Moroccan Journal of Chemistry ISSN: 2351-812X http://revues.imist.ma/?journal=morjchem&page=login
Ghassab & al. / Mor. J. Chem. 6 N°1 (2018) 195-202
Inhibitive action of Chamomile extract on the corrosion of Iron: Density Functional Theory Ghassab M. Al-Mazaideh*1, Saleh A. Al-Quran2 1
Department of Chemistry and Chemical Technology, Faculty of Science, Tafila Technical University, P.O. Box 179, Tafila 66110, Jordan 2 Department of Biological Sciences, Faculty of Science, Mutah University, P.O. Box 7, Mutah 61710, AlKarak, Jordan
Abstract DFT calculations have been performed on major compounds of Chamomile extract as a green source of environmentally friendly corrosion inhibitors for Fe using B3LYP/631G* level (d, p). Several global Quantum parameters were calculated on inhibitors and thermodynamic Gibbs function ∆Gads of adsorption of Fe has been calculated and used * Corresponding author: to evaluate the inhibitive action of the each inhibitor. Quercetin has been found the
[email protected]
highest anti-corrosion efficiency as compared to other compounds. Consequently,
Received 14 May 2017, calculated global quantum parameters and thermodynamic function ∆Gads show Revised
01
Sept
2017, spontaneous physical adsorption of Apigenin-7-glucoside, luteolin-7-glucoside and
Accepted 11 Dec 2017.
Quercetin on Fe, wherase other inhibitors show non- spontaneous chemical adsorption.
Keywords: Fe, DFT, Inhibitors, Chamomile
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1. Introduction There are lots of reports of a retun to natural products such as herb plants in pharmaceutical chemistry in order to find drugs and develop potential compounds to find new drugs, antimicrobial, cytotoxic activities and anticancer [1]. Furthermore, the natural products is proved as new cleaning inhibitors for green environment. Several studies have been showed the use of natural products as friendly corrosion inhibitors for importanr metals like Fe, Al and Cu alloys in aggressive media [2-5]. These cleaning inhibitors are biodegradable, nontoxic and available in different plants. Recent research showed that the extracts of every part of plant such as seeds, fruits, flowers, leaves, stems and roots have used as corrosion inhibitors [6-9]. The extract solution of Chamomile (Chamaemelum mixtum L.) showed an excellent effective inhibitionfor the corrosion of steel in H2SO4. The main chemical compositions of Chamomile extracts are shown in Fig 1[10].
Figure 1: Structures of main chemical constituents of Chamomile To the best of our knowledge [11-17], DFT model has been used to compute a spread array of properties like optimized structure, thermochemistry and kinetic of different types of inhibitors. Such information will help in explain the effect of these compounds as inhibitors for Fe corrosion. The target of this paper is test the theoretical chemistry and molecular dynamics simulations of the inhibitors. In addition to discuss their mechanism of inhibitive action. These methods were based on quantum chemical calculations and have been proved to be a very suitable tools and cost effective for finding the corrosion inhibition mechanism. Mor. J. Chem. 6 N°1 (2018) 195-202
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Density functional theory (DFT) model has classified as an important tool to investigate the efficiency of each compounds as a corrosion inhibitor of Fe. Predict the systematic way for the analysis of the interaction of inhibitor with Fe surface is very interesting and very aim of this work. Theoretical calculations have been used to predict the inhibitive activity of inhibitors and the efficiency of each one on the corrosion of Fe. In the present work, the chemical reactivity of the inhibitor has been reprted as a function of different quantum parameters such as EHOMO (highest occupied molecular orbital), ELUMO (the lowest unoccupied molecular orbital), ΔEgap (energy gap), η (global hardness), σ (softness), X (electronegativity), ΔN (the fraction of electron transferred), and ω (electrophilicity index).
2. Computational Methodology DFT model were used with B3LYP as hybrid functional with 6-31G* (d, p) basis set. Gaussian 09 (G09) [18] with DFT-B3LYP was used to calculate the quantum chemical parameters by optimizing the inhibitor structure under no constraint. Moreover, the results of these parameters were used to calculate thermodynamic function of adsorption ∆Gads (Gibbs free energy of adsorption) of the Fe and the studied inhibitors. In this work, the theoretical values of XFe = 4.026 eV and ηFe = 3.875 eV were used for calculating the number of electrons transferred [19]. All calculations have been performed in gas phase.
3.
