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Volume 14, Issue 2, 2007
Chemistry and Chemical Engineering


An Overview of Drug Binding to Human Serum Albumin: Protein Folding and Unfolding
 
        H.A. Tajmir-Riahi (PhD.)

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Human Serum Albumin (HSA) is a principal extracellular protein with a high concentration in blood plasma and a carrier of many drugs to different molecular targets. Drug binding to HSA can alter the protein biophysical and biochemical properties of protein. The structural analysis of human serum albumin complexes, with naturally occurring flavonoids quercetin(antioxidant), kaempferol (antioxidant), delphinidin (antioxidant), AZT (3'-azido-3'-deoxythymidine) (anti-AIDS), aspirin (anti inflammatory), taxol (anticancer), cisplatin (anticancer), atrazine (herbicide), 2,4-D (herbicide), polyamines (biogenic), chlorophyll (antimutagenic), chlorophyllin (antitumor), poly(ethylene glycol) (polymer), vandyl cation and vanadate anion in aqueous solution are reported. Using capillary electrophoresis, FTIR (Fourier transform infrared), UV-Visible and CD (Circular dichroism) spectroscopic methods, the drug binding mode, the binding constant and the effects of drug complexation on protein secondary structure are determined. The concentrations of HSA used were 0.6 to 0.3 mM, while different drug concentrations were 1~$\mu$M to 1 mM. Structural analysis showed drugs are mostly located along the polypeptide chains, with both specific and non-specific interactions. The stability of drug-HSA complexes were in the order: K_VO^2+=1.2\times 10^8M^-1 > K_AZT=1.9 \times 10^6M^-1>K_del=4.7\times 10^5M^-1>K_PEG=4.1\times 10^5M^-1>K_kae=2.6\times 10^5M^-1>K_que=1.4\times 10^5M^-1>K_atrazine=3.5\times 10^4M^-1>K_chlorophyll=2.9\times 10^4M^-1>K_2,4-D=2.5\times 10^4M^-1>K_spermine=1.7\times 10^4M^-1>K_taxol=1.43\times 10^4M^-1>K_aspirin=1.04\times 10^4M^-1>K_chlorophyllin=7.0\times 10^3M^-1>K_VO3^-=6.0\times 10^3M^-1>K_spermidine=5.4\times 10^3M^{-1}>K_putrescine=3.9\times 10^3M^1>K_cisplatin=1.2\times 10^2M^-1. At low drug concentration (1 \muM), protein conformation was not altered (infrared and CD results), while, at high drug content(1 mM), a major reduction of \alpha-helix from 60-55% (free HSA) to 49-40% and an increase of \beta-structure from 22-15% (free HSA) to 33-23% in the drug-protein complexes occurred. These observations indicated that low drug content induced protein stabilization (folding), whereas, at high drug concentration, a partial protein destabilization (unfolding)occurred in these drug-HSA complexes.


Development of Hyphenated Techniques with ETAAS for Determination of Ultra-Traces of Manganese and Vanadium and Their Speciation in Environmental Samples
 
        N. Mashkouri Najafi (PhD.)
  • A.R. Ghasempour [PhD.]
  • R. Sepehri [PhD.]

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The technique of in-situ electrodeposition, coupled with ETAAS (ED ETAAS), has been developed for determination of ultra-traces of manganese and vanadium in environmental samples. The goal is electrodeposition of ultra traces of analyte onto the renewable Pd-coated substrate at optimized conditions of voltage, time of deposition and pH of sample solution prior to measurement by ETAAS. The characteristic masses in the determination of manganese and vanadium are superior to those of conventional ETAAS (Conv-ETAAS) measurements. The detection limits for the interested elements have been improved over those of Conv-ETAAS, with precision of the determinations in the range of 1-3 RSD%. In this work, a technique was developed for speciation of these elements in the environmental samples. Therefore, a solid phase extraction method, coupled with ETAAS or ED-ETAAS, has been investigated for this purpose. The results showed that it could be a fast and sensitive method for manganese and vanadium speciation. A C_18 cartridge, modified with sodium diethyldithiocarbamate (SDDTC), has been employed for the selective separation of manganese (VII) ions from other associated metal ions, especially manganese (II), even at much higher concentrations, followed by ED-ETAAS determination. To separate vanadium (IV) from vanadium (V), a modified membrane disk loaded with disodium ethylenediaminetetraacetic acid (Na_2EDTA) was used to trap both vanadium species, then, the vanadium (IV) ion was eluted selectively and ED ETAAS was used for determination.


