Computational insights into the corrosion inhibition potential of some pyridine derivatives: A DFT approach European Journal of Chemistry 14 (2) (2023) 246-253 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2023 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.14.2.246-253.2408 European Journal of Chemistry View Journal Online View Article Online Computational insights into the corrosion inhibition potential of some pyridine derivatives: A DFT approach Abhinay Thakur 1 and Ashish Kumar 2,* 1 Department of Chemistry, School of Chemical Engineering and Physical Sciences, Lovely Professional University, Phagwara, 144411, India 2 Nalanda College of Engineering, Bihar Engineering University, Department of Science and Technology, Government of Bihar, 803108, India * Corresponding author at: Department of Science and Technology, Nalanda College of Engineering, Bihar Engineering University, Government of Bihar, 803108, India. e-mail: drashishchemlpu@gmail.com (A. Kumar). 10.5155/eurjchem.14.2.246-253.2408 Received: 26 December 2022 Received in revised form: 30 January 2023 Accepted: 19 February 2023 Published online: 30 June 2023 Printed: 30 June 2023 In the present investigation, the corrosion inhibition potency of five pyridine derivatives was computationally simulated and investigated by utilizing the Density Functional Theory (DFT) technique using a basis set of B3LYP/6-31++G (d,p). The predicted corrosion inhibition capacity was shown to improve in the order of 6-(trifluoromethyl) nicotinic acid > 4-(trifluoromethyl) nicotinic acid > N-methyl-4-chloropyridine-2-carboxamide > 2-chloro- 6-trifluoromethylnicotinic acid > methyl 2-aminopyridine-4-carboxylate. Anticorrosion potentials were predicted using quantum chemical variables such as energy gap (∆E) i.e. HOMO-LUMO, ionization potential (I), electron affinity (A), proportion of electrons transmitted (∆N), hardness (η), softness (σ) and electronegativity (χ) of chemical species. It was often observed that the corrosion inhibiting rate improved with enhancement of EHOMO, σ, and reduced ELUMO, ∆E and η. Additionally, the electrostatic potential (ESP) mapping revealed that the heteroatoms, including the oxygen and nitrogen atoms, were the regions of anticipated electrophilic attack. This meant that atoms of oxygen and nitrogen could form bonds between the metallic substrate atoms and the investigated inhibitors. With the findings obtained, 4-methyl-2-aminopyridine-4-carboxylate showed the highest EHOMO (- 0.23167 eV), softness (12.40694 eV-1) and the lowest ELUMO (-0.7047 eV), energy gap (0.1612 eV) and hardness (0.15107 eV), therefore revealed the excellent corrosion inhibiting attribution for several crucial metals and alloys, including aluminum, mild steel, stainless steel, zinc, brass, copper, etc. Metals Corrosion Inhibition DFT approach Pyridine derivatives Computational analysis Cite this: Eur. J. Chem. 2023, 14(2), 246-253 Journal website: www.eurjchem.com 1. Introduction The term 'corrosion' refers to the deterioration of metals and alloys caused by chemical/electrochemical contact with their surroundings [1-3]. The composition of the metal and the characteristics of the corroding surroundings are two major elements that affect the degree of metal corrosion. The integrity of the metal, the nature of the surface film, the physical state of the metal, and the position of the metal in the galvanic series are all included in the essence of the metal. Metals in the active site of the galvanic series corrode more rapidly than those of the noble region [4-9]. The essence of the corroding surroundings has been determined correspondingly by moisture (elevated frequency of corrosion), temperature (which is directly related to the corrosion rate), pH value, and the essence of the electrolyte (the existence of salts in the electrolyte accelerates the corrosion rate). Additionally, some industrial processes, such as acidic cleaning of boilers, acid pickling, descaling, etc., accelerate metallic corrosion [10-12]. The devasting conse- quences are immense and involve: risks to individuals owing to architectural collapse (e.g., flyovers, automobiles, aeroplanes, etc.); valuation amortization of metals owing to degradation of appearance; perforation of pipelines and vessels enabling evacuation of their inclusion and potential environmental pollution; structural stress, etc.; or obstruction of pipelines by sturdy corrosive