Journal of the Iranian Chemical Society
Volume:7 Issue: 3, Sept 2010

Protein aggregates, whether amorphous or structured (amyloid), have attracted much attention in recent years and despite extensive efforts, the mechanism of their formation is poorly understood. While”natural” aggregation (polymerization) of monomers could improve the biological function of some proteins, it is usually the darker side of this phenomenon which is discussed in many studies: deleterious aggregation that could lead to loss of biological activity under in vitro conditions or cause misfolding diseases. In this review, protein aggregation has been overviewed, starting from some general concepts involved in its formation, followed by mentioning studies aimed at elucidation of its kinetics and mechanism, or characterization of intermediates that would be aggregation-prone, and finally, reporting some of the studies related to the design of methods that would control the process. Similarly, amyloid aggregates have been defined, and current methods used in their characterization have been briefly described, with an emphasis on in silico studies. Finally, identification and design of such molecules which may be effective in control of this process is discussed.

The extraction behaviors of strontium from nitric acid solution were investigated with N,N,N’,N’-tetraisobutyl diglycolamide (TiBDGA). Effects of acidity, diluents, concentration of extractant and temperature on the distribution ratio of strontium (DSr) were examined. The stoichiometry of the extracted molecule was Sr2+:TiBDGA of 1:3. The apparent extraction equilibrium concentration constant logKex was 3.25. The enthalpy change ΔH and entropy change ΔS were -55.6 kJ mol-1 and -124 J mol-1 K-1, respectively. The extraction is an exothermic process. Through two strip stages, strontium could be stripped effectively by 0.01 M nitric acid solution.

A comparative study on the influence of the substituents on the Diels-Alder reaction was performed. The energy profiles for 11 sets of Diels-Alder reaction between monosubstituted derivatives of butadiene and ethylene have been studied and the structures of all transition states were located at B3LYP/6-31+G* level. Four pathways were independently investigated; the reaction between substituted ethylene and 1-substituted butadiene leading to ortho (a1) and meta (a­2) adducts, and in the same manner, the reaction between substituted ethylene and 2-substituted butadiene yields para (b1) and meta (b­2) adducts. Inspection of both the activation barriers and the reaction energies for 44 reactions revealed that the pathway b1 is both thermodynamically and kinetically more favorable in all types of Diels-Alder reactions; while the pathway a1 can be labeled only as kinetic pathway. The aromaticity of all 44 transition state structures was measured using para delocalization index to study the effect of aromaticity on the reaction path. The calculations suggest that in normal and neutral DA reactions there is a gain in aromatic stabilization of the transition state which reduces slightly the activation barrier of the kinetic pathway a1.

Solid-oxide fuel cells (SOFCs) can be used for clean, efficient and environment-friendly energy conversion with a variety of fuels at high temperature (1273 K). The high temperature operation accelerates unwanted reactions and creates materials challenges; so, intermediate-temperature SOFCs (IT-SOFCs) have been developed. Reduction of the operating temperature (between 873-1073 K) requires solid electrolyte materials with higher conductivities. In this study, partially substituted ceria as solid electrolyte is experimented systematically for use in solid oxide fuel cells operating below 1073 K (intermediate temperature range). Nine compositions namely, CeO2, Ce0.95Gd0.05O2-δ (CGO9505), Ce0.90Gd0.10O2-δ (CGO9010), Ce0.85Gd0.15O2-δ (CGO8515), Ce0.80Gd0.20O2-δ (CGO8020), Ce0.95Sm0.05O2-δ (SDC9505), Ce0.90Sm0.10O2-δ (SDC9010), Ce0.85Sm0.15O2-δ (SDC8515) and Ce0.80Sm0.20O2-δ (SDC8020) were synthesized by Glycine Nitrate (GN) combustion technique and investigated. The physical properties and the other relevant features of the data obtained are analyzed with a view to use these alternate electrolyte materials in IT-SOFC.

Ozone water reaction including a complex was studied at the MP2/6-311++G(d,p) and CCSD/6-311++G(2df,2p)//MP2/6-311++G(d,p) levels of theory. The interaction between water oxygen and central oxygen of ozone produces stable H2O-O3 complex with no barrier. With decomposition of this complex through H-abstraction by O3 and O-abstraction by H2O, three possible product channels were found. Intrinsic reaction coordinate, topological analyses of atom in molecule, and vibrational frequency calculation have been used to confirm the preferred mechanism. Thermodynamic data at T = 298.15 K and atmospheric pressure have been calculated. The results show that the production of hydrogen peroxide is the main reaction channel with ΔG = -21.112 kJ mol-1.

