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Two Schiff bases, HL1 and HL2, were synthesized in two different reactions involving 2-hydroxynaphthaldehyde with 2-amino-6-methylbenzothiazole and 2-amino-6-florobenzothiazole respectively. Copper(II) and nickel(II) complexes of the Schiff bases were subsequently prepared in 1:1 metal-to-ligand stoichiometric reactions. The compounds were characterized extensively by 1H NMR, 13C NMR, Dept-90, UV–Vis, and IR spectroscopic techniques, magnetic susceptibility, TGA, DTG, and molar conductivity analysis. The spectroscopic results confirm bidentate nature of the Schiff bases and a four coordinate geometry for all the complexes: [CuL1ClH2O], [NiL1ClH2O], [Cu(L2)2], and [NiL2ClH2O]. Quantum chemical studies gave fully optimized geometries of the Schiff bases and metal complexes using the 6-31+g(d,p) basis set. The compounds were studied for their in vitro antibacterial activities against some selected Gram-positive and Gram-negative bacteria, using agar well diffusion. The metal complexes exhibited better antibacterial activities compared to the free ligand due to the effects of chelation, which improved the lipophilicity. Furthermore, the antioxidant potentials of the compounds were ascertained using DPPH radical scavenging and ferrous chelating assay. The copper complexes had the best antioxidant properties of all the tested compounds. The results of the biological analysis were in agreement with the theoretical data from quantum chemical calculations. The study presented biologically active coordination compounds with benzothiazole moiety that could be used as compounds of interest in the drug discovery processes.

The inhibition performance of cerium sulphate tetrahydrate on the corrosion of steel in 1.0 M HCl solutions was investigated by using chemical (weight loss), electrochemical (electrochemical frequency modulation, electrochemical impedance spectroscopy, potentiodynamic polarization) and atomic force microscopy (AFM) at 25 ± 1 °C. Cerium sulphate tetrahydrate gave sufficient inhibition for the steel surface in molar hydrochloric acid solutions. AFM measurements show that the steel surface roughness was 123.08 nm before immersion, increased to 764.24 nm after immersion in uninhibited solution, and became 122.62 nm in the presence of the salt owing to the protective formation of an inhibitor layer.

The adsorption and corrosion inhibition behavior of cefuzonam (CZM) at mild steel surface were studied gravimetrically and electrochemically by using electrochemical impedance spectroscopy and Tafel polarization techniques. The increase in concentration and immersion time showed a positive effect. Inhibitor molecules directly adsorb on the surface on the basis of donor acceptor interactions between the p-electrons of benzene, sulfur and nitrogen atoms and the vacant d-orbital of iron atoms. The adsorption of CZM followed the Langmuir adsorption isotherm. A potentiodynamic polarization study revealed that CZM acted as mixed type of inhibitor. The results obtained from different methods are in good agreement. The adsorption behavior of CZM was experimentally investigated by contact angle measurement on metal surface. The contact angle of metal surface to the acid solution increased with inhibitor concentration, thereby confirming the increased hydrophobic nature of metal surface to the acid solution having the inhibitor.

The corrosion inhibition properties of ceforanide for mild steel in HCl solution were analyzed by electrochemical impedance spectroscopy, potentiodynamic polarization, and gravimetric methods. The increase in inhibitor concentration and immersion time showed a positive effect on inhibition efficiency. The experimental data showed a frequency distribution and therefore a modeling element with frequency dispersion behavior and a constant phase element have been used. In aqueous acid solution, mild steel reacts by evolution of hydrogen. Visual observations showed that the hydrogen evolution decreased (i.e., corrosion inhibition effect increased) with increasing concentration of ceforanide. Potentiodynamic polarization study revealed that ceforanide acted as a mixed type of inhibitor. The results obtained from different methods are in good agreement. The adsorption behavior of ceforanide is experimentally investigated by contact angle measurement on metal surface. The contact angle of metal surface to the acid solution increased with inhibitor concentration; thereby confirming the increased hydrophobic nature of metal surface to the acid solution having inhibitors.