Critical Behavior of Iron(III) with a Typical Catecholate Siderophore
 
        I. Abdul Tawab Khan (PhD.)
  • Z.T. Maqsood [PhD.]

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Siderophores are ligands that serve as iron scavengers or iron chelators, which hinder the absorption of iron in the body

    tannic acid is one of them. Since a tannic acid molecule has 8 gallic acid groups, it can bind 1-4 Fe(III) ions, depending upon ligand concentration. pH 3, 4, 5, 8 and 10 were selected for this study. The \lambda max and M:L molar ratio of the complexes varies with pH, as well as with ligand concentration. For low ligand concentration at pH 3, 4 and 5, the maximum absorbance of the complex was found at 650 nm, while, at pH 8 and 10, 500 nm was the \lambda max. For high ligand concentration, pH 550 nm was the \lambda max. Stability constant values of iron(III)tannic acid complexes were measured spectrophotometrically using the mole ratio method, as well as the slope ratio method, potentiometrically. The experimental results of pH titrations were treated by program ``Best''. The $\beta$ values obtained by these methods were compared. Stability constant values were found to be 10^3, 10^8 and 10^16 for ML, M_2L and M_4L, respectively.


Studies on the Activity and Stability of Immobilized Thermophilic Alcohol Dehydrogenase
 
        M. Miroliaei (PhD.)

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A thermophilic alcohol dehydrogenase from Thermoanaerobacter brockii (TBADH) was immobilized by adsorption on Fractosil, methyl-, octyl-, and hexadecyl-Fractosil. As compared to its free form, the thermal stability of the enzyme was enhanced upon immobilization and its pH and temperature optima were altered. The immobilized preparations were used in continuous catalytic operations using a packed-bed reactor. It was demonstrated that the inorganic supports are suitable candidates for operating reactors, especially at high temperatures. Furthermore, larger volumes of the substrates could be converted to a product using enzyme preparations immobilized on the derivatized (hydrophobic) Fractosil, as compared with the unsubstituted form.


Effect of the Attraction Range of Pair Potential on the Thermodynamic Properties of Fluids
 
        G.A. Parsafar (PhD.)
  • I. Ahadzadeh [PhD.]

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Recently, a new potential model has been proposed for the intermolecular interactions of model pure fluids and it was shown that the derived Equation Of State (EOS), based on this potential, can properly predict the thermodynamic properties of these fluids. In addition to simplicity and, to some extent, the realistic form, this potential has a parameter (\alpha) which controls the range of the attraction tail. In the first part of this study, the proposed potential and derived EOS are extended to binary mixtures of model fluids. In a similar manner to that of the pure fluids, the results obtained are consistent with the data available from simulation studies. In the second part, after modification of the model potential through finding a general temperature dependency for \alpha, the modified potential is used to calculate some equilibrium thermodynamic properties of real pure fluids and their binary mixtures. Again, it was found that the modified potential can suitably predict the thermodynamic properties for pure, as well as binary, mixtures of real fluids.


Relaxation Time for Bulk Viscosity of Soft-Sphere and Lennard-Jones Fluids
 
        B. Najafi (PhD.)
  • M. Vahedpour [PhD.]
  • S. Alavi [PhD.]
  • E. Keshavarzi [PhD.]

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The density and temperature dependence of bulk relaxation time is studied for soft-sphere and Lennard-Jones fluids. For soft-sphere fluid, the bulk relaxation time is determined by numerical solution of the Zwanzig Mountain equation, using the data of Hansen and Weis for the radial distribution function. The bulk relaxation time for soft sphere fluids decreases monotonically with density and increases with temperature. The bulk relaxation times of Lennard-Jones fluids are determined by numerical integration of the Zwanzig-Mountain equation with the Matteoli-Mansoori radial distribution function. For isotherms up to T^*<2.1, the density dependence of the relaxation time of Lennard-Jones fluids goes through a minimum at a reduced density of approximately 0.85.


Kinetic Investigation of the Reactions Between Triphenylphosphine, Dialkyl Acetylenedicarboxilates and NH-Acid, such as 5,6-Dimethyl Benzimidazole by the UV Spectrophotometry Technique
 
        S.M. Habibi Khorassani (PhD.)
  • M.T. Maghsoodlou [PhD.]
  • A. Ebrahimi [PhD.]
  • P. Mohammadzadeh [PhD.]
  • M. Zakarianezhad [PhD.]
  • M. Fattahi [PhD.]

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The work was undertaken to carry out kinetic studies of the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of NH-acid, such as 5,6-dimethyl benzimidazole. To determine the kinetic parameters of the reactions, they were monitored by UV spectrophotometery. The second order fits were automatically drawn by the software associated with the UV instrument at an appropriate wavelength. The values of the second order rate constant (k_2) were automatically calculated, using standard equations within the program. At the temperature range studied, the dependence of the second order rate constant (ln k_2) on reciprocal temperature was in agreement with the Arrhenius equation. This provided the relevant plots to calculate the activation energy of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent, the structure of the reactants (different alkyl groups within the dialkyl acetylenedicarboxylates)and, also, the concentration of the reactants on the rate of the reactions.


Designing an Efficient Probabilistic Neural Network for Fault Diagnosis of Nonlinear Processes Operating at Multiple Operating Regions
 
        M. Shahrokhi (PhD.)
  • R. Eslamloueyan [PhD.]
  • R.B. Boozarjomehry [PhD.]

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Neural networks have been used for process fault diagnosis. In this work, the cluster analysis is used to design a structurally optimized Probabilistic Neural Network. This network is called the Clustered-Based Design Probabilistic Neural Network (CBDPNN). The CBDPNN is capable of diagnosing the faults of nonlinear processes operating over several regions. The performance and training status of the proposed CBDPNN is compared to a conventional Multi-Layer Perceptron (MLP) that is trained on the whole operating region. Simulation results indicate that both schemes have the same performance, but, the training of CBDPNN is much easier than the conventional MLP, although it has about 50% more neurons in its hidden layer. Both schemes can reasonably handle an increase in fault deteriorations. However, the training time for CBDPNN is much less than that of MLP. This issue gets severely important when the number of measured variables, along with process faults, increases. Since, for plant-wide fault diagnosis, the reduction in training time is crucial, the advantages of CBDPNN make it more appropriate for fault diagnosis compared to other alternatives for such a case.


Development of a Continuous Kinetic Model for Catalytic Hydrodenitrogenation of Bitumen
 
        F. Khorasheh (Professor)
  • E. Ashuri [PhD.]
  • M.R. Gray [PhD.]

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Catalytic hydrocracking of topped Athabasca bitumen was investigated in a continuous stirred-basket reactor, using a fresh and spent commercial catalyst, as well as in the presence of no catalyst. A continuous lumping model was developed for kinetic analysis of hydrodenitrogenation and hydrocracking reactions. The normalized boiling point was used to describe the reactant mixture as a continuous mixture. The continuous model, with five adjustable parameters, was used to describe hydrocracking reactions. Reactions of nitrogen compounds were described by series reactions, involving cracking to lower molecular weight products, as well as direct denitrogenation. The model was able to accurately predict the weight percent of distillation fractions and their nitrogen content in the products.


Analysis of MEOR Efficiency to Increase Recovery in an Iranian Reservoir
 
        R. Roostaazad (PhD.)
  • D. Biria [PhD.]
  • E. Darouneh [PhD.]
  • H. Izadi [PhD.]

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Rock samples from the Asmary outcrop formation of the Ahwaz oil rich zone with a porosity of 16\% and permeability of 1 md and MIS crude oil with an API value of 42.5 and moderate asphaltene content of 3\%, were used to study the effect of the incubation time and flow rate of the displacing fluid in MEOR operations. Five species of rod shaped, gram positive, thermophile and facultative bacteria were isolated and purified from the crude. Due to the high sweep efficiency prevailing in the core flooding system, the effect of the displacing brine flow rate on the oil recovery efficiency was found not to be significant. On the other hand, a 100\% increase in incubation time from 7 to 14 days resulted in an increase from 3\% to 4\% in the total cumulative production. Application of a cyclic operation was not effective in promoting the efficiency of the MEOR operation, probably due to the stronger effect of flooding on the removal of valuable metabolites, as compared to undesired ones, before the stationary phase of the microbial kinetics. While qualitative measurements did not show a strong change in the water-rock contact angle, more than a 4-fold increase in capillary number occurred after microbial treatment, implying that reduction of interfacial tension was the stronger mechanism of oil recovery in this work.


