Electroanalysis and determination of acetaldehyde in fuel ethanol using the reaction with 2,4-dinitrophenylhydrazine

The voltammetric reduction of acetaldehyde was studied in 0.1 M LiOH: LiCl (60: 40 v/v). Well-defined waves can be seen at −1.77 and −1.60 V with the use of hanging mercury and glassy carbon electrodes. Acetaldehyde was shown to react at room temperature with the 2,4-dinitrophenylhydrazine and the product exhibited a differential pulse voltammetric peak at −0.90 V, which was well separated from the peaks of the derivative. This allowed the indirect determination of acetaldehyde in the presence of 0.1 M ethanol/tetrabutylammonium perchlorate after 10 min of reaction. Calibration graphs were obtained for 1.00 × 10⁻⁶−1.00 × 10⁻⁴ M of acetaldehyde. The detection limit is 8.14 × 10⁻⁷ M. The method has been applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pretreatment. The text was submitted by the authors in English.     

First total synthesis of JS isoprostane

A stereoselective Julia-Lythgoe olefination followed by an efficient 1,3-allylic transposition of the C-9 hydroxyl group of compound 13 has allowed the first total synthesis of J(2) isoprostane (1), a recently discovered member of the growing isoprostane family. This elusive compound opens up numerous new avenues for the molecular biology of cyclopentenone prostaglandins which are endowed of intriguing biological effects such as antitumor, antiinflammatory, and antiviral activities. In principle, our approach is flexible enough to allow an easy synthesis of other isoprostanes of the J family following the same methodology.     

A general enantioselective approach to jasmonoid fragrances: synthesis of (+)-(1R,2S)-methyl dihydrojasmonate and (+)-(1R,2S)-magnolione

Methyl dihydrojasmonate 1 and magnolione 3 are of both academic and industrial interest. In this paper, we describe a flexible, high-yielding route to diastereomerically pure (+)-cis-(1R,2S)-methyl dihydrojasmonate 1 and the first synthesis of (+)-cis-(1R,2S)-magnolione 3, both with enantiomeric excesses up to 93%. The two syntheses diverged from the same advanced intermediate 5, readily available from the enantioenriched hydroxymethyl delta-lactone (-)-(3aS,4S,6aR)-6. The olfactory properties of (1R,2S)-1 and (1R,2S)-3 are reported.     

Square‐Wave Voltammetry Applied to the Analysis of the Dye Marker,Solvent Blue 14, in Kerosene and Fuel Alcohol

The purpose of this paper is to develop an electroanalytical method based on square‐wave voltammetry (SWV) for the determination of the solvent blue 14 (SB‐14) in fuel samples. The electrochemical reduction of SB‐14 at glassy carbon electrode in a mixture of Britton‐Robinson buffer with N,N‐dimethylformamide (1 : 1, v/v) presented a well‐defined peak at?0.40 V vs. Ag/AgCl. All parameters of the SWV technique were optimized and the electroanalytical method presented a linear response from 1.0×10^?6 to 6.0×10^?6 mol L^?1 (r=0.998) with a detection limit of 2.90×10^?7 mol L^?1. The developed method was successfully utilized in the quantification of the dye SB‐14 in kerosene and alcohol samples with average recovery from 93.00 to 98.10%.     

Metallorganic routes to nanoscale iron and titanium oxide particles encapsulated in mesoporous alumina: formation, physical properties, and chemical reactivity

Iron and titanium oxide nanoparticles have been synthesized in parallel mesopores of alumina by a novel organometallic "chimie douce" approach that uses bis(toluene)iron(0) (1) and bis(toluene)titanium(0) (2) as precursors. These complexes are molecular sources of iron and titanium in a zerovalent atomic state. In the case of 1, core shell iron/iron oxide particles with a strong magnetic coupling between both components, as revealed by magnetic measurements, are formed. M?ssbauer data reveal superparamagnetic particle behavior with a distinct particle size distribution that confirms the magnetic measurements. The dependence of the M?ssbauer spectra on temperature and particle size is explained by the influence of superparamagnetic relaxation effects. The coexistence of a paramagnetic doublet and a magnetically split component in the spectra is further explained by a distribution in particle size. From M?ssbauer parameters the oxide phase can be identified as low-crystallinity ferrihydrite oxide. In agreement with quantum size effects observed in UV-visible studies, TEM measurements determine the size of the particles in the range 5-8 nm. The particles are mainly arranged alongside the pore walls of the alumina template. TiO2 nanoparticles are formed by depositing 2 in mesoporous alumina template. This produces metallic Ti, which is subsequently oxidized to TiO2 (anatase) within the alumina pores. UV-visible studies show a strong quantum confinement effect for these particles. From UV-visible investigations the particle size is determined to be around 2 nm. XPS analysis of the iron- and titania- embedded nanoparticles reveal the presence of Fe2O3 and TiO2 according to experimental binding energies and the experimental line shapes. Ti