Performance tests on caffeine’s corrosion inhibition properties and their derivatives against copper corrosion have been previously reported experimentally using gravimetric and electrochemical analyses. The test was able to measure the efficiency of their corrosion inhibition accurately. However, the caffeine and its derivatives’ structure patterns and coating mechanisms when interacting with metals during copper corrosion inhibition have not been explained in detail by experimental studies. In the present study, the theoretical density functional study (DFT), ab initio MP2, and Monte Carlo simulation approaches explain the problem. The geometrical and quantum chemical parameters of inhibitors were compared under normal and protonated conditions in the gas and aqueous environments. Theoretical studies can accurately determine the molecule’s geometrical parameters and successfully explain the quantum parameters of inhibitors. Molecular dynamics are applied to study the mechanism of interaction between inhibitors and metal surfaces in an explicit water molecule environment. The energy absorption of caffeine and its derivatives on metal surfaces was linear, with quantum parameters calculated from the density functional theory and an ab initio approach. Furthermore, these theoretical study results align with the previously reported experimental studies published by de Souza et al. The inhibition efficiency ranking of studied molecules preventing copper corrosion was caffeine > theobromine > theophylline. This theoretical approach is expected to bridge the gap in designing effective corrosion inhibitors.
Abstrak. Program pengembangan praktikum kimia berbasis kimia komputasi untuk Sekolah Menengah Atas telah dilaksanakan pada kelompok kerja guru kimia mitra (SMAN 1 Narmada dan SMAN 2 Narmada) di Kabuaten Lombok Barat, Indonesia. Kegiatan dilaksanakan dengan dengan mengadopsi langkah-langkah penelitian tindakan yang terdiri dari empat tahapan, yaitu: perencanaan, tindakan, observasi dan evaluasi, dan refleksi. Target yang telah dicapai melalui kegiatan ini adalah 1) Teridentifikasinya konsep-konsep kimia SMA yang esensial yang bisa diajarkan dengan lebih mudah bila melibatkan eksperimen berbasis kimia komputasi sebagai alternatif pengganti praktikum di laboratorium. 2) Teridentifikasinya perangkat lunak yang dapat digunakan oleh guru sebagai alternative pengganti praktikum kimia. 3) Mengukur tingkat motivasi guru sebelum dan setelah kegiatan untuk melaksanakan praktikum kimia di sekolah. 4) Adanya produk berupa buku panduan praktikum kimia SMA berbasis kimia komputasi yang dapat digunakan sebagai alternatif pengganti praktikum di laboratorium. Program ini sangat berguna untuk meningkatkan proses belajar mengajar kimia di sekolah.Kata kuci: kimia komputasi, praktikum kimia, SMA Abstract. Computer-based chemistry practicum development program for high school has been implemented at partner chemistry teacher group (SMAN 1 Narmada and SMAN 2 Narmada) in West Lombok District, Indonesia. The activities were carried out by adopting four stages of action research: planning, action, observation and evaluation, and reflection. This program has resulted in 1) the identification of essential high school chemistry concepts that can be taught more easily if they contain alternative lab-based alternatives in the laboratory. 2) the identification of software that can be used by teachers as an alternative to chemistry lab. 3) the identification of teacher motivation level before and after activities to carry out chemical lab work in school. 4) laboratory manual based on computational chemistry for high school chemistry. This program is very useful to improve the learning process of chemistry in high school.
The effect of macrocycle ring size on the corrosion inhibition efficiency of dibenzo-12-crown-4 (DB12C4), dibenzo-15-crown-5 (DB15C5), dibenzo-18-crown-6 (DB18C6), dibenzo-21-crown-7 (DB21C7) and dibenzo-24-crown-8 (DB24C8) have been elucidated by mean of density functional calculation at B3LYP/6-31G(d) level of theory in the gas and aqueous environment. The quantum chemical parameters including the frontier orbital energies (EHOMO, ELUMO), ionization potential (I), electron affinity (A), the absolute electronegativity (χ), hardness (η), softness (σ), and the fraction of electron transferred (ΔN) are positively correlated to the corrosion inhibition efficiency (IE%) of the studied crown ethers. The calculation results indicate that DB24C8 exhibits the highest corrosion inhibition efficiency, whereas DB12C4 exhibits the lowest corrosion inhibition efficiency. The results of this study will contribute to design crown ethers potential as corrosion inhibitors.
The substituent effects of electron-donating and-withdrawing on the efficiency of corrosion inhibition of benzimidazole and its derivatives have been studied by density functional theory DFT and Møller-Plesset perturbation theory MP2 calculations at aqueous medium. For this investigation, the corrosion inhibition efficiencies of the protonated and non-protonated spesies of benzimidazole and its derivatives were correlated with molecular electronic properties: high occupied molecular orbital (HOMO) and low unoccuppied molecular orbital (LUMO) energies, ionization potential, electron affinity, electronegativity and fraction number of electron transfer. The dipole moment and interaction energy represent the total surface coverage and the strength of the adsorption of inhibitors on the metal surface. Natural bond orbital NBO analysis in term of the second order interaction energies were used to study the contributions of the active sites of inhibitors toward corrosion inhibition performances. The ionization potential of the inhibitors has a strong influence on the efficiency of corrosion inhibitors. It was found that the MP2 method accurately predicted the ionization potential while the DFT failed to mimic the ionization potential of the experimental results. The linear correlation was shown between electronic properties and corrosion inhibition efficiency. Electron donating substituents increase the corrosion inhibition efficiency, whereas electron withdrawing substituents give the opposite effect. The NH 2 substituent contributes highest, whereas NO 2 provides the weakest contribution to the corrosion inhibition efficiency for both non-protonated and protonated species of inhibitors. The second order interaction energy indicated that heteroatom at imidazole position was the main center of electron donating and they received simultaneously significant amount of electron back donation from the metal.
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