Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the novel coronavirus behind the fast-spreading coronavirus disease 2019 (COVID-19). Pharmaceutical researchers are currently researching medications or preventive vaccines that may be used to treat and combat the spread of COVID-19. Health practitioners all over the world are treating patients with currently available antiviral drugs, primarily the protease inhibitors used for HIV treatment. The present study mainly aims to evaluate the potencies of eight anti-HIV drugs to inhibit coronavirus protease using in silico methods. Derivation of pharmacophore, identification of hit molecules, and checking their virtual inhibition efficacies on the COVID-19 protease were also carried out in the present investigation. Classification of eight drug molecules (atazanavir, darunavir, fosamprenavir (amprenavir—metabolised product), saquinavir, lopinavir, ritonavir, nelfinavir, and indinavir) based on their molecular structures was completed and reported. The X-ray crystallographic structure of the main protease of coronavirus (SARS-CoV-2 protease) was obtained from the Protein Data Bank and prepared for computational studies using Edu PyMOL software. Docking studies were performed with AutoDock Vina software, and the results were evaluated with Discovery Studio software. The binding scores of the drugs on protease followed the order saquinavir > nelfinavir > lopinavir = indinavir > darunavir > amprenavir > ritonavir > atazanavir. Web servers such as PharmaGist and ZINCPharmer were employed to derive the 3D pharmacophore and to identify potential hit compounds, respectively. The identified hit molecules were docked with the SARS-CoV-2 protease and analysed. A detailed account of the type of interaction between the protease and the molecules is discussed. The majority of hit compounds displayed appreciable binding affinities on coronavirus protease. Three hit compounds possess structures similar to that of natural products, viz., flavonoids, and nucleoside. These molecules were hydrophilic and slightly deviated from Lipinski parameters. All other derived molecules obeyed the Lipinski rule. In vitro, in vivo, and toxicological studies of these compounds have to be performed before checking the actual druggability of these compounds.

The corrosion inhibition efficiency of thiophene-2-carbaldehyde tryptophan (T2CTRY) on mild steel (MS) in 1 M HCl solution has been investigated and compared using weight loss measurements, electrochemical impedance spectroscopy, and potentiodynamic polarization analysis. The Schiff base exhibited very good corrosion inhibition on mild steel in HCl medium and the inhibition efficiency increased with the increase in concentration of the inhibitor. The adsorption of the inhibitor on the surface of the corroding metal obeys Freundlich isotherm. Thermodynamic parameters (K ads , ΔG 0 ads ) were calculated using adsorption isotherm. Polarization studies revealed that T2CTRY acts as a mixed type inhibitor. A maximum of 96.2% inhibition efficiency was achieved by EIS studies at a concentration of 1 mM. Experimental2.1. Inhibitor. Heterocyclic Schiff base T2CTRY was synthesized by the condensation of equimolar mixture of thiophene-2-carbaldehyde and tryptophan in ethanol medium. The reaction mixture was refluxed for 3 hours, concentrated, and cooled. The yellow coloured solid was filtered, washed, and dried. Figure 1 shows the molecular structure of the heterocyclic Schiff base T2CTRY. Anal. calcd. for C 16 H 14 N 2 O 2

The adsorption behavior of a potential polynuclear Schiff base, (s)-2-(anthracen-9(10H)-ylideneamino)-3-phenyl propanoic acid (A9Y3PPA) on carbon steel (CS) in 1M hydrochloric acid solution has been investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies. The surface morphology of the carbon steel specimens in the presence and absence of the inhibitor was evaluated by AFM analysis. The corrosion inhibition efficiencies of parent amine and parent ketone on carbon steel in 1M HCl solution have also been investigated using weight loss studies. The adsorption of A9Y3PPA obeys Langmuir adsorption isotherm. Thermodynamic parameters (Kads, ∆G 0 ads) were calculated using the adsorption isotherm. Activation parameters of the corrosion process (Ea, ∆H* and ∆S*) were also calculated from the corrosion rates obtained from temperature studies. Tafel plot analysis revealed that A9Y3PPA acts as a mixed type inhibitor. A probable inhibition mechanism was also proposed.

A heterocyclic phenylhydrazone 2-[(E)-(2-phenylhydrazinylidene)methyl]pyridine (P2APH) and its reduced form 2-[(2-phenylhydrazinyl)methyl]pyridine (RP2APH) were synthesized, characterized, and subjected to corrosion inhibition investigation on carbon steel (CS) in 1 M HCl using gravimetric, polarization, electrochemical noise, quantum chemical, and surface studies. P2APH showed more inhibition capacity than RP2PPH. But RP2PPH was very stable in acid medium and showed pronounced corrosion inhibition efficacy for days. Energy of HOMO and LUMO, their difference, number of electrons transferred, electronegativity, chemical hardness, and so forth were evaluated by quantum chemical studies. Agreeable correlation was observed between the results of quantum chemical calculations and other corrosion monitoring techniques.

Synergistic effect of KI on the corrosion inhibition efficiency of 3-acetylpyridine phenylhydrazone (3APPH) on carbon steel (CS) in 0.5 M sulphuric acid solution has been investigated using gravimetric studies, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization studies. Gravimetric corrosion studies revealed that 3APPH showed moderate corrosion inhibition efficiency up to 8 h and beyond this period it showed corrosion accelerating behavior. This antagonistic effect of 3APPH is due to the hydrolysis of the molecule in acidic medium. A very high percentage of inhibition efficiency at 24 h was obtained on the addition of KI due to the synergistic effect of iodide ions. The adsorption of 3APPH and 3APPH + KI on the surfaces of the corroding metal obey Langmuir isotherm as obtained by impedance measurements. Polarization studies revealed that 3APPH act as a mixed type inhibitor. Thermodynamic parameters (ads , Δ 0 ads) were derived from the adsorption isotherms. Surface morphology of the corroding metal was investigated by SEM analysis.