2-(6-Methylpyridin-2-yl)oxazolo[5,4-f][1,10]phenanthroline (MOP) was synthesized and characterized by elemental analysis and Fourier-transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), and 13C NMR spectra. MOP was evaluated as a corrosion inhibitor for carbon steel in 0.5 M H2SO4 solution using the standard gravimetric technique at 303–333 K. Quantum chemical calculations and molecular dynamic (MD) simulations were applied to analyze the experimental data and elucidate the adsorption behavior and inhibition mechanism of MOP. Results obtained show that MOP is an efficient inhibitor for mild steel in H2SO4 solution. The inhibition efficiency was found to increase with increase in MOP concentration but decreased with temperature. Activation parameters and Gibbs free energy for the adsorption process using statistical physics were calculated and discussed. The adsorption of MOP was found to involve both physical and chemical adsorption mechanisms. Density functional theory (DFT) calculations suggest that nitrogen and oxygen atoms present in the MOP structure were the active reaction sites for the inhibitor adsorption on mild steel surface via donor–acceptor interactions between the lone pairs on nitrogen and oxygen atoms together with the π-electrons of the heterocyclic and the vacant d-orbital of iron atoms. The adsorption of MOP on Fe (1 1 0) surface was parallel to the surface so as to maximize contact, as shown in the MD simulations. The experiments together with DFT and MD simulations provide further insight into the mechanism of interaction between MOP and mild steel.

Corrosion inhibition of mild steel (MS) by chloroquine (CQ) in 1 M HCl was investigated using weight loss, polarization, electrochemical impedance spectroscopy (EIS) and quantum chemical techniques. The inhibitor showed 99 % inhibition efficiency at concentration of 3.1 × 10−4 M. Polarization studies showed that CQ is a mixed-type inhibitor. Adsorption of inhibitor molecules on the MS surface showed Langmuir adsorption isotherm. Thermodynamic parameters led to the conclusion that adsorption is predominantly chemisorption. Quantum chemical calculations were carried out to investigate the corrosion-inhibiting property of CQ. Various parameters such as energy of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), softness of molecule, Mullikan charges on various atoms and number of electrons transferred from inhibitor molecule to metal were calculated and correlated with the inhibiting property of CQ.

The inhibition ability of Dapsone’s Schiff’s base with salicylaldehyde (1:2) for mild steel corrosion in 1 M HCl solution at 308 K was studied by means of potentiodynamic polarization, electrochemical impedance spectroscopy techniques, and gravimetric analysis. Results showed that Dapsone salicylaldehyde performed well as a good inhibitor for mild steel in 1 M HCl solution with maximum inhibition efficiency of 95 % at 500 ppm. The adsorption isotherm of the inhibitor followed the Langmuir adsorption. The value of free energy of adsorption showed that it is a spontaneous process and followed typical physical adsorption.

The adsorption and inhibition effect of itraconazole (ICZ) on mild steel in 0.5 M HCl at 303–333 K was studied using gravimetric and quantum chemical methods. The adsorption of ICZ has been tested thermodynamically and was found to be mainly a physical adsorption mechanism and weak chemisorption. The activation and thermodynamic functions (such as Ea, \( \Updelta H^{*} ,\,\Updelta G_{\text{ads}}^{\text{o}} \)) of dissolution and adsorption processes have been evaluated and discussed. The analyses of the results obtained showed that ICZ inhibits the corrosion of mild steel effectively at moderate temperatures and adsorbs according to the Temkin adsorption isotherm. An attempt to correlate the molecular structure to quantum chemical indices was made using a semi-empirical (PM3) method. Results of the theoretical study indicate that nitrogen and oxygen atoms (O10, O13, N17, N19, O21, N28, N42, N43, and O45) were the reactive sites.