materials. Numerous strategies have been used to reduce or prevent corrosion to some extent [13,14]. Among the various ways to prevent metals against corrosion is by employing inhibitors, and currently, numerous researchers are focusing their studies on the use of corrosion inhibitors, as they are widely accessible, have minimal price, are less toxic, and offer significant corrosion inhibition efficacy. In an effort to slow down the deterioration of precious metals, such molecules are segregated from the system and introduced to the abrasive environment. In particular, organic molecules with hetero- atoms like nitrogen, sulphur, and oxygen in their compositions, in addition to aromatic rings, operate as effective corrosion inhibitors. The use of such molecules over the metallic-media interface allows the inhibitors to engage with the metallic substrate by adsorption across the p orbitals, donating atoms, electron density, and electronic configuration of the inhibitor, thus preventing metal degradation by displacing water molecules away from the metallic substrate and forming a defensive layer over the metallic substrate by shielding the metal against further corrosive ion attacks [4,5,7,9,15-23]. Physical (electrostatic) and chemical (chemisorption) adsorption could be used to assess this adsorption. Intense electronic bonds are formed by a chemical interaction between ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.14.2.246-253.2408 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.14.2.246-253.2408 mailto:drashishchemlpu@gmail.com http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.14.2.246-253.2408&domain=pdf&date_stamp=2023-06-30 Thakur and Kumar / European Journal of Chemistry 14 (2) (2023) 246-253 247 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.246-253.2408 the metallic substrate and the inhibitor molecules during the chemisorption process. On the contrary, electrostatic couplings are prominently generated by the van der Waals force [24-30]. The type and amount of metallic charge, the electrolytes, the electronic configuration of the inhibitory molecules, the temperature of the media, the subjection period, the type of substituents, etc. all affect the inhibitors’ ability to adsorb on the metallic surface [31-35]. Pyridine and its derivatives have demonstrated excellent inhibitory efficacy in numerous acidic and corrosive media, offering a crucial role in several disciplines, including the corrosion sciences. The six-member heteroaromatic molecule pyridine has the chemical formula C5H5N and is nitrogen-based. Compared to pyridine derivatives with no substitution or containing electron-withdrawing substituents, substituted pyridine derivatives having electron-donating substituents enable robust interaction with metal surfaces and function as excellent corrosion inhibitors. However, when contrasted with unsubstituted pyridine derivatives substituted at other sites, pyridine derivatives bearing either electron-withdrawing or donating substituents at the sixth or second locations exhibit comparatively significant inhibitory efficacy by developing a robust resilient chelating complex [36-39]. Many studies have recently focused on understanding the interaction involving inhibitor compounds and metallic substrates using quantum chemical methods [6,8,40-46]. To correlate the inhibitors’ molecular characteristics to their effectiveness as inhibitors, a number of quantum chemical techniques have been devised. The hypothesis of functionality of conceptual density such as DFT analysis, although, is arguably the most liked and optimistic theory in use today [37,39,47-51]. A computational modelling technique called density functional theory (DFT) is frequently utilised to explore the innate characteristics of molecules. For inhibitors, research is focused mainly on predicting chemical quality, including energy gap, HOMO- LUMO, chemical hardness and softness, ionization potential, electronegativity, and electron affinity of chemical species [52- 54]. Tang et al. [39] used the DFT strategy to examine the effects of different molar proportions of pyridine derivatives (4- methylpyridine i.e., 4-MP and 4-PQ) and sulfur including compounds (4-methylpyridine and its quaternary ammonium salts i.e. TU and TZ) for the ability of carbon steel to resist corrosion in a CO2-saturated 3.5 weight percent NaCl media. While sulphur-containing molecules having lower volumes fill in