SSZ-53 and SSZ-59: two novel extra-large pore zeolites

The syntheses, structure solutions, and physicochemical and catalytic characterizations of the novel zeolites SSZ-53 and SSZ-59 are described. SSZ-53 and SSZ-59 were synthesized under hydrothermal conditions with the [1-(4-fluorophenyl)cyclopentylmethyl]trimethyl ammonium cation and 1-[1-(4-chlorophenyl)cyclopentylmethyl]-1-methyl azocanium cation, respectively, as structure-directing agents. The framework topology of SSZ-53 was solved with the FOCUS method, and the structure of SSZ-59 was determined by model building. Rietveld refinement of synchrotron X-ray powder diffraction data confirms each proposed model. SSZ-53 and SSZ-59 each possess a one-dimensional channel system delimited by 14-membered rings. Results from transmission electron microscopy, electron diffraction, catalytic experiments (spaciousness index and constraint index tests), and argon and hydrocarbon adsorption experiments are consistent with the proposed structures.     

Efficient and stereoselective synthesis of bicyclo[3.2.1]octan-8-ones: synthesis and palladium-catalyzed isomerization of functionalized 2-vinyl-2,3,3a,4,5,6-hexahydro-2,3-benzofurans

A new C,O-cyclodialkylation of dilithiated cyclic beta-keto esters and beta-keto sulfones with 1,4-dibromo-2-butene is reported which results in regio- and diastereoselective formation of 2-vinyl-2,3,3a,4,5,6-hexahydro-2,3-benzofurans. The products could be efficiently transformed into functionalized bicyclo[3.2.1]octan-8-ones by a palladium-catalyzed rearrangement reaction. In case of sulfone derivatives, this rearrangement proceeds with high stereospecifity to give exclusively the endo-configured diastereomers. The bicyclo[3.2.1]octane skeleton is present in a large number of pharmacologically important natural products.     

Study of ion beam induced mixing in Sn/Si system using electrical resistivity measurements

The ion-beam mixing of Sn thin film evaporated on silicon has been investigated by continuously measuring the electrical resistivity of the sample during irradiation by Kr ions. The resistivity results exhibit a tendency toward a saturation process and allow the determination of the critical dose corresponding to the total mixing condition. The variation of the volume fraction of intermixed atoms as a function of the ion dose has been deduced and compared with a semiempirical formula to explain the observed mixing kinetics. A linear dependence of the volume fraction of the intermixed atoms on the fluence is observed, which is a signature of recoil type mixing.     

Microwave-assisted synthesis of new pyrimido[4′,5′：4,5]thiazolo[3,2-α] benzimidazol-4（3H）-one derivatives in solvent-free condition

Microwave-assisted synthesis of new 2-arylpyrimido[4′,5′：4,5]thiazolo[3,2-α]benzimidazol-4（3H）-ones from 3-aminothia- zolo[3,2-α]benzimidazol-2-earboxamide and aroyl halides in solvent-free condition is described. In comparison with classical conditions the reactions are faster and the yields are higher under microwave irradiation.     

Enaminones in heterocyclic synthesis: Synthesis and chemical reactivity of 3‐anilino‐1‐substituted‐2‐propene‐1‐ one

The 3‐anilinoenones 3a,b were prepared from the corresponding 3‐dimemyl‐aminopropenones. The reactivity of 3a,b towards a variety of carbon and nitrogen nucleophiles as well as naphthoquinones is reported.     

Variable coordination geometries at the diiron(II) active site of ribonucleotide reductase R2

The R2 subunit of Escherichia coli ribonucleotide reductase contains a dinuclear iron center that generates a catalytically essential stable tyrosyl radical by one electron oxidation of a nearby tyrosine residue. After acquisition of Fe(II) ions by the apo protein, the resulting diiron(II) center reacts with O(2) to initiate formation of the radical. Knowledge of the structure of the reactant diiron(II) form of R2 is a prerequisite for a detailed understanding of the O(2) activation mechanism. Whereas kinetic and spectroscopic studies of the reaction have generally been conducted at pH 7.6 with reactant produced by the addition of Fe(II) ions to the apo protein, the available crystal structures of diferrous R2 have been obtained by chemical or photoreduction of the oxidized diiron(III) protein at pH 5-6. To address this discrepancy, we have generated the diiron(II) states of wildtype R2 (R2-wt), R2-D84E, and R2-D84E/W48F by infusion of Fe(II) ions into crystals of the apo proteins at neutral pH. The structures of diferrous R2-wt and R2-D48E determined from these crystals reveal diiron(II) centers with active site geometries that differ significantly from those observed in either chemically or photoreduced crystals. Structures of R2-wt and R2-D48E/W48F determined at both neutral and low pH are very similar, suggesting that the differences are not due solely to pH effects. The structures of these "ferrous soaked" forms are more consistent with circular dichroism (CD) and magnetic circular dichroism (MCD) spectroscopic data and provide alternate starting points for consideration of possible O(2) activation mechanisms.     

Oil-in-water emulsions stabilized by highly charged polyelectrolyte-grafted silica nanoparticles

Fully sulfonated poly(styrenesulfonate) brushes were grown from the surface of colloidal silica particles and used to prepare stable trichloroethylene-in-water and heptane-in-water Pickering emulsions. These particles were highly charged and colloidally stable in water but could not be dispersed in trichloroethylene or heptane. Both two-phase (emulsion plus neat water) and three-phase (emulsion separating neat oil and water phases) systems were observed, with water-continuous emulsion phases in all cases. Emulsion phases containing as much as 83% (v/v) oil were stable for over six months. Poly(styrenesulfonate)-grafted particles were very efficient emulsifiers; stable emulsion phases were prepared when using as little as 0.04 wt% particles. The emulsifying effectiveness of the poly(styrenesulfonate)-grafted silica particles can be attributed to the hydrophobicity of the vinylic polymer backbone that makes this highly charged polyelectrolyte unusually surface active at the oil/water interface.     

Charge-transfer complexes of barbiturates and phenytoin

Simple and sensitive spectrophotometric methods are described, for the first time, for the determination of sodium salts of phenobarbital (1), thiopental (2), methohexital (3) and phenytoin (4). The methods are based on the reaction of these drugs as n-electron donors with the sigma-acceptor iodine and various pi-acceptors: 7,7,8,8-tetracyanoquinodimethane; 2,3-dichloro-5,6-dicyano-1,4-benzoquinone; 2,3,5,6-tetrachloro-1,4-benzoquinone; 2,3,5,6-tetrafluoro-1,4-benzoquinone; 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone; tetracyanoethylene and 2,4,7-trinitro-9-fluorenon. Depending on the solvent polarity, different coloured charge-transfer complexes and radicals were developed. Different variables and parameters affecting the reactions were studied and optimized. The formed complexes were examined by UV/VIS, infrared and (1)H-NMR. Due to the rapid development of colours at ambient temperature, the obtained results were used on thin layer chromatograms for the detection of the investigated compounds. Beer's plots were obeyed in a general concentration range of 1-400 mug ml(-1) for the investigated compounds with different acceptors. Interference from some co-formulated drugs was also studied. No interference was observed due to additives commonly present in the pharmaceutical preparations. The proposed methods could be applied successfully to the determination of the investigated compounds in pure and pharmaceutical dosage forms with good accuracy and precision, the recoveries ranged from 98.7+/-0.5 to 101.1+/-0.5%. The results were compared favourably with the official methods.     

Solvent extraction of lanthanum(III), europium(III) and lutetium(III) with fluorinated 1-phenyl-3-methyl-4-benzoyl-5-pyrazolones into chloroform

A series of chelating reagents, 1-phenyl-3-methyl-4-(2-fluorobenzoyl)-5-pyrazolone, 1-phenyl-3-methyl-4-(3-fluorobenzoyl)-5-pyrazolone and 1-phenyl-3-methyl-4-(4-fluorobenzoyl)-5-pyrazolone, has been synthesized. The extraction of Ln(III), (Ln = La, Eu and Lu) into chloroform with these reagents at 30 +/- 1 degrees has been studied. The composition of the complexes extracted has been determined by the slope method, and the extraction constants K(ex), were measured. The presence of the fluorine atom in the reagents does not make the K(ex), values much different from those obtained with the parent pyrazolone.     

Selective spectrophotometric determination of ascorbic acid in drugs and foods

A new analytical method was developed for the determination of ascorbic acid. The method is based on the reaction of ascorbic acid with 4-chloro-7-nitrobenzofurazane (NBD-Cl) in the presence of 0.2M sodium hydroxide, where a bluish green colour (lambda(max) 582 nm) is developed after dilution with 50% (v/v) aqueous acetone solution. Beer's law was obeyed in a concentration range of 5-20 microg ascorbic acid/ml with a good correlation coefficient (r = 0.9990). The method was found to be highly specific for the determination of ascorbic acid in the presence of dehydro-ascorbic acid, all other vitamins and minerals possibly present in multivitamin preparations, rutin, salicylamide, acetyl salicylic acid, paracetamol, caffeine, phenylephrine hydrochloride and dipyrone. Moreover, the proposed procedure was also successfully applied for the determination of ascorbic acid in some canned and fresh fruit juices, some vegetables and infant milk products without interference from coloured and other substances present in the plant extracts.