NO2 Substituents Research Articles

Synthesis, crystal structure, Hirshfeld surface investigation and comparative DFT studies of ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate

The ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate (1), a thiazole ester, was synthesized by refluxing 1-(2-nitrobenzylidene)thiosemicarbazide and ethyl bromopyruvate. The compound is characterized by spectrometric, spectroscopic and single crystal (SC-XRD) techniques. Non-covalent interactions that are responsible for crystal packing are explored by Hirshfeld surface analysis. All theoretical calculations were performed by DFT quantum chemical methods using 6-311G(d,p) and cc-pVTZ basis sets and compared. Theoretical harmonic frequencies of ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate (1) were optimized. Confirmation of hydrogen bonding sites was analyzed by molecular electrostatic potential (MEP) and Mulliken population analysis. The vibrational frequencies of characteristic functional groups and chemical shifts were found in good agreement with experimental assignments. Frontier molecular orbital (FMO) revealed relatively small HOMO–LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gape, which speaks off the nearly planar geometry and extended conjugation, as compared to the substituents with no conjugation possible. It has also been observed that –NO2 substituent plays a vital role for this relatively small HOMO–LUMO gape and overall electronic properties when compared with similar thiazole carboxylates (2–6, Table 6). Ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate (1) was also evaluated for its anti-oxidant and anti-microbial activities.Graphical

Synthesis and antimicrobial evaluation of novel tris‐thiadiazole derivatives

Abstract1,1′,1″‐(((1,3,5‐triazine‐2,4,6‐triyl)tris(oxy))tris(benzene‐4,1‐diyl))tris(ethan‐1‐one) 1 reacted with extra bromine to afford the corresponding 1,1′,1″‐(((1,3,5‐triazine‐2,4,6‐triyl)tris(oxy))tris(benzene‐4,1‐diyl))tris(2‐bromoethan‐1‐one) 2. Also, reaction of acetophenone derivatives 3 with 5‐amino‐1,3,4‐thiadiazole‐2‐thiol 4 give the 5‐((1‐arylethylidene)amino)‐1,3,4‐thiadiazole‐2‐thiol 5. Compounds 5a–h reacted with 2 in the presences of acetic acid to afford novel 1,1′,1″‐(((1,3,5‐triazine‐2,4,6‐triyl)tris(oxy))tris(benzene‐4,1‐diyl))tris(2‐((5‐((1‐arylethylidene)amino)‐1,3,4‐thiadiazol‐2‐yl)thio)ethan‐1‐one) derivatives 6a–h. Antimicrobial activities of the products were evaluated against five bacterial strains including Streptococcus pneumoniae, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Serratia marcescens. The antimicrobial results indicated that products 6b, 6d, and 6h had excellent activities as compared to other synthesized products against a variety of bacterial strains. The compounds having Cl and NO2 substituents showed notable inhibition of bacterial growth almost near to Ciprofloxacin as standard.

Diarylation of N- and O-nucleophiles through a metal-free cascade reaction

Diarylation of N- and O-nucleophiles through a metal-free cascade reaction

Synthesis and biological evaluation of novel 1,3,4‐oxadiazole derivatives as anticancer agents and potential EGFR inhibitors

AbstractEGFR (epidermal growth factor receptor) tyrosine kinases are frequently used in recent years, especially in small cell lung cancer. As with all other anticancer drugs, problems such as high side‐effect profiles and resistance to anticancer drugs call for new antiproliferative compounds. In the light of the above information, novel quinoxalin‐oxadiazole derivatives were synthesized as EGFR inhibitors in this study. Synthesis of compounds (3a–3j) was performed according to the literature methods. Their structures were elucidated by 1H‐NMR, 13C‐NMR, and HRMS spectroscopic methods. Structure elucidation was performed for compound 3e using 2D NMR technique. MTT test was performed to assess the cell proliferation effects of the different compounds on lung and mammary cell lines (A549, MCF7). In addition, obtained compounds (3a–3j) were screened against healthy CCD19‐Lu cell line (human lung fibroblast normal cells) to determine selectivity of the cytotoxic activities. Among the tested compounds, 3e and 3j showed significant cytotoxic activity against A549 cancer cell. Moreover, compound 3g and 3h displayed good activity. And the compounds 3e and 3j performed significant EGFR inhibition. Interaction modes of the compounds 3e, 3j were investigated against EGFR tyrosine kinase by means of docking studies. As a result of the studies, the importance of the quinoxaline ring and the NO2 substituent has been understood. In future studies, it is planned to make modifications by keeping these two structures constant. The activity can be contributed by using other heterocyclic rings instead of the oxadizaole ring.

