JOURNAL OF THE IRANIAN CHEMICAL SOCIETY(JICS)
Year:2009 | Volume:6 | Issue:2|Papers Count:27

The rate of an enzymatic reaction may be changed by a moderator. Usually, the effect is to reduce the rate, and this is called inhibition. Sometimes the rate of enzyme reaction is raised, and this is called activation. Not only enzyme activation is subject of a less detailed presentation, but also enzyme inhibition and activation are very often discussed independently in enzymology. I attempt to introduce a general model of enzyme inhibition and activation to allow one to interpret inhibition and activation from a mechanistic or physical perspective using the significance of cooperativity as a new approach. The magnitude of interaction between substrate and inhibitor binding sites is given by the a parameter and the magnitude of increasing catalytic reaction constant is given by the b parameter, which both parameter values characterize the type of inhibition and activation. The moderation of mushroom tyrosinse is described by application of the model as a typical.

Two distinct approaches are used to derive a unique and exact analytical expression for the heat of vaporization with respect to the nanocavity energy formation and the molecular hard-core diameter. This expression provides a new method to compare different models of cavity formation in the liquids as well as to predict the effective molecular hard-core diameter at different temperatures and pressures. The effective hard-core diameters and cavity formation energies of liquid Ar, Xe and CH4 are calculated at various temperatures and pressures using different cavity formation models and they are compared. It is found that the effective hard-core diameter generally decreases with increase of temperature as expected and it increases with increase of pressure.

The oxidation of glycine and alanine by bis (dihydrogen-tellurto) argentite (III) ion was studied by stopped-flow spectrophotometery. The reaction is of first order in Ag (III) complex and has less than unit order in glycine and alanine. A plausible mechanism was proposed form the kinetic studies. The rate equations derived from mechanism found to explain all experimental phenomena. The activation parameters with respect to the rate determining step of the mechanism were calculated.

Efficient synthesis of 2-oxazolines by the reaction of nitriles with b-aminoalcohols using InCl3 as catalyst under reflux conditions is reported. This catalyst can be successfully applied to the chemoselective conversion of dicyanobenzenes to their corresponding mono- and bis-oxazolines. The application of ultrasonic and microwave irradiation improved the yields and reduced the reaction times. Another advantage of this catalytic system is its ability to carry out large-scale reactions under ultrasonic and MW irradiations. Alkylnitriles such as acetonitrile was also converted to its corresponding 2-methyloxazoline in the presence of catalytic amounts of InCl3.

A series of metal complexes of Zn(II) have been synthesized with newly synthesized biologically active 1,2,4-triazole Schiff bases derived from the condensation of 3-substituted-4-amino-5-mercapto-1,2,4-triazole with 8-formyl-7-hydroxy-4- methylcoumarin. The structure of the complexes has been proposed in the light of elemental analyses, spectroscopic data (IR, UV-Vis, 1H NMR and FAB-mass), thermal studies. Electrochemical study of the complexes is also reported. All the complexes are soluble to limited extent in common organic solvents but soluble to larger extent in DMF and DMSO and are non-electrolytes in these two solvent. All these Schiff bases and their complexes have also been screened for their antibacterial (Escherichia. coli, S. aureus, S. pyogenes, P. aeruginosa and Salmonella typhi) and antifungal activities (Aspergillus niger, Aspergillus flavus and cladosporium) by MIC method. The brine shrimp bioassay was also carried out to study their in vitro cytotoxic properties.

Three novel Schiff base adducts [SnMe2Cl2(Hcdacacen)] (1), [SnBu2Cl2(Hcdacacen)2] (2) and [SnPh2Cl2(Hcdacacen)2] (3) have been synthesized by reaction of SnR2Cl2 (R=Me, Bu and Ph) with a new Schiff base ligand methyl-2-[2-(acetylacetoneimino)ethylamino]-1-cyclopentene-1-dithiocarboxylate (Hcdacacen). The ligand and complexes were characterized by elemental analysis and spectroscopic studies. Spectroscopic data suggest that Hcdacacen exists predominately in ketamine tautomeric form and in all complexes acts as a monodentate neutral ligand coordinates to the metal through oxygen atom, while the sulfur atom and imine nitrogen is not involved in the coordination to the tin.