Results and Discussion
The optimized structure of Inhibitors under investigation and together with their HOMO and LUMO orbitals are shown in Figure .2 which obtained by B3LYP/6-31G* level. The values of EHOMO and ELUMO for Fe metal [20] have been compared to the calculated values for inhibitors to determine the type of the interaction. The calculated results of EHOMO and ELUMO for inhibitors are shown in Table .1. The adsorption ability of the inhibitor over Fe surface can be calculated by frontier molecular orbital theory [21]. The capability of an inhibitor to donate electrons to a suitable acceptor of inhibitor with unoccupied d-orbital of Fe can be determined by EHOMO. While ELUMO shows its ability to accept electrons. Consequently, Better inhibitor efficiency means lower ELUMO value which leads to more ability of the molecule to accept electrons [22]. In this case, increasing EHONO and decreasing ELUMO level lead to increase in the binding capability of the inhibitor to the Fe surface. Herein, Fe will act as a Lewis acid while the inhibitors act as a Lewis base. So, inhibitor utilizes the HOMO to initiate the reaction with LUMO of Fe. The interaction has a certain amount of ionic character because the values of ELUMO, Fe EHOMO, inh gap approximately fall between 5 to 5.9 eV (Table 2). Strong covalent bond can be obtained only if the ELUMO, inh - EHOMO, Fe gap is approximately zero [23]. In this case, all inhibitors act as an anodic inhibitor. ∆Egap is a good parameter to predict the adsorption of inhibitor on metallic surface. i.e the reactivity of the inhibitors incrases with decrasing ∆Egap which leads to increase the inhibitor efficiency [24]. Consequently, Quercetin (lowest ∆Egap) has the strongest ability for co-ordinate bonds the vacant d-orbitals of Fe by donating and accepting electrons. The ∆Egap values of the other inhibitors (Table 3) increases in the order Quercetin < trans-spiroeth < luteolin-7glucoside < Apigenin 7-glucoside < cis-spiroeth < Bisabolol oxides = A Bisabolol oxides B. The effectiveness of Chamomile compounds under investigation as inhibitors has been further studied by evaluating the global reactivity parameters such as: η (the global chemical hardness), X
(the electronegativity), σ (the global
Inhibitor
softness), ΔN (the fraction of electrons transferred) and ω (the electrophililcity) are shown in Table 3 After Optimization
HOMO
LUMO
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Apigenin 7-
glucoside
luteolin-7-
glucoside
cis-spiroeth trans-spiroeth Quercetin Bisabololoxides B Bisabololoxides A Figure 2: Optimized structure with HOMO and LUMO of studied inhibitors
Table 1. Calculated EHOMO and ELUMO of the inhibitors by the DFT Substance
EHOMO (eV)
ELUMO (eV)
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Fe
-7.902
Apigenin 7-glucoside
-0.151
-5.920
-1.780
-5.870
-1.770
cis-spiroeth
-5.240
-0.640
trans-spiroeth
-5.180
-1.360
Quercetin
-5.560
-1.910
Bisabolol oxides A
-6.060
1.000
Bisabolol oxides B
-6.070
0.990
luteolin-7-glucoside
Table 2. Calculated energy gap interaction of Fe- inhibitor by the DFT method Inhibitors
ELUMO, inh – EHOMO, Fe Cu(eV)
ELUMO, Fe – EHOMO, inh (eV)
Apigenin 7-glucoside
6.122
5.769
6.132
5.719
cis-spiroeth
7.262
5.089
trans-spiroeth
6.542
5.029
Quercetin
5.992
5.409
Bisabolol oxides A
8.902
5.909
Bisabolol oxides B
8.892
5.919
luteolin-7-glucoside
Table 3. Calculated quantum chemical parameters for the inhibitors Apigenin Inhibitors
luteolin
7-
cis-
trans-
Quercetin
Bisabolol
Bisabolol
oxides A
oxides B
7-glucoside
glucoside
spiroeth
spiroeth
EHOMO
-5.920
-5.870
-5.240
-5.180
-5.560
-6.060
-6.070
ELUMO
-1.780
-1.770
-0.640
-1.360
-1.910
1.000
0.990
∆Egap I= - EHOMO
4.140
4.100
4.600
3.820
3.650
7.060
7.060
5.920
5.870
5.240
5.180
5.560
6.060
6.070
A= - ELUMO
1.780
1.770
0.640
1.360
1.910
-1.000
-0.990
χ = (I+A) / 2
3.850
3.820
2.940
3.270
3.735
2.530
2.540
η =(I-A) / 2
2.070
2.050
2.300
1.910
1.825
3.530
2.540
σ = 1/η
0.483
0.488
0.435
0.524
0.548
0.283
0.394
0.015
0.017
0.088
0.065
0.026
0.101
0.116
ω = μ2/2η
1.913
1.883
1.115
1.380
1.800
0.826
0.832
µ (Debye)
2.630
4.030
3.770
2.800
1.070
1.340
1.830
ΔN = (χ Fe - χ inh) / 2 (η Fe + η inh)
