Study of expired Fuclo 500 drug as an environmentally sustainable corrosion inhibitor European Journal of Chemistry 14 (3) (2023) 353-361 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.14.3.353-361.2443 European Journal of Chemistry View Journal Online View Article Online Study of expired Fuclo 500 drug as an environmentally sustainable corrosion inhibitor Aphouet Aurélie Koffi 1, N’guadi Blaise Allou 1,*, Mougo André Tigori 2, Teminfolo Yaya Soro 1, Albert Trokourey 1 and Paulin Marius Niamien 1 1 Laboratoire de Constitution et Réaction de la Matière, Unité de Formation et de Recherche des Sciences des Structures de la Matière et de Technologie, Université Félix Houphouët Boigny, Abidjan, Côte d’Ivoire 2 Laboratoire des Sciences et Technologies de l’Environnement, Unité de Formation et de Recherche Environnement, Université Jean Lorougnon Guédé, Daloa, Côte d’Ivoire * Corresponding author at: Laboratoire de Constitution et Réaction de la Matière, Unité de Formation et de Recherche des Sciences des Structures de la Matière et de Technologie, Université Félix Houphouët Boigny, Abidjan, Côte d’Ivoire. e-mail: alloub.neist15a@acsir.res.in (N.B. Allou). 10.5155/eurjchem.14.3.353-361.2443 Received: 25 April 2023 Received in revised form: 28 May 2023 Accepted: 04 June 2023 Published online: 30 September 2023 Printed: 30 September 2023 This work deals with aluminium corrosion inhibition by expired drugs containing flucloxacillin in 1 M hydrochloric acid medium, using the gravimetric method and density functional theory. Weight loss results showed that the inhibitory efficiency of this compound increases with concentration and decreases with increasing temperature. The study also indicates that this molecule is adsorbed according to the modified Langmuir model (Villamil model). Furthermore, the thermodynamic parameters of adsorption (∆Goads, ∆Hoads, ∆Soads) and activation (Ea*, ΔHa*, ΔSa*) show that the adsorption is mixed type (chemisorption and physisorption). In addition, density functional theory provides access to the quantum chemical parameters of the molecule such as the lowest vacant orbital energy (ELUMO), the highest occupied orbital energy (EHOMO), the absolute electronegativity (χ), the global hardness (η), the global softness (S), the fraction of transferred electrons (ΔN) as well as the electrophilicity index (ω) for finding correlation between the inhibitor structure and the experimental data. DFT Aluminium Flucloxacillin Hydrochloric acid Weight loss method Corrosion inhibition Cite this: Eur. J. Chem. 2023, 14(3), 353-361 Journal website: www.eurjchem.com 1. Introduction Metallic materials and more particularly aluminium are corrosion sites in an acid environment. The use of corrosion inhibitors is the most suitable and economical method to cope with this phenomenon that generates several problems [1-3]. However, fighting against corrosion without taking into account environmental pollution is another more serious one. In fact, the directives on industrial waste are becoming increasingly stringent. Therefore, environmental protection has become an essential issue for every nation in the last decade. Developing biodegradable and eco-compatible corrosion inhibitors is now a major challenge [4-6]. Current studies are directed towards the development of organic compounds that are non-toxic and stable at high tempe- ratures [4], leading several researchers to take an interest in pharmaceutical products. Therefore, several classes of mole- cules, including antibiotics [7,8], antifungals [9,10], analgesics [11], and vitamins [12,13], were used as corrosion inhibitors for metals in an acidic environment. In this light, the flucloxacillin molecule has already shown inhibiting properties with respect to the corrosion of mild steel in sulfuric acid medium, but the inhibition mechanism was not clearly elucidated [14]. These organic inhibitors act by adsorption on the surface of the metal to be protected [15,16]. This action mechanism can be described using the thermodynamic adsorption and activation parameters of the inhibiting species. Quantum chemical calculations are very useful for investigating descriptor para- meters and for better understanding the inhibition mechanism of molecules [17,18]. In this sense, this research project aims to investigate the inhibitory properties of expired Fuclo 500 tablets containing a flucloxacillin molecule in 1 M hydrochloric acid medium using the weight loss technique and DFT calculations. The study drug is six months out of date. In fact, expired drugs should be destroyed after their expiration date, and reuse as corrosion inhibitors for metals could have great economic value. Therefore, a large amount of money used for metal and alloy protection can be saved. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.14.3.353-361.2443 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.14.3.353-361.2443 mailto:alloub.neist15a@acsir.res.in http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.14.3.353-361.2443&domain=pdf&date_stamp=2023-09-30 354 Koffi et al. / European Journal of Chemistry 14 (3) (2023) 353-361 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.3.353-361.2443 F Cl N O O NH N O S O OH H (a) (b) Figure 1. (a) Chemical structure and (b) optimised flucloxacillin structure by DFT/B3LYP/6-31G(d). 