Journal of the Iranian Chemical Society
Volume:7 Issue: 2, June 2010

Water clusters”, group of water molecules held together by hydrogen bonds, have been the subject of a number of intense experimental and theoretical investigations because of their importance in understanding cloud and ice formation, solution chemistry, and a large number of biochemical processes. “Water clusters” can play an important role in the stabilization of supramolecular systems both in solution and in the solid state and there is clearly a need for chemists a better understanding of how such aggregates influence the overall structure of their surroundings. The present brief review deals with (H2O)n clusters, identified/observed crystallographically upon 170 crystal structures of synthesized coordination compounds based upon proton transfer compounds by Hossein Aghabozorg’s research groups since 2000. The structural details of water clusters, (H2O)n, n = 2, 3, 4, 5, 6, 7, 8, 9, 15, 16 and ∞ are described systematically.

This paper is concerned with an easy preparation of THP ethers from primary, secondary and tertiary alcohols and oxazoline compounds from various aldehydes using poly(N-bromo-N-ethyl-benzene-1,3-disulfonamide), N,N,N'',N''-tetrabromobenzene-1,3-disulfonamide [TBBDA] as new and efficient reagents under ambient conditions without over-oxidation.

The applicability of pair potential functions to liquid alkali metals is questionable. On the one hand, some recent reports in the literature suggest the validity of two-parameter pair-wise additive Lennard-Jones (LJ) potentials for liquid alkali metals. On the other hand, there are some reports suggesting the inaccuracy of pair potential functions for liquid metals. In this work, we have performed extensive molecular dynamics simulations of vapor-liquid phase equilibria in potassium to check the validity of the proposed LJ potentials and to improve their accuracy by changing the LJ exponents and taking into account the temperature-dependencies of the potential parameters. We have calculated the orthobaric liquid and vapor densities of potassium using LJ (12-6), LJ (8.5-4) and LJ (5-4), effective pair potential energy functions. The results show that using an LJ (8.5-4) potential energy function with temperature-independent parameters, µ and σ, is inadequate to account for the vapor-liquid coexistence properties of potassium. Taking into account the temperature-dependencies of the LJ parameters, µ(T) and σ(T), we obtained the densities of coexisting liquid and vapor potassium in a much better agreement with experimental data. Changing the magnitude of repulsive and attractive contributions to the potential energy function shows that a two-parameter LJ (5-4) potential can well reproduce the densities of liquid and vapor potassium. The results show that LJ (5-4) potential with temperature-dependent parameters produces the densities of liquid and vapor potassium more accurately, compared to the results obtained using LJ (12-6) and LJ (8.5-4) potential energy functions.

A novel synthesis of 3,4-dihydropyrimidin-2-(1H)-ones by one-pot cyclocondensation of aldehydes, 1,3-dicarbonyl compounds and urea or thiourea using nafion-H as the catalyst under ultrasound irradiation and solvent-free conditions was developed. Compared with the classical Biginelli reactions, this method consistently enjoys the advantages of mild reaction conditions, excellent yields, easy work up and short reaction time.

Organophosphorous compounds are important neuroactive molecules whose presents significant analytical challenges. New monoenzyme biosensor introduced here, is used for the measurement of the level of two organophosphorous compounds, paraoxon (POX) and ethyl parathion (EPA), in phosphate buffer. Prussian blue electrodepositionized on a graphite electrode served as a template for immobilization of monoenzyme layer. A monoenzyme layer containing choline oxidase was immobilized along with nafion and bovine serum albumin, by cross-linking with glutaraldehyde. The results revealed that the response of the proposed biosensor was linear between 5 µM and 80 µM in the presence of POX and EPA. Detection limits were 0.4 µM in both cases. Also, for the optimization of the biosensor performance, temperature and pH dependency, concentration of choline chloride as substrate of choline oxidase and incubation time were determined. The results showed that the optimum values for temperature, pH, substrate concentration and incubation time were room temperature, pH 7, 4 mM and 30 min, respectively.

A new PVC membrane electrode for the determination of phenylephrine hydrochloride based on the formation of an ion-association complex of phenylephrine hydrochloride with the phosphotungstate counter anion as an electroactive material dispersed in a PVC matrix is described. The sensor shows a fast, stable, near-Nernstian response for 1.0 × 10-5 to 1.0 × 10-1 M phenylephrine hydrochloride at 25 °C over the pH range of 3.5-8.0 with a cationic slope of 58.1 ± 0.6 mV decade-1. The electrode was successfully used for potentiometric determination of phenylephrine hydrochloride in some pharmaceutical drugs.

This research deals with the application of wood sawdust obtained from walnut and its polypyrrole (PPy) coated form for the removal of methylene blue (MB) from aqueous solutions. MB, a typical cationic dye, was used as a test probe. Coating of sawdust was carried out chemically via direct addition of chemical oxidant (FeCl3) on the sawdust which was previously soaked in monomer solution (0.2 M pyrrole). Adsorption experiments were carried out using both batch and fixed bed column systems. The effects of different system variables such as adsorbent dose, initial dye concentration, pH of test solution, contact time and breakthrough curves were studied. In order to find out the possibility of reuse, desorption study was also carried out in this investigation. It was found that both SD and PPy/SD are efficient and cost-effective adsorbents for the removal of MB dye from aqueous solutions. The collected data in this research indicate that compared with PPy/SD, adsorption of MB by SD is not a very pH dependent process, at least from pH 4 to 10. Higher sorption percentage of MB is obtained for PPy/SD at alkaline pHs.

Hydrogen peroxide/MoO3, as an efficient and clean oxidizing system was used to afford diasteroselective oxidative cyclization of bisnaphthols to spirans in ethanol at 60 °C with high yields. Bisnaphthols were prepared by the reaction of a series of aldehydes and 2-naphthol in the presence of a catalytic amount of H3[P(Mo3O10)4].nH2O (HPA) in refluxing dichloromethane.

A new spectrophotometric method was developed for the determination of two important nitroimidazoles; metronidazole (MZ) and tinidazole (TZ). The method was based on the charge-transfer (CT) complexation reaction of reduced forms of metronidazole and tinidazole as n-electron donors and chloranilic acid (CAA) as π-electron acceptor to form a purple-colored complex with a new absorption band at 520 nm which was adopted as the analytical wavelength. Molar absorptivities of 2.741 × 102 L M-1 cm-1 and 2.681 × 102 L M-1 cm-1 were obtained for MZ and TZ, respectively. Optimization of reducing agent and time of reduction revealed the superiority of metal hydrides over reducing metals. Reduction of MZ and TZ was completed at 30 °C within 10 min. Optimizations of temperature and time for the complexation reaction revealed that the reaction was completed at 30 °C within 5 min. A 60:40 mixture of 1,4-dioxane:acetonitrile was found to be the best diluting solvent for optimal detector response. The complexes were stable at room temperatures for weeks. Beer’s law was observed in the concentration of 5-40 µg ml (MZ) and 4.8-79.2 µg ml-1 (TZ) with low limits of detection of 1.88 and 0.74 µg ml-1, respectively. Overall recoveries of MZ and TZ from quality control samples were 103.19 ± 2.05 (%RSD = 1.99, n = 12) and 101.63 ± 1.41 (%RSD = 1.39) over three days. There was no interference from commonly utilized tablet excipients. No significant difference existed between the results of the new method and the BP titrimetric procedures (p > 0.05). The new CT procedure described in this paper is simple, fast, convenient, accurate and precise and has the novelty of carrying out the reactions at room temperature compared to previously described procedures. The new method could be adopted as an alternative procedure for the quality assessment of MZ and TZ in bulk and dosage forms.

A functionalized cyclotriphosphazene with four pyrazolyl substituents, N3P3(MeNC2H4O)(dmp)4 where dmp = 3,5-dimethyl-pyrazole, has been synthesized and characterized. The reaction of this potentially multi-site coordinating cyclotriphosphazene with diorganotin(IV) dichlorides, SnR2Cl2 (R = Ph, Me), leads to dinuclear [(SnPh2Cl2)2{N3P3(MeNC2H4O)(dmp)4}] (1) and mononuclear [(SnMe2Cl2){N3P3(MeNC2H4O)(dmp)4}] (2) complexes. These new compounds were characterized by elemental analysis and IR, 1H, 31P and 119Sn NMR spectroscopy. On the basis of these data, in the complex 1pyrazolylcyclotriphosphazene acts as a bis-bidentate ligand and coordinates to two SnPh2Cl2 molecules via two geminal pyrazolyl nitrogen atoms. As for complex 2, coordination to one SnMe2Cl2 molecule occurs through two nongeminally substituted pyrazolyl nitrogens. The 119Sn NMR data are consistent with the increasing of coordination number of tin(IV) in solution.

The chemiluminescence (CL) arising from reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) with hydrogen peroxide in the presence of a diethyl-2-(cyclohexylamino)-5-[(E)-2-phenyl-1-ethenyl]-3,4-furandicarboxylate as a novel fluorescer (Flu) has been studied. The relationship between the chemiluminescence intensity and concentrations of TCPO, sodium salicylate, hydrogen peroxide and fluorescer is reported. The chemiluminescence parameters including intensity at maximum CL, time at maximum intensity, total light yield, theoretical maximum level of intensity and pseudo-first-order rate constants for the rise and fall of the CL burst (kr and kf) were evaluated from computer fitting of the resulting intensity-time plots. The activation parameters Ea, ΔH‡, ΔS‡ and ΔG‡ for the rise and fall steps were evaluated from the temperature dependence of kr and kf values.

The new {[Ni(phen)3][Ni(dipic)2]}2.17H2O (1) (phen = 1,10-phenanthroline, dipic = dipicolinate)) has been prepared and characterized by elemental analysis, IR, UV-Vis, magnetic measurement and single crystal X-ray diffraction. The complex consists of two tris(1,10-phenanthroline)nickel(II) cations, two bis(dipicolinato)nickelate(II) anions and seventeen uncoordinated water molecules. The Ni(II) complex crystallizes in the triclinic space group P-1.The complex consisting of cation has distorted octahedral coordination by three bidentate phen ligands. In the complex anion, each dipic ligand simultaneously exhibits tridentate coordination modes through N atom of pyridine ring and oxygen atoms of the carboxylate groups. The crystal packing of 1 is a composite of intermolecular hydrogen bonding, π-π and C-H∙∙∙π interactions. The complex has also been investigated in terms of biological activity and it showed high activity against S. aureus fromGram positive bacteria and C. albicans from yeast tested.

In the present work, a novel Schiff-base was synthesized by the reaction of saccharin with tryptophan and characterized by elemental analysis as well as UV-Vis, FT-IR, 1H NMR spectroscopic data. The voltammetric behavior of Schiff-base was also studied on the hanging mercury drop electrode (HMDE) by using Square-Wave Voltammetry (SWV) and Cyclic Voltammetry (CV) techniques. The voltammograms of the Schiff-base exhibited two irreversible reduction peaks in Britton-Robinson buffer (pH 7.0-10.0) for the potential range from 0.0 V to -1.4 V. These peaks which appeared at more positive potentials than the reduction peaks of tryptophan and saccharin, may be assigned to the cathodic reductions of C-N+ and >C=N- moieties of Schiff-base.

Two novel compounds with formulae [Sn2(pydcH)2(H2O)2O]n, 1, and (4,4΄-bpyH2)0.5[Pb(pydc)2(4,4΄-bpyH)].4,4΄-bpy.4H2O, 2, were obtained from a one-pot reaction between pyridine-2,6-dicarboxylic acid (pydcH2) and 4,4΄-bipyridine (4,4΄-bpy) with corresponding Sn(II) and Pb(II) salts. In compound 1 with a polymeric structure, each Sn(II) atom is six-coordinated by one water molecule, two (pydcH)- groups and one oxide group resulted in a coordination polymer. Compound 2 has a seven-coordinated environment around Pb(II) atom by two (pydc)2- groups and one (4,4΄-bpyH). The anionic complex is balanced by half a (4,4΄-bpyH2)2+ as counter ion. There are four uncoordinated water molecules and one 4,4΄-bpy in the crystal lattice. Therefore, in compound 2, we have neutral, mono- and biprotonated forms of 4,4΄-bipyridine, simultaneously. Several interactions including O-H∙∙∙O, O-H∙∙∙N and C-H∙∙∙O hydrogen bonds, ion pairing, C-O∙∙∙π (O···Cg 3.324(3) Åand 3.381(3) Å in 1 and O···Cg 3.346(4) Å in 2), C-H∙∙∙π (C···Cg 3.618(4) Å in 2), and π∙∙∙π stackings (with Cg ···Cg distances of 3.613(2) and 3.641 (2) Å in 2) are present to expand and stabilize the structure. The complexation reactions of bpy and pydc-bpy with Sn2+ and Pb2+ ions in aqueous solution were investigated by potentiometric pH titrations, and the resulting equilibrium constants and species distributions at various pHs for major formed complexes are described.

The reactions between cephradine and VOSO4.3H2O in 1:1, 1:2 and 1:3 molar ratios in methanol were investigated at room temperature, 0 °C and -10 °C. In various pH conditions, the different complexes formulated as VO(H2O)3L2-, VO(H2O)L22- and VL3- were formed by titration of VOSO4.3H2O and cephradine with NaOH. These complexes were characterized by elemental analysis and IR spectroscopy. IR spectra of all the complexes show the disappearance of n(O-H) band of cephradine, which confirms complexation. Estimation of vanadium in the complexes was carried out by ICP-AES. The stability constants of each complex were calculated on the basis of which a general mechanism is hereby proposed with regard to the formation of these complexes. In complex (1) the cephradine ligand bind in bidentate [O,O] fashion together with a terminal oxo ligand and water molecules complete the metal coordination sphere. In complex (2) the cephradine ligands bind in bis-bidentate [O,O] fashion and the axial positions are occupied by the oxo ligand and a trans-water molecule. Biological screening tests show significant anti-bacterial and anti-fungal activities against various bacterial and fungal strains.

More efficient, cost effective and metal free DHP/TMSCl system for one pot reductive amination of aldehydes was developed. The method allows the efficient one pot synthesis of structurally diverse amines with Hantzsch ester as the hydrogen source in the presence of trimethylsilyl chloride as a catalyst in high to quantitative yields under mild conditions.

Bacillus sp. GHA1 was isolated from water samples and screened for the production of a-amylase. Maximum production of amylase by this strain occurs at 42 °C, pH 6.5 and 72 h after cultivation in production medium. The enzyme was purified through successive applications of ammonium sulfate precipitation, ion exchange and hydrophobic interaction chromatography, resulting in a single band with an apparent molecular weight of 66 kDa, as judged by SDS-PAGE. Calcium analysis of the purified enzyme revealed that it contained three metal ions per molecule. The new extracellular a-amylase is active in a wide range of pH with its maximum activity at pH values 5.5-8.0. The optimum temperature for enzyme activity is 57 °C and the presence of calcium has relatively low influence on its activity and thermostability. The Bacillus sp. GHA1 a-amylase with these properties may be suitable for use in detergent and food industries.

Anderson type hexamolybdochromate(III) was utilized as a catalyst for facile conversion of various aliphatic, benzylic and heterocyclic alcohols to corresponding aldehydes and ketones in good yields. The reaction was carried out in 50% aq. acetonitrile using hydrogen peroxide as the oxidant at 50 °C. The reaction was found to involve oxidation of the catalyst to its active Cr(V) intermediate by hydrogen peroxide.

A mild and efficient method has been developed for the preparation of α-amino nitriles from the condensation of aldehydes and ketones with aniline and TMSCN in the presence of a catalytic amount of Zr(HSO4)4 under solvent-free conditions at room temperature.

The use of polymeric reagents simplifies routine acylation of carboxylic acid because it eliminates the traditional purification. We describe the use of readily available cross-linked poly(4-vinylpyridine) supported tosyl chloride, [P4VP].TsCl, in the suspended solution phase synthesis of symmetrical anhydrides from carboxylic acids in the presence of K2CO3 in high yields and purity. The products can be obtained by filtration and evaporation of the solvent.

A highly efficient and simple method for the synthesis of N-aryl derivatives of pyrimidine and purine nucleobases via N-arylation of nucleobases using zinc oxide in 1-butyl-3-methylimidazolium bromide ([bmim]Br) under microwave as well as thermal conditions is described. In both conditions, the title compounds were produced in high to excellent yields and in short reaction times.

Direct electrochemistry of hemoglobin (Hb) was realized on a Nafion and CuS microsphere composite film modified carbon ionic liquid electrode (CILE) with N-butylpyridinium hexafluorophosphate (BPPF6) as binder. Scanning electron microscopy (SEM), UV-Vis absorption spectroscopy and cyclic voltammetry were used to characterize the fabricated Nafion/CuS/Hb/CILE. Experimental results showed that a pair of well-defined quasi-reversible redox peaks appeared with the formal potential as -0.386 V (vs. SCE) in pH 7.0 Britton-Robinson (B-R) buffer solution, which was attributed to the Hb heme Fe(III)/Fe(II) redox couples. The electrochemical parameters of Hb in the composite film were carefully investigated with the charge transfer coefficient (α), the electron transfer number (n) and the electron transfer rate constant (ks) as 0.505, 1.196 and 0.610 s-1, respectively. The composite film provided a favorable microenvironment for retaining the native structure of Hb. The presence of CuS microspheres showed great improvement on the electron transfer rate of Hb with the CILE, which maybe due to the contribution of specific characteristics of CuS microspheres and the inherent advantages of ionic liquid on the modified electrode. The fabricated Hb modified electrode showed good electrocatalytic ability in the reduction of H2O2. The proposed bioelectrode can be used as a new third generation H2O2 biosensor.

Corrosion behaviour of copper metal in acid solutions (HCl, H2SO4 and H3PO4) containing 2-amino-5-mercapto-1,3,4-thiadiazole (AMT) was investigated experimentally and theoretically via gravimetric, potentio-dynamic and quantum electrochemical approaches. Similar behavior was observed for H2SO4 and H3PO4 media, and related to the nature of anions at metal/solution interface. With regard to HCl, however, the rate of corrosion was determined to be low at initial stages, but high later on using an auto-catalyzing mechanism. In the presence of AMT, the experimental studies revealed that this molecule was a good anodic-type inhibitor causing substantial changes in corrosion potential. Moreover, its adsorption obeys the Langmuir isotherm. The values of ΔGads were determined and correlated to the inhibitor powers. Finally, the influence of media (anions) on metal corrosion was also investigated from molecular point of view by calculations of the copper-anions interaction using density functional theory.

In this study, 3,4-dimethylbenzaldehyde was obtained in 82.3% total yield by oxidation of 3,4-dimethylbenzyl chloride with NaNO3/AcOH catalyzed by PEG-600 in aqueous media. The starting material 3,4-dimethylbenzyl chloride was prepared by chloromethylation of o-xylene in CTAB micellar catalytic system. Compared with other synthetic methods, this method not only enhanced the yield, but also afforded an efficient work-up procedure. The structures of the products were confirmed by Elemental analysis, 1H NMR and 13C NMR or compared with authentic samples.

Organotin(IV) complexes with the general formulae R3ML [R: alkyl (Et, Ph and Bz), M: Sn and L: 1,3-bis(2-hydroxybenzylidene)thiourea were synthesized. The newly synthesized schiff base and its complexes were characterized by elemental analysis, melting point, molecular weight determination, IR and NMR [1H, 13C and 119Sn] spectral methods. In the light of these techniques, a tetrahedral geometry around the tin atom is proposed for the synthesized complexes. The experimental data have been compared with those in the literature which were found to coincide very well with the assigned structures. The ligands and their tin(IV) complexes were screened in vitro for their antibacterial activities. It was found that they possessed significant antibacterial activity and the effect of Ph3SnL was possibly superior to those of Et3SnL, Bz3SnL and ligand. These findings add new insights onto the synthesis of antibacterial drugs as the synthesized compounds showed promising antimicrobial activity.

A new compound of Sb(III), formulated as (pipzH2)[Sb2(pydc)4].2H2O (1), was synthesized and characterized by IR, 1H and 13C NMR spectroscopy, elemental analysis and single crystal X-ray diffractometry. The compound (1) is a member of a great family of supramolecular metallic compounds recently derived from a proton transfer ion pair i.e. (pipzH2)(pydc), where pipz is piperazine and pydcH2 is pyridine-2,6-dicarboxylic acid. In the title compound with a binuclear structure, Sb(III) atoms are pentacoordinated and the coordination polyhedra show distortion from a regular trigonal bipyramid due to stereochemically active lone pair on metallic centers. The four (pydc)2- ligands of the formula unit behave differently against metallic centers, i.e. two act as tridentate, and the other two as bidentate ligands. A variety of intermolecular O-H···O, N-H···O and C-H···O hydrogen bonds involving water molecules, cationic and anionic fragments are responsible for the extension of the supramolecular network of the compound. Optimized geometries were calculated for the title compound with the HF, B3LYP, B3PW91, B3P86 and B1LYP methods of theory by using the combination of LanL2DZ basis set with standard basis set 6-31G (d,p). The agreement between the optimized and experimental geometries was in the decreasing order: B3P86, B3PW91, B1LYP, B3LYP and HF. Electronic properties of the title compound were also investigated based on the natural bond orbital (NBO) analysis.

The first example of isonicotinic acid compounds with infinite mercury halide chains, [HgCl2(C6NO2H5)]n n[HgCl2]n(C6NO2H5) (1), was synthesized through hydrothermal reactions and structurally characterized by X-ray single crystal diffraction. Compound 1 features a one-dimensional (1-D) motif, based on infinite 1-D [HgCl2(C6NO2H5)]n chains, neutral HgCl2 moieties and isolated isonicotinic acid molecules. The [HgCl2(C6NO2H5)]n chains, HgCl2 moieties and isonicotinic acid molecules are interlinked by hydrogen bonds and π-π interactions to give a two-dimensional supramolecular layer. Photoluminescent investigation reveals that the title compound exhibits a strong emission in blue region. The emission band is identified as the π-π* transitions of the isonicotinic acid moieties.

A simple and sensitive method was developed for the analysis of preservatives sodium benzoate, methylparaben and propylparaben in nystatin suspensions by reversed-phase high performance liquid chromatography (HPLC), equipped with a C18 column and PDA detector. The mobile phase was a mixture of acetonitrile and acetate buffer of pH 4.4 (35:65 v/v). Under the optimized experimental conditions, separation of the preservatives was achieved in less than 20 min. The limits of quantifications (LOQs) and the linear dynamic ranges (LDRs) of sodium benzoate, methylparaben and propylparaben were 0.3 and 50-1000 µg ml-1, 0.5 and 50-600 µg ml-1 and 0.3 and 50-900 µg ml-1, respectively; the respective precisions (%RSD) at 500 µg ml-1 level were 0.72%, 0.73% and 0.51% (n = 6). The average recoveries of sodium benzoate, methylparaben and propylparaben for spiked nystatin samples were obtained as 98%, 97% and 98%, respectively.