Scientia Iranica
Volume:20 Issue: 3, 2013

Any molecular dynamical calculation requires a precise knowledge of interaction potential as an input. In an appropriate form, such that the potential, with respect to the coordinates, can be evaluated easily and accurately at arbitrary geometries (in our study parameters for geometry are image and image), a good potential energy expression can offer the exact intermolecular behavior of systems. There are many methods to create mathematical expressions for the potential energy. In this study for the first time, we utilized the Multi-gene Genetic Programming (MGGP) method to generate a potential energy model for the He–F2 system. The MGGP method is one of the most powerful methods used for non-linear regression problems. A dataset of size 714 created by the SAPT 2008 program is used to generate models of MGGP. The results obtained show the power of MGGP for producing an efficient nonlinear regression model, in terms of accuracy and complexity.

An efficient one-pot three-component condensation of aldehydes, thiols and malononitrile has been developed in the presence of calcium oxide nanoparticles. Highly substituted pyridines as privileged medicinal scaffolds have been efficiently prepared via carbon–carbon and carbon–heteroatom bond formation. This method provides a novel and improved approach for the synthesis of 2-amino-4-aryl-3,5-dicyano-6-sulfanylpyridines in terms of excellent yields, short reaction times, reusability and little catalyst loading.

A one-pot room-temperature procedure is developed for an efficient reaction of 2-aminothiophenols with 2-bromoalkanoates in ionic liquid [bmim][NO3] to obtain high yields of different benzothiazin-3-ones under base- and additive-free conditions. Products are easily separated from the reaction mixtures by Et2O extraction. Notably, condensation of the extract under reduced pressure results in precipitation of the products and, consequently, no chromatographic separation is needed. The ionic liquid can be recovered and successfully recycled into subsequent reactions without significant loss of activity.

A novel acidic ionic liquid (AIL), 3-(2-carboxybenzoyl)-1-methyl-1H-imidazol-3-ium chloride {[Cbmim]Cl}, was synthesized and used as an efficient and green catalyst for the Biginelli reaction under solvent-free conditions. The present study aims to develop an improved synthesis procedure, based on a one-pot Biginelli condensation reaction, by using different aldehydes, image-dicarbonyl compounds, and urea or thiourea. This method, in comparison with the classical Biginelli reaction, has several advantages, including high yield, short reaction time and experimental simplicity.

The effects of ascorbic acid concentration in pomegranate juice as an antioxidant and its bi-functional role in Fenton reaction was investigated. Hydroxyl radical (OH.) produced through Fenton reaction plays a major role in the formation of DNA oxidative damage. The study of DNA damage by Fenton reaction was performed using Glassy Carbon Electrode (GCE). The damaged DNA is adsorbed on the electrochemically modified GCE, and results in oxidative peaks corresponding to the oxidized adenine and guanine residues in DNA. The effects of hydroxyl-radical scavenger (glucose), Fe2+ as reactant and EDTA as iron chelator on the DNA damage were also investigated. The proposed electrochemical method can be used for the estimation of DNA oxidative damage from a new point of view.

Pyrazolo[1,2-a][1,2,4]triazole-1,3-dione derivatives were synthesized via a three component reaction of arylaldehydes, 4-phenylurazole and malononitrile in the presence of a catalytic amount of 2-hydroxyethylammonium formate and 2-hydroxyethylammonium acetate as effective mild basic ionic liquids, without using any additional co-catalyst, under solvent-free conditions at room temperature in good yields. Ionic liquids as catalysts were recovered and reused. In addition, the preparation of 2-amino-3-cyano-5,10-dioxo-4-phenyl-5,10-dihydro-4H-benzo[g]chromene derivatives from the reaction of arylaldehydes, malononitrile and 2-hydroxy-1,4-dihydronaphthalene-1,4-dione under solvent-free conditions at ambient temperature in the presence of mentioned catalysts is reported.

A simple and efficient method for the synthesis of spiro[indoline-3, 9′-xanthene]trione derivatives has been achieved through the condensation reaction of isatins and two moles of dimedone or 1,3-cyclohexanedione, under solvent-free conditions, in the presence of SBA-15-Pr–SO3H as an efficient heterogeneous nano solid acid catalyst. The features of this procedure are short reaction times, good yields, solvent-free reaction conditions, and simple workup. The absence of solvent allows avoiding the use of toxic organic solvents, which makes this reaction safe and environmentally friendly. Furthermore, the use of SBA-15-Pr–SO3H with a pore size of 6 nm has the advantage of being a nano-reactor in whose nano-pores the reaction proceeds easily.

Nano- SnCl4⋅SiO2 as a solid Lewis acid has been synthesized by the reaction of nano- SiO2 and SnCl4. The structure characterization of this acid has been studied by FT-IR (ATR), XRD and SEM. Nano- SnCl4⋅SiO2 has been found to be an extremely efficient catalyst for the preparation of 2,4,5-trisubstituted imidazoles via three-component reactions of benzil, aldehydes and ammonium acetate under mild conditions. This process was simple and environmentally benign with high to excellent yields. Furthermore, the catalyst could be recovered conveniently and reused for at least three times.

