نشریه پژوهش های شیمی
سال چهارم شماره 2 (پیاپی 7، پاییز و زمستان 1400)

Spectrophotometer is one of the instruments which is vastly used in variety of chemical and biochemical tests in laboratories. Performance qualification and reproducibility of this instrument can affect the different tests results. Validation or qualification of an instrument is a process during which suitable performance of the device and its compliance with intended purpose is proven by documentation. Calibration of a device is one of the most important parts of its qualification.Calibration of spectrophotometer consists of some steps including the evaluation of accuracy, precision and likely error of the instrument. This article describes the calibration of Spectrophotometer using the control of wavelengths, absorbance, and limit of stray light and equality of cuvettes. The most important parameters in the calibration of the visible-ultraviolet spectrophotometer are the control of the absorbance and also the control of the wavelength generated by the spectrophotometer. Control is done by cells or reference materials and comparing between the values created by the device and true values.

In this work, the density functional theory is used to study the kinetic-isotope effect on the catalytic reaction on the S-substrate of Escherichia coli Glyoxalase I. The quantum mechanical cluster approach was used to model the enzyme’s active site based on its crystal structure. Energies of the stationary structure along the reaction path were optimized, and their energies were calculated. The effect of the solvent on the energy profiles was calculated by the CPCM model. Results show that replacing H1 (hydrogen atom attached to the chiral carbon of substrate) with deuterium increases the activation energy of the reaction and gives a value greater than 2 for kH/kD. This result confirms that breaking the H1-C1 happens in the rate-determining step of the reaction. Also, results showed that replacing the H2 atom (hydrogen atom of the alcohol group of the substrate) gives a kH/kD less than 1.0 and introduces a reverse isotopic effect to the reaction.

In this work, a nanosensor for Cu(II) and ascorbic acid (AA) based on anti-aggregation and aggregation mechanisms of gold is proposed. In the first part, a selective method for Cu2+ based on the anti-aggregation process of gold nanoparticles by neocuproine (NC) is proposed. In the presence of a constant concentration of NC, Cu(II) decreases the aggregation of gold nanoparticles by forming a four-dentate complex with NC. The anti-aggregation process of gold nanoparticles is performed in the range of 5-500 nM of Cu(II). A value of detection limit of 1 nM is estimated for Cu(II). This is lower than the allowable levels of Cu(II) in drinking water. The results revealed that the proposed method shows good selectivity for Cu(II) compared to other ions to decrease the aggregation of gold nanoparticles. The proposed method for Cu(II) is employed in drinking water samples. In the second part, the anti-aggregation process of gold nanoparticles is used for AA. AA as a competitive ligand with NC for Cu(II) enters the anti-aggregation process of gold nanoparticles and can react with it by removing Cu(II) from the NC- Cu(II) complex. During this, AA is oxidized and Cu(II) is converted to Cu(I). Rereleasing of NC from the complex causes re-aggregation of nanoparticles. The aggregation is performed in the range of 9-75 nM of AA. The result of this competition was to measure AA with high selectivity and a detection limit of 1.8 nM. This method is used to measure AA in a sample of vitamin C tablet.

Easy and selective separation of lithium ions from other self-accompanying ions in nature such as magnesium, it is still a challenge for researchers due to their similar chemical properties. Here, the simple in situ solvent extraction method (ISFME) derived from the homogeneous liquid-liquid extraction method (HLLME) using ionic liquids as the organic phase is described. The organic phase containing ionic liquid of 1-hexyl-3-methylimidazolium hexafluorophosphate [C6mim][PF6] and a phosphorous ligand (extracting agent) called n-tributyl phosphate (n-TBP). To optimize lithium ion extraction conditions, analytical parameters such as pH of the sample solution, amount of ionic liquid in the organic phase, ratio of organic to aqueous phase (O/A), amount of hexafluorophosphate anion as counter-ion and centrifugation conditions for phase separation were studied and optimized. Under the best conditions, the method is capable to extraction 95% of lithium ions in the presence of very high magnesium concentrations (about 100 times the concentration of lithium ions). The mechanism of lithium ion extraction by ionic liquid as well as the metal-ligand extraction ratio (1:1) have been investigated using conventional techniques such as ultraviolet spectroscopy (UV-Vis) and Fourier Transform Infrared spectroscopy (FTIR). It is also the method was able to determination of lithium ions in different real samples, successfully.