Substituent-mediated quantum interference toward a giant single-molecule conductance variation

Quantum interference (QI) in single molecular junctions shows a promising perspective for realizing conceptual nanoelectronics. However, controlling and modulating the QI remains a big challenge. Herein, two-type substituents at different positions of meta-linked benzene, namely electron-donating methoxy (–OMe) and electron-withdrawing nitryl (–NO2), are designed and synthesized to investigate the substituent effects on QI. The calculated transmission coefficients T(E) indicates that –OMe and –NO2 could remove the antiresonance and destructive quantum interference (DQI)-induced transmission dips at position 2. –OMe could raise the antiresonance energy at position 4 while –NO2 groups removes the DQI features. For substituents at position 5, both of them are nonactive for tuning QI. The conductance measurements by scanning tunneling microscopy break junction show a good agreement with the theoretical prediction. More than two order of magnitude single-molecule conductance on/off ratio could be achieved at the different positions of –NO2 substituent groups at room temperature. The present work proves chemical substituents can be used for tuning QI features in single molecular junctions, which provides a feasible way toward realization of high-performance molecular devices.

Benzimidazole Derivatives as Energetic Materials: A Theoretical Study.

The explosive properties and stability of benzimidazole compounds are studied to determine the influence of substituents and their position. The results obtained reveal the conjugation of substituents as one of the crucial factors for the thermal stability of these compounds. We also found that two -CH3 substituents increase the thermal stability of the parent compound, while nitro groups decrease it. Moreover, the study clearly exhibits that the combination of an -NO2 substituent with -CH3 does not change the stability of the benzimidazole. On the other hand, nitro groups increase the chemical stability and explosive properties of the compounds under investigation, but their sensitivity could not fully satisfy the requirements of their safety and increase their toxicity. The main results of the study indicate that high thermal and chemical stability, low toxicity and sensitivity, and good explosive properties could be achieved by the precise combination of nitro, -CH3, and triazole ring substituents. These findings are very important for the design of new, effective, and non-sensitive explosives.

Competition of Intra- and Intermolecular Forces in Anthraquinone and Its Selected Derivatives.

Intra- and intermolecular forces competition was investigated in the 9,10-anthraquinone (1) and its derivatives both in vacuo and in the crystalline phase. The 1,8-dihydroxy-9,10-anthraquinone (2) and 1,8-dinitro-4,5-dihydroxy-anthraquinone (3) contain Resonance-Assisted Hydrogen Bonds (RAHBs). The intramolecular hydrogen bonds properties were studied in the electronic ground and excited states employing Møller-Plesset second-order perturbation theory (MP2), Density Functional Theory (DFT) method in its classical formulation as well as its time-dependent extension (TD-DFT). The proton potential functions were obtained via scanning the OH distance and the dihedral angle related to the OH group rotation. The topological analysis was carried out on the basis of theories of Atoms in Molecules (AIM—molecular topology, properties of critical points, AIM charges) and Electron Localization Function (ELF—2D maps showing bonding patterns, calculation of electron populations in the hydrogen bonds). The Symmetry-Adapted Perturbation Theory (SAPT) was applied for the energy decomposition in the dimers. Finally, Car–Parrinello molecular dynamics (CPMD) simulations were performed to shed light onto bridge protons dynamics upon environmental influence. The vibrational features of the OH stretching were revealed using Fourier transformation of the autocorrelation function of atomic velocity. It was found that the presence of OH and NO substituents influenced the geometric and electronic structure of the anthraquinone moiety. The AIM and ELF analyses showed that the quantitative differences between hydrogen bonds properties could be neglected. The bridged protons are localized on the donor side in the electronic ground state, but the Excited-State Intramolecular Proton Transfer (ESIPT) was noticed as a result of the TD-DFT calculations. The hierarchy of interactions determined by SAPT method indicated that weak hydrogen bonds play modifying role in the organization of these crystal structures, but primary ordering factor is dispersion. The CPMD crystalline phase results indicated bridged proton-sharing in the compound 2.