voids, pyridine derivative molecules having higher volumes bind first on the metallic substrate. Figure 1 shows the density profiles of FMOs of 4-MP and 4-PQ, as well as TU and TZ. The heterocyclic ring comprising the sulphur and nitrogen atoms is where the forefront orbit dispersion is primarily focused. The chemical potential is related to quantum characteristics such as electronegativity (χ), in which a higher value indicates a stronger inhibition effectiveness. While, the greater polari- zability and improved inhibitory efficacy are implied by the lower chemical hardness (η). The ∆E is the most important variable, and a drop in ∆E results in an elevation in the action of reactivity. Softness is the inverse of η; therefore, a higher value is associated with increased effectiveness. The lowest E for the four inhibitors was for TU and the highest E for the mixture of TU and 4-PQ was for 4-PQ. It matches the results of the investigation itself. While sulphur-containing compounds and 4-PQ were combined in the right mole proportion, a thick adsorption layer was created. Similarly, Saddy et al. [38] evaluated the inhibition effect of 6-bromo-2-(4-chlorophenyl)-3-pyridine derivatives of imida- zole[4, 5-b](prop-2-yn-1-yl)6-bromo-2-(3H)-imidazol[4, 5-b] pyridine (SB9a) and (4-chlorophenyl)-3-decyl-3H-imidazo [4,5-b]pyridine (SB14a) for mild steel (MS) corrosion in 1 M HCl. The DFT approach at the B3LYP level using the 6-31G(d,p) basis set was utilized to optimize molecular configurations and find specific geometric variables. The dihedral angles and bond lengths confirmed the optimum structural layouts of the two examined variants. Because of their considerable polarization, bromine and chlorine molecules are likely to adhere to the MS interface more effectively. As the examined inhibitors were able to achieve a rate of 8% for SB9a and 90% for SB14a 0.1 mM, they demonstrated a significant level of inhibitory efficacy. In this article, we provide the results of an investigation of various pyridine derivatives as corrosion inhibitors utilising the DFT technique basis set of DFT/B3LYP/6-31++G (d,p). Pyridine derivatives including 2-chloro-6-trifluoromethyl nicotinic acid, 4-(trifluoromethyl) nicotinic acid, 6-(trifluoro methyl) nicotinic acid, methyl 2-aminopyridine-4-carboxylate and N-methyl-4-chloropyridine-2-carboxamide, meet all the criteria for the effectiveness of a significant corrosion inhibitor according to the literature [36-39,55-58]. 2. Calculation methodology The behavior of corrosion inhibitors in various abrasive solutions and on the metallic substrate is gradually being explained by computational software, which is emerging as a widely used and trustworthy technique [59,60]. A computa- tional modelling technique called density functional theory (DFT) is frequently used to explore the innate characteristics of molecules. For inhibitors, research is primarily focused on predicting chemical characteristics of chemical species, including the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO), electron affinity (A), ionization potential (I), energy gap (∆E), hardness (η), the fraction of electrons transferred (∆N), softness (σ) and electronegativity (χ) of chemical species. The effectiveness of the five specified pyridine derivatives was predicted using theoretical analyses in the following work: Initially, the structural characteristics of the pyridine derivatives including 2-chloro-6-trifluoromethylnicotinic acid, 4-(trifluoromethyl) nicotinic acid, 6-(trifluoromethyl) nicotinic acid, methyl 2-aminopyridine-4-carboxylate and N-methyl-4- chloropyridine-2-carboxamide were investigated (Table 1). All compounds were geometrically optimized using the DFT / B3LYP approach linked to 6-31G++(d,p) basis sets, which is frequently used in the analysis of organic corrosion inhibitors (CI) using the Gaussian 03W programming suite. Then, numerous pertinent global and local variables of the electronic configuration of the molecule were calculated. In addition to the lowest unoccupied molecular orbital (ELUMO) and the highest occupied molecular orbital (EHOMO), as well as the ionization potential (I, Equation (1)), electron affinity (A, Equation (2)), energy gap (∆E, Equation (3)), the fraction of electrons transferred (∆N, Equation (4)), hardness (η, Equation (5)), softness (σ, Equation (6)) and electronegativity (χ, Equation (7)) are included. Furthermore, the FMOs of each pyridine