Syntheses of dinucleotide analogs, (S,R) cis-(4-((4-amino-2-oxopyrimidin-1(2H)-yl)methyl)-1,3-dioxolan-2-yl)methyl (2R,3R,5R)-2-(hydroxymethyl)-5-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-tetrahydrofuran-3-yl hydrogen phosphate (5a) and (S,R) cis-(5-((4-amino-2-oxopyrimidin-1(2H)-yl)methyl)-1,3-oxathiolan-2-yl)methyl (2R,3R,5R)-2-(hydroxymethyl)-5-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-tetrahydrofuran-3-yl hydrogen phosphate (5b), were accomplished by the use of a new strategy. The use of phenyldichlorophosphate (Method A) as the coupling reagent was shown to possess superiority relative to the reported use of di(1H-benzo[d][1,2,3]triazol-1-yl)phenyl phosphonate (Method B).

Saccharin sulfonic acid (SaSA), as a stable reagent is easily prepared by the reaction of saccharin with neat chlorosulfonic acid at room temperature. This compound is able to catalyze conversion of amines to their corresponding N-Boc protected amines with (Boc)2O. Alcohols were also converted to their corresponding tert-butyl ethers. All reactions took place under mild conditions giving the desired products in good to high yields.

A systematic study on interaction of Pd(II) with 7-iodo-8-hydroxyquinoline-5 sulfonic acid (Ferron) and the strongly basic anion exchange resin Purolite A-500 in its chloride form was carried out. It was found that for Ferron/resin ratio ranging from 0.15 to 0.70 mmol g-1, the retention of chelating reagent on the investigated ion exchanger is practically quantitative. The sorption increase of Pd(II) on Ferron-loaded resin was observed for higher values of parameters like: pH solution, initial concentration and temperature. It was observed that the equilibrium distribution of Pd(II) between sorbent and solution could adequately be described by the Langmuir model with two parameters. The thermodynamic quantities characteristic of Pd(II) sorption process (DG = -18.4 kJ mol-1; ΔH = 11.7 kJ mol-1; ΔS = 104.4 J mol-1 K-1) suggest a strong affinity between Ferron-loaded resin and the tested cation.

This is a report of an efficient, clean and facile method for the synthesis of 1,4-dihydropyrano[2,3-c] pyrazole and pyrano[2,3-d]pyrimidine derivatives via three-component one-pot condensation of 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one or barbituric acid, aldehydes and malononitrile in the presence of a catalytic amount of preyssler type heteropolyacid as a green and reusable catalyst in water or ethanol under refluxing conditions.

The vapor-liquid equilibria properties of sodium n-heptyl sulfonate (C7SO3Na) in pure water and in aqueous poly(ethylene glycol) (PEG) solutions were determined at different temperatures below and above the critical micelle concentration (CMC). Vapor-liquid equilibrium data such as water activity, vapor pressure, osmotic coefficient, activity coefficient and Gibbs free energies were obtained through isopiestic method. The concentration dependence of all investigated thermodynamic properties exhibit a change in slope at the concentration in which micelles are formed. It was found that the vapor pressure depression for a ternary aqueous C7SO3Na + PEG system is more than the sum of those for the corresponding binary solutions and, at higher temperatures, the higher concentration of PEG is in equilibrium with a certain concentration of surfactant.

The transport properties of oligo(ethyne) dithiolates coupled with gold electrodes is calculated using the non-equilibrium Green’s functions technique. The effect of molecular wire length on current-voltage characteristics for (-C≡C-)n n = 1-5 is investigated. The calculated decay coefficient at low bias voltage is (0.025 ± 0.002 A°-1) which is found to be lower than that of alkanthiols. Results reveal that the HOMO-LUMO gap of the oligo(ethyne)s are correlated to the reciprocal of the number of triple bonds.

The catalytic activity of Mn(III)salophen complex supported on polystyrene-bound imidazole, [Mn(salophen)Cl-PSI], was studied in the oxidation of primary aromatic amines in acetonitrile/water, using sodium periodate as an oxygen source. Amines were oxidized efficiently to their corresponding azo derivatives in the presence of this catalyst. The heterogeneous catalyst showed high stability and reusability in the oxidation reactions and could be reused several times without loss of its activity. The effect of different solvents was studied in the oxidation of p-toluidine and CH3CN/H2O was chosen as the solvent.

New Brønsted acidic ionic liquid, 3-methyl-1-sulfonic acid imidazolium chloride {[Msim]Cl} was used as an efficient, green and reusable catalyst and solvent for the synthesis of N-sulfonyl imines via the condensation of sulfonamides with aldehydes as well as isatin. The reactions proceeded at room temperature and the title compounds were obtained in high to excellent yields and in relatively short reaction times.

A novel and smart biopolymer-based hydrogel was synthesized by graft copolymerization of acrylic acid onto the salep backbones. The new superabsorbent hydrogel was synthesized via simultaneous crosslinking and graft copolymerization of acrylic acid (AA) monomer onto salep backbones using radiochemical methods. In radiochemical methods, γ-rays as initiator, energy source and crosslinker are applied. In our experiments, the effects of reaction variables such as relative contents of salep and AA, as well as γ-rays total dose were examined. According to water absorbency of the entitled network, the best synthesis condition is reported. FTIR spectroscopy, SEM photograph and TGA analysis were used for confirming the structure of the final product and a mechanism for superabsorbent hydrogel formation is also suggested. Furthermore, in this research, several factors affecting the swelling behavior of hydrogel including pH of medium, sensitivity to the salt solution and mixture of solvents were studied.

Manganese(III) tetrakis(p-sulfonatophenyl)porphyrin was successfully bound to silica modified with zirconium. The heterogeneous catalyst, MnTPPS-silica, was characterized by SEM, FT-IR and diffuse reflectance UV-Vis spectroscopic techniques. MnTPPS-silica catalyzes alkene epoxidation and alkanes hydroxylation with sodium periodate under agitation with magnetic stirring and ultrasonic irradiation in the presence of imidazole as an axial ligand. This catalytic system shows a good activity in the epoxidation of linear alkenes. Alkyl aromatic and cycloalkanes were efficiently oxidized to their corresponding alcohols and ketones in the presence of this catalyst. This new heterogeneous catalyst is of high stability and reusability in the oxidation reactions and can be reused several times without loss of its activity.

The use of ultrasonic irradiation for the selective synthesis of sulfone in the oxidation of sulfides with NaIO4 catalyzed by Mn(Salophen) supported on chloromethylated polystyrene-bound imidazole, [Mn(Salophene)-PSI], is reported. This heterogeneous catalyst efficiently catalyzed selective oxidation of sulfides to sulfones under ultrasonic irradiation and no sulfoxide was detected in the reaction mixture.

Cloud point extraction process using non-ionic surfactant, Triton X-114, to extract codeine from aqueous solution was investigated. The method was based on the extraction of codeine and bromothymol blue from acetate buffer media to surfactant-rich phase and formed a charge transfer-ion pair complex. The extracted surfactant-rich phase was diluted with ethanol and its absorbance was measured at 430 nm. The effect of different variables such as pH, Triton X-114 concentration, cloud point temperature and time was established. The calibration graph was linear in a wide range of 100-700 ng ml-1 of codeine with r = 0.998 (n = 7). The detection limit based on three times standard deviation of the blank (3s) was 4.6 ng ml-1 and relative standard deviation (R.S.D) is 2.15% for 500 ng ml-1 codeine (n = 5). The proposed method was applied to the determination of codeine in acetaminophen codeine tablets and blood samples.

Heteroaryl substituted analogs of antirhnoviral (A), was prepared by a convergent approach. 3-Nitrophenyl-5-bromooromethylisoxazoles 5a-b were synthesized by [3+2] cycloaddition of 3-(benzoyloxy)-propyne 2 to in situ generated arylnitrile oxides followed by deprotection of cycloadducts 3a-b and bromination of the resulting alcohols 4a-b. Coupling of 3-nitrophenyl-5-bromooromethylisoxazoles (5a-b) with 4-[5-(2-alkyl-2H-tetrazolyl)]phenols (6a-d) in N-methylpyrrolidinone under mild conditions afforded a new series of 2-alkyl-5-{4-[1-(3-nitrophenyl-5-isoxazolyl)methyloxy]phenyl}-2H-tetrazoles (7a-h) in high yields. The structures of the synthesized compounds were confirmed by their 1H NMR, Mass spectral, and Elemental Analysis data.

Cobalt(II) Schiff base functionalized mesoporous silica was synthesized from covalent attachment via the introduction of Co(OAc)2 to salicylaldimine functionalized mesoporous silica. The catalyst proved to be chemoselective one for the acetalization of aldehydes to the corresponding acetals in alcohol. The immobilized catalyst can be easily recovered and reused for at least ten reaction cycles without significant loss of its catalytic activity.

A novel Mitsunobu-based technique has been developed for the synthesis of a variety of symmetrical and unsymmetrical S,S-dialkyl dithiocarbonates from various corresponding primary, secondary and tertiary thiols using gaseous carbon dioxide, in good to excellent yields.

A series of new organic dyes comprising carbazole, iminodibenzyl, and phenothiazine moieties as the electron donors and rhodanine ring as the electron acceptor/anchoring groups were designed and developed for use in dye-sensitized solar cells. HOMO and LUMO energy level tuning was achieved by varying the carbazole, iminodibenzyls and phenothiazine donors. This was evidenced by spectral and electrochemical experiments and density functional theory calculations. Electrochemical studies indicated that the phenothiazine unit was much more effective in lowering the ionization potential than were the iminodibenzyl and carbazole units. The phenothiazine dye shows a solar-energy-to-electricity conversion efficiency (η) of 4.87%; the carbazole and iminodibenzyl dyes show η of 2.54% and 3.52%, respectively. These findings reveal that using carbazole, iminodibenzyl and phenothiazine donors as light-harvesting sensitizers are promising candidates for dye-sensitized solar cells.

Fe/FeO/Fe3O4 composite was synthesized by a simple solid method using ferric citrate and phenolic resin as raw materials. The reaction processes of raw materials mixture were characterized by thermogravimetric analysis (TGA) under nitrogen. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the structure and morphology of the products. The results showed that the obtained material was octahedral Fe/FeO/Fe3O4 composite with a size of 2-4 µm. The electrochemical performances of Fe/FeO/Fe3O4 composite as anode material were also evaluated, which exhibited a stable specific capacity of 260.3 mAh g-1 and an ideal initial coulombic efficiency of 90.8% in the range of 0.05~3 V at the 5C rate. A good rate capacity of Fe/FeO/Fe3O4 composite electrode was also shown by the charge-discharge testing even at the rate of 60C. The better rate capability of Fe/FeO/Fe3O4 electrode could be measured in higher temperature.

Two compounds containing a proton transfer ion pair (pipzH2)(btcH2), 1, and its Co(II) complex, were synthesized and characterized using IR spectroscopy and single crystal X-ray diffraction method. The chemical formula is {(pipzH2)[Co(btc)(H2O)4].4H2O}n for Co(II) complex, 2, (pipz:piperazine, btcH4:benzene-1,2,4,5-tetracarboxylic acid). The space group and crystal system of both compounds are P1and triclinic. The proton transfer ion pair 1 was prepared by the reaction between piperazine and benzene-1,2,4,5-tetracarboxylic acid, and its Co(II) complex, 2, was synthesized by the reaction of 1 with cobalt(II) sulphate. The complex 2 is a polymeric substance with Co(II) atoms linked by two O atoms from one benzene-1,2,4,5-tetracarboxylate. In both crystal structures, a wide range of noncovalent interactions consisting of hydrogen bonding (types of O-H∙∙∙O, N-H∙∙∙O and C-H∙∙∙O) and ion pairing interactions connecting the various components into a supramolecular structure. There are also C-H···O and C-H∙∙∙π intermolecular interactions in compound 2 which take part in the stabilization of molecular packing. The protonation constants of pipz and btcH4, the equilibrium constants for the btcH4-pipz proton transfer system and the stoichiometry and stability of this system with Co2+ ion in aqueous solution were investigated by potentiometric pH titrations. The stoicheiometry of one of the most abundant complexed species in solution was found to be the same as that of the crystalline cobalt(II) complex.

Two new cobalt(III) complexes of the Schiff base N,N''-disalicylidene-1,2-phenylendiimine dianion (salophen), trans-[CoIII(salophen)(ta)2]ClO4, (ta = thioacetamide) (1) and trans-[CoIII(salophen)(tb)2]ClO4, (tb = thiobenzamide) (2) were synthesized and characterized using single-crystal X-ray diffraction and spectroscopic techniques. Both complexes show solvatochromism in a variety of solvents. Complex (1) crystallized from CHCl3 as a solvate of orthorhombic symmetry, space group Pca21 with a = 17.3480(10) Å, b = 18.7522(10) Å, c = 18.8128(11) Å, a = β = γ = 90°, and Z = 8. The cobalt(III) center lies in a distorted octahedral environment. The crystal structure of (1) consists of two independent [CoIII(salophen)(ta)2]+ cations and ClO4- anions held together essentially via hydrogen bonds and π-π stacking interactions. Complex (2), forming also a CHCl3 solvate, crystallized in the monoclinic space group P21/n with a = 14.710(3) Å, b = 13.506(3) Å, c = 18.595(4) Å, β = 100.295(4)Å, and Z = 4. The geometry around cobalt(III) center is a distorted octahedron. The crystal structure of (2) contains a [CoIII(salophen)(tb)2]+ complex with a remarkably twisted salophen ligand. Both complexes, (1) and (2), contain approximately one disordered CHCl3 molecule per Co in the solid state.

A simple, efficient, facile and eco-friendly process for the synthesis of thioamides from nitriles using 1,6-bis(3-methylimidazolium-1-yl)hexane chloride [C6(mim)2Cl2] as a dicationic ionic liquid (DIL) was developed. The ionic liquid was easily separated from the reaction mixture and was recycled at least four times without any loss of its activity.

A PVC-based membrane containing metoprolol molecularly imprinted polymer (MIP) coated directly on graphite electrode for the determination of metoprolol in real samples is reported. This potentiometric sensor was designed by dispersing the MIP particles in dioctylphthalate plasticizer as solvent mediator and then embedded in polyvinyl chloride matrix. The electrode exhibited a near-Nernstian slope of 55.4 ± 1 mV decade-1 for metoprolol over a wide concentration range between 2.0 × 10-7-8.0 × 10-3 M and a detection limit of 1.3 × 10-7 M. With a response time of about 14 s it could be used for at least 6 months without any divergence in potential. The proposed electrode can be used in the pH range of 3.5-10.5 and can reveal good selectivities for metoprolol over a wide variety of ions. Finally, the designed sensor was successfully applied as an indicator electrode to determine the concentration of metoprolol in tablets, human urine and plasma. The results were compared favorably with those obtained by HPLC method and showed satisfactory agreements with them.

1,2-Dihydro-1-arylnaphtho[1,2-e][1,3]oxazine-3-one derivatives were synthesized in high yields using a facile and one-pot condensation of 2-naphthol, aromatic aldehydes and urea catalyzed by perchloric acid supported on silica under thermal solvent-free conditions.

An unusual mixed crystal of a square-pyramidal oxorhenium(V), [ReOCl(Hdua)], and an octahedral imidorhenium(V) complex, [Re(dua)Cl2(PPh3)], was prepared from the reaction of trans-[ReOCl3(PPh3)2] and (6Z)-6-(2-aminobenzylideneamino)-5-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione (H3dua) in ethanol. Characterization was performed by single crystal X-ray structure determination and IR spectroscopy. The chelate Hdua is coordinated as a tridentate diamido-imine, and dua is chelated as an imido-imino-amide.

Spiro thio-oxindoles are prepared in situ by the reaction of the corresponding aldehydes and thio-oxindoles in a straightforward, environmentally friendly, highly efficient and simple procedure. The reaction took place in water with no catalyst added. This one-pot reaction afforded regio- and diastereoselective products in high yields (61-93%).

Commercially available chloromethylated polystyrene (cross-linked with 2% divinylbenzene) was used to prepare novel and stable polymer supported pyridine-2,6-dicarboxylate. This polymer was found to accelerate the selective removal of Hg(II) from aqueous solutions containing different amounts of Hg(II) (10-100 ppm). Adsorption rate was high at the beginning and then equilibrium was reached in about 25 min. Maximum Hg(II) adsorption capacity of the resin was about 41.5 mg/g of the dry polymer. The Hg(II) adsorption ability increased with the increase in pH, in the range where the solubility of the Hg(II) was not affected by pH. More than 95% of the adsorbed Hg(II) was desorbed in 15 min by using 0.1 M HNO3 as an elution agent. The regeneration of this resin by strong acid was feasible and desorption ratio was very high (up to 96%).