Positional Electronic Effects in Iminopyridine‐N‐oxide Nickel Catalyzed Ethylene Polymerization†

Main observation and conclusionA series of dibenzhydryl‐based iminopyridine‐N‐oxide ligands bearing a range of electron‐donating or ‐withdrawing substituents (OMe, H, and NO2) and corresponding nickel pre‐catalysts are prepared and characterized. The substituents are installed at different positions on the ligand structure, including 4‐position of the pyridine‐N‐oxide moiety (position X) and 4‐position of the aniline moiety (position Y). These nickel pre‐catalysts are highly active in ethylene polymerization with the addition of very little amount of aluminum cocatalysts, leading to the formation of polyethylenes with molecular weights of well above one million. Electron‐donating substituents make the catalysts sensitive to polymerization temperature. In contrast, the catalysts bearing electron‐withdrawing NO2 substituents show relatively steady performances at different temperatures. Most importantly, we demonstrate that different substituents and different positions both play important roles in determining the properties of nickel catalysts. This provides an alternative strategy for the future design of high‐performance polymerization catalyst.

New Nitro-Laterally Substituted Azomethine Derivatives; Synthesis, Mesomorphic and Computational Characterizations.

Two new homologues series, based on two rings of the azomethine central group bearing the terminal alkoxy group of various chain lengths, were prepared. The alkoxy chain length varied between 6 and 16 carbons. The other terminal wing in the first series was the F atom, and the compound is named N-4-florobenzylidene-4-(alkoxy)benzenamine (In). The second group of compounds included a lateral NO2 substituent in addition to the terminal F atom, named N-(4-fluoro-3-nitrobenzylidene)-4-(alkyloxy)aniline (IIn). Mesomorphic and optical properties were carried out via differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Elemental analyses, FT-IR, and NMR spectroscopy were carried out to elucidate the molecular structures of the synthesized groups. Mesomorphic investigations indicated that all the synthesized homologues (In) were monomorphic, possessing the smectic A (SmA) phase monotropically, while the second group (IIn) members were non-mesomorphic. The experimental data indicated that the formation of the mesophase is affected by the protrusion of the lateral nitro group. The disruption of the mesophase in the second group was attributed to the increase of its molecular width, which affects its lateral intermolecular interactions. The computational simulations were in agreement with the experimental data. On the other hand, the location of NO2 group within the molecular geometry increased the melting temperature of the molecule, and thus, affected their thermal and physical properties. By discussing the estimated parameters, it was found that the molecular architecture, the dipole moment, and the polarizability of the investigated compounds are highly affected by the electronic nature and position of the terminal and lateral substituents as well as their volumes.

Synthesis and exploring the excited-state PES of photochromic hydrogen bond-assembled [2]rotaxane based on 1,3-Diazabicyclo-[3.1.0]hex-3-enes

Here, the synthesis of photochromic hydrogen bond-assembled [2]rotaxanes using bis-fumarate as a thread for the first time is reported. In fact, photochromic 1,3-diazabicyclo[3.1.0]hex-3-ene moieties were used as stoppers and two-atom spacers managed good binding sites for the tetralactam macrocycles in clipping reactions. Moreover, the yields of photochromic [2]rotaxanes highly depended on the NO2 substituent stoppers. While the thread with a para –NO2 substituent as stopper units was shown to be an excellent template for the synthesis of photochromic [2]rotaxanes. The structures of the [2]rotaxanes are established clearly in solution by chemical shifts of the 1H 13C NMR signals and UV–Vis spectra. A pronounced bathochromic shift was occurred in the excitation wavelength of photochoromic [2]rotaxanes compared with the absorption band of photochromic threads. Therefore, these organizations can be applied in light-driven molecular switches and motors. The reversible transformation of trans and cis geometric photoisomers under UV radiation was identified. In other efforts, the possibility of the process of trans to cis interconversion of the fumarate linker under UV irradiation has been examined computationally and it has appeared that it may cause the transverse of the bis-fumarate linker inside the tetralactam macrocycle to some extent.

Application of niclosamide and analogs as small molecule inhibitors of Zika virus and SARS-CoV-2 infection

Zika virus has emerged as a potential threat to human health globally. A previous drug repurposing screen identified the approved anthelminthic drug niclosamide as a small molecule inhibitor of Zika virus infection. However, as antihelminthic drugs are generally designed to have low absorption when dosed orally, the very limited bioavailability of niclosamide will likely hinder its potential direct repurposing as an antiviral medication. Here, we conducted SAR studies focusing on the anilide and salicylic acid regions of niclosamide to improve physicochemical properties such as microsomal metabolic stability, permeability and solubility. We found that the 5-bromo substitution in the salicylic acid region retains potency while providing better drug-like properties. Other modifications in the anilide region with 2′-OMe and 2′-H substitutions were also advantageous. We found that the 4′-NO2 substituent can be replaced with a 4′-CN or 4′-CF3 substituents. Together, these modifications provide a basis for optimizing the structure of niclosamide to improve systemic exposure for application of niclosamide analogs as drug lead candidates for treating Zika and other viral infections. Indeed, key analogs were also able to rescue cells from the cytopathic effect of SARS-CoV-2 infection, indicating relevance for therapeutic strategies targeting the COVID-19 pandemic.