derivative’s FMOs (HOMO and LUMO) repartitions and 2D electrostatic potential maps were calculated. The Equation (1) relates an inhibiting molecule’s ionization potential (I), which is correlated with the EHOMO, to its capability to donate electrons into the minimally positioned vacant orbitals of a metal: 𝐼𝐼 = −𝐸𝐸𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻 (1) Additionally, as stated in Equation (2), an inhibitor’s electron affinity (A), which relates to the ELUMO and denotes the propensity of the inhibitor to receive electrons: 𝐴𝐴 = −𝐸𝐸𝐿𝐿𝐿𝐿𝐻𝐻𝐻𝐻 (2) The predicted corrosion inhibition ability improves when the ΔE of inhibitors narrows due to a commensurate rise in their reactivity. The term relates this band gap to I and A, as shown in Equation (3): 248 Thakur and Kumar / European Journal of Chemistry 14 (2) (2023) 246-253 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.246-253.2408 HOMO LUMO 4-Methylpyridine (4-MP) 4-Quaternary ammonium salts (4-PQ) 4-Thiourea (TU) 4-Mercaptoethanol (TZ) Figure 1. Illustration of the FMOs, i.e., HOMO and LUMO of pyridine derivatives and sulphur-containing compounds. Adapted with permission from [39]. Δ𝐸𝐸 = 𝐼𝐼 − 𝐴𝐴 (3) The global hardness (η) is another variable connected to I and A, as indicated in Equation (5). This metric, which measures the resistance of a system to releasing electrons, is used to forecast the reactivity of a molecule. According to Equation (4), ∆N (amount of electrons transit) is the second derivative of ∆E with regard to ∆N: 2( ) Fe inh Fe inh N φ χ η η − ∆ = + (4) η 2 − =     I A (5) Global softness (σ) is an additional indicator of chemical reactivity and the inverse of global softness in half, as noticed in Equation (6): 1/ ησ = (6) The variable utilized to compute ΔN is electronegativity (χ), which describes the orientation of electron transport across an inhibitor and metal until a similar chemical potential is reached between the two (number of transferred electrons). According to the expression, the EHOMO and ELUMO of a molecule are connected to I and A as stated in Equation (7): 2 I Aχ + =     (7) 3. Results and discussion Using the Gaussian 09 tool, the quantum chemistry compu- tations were carried out. The computations are predicated on the DFT methodology, another technique for describing the basic state of molecular systems. Its effectiveness could be attributed to the fact that it applies to a wide range of systems (organic molecules, materials, complexes, etc.) and that its computing period is considerably shorter than that of post- Hartree-Fock approaches. It is commonly employed to charac- terize interactions amongst metal inhibitors. DFT analyses for molecules have been performed and optimized utilizing the hybrid functional B3LYP. Numerous observations have been provided in this subsection, including electrostatic potential maps (ESP), total density, surface contours, and HOMO and LUMO findings. The configuration of the HOMO and LUMO orbitals is considered crucial to determining a molecule’s reactivity and the evolution of chemical reactions. It is feasible to observe the electron dispersion and, consequently, locate the centers or regions of electron density in each molecule by employing ESP mapping. The contour mappings of electron density show that heteroatoms on the investigated molecular inhibitors, including oxygen and nitrogen atoms, present favorable interaction locations when considering the distinction between the roles of the heteroatoms and the other atom. Bonding contacts across inhibitor substrates and metallic surfaces are formed by interaction regions enclosed by a dark red border. As per the contour depiction of electrostatic by using the DFT/B3LYP/6- 31++G(d,p) basis set, the dark red color is specifically surrounded by electronegative molecules and their areas in pyridine derivative molecules, while the green color is dispersed in the positive potential area. In contrast to the ∆N, which is regarded as the most important variable because it incorporates multiple earlier variables, the electronegativity (χ) and global hardness (η) parameters are crucial to thoroughly describing the reactivity of an inhibitor. A high level of electrophilicity denotes a strong electrophile, whereas a low number denotes a strong nucleophile that features positive charges, the former of which often corresponds to the charges on a metal substrate. FMOs such as EHOMO and ELUMO are