2. Experimental 2.1. Aluminium samples An aluminium rod of 3 mm in diameter and 99.6% in purity is cut into 1 cm high. These samples are pre-treated to remove any impurity. This pre-treatment consisted of polishing them with abrasive paper, washing with acetone solution then with distilled water; finally, drying them in an oven at 343 K for 10 minutes. 2.2. Inhibitor The molecule studied is flucloxacillin (Figure 1) with chemical formula C19H17FClN3O5S and molar mass Mw = 453.87 g/mol contained in expired Fuclo 500 tablets. 2.3. Electrolyte medium The aluminium samples were immersed in a 1 M hydro- chloric acid solution without or with flucloxacillin. Inhibitor concentrations vary between 5×10-5 and 5×10-4 M. 2.4. Experimental method: Gravimetry The corrosion rate and inhibition efficiency of the inhibitor tested were analysed at various temperatures (303-323 K) by determining the mass loss that the metal underwent after 1 hour of immersion in the electrolyte medium. The corrosion rate 𝑊𝑊 (g. cm−2. h−1) is evaluated by the Equation (1): 𝑊𝑊 = ∆𝑚𝑚 𝑆𝑆.𝑡𝑡 (1) where 𝛥𝛥𝛥𝛥 = 𝛥𝛥1 −𝛥𝛥2 is the mass loss (g); 𝑆𝑆 is the total area of the specimen (cm2) and 𝑡𝑡 is the immersion time (h). The inhibition efficiency 𝐸𝐸(%) is calculated according to the expression below: 𝐸𝐸(%) = 𝑊𝑊𝑜𝑜−𝑊𝑊 𝑊𝑊𝑜𝑜 × 100 (2) where, 𝑊𝑊𝑜𝑜 and 𝑊𝑊 are the corrosion rates without and with inhibitor, respectively. The corrosion rate value is the average of three tests performed under the same conditions. The gravimetry results are comparable to those of other methods (electrochemical, thermometric, spectroscopic methods, etc.) used for the study of corrosion [19]. 2.5. Theoretical analysis by density functional theory calculation Quantum chemistry calculations were carried out to investigate the electronic properties of the molecule. In this study, the flucloxacillin molecule was drawn and preoptimized using GaussView 5. Calculations were performed using the Gaussian 09W software package [20] at DFT/B3LYP method [21,22] with 6-31G(d) basis set [23]. Global reactivity descriptors such as chemical potential (μ), hardness (η), softness (S), electronegativity (χ), and electrophilicity index (ω) were evaluated from the energy values of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). 3. Results and discussion 3.1. Aluminium corrosion rate and inhibitory efficiency of flucloxacillin The corrosion rate of aluminium in 1 M hydrochloric acid medium was evaluated within a temperature range of 303 to 323 K. The results obtained are shown in Figure 2. It was observed that the metal dissolution rate in the corrosive medium is 0.0163 g.cm-2h-1 at room temperature and increases up to 0.0755 g.cm-2h-1 at T = 323 K. However, the addition of flucloxacillin to the acid medium reduces the corrosion rate. This decrease indicates that the corrosion inhibiting effect of the study molecule is improved by increasing the inhibitor concentration. Therefore, the inhibition performance of flucloxacillin was plotted against the concentration of inhibitory species and the medium temperature (Figure 3). Koffi et al. / European Journal of Chemistry 14 (3) (2023) 353-361 355 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.3.353-361.2443 Figure 2. Evolution of the aluminium corrosion rate in 1 M HCl solution with flucloxacillin concentration at various temperatures. Figure 3. Plot of the evolution of inhibitory efficacy versus flucloxacillin concentration and temperature. The figure shows that the inhibitory efficiency increases with the concentration of the inhibitor but decreases when the temperature increases. In fact, increasing temperature pro- motes the desorption of some inhibitory species from the metal surface, as well as the dissolution of the inhibiting barrier due to thermal agitation [24]. Therefore, the inhibition rate moved from 87.12 to 66.75% at room temperature and 323 K, respectively, with 5×10-4 M inhibitory species. However, this result is quite high compared to those found in the literature [25-27]. 3.2. Adsorption isotherms Adsorption isotherms are essential to understand the mechanism of the corrosion inhibition reaction [28]. Thus, to learn more about the adsorption process of flucloxacillin, the experimental data were correlated with some mathematical models, such as Langmuir and Dubinin-Radushkevich iso- therms. The Langmuir adsorption isotherm describes the variation of 𝐶𝐶𝑖𝑖𝑖𝑖ℎ⁄𝜃𝜃 with 𝐶𝐶𝑖𝑖𝑖𝑖ℎ. The experimental data gave straight lines (Figure 4a) with the best fit (Table 1) of this model. Therefore, the Langmuir adsorption model explains the adsorption of flucloxacillin on the aluminium surface. However, the slopes of the obtained lines are higher than unity. This deviation from the ideal could be attributed to interactions between adsorbed species and the binding of an inhibitor to multiple adsorption sites [29]. To take the deviation into account, the corrected Langmuir model (Villamil model) with the following equation was considered: 𝐶𝐶𝑖𝑖𝑖𝑖ℎ 𝜃𝜃 = 𝑛𝑛 𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎 + 𝑖𝑖𝐶𝐶𝑖𝑖𝑛𝑛ℎ (3) The slope (𝑖𝑖) and the intercept ( 𝑛𝑛 𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎 ) were used to calculate the adsorption equilibrium constant 𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎. In turn, 𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎 values were used to determine the thermodynamic parameters. In order to clarify the type of adsorption (chemisorption or physisorption) involved, the Dubinin-Radushkevich isotherm was also used in this study [27,30]. This model is described by Equation (4). ln 𝜃𝜃 = 𝑙𝑙𝑖𝑖𝜃𝜃𝑚𝑚𝑎𝑎𝑚𝑚 − 𝑎𝑎𝛿𝛿2 (4) In this expression, δ corresponds to the Polanyi potential and is defined as follows: 𝛿𝛿 = 𝑅𝑅𝑅𝑅 𝑙𝑙𝑖𝑖 (1 + 1 𝐶𝐶𝑖𝑖𝑖𝑖ℎ ) (5) In addition, the constant 𝑎𝑎 was used to calculate the average adsorption energy 𝐸𝐸𝑚𝑚 (Equation (6)), corresponding to the energy required to move one mole of the adsorbate from infinity (solution) to the metal surface. 𝐸𝐸𝑚𝑚 = 1 √2 𝑎𝑎 (6) The plots of 𝑙𝑙𝑖𝑖 𝜃𝜃 versus 𝛿𝛿2 are shown in Figure 4b. The maximum surface coverage θmax, the parameter 𝑎𝑎 as well as the calculated values of Em are recorded in Table 1. 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.0 1.0 2.0 3.0 4.0 5.0 W (g .c m -2 .h -1 ) Cinh (×10-4 mol/L) 303 K 308 K 313 K 318 K 323 K 20 30 40 50 60 70 80 90 100 0.00 1.00 2.00 3.00 4.00 5.00 E (% ) Cinh (×10-4 mol/L) 303 K 308 K 313 K 318 K 323 K 356 Koffi et al. / European Journal of Chemistry 14 (3) (2023) 353-361 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.3.353-361.2443 Table 1. Adsorption isotherm parameters for aluminium in 1 M HCl medium. Temperature (K) Langmuir isotherm Dubinin-Radushkevich isotherm R2 Slope R2 𝒂𝒂 (kJ−2 mol2) θmax Em (kJ/mol) 303 0.9997 1.1407 0.8902 0.0009 1.144 23.57 308 0.9873 1.2595 0.3793 0.0015 1.334 18.26 313 0.9996 1.3865 0.9075 0.0022 1.354 15.08 318 0.9992 1.5182 0.9586 0.0021 1.514 15.43 323 0.9984 1. 3625 0.9332 0.0077 1.243 8.06 (a) (b) Figure 4. (a) Langmuir and (b) Dubinin-Radushkevich isotherms for the adsorption of flucloxacillin on aluminium in 1 M HCl medium at various temperatures. According to Tan et al. [31], Em values between 8 and 16 kJ/mol indicate that chemisorption is predominant, while values below 8 kJ/mol correspond to the physisorption of inhibiting species. As shown in Table 1, the average adsorption energy indicates that chemical bonds are formed between the inhibitor and the aluminium surface in the temperature range studied. 3.3. Thermodynamic parameters 3.3.1. Adsorption parameters Thermodynamic adsorption parameters further distinguish physisorption from chemisorption [32]. Thus, the Gibbs free energy of adsorption (∆𝐺𝐺𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 ) can be deduced from Equation (7): K𝑎𝑎𝑎𝑎𝑎𝑎 = 1 55.5 exp(− ∆Gads o 𝑅𝑅𝑅𝑅 ) (7) In which, 55.5 (in mol/L) corresponds to the concentration of water [33], R the perfect gas constant and T the absolute temperature. The standard adsorption enthalpy and entropy (∆𝐻𝐻𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 and ∆𝑆𝑆𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 ) can be obtained by using the Equation (8); ln𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎 = −∆𝐻𝐻𝑎𝑎𝑎𝑎𝑎𝑎 𝑜𝑜 𝑅𝑅𝑅𝑅 + ∆𝑆𝑆𝑎𝑎𝑎𝑎𝑎𝑎 𝑜𝑜 𝑅𝑅 − 𝑙𝑙𝑖𝑖𝐶𝐶𝐻𝐻2𝑂𝑂 (8) Figure 5 represents the plot of 𝑙𝑙𝑖𝑖 𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎 against 1000/ 𝑅𝑅 giving a straight line with slope −∆𝐻𝐻𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 𝑅𝑅⁄ and inter- cept −∆𝑆𝑆𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 𝑅𝑅⁄ − 𝑙𝑙𝑖𝑖 55.5. The values obtained are given in Table 2. The strong adsorption capacity of flucloxacillin on the aluminium surface in 1 M HCl is revealed through the high values of 𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎. Indeed, the flucloxacillin structure contains nitrogen, sulfur and oxygen heteroatoms and π electrons allowing for better protection against corrosion [34,35]. However, increasing the temperature from 303 to 313 K causes the value of 𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎 to decrease, leading to the weakness of the protective layer. Furthermore, an exception is observed at 308 K due to the results obtained for Cinh = 2×10-4 M (Figure 3). Indeed, the flucloxacillin efficiency is not as expected. Consequently, the R2 value is not close enough to unity, but it is acceptable. Besides, the negative values of ∆𝐺𝐺𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 highlight the spontaneous adsorption of inhibitory species on the aluminium surface. Moreover, it is reported that ∆𝐺𝐺𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 values for physi- sorption are higher than –20 kJ/mol while those of chemi- sorption are less than –40 kJ/mol [36]. In this study, the inhibitor shows mixed adsorption behaviour with a pre- dominance of chemical adsorption. 0 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 0.0007 0.0008 0.0009 0 1 2 3 4 5 C i nh /θ (m ol /L ) Cinh (×10-4 mol/L) 303 K 308 K 313 K 318 K 323 K -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 10 30 50 70 90 110 ln θ δ2 (kJ .mol-2) 303 K 308 K 313 K 318 K 323 K Koffi et al. / European Journal of Chemistry 14 (3) (2023) 353-361 357 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.3.353-361.2443 Table 2. Thermodynamic adsorption parameters derived from the Langmuir isotherm for aluminium in 1M HCl with flucloxacillin. T (K) 𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎 (L/mol) −∆𝑮𝑮𝒂𝒂𝒂𝒂𝒂𝒂𝒐𝒐 (kJ/mol) ∆𝑯𝑯𝒂𝒂𝒂𝒂𝒂𝒂 𝒐𝒐 (kJ/mol) ∆𝑺𝑺𝒂𝒂𝒂𝒂𝒂𝒂𝒐𝒐 (J/mol.K) 303 142588 40.00 −61.67 −73.39 308 41983 37.53 313 69325 39.44 318 50607 39.24 323 19464 37.29 Table 3. Thermodynamic parameters for aluminium dissolution in 1 M HCl without and with flucloxacillin. Cinh (×10-4 mol/L) 𝑬𝑬𝒂𝒂∗ (kJ/mol) ∆𝑯𝑯𝒂𝒂 ∗ (kJ/mol) ∆𝑺𝑺𝒂𝒂∗ (J/mol.K) 0 61.000 58.399 309.683 0.5 107.348 104.750 449.842 1 99.425 96.825 423.240 2 94.599 92.000 407.566 3 94.352 91.753 406.150 4 95.923 93.324 410.552 5 101.324 98.723 426.934 Figure 5. Plot of 𝑙𝑙𝑖𝑖 𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎 versus 1000/T for aluminium in 1 M HCl with flucloxacillin. Negative values of ∆𝑆𝑆𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 confirm the adsorption of flucloxacillin. It also reflects a decrease in disorder during the adsorption of the inhibitor, since a compound in the condensed state is more ordered than in aqueous solution. The enthalpy variation ∆𝐻𝐻𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 , accompanying this adsorption process is also negative, which indicates the exothermic nature of the phenomenon and is generally attributed to the presence of the two physisorption and chemisorption [35]. 3.3.2. Activation parameters To take into account the effect of temperature on the corrosion rate, the activation energy was determined using the Arrhenius equation (Equation (9)). 𝑊𝑊 = 𝐴𝐴 × 𝑒𝑒𝑒𝑒𝑒𝑒 � −𝐸𝐸𝑎𝑎∗ 2.303×𝑅𝑅×𝑅𝑅 � (9) The plot of 𝑙𝑙𝑙𝑙𝑙𝑙 𝑊𝑊 against 1000/T (Figure 6a) was used to determine the activation energy (Table 3). The data show that 𝐸𝐸𝑎𝑎∗ is higher in the presence of inhibitor. The increase of the concentration of flucloxacillin reveals that aluminium dissolution decreases as a result of the formation of an energy barrier by the adsorbed inhibitors on the substrate surface. The comparison of the values obtained also underlines the type of absorption [19,37,38]. According to the results, 𝐸𝐸𝑎𝑎∗ is higher in the presence of inhibitor, so physical adsorption is responsible for the inhibitory properties of flucloxacillin. However, a decrease in 𝐸𝐸𝑎𝑎∗ values can be observed as inhibitor amount increases. This decrease is attributed to a slight improvement with increasing flucloxacillin concent- ration. Thus, the corrosion rate does not decrease as much as expected by increasing 𝐶𝐶𝑖𝑖𝑛𝑛ℎ (Figure 2). This slow decrease is therefore reflected in the plot of 𝑙𝑙𝑙𝑙𝑙𝑙 𝑊𝑊 versus 1000/T because the points are almost the same at a given temperature. Enthalpy and entropy activation values for metal corrosion can be determined from the alternative formula of the Arrhenius equation given below: 𝑊𝑊 = 𝑅𝑅.𝑅𝑅 ℵ.ℎ 𝑒𝑒𝑒𝑒𝑒𝑒 �∆𝑆𝑆𝑎𝑎 ∗ 𝑅𝑅 � . 𝑒𝑒𝑒𝑒𝑒𝑒 �−∆𝐻𝐻𝑎𝑎∗ 𝑅𝑅.𝑅𝑅 � (10) The plot of 𝑙𝑙𝑙𝑙𝑙𝑙(𝑊𝑊 T ) versus 1000/T gives Figure 6b. Values of enthalpy ∆𝐻𝐻𝑎𝑎∗ and entropy ∆𝑆𝑆𝑎𝑎∗ of activation are given in Table 3. The activation enthalpy is positive, reflecting the endothermic nature of the aluminium dissolution process without and with the addition of inhibitor [32]. Moreover, magnitude of ∆𝐻𝐻𝑎𝑎∗ almost matches with 𝐸𝐸𝑎𝑎∗, confirming the endothermic process of dissolution. Besides, activation entropy values are more positive in the presence of flucloxacillin, showing better resistance of aluminium in the aggressive solution and a dissociative mechanism during which the activated complex is loosely bound and about to dissociate [39]. Similarly, ∆𝐻𝐻𝑎𝑎∗ and ∆𝑆𝑆𝑎𝑎∗ values decrease when flucloxacillin is more concentrated. This behaviour is due to overlapping points. 3.4. Analysis of the electronic properties of flucloxacillin by DFT 3.4.1. Global reactivity descriptors Theoretical quantum chemistry is a very useful tool for understanding the behaviour of species and particularly the corrosion inhibition mechanism. Therefore, several electronic parameters of flucloxacillin were studied using DFT. y = 7.4212x - 12.848 R² = 0.6809 8 9 10 11 12 13 3.09 3.14 3.19 3.24 3.29 Ln (K ad s) 1000/T (K-1) 358 Koffi et al. / European Journal of Chemistry 14 (3) (2023) 353-361 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.3.353-361.2443 Table 4. Quantum chemical parameters of neutral flucloxacillin by B3LYP/6-31G(d). 𝑬𝑬𝑯𝑯𝑯𝑯𝑯𝑯𝑯𝑯 (𝐞𝐞𝐞𝐞) 𝑬𝑬𝑳𝑳𝑳𝑳𝑯𝑯𝑯𝑯 (𝐞𝐞𝐞𝐞) 𝜟𝜟𝑬𝑬 (𝐞𝐞𝐞𝐞) 𝝁𝝁 (𝐃𝐃) 𝑬𝑬𝑻𝑻 (𝐇𝐇𝐇𝐇) 𝝌𝝌 (𝐞𝐞𝐞𝐞) 𝜼𝜼 (𝐞𝐞𝐞𝐞) 𝑺𝑺 (𝐞𝐞𝐞𝐞−𝟏𝟏) 𝝎𝝎 (𝐞𝐞𝐞𝐞) 𝜟𝜟𝜟𝜟 −6.688 −1.012 5.676 4.431 −2232.817 3.850 2.838 0.352 2.611 0.076 (a) (b) Figure 6. Plots of (a) log W and (b) log (W/T) versus 1000/T for aluminium immersed in 1 M HCl without and with flucloxacillin. On the one hand, the optimised structure as well as the electronic densities of the highest occupied (HOMO) and lowest vacant (LUMO) molecular orbitals (Figure 7) were obtained. On the other hand, DFT was used to determine the descriptor parameters of the studied molecule, namely, energy of frontier molecular orbitals, energy gap, electrophilicity index, etc. The values of these various parameters are reported in Table 4. Figure 7 shows that the HOMO density of the studied molecule is almost localised around the entire molecule, while the LUMO density is mainly distributed over the isoxazole ring. The ability for a chemical species to donate or receive electrons is associated with the frontier orbitals energies 𝐸𝐸HOMO and 𝐸𝐸𝐿𝐿UMO, respectively. Thus, compared to the literature [21- 23], 𝐸𝐸HOMO is high and 𝐸𝐸LUMO low. Accordingly, the inhibitory properties of flucloxacillin are due to its capacity to exchange electrons with the aluminium surface. Moreover, the chemical reactivity of an organic molecule is closely correlated with a low energy gap (ΔE) between LUMO and HOMO orbitals [4,24]. Therefore, the value of 5.676 eV corroborates interactions between the molecule and the substrate. DFT calculations also provide for the molecule electro- negativity χ, the electrophilicity index ω, the hardness η and the softness S parameters. The first parameter characterises the tendency of a chemical species to attract electrons toward itself. The second measures the propensity of a chemical species to accept electrons, while hardness and softness evaluate both stability and reactivity of a molecule [40,41]. In this study, the theoretical value of 3.850 eV is lower than 4.280 eV of the aluminium work function (𝜙𝜙𝐴𝐴𝐴𝐴 was rather used because 𝜒𝜒𝐴𝐴𝐴𝐴 is conceptually wrong here). Therefore, during interactions, electrons flow from flucloxacillin to the aluminium surface with a fraction of transferred electrons Δ𝑁𝑁 = 0.076 eV [35]. 3.4.2. Local selectivity The Fukui functions (𝑓𝑓𝑘𝑘+,𝑓𝑓𝑘𝑘−) and the dual des- criptor ∆𝑓𝑓𝑘𝑘 were calculated to analyse the selective reactivity of flucloxacillin molecule (Table 5). The first parameter can be obtained, for each atom of a species, from the following Equations: 𝑓𝑓+(𝑟𝑟) = 𝑞𝑞𝑘𝑘(𝑁𝑁 + 1) − 𝑞𝑞𝑘𝑘(𝑁𝑁) (11) 𝑓𝑓−(𝑟𝑟) = 𝑞𝑞𝑘𝑘(𝑁𝑁) − 𝑞𝑞𝑘𝑘(𝑁𝑁 + 1) (12) 𝑞𝑞𝑘𝑘(𝑁𝑁), 𝑞𝑞𝑘𝑘(𝑁𝑁 − 1), and 𝑞𝑞𝑘𝑘(𝑁𝑁 + 1) are Mulliken charge of 𝑘𝑘 atom in the neutral, anionic and cationic system, respectively. -3.0 -2.5 -2.0 -1.5 -1.0 3.090 3.115 3.140 3.165 3.190 3.215 3.240 3.265 3.290 lo g W 1000/K (K-1) Blank 0.00005 M 0.0001 M 0.0002 M 0.0003 M 0.0004 M 0.0005 M -5.5 -5.0 -4.5 -4.0 -3.5 3.090 3.115 3.140 3.165 3.190 3.215 3.240 3.265 3.290 lo g (W /T ) 1000/K (K-1) Blank 0.00005 M 0.0001 M 0.0002 M 0.0003 M 0.0004 M 0.0005 M Koffi et al. / European Journal of Chemistry 14 (3) (2023) 353-361 359 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.3.353-361.2443 Table 5. Pertinent Mulliken charges, Fukui functions and dual descriptor of flucloxacillin by B3LYP/6-31G(d). Atom no 𝒒𝒒𝒌𝒌(𝜟𝜟 + 𝟏𝟏) 𝒒𝒒𝒌𝒌(𝜟𝜟) 𝒒𝒒𝒌𝒌(𝜟𝜟− 𝟏𝟏) 𝒇𝒇𝒌𝒌+ 𝒇𝒇𝒌𝒌− ∆𝒇𝒇𝒌𝒌 C1 −0.211 −0.200 −0.173 −0.011 −0.027 0.016 C2 0.324 0.400 0.390 −0.076 0.010 −0.086 C3 −0.020 0.025 0.063 −0.045 −0.038 −0.007 C4 −0.139 −0.094 −0.103 −0.045 0.009 −0.054 C5 −0.143 −0.141 −0.115 −0.002 -0.026 0.024 C6 −0.179 −0.117 −0.110 −0.062 −0.007 −0.055 Cl10 −0.078 0.008 0.123 −0.086 −0.115 0.029 F11 −0.311 −0.280 −0.264 −0.031 −0.016 −0.015 C12 0.188 0.223 0.236 −0.035 −0.013 −0.022 C13 −0.071 −0.094 −0.101 0.023 0.007 0.016 C14 0.393 0.386 0.408 0.007 −0.022 0.029 N15 −0.295 −0.207 −0.188 −0.088 −0.019 −0.069 O16 −0.407 −0.363 −0.342 −0.044 −0.021 −0.023 C17 0.513 0.589 0.588 −0.076 0.001 −0.077 O18 −0.544 −0.513 −0.491 −0.031 −0.022 −0.009 N19 −0.583 −0.625 −0.601 0.042 −0.024 0.066 C21 0.581 0.574 0.594 0.007 −0.020 0.027 C22 −0.005 −0.071 −0.093 0.066 0.022 0.044 C24 −0.091 −0.095 −0.134 0.004 0.039 −0.035 O25 −0.492 −0.461 −0.394 −0.031 −0.067 0.036 N26 −0.454 −0.409 −0.398 −0.045 −0.011 −0.034 S27 0.093 0.075 0.312 0.018 −0.237 0.255 C28 −0.440 −0.451 −0.457 0.011 0.006 0.005 C32 −0.472 −0.458 −0.470 −0.014 0.012 −0.026 C36 0.576 0.602 0.617 −0.026 −0.015 −0.011 O37 −0.580 −0.557 −0.567 −0.023 0.010 −0.033 O39 −0.456 −0.458 −0.425 0.002 −0.033 0.035 C40 −0.528 −0.558 −0.567 0.030 0.009 0.021 C44 −0.074 −0.060 −0.093 −0.014 0.033 −0.047 C46 −0.134 −0.129 −0.132 −0.005 0.003 −0.008 (a) (b) Figure 7. (a) HOMO and (b) LUMO maps of flucloxacillin using B3LYP/6-31G(d). The dual descriptor ∆𝑓𝑓𝑘𝑘 can be defined as the difference between 𝑓𝑓+(𝑟𝑟) and 𝑓𝑓−(𝑟𝑟), respectively the nucleophilic and electrophilic Fukui functions [42]. ∆𝑓𝑓𝑘𝑘 = 𝑓𝑓𝑘𝑘+ − 𝑓𝑓𝑘𝑘− (13) This parameter is positive in the electrophilic zones and negative in the nucleophilic zone [33]. Therefore, the most positive value of ∆𝑓𝑓𝑘𝑘 indicate that the site may be favoured for attack by a nucleophile, whereas the site expected for electro- philic attack is indicated by the most negative value of ∆𝑓𝑓𝑘𝑘. Moreover, maximum values of 𝑓𝑓𝑘𝑘+ and 𝑓𝑓𝑘𝑘− are also important in determining the preferred sites for attack by nucleophile and electrophile, respectively. In the molecule studied, N19 and C22 exhibit the highest values of the nucleophilic attack index (𝑓𝑓𝑘𝑘+). However, the highly positive dual descriptor (∆𝑓𝑓𝑘𝑘) suggests that S27 may be a good electrophilic site. Otherwise, the nucleophilic attack site should belong to the HOMO of the molecule. Therefore, the probable zones for attack by a nucleophilic are N19 and S27. Analysis of these results also shows that the highly negative values of ∆𝑓𝑓𝑘𝑘 are localized on the atoms C2, C4, C6, C17 and N15 implying that these sites are electrons acceptors. The highest values of 𝑓𝑓𝑘𝑘− suggest, on the contrary, that C24 and C44 act as nucleophilic zones. However, the LUMO map of the fluclo- xacillin molecule supports that the preferred sites for electrophilic attack are C2, C17, and N15. 