A second generation of 1,2,4-oxadiazole derivatives with enhanced solubility for inhibition of 3-hydroxykynurenine transaminase (HKT) from Aedes aegypti.

The most widely used method for the control of the Aedes aegypti mosquito population is the chemical control method. It represents a time- and cost-effective way to curb several diseases (e.g. dengue, Zika, chikungunya, yellow fever) through vector control. For this reason, the discovery of new compounds with a distinct mode of action from the available ones is essential in order to minimize the rise of insecticide resistance. Detoxification enzymes are an attractive target for the discovery of new insecticides. The kynurenine pathway is an important metabolic pathway, and it leads to the chemically stable xanthurenic acid, biosynthesized from 3-hydroxykynurenine, a precursor of reactive oxygen and nitrogen species, by the enzyme 3-hydroxykynurenine transaminase (HKT). Previously, we have reported the effectiveness of 1,2,4-oxadiazole derivatives acting as larvicides for A. aegypti and AeHKT inhibitors from in vitro and in silico studies. Here, we report the synthesis of new sodium 4-[3-(aryl)-1,2,4-oxadiazol-5-yl] propanoates and the cognate HKT-inhibitory activity. These new derivatives act as competitive inhibitors with IC50 values in the range of 42 to 339 μM. We further performed molecular docking simulations and QSAR analysis for the previously synthesized sodium 4-[3-(aryl)-1,2,4-oxadiazol-5-yl] butanoates reported earlier by our group and the data produced herein. Most of the 1,2,4-oxadiazole derivatives, including the canonical compounds for both series, showed a similar binding mode with HKT. The binding occurs similarly to the co-crystallized inhibitor via anchoring to Arg356 and positioning of the aromatic ring and its substituents outwards at the entry of the active site. QSAR analysis was performed in search of more than 770 molecular descriptors to establish a relationship between the lowest energy conformations and the IC50 values. The five best descriptors were selected to create and validate the model, which exhibited parameters that attested to its robustness and predictability. In summary, we observed that compounds with a para substitution and heavier groups (i.e. CF3 and NO2 substituents) had an enhanced HKT-inhibition profile. These compounds comprise a series described as AeHKT inhibitors via enzymatic inhibition experiments, opening the way to further the development of new substances with higher potency against HKT from Aedes aegypti.

Hammett Relationship in Oxidase-Mimicking Metal-Organic Frameworks Revealed through a Protein-Engineering-Inspired Strategy.

While the unique physicochemical properties of nanomaterials that enable regulation of nanozyme activities are demonstrated in many systems, quantitative relationships between the nanomaterials structure and their enzymatic activities remain poorly understood, due to the heterogeneity of compositions and active sites in these nanomaterials. Here, inspired by metalloenzymes with well-defined metal-ligand coordination, a set of substituted metal-organic frameworks (MOFs) with similar coordination is employed to investigate the relationship between structure and oxidase-mimicking activity. Both experimental results and density functional theory calculations reveal a Hammett-type structure-activity linear free energy relationship (H-SALR) of MIL-53(Fe) (MIL = Materials of Institute Lavoisier) nanozymes, in which increasing the Hammett σm value with electron-withdrawing ligands increases the oxidase-mimicking activity. As a result, MIL-53(Fe) NO2 with the strongest electron-withdrawing NO2 substituent shows a tenfold higher activity than the unsubstituted MIL-53(Fe). Furthermore, the generality of H-SALR is demonstrated for a range of substrates, one other metal (Cr), and even one other MOF type (MIL-101). Such biologically inspired quantitative studies demonstrate that it is possible to identify quantitative structure-activity relationships of nanozymes, and to provide detailed insight into the catalytic mechanisms as those in native enzymes, making it possible to use these relationships to develop high-performance nanomaterials.