crucial indicators for predicting reactive chemical entities. Thakur and Kumar / European Journal of Chemistry 14 (2) (2023) 246-253 249 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.246-253.2408 Table 1. Name, formulas, and molecular configuration of the investigated pyridine derivatives. Name Formula Molecular configuration 3D Molecular configuration 2-Chloro-6-trifluoromethylnicotinic acid C7H3CIF3NO2 N O OH F F F Cl 4-(Trifluoromethyl)nicotinic acid C7H4F3NO2 N O OH F F F 6-(Trifluoromethyl)nicotinic acid C7H4F3NO2 N O OH F F F Methyl 2-aminopyridine-4-carboxylate C6H7N3O2 N O O H2N N-Methyl-4-chloropyridine-2-carboxamide C7H7CIN2O N O N H Cl Typically, EHOMO refers to a molecule’s capacity to offer an electron. Therefore, if EHOMO increases, it means that there is a larger propensity to contribute electrons to the suitable acceptor that possesses an unoccupied orbital. The metallic substrate may absorb protective elements more easily due to the significant value of EHOMO. By accelerating the mechanism of transfer by the adsorbent sheet, the inhibitor’s preventive effectiveness was improved. Both the chemisorption and physisorption processes are confirmed by the acquired quantum chemical information, according to the EHOMO that has the negative value assessed and other thermodynamic proper- ties. Because the energy gap is correlated with the softness and/or hardness of the inhibitor molecules, a significant value for ∆E denotes poor reactivity of the inhibitor molecules. Although the soft molecule possesses an energy gap smaller than that of the rigid one, the soft molecule is less reactive. Figures 2-6 depict the optimized molecular geometries, frontier molecular orbitals (FMOs) (i.e., HOMO and LUMO), ESP maps, surface contours, and total electronic density of the pyridine derivatives. Through the investigation of Figures 2-6, it can be observed that HOMO and LUMO in the molecules of 2-chloro-6-trifluoro methylnicotinic acid, 6-(trifluoromethyl) nicotinic acid, 4- (trifluoromethyl) nicotinic acid, methyl 2-aminopyridine-4- carboxylate, and N-methyl-4-chloropyridine-2-carboxamide are located approximately throughout the molecular fractions. This finding suggests that all five molecules are involved in charge sharing. The presence of heteroatom moieties and an aromatic ring configuration in their molecular compositions, correspondingly, is related to their relatively large participation in charge. Following these considerations, it has been shown that the molecules 2-chloro-6-trifluoromethylnicotinic acid, 6- (trifluoromethyl) nicotinic acid, methyl 2-aminopyridine-4- carboxylate, 4-(trifluoromethyl) nicotinic acid and N-methyl-4- chloropyridine-2-carboxamide have exceptional anticorrosive capabilities that are responsible for corrosion mitigation. Electrostatic potential surface ESP maps could offer an instinctive approach to quantifying polarity that facilitates the evaluation of the corrosion process. The negative electrostatic potential portion (red tint) is susceptible to nucleophilic attack, whereas the positive potential portion (blue tint) is susceptible to electrophilic attacks. Red areas are typically found around the heteroatom (oxygen), which could establish a covalent bond with the Fe atom, as shown in Figures 2-6. Positive potential regions are found near hydrogen and carbon atoms, which are ideal targets for electrophilic attack. 2-Chloro-6-trifluoromethylnicotinic acid, 6-(trifluoro methyl) nicotinic acid, methyl 2-aminopyridine-4-carboxylate, 4-(trifluoromethyl) nicotinic acid and N-methyl-4-chloro pyridine-2-carboxamide offer a superior potential to gain electrons from the metallic surface because it has a higher negative potential. Similar findings were obtained from the ΔN and the frontier molecular orbitals (EHOMO and ELUMO) investigations (Table 2). The acquired quantum chemical characteristics of the listed molecules are reported in Table 2. Low ELUMO levels resemble the electron acceptance capacity of a molecule, while the maximum EHOMO level of a molecule demonstrates its electron transmission capacity. Another statistic is the energy gap (ΔE); the difference in energy between EHOMO and ELUMO, which is crucial to consider when examining and explaining the resilience indices of a corrosion inhibitor. The stronger and more reciprocal the interaction between the metallic substrate and the inhibitor, the lower ΔE value must be. In this scenario, among all, the value of ΔE of methyl 2- aminopyridine-4-carboxylate comes out to be the smallest, i.e., 0.1612 eV, which could be ascribed to the availability of the hetero atom and the aromatic ring in its structure as compared 250 Thakur and Kumar / European Journal of Chemistry 14 (2) (2023) 246-253 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.246-253.2408 Optimized structure HOMO LUMO ESP map Surface contour Total electronic density Figure 2. Optimized molecular geometries, FMOs (HOMO and LUMO), ESP maps, surface contours and total electronic density illustration of the 2-chloro-6- trifluoromethylnicotinic acid. Optimized structure HOMO LUMO ESP map Surface contour Total electronic density Figure 3. Optimized molecular geometries, FMOs (HOMO and LUMO), ESP maps, surface contours and total electronic density illustration of the 4- (trifluoromethyl)nicotinic acid. Optimized structure HOMO LUMO ESP map Surface contour Total electronic density Figure 4. Optimized molecular geometries, FMOs (HOMO and LUMO), ESP maps, surface contours and total electronic density illustration of the 6- (trifluoromethyl)nicotinic acid. Thakur and Kumar / European Journal of Chemistry 14 (2) (2023) 246-253 251 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.246-253.2408 Table 2. Data findings of quantum chemical variables using the DFT/B3LYP/6-31++G(d, p) basis set. Parameters 2-Chloro-6-trifluoro methylnicotinic acid 4-(Trifluoromethyl) nicotinic acid 6-(Trifluoromethyl) nicotinic acid Methyl 2-amino pyridine-4-carboxylate N-Methyl-4-chloropyridine -2-carboxamide EHOMO (eV) -0.29708 -0.29299 -0.29951 -0.23167 -0.26578 ELUMO (eV) -0.10600 -0.09613 -0.09990 -0.07047 -0.07285 ΔE (eV) 0.19108 0.19686 0.19961 0.16120 0.19293 I (eV) 0.29708 0.29299 0.29951 0.23167 0.26578 A (eV) 0.10600 0.09613 0.09990 0.07047 0.07285 ƞ (eV) 0.20154 0.19456 0.19970 0.15107 0.16932 χ (eV) 0.09554 0.09843 0.09981 0.08060 0.09647 σ (eV-1) 10.46680 10.15950 10.01953 12.40694 10.36645 ∆Nmax (eV) 0.23256 0.23994 0.24304 0.25823 0.23637 Optimized structure HOMO LUMO ESP map Surface contour Total electronic density Figure 5. Optimized molecular geometries, FMOs (HOMO and LUMO), ESP maps, surface contours and total electronic density illustration of the methyl 2-aminopyridine-4-carboxylate. Optimized structure HOMO LUMO ESP map Surface contour Total electronic density Figure 6. Optimized molecular geometries, FMOs (HOMO and LUMO), ESP maps, surface contours and total electronic density illustration of the N-methyl-4- chloropyridine-2-carboxamide. to 2-chloro-6-trifluoromethylnicotinic acid, 6-(trifluoromethyl) nicotinic acid, N-methyl-4-chloropyridine-2-carboxamide and 4-(tri fluoromethyl) nicotinic acid. Table 2 shows that all molecules have low ELUMO and significant EHOMO values. This indicates that each inhibitor molecule has a substantial capacity for attaching to metallic surfaces, which significantly reduces corrosion. It is also explained in several articles that the negative value of EHOMO represents physical adsorption. In the latest study, the EHOMO values of all compounds come out to be negative, therefore, depicting more chances of physical adsorption than chemical adsorption. The tendency of a molecule to transmit electrons to the vacant orbital is denoted by the character ΔN. The ΔN value is a sign of the persistence and chemical interaction of the inhibitor substances. In reality, a positive and higher value of N reveals the stronger inhibitory activity of a molecule. In this case, again the ΔN value of methyl 2-aminopyridine-4- carboxylate (0.258232 eV) came out to be the maximum after all remaining molecules 2-chloro-6-trifluoro methylnicotinic acid, 6-(trifluoromethyl)nicotinic acid, N-methyl-4-chloro- pyridine-2-carboxamide and 4-(trifluoromethyl) nicotinic acid have quite positive and similar ΔN values of 0.23256, 0.243039, 0.2363722 and 0.23994 eV which corresponds to their better chemical reactivity and stability. It is also well mentioned that η with a low value proposes a higher IE%. Through Table 2, it can be observed that methyl 2-aminopyridine-4-carboxylate has a low value of η, i.e., 0.15107 eV followed by 2-chloro-6- trifluoromethylnicotinic acid (0.20154 eV), 6-(trifluoromethyl) nicotinic acid (0.19970 eV), N-methyl-4-chloropyridine-2- carboxamide (0.169315 eV) and 4-(trifluoromethyl) nicotinic acid (0.19456 eV), again corresponds to the better inhibitor efficiency of the derivatives. Unlike the value of ΔN, the value of η is also in great agreement with the empirical findings. This shows that all investigated pyridine derivatives are the least susceptible to charge donation and acceptance. As a result, they 252 Thakur and Kumar / European Journal of Chemistry 14 (2) (2023) 246-253 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.246-253.2408 show that the listed pyridine derivatives can possess a strong corrosion inhibitory effect on metal surfaces. 4. Conclusion In summary, a DFT calculation was performed with the DFT/B3LYP/6-31++G (d,p) basis set to analyse and measure the corrosion inhibition potential of five pyridine derivatives including 2-chloro-6-trifluoromethylnicotinic acid, 6-(trifluoro methyl) nicotinic acid, 4-(trifluoromethyl) nicotinic acid, methyl 2-aminopyridine-4-carboxylate and N-methyl-4-chloro pyridine-2-carboxamide for their possible potent corrosion inhibition potential for several metals and alloys. From the findings of the DFT analysis, it was observed that methyl-2- aminopyridine-4-carboxylate has a minimal electronegativity value compared to 2-chloro-6-trifluoromethylnicotinic acid, 4- (trifluoromethyl) nicotinic acid, 6-(trifluoromethyl) nicotinic acid and N-methyl-4-chloropyridine-2-carboxamide. Additi- onally, the value of ΔE of methyl 2-aminopyridine-4- carboxylate comes out to be the smallest, that is, 0.1612 eV, which could be ascribed to the availability of the heteroatom and aromatic ring in its structure compared to other molecules, which showed its stronger and mutual connection across the metallic surface and the inhibitor. Moreover, the ΔN value of methyl 2-aminopyridine-4-carboxylate (0.258232 eV) came out to be the maximum after all remaining molecules 2-chloro-6- trifluoromethylnicotinic acid, 6-(trifluoromethyl) nicotinic acid, 4-(trifluoromethyl) nicotinic acid and N-methyl-4-chloro pyridine-2-carboxamide have quite positive and similar ΔN values of 0.23256, 0.243039, 0.23994 and 0.2363722 eV, which corresponds to their better chemical reactivity and stability. Therefore, methyl 2-aminopyridine-4-carboxylate is more prone to react as an electron donor compared to other compounds, making it an effective corrosion inhibitor for a range of vital metals and alloys such as mild steel, aluminium, stainless steel, zinc, brass, copper, etc. Acknowledgements The authors thank Lovely Professional University for providing the necessary facilities to carry out this research. Disclosure statement Conflict of interest: The authors declare that they have no conflict of interest. Ethical approval All ethical guidelines have been adhered to. CRediT authorship contribution statement Conceptualization, Me: Abhinay Thakur; Methodology: Abhinay Thakur; Software: Abhinay Thakur; Validation: Ashish Kumar and Abhinay Thakur; Formal Analysis: Abhinay Thakur; Investigation: Ashish Kumar; Data Curation: Ashish Kumar; Writing - Original Draft: Abhinay Thakur and Ashish Kumar. ORCID and Email Abhinay Thakur thakurabhinay96@gmail.com https://orcid.org/0000-0002-7186-1639 Ashish Kumar drashishchemlpu@gmail.com https://orcid.org/0000-0002-2003-6209 References [1]. Bawazeer, T. M.; El-Ghamry, H. A.; Farghaly, T. A.; Fawzy, A. Novel 1,3,4-thiadiazolethiosemicarbazones derivatives and their divalent cobalt-complexes: Synthesis, characterization and their efficiencies for acidic corrosion inhibition of carbon steel. J. Inorg. Organomet. Polym. Mater. 2020, 30, 1609–1620. [2]. Li, P.; School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, China Corrosion inhibition effect of N-(4-diethylaminobenzyl) Quaternary ammonium chitosan for X80 pipeline steel in hydrochloric acid solution. Int. J. Electrochem. Sci. 2021, 150931. [3]. 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Thomas, A.; Prajila, M.; Shainy, K. M.; Joseph, A. A green approach to corrosion inhibition of mild steel in hydrochloric acid using fruit rind extract of Garcinia indica (Binda). J. Mol. Liq. 2020, 312, 113369. Copyright © 2023 by Authors. This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at http://www.eurjchem.com/index.php/eurjchem/pages/view/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution, or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Calculation methodology 3. Results and discussion 4. Conclusion Acknowledgements Disclosure statement CRediT authorship contribution statement ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: