In the present work, the inhibitive action of cationic terthiophene, namely, [2,2′:5′,2′′-terthiophene]-5-amidine (MA-1112), was compared with those of three bithiophene isosteres against corrosion of carbon steel (CS) in 1.0 M HCl. Their inhibition efficiencies (%IE) were assessed by the weight loss method (WL) and electrochemical measurements such as EIS, EFM, and potentiodynamic polarization. The %IE shows a stable performance with an increasing tendency at elevated temperature with exposure time in acid solutions. The adsorption of the investigated derivatives on the CS surface was best described by a Langmuir isotherm and the compounds act as mixed-type inhibitors as evidenced by Tafel polarization experiments. Morphological analysis, via SEM, EDX, AFM analysis, and FTIR spectra manifested significant improvement of the CS surface in inhibited solutions. Computational chemical approaches including quantum-chemical and molecular dynamics simulation methods were applied with insightful outputs consistent with the results from practical experiments. The effect of molecular structure was also discussed in more detail. Compound MA-1112 was demonstrated to be the most efficient inhibitor with %IE around 96% at 18 × 10⁻⁶ M. This compound is a modified form of the naturally occurring α-terthienyl compound.

中文翻译：

---

阳离子对噻吩和联噻吩作为缓蚀剂作用的综合研究：实验和理论研究†

在目前的工作中，比较了阳离子对噻吩，即[2,2'：5'，2''-对噻吩] -5- MA（MA-1112）与三种对噻吩类的立体异构体的腐蚀抑制作用。碳钢（CS）在1.0 M HCl中的溶液。通过失重法（WL）和电化学测量（例如EIS，EFM和电位动力学极化）评估了它们的抑制效率（％IE）。％IE表现出稳定的性能，并且在高温下随着在酸性溶液中的暴露时间的增加而呈增加趋势。Langmuir等温线最好地描述了被研究衍生物在CS表面的吸附，并且这些化合物充当混合型抑制剂，如Tafel极化实验所证明的那样。形态分析，通过SEM，EDX，AFM分析和FTIR光谱表明，受抑制溶液中CS表面的显着改善。计算化学方法（包括量子化学方法和分子动力学模拟方法）的应用与实际实验的结果相符，具有深刻的见解。还详细讨论了分子结构的影响。已证明化合物MA-1112是最有效的抑制剂，在18×10 ^-6 M时％IE约为96％。该化合物是天然存在的α-噻吩基化合物的修饰形式。