A quantum chemical insight into corrosion inhibition effects of moxifloxacin and betamethasone drugs

The corrosion protection properties of several drugs attract too much attention in recent years due to the structural closeness they share with effective corrosion inhibitors. It is obvious that the mainstay for the choice of drugs as corrosion inhibitors is mostly due to their environmentally friendly nature. In parallel, interest in the use of expired drugs has also seen a resurgence in corrosion research community. However, there still exists much skepticism about the value such usage can add to corrosion inhibition of metals. In this regard, in a previous study, two expired drugs, i.e., moxifloxacin and betamethasone (betnesol), which are widely used for the systemic treatment of bacterial infections and inflammation respectively, have been experimentally investigated as effective corrosion inhibitors for aluminum in sulfuric acid solution. According to the experimental findings, an increase in inhibitor concentration resulted in an increase of the inhibition efficiency of the inhibitors and transfer resistance. The anodic type nature of moxifloxacin and betamethasone has also been illustrated by polarization curve, and from a thermodynamical aspect, both chemisorption and physisorption of these drugs on aluminum metal surface have been proposed. However, very little is known about the relation between molecular structure/electronic properties and inhibition efficiencies of these compounds at the atomic level. For this purpose, the structures and the ground-state energies of moxifloxacin and betamethasone have been analyzed employing density functional theory (DFT) calculations. The reported optimized geometries, molecular properties such as highest occupied molecular orbital energy (E-HOMO), the lowest unoccupied molecular orbital energy (E-LUMO) and the energy gap (Delta E) as well as essential global reactivity parameters have also been used to reveal the inhibition efficiency of moxifloxacin and betamethasone. The experimental data which suggest better inhibition by betamethasone have been theoretically acknowledged.