3.5. Corrosion and inhibition mechanism 3.5.1. Corrosion process mechanism The metal is naturally covered with a protective layer of aluminium oxide. However, this barrier film is damaged in acid medium and the metal dissolves according to the following equations: 360 Koffi et al. / European Journal of Chemistry 14 (3) (2023) 353-361 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.3.353-361.2443 𝐴𝐴𝑙𝑙 → 𝐴𝐴𝑙𝑙3+ + 3𝑒𝑒− (14) 3𝐻𝐻+ + 3𝑒𝑒 − → 3 2 𝐻𝐻2 (15) As a result, corrosion leads to complete dissolution of the metal or depletion of the 𝐻𝐻+ protons in the electrolyte. This mechanism is generally not affected by the addition of an organic inhibitor that acts by adsorption on the metal surface [43]. 3.5.2. Adsorbed species inhibition mechanism Adsorption depends mainly on the substrate surface charge and the inhibitor structure. Thus, molecular and protonated flucloxacillin can participate in the inhibition of aluminium corrosion. In acidic medium, the inhibitor molecule can be protonated due to its heteroatom according to the following equation. [𝐼𝐼𝑖𝑖ℎ] + 𝑒𝑒 𝐻𝐻+ → [𝐼𝐼𝑖𝑖ℎ𝐻𝐻𝑚𝑚]𝑚𝑚+ (16) Adsorption of the formed [𝐼𝐼𝑖𝑖ℎ𝐻𝐻𝑚𝑚]𝑚𝑚+ would occur on the metal surface previously charged by the 𝐶𝐶𝑙𝑙− ions. Indeed, the adsorption of chloride ions facilitates that of inhibiting cations [44]. In addition, these cations can be adsorbed in competition with 𝐻𝐻+ ions [13]. Interactions between protonated inhibitors and the aluminium surface could be electrostatic in nature but could be also due give rise to chemical bonds [44]. Inhibition of aluminium corrosion can also be performed through the adsorption of metal complexes formed by the combination of 𝐴𝐴𝑙𝑙3+ ions and flucloxacillin [45]. Besides these inhibitory cations, molecular flucloxacillin can replace previously adsorbed water molecules through the following relationship: 𝐼𝐼𝑖𝑖ℎ(𝑎𝑎𝑜𝑜𝐴𝐴) + 𝑖𝑖 𝐻𝐻2𝑂𝑂𝑎𝑎𝑎𝑎𝑎𝑎 → 𝐼𝐼𝑖𝑖ℎ𝑎𝑎𝑎𝑎𝑎𝑎 + 𝑖𝑖 𝐻𝐻2𝑂𝑂(𝑎𝑎𝑜𝑜𝐴𝐴) (17) However, the steric hindrance of the inhibitory species would not facilitate its adsorption and would constitute an obstacle to greater inhibitory efficacy. 4. Conclusion The study of the corrosion rate in the absence and presence of flucloxacillin at various concentrations and temperatures showed that the chosen molecule has inhibiting properties. Inhibition efficiency increases with flucloxacillin concentration but decreases with increasing temperature. The adsorption isotherms revealed that an inhibiting species adsorbs at several sites, and there are repulsions between adsorbed species, which characterises the Villamil (or modified Langmuir) model. Furthermore, thermodynamic adsorption parameters (∆𝐺𝐺ads o , ∆𝐻𝐻𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 ∆𝑆𝑆𝑎𝑎𝑎𝑎𝑎𝑎𝑜𝑜 ) indicate that the adsorption of the inhibitor is mixed (physisorption and chemisorption) and is facilitated by the presence of heteroatoms. The descriptors of global reactivity indicate a possible protonation of the flucloxacillin molecule. DFT results also showed that HOMO is distributed throughout the molecule while LUMO is mainly localised around the isoxazole ring. The positive value of ∆N confirms the preponderance of chemisorption in the adsorption process between flucloxacillin and aluminium. Electro- negativity χ also indicates that during interactions, electrons mainly flow from flucloxacillin to the aluminium surface. Thus, DFT corroborates the gravimetric findings because the inhibiting species can share electrons with other species in the medium. Disclosure statement Conflict of interest: The authors declare that they have no conflict of interest. Ethical approval: All ethical guidelines have been adhered to. Sample availability: Samples of the compounds are available from the author. CRediT authorship contribution statement Conceptualization: Aphouet Aurélie Koffi; Methodology: Aphouet Aurélie Koffi; Software: Aphouet Aurélie Koffi; Formal Investigation: Aphouet Aurélie Koffi, Teminfolo Yaya Soro; Writing - Original Draft: Teminfolo Yaya Soro, Aphouet Aurélie Koffi; Writing - Review and Editing: N’guadi Blaise Allou; Supervision: Albert Trokourey, Paulin Marius Niamien. ORCID and Email Aphouet Aurélie Koffi koffiaphouet@yahoo.fr https://orcid.org/0000-0003-2306-7593 N’guadi Blaise Allou allounguadi@yahoo.fr alloub.neist15a@acsir.res.in https://orcid.org/0000-0002-4367-2128 Mougo André Tigori tigori20@yahoo.fr https://orcid.org/0000-0002-3722-7896 Teminfolo Yaya Soro teminfolosoro@gmail.com https://orcid.org/0009-0001-1494-7452 Albert Trokourey trokourey@gmail.com https://orcid.org/0000-0001-7139-5976 Paulin Marius Niamien niamienfr@yahoo.fr https://orcid.org/0000-0002-0744-9623 References [1]. Functional materials: Preparation, processing and applications; Banerjee, S.; Tyagi, A. K., Eds.; Elsevier Science Publishing: Philadelphia, PA, 2011. [2]. Kutz, M. Handbook of environmental degradation of materials; 2nd ed.; William Andrew Publishing: Norwich, CT, 2012. [3]. Plieth, W. Electrochemistry for Materials Science; Elsevier Science: London, England, 2007. [4]. Herrag, L.; Hammouti, B.; Elkadiri, S.; Aouniti, A.; Jama, C.; Vezin, H.; Bentiss, F. Adsorption properties and inhibition of mild steel corrosion in hydrochloric solution by some newly synthesized diamine derivatives: Experimental and theoretical investigations. Corros. Sci. 2010, 52, 3042–3051. [5]. Chevalier, M.; Robert, F.; Amusant, N.; Traisnel, M.; Roos, C.; Lebrini, M. Enhanced corrosion resistance of mild steel in 1M hydrochloric acid solution by alkaloids extract from Aniba rosaeodora plant: Electrochemical, phytochemical and XPS studies. Electrochim. Acta 2014, 131, 96–105. [6]. Gece, G. Drugs: A review of promising novel corrosion inhibitors. Corros. Sci. 2011, 53, 3873–3898. [7]. Eddy, N. O.; Odoemelam, S. A. Inhibition of the corrosion of mild steel in acidic medium by penicillin V potassium. Advances in Natural and Applied Sciences 2008, 2, 225-232 http://www.aensiweb.com/old/anas/2008/225-232.pdf. [8]. Eddy, N. O.; Odoemelam, S. A.; Ekwumemgbo, P. Inhibition of the corrosion of mild steel in HSO by penicillin G. Sci. Res. Essays 2009, 4, 33-38 https://academicjournals.org/article/article1380720172_Eddy%20 et%20al%20Pdf.pdf. [9]. Obot, I. B. Synergistic effect of nizoral and iodide ions on the corrosion inhibition of mild steel in sulphuric acid solution. Port. Electrochim. Acta 2009, 27, 539–553. [10]. Obot, I. B.; Obi-Egbedi, N. O. Inhibition of aluminium corrosion in hydrochloric acid using nizoral and the effect of iodide ion addition. E- J. Chem. 2010, 7, 837–843. [11]. Prabhu, R. A.; Shanbhag, A. V.; Venkatesha, T. V. Influence of tramadol [2-[(dimethylamino)methyl]-1-(3-methoxyphenyl) cyclohexanol hydrate] on corrosion inhibition of mild steel in acidic media. J. Appl. Electrochem. 2007, 37, 491–497. mailto:koffiaphouet@yahoo.fr https://orcid.org/0000-0003-2306-7593 mailto:allounguadi@yahoo.fr mailto:alloub.neist15a@acsir.res.in https://orcid.org/0000-0002-4367-2128 mailto:tigori20@yahoo.fr https://orcid.org/0000-0002-3722-7896 mailto:teminfolosoro@gmail.com https://orcid.org/0009-0001-1494-7452 mailto:trokourey@gmail.com https://orcid.org/0000-0001-7139-5976 mailto:niamienfr@yahoo.fr https://orcid.org/0000-0002-0744-9623 http://www.aensiweb.com/old/anas/2008/225-232.pdf https://academicjournals.org/article/article1380720172_Eddy%20et%20al%20Pdf.pdf https://academicjournals.org/article/article1380720172_Eddy%20et%20al%20Pdf.pdf Koffi et al. / European Journal of Chemistry 14 (3) (2023) 353-361 361 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.3.353-361.2443 [12]. Kesari, P.; Udayabhanu, G. Investigation of Vitamin B12 as a corrosion inhibitor for mild steel in HCl solution through gravimetric and electrochemical studies. Ain Shams Eng. J. 2023, 14, 101920. [13]. Solmaz, R. Investigation of corrosion inhibition mechanism and stability of Vitamin B1 on mild steel in 0.5M HCl solution. Corros. Sci. 2014, 81, 75–84. [14]. Alfakeer, M.; Chemistry Department, Faculty of Science, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia Corrosion inhibition effect of expired ampicillin and flucloxacillin drugs for mild steel in aqueous acidic medium. Int. J. Electrochem. Sci. 2020, 3283– 3297. [15]. Hegazy, M. A.; Hasan, A. M.; Emara, M. M.; Bakr, M. F.; Youssef, A. H. Evaluating four synthesized Schiff bases as corrosion inhibitors on the carbon steel in 1 M hydrochloric acid. Corros. Sci. 2012, 65, 67–76. [16]. Nathan, C. C. Corrosion Inhibitors; National Association of Corrosion Engineers (NACE), Houston: Texas, USA, 1973. [17]. Gece, G. The use of quantum chemical methods in corrosion inhibitor studies. Corros. Sci. 2008, 50, 2981–2992. [18]. El Adnani, Z.; Mcharfi, M.; Sfaira, M.; Benzakour, M.; Benjelloun, A. T.; Ebn Touhami, M. DFT theoretical study of 7-R-3methylquinoxalin- 2(1H)-thiones (RH; CH3; Cl) as corrosion inhibitors in hydrochloric acid. Corros. Sci. 2013, 68, 223–230. [19]. El-Naggar, M. M. Corrosion inhibition of mild steel in acidic medium by some sulfa drugs compounds. Corros. Sci. 2007, 49, 2226–2236. [20]. Tüzün, B.; Bhawsar, J. Quantum chemical study of thiaozole derivatives as corrosion inhibitors based on density functional theory. Arab. J. Chem. 2021, 14, 102927. [21]. Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B Condens. Matter 1988, 37, 785–789. [22]. Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Results obtained with the correlation energy density functionals of becke and Lee, Yang and Parr. Chem. Phys. Lett. 1989, 157, 200–206. [23]. Petersson, G. A.; Bennett, A.; Tensfeldt, T. G.; Al-Laham, M. A.; Shirley, W. A.; Mantzaris, J. A complete basis set model chemistry. I. The total energies of closed-shell atoms and hydrides of the first-row elements. J. Chem. Phys. 1988, 89, 2193–2218. [24]. Sellaoui, L.; Guedidi, H.; Knani, S.; Reinert, L.; Duclaux, L.; Ben Lamine, A. Application of statistical physics formalism to the modeling of adsorption isotherms of ibuprofen on activated carbon. Fluid Phase Equilib. 2015, 387, 103–110. [25]. Hassan, H. H.; Abdelghani, E.; Amin, M. A. Inhibition of mild steel corrosion in hydrochloric acid solution by triazole derivatives. Electrochim. Acta 2007, 52, 6359–6366. [26]. Ramesh, S.; Rajeswari, S. Corrosion inhibition of mild steel in neutral aqueous solution by new triazole derivatives. Electrochim. Acta 2004, 49, 811–820. [27]. Beda, R. H. B.; Niamien, P. M.; Avo Bilé, E. B.; Trokourey, A. Inhibition of aluminium corrosion in 1.0 M HCl by caffeine: Experimental and DFT studies. Adv. Chem. 2017, 2017, 1–10. [28]. Khamaysa, O. M. A.; Selatnia, I.; Zeghache, H.; Lgaz, H.; Sid, A.; Chung, I.-M.; Benahmed, M.; Gherraf, N.; Mosset, P. Enhanced corrosion inhibition of carbon steel in HCl solution by a newly synthesized hydrazone derivative: Mechanism exploration from electrochemical, XPS, and computational studies. J. Mol. Liq. 2020, 315, 113805. [29]. Karthikaiselvi, R.; Subhashini, S. Study of adsorption properties and inhibition of mild steel corrosion in hydrochloric acid media by water soluble composite poly (vinyl alcohol-omethoxy aniline). J. Assoc. Arab Univ. Basic Appl. Sci. 2014, 16, 74–82. [30]. Chen, Y.; Chen, Z.; Zhuo, Y. Newly synthesized morpholinyl Mannich bases as corrosion inhibitors for N80 steel in acid environment. Materials (Basel) 2022, 15, 4218. [31]. Tan, C. H. C.; Sabar, S.; Hussin, M. H. Development of immobilized microcrystalline cellulose as an effective adsorbent for methylene blue dye removal. S. Afr. J. Chem. Eng. 2018, 26, 11–24. [32]. Akinbulumo, O. A.; Odejobi, O. J.; Odekanle, E. L. Thermodynamics and adsorption study of the corrosion inhibition of mild steel by Euphorbia heterophylla L. extract in 1.5 M HCl. Results in Materials 2020, 5, 100074. [33]. Diki, N. Y. S.; Coulibaly, N. H.; Kassi, K. F.; Trokourey, A. Mild steel corrosion inhibition by synthesized 7-(Ethylthiobenzimidazolyl) Theophylline. J. Electrochem. Sci. Eng. 2021, 11, 97–106. [34]. Abdul Rahiman, A. F. S.; Sethumanickam, S. Corrosion inhibition, adsorption and thermodynamic properties of poly(vinyl alcohol- cysteine) in molar HCl. Arab. J. Chem. 2017, 10, S3358–S3366. [35]. Abdelshafi, N. S.; Sadik, M. A.; Shoeib, M. A.; Halim, S. A. Corrosion inhibition of aluminum in 1 M HCl by novel pyrimidine derivatives, EFM measurements, DFT calculations and MD simulation. Arab. J. Chem. 2022, 15, 103459. [36]. Chen, L.; Lu, D.; Zhang, Y. Organic compounds as corrosion inhibitors for carbon steel in HCl solution: A comprehensive review. Materials (Basel) 2022, 15, 2023. [37]. Merimi, I.; EL Ouadi, Y.; Benkaddour, R.; Lgaz, H.; Messali, M.; Jeffali, F.; Hammouti, B. Improving corrosion inhibition potentials using two triazole derivatives for mild steel in acidic medium: Experimental and theoretical studies. Mater. Today 2019, 13, 920–930. [38]. Khadom, A. A.; Abd, A. N.; Ahmed, N. A. Xanthium strumarium leaves extracts as a friendly corrosion inhibitor of low carbon steel in hydrochloric acid: Kinetics and mathematical studies. S. Afr. J. Chem. Eng. 2018, 25, 13–21. [39]. Ben Aoun, S. On the corrosion inhibition of carbon steel in 1 M HCl with a pyridinium-ionic liquid: chemical, thermodynamic, kinetic and electrochemical studies. RSC Adv. 2017, 7, 36688–36696. [40]. Madkour, L. H.; Elshamy, I. H. Experimental and computational studies on the inhibition performances of benzimidazole and its derivatives for the corrosion of copper in nitric acid. Int. J. Ind. Chem. 2016, 7, 195– 221. [41]. Diki, N. Y. S.; Coulibaly, N. H.; Kambiré, O.; Trokourey, A. Experimental and theoretical investigations on copper corrosion inhibition by cefixime drug in 1M HNO3 solution. J. Mater. Sci. Chem. Eng. 2021, 09, 11–28. [42]. Al-Amiery, A. A.; Mohamad, A. B.; Kadhum, A. A. H.; Shaker, L. M.; Isahak, W. N. R. W.; Takriff, M. S. Experimental and theoretical study on the corrosion inhibition of mild steel by nonanedioic acid derivative in hydrochloric acid solution. Sci. Rep. 2022, 12, 4705. [43]. Li, X.; Deng, S.; Fu, H. Triazolyl blue tetrazolium bromide as a novel corrosion inhibitor for steel in HCl and H2SO4 solutions. Corros. Sci. 2011, 53, 302–309. [44]. Faustin, M.; Maciuk, A.; Salvin, P.; Roos, C.; Lebrini, M. Corrosion inhibition of C38 steel by alkaloids extract of Geissospermum laeve in 1M hydrochloric acid: Electrochemical and phytochemical studies. Corros. Sci. 2015, 92, 287–300. [45]. Deng, S.; Li, X. Inhibition by Jasminum nudiflorum Lindl. leaves extract of the corrosion of aluminium in HCl solution. Corros. Sci. 2012, 64, 253–262. 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. Experimental 2.1. Aluminium samples 2.2. Inhibitor 2.3. Electrolyte medium 2.4. Experimental method: Gravimetry 2.5. Theoretical analysis by density functional theory calculation 3. Results and discussion 3.1. Aluminium corrosion rate and inhibitory efficiency of flucloxacillin 3.2. Adsorption isotherms 3.3. Thermodynamic parameters 3.3.1. Adsorption parameters 3.3.2. Activation parameters 3.4. Analysis of the electronic properties of flucloxacillin by DFT 3.4.1. Global reactivity descriptors 3.4.2. Local selectivity 3.5. Corrosion and inhibition mechanism 3.5.1. Corrosion process mechanism 3.5.2. Adsorbed species inhibition mechanism 4. Conclusion Disclosure statement CRediT authorship contribution statement ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField18: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: PrintField28: