Journal of the Iranian Chemical Society
Volume:6 Issue: 1, Mar 2009

Heteropolyacids, their salts and polyoxometalateshave been used as catalysts in wide range of organic reactions such as multi components, oxidation, reductions, electrochemical and photochemical reactions. There have been tremendous and continued efforts to modify the catalytic performance of heteropoly acids such as supporting them on MCM, silica gel, etc. In this review, we have attempted to bring some of new applications of heteropolyacids in organic reactions and recent approaches on modifying them, into focus.

The homonuclear water-soluble and air stable compounds (dmpH) (H5O2) [M(pydc)2].0.5H2O (M = Ni(II) (1), Cu(II) (2), Zn(II) (3); pydcH2 = pyridine-2,6-dicarboxylic acid, dipicolinic acid, dmp = 2,9-dimethyl-1,10-phenanthroline) have been prepared by self-assembly synthesis in aqueous solution at room temperature, and characterized by IR, 1H NMR, 13C NMR, elemental analysis and X-ray diffraction single crystal analyses for 1, 2 and 3. The complexes 1-3 represent the isostructural features. Extensive hydrogen bonding interactions involving all aqua ligands, dipicolinate oxygens and lattice water molecules further stabilize the complex units by linking them to form three dimensional polymeric networks. The stoichiometry and stability of the all three complexes in aqueous solution were investigated by potentiometric pH titration.

Sensitive cathodic stripping voltammetric methods have been developed for two quinolone antibacterial drugs, pipemidic acid (PIP) and ofloxacin (OFL) using hanging mercury drop electrode as working electrode vs. Ag/AgCl reference electrode. The methods were developed for the determination of drugs individually as well as simultaneously. 0.1 M and 0.01 M hydrochloric acid was used as medium for PIP and OFL, respectively, 0.1 M potassium chloride was used as base electrolyte. Reduction waves were observed for PIP within -700 mV to -800 mV and for OFL within -1100 mV to -1200 mV. Linear calibration ranges for PIP and OFL were observed within 10-100 µg ml-1 with detection limits of 50 ng ml-1 and 1 µg ml-1, respectively. Relative standard deviations (RSD) for the analysis of 10 µg ml-1 of PIP and OFL (n = 6) were 0.5% and 1.4%, respectively. The presence of glucose, lactose, sorbitol, gum arabic, starch, magnesium stearate, methylparaben and propylparaben did not affect the determinations of both PIP and OFL. The methods were used for the analysis of pharmaceutical preparations and the results indicated relative deviation of 0.5-5.5% from labeled values with RSD within 0.49-2.5%. PIP and OFL could also be determined simultaneously, and were determined from spiked human urine.

Some new 2-[5-(aryl)-[1,3,4]oxadiazole-2-ylsulfanyl]alkanoic acids were synthesized and studied for their antibacterial activity. These compounds were prepared from aromatic carboxylic acid hydrazides. Aromatic carboxylic acid hydrazides 1 on refluxing with carbon disulfide and methanolic potassium hydroxide and then on subsequent acidification with hydrochloric acid furnish 5-aryl-1,3,4-oxadiazole-2-thiones 2. 2-Chloro alkanoic acids react with 2 in alkaline media and on acidification yield the title compounds 3. These compounds were characterised by CHN analyses, IR, mass and 1H NMR spectral data. All the compounds were evaluated for their in vitro antibacterial activity against two Gram negative strains (Escherichia coli and Pseudomonas aeruginosa) and two Gram positive strains (Bacillus subtilis and Staphylococcus aureus) and their minimum inhibitory concentration (MIC) were determined.

A novel complex [Cu(acac)(dppe)]n (1) [acac = acetylacetone; dppe = 1,2-bis(diphenylphosphino)ethane] was obtained by solution reactions and structurally characterized by X-ray diffraction. The crystal structure analysis indicates that the title complex is characteristic of a polymeric chain formed by the dppe ligands bridging neighboring copper centers. The copper atom is in a distorted tetrahedral geometry. Photoluminescent investigation reveals that the title complex displays a strong emission in blue-light region.

The di- and tri-organotin(IV) complexes of n-butyl hydrogenphthalate and (Z) 3-(4-nitrophenyl)-2-phenyl-2-propenoate were subjected to thermal decomposition by mean of thermogravimetry (TG). The decomposition occurred in steps and the kinetics of every set of reactions was determined using the method described by Coats and Redfern. These results were analyzed to establish the decomposition kinetics and, hence, to calculate the activation energies. The activation energies were also determined by applying the methods described by Horowitz and Metzger, which yielded comparable results. These results confirm that both the ligands act as bidentate in the solid state.

An attempt is made to maximize the solar energy storage in norbornadiene (1)/quadricyclane (2) system, through exchanging of heteroatoms at C7 of 1 and 2; calculating the corresponding energies at MP2/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p) and B3LYP/6-311++G** levels of theory. Free energy gaps between 1X and 2X, ΔG(1x)-(2x), and solar energy storage is the most for 1Se, 1As and 1Alfrom group VIII, VII and III of the Table, respectively.

Application of immobilized metal cations on the topside of gold-5-amino-2-mercaptobenzimidazole self-assembled monolayer (Au-5A2MBI-Mn+ SAM, Mn+:Cu2+ or Ag+) for electrocatalytic determination of hydroquinone (H2Q) is described by voltammetric method. Several parameters were investigated to evaluate the performance of the sensors. Calibration curves for H2Q concentrations were linear from 1.0 × 10-5 to 4.0 × 10-4 M (r = 0.998) for Au-5A2MBI, from 1.0 × 10-5 to 6.0 × 10-4 M (r = 0.998) for Au-5A2MBI-Cu2+, and from 2.0 × 10-6 to 2.0 × 10-5 M (r = 0.996) and 1.0 × 10-4 to 1.0 × 10-3 M (r = 0.991) for Au-5A2MBI-Ag+SAM modified electrode. The respective detection limits were found as 6.5 × 10-6, 4.6 × 10-6 and 1.8 × 10-7 M. Both Cu2+ and Ag+ ions were found to have a good electrocatalytic effect on the oxidation of H2Q; however, Ag+ was a more effective catalyst and showed better sensitivity and lower detection limit than all other tested electrodes. Au-5A2MBI-Ag+ SAM electrode was used as a suitable sensor for determination of H2Q in a radiolysis developing agent as real sample. The results obtained by using proposed sensor and that obtained by an ASTM reference method were in good agreement at the 95% confidence level.

A simple, accurate, sensitive and economical procedure for the estimation of amlodipine besylate and nifedipine, both in pure and dosage forms, has been developed. The method is based on the reduction of iron(III) by the studied drugs and subsequent interaction of iron(II) with ferricyanide to form Prussian blue. The reaction develops through a slow kinetics and completes in about 10 min. Both initial slope and fixed time methods were used to derive calibration graphs. The resulted calibration equations were linear in the concentration ranges of 1.0-20.0 and 3.0-19.0 μg ml-1 for AML and NIF, and the detection limits were 0.10 and 0.19 μg ml-1, respectively. Seven replicate analyses of solutions containing three different levels of each drug resulted in very low relative error of prediction (less than 1.6%) and relative standard deviation (less than 4%) confirming accuracy and precision of the proposed method. The proposed method was applied to the determination of these drugs in pharmaceutical formulations and excellent recoveries were obtained.

The sulfur containing ligand viz., thiosulfate is found to inhibit the Ag(I) catalyzed substitution of cyanide in hexacyanoferrate(II) by phenylhydrazine. The inhibitory effect of thiosulfate is attributed due to its tendency to form complexes with Ag(I), leading to the production of inhibitor-catalyst complexes. The reactions, followed spectrophotometrically in aqueous medium at 488 nm, was possible by the increase in absorbance of the cherry-red product, [Fe(CN)5PhNHNH2]3- at pH 2.8 (±0.02), at 30 (±0.1) °C, and an ionic strength (µ) of 0.02 M (KNO3). The linear calibration curves were obtained using the absorbance measured at different times (At) and thiosulfate concentrations under specified conditions. The calculated detection limit was 4.9 × 10-7 M. The Michaelis-Menten constant (Km) and equilibrium constants for the formation of complexes between catalyst and inhibitor (KCI), and the catalyst and substrate (KS) were computed from the kinetic data. A general mechanistic scheme is proposed for this reaction.

AB Azo-coupling of a series of 6-ketomethylphenanthridines products was performed starting from 6-ketomethylphenanthridines and benzene diazonium chloride. The products were characterised using 1H, 13C and 15N NMR, IR, UV and MS spectroscopic methods. The hydrazoimine forms were the only tautomer present in chloroform solution. Two rotamers were detected in chloroform solutions of the compounds studied. Analysis of the NMR data shows that the ratio of rotamers depends on electron-donating and electron-withdrawing properties of the substituent present in the benzene ring.

IR, Raman and surface-enhanced Raman scattering (SERS) spectra of L-proline were recorded and analyzed. The molecular plane assumes a tilted orientation with respect to the metal surface. The vibrational wavenumbers and corresponding vibrational assignments are examined theoretically using the Gaussian 03 set of quantum chemistry codes.

The complex of cobalt(III) ethylenediamine was synthesized, isolated and characterized by UV-Vis, IR, and 1H NMR spectral methods. The binding of the complex with calf thymus DNA was investigated by absorption and emission spectroscopy, viscosity measurements, DNA melting and DNA photocleavage. The spectroscopic studies together with the viscosity measurements and DNA melting studies indicated that the complex binds to calf thymus DNA in a nonintercalative mode. This complex is found to promote photocleavage of the DNA plasmid pBR322 and shows a cytotoxic effect against CHO cells.

Ammonium heptamolybdate tetrahydrate [(NH4)6Mo7O24.4H2O] efficiently catalyzes the condensation of aryl-1,2-diamines with 1,2-diketones in EtOH/H2O as a green media at room temperature to afford quinoxaline derivatives as biologically interesting compounds. Ease of recycling of the catalyst is one of the most advantages of the proposed method.

Selective nitration of phenols with sodium nitrate was carried out in the presence of acidic ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate at room temperature in good to high yields and short reaction times. The use of inexpensive and relatively non toxic acidic reagent is an advantage of this method.

An environmentally benign and efficient process for the preparation of b-hydroxysulfides was developed by a practical and simple reaction of thiols with epoxides in water catalyzed by K2CO3 in high yields and short reaction times.

The 1-octanol-water partition coefficient is an important property to measure the hydrophobicity of organic compounds, which has been demonstrated to be a parameter in studying the conformation of biomolecules in aqueous solutions. For biological systems, electrolytes play an important role in thermodynamic properties. The salt addition effect on the distribution of phenolic compounds between water and 1-octanol at 298.15 K has been studied. The phenolic compounds used were vanillic acid, protocatechuic acid, vanillin, tyrosol, cathecol, caffeic acid and syringic acid, and the considered salts were potassium chloride, sodium chloride and lithium chloride. The influence of both the concentration and size of the added salt on the partition coefficient (Kow) have been considered. This study shows a salting in with the following decreasing order: LiCl > NaCl > KCl. The Gibbs energies of transfer of phenolic compounds (ΔG) form chloride solutions to organic phase have been calculated using experimental 1-octanol-water partition coefficients.

Micellar media under neutral conditions catalyzed successful reductive amination of aldehydes and ketones by bis(triphenylphosphine)(tetrahydroborato)zirconium(II), [Zr(BH4)2(Ph3P)2], as a newly developed hydride transfer agent and a highly water tolerant tetrahydroborate reagent.

Nano sized ZSM-5 zeolite samples were synthesized successively from kaolin clay as alumina source having a large amount of quartz (39%) and silicic acid as silica source by hydrothermal treatment with NaOH in the presence of tetrapropylammonium hydroxide as a template. Then the effect of kaolin content, crystallization temperature and time on the size and crystallinity of the products were investigated. The prepared samples were characterized using XRD, SEM, EDS and FT-IR techniques. The results showed that the synthesized ZSM-5 zeolite samples were almost pure and their crystallization was almost complete. The average particle size, as determined by Debye-Scherrer equation, was in the range of 20-42 nm. Increasing kaolin content on crystal size was more effective than increase in crystallization temperature and time. Additional evidences for the nano sized ZSM-5 zeolite were the asymmetric stretch vibration band at 1225 cm-1 in the FT-IR spectra and TEM images. The scanning electron micrographs of the synthesized zeolites showed that they are spherical shape crystals.

Hydrogen bond interaction properties of backbone uracil was studied in crystalline structure of 5-nitrouracil. To this aim the electric field gradient tensors were calculated at the level of density functional theory in two single (non-hydrogen bonded) and cluster (hydrogen-bonded four-molecule) models of 5-nitrouracil. The electric field gradient tensors at the sites of O-17, N-14, and H-2 nuclei were converted to the experimentally measurable nuclear quadrupole resonance spectroscopy parameters, quadrupole coupling constant and asymmetry parameter. The results indicated different hydrogen bond interaction properties at the sites of various nuclei and also the protective role of -NO2 group for contribution of O1 to hydrogen bond interactions in comparison with uracil. The density functional theory calculations were performed using GAUSSIAN 98 package employing B3LYP method and 6-311G** and 6-311++G** basis sets.

Extraction processes of indium(III) with 2-octylaminopyridine (2-OAP) from media of various complexing ability, succinate and salicylate, in chloroform have been elucidated. The ion-pair complex has also quantitative extraction in xylene and 1,2-dichloroethane. Indium(III) from organic phase was stripped with 1.0 M hydrochloric acid and determined complexometrically with EDTA. The stoichiometry of the extracted species was found out on the basis of slope analysis. The extraction of indium(III) proceeds by an anion exchange mechanism and the extracted species is [RR′NH2+In(succinate)2-](org). Temperature dependence of the extraction equilibrium constant was also examined to estimate the apparent thermodynamic functions (ΔH, ΔG and ΔS)for extraction reaction. It is possible to separate indium(III) from Zn(II), Cd(II), Pb(II), Hg(II), Bi(III), Tl(I), Tl(III), Ga(III), Al(III), Te(IV), Se(IV), Sb(III), Fe(III) and Sn(IV). The method is simple, rapid and reproducible and can be used to determine the indium from samples like alloys.

A new compound (MQ)(CdBr4) (1; MQ2+ = N-Me-4,4′-bipyridinium), in which the MQ2+ was generated in situ, has been synthesized via hydrothermal reaction. The title compound features an isolated structure, based on discrete MQ2+ moieties and tetrahedral cadmium atoms terminally coordinated by four bromine atoms. The MQ2+ moieties and tetrabromo-cadmium dianions are linked via hydrogen bonds. Photoluminescent investigation reveals that the title compound displays a strong blue-light emission, which is attributed to a ligand-to-ligand charge-transfer (LLCT; from the HOMO of the bromine atoms to the LUMO+1 of the MQ2+ moieties) mechanism probed by molecular orbital (MO) calculations.