I , A , χ, η, σ, ω [25] / ΔN, μ (-X) [26,27]
Hard- Soft- Acid- Base principle says that Hard acids tend to co-ordinate hard bases while soft acids tend to coordinate soft bases. So that, hard molecules have high ∆Egap wherase small molecules have small ∆Egap [24]. According to this principle, soft bases inhibitor is the most effective ones for metals [28]. For this reason, Quercetin Mor. J. Chem. 6 N°1 (2018) 195-202
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which has the small ∆Egap and the highest softness (σ) is expected to have the good inhibitor efficiency as compared to other compounds. This result is confirmed by calculating softness (σ) of the inhibitor and so its reactivity. Table 3 shows that Quercetin has the highest value compared to other inhibitors. In addition, it can be observed (Table 3) that the hardness (η) of all inhibitors are the largest values than Quercetin. This tendency is the revers of what has been obtained for softness (σ). Consequently, Quercetin with highest values of softness (σ) and smallest value of hardness (η) is the best inhibitor. Soft molecule is more reactive than a hard molecule [29]. The fraction of transferred electrons (ΔN) is also calculated and shows that most electrons transferred to the Fe surface comes from the Quercetin molecules when compared to other inhibitors. The electrophililcity index (ω) indicates the ability of the inhibitor to accept electrons from Fe. Quercetin exhibits the highest electrophililcity index (ω) value as compared to other inhibitor because of low ELUMO. As a result, Quercetin has high capacity to accept electrons from Fe. That is, Fe acts as Lewis base while all inhibitors act as Lewis acids (cathodic inhibitor). Fe will act as anodic inhibitor, because it can accept electrons from all inhibitor to form a co-ordinated bond. In addition, the inhibitor can accept electrons from Fe atom to form back-donating bond depending on the orientation of inhibitors’optimized structure on the spatial. In this case, the inhibition efficiency will be increase, because of donation and back-donation processes strengthen the adsorption of inhibitors onto the Fe surface. By assuming that Fe act as anode and inhibitors act as cathode, the ∆Gads values of the inhibitors on Fe surface are calculated by the following relations: ∆Gads (cathodic inhibitor) = μ (inhibitor) - μ (Fe) ∆Gads (anodic inhibitor) = μ (Fe) - μ (inhibitor) Where μ indicates the chemical potential and is equal to the negative value of the absolute electronegativity (X) as in ref. [30]. The calculated values of ∆Gads for inhibitors are given in Table 4. Table 4. Calculated ∆Gads (kJ /mol) and Dipole moment of the investigated inhibitors Inhibitors
Anodic Inhibitors
Apigenin-7-glucoside luteolin-7-glucoside cis-spiroeth trans-spiroeth Quercetin Bisabolol oxides A Bisabolol oxides B
-16.981 -19.876 -104.783 -72.943 -28.077 -144.342 -143.377
µ (Debye) 2.630 4.030 3.770 2.800 1.070 1.340 1.830
The adsorption of the inhibitors on Fe, shows that all inhibitors have negative ∆G ads values. The value of ∆Gads changes depends on the differences between chemical and physical adsorption [31,32]. So that, physical adsorption when ∆Gads value is in the range of 0 to - 40 kJ.mol-1, whereas chemical adsorption when ∆Gads value is in the range of -80 to -400 kJ.mol-1 [33]. The suggested mechanism for Apigenin-7-glucoside, luteolin-7-glucoside and Quercetin is spontaneous physical adsorption because ∆Gads value is in the range of 0 to -40 kJ.mol-1 wherase other inhibitors show non- spontaneous chemical adsorption.
4. Conclusion The theoretical calculations gave a good picture about the effect of main chemical constituents of Chamomile extract by suggesting that Quercetin shows the most inhibition efficiency as compared to the other compounds, because they have Mor. J. Chem. 6 N°1 (2018) 195-202
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low ELUMO. Therefore, it is expected that inhibitors can form a strong interaction with Fe to act as cathodic inhibitors. All inhibitors show spontaneous energy and suggest that Chamomile extract have inhibitive action which is mainly from Quercetin.
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