactam antibiotics including ampicillin (AP), amoxicillin (AX) and benzylpenicillin (BP) on the vermiculite surface were investigated using density functional theory computations. The C09-vdW density functional was used to include van der Waals interactions for determination of the most stable configurations governing the interactions between AP, AX and BP molecules and the vermiculite surface. Each molecule prefers to arrange horizontally on the surface to form both Mg∙∙∙S and Mg∙∙∙π contacts, or two Mg∙∙∙O electrostatic interactions between S atom in CS, π-electrons of benzene ring or O atoms of -COOH, OH groups in molecules and Mg2+ sites on surface. Remarkably, an important role of Mg∙∙∙π interaction in the complex stabilization has been observed for the first time. These are strong chemisorption processes with adsorption energies ranging from −72 to −78 kcal.mol−1. AIM calculations show a significant contribution of Mg∙∙∙O/S/π interactions and OH∙∙∙O hydrogen bonds to the complex stabilization. Formation and role of different interactions on the stability of complexes were thoroughly examined by MOs and EDTs analysis based on NBO approach. Overall, vermiculite, a clay mineral, emerges to offer an efficient adsorption surface and can be used as a material to remove antibiotic molecules from waste water sources.