Corrosion inhibition activity of 2-cyclohexylthiophene (2CHT) for mild steel in acidic media was predicted using QSAR tool. The model used two descriptors namely; Moran autocorrelation of lag4 weighted by mass (MATS4M) which explained the linearity and branching of the compounds and largest eigen values n3 of burden matrix weighted by mass (SPMAX3-Bh(m)) describes the nature and size of the neighboring atom. The modeling results revealed the potential of the compounds as a good corrosion inhibitor with percentage inhibition efficiency (%IE) of 76.5%. Quantum chemical calculation using DFT with 6-311G++(d,p) basis was used to evaluate the performance of the predicted compound as corrosion inhibitor by quantum chemical parameters such as EHUMO, ELUMO, Energy gap (Egap), hardness (?), softness (S), dipole moment (µ), electronegativity (X), electron affinity (A), ionization energy (I) and total energy (TE). The results obtained from quantum chemical parameters were found to be consistent with predicted result

Abdallah, Hassan H.

Al-Fakih, Abdo M.

Aziz, Madzlan

Jamaludin, Rosmahaida

Maarof, Hasmerya

Usman, Bishir

Universiti Teknologi Malaysia Institutional Repository

Proceeding of 2nd International Science Postgraduate Conference 2014 (ISPC2014) © Faculty of Science, Universiti Teknologi Malaysia 490  Predictive Model of 2-cyclohexylthiophene for corrosion inhibition in mild steel using Computational Method. Bishir Usman1,2, Hasmerya Maarof1, Hassan H. Abdallah1,3, Rosmahaida Jamaludin1, Abdo M. Al-Fakih1,4, Madzlan Aziz1*  1Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia,  81310,  UTM  Johor  Bahru,  Johor  Darul  Ta’azim,  Malaysia 2Department of Pure and Industrial Chemistry, Faculty of Science, Bayero University, Kano. P. M. B. 3011, Kano, Nigeria. 4Department of Chemistry, Education College, Salahaddin University, Erbil, Iraq.   4Department  of  Chemistry,  Faculty  of  science,  Sana’a  University,  Sana’a, Yemen *1 madzlan@utm.my;2 bishirbum@yahoo.com  Abstract: Corrosion inhibition activity of 2-cyclohexylthiophene (2CHT) for mild steel in acidic media was predicted using QSAR tool. The model used two descriptors namely; Moran autocorrelation of lag4 weighted by mass (MATS4M) which explained the linearity and branching of the compounds and largest eigen values n3 of burden matrix weighted by mass (SPMAX3-Bh(m)) describes the nature and size of the neighboring atom. The modeling results revealed the potential of the compounds as a good corrosion inhibitor with percentage inhibition efficiency (%IE) of 76.5%. Quantum chemical calculation using DFT with 6-311G++(d,p) basis was used to evaluate the performance of the predicted compound as corrosion inhibitor by quantum chemical parameters such as EHUMO, ELUMO, Energy gap (Egap), hardness   (η),   softness (S), dipole   moment   (μ),  electronegativity (X), electron affinity (A), ionization energy (I) and total energy (TE). The results obtained from quantum chemical parameters were found to be consistent with predicted result. Keywords ; Corrosion Inhibtion, QSAR, 2-cyclohexylthiophene, DFT calculation    Proceeding of 2nd International Science Postgraduate Conference 2014 (ISPC2014) © Faculty of Science, Universiti Teknologi Malaysia 491   1.0 Introduction  Organic corrosion inhibitors are the most widely used inhibitors in corrosion protection for fast few years. Organic compounds containing hetero atoms such as N, O, S and P were found to be promising in reducing corrosion damage [1]. The mechanism of corrosion inhibition of the metal surface in acidic media can best be explained by ability of the inhibitor to be adsorbed onto the metal surface which acts as a barrier against reaction to continue [2]. The presence of functional groups that are electron sufficient, pi-electron and lone pair of electron are the other important structural features facilitating the adsorption activity of the inhibitor [3,4]. Many studies have been reported extensively on effect of heterocyclic compounds containing N, O and S, as corrosion inhibitors [5-11].  