Insights into corrosion inhibition mechanism of mild steel in 1 M HCl solution by quinoxaline derivatives: electrochemical, SEM/EDAX, UV-visible, FT-IR and theoretical approaches

Three quinoxaline-based heterocycles namely, 6-methyl-2,3-diphenylquinoxaline (Q-CH3), 6-nitro-2,3-diphenylquinoxaline (Q-NO2) and 2,3-diphenylquinoxaline (Q-H) were evaluated as inhibitor for mild steel (MS) in 1 M HCl. Inhibition effectiveness of the Q-H, Q-CH3 and Q-NO2 tested using different computational simulations and experimental methods. Results showed that inhibition effectiveness of Q-H, Q-CH3 and Q-NO2increases with their concentration. Polarization results showed that Q-H, Q-CH3 and Q-NO2displayed anodic-type behaviour. Inhibition efficiencies of Q-H, Q-CH3 and Q-NO2 followed the order: 87.6% (Q-NO2) < 90.2% (Q-CH3)< 92.4%(Q-H) for Q-CH3. Presence of both electron withdrawing (-NO2) and donating (-CH3) substituents decrease the inhibition efficiency as compared to the parent compound however in decrease in protection power is more prominent in the presence of –NO2 substituent. Q-H, Q-CH3 and Q-NO2inhibit corrosion by adsorbing on MS surface and their adsorption mode followed Langmuir adsorption isotherm. Adsorption of Q-H, Q-CH3 and Q-NO2 on metallic surface reinforced with SEM-EDS and UV-visible studies of MS surfaces. Interaction mechanism of Q-H, Q-CH3 and Q-NO2with MS surface and their mode of adsorption was studies using DFT and MD (MD) simulations, respectively. Negative sign of adsorption energies (Eads) for Q-H, Q-CH3 and Q-NO2suggested that they adsorb spontaneously over MS surface.

Thousands of reactants and transition states for competing E2 and S2 reactions

Reaction barriers are a crucial ingredient for first principles based computational retro-synthesis efforts as well as for comprehensive reactivity assessments throughout chemical compound space. While extensive databases of experimental results exist, modern quantum machine learning applications require atomistic details which can only be obtained from quantum chemistry protocols. For competing E2 and S2 reaction channels we report 4,466 transition state and 143,200 reactant complex geometries and energies at MP2/6-311G(d) and single point DF-LCCSD/cc-pVTZ level of theory, respectively, covering the chemical compound space spanned by the substituents NO2, CN, CH3, and NH2 and early halogens (F, Cl, Br) and hydrogen as nucleophiles and early halogens as leaving groups. Reactants are chosen such that the activation energy of the competing E2 and S2 reactions are of comparable magnitude. The correct concerted motion for each of the one-step reactions has been validated for all transition states. We demonstrate how quantum machine learning models can support data set extension, and discuss the distribution of key internal coordinates of the transition states.

Synthesis, Electronic Properties and Reactivity of [B12 X11 (NO2 )]2- (X=F-I) Dianions.

Nitro‐functionalized undecahalogenated closo‐dodecaborates [B12X11(NO2)]2− were synthesized in high purities and characterized by NMR, IR, and Raman spectroscopy, single crystal X‐diffraction, mass spectrometry, and gas‐phase ion vibrational spectroscopy. The NO2 substituent leads to an enhanced electronic and electrochemical stability compared to the parent perhalogenated [B12X12]2− (X=F–I) dianions evidenced by photoelectron spectroscopy, cyclic voltammetry, and quantum‐chemical calculations. The stabilizing effect decreases from X=F to X=I. Thermogravimetric measurements of the salts indicate the loss of the nitric oxide radical (NO.). The homolytic NO. elimination from the dianion under very soft collisional excitation in gas‐phase ion experiments results in the formation of the radical [B12X11O]2−.. Theoretical investigations suggest that the loss of NO. proceeds via the rearrangement product [B12X11(ONO)]2−. The O‐bonded nitrosooxy structure is thermodynamically more stable than the N‐bonded nitro structure and its formation by radical recombination of [B12X11O]2−. and NO. is demonstrated.

