Heat capacity studies of the iron oxyhydroxides akaganéite (β-FeOOH) and lepidocrocite (γ-FeOOH)

The iron oxides and iron oxyhydroxides exist as several different polymorphs, and a thermodynamic understanding of these polymorphs can provide us with an understanding of their relative stability and chemical reactivity. This study provides heat capacity measurements for lepidocrocite (γ-FeOOH) over the temperature range (0.8 to 38) K and akaganéite (β-FeOOH) over the range (0.7 to 302) K. Fits of the heat capacity of the two samples below T = 15 K showed similar behavior to previously published fits of goethite (α-FeOOH), which required a linear term and an anisotropic gap parameter to model accurately the antiferromagnetic spin–wave contributions. The akaganéite measurements were compared to previously reported measurements all of which showed significant disagreement. It is believed that the measurements reported here are the most reliable. Also, the presence of adsorbed water contributes significantly to the heat capacity of akaganéite, and the standard molar entropy at T = 298.15 K of the hydrated form was calculated to be (81.8 ± 2) J · mol^?1 · K^?1.     

Direct injection of native aqueous matrices by achiral-chiral chromatography ion trap mass spectrometry for simultaneous quantification of pantoprazole and lansoprazole enantiomers fractions

A two-dimensional liquid chromatography system coupled to ion-trap tandem mass spectrometer (2DLC-IT-MS/MS) was employed for the simultaneous quantification of pantoprazole and lansoprazole enantiomers fractions. A restricted access media of bovine serum albumin octyl column (RAM-BSA C(8)) was used in the first dimension for the exclusion of the humic substances, while a polysaccharide-based chiral column was used in the second dimension for the enantioseparation of both pharmaceuticals. The results described here show good selectivity, extraction efficiency, accuracy, and precision with detection limits of 0.200 and 0.150 μg L(-1) for the enatiomers of pantoprazole and lansoprazole respectively, while employing a small amount (1.0 mL) of native water sample per injection. This work reports an innovative assay for monitoring work, studies of biotic and abiotic enantioselective degradation and temporal changes of enantiomeric fractions.     

Evaluation of comprehensive two-dimensional gas chromatography with micro-electron capture detection for the analysis of seven pesticides in sediment samples

A GC-μECD and a GC×GC-μECD method were developed for the analysis of pesticides in sediments. For 1D-GC, instrumental LOD and LOQ were found in the range from 0.60 to 2.31μgL(-1) and 1.83 to 5.62μgL(-1), respectively. For GC×GC method development two sets of columns were tested (DB-5/DB-17ms, and HP-50+/DB-1ms), and the best results were obtained with the set of columns DB-5/DB-17ms. Instrumental LOD and LOQ were found in the range from 0.08 to 1.07μgL(-1) and 0.25 to 3.23μgL(-1), respectively. The LOD for the GC×GC was about 36% lower than those obtained for the 1D-GC. Concentrations of 21.18μgkg(-1) through 1D-GC method and 3.34μgkg(-1) for GC×GC for trifloxystrobin were found in a sediment sample which was collected close to an area of rice plantation.     

Unimolecular reactions in the CF3CH2Cl ↔ CF2ClCH2F system: isomerization by interchange of Cl and F atoms

The recombination of CF(2)Cl and CH(2)F radicals was used to prepare CF(2)ClCH(2)F* molecules with 93 ± 2 kcal mol(-1) of vibrational energy in a room temperature bath gas. The observed unimolecular reactions in order of relative importance were: (1) 1,2-ClH elimination to give CF(2)═CHF, (2) isomerization to CF(3)CH(2)Cl by the interchange of F and Cl atoms and (3) 1,2-FH elimination to give E- and Z-CFCl═CHF. Since the isomerization reaction is 12 kcal mol(-1) exothermic, the CF(3)CH(2)Cl* molecules have 105 kcal mol(-1) of internal energy and they can eliminate HF to give CF(2)═CHCl, decompose by rupture of the C-Cl bond, or isomerize back to CF(2)ClCH(2)F. These data, which provide experimental rate constants, are combined with previously published results for chemically activated CF(3)CH(2)Cl* formed by the recombination of CF(3) and CH(2)Cl radicals to provide a comprehensive view of the CF(3)CH(2)Cl* ? CF(2)ClCH(2)F* unimolecular reaction system. The experimental rate constants are matched to calculated statistical rate constants to assign threshold energies for the observed reactions. The models for the molecules and transition states needed for the rate constant calculations were obtained from electronic structures calculated from density functional theory. The previously proposed explanation for the formation of CF(2)═CHF in thermal and infrared multiphoton excitation studies of CF(3)CH(2)Cl, which was 2,2-HCl elimination from CF(3)CH(2)Cl followed by migration of the F atom in CF(3)CH, should be replaced by the Cl/F interchange reaction followed by a conventional 1,2-ClH elimination from CF(2)ClCH(2)F. The unimolecular reactions are augmented by free-radical chemistry initiated by reactions of Cl and F atoms in the thermal decomposition of CF(3)CH(2)Cl and CF(2)ClCH(2)F.     

Antileishmanial activity of the hydroalcoholic extract of Miconia langsdorffii, isolated compounds, and semi-synthetic derivatives

The in vitro activity of the crude hydroalcoholic extract of the aerial parts of Miconia langsdorffii Cogn. was evaluated against the promastigote forms of L. amazonensis, the causative agent of cutaneous leishmaniasis in humans. The bioassay-guided fractionation of this extract led to identification of the triterpenes ursolic acid and oleanolic acid as the major compounds in the fraction that displayed the highest activity. Several ursolic acid semi-synthetic derivatives were prepared, to find out whether more active compounds could be obtained. Among these ursolic acid-derived substances, the C-28 methyl ester derivative exhibited the best antileishmanial activity.     

Rheological Analysis of Biopolymer Produced by Aureobasidium Pullulans in Different Sources of Nitrogen

Summary: In this study, the rheological behaviors of media fermented by two Aureobasidium pullulans strains (IOC 3467 and IOC 3011) were evaluated in different nutritional conditions. The media consisted of crystal sugar (sucrose), as the main carbon source, and different nitrogen sources (ammonium sulfate, sodium nitrate, ammonium nitrate, urea or residual brewery yeast - RBY). Viscosity measurements were performed on cell-free supernatants, from 48-hour fermentation assays, at 25 ^°C. Shear rates ranged between 0.1000 and 500 s⁻¹. All samples showed pseudoplastic behavior. Nevertheless, the viscosimetric profile of each one varied according to the nitrogen source, its concentration and the strain used. The maximum viscosity of 0.06 Pa.s. was achieved at 15.6 s⁻¹ for IOC 3011 strain grown on RBY as nitrogen source.     

Observation of vinylidene emission in mixed phosphine/diimine complexes of Ru(II) at room temperature in solution

The mixed ruthenium(II) complexes trans-[RuCl₂(PPh₃)₂(bipy)] (1), trans-[RuCl₂(PPh₃)₂(Me₂bipy)](2), cis-[RuCl₂(dcype)(bipy)](3), cis-[RuCl₂(dcype)(Me₂bipy)](4) (PPh₃ = triphenylphosphine, dcype = 1,2-bis(dicyclohexylphosphino)ethane, bipy = 2,2′-bipyridine, Me₂bipy = 4,4′-dimethyl-2,2′-bipyridine) were used as precursors to synthesize the associated vinylidene complexes. The complexes [RuCl(CCHPh)(PPh₃)₂(bipy)]PF₆ (5), [RuCl(CCHPh)(PPh₃)₂(Me₂bipy)]PF₆ (6), [RuCl(CCHPh)(dcype)(bipy)]PF₆ (7), [RuCl(CCHPh)(dcype)(bipy)]PF₆ (8) were characterized and their spectral, electrochemical, photochemical and photophysical properties were examined. The emission assigned to the π–π1 excited state from the vinylidene ligand is irradiation wavelength (340, 400, 430 nm) and solvent (CH₂Cl₂, CH₃CN, EtOH/MeOH) dependent. The cyclic voltammograms of (6) and (7) show a reversible metal oxidation peak and two successive ligand reductions in the +1.5-(?0.64) V range. The reduction of the vinylidene leads to the formation of the acetylide complex, but due the hydrogen abstraction the process is irreversible. The studies described here suggest that for practical applications such as functional materials, nonlinear optics, building blocks and supramolecular photochemistry.     

A forensic study: Lead determination in gunshot residues

Electrochemical lead analyses of gunshot residues (GSRs) were performed using an acidic solution with a bare gold microelectrode in the presence of chloride ions. GSRs from four different guns (0.38 in. revolver, 12 caliber pump-action shotgun, 0.38 repeating rifle, and a 0.22 caliber semi-automatic rifle) and six different types of ammunition (CleanRange®, normal, semi-jacketed, especial 24g®, 3T®, CBC®, and Eley®) were analyzed. Results obtained with the proposed methodology were compared with those from an atomic absorption spectrometry analysis, and a paired Student's t-test indicated that there was no significant difference between them at the 95% confidence level. With this methodology, a detection limit of 1.7 nmol L^? 1 (3σ/slope), a linear range between 10 and 100 nmol L^? 1, and a relative standard deviation of 2.5% from 10 measurements were obtained.     

Simultaneous Analysis of Isoniazid and Its Impurities by CZE

An alternative methodology for simultaneous determination of isoniazid, isonicotinic acid, 4-cyanopyridine, ethyl isonicotinate and isonicotinamide by capillary zone electrophoresis, within an analysis time of 11 min, is proposed. An electrolyte composed by 50 mmol L⁻¹ of acetic acid/sodium acetate buffer and 12.5 mmol L⁻¹ of Cu²⁺, an analyte dilution in 1 mmol L⁻¹ of Brij 35 and 12.5 mmol L⁻¹ of Cu²⁺ and +20 kV voltage were optimized. After evaluating some figures of merit, such as linearity, precision, recovery and quantification limit, the method was successfully applied to the isoniazid analysis in tablets. The contents found were 99.3 mg of isoniazid and 0.3 mg of isonicotinic acid, corresponding to 0.3 % of impurity regarding the content of the active ingredient in the pharmaceutical formulation.

     

Formation of Integral Asymmetric Membranes of AB Diblock and ABC Triblock Copolymers by Phase Inversion

The formation of integral asymmetric membranes from ABC triblock terpolymers by non‐solvent‐induced phase separation is shown. They are compared with the AB diblock copolymer precursors. Triblock terpolymers of polystyrene‐block‐poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (PS‐b‐P2VP‐b‐PEO) with two compositions are investigated. The third block supports the formation of a membrane in a case, where the corresponding diblock copolymer does not form a good membrane. In addition, the hydrophilicity is increased by the third block and due to the hydroxyl group the possibility of post‐functionalization is given. The morphologies are imaged by scanning electron microscopy. The influence of the PEO on the membrane properties is analyzed by water flux, retention, and dynamic contact angle measurements.