35 Iranian Journal of Materials Science & Engineering Vol. 14, No. 4, December 2017 1. INTRODUCTION Copper is widely used in many industries as a conductor in electrical power lines, pipelines for domestic and industrial water utilities including sea water, heat conductors, heat exchangers, etc. In these industries, to restrain the corrosion and oxidation after several working cycles, chemical cleaning treatment by acid is used which results in severe corrosion during exposure to aggressive media. One of the most effective and economic approaches to avoid corrosive effect of this acid on the copper is the use of a corrosion inhibitor [1-4]. Widespread researches are made to find corrosion inhibitors which are less toxic, environmentally-friendly, ecologically acceptable, readily available, and relatively low- cost drugs are used as good inhibitors for metals in acidic solution [5]. Theoretical calculations have proven to be a powerful tool in studying the interactions between the inhibitor molecules and the metal surfaces. Therefore, recently an increasing attention has been seen on the involvement of these theoretical approaches in corrosion studies [6-17]. The purpose of this investigation is the evaluation of the corrosion inhibition of penicillin G, nafcillin, methicillin for copper in an acidic medium using gravimetric measurement, potentiodynamic polarization and isotherm calculations. We have also studied both the quantum chemical calculations and MD simulation to confirm the experimental outcomes. 2. EXPERIMENTAL PROCEDURE 2.1. Materials Three compounds of penicillin G (CID 5904), nafcillin (CID 8982), and methicillin (CID 6087) Abstract: The inhibition performances of nafcillin (III), methicillin (II) and penicillin G (I) on the corrosion of copper in HCl was studied and tested by weight loss, Tafel polarization, SEM, UV-vis spectrophotometry, molecular dynamics method and quantum chemical calculations. Polarization curves indicated that the studied inhibitors act as mixed-type inhibitors. The values of inhibition efficiency and surface coverage were found to follow the order: Blank <penicillin <methicillin <nafcillin. The maximum inhibition efficiency of 98.28% was exhibited by nafcillin, and the minimum inhibition efficiency of 43.10% was showed by penicillin. The adsorption of inhibitors obeys the Temkin adsorption isotherm. The negative value of free energy of adsorption ∆Gads, indicated that the adsorption of three inhibitors was a spontaneous process. The SEM micrographs confirmed the protection of copper in a 1 M HCl solution by penicillin G, nafcillin, and methicillin. The shape of the UV/vis spectra of inhibitors in the presence of the immersion of Cu showed a strong support to the possibility of the chemisorbed layer formation on Cu surface by nafcillin (between nafcillin and Copper) and physisorption between penicillin and methicillin with copper. DFT calculations were performed to provide further insight into the inhibition efficiencies which were determined experimentally. Molecular dynamics (MD) simulations were applied to find the most stable configuration and adsorption energies of penicillin G, nafcillin and methicillin molecules on Cu (110) surface. The interaction energy followed the order: nafcillin (III)> methicillin (II)> penicillin G (I), which confirmed that nafcillin has the strongest interaction with the metal surface. The obtained results from experimental and theoretical methods were in reasonable agreement. Keywords: Copper, Antibacterial Drugs, Corrosion, Inhibitor, SEM, Molecular Dynamic Simulations Corrosion Inhibition of Copper in Acid Medium by Drugs: Experimental and Theoretical Approaches M. Shahraki, S. M. Habibi-Khorassani*, M. Noroozifar, Z. Yavari, M. Darijani and M. Dehdab * smhabibi@chem.usb.ac.ir Received: March 2017 Accepted: Octorber 2017 Department of Chemistry, University of Sistan and Baluchestan, Zahedan, Iran. DOI: 10.22068/ijmse.14.4.35