Three-component reaction between arylglyoxals, acetylacetone and pyrrole in the presence of catalytic amounts of ZnCl2 in ethanol as the solvent lead to the synthesis of new symmetrical two-substituted pyrrole derivatives in high yields. All of the products of this reaction were solid and separated and purified by simple filtration and washing with diethyl ether and there was not need to time-consuming and laborious chromatography methods for purification of the products. When the reaction was conducted in the presence of a primary amine, the four-component reaction between arylglyoxal, pyrrole, acetylacetone and the primary amine, symmetrical terpyrrole derivatives were obtained in low yields in the cases of 2-naphthylglyoxal and 4-chlorophenylglyoxal; but further reactions lead to complex mixture of products and the isolation of product from the reaction mixture was impossible. All the products isolated from the above reactions were new and their structures were deduced from their 1H and 13C NMR and IR spectral data.

This paper aims to study the modified zeolite Y using different dealumination methods and the effect of each of these methods on the structural framework of zeolite. The dealumination is performed by EDTA solution (acidic form), ammonium chloride (NH4Cl), and hydrochloric acid (HCl) solution. To investigate the effect of the dealumination process on the stability of the structures modified samples are studied using X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersion X-ray (EDX). By comparing the three methods, it can be concluded that EDTA is the most suitable method because it is not only preserved the structure but also removed the extra-framework aluminum and increases the Si/Al ratio. In addition, in the hydrochloric acid treatment, the extra-framework aluminum is also removed, but in the calcination process (NH4Cl), the extra-framework aluminum is still present, and therefore, the Si/Al ratio is lower than the previous two methods.

A new organic compound, namely dihydropyrimido [4,5-b][1,6] naphthyridine-2,4,‌6, 8(1H,3H,7H,9H)-tetraones with amino acid moiety (DHPN) was synthesized and characterized by 1H, 13C Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy experiments. DHPN was investigated for the first time as a green inhibitor of mild steel (A105) corrosion in acidic (0.1, 0.5 mol L-1 H2SO4 and HCl) solutions using potentiodynamic polarization (PDP) technique. The inhibition concentration used range from of 1.86-17.16 mg L-1. The results showed that, the inhibition efficiency increased with an increased in the concentration of DHPN and, reached a maximum value of 78% at 5.15 mg L-1. This can be explained by strong adsorption of inhibitor molecules on the metal surface, which blocks more corrosion active sites. The polarization curves demonstrated that, this compound act as a mixed type inhibitor and, do not modify the reaction mechanism of the corrosion process. The adsorption of the DHPN molecule on the surface of mild steel was found to obey the Langmuir adsorption isotherm.

Excessive increase in industrial activities in recent years has led to the uncontrolled entry of industrial effluents containing large amounts of heavy metals into the environment and can have irreversible effects on human, animal and plant health. In this project, the preparation of magnetic hybrid nanomaterial (Fe3O4@SiO2-PMT) was presented by a simple method and used as an adsorbent to remove Cu2+ and Ni2+ ions. The maximum removal efficiency was 91% for copper and 96% for nickel. The highest removal efficiencies for copper and nickel were obtained at pH=7, a concentration of 0.05 g of adsorbent and a duration of 90 minutes. The desorption results showed that about 90% of the nanomaterials were recycled and significant reduction in nanoparticle adsorption capacity was not observed. The leaching test also showed good stability of the prepared adsorbent under acidic conditions, because a small amount of iron had entered the solvent after 72 hours. Advantages of this method include high removal ability, low cost, reusability of the adsorbent, and the easy separation of the adsorbent.

In this study, the reaction mechanism between dimethyl acetylene, dicarboxylate and triphenylphosphine in the presence of 1-aminoanthraquinone as NH-acid was examined theoretically using the method B3lyp / 6-311++G(d, p):HF/6-31G. According to the theoretical results, a logical mechanism for the reaction was proposed and the most desirable reaction path for the product was predicted. In the present work, the reaction between a kinetic study, including determining the preferred kinetic path, investigation of intermediate structures and transition states in the reaction path, determination of the kinetic and thermodynamic stability of products, recognition of rate-determining step, calculation of the reaction rate, and finally, identifying and confirming the reaction mechanism are the issues that have been first explored for this reaction. To check the effect of solvent on the potential energy surfaces, condensed phase calculations in dichloroethane were carried out with the polarizable continuum model (PCM). Finally, in order to better understand molecular interactions, the natural graft orbital method (NBO) was used.

In this study, Hydrodesulfurization (HDS) process was used to remove sulfur compounds from refined petroleum products such as naphtha. 2D MoS2/G nanocomposite and nano MoS2 catalysts were prepared via ball-milling system and characterized by XRD, Raman spectroscopy, XPS, SEM, TEM, STEM, ICP, BET surface, TPR and NH3-TPD techniques. During the HDS process, the performance of the synthesized catalysts was investigated and then the optimal HDS catalyst was selected and evaluated to mitigate the operating conditions. The results indicated that 2D MoS2/G nanocomposite catalyst reduced the total sulfur content in naphtha from 2500 ppm to 0 ppm in facile operating conditions, which maintained a higher conversion rate compared to industrial catalysts in milder operating conditions. Also, the effect of surface area, pore diameter and acidity of nanocatalysts on the performance of hydrogen desulfurization activity has been investigated. The results showed that the higher the surface area, porosity and nanocatalyst acidity, the better the efficiency of hydrogen desulfurization process.

In this work, graphene–magnetic palladium nanohybrid catalyst (G@Fe3O4@SiO2@Im-Pd) has been fabricated via a facile approach, and be developed as a highly active and stable photocatalyst for degradation of 2,4- dichlorophenol (2,4-DCP) under visible light irradiation. The influence of reaction parameters such as time, the dependence of degradation to the presence of the catalyst and light irradiation, pH, and also the reusability of the photocatalyst on the degradation yield have been investigated. The best yield for degradation of 2,4-dichlorophenol was obtained at acidic pH under visible light irradiation. The presence of Fe3O4 nanoparticles in the composite gives it a magnetic property and therefore can be easily recovered from the reaction mixture using an external magnet and used repeatedly. The use of recycled catalyst after five recycling times did not show a significant reduction in activity. Also, Magnetic separation is an environmentally friendly method for the separation and recovery of catalysts, since it minimizes the use of solvents, reduces operation time, minimizes catalyst loss by preventing mass loss and oxidation.

In the present study, the electrochemical behavior of mefenamic acid in the presence of 2-nitropropane (2-NP) was studied in buffer solution /ethanol ( 70:30 v/v) in pH=10 by using of cyclic voltammetry and controlled-potential-coulometry techniques. In this situation mefenamic acid (MFA) was used as electrophile in the synthesis of nitropropane derivative based on the mefenamic acid. The results showed that the 2-nitropropane (2-NP) group in the solution attacked the intermediate resulting from mefenamic acid oxidation and resulted in the formation of 2 ((3,2-dimethyl-6- (2-nitropropane-2-yl) phenyl) amino) benzoic acid (MNP) as a new product via michael addition reaction. On the other hand, the electrochemical behavior of this new produce (MNP) and its dye properties were investigated and confirmed as a textile acid dye. Our results show that this new product can be used as an acidic color in dyeing fabrics. Also, two different crystals of 2-nitropropane dimer were obtained and identified by electrochemical oxidation of 2-nitropropane (2-NP) in the absence and presence of mefnamic acid (MFA).