Modulation of benzofuran structure as a fluorescent probe to optimize linear and nonlinear optical properties and biological activities

The study presents the influence of structure modulation by introducing selected donor and acceptor substituents on optical properties of benzofuran used in biological imaging. As the starting form, 2-(5-formylbenzofuran-2-yl)acetamide described experimentally was used. This molecule contains an aldehyde group as reactive site, through which conjugation with protein occurs. Structure modulation was carried out by attaching additional electron-donating and electron-withdrawing substituents to the amino group, namely -NH2, -NHCH3, -NO2, -OH, and -OCH3. Studies have shown that the -NH2, -NHCH3, -OH, and -OCH3 substituents do not induce a significant change in the position of maximum absorption and fluorescence relative to each other. They also do not change the parameters describing the nonlinear response. Only the presence of the -NO2 substituent results in significant solvatochromic shifts. Changing substituents also does not significantly affect the LD50 value, and all tested fluorescent probes should not be considered toxic to humans. Modulation of the benzofuran derivative structure also does not change the active center in which the biocomplex with the protein is formed. In each case, the conjugation takes place via LYS114. In addition, the study was prompted to analyze the linear and nonlinear optical properties of conjugates formed after the reaction with Concanavalin A.Graphical abstract

Contribution of stilbene-imine additives on the structural, ionic conductivity performance and theoretical evaluation on CMC-based biopolymer electrolytes

New solid biopolymer electrolytes (SBEs) were prepared by integrating stilbene-imine derivatives bearing vinylene (CHCH) and azomethine (CHN) as additives in carboxymethyl cellulose (CMC) based electrolyte. The investigation on their spectroscopic and theoretical assessments were conducted to alter the energy level in improving the structural and ionic conductivity performance. The simulated results from frontier molecular orbitals (FMO) and Mulliken-charge analysis revealed that -CF3 and -NO2 substituents significantly reduce the HOMO-LUMO gap up to 0.68 eV. The highest ionic conductivity of SBEs achieved at ambient temperature was ∼8 × 10−3 Scm-1 upon the addition of additive, obeying an Arrhenius model with reciprocal of temperature (303 K–373 K). The coordination interaction of CO bond and CHN band facilitated the dissociation of more cation (H+) of NH4Cl which permits alternative route for H+ to hop into coordinating site in CMC. The outcomes are ideal in the development of electrochemical devices.

Synthesis and biological evaluation of copper and cobalt complexes of (5-substituted-salicylidene) isonicotinichydrazide derivatives as antitubercular agents

Cobalt(II) and copper(II) complexes of a series (E)-N’-(5-X-salicylidene)isonicotinohydrazide Schiff bases derived from isonicotinic acid hydrazide and 5-substituted-salicylaldehydes have been synthesized and characterized by FTIR, AAS, UV-Visible spectroscopy and elemental analysis. Evaluation of the in-vitro antitubercular, antioxidant and cytotoxic activities of the compounds was carried out to establish their potential as antituberculosis agents.The FTIR spectra showed that the ligands behave as tridentate dibasic ligands towards the metal ions. The antioxidant activities of the compounds investigated through their scavenging effect on DPPH revealed that the IC50 for the nitro substituted Schiff base was highest, similarly, the LC50 value was much lower than the values for other compounds. The ligand complexes containing the nitro NO2 substituent exhibited enhanced in vitro Mycobacterium tuberculosis and antioxidant activities compared with the ligands and reference compounds (Isoniazid and vitamin C).

Experimental and Theoretical Study of Pinostrobin as Copper Corrosion Inhibitor at 1 M H2SO4 Medium

The effect of variations in concentration and temperature on the efficiency of pinostrobin corrosion inhibition of copper in 1M H2SO4 was studied using an experimental and theoretical approach. Pinostrobin was isolated from the Boesenbergia rotunda L rhizome and was tested for corrosion inhibition of copper in acidic medium. Variations in the concentration of 300 ppm, 400 ppm, and 500 ppm and temperature (308 K, 318 K, and 328 K) were carried out in the weight loss method of corrosion inhibition test. Pinostrobin crystals were isolated with a yield of 57.65 %, a melting point of 98.5 °C and with a purity of 100 %. The optimum corrosion inhibition efficiency of pinostrobin is 65.71 % at a concentration of 500 ppm and a temperature of 328 K. The activation energy value of Ea < 80 kJ.mol−1 indicates the adsorption of pinostrobin on copper surfaces is physical and spontaneously ΔG°ads < -20 kJ.mol−1. The effect of substituent on the efficiency of corrosion inhibition from pinostrobin was studied using density functional theory. The addition of NH2 increased the efficiency of corrosion inhibition to 73.07 %, whereas the addition of NO2 substituents decreased the efficiency of inhibition to 60.97 %. Experimental and theoretical studies have a good correlation in explaining the efficiency of corrosion inhibition from pinostrobin.