Metronidazole (MTZ) and tinidazole (TNZ) belong to nitroimidazole group of drugs used to treat infections such as ameobiasis, giardiasis and trichomoniasis. The kinetics of oxidation of MTZ and TNZ with N-bromosuccinimide (NBS) in perchloric acid medium has been investigated at 308 K. A 1:1 stoichiometry has been observed in both MTZ and TNZ cases. The oxidation reactions of both MTZ and TNZ follow the same rate law, -d[NBS]/dt = [NBS][Sub][H+]. However, in case of MTZ, at higher concentrations of H+ (0.006-0.01 mol dm-3), the rate law obtained is -d[NBS]/dt=[NBS][MTZ][H+]-1. Accelerating effect of [Cl-] and retardation of the added succinimide on the reaction rate have been observed in the case of MTZ. The reactions were examined with reference to changes in concentration of added neutral salt, ionic strength and dielectric permittivity of the medium. The overall activation parameters have been evaluated from the Arrhenius plot. The reactive oxidizing species of NBS have been determined. The main oxidation products were identified by IR and 1H NMR spectral analyses. The observed results have been explained by plausible mechanisms and the relative rate laws have been deduced.

Sodium hypochlorite, a cheap and readily available compound, when supported on silica gel can selectively oxidize benzylic and allylic alcohols to their carbonyl compounds in the presence of catalytic amount of DMSO.

Ternary oxides have been used as effective photocatalyst for carrying out number of chemical reactions. Method of preparation has major effect on the performance of these mixed oxide catalysts. In the present work, cerium iron oxide catalyst was synthesized using co-precipitation method and specific heating cycle. Synthesized catalyst was characterized using X-ray diffraction patterns. Photocatalytic degradation on gentian violet dye was observed using this catalyst and progress of the reaction was monitored spectrophotometrically. The effect of variation of different parameters like concentrati on of gentian violet, pH, amount of semiconductor and light intensity was also studied. A tentative mechanism for the photocatalytic bleaching of gentian violet has been proposed.

A series of mononuclear salen type copper (II) complexes, [CuLn] (n=1-4), and their corresponding tetrahydrosalen complexes, [CuH2Ln] (n=1,2) were prepared by the reaction of the N2O2 ligands with Cu (II) ion in ethanol, where H2L1=N,Nbis (3,5-di-tert-butylsalicylidene)-2,2-dimethyle-1,3-diaminopropan, H2L2 = N,N-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminopropane, H2L3=N,N-bis(4-methoxysalicylidene)-2,2-dimethyle-1,3-diaminopropan; H2L4=N,N-bis(4-methoxysalicylidene)-1,2-diaminopropane, H2[H2L1]=N,N-bis(2-hydroxyl-3,5-di-tert-butylphenyl)-2,2-dimethyle-1,3-diaminopropan and H2[H2L2]=N,Nbis(2-hydroxyl-3,5-di-tert-butylphenyl)-1,2-diaminopropane. The prepared ligands and complexes were characterized by the combination of IR, UV-Vis, NMR (as far as possible), elemental and thermal analyses. All prepared compounds were also evaluated for their antibacterial (Escherichia coli and Staphylococcus aureus) and antifungal (Candida albicans) activities by the disc diffusion method. The compounds were found have no remarkable antimicrobial activities.

Manganese (II), cobalt (II), nickel (II) and copper (II) complexes with 1,5,11,15-tetraaza-21,22-dioxo-tricyclo [19,3,1,I6,10]- 5,10,15-20-dicosatetraene (L), as a new macrocyclicligand, have been synthesized with and characterized by elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, IR, electronic and EPR spectral studies. The molar conductance measurements of the complexes in DMF correspond to non-electrolytic nature of Mn (II), Co (II) and Cu (II) complexes, while showing a 1:2 electrolyte for thew Ni (II) complexe. Thus, these complexes may be formulated as [M(L)X2] and [Ni(L)]X2 (where M=Mn (II), Co (II) and Cu (II) and X=Cl- and NO3-). On the basis of IR, electronic and EPR spectral studies, an octahedral geometry has been assigned for Mn(II) and Co(II), a square planar for Ni(II) and tetragonal for Cu(II) complexes. In vitro ligand and its metal complexes were also screened against the growth of some fungal and bacterial species in order to assess their antimicrobial properties.

