Corrosion inhibitors part V: QSAR of benzimidazole and 2-substituted derivatives as corrosion inhibitors by using the quantum chemical parameters

Quantum chemical SCF calculations of some parameters of benzimidazoles were correlated with their inhibition efficiency in case of steel in aqueous acidic medium. Geometric structures, total negative charge on the molecule (TNC), highest occupied molecular orbital (E_HOMO), lowest unoccupied molecular orbital (E_LUMO), dipole moment (μ) and linear solvation energy terms, molecular volume (Vi) and dipolar-polarization (π*) were correlated to corrosion inhibition efficiency. The correlation between quantum parameters obtained by AM1 calculation and experimental inhibition efficiency has been validated by single point calculations for the semi-empirical AM1 structure using B3LYP/6-31G* as a higher level of theory. Equations were proposed using linear regression analysis to calculate corrosion inhibition efficiency. It was established that the increase of the orbital energies E_HOMO favors the inhibition efficiency toward steel corrosion. The proposed linear equations were applied to predict the corrosion inhibition efficiency of some related structures in order to select molecules of possible activity from a library compounds.     

Corrosion inhibitors : Part II: Quantum chemical studies on the corrosion inhibitions of steel in acidic medium by some triazole, oxadiazole and thiadiazole derivatives

The corrosion inhibition efficiencies of some triazole, oxadiazole and thiadiazole derivatives for steel in presence of acidic medium have been studied by using AM1, PM3, MINDO/3 and MNDO semi-empirical SCF molecular orbital methods. Geometric structures, total negative charge on the molecule (TNC), highest occupied molecular energy level (E_HOMO), lowest unoccupied molecular energy level (E_LUMO), core-core repulsion (CCR), dipole moment (μ) and linear solvation energy terms, molecular volume (V_i) and dipolar-polarization (π^*), were correlated to corrosion inhibition efficiency. Four equations were proposed to calculate corrosion inhibition efficiency. The agreement with the experimental data was found to be satisfactory; the standard deviations between the calculated and experimental results ranged between ±0.03 and ±4.18. The inhibition efficiency was closely related to orbital energies (E_HOMO and E_LUMO) and μ. The correlation between quantum parameters and experimental inhibition efficiency has been validated by single point calculations for the semi-empirical AM1 structures using B3LYP/6-31G^** as a higher level of theory. The proposed equations were applied to predict the corrosion inhibition efficiency of some related structures to select molecules of possible activity from a presumable library of compounds.     

Experimental and theoretical investigation of the adsorption behaviour of new triazole derivatives as inhibitors for mild steel corrosion in acid media

Three triazole derivatives (4-chloro-acetophenone-O-1′-(1′,3′,4′-triazolyl)-metheneoxime (CATM), 4-methoxyl-acetophenone-O-1′-(1′,3′,4′-triazolyl)-metheneoxime (MATM) and 4-fluoro-acetophenone-O-1′-(1′,3′,4′-triazolyl)-metheneoxime (FATM)) have been synthesized as new inhibitors for the corrosion of mild steel in acid media. The inhibition efficiencies of these inhibitors were evaluated by means of weight loss and electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and polarization curves. Then the surface morphology was studied by scanning electron microscopy (SEM). The adsorption of triazole derivatives is found to obey Langmuir adsorption isotherm, and the thermodynamic parameters were determined and discussed. The relationship between molecular structure of these compounds and their inhibition efficiency has been investigated by ab initio quantum chemical calculations. The electronic properties such as the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energy levels, energy gap (LUMO-HOMO), dipole moment and molecular orbital densities were computed.     

吡啶类缓蚀剂及其在Al(111)表面吸附行为的密度泛函理论分析

利用密度泛函理论方法研究了3种吡啶类缓蚀剂分子(吡啶、3-甲基吡啶和4-甲基吡啶)的反应活性及溶剂条件下在Al(111)表面的吸附行为。分子反应活性的量化计算结果表明,3种缓蚀剂分子的前线轨道均分布在吡啶环上,亲核和亲电活性中心均位于吡啶环的N原子上。分子与Al表面吸附的量化计算结果表明,3种分子均能与Al(111)面发生化学吸附,吸附强度顺序与实验测得的缓蚀效率顺序相一致,且缓蚀剂分子与Al(111)面的相互作用是由成键原子的轨道杂化所致。此外,3-甲基吡啶和4-甲基吡啶两个分子还能平行于Al(111)面发生物理吸附。     

Quantitative structure-property relationship study on first reduction and oxidation potentials of donor-substituted phenylquinolinylethynes and phenylisoquinolinylethynes: Quantum chemical investigation

The relationship between the chemical structure, first reduction and oxidation potentials of 30 Phenylquinolinylethyne (PhQE), and Phenylisoquinolinylethyne (PhIE) derivative compounds has been elucidated employing ab initio calculations. Quantum chemical calculations (HF/6-31G) were carried out to obtain: the optimized geometry, energy levels, quantum chemical indices, charges and dipole moments of these compounds. The quantitative structure-property relationship (QSPR) of PhQE and PhIE was studied for the first reduction (E_red), and the first oxidation (E_ox) potentials. The genetic algorithm (GA) was applied to select the variables that resulted in the best-fit models. After the variable selection, multiple linear regression (MLR) was utilized to construct linear QSPR models. The resulting QSPR equations indicated that the orbital energies, quantum chemical indices (i.e. electronegativity and softness) and localization of charge in molecules are important factors in the first oxidation and reduction potentials of PhQE and PhIE. The quantum-chemical calculations show that the HOMO and LUMO of both PhQE and PhIE derivatives are localized on the donor-substituted phenyl moiety, and the quinolinyl and isoquinolinyl acceptor moiety respectively. Thus, it was proposed that the first reduction and oxidation potentials can be ascribed to reduction at the quinolinyl acceptor moiety, and oxidation at the donor-substituted phenyl moiety.     

Experimental and atomistic simulation studies of corrosion inhibition of copper by a new benzotriazole derivative in acid medium

The efficiency of N-(2-thiazolyl)-1H-benzotriazole-1-carbothioamide (TBC) as a non-toxic corrosion inhibitor for copper in 0.5 M HCl has been tested by weight loss and electrochemical techniques. Electrochemical techniques show that TBC is a mixed-type inhibitor and its inhibition mechanism on copper surface is adsorption assisted by H-bond formation. Impedance measurements show a wide peak presumably given by more than one time constant in the presence of TBC. Also, impedance results show that the values of CPEs (constant phase elements) tend to decrease and both polarization resistance and inhibition efficiency tend to increase with increasing of TBC concentration due to an increase in the electric double layer. Monte Carlo simulations incorporating molecular mechanics and molecular dynamics show that the TBC adsorb on the copper surface firmly through the thiazolyl and carbothioamide groups, the adsorption energy as well as hydrogen bond length have been calculated for both TBC and benzotriazole (BTA) for comparison. Quantum chemical calculations reveal that TBC has higher HOMO, lower LUMO, lower energy gap and lower dipole moment (μ) than BTA, which proves that TBC is better copper corrosion inhibitor compared with BTA in 0.5 M HCl.     

Corrosion Inhibition Efficiency,Electrochemical and Quantum Chemical Studies of Some New Nonionic Surfactants for Carbon Steel in Acidic Media

In this work, three types of nonionic surfactant as corrosion inhibitors were synthesized. The chemical structure of the prepared inhibitors was confirmed using FT‐IR and ¹H‐NMR spectroscopy. The surface tension and thermodynamic properties of these inhibitors were investigated. The corrosion inhibition efficiency of these surfactants was investigated on a carbon steel surface in 1 M HCl solution by weight loss and electrochemical measurements. Untreated and treated steel surfaces were characterized by scanning electron microscopy. Results show that the inhibition efficiency of the prepared inhibitors increases with increasing the ethylene oxide units. Also, the potentiodynamic polarization curves indicated that the investigated inhibitors behave as a mixed type inhibitor. Adsorption of these surfactants on the carbon steel surface was found to obey Langmuir's adsorption isotherm. The computed quantum chemical properties viz., electron affinity (EA), highest occupied molecular orbital (E_HOMO), the lowest unoccupied molecular orbital (E_LUMO), energy gap ΔE = E_HOMO ? E_LUMO, dipole moment (μ), polarizability and total energy (E_T) show good correlation with experimental inhibition efficiency.     

THE STRENGTH OF MUTAGENICITY, 13C NMR CHEMICAL SHIFTS,AND ELECTRONIC STATES OF NITROBENZANTHRONES

Mutagenic activities of nitrated benzanthrones (NBAs) vary largely with the position and the number of the nitro group. To investigate the structure-activity correlations for NBAs, we have performed nuclear magnetic resonance (NMR) measurements and molecular orbital calculations for the three nitrobenzanthrones, 2-NBA, 3-NBA, 11-NBA; the three dinitrobenzanthrones, 1,9-DNBA, 3,11-DNBA, 3,9-DNBA; and the trinitrobenzanthrone, 3,9,11-TNBA. It was confirmed that the ¹³ C chemical shifts (δ) of the ortho carbon atoms with respect to the nitro group of the compounds tend to be more upfield with decreasing mutagenic activities. The molecular orbital calculations revealed that the LUMO energies of the compounds decrease with mutagenic activities, and that the HOMO and LUMO densities tend to decrease and increase, respectively, with decreasing mutagenic activities. These results indicate that reduction is very important in the metabolism of nitrobenzanthrones.     

利用量子化学特征的模糊人工神经网络预测咪唑啉衍生物缓蚀效率

针对咪唑啉衍生物的量子化学特征参数与缓蚀效率存在复杂非线性关系，在利用多因素方差分析判断其相关性的基础上建立以最高占据轨道能量、最低未占据轨道能量、分子偶极矩、单点能、硬度、软度、亲核进攻指数、亲电进攻指数、电子转移参数以及咪唑环上非氢原子静电荷之和等量子化学特征参数为输入，以缓蚀效率为输出的模糊人工神经网络。结果表明，咪唑啉衍生物的量子化学特征参数及其缓蚀效率之间具有非常显著的相关性，据此所创建的Takagi-Sugeno型模糊人工神经网络预测模型采用10-30-1网络结构，通过Momentum优化算法对其进行反复训练直至其均方误差小于容许收敛误差限0.005，训练、测试阶段模型输出值与期望值近似呈线性关系，决定系数为0.9999，关联度较高，验证阶段该模型亦表现出良好的可靠性。因此利用量子化学特征的模糊人工神经网络预测模型能够准确预测不同咪唑啉系列衍生物的缓蚀效率。     

Inhibition Effects of a Synthesized Novel 4-Aminoantipyrine Derivative on the Corrosion of Mild Steel in Hydrochloric Acid Solution together with Quantum Chemical Studies

1,5-Dimethyl-4-((2-methylbenzylidene)amino)-2-phenyl-1H-pyrazol-3(2H)-one (DMPO) was synthesized to be evaluated as a corrosion inhibitor. The corrosion inhibitory effects of DMPO on mild steel in 1.0 M HCl were investigated using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, open circuit potential (OCP) and electrochemical frequency modulation (EFM). The results showed that DMPO inhibited mild steel corrosion in acid solution and indicated that the inhibition efficiency increased with increasing inhibitor concentration. Changes in the impedance parameters suggested an adsorption of DMPO onto the mild steel surface, leading to the formation of protective films. The novel synthesized corrosion inhibitor was characterized using UV-Vis, FT-IR and NMR spectral analyses. Electronic properties such as highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy (EHOMO and ELUMO, respectively) and dipole moment (μ) were calculated and discussed. The results showed that the corrosion inhibition efficiency increased with an increase in the EHOMO values but with a decrease in the ELUMO value.     

黄顶菊中除草活性成份的量子化学研究

黄顶菊提取物中含有除草活性的香豆素类化合物,利用量子化学方法对香豆素类化合物的结构与除草活性关系进行了研究。采用DFT方法和6-31G基组,对8种香豆素类化合物进行全参数优化,得到了它们的稳定构型。并对化合物中原子的NBO电荷分布、前线分子轨道能级等性质进行了分析,结果表明,化合物的除草活性与分子的前线轨道(HOMO、LUMO)能级存在一定的关系。     

L-半胱氨酸改性聚环氧琥珀酸的合成及其阻垢缓蚀性能

以L-半胱氨酸（LCY）为改性剂改性聚环氧琥珀酸（PESA）得到了一种聚环氧琥珀酸衍生物L-半胱氨酸改性聚环氧琥珀酸（LCY-PESA）,用红外光谱和核磁共振谱表征了LCY-PESA的物质结构,用红外光谱、X射线衍射光谱和扫描电镜研究了钙垢的晶型（形）,探讨了LCY-PESA的静态阻垢、动态阻垢、静态缓蚀、分散氧化铁和生物降解等性能,通过量子化学计算方法研究了LCY-PESA的缓蚀机理。静态阻垢结果表明,在c（Ca²⁺）为400 mg·L^-1、c（HCO₃^-）为800 mg·L^-1的实验介质中,LCY-PESA投放量为6 mg·L^-1,阻垢率即可达到94.6%;当c（Ca²⁺）为150 mg·L^-1、c（Fe²⁺）为10 mg·L^-1、LCY-PESA投放量为15 mg·L^-1时,最小透光率为61.5%。动态阻垢测试显示：随着加药量的增加,动态污垢热阻减小,当加药量为1 mg·L^-1时LCY-PESA的动态阻垢率比PESA提高了约15%。红外光谱、X射线衍射光谱和扫描电镜结果表明,LCY-PESA对钙垢有明显的晶格扭曲作用,把方解石变为球霰石,表现出良好的阻垢分散性能。该衍生物还表现出了优良的可生物降解性能。量子化学计算表明：LCY-PESA分子中的S原子和N原子对HOMO轨道的电荷密度影响较大,导致LCY-PESA的HOMO轨道和LUMO轨道的能隙差值小于PESA分子的能隙差值,因此LCY-PESA分子抑制金属腐蚀的效果好于PESA。     

Synthesis and characterization of novel polyazomethines containing perylene units

Polyazomethines including perylene units in the main chain were synthesized via polycondensation of diaminoperylene with aromatic dialdehydes. UV/vis, FT-IR, ¹H NMR, ¹³C NMR and elemental analysis techniques were carried out for the characterization of the synthesized diaminoperylene, dialdehydes and polyazomethines including perylene units (PAM-PERs). The number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of PAM-PERs were determined by size exclusion chromatography (SEC). Thermal properties of PAM-PERs was determined by using TGA/DTA and DSC systems. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels, and electrochemical and optical (E_g) band gap values were calculated by using the results of cyclic voltammetry and UV/vis, respectively. Conductivity measurements of PAM-PERs were carried out with electrometer by using four-point probe technique. The conductivity was observed to be increased by doping agent iodine.     

量子化学方法研究缓蚀剂结构与耐蚀性的关系

本文概述了缓蚀剂研究中使用的量子化学计算方法,讨论了酸性介质中缓蚀剂分子的结构参数,如HOMO能量、LUMO能量、电荷分布和自由价与缓蚀剂效率间的关系.对于缓蚀剂量子化学研究中的一些问题,提出了看法.     

Electrochemical and surface analytical studies of the self-assembled monolayer of 5-methoxy-2-(octadecylthio)benzimidazole in corrosion protection of copper

5-Methoxy-2-(octadecylthio)benzimidazole (MOTBI) monolayer was self-assembled on fresh copper surface obtained after etching with nitric acid at ambient temperature. The optimum conditions for formation of self-assembled monolayer (SAM) were established using impedance studies. The optimum conditions are methanol as solvent, 10 mM concentration of the organic molecule and an immersion period of 24 h. The MOTBI SAM on copper surface was characterized by contact angle measurements, X-ray photoelectron spectroscopy and reflection absorption FTIR spectroscopy and it is inferred that chemisorption of MOTBI on copper surface is through nitrogen. Corrosion protection ability of MOTBI SAM was evaluated in aqueous NaCl solution using impedance, electrochemical quartz crystal nanobalance, potentiodynamic polarization and weight-loss studies. While bare copper showed a charge-transfer resistance (R_ct) value of 1.89 kΩ cm² in 0.20 M NaCl aqueous environment, the R_ct value for SAM covered copper surface is 123.4 kΩ cm². The MOTBI SAM on copper afforded corrosion inhibition efficiency of 98-99% in NaCl solution in the concentration range and in the temperature range studied. The SAM functions as a cathodic inhibitor. Quantum chemical calculations showed that MOTBI has relatively small ΔE between HOMO and LUMO and large negative charge in its benzimidazole ring, which facilitate formation of a polymeric [Cu⁺-MOTBI] complex on copper surface.     

Molecular structure-property engineering for photovoltaic applications: Fluorene-acceptor alternating conjugated copolymers with varied bridged moieties

A series of novel soluble conjugated copolymers consisting of electron-accepting 2-pyran-4-ylidenemalononitrile (PM) and electron-donating fluorene connected by different electron-donating ability conjugated moieties were synthesized by Suzuki coupling polymerization. The structures of the copolymers were characterized and their physical properties were investigated. High molecular weight (M_n up to 43.8 kg/mol) and thermostable copolymers were obtained. The conjugated bridge between PM and fluorene building block with gradually increased electron-donating ability moieties results in enhanced intramolecular charge transfer (ICT) transition bands, which lead to an extension of their absorption spectral range. Cyclic voltammetry measurement displayed that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers can be fine-tuned. The resulting copolymers possessed relatively low HOMO energy levels, promising good air stability and high open circuit voltage (V_oc) for photovoltaic application. Bulk heterojunction photovoltaic devices were fabricated by using the copolymers as donors and (6,6)-phenyl C₆₁-butyric acid methyl ester (PCBM) as acceptor. The power conversion efficiencies (PCE) of the devices were in the range of 0.02-0.52% under simulated AM 1.5 solar irradiation of 100 mW/cm², and the highest V_oc reached 0.82 V. The significant improvement of PCE indicates a novel concept for developing donor-acceptor (D-A) conjugated copolymers with high photovoltaic performance by adjusting electron-donating ability of conjugated bridge.     

Quantum mechanical calculations of amino pyrazole derivatives as corrosion inhibitors for zinc,copper and α-brass in acid chloride solution

Quantum mechanical calculations have been applied to a series of pyrazole derivatives used as corrosion inhibitors for zinc, copper and -brass in order to assess quantum chemistry as a means of evaluating effectiveness of corrosion inhibitors. The corresponding structures have been optimized and the energies and coefficients of their molecular orbitals (HOMO and LUMO) have been computed using the semi-empirical method, MNDO. The theoretical results are then compared with experimental data.     

ac impedance, X-ray photoelectron spectroscopy and density functional theory studies of 3,5-bis(n-pyridyl)-1,2,4-oxadiazoles as efficient corrosion inhibitors for carbon steel surface in hydrochloric acid solution

The corrosion inhibition properties of a new class of oxadiazole derivatives, namely 3,5-bis(n-pyridyl)-1,2,4-oxadiazoles (n-DPOX) for C38 carbon steel corrosion in 1 M HCl medium were analysed by electrochemical impedance spectroscopy (EIS). An adequate structural model of the interface was used and the values of the corresponding parameters were calculated and discussed. The experimental results showed that these compounds are excellent inhibitors for the C38 steel corrosion in acid solution and that the protection efficiency increased with increasing the inhibitors concentration. Electrochemical impedance data demonstrate that the addition of the n-DPOX derivatives in the corrosive solution decreases the charge capacitance and simultaneously increases the function of the charge/discharge of the interface, facilitating the formation of an adsorbed layer over the steel surface. Adsorption of these inhibitors on the steel surface obeys to the Langmuir adsorption isotherm. X-ray photoelectron spectroscopy (XPS) and the thermodynamic data of adsorption showed that inhibition of steel corrosion in normal hydrochloric solution by n-DPOX is due to the formation of a chemisorbed film on the steel surface. Quantum chemical calculations using the Density Functional Theory (DFT) and the Quantitative Structure Activity Relationship (QSAR) approach were performed on n-DPOX derivatives to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental inhibition efficiency were subjected to correlation analysis and indicate that their inhibition effect is closely related to E_HOMO, E_LUMO, and dipole moment (μ).     

D-A copolymers based on dithienosilole and phthalimide for photovoltaic materials

Two D-A copolymers containing dithienosilole (DTS) donor unit and phthalimide (Ph) acceptor unit, PDTSPh and PDTSBTPh, were synthesized by the Pd-catalyzed Stille-coupling method. The copolymers have a strong absorption ranging from 350 to 650 nm, exhibit good solubility and thermal stability. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers determined by cyclic voltammetry were about −5.2 and −3.0 eV, respectively. The power conversion efficiency of the polymer solar cells based on PDTSBTPh:PC₇₀BM (1:2, w/w) reached 2.1% with open-circuit voltage of 0.83 V and a short-circuit current of 6.27 mA/cm², under the illumination of AM1.5, 100 mW/cm².