An Investigation into the Structure and Thermal Properties of Lead Hydroxide
 
        S.A.A. Sajadi (PhD.)
  • A.A. Alamolhoda [PhD.]
  • S.J. Hashemian [PhD.]
  • Md. Jobair Bin Alam [PhD.]

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The compound, lead hydroxide Pb_6O_4(OH)_4, was prepared by a method used for the first time in the authors laboratory. The compound was identified by XRD and it's purity was determined by analytical methods (100%). The thermal characteristics of this compound were investigated by using a thermogravimetry (TGA). This compound was found to be stable at room temperature and at 160\degree C will decompose completely to produce lead (II) oxide.


Efficiency of Copper Bioleaching of Two Mesophilic and Thermophilic Bacteria Isolated from Chalcopyrite Concentrate of Kerman-Yazd Regions in Iran
 
        S. Yaghmaei (PhD.)
  • S.M. Mousavi [PhD.]
  • M. Vossoughi [PhD.]

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A mesophilic iron oxidizing bacterium, Acidithiobacillus ferrooxidans, has been isolated (33\degree C) from a typical chalcopyrite copperconcentrate of the Sarcheshmeh Copper Mine in the region of Kerman located in the south of Iran. In addition, a thermophilic iron oxidizing bacterium, Sulfobacillus spp., has been isolated (60\degree C) from the Kooshk Lead and Zinc Mine near the city of Yazd in the mid-west region of Iran. The variation of pH, ferrous and ferric concentration and cell growth on the time and effects of some factors, such as temperature and initial ferrous concentration, on the bioleaching of chalcopyrite concentrate obtained from Sarcheshmeh Copper Mine, were investigated. Bioleaching experiments were carried out batch wise using 5% (v/v) inoculum and 2% (w/v) of concentrate. The control tests were conducted using the sterilized concentrate and without the inoculum. The results obtained showed the importance of the influence of all the tested variables on the efficiency of the copper bioleaching. The effects of temperature and initial ferrous iron concentration were found to be considerable. Maximum copper recovery was obtained when the thermophilic culture had been used. Copper dissolution reached up to 80\% using Sulfobacillus spp., while this value was 72% when Acidithiobacillus ferrooxidans was used at pH = 1.5. The initial Fe^2+ concentrations for the tested mesophilic and thermophilic strains were 7 and 9 g/L, respectively. The test duration was 30 days.


Investigation into Some Parameters A ecting Pectin Gel Quality
 
        I. Alemzadeh (PhD.)
  • B. Ebrahimi [PhD.]
  • S.K. Seifkordi [PhD.]

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In this research, gel production from the extracted pectin gel of shahroud sugar beet pulp has been investigated. The pectin extractions were performed in a cold alkaline solution and a hot acid solution, respectively. The e ects of di erent parameters, such as percent of sugar, pectin concentration, calcium content and quantity of peroxidase enzyme, hardness and content of water absorbed by the gel, were studied. Optimum conditions for production of favorable gel, from extracted pectin in this research are, as follows: Percent of sugar (glucose): 15%, peroxidase enzyme content: (pectin unit) 170 pu g of pectin , pectin concentration (if only gel water uptake is important): 10%, pectin content (if only strength and hardness of gel are important): 15%, calcium content (if only gel water uptake is important): 60 mg CaCl2 g of pectin and calcium content (if only gel uptake strength is important): 80 mg CaCl2 g of pectin . Simultaneous application of peroxidase enzyme and hydrogen peroxide as oxidizing agents, besides calcium, glucose and suitable content of LM (Low Methoxyl) pectin, resulted in interesting properties and a decrease in gel formation time from \5 minutes - 24 hours", to \15 - 20 seconds" and a favorable increase in gel strength.