A one-pot four-component reaction of aldehydes, ethyl acetoacetate/5,5-dimethyl-1,3-cyclohexanedione, ethyl acetoacetate and ammonium acetate in the presence of 10 mol% of ZnO as a heterogeneous catalyst for the synthesis of corresponding 1,4-dihydropyridine and polyhydroquinoline derivatives via the Hantzsch condensation is described. The present methodology offers several advantages such as simple procedure, excellent yields, and short reaction time.

A series of N-[2-(2-naphthyl)ethyl]piperazinyl quinolones containing a carbonyl related functional groups (oxo- or oxyimino-) on the ethyl spacer was synthesized and evaluated for antibacterial activity. The synthesis of N-[2-(2-naphthyl)ethyl]piperazinyl quinolones was achieved through the versatile and efficient synthetic route that involved reaction of piperazinyl quinolones with appropriate α-bromoketone or α-bromooxime derivatives. The structures of new compounds were confirmed by elemental analysis, IR and NMR spectra. Antibacterial data indicated that some of the new N-[2-(2-naphthyl)ethyl]piperazinyl quinolones showed good antibacterial activity and modification of the position 8 and N-1 substituent on quinolone ring, and ethyl spacer functionality produced significant changes in activity against Gram-positive and Gram-negative bacteria.

A high-performance liquid chromatographic (HPLC) method and a cyclodextrin-modified micellar electrokinetic chromatographic (CD-MEKC) method were developed to separate and determine oleanolic acid (OA) and ursolic acid (UA) in Prunella vulgaris. HPLC separations were carried out on a Hedera ODS C18 column with methanol -H2O- acetic acid (85:15:0.3, v/v/v) as mobile phase at a flow-rate of 0.8 ml min-1. CD-MEKC analysis was performed on a CL1030 capillary electrophoresis system with a 6% (v/v) methanol solution (pH=9.0) containing 10 mM disodium tetraborate, 10 mM sodium dihydrogen phosphate, 50 mM sodium dodecylsulfate (SDS), 15 mM 2-hydroxypropyl-b-cyclodextrin (2-HP-b-CD) as background electrolyte. The analytical results of HPLC and CD-MEKC were compared with each other. CD-MEKC has better analytical efficiency for two components, and the analytical time (15 min) was shorter than that of HPLC (35 min).

In the framework of the Tsallis statistical mechanics, we study the change of the population of states when the parameter q is varied, for some model systems; the results show that the difference between predictions of the Boltzmann-Gibbs and Tsallis statistics can be much smaller than the precision of any existing experiment. Also, the relation between privilege of rare and frequent events and the value of q is restudied. It is shown that positive q privilege frequent and negative q privilege rare events. Finally, the convergence criteria of the partition function of some simple model systems, in the framework of Tsallis statistical mechanics, is studied. Based on this study, we conjecture that q£1, in the thermodynamic limit.

The present paper firstly announces the possibility of using a Schiff base as an acid-base indicator. This surprising phenomenon can be considered as an interest due to the fact that Schiff bases are usually unstable in solutions and definitely undergo hydrolysis. It was found that such a specific observation depends merely upon the chemical structure and type of the substitute of amine that reacts with aldehyde to give the Schiff base. The latter reagent 4[(4-dimethylamino-benzylidene)-amino]-benzene sulfonamide was synthesized from the condensation of sulfanilamide with p-dimethylaminobenzaldehyde. The reagent solution shows a reproducible change in its color due to the addition of acid and base. A UV-Vis spectroscopic characterization and acid-base equilibrium study of the reagent for its possible use as an indicator were investigated. The results show that the reagent is an amphoteric which possesses four ionization constants Ka1, Ka2, Kb1 and Kb2 of weak dibasic and diacidic properties. The value of pKa2 (9.80) is parallel to the observed transition interval pH 9.5 (yellow) and pH 10.5 (colorless), which is considered to be the indicator exponents pKi. It was concluded that the benzyl sulfonamide group plays a key role in the stability of the reagent towards hydrolysis and also for indicator characteristics through breaking the conjugation.

The inhibition action of carmine and fast green dyes on corrosion of mild steel in 0.5 M HCl was investigated using mass loss, polarization and electrochemical impedance (EIS) methods at 300 K. The inhibition efficiency was found to increase with increasing concentration of the inhibitors. The inhibition efficiency of fast green (%h-98) is higher than that of carmine (% h-92) and found to be maximum in 1×10-3 M solution. The inhibitors act as mixed type with predominant cathodic effect. The inhibitors were adsorbed on the mild steel surface according to the Temkin adsorption isotherm. The surface morphology of the mild steel specimens was evaluated using SEM images.

In the present work both FTIR and Flame AAS were jointly used to investigate the uptake of pollutants by the aquatic plant water hyacinth. The plant was immersed alive in synthetic standard solutions containing acetic acid up to 0.40 M for 19.0 h. Then it was immersed in 0.10 M acetic acid for different periods of time up to 210.0 h. Later on, both the acetic acid treated beside non treated ones was immersed separately in 1.0, 3.0 and 5.0 mg l-1 concentrates derived from Cd and Pb up to 240.0 h. The obtained results demonstrate the capability of the plant to remove both organic and inorganic pollutants. It is recommended that the plant be used to remediate Pb and Cd as well as other organic pollutants containing COOH. The results also indicate that the selectivity for Pb is higher than that of Cd. Additionally, pentahydrated divalent metal acetate model is presented to describe the coordination of the divalent metal ion with the acetic acid.

The Cr(III) and Ca(II) complexes (dmpH)[Cr(pydc)2]·H2O (1) and [Ca2(pydc)2(H2O)6].2pydcH2 (2) were synthesized by reaction of 2,9-dimethyl-1,10-phenanthroline (dmp) and pyridine-2,6-dicarboxylic acid (pydcH2) with Cr(NO3)3 and Ca(NO3)2, respectively, and characterized using IR spectroscopy, single crystal X-ray diffraction method and solution studies. The space group and crystal system of these two compounds are P21/c and monoclinic. The crystal dimensions are a=9.785(3) Å, b=25.671(4) Å, c=9.3402(16) Å, b=90.790(17)o for (1) and a=9.1319(4) Å, b=14.8430(8) Å, c=12.2449(7) Å, b=98.227(5)o for (2). In complex (1), a water molecule presents in the crystal packing, linking the anionic and cationic fragments together by hydrogen bonding and thus increases the stabilization of crystal lattices. In complex (2), the coordinated water molecules relate each dimer to adjacent dimers forming infinite molecular ribbons by strong hydrogen bondings. Hydrogen bonding and ion pairing play an important role in stabilizing these crystals. The complexation reactions of pydc, dmp and pydc+dmp with Cr3+ and Ca2+ ions in aqueous solution were investigated by potentiometric pH titrations and the equilibrium constants for all major complexes formed were evaluated.

The main purpose of this study is to investigate the colloidal stability of hydroxyapatite (HAp) nanoparticles prepared by different methods. Nano-sized hydroxyapatite particles are synthesized by two different methods including hydrothermal and solvo-treatment processes. In hydrothermal process nanoparticles are synthesized at high temperature, while in solvo-treatment method nanoparticles are synthesized at room temperature by the use of surfactants and organic solvent. The samples are characterized by powder X-ray diffraction (XRD), fourier-transformed infrared spectroscopy (FT-IR), scanning electron microscopy coupled with energy dispersive X-ray analysis detector (SEM+EDXA), and phase separation analyzer. The produced nanoparticles are different in size, stoichiometric ratio, morphology, crystallinity and colloidal stability in a dilute dental adhesive. The results show that the nanoparticles synthesized by these two methods are quite dissimilar and particles prepared by hydrothermal method have a smaller size and higher colloidal stability.

The kinetics of oxidation of 2-aminoethanol and 3-amino-1-propanol by diperiodatoargentate (III) (DPA) were carried out spectrophotometrically in alkaline medium in the temperature range of 293.2-308.2 K. The reaction showed first order with respect to [DPA] and each reductant. The observed rate constant (kobs) decreased with the increase of [IO4-] and increased with the increase of [OH-]. Increasing ionic strength of the medium decreased the rate. Investigations of the reaction at different temperatures allowed the determination of the activation parameters for the slow step of proposed mechanism. The proposed mechanism and the derived rate laws found consistent with the observed kinetics.

Oxidation of anilines by isoquinolinium bromochromate (IQBC) in aqueous acetic acid leads to the formation of corresponding azobenzenes. The reaction is first order with respect to both aniline and IQBC and is catalyzed by hydrogen ion. The rate of oxidation decreases with increasing dielectric constant of solvent, indicating the presence of an ion-dipole interaction. The rate of oxidation decreases with increase in concentration of KCl, possibly due to the formation of less reactive species by interaction of Cl- and protonated IQBC. The specific rate of oxidizing species anilines reaction correlates with substituents constant affording a negative reaction constant. Hammett plot is found to be valid and the correlation between enthalpies and free energies of activation is reasonably linear with an isokinetic temperature of 401 K.

A convenient synthetic method for N-acylation of sulfonamides in the presence of P2O5/SiO2 is described. Carboxylic acid anhydrides and carboxylic acid chlorides were used as acylating agents and the reactions were carried out in CH2Cl2 or solventfree conditions. The catalyst can be recovered by simple filtration and can be used in the subsequent reactions.

In this paper a carbon ionic liquid electrode (CILE) was fabricated by using a room temperature ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) as binder. By using the CILE as basal electrode, the hemoglobin (Hb) molecule was immobilized on the surface of CILE with a sodium alginate (SA) hydrogel and SiO2 nanoparticles organic-inorganic composite material. The direct electrochemical behaviors of Hb in the bionanocomposite film were further studied in a pH 7.0 Britton-Robinson (B-R) buffer solution. A pair of well-defined quasi-reversible cyclic voltammetric peaks of Hb was obtained on SA/nano-SiO2/Hb/CILE with the formal potential (E0') at -0.355 V (vs. SCE), which was the characteristic of heme Fe(III)/Fe(II) redox couples. The formal potential of Hb Fe(III)/Fe(II) couple shifted negatively with increasing pH of solution with a slope of -45.2 mV/pH, which indicated that a one electron transfer accompanied with one proton transportation. The immobilized Hb showed good electrocatalytic manner to the reduction of trichloroacetic acid (TCA).

Two data sets of natural antiviral agents including 107 anti-HIV1 and 18 anti-polio molecules were collected and subjected to quantitative structure-activity relationship (QSAR) analyses. A wide variety of molecular descriptors belonging to various structural properties were calculated for each molecule. Multiple linear regression (MLR) based on stepwise variable selection was employed to find the most convenient quantitative models. For each antiviral data set different QSAR models were established in two steps. Firstly, for each type of molecular descriptors separate QSAR analysis was performed, and then a new QSAR model was calculated using the selected descriptors in the first phase. For both types of antiviral data sets significant QSAR models were obtained. The atom-centered fragment descriptors represented the highest impact on the anti-HIV1 activity whereas for anti-polio agents, radial distribution function and three-dimensional MoRSE descriptors showed the most significant influences. Cross-validation and a separate prediction set were used to evaluate the stability and prediction ability of the models. It was found the discovered QSAR models for anti-HIV1 and anti-polio agents could reproduce about 80% and 90% of variances in the antiviral activity data with root mean square error of prediction of 0.421 and 0.171, respectively.

An efficient protocol has been developed for the synthesis of various pyrano[2,3-d]pyrimidinones from condensation of aromatic aldehydes, malononitrile and barbituric-or thiobarbituric acid in aqueous ethanol using L-proline as a neutral bifunctional catalyst.

Microwave-assisted synthesis of a variety of 1,1-diacetates catalyzed by SbCl3 from corresponding aldehydes and acetic anhydride was reported. Only 10 mol% of catalyst was sufficient to push the reaction forward and high amounts of the catalyst did not improve the yields to a great extent. The present protocol offered several advantages including low cost of the catalyst, high yields, short reaction time and simple work-up procedure.