Nowadays the use of theoretical chemistry has become very popular in predicting corrosion inhibition with the introduction of developmental computational hardware with efficient algorithm that can be used in molecular quantum mechanical calculations [12]. Quantitative Structure activity relationship is the mathematical relationship established between the property of a chemical (activity) and different combination of molecular descriptors. The essential target is to derive a significant and useful equation which could explain the corrosion efficiency of a compound that depends on physical and chemical properties of the molecules [13]. Therefore this approach can be applied to any area and predict certain activity of interest apart from corrosion inhibition performance. However, different quantum chemical approach and Quantum chemical calculation have been reported as a promising method used to evaluate the corrosion inhibition activity of the inhibitor in which structure and electronic properties are obtained from the use of computational methodologies by quantum chemical calculations [2]. Proceeding of 2nd International Science Postgraduate Conference 2014 (ISPC2014) © Faculty of Science, Universiti Teknologi Malaysia 492  The aim of this paper is to use QSAR model and predict the corrosion inhibition activity of 2-cylohexylthiophene as potential corrosion inhibitors and to perform quantum chemical calculation based on quantum chemical parameters of the inhibitor compound.  2.0 Computational Details 2.1 QSAR  QSAR model was developed and used to predict the corrosion inhibition efficiency of 2-cyclohexylthiophene. The molecules were drawn in 2D with ChemDraw Ultra version 8, and the structure is converted to 3D by chem3D Ultra 08 and optimized using AM1 with MOPAC. Dragon software version 6.0 [14], was used to calculate the descriptors of the compound. Statistical analysis was performed using Matlab Version 6 to obtain the model. The details of this method is described elsewhere [15].   S  Figure 1. 2-cyclohexylthiophene  2.2 Quantum chemical calculations Quantum chemical calculations and geometrical optimization of the compound (2-cyclohexylthiophene) were conducted using Density Functional Theory (DFT) with   Beeck’s Three Parameters (B3) and Lee Yang-Parr (BYP) as (B3LYP)  [16,17], (B3LYP) with 6-311G++(d,p) basis set implemented on Gaussian09 Proceeding of 2nd International Science Postgraduate Conference 2014 (ISPC2014) © Faculty of Science, Universiti Teknologi Malaysia 493  program package version 09. Following the geometry optimization different quantum chemical parameters were calculated for the optimized structure such as EHUMO, ELUMO,   ΔEgap,   Hardness   (η),   softness   (S),   dipole   moment   (μ),  electronegativity (X), electron affinity (A), ionization energy (I) and total energy (TE).        Figure 2. Optimised molecular structure using B3LYP with 6-311++(d,p)  3.0 Results and Discussion  QSAR model correlates the structure and properties of 2-cyclohexylthiophene as corrosion inhibitors, the model recognised to most important descriptors which explained the behaviour of the compound as corrosion potential. The Moran autocorrelation of lag4 weighted by mass (MATS4M) explained the linearity and branching of the compounds while Largest eigen values n3 of Burden matrix weighted by mass (SPMAX3-Bh(m)) shows the role of the nature and size of the neighboring atoms, are the properties responsible for the corrosion inhibition of the compounds. With SPMAX3Bh(m) as the most effective descriptor, with bo, b1 and b2 are the regression model constant and coffiecient for descriptor 1 and 2 respectivelyl as shown in Table1. and equation 1 Proceeding of 2nd International Science Postgraduate Conference 2014 (ISPC2014) © Faculty of Science, Universiti Teknologi Malaysia 494   %IE = bo + b1(MATS4M)  + b2(SPMAX3-Bh(m))    1.  Table 1. QSAR Model  prediction of corrosion inhibition efficiency of 2-cyclohexylthiophee Compound bo b1 b2 MATS4M SPMAX3-Bh(m %IE CHT -88.25 -9.88 57.27 -0.047 2.87 76.5  Computational chemistry is the approach, which involves quantum chemical calculation and molecular modeling. QSAR approach, was used to obtain many information based on molecular properties of the compounds. However, geometry of the inhibitors and the nature or behaviour of frontier orbital i.e. HOMO and LUMO were among the most significant properties related to inhibition effect. Therefore the inhibiting effect of 2-cyclohexylthiophene was investigated by quantum chemical calculation using Quantum chemical parameters. The optimized structure of the compound and frontier orbital are shown in Figure 2 and quantum chemical parameters calculated are shown in Table 2. Frontier orbital are reported to be responsible for adsorption of the inhibitor on to the metal surface [18,13,19]. Therefore, HOMO energy value of the inhibitor, -6.259eV, as shown in Table 2, makes the inhibitor to have greater tendency to offer electron to the empty d-orbital’s  of  the  metals  surface  and  lead  to  higher  corrosion inhibition efficiency of 2-cyclohexylthiophene. LUMO energy was found to be 0.490 eV which make the inhibitor easier to accept electron from the metal atom. More over the energy gap, ΔEgap = ELUMO -EHUMO, was calculated to be 5.769eV which gives better adsorption and increases the reactivity and at the same time lower the energy to remove electron from the  unoccupied molecular orbital. It has been reported   that lower energy gives better adsorption with the metal surface and hence higher inhibition efficiency and stability [20-22,13]. Dipole  moment  (μ)  of  the  compound  was found to be 0.915 debye which shows an improvement of the adsorption of Proceeding of 2nd International Science Postgraduate Conference 2014 (ISPC2014) © Faculty of Science, Universiti Teknologi Malaysia 495  the inhibitor to the metal surface, as the higher  μ  value  increases the adsorption of the inhibitor to the metal surface [23]. Softness and hardness are the properties which measured the stability and reactivity of the molecule. Softness of the inhibitor describes the ability of atom or group of atoms to receive electrons while the hardness shows the resistance toward deformation or polarization of the electron cloud of an atom or group of atoms. Therefore, simple electron transfer is usually taken place at the part of the molecules where there is  higher value of softness hence higher inhibition efficiency [24-26]. The softness of the inhibitor (S) was found to be 123.236 eV and the hardness η  =  6.259eV. According to the Kopman theorem [27], the electroaffinity (A) and ionization energy can be calculated from the HOMO and LUMO energy values. I = -EHUMO, A= -ELUMO and the value of electronegativity (X), hardness   (η),   Softness   (S)   are   calculated  using values of I and A. X = ூା஺ଶ, η  =  ூି஺ଶ and  S = ଵ  ஗ =  ଶூି஺ and the values are shown in Table 2. Table 2.  Quantum chemical parameters calculated using B3LYP/6-311G++(d,p) Quantum chemical parameters  Values  EHUMO / eV -6.259 ELUMO / eV -0.490 ΔEgap  eV 5.769 Dipole Moment (Debye) 0.915 Hardness  (η)  eV 6.014 Softness eV 123.266 Ionization energy(I) eV 6.259 Electron affinity(A) eV 0.490 Electronegativity (X) eV 3.320 Total energy (TE) Ev -21436.826  Proceeding of 2nd International Science Postgraduate Conference 2014 (ISPC2014) © Faculty of Science, Universiti Teknologi Malaysia 496  Previous work reported that values of quantum chemical parameters explained the inhibition effect as a result of electron donation to the metal surface [23,12,22]. Therefore, cycloakyl in 2CHT molecule is an electron donor while mild steel is the electron acceptor, thus forming adsorption inhibition layer against corrosion. This could best be explained by the presences of N or S or O in an organic compound with one pole is adsorbed on to metal surface forming a complex layer bonding to the metal surface polar bonds. Steric hindrance, geometry of the compound, also may explain how the adsorption performance and corrosion inhibition efficiency might be [28]. Therefore, the presence of sulphur atom, lone pair of electron and delocalized ᴨ- electron as well as the donor group (cycloalkyl) make the electronic density of 2-cyclohexylthiophene to increase and hence increases adsorption on metal with good corrosion inhibition efficiency.  4.0 CONCLUSIONS Computational chemistry calculation shows that corrosion inhibition efficiency can be predicted using QSAR as a detecting tool before running the experimental evolution. In addition, calculated quantum chemical parameters such as EHUMO, ELUMO,  ΔEgap,  dipole  moment  (μ),  softness  (S), hardness  (η),  electonegativity  (χ), electron affinity (A), ionization energy (I) and total energy (TE) were efficiently suggested that 3cyclohexylthiophene is a good potential corrosion inhibitor. This conclusion was supported by the prediction of the QSAR model based on the molecular descriptors as Moran autocorrelation of lag4 weighted by mass (MATS4M) which explain the linearity and branching of the compounds and largest eigen values n3 of Burden matrix weighted by mass (SPMAX3-Bh(m)) which describes the nature and size of the neighboring atom.  Proceeding of 2nd International Science Postgraduate Conference 2014 (ISPC2014) © Faculty of Science, Universiti Teknologi Malaysia 497  ACKNOWLEDGEMENT The authors thanks computational chemistry laboratory and Research Management Centre (RMC), Universiti Teknologi Malaysia. 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Predictive model of 2-cyclohexylthiophene for corrosion inhibition in mild steel using computational method

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Predictive model of 2-cyclohexylthiophene for corrosion inhibition in mild steel using computational method

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