Nano-ordered MCM-41 anchored sulfonic acid (MCM-41- SO3H) was used as an efficient heterogeneous catalyst for the synthesis of Schiff bases by the reaction of different aryl/alkyl aldehydes or ketones with primary amines at room temperature with high to excellent yields. This mesoporous catalyst can be reused at least four times without significant loss to its catalytic potential.

In this study, 1,4-diazabicyclo[2.2.2] octane (DABCO) tribromide was immobilized on silica support by using 3-chloro propyl trimethoxy silane to obtain a silica-supported DABCO tribromide reagent. The synthesized reagent was characterized with elemental analysis, FT–IR spectroscopy, and thermo-gravimetric analysis (TGA). This reagent has been applied in the conversion of alcohol to corresponding carbonyl compounds. Alcohol oxidation reactions yield in 52–95%, and the reagent may be recycled five times with further bromine treatment.

In this paper, a new and convenient method is introduced for the oxidation of a variety of Hantzsch 1, 4-dihydropyridine derivatives to their corresponding pyridine compounds using guanidinium nitrate and silica sulfuric acid. The reactions were carried out in dichloromethane at room temperature and the products were isolated at high to excellent yields.

In recent years there has been potential increase in the use of alkaline protease as industrial catalysts. Many major industrial and commercial applications, such as food and textile industries, and medical diagnoses, are highly dependent on the protease enzyme. In the cell immobilization technique, the free movement of microorganisms is restricted in the process, and a continuous system of fermentation can be used. In the present work, this technique has been used for alkaline protease production using different carriers, such as chitosan, corn cob and corn tassel. Enzyme activity before immobilization (72 h) was 78.3 U/ml. Corn cob, with 65% immobilization capacity and the highest enzyme activity, was selected as the best carrier. After immobilization on the corn cob enzyme, activity was obtained (119.67 U/ml).

This work is concerned with the monitoring of ultrasound effects on inhibition, as well as the reversible kinetics modeling of asphaltene flocculation in toluene-n-alkane systems, which has been rarely reported in the literature. A crude oil sample was exposed to ultrasound waves, and then the colloidal structural evolutions of flocculated asphaltene particles induced by addition of n-alkane were studied, using a confocal microscopy. Observations confirmed that radiation of ultrasound can change the irreversibility of asphaltene flocculation in crude oil. To interpret the kinetics of asphaltene flock aggregation, the Smoluchowski model was used, and the time dependent size distribution of asphaltene flocks was predicted. Fractal analysis was applied and the parameters of the kinetic model were determined. The values for the regressed parameters of the kinetic model show that for sonicated oil, the formation coefficient decreases, while the disintegration coefficient did not considerably change. The reason might be that sonication prevents flocks from aggregating rather than disintegrating them into smaller flocks. It might be the reason for its lingering effect on flocculation. This work illustrates the successful application of the Smoluchowski model for predicting the kinetics of asphaltene flocks under the influence of ultrasonic radiation for the entire range of reversible flocculation processes.

In this study, Response Surface Methodology (RSM) and Artificial Neural Network (ANN) predictive models are developed, based on experimental data of the Oxidative Coupling of Methane (OCM) over Na–W–Mn/ SiO2 at 0.4 MPa, which was obtained in an isothermal fixed bed reactor. Results show that the simulation and prediction accuracy of ANN was apparently higher compared to RSM. Thus, the Hybrid Genetic Algorithm (HGA), based on developed ANN models, was used for simultaneous maximization of CH4 conversion and C2+ selectivity. The pareto optimal solutions show that at a reaction temperature of 987 K, feed GHSV of 15790 h−1, diluents amounts of 20 mole%, and methane to oxygen molar ratio of 3.5, the maximum C2+ yield obtained from ANN-HGA was 23.91% (CH4 conversion of 34.6% and C2+ selectivity of 69%), as compared to 22.81% from the experimental measurements (CH4 conversion of 34.0% and C2+ selectivity of 67.1%). The predicted error in optimum yield by ANN-HGA was 4.81%, suggesting that the combination of ANN models with the hybrid genetic algorithm could be used to find a suitable operating condition for the OCM process at elevated pressures.

Reliable relative permeability curves of oil–gas systems are important for successful simulation and modeling of gas injection, especially when the miscibility condition approaches. In this work, the relative permeability of a CO2-light oil system has been measured under different conditions, using the Civan and Donaldson (1989) method. Dolomite and sandstone core samples were used in the experiments. The minimum miscibility pressure was calculated using an empirical correlation, as well as slim-tube simulation. Due to some controversial assumptions of the Civan and Donaldson method, such as immiscible and incompressible displacement, history matching was used for predicting the reliable relative permeability of each phase at near miscible conditions. The Civan and Donaldson method was used to predict the relative permeabilities as the initial guesses for the history matching. We found that the Civan and Donaldson method underestimates oil relative permeability. Moreover, the effect of near miscibility on the gas phase relative permeability curve was stronger and the intersection point of the oil and gas phase relative permeability curves occurred at lower gas phase saturations. The results are helpful for understanding near miscible relative permeability behavior and provide knowledge on fluid flow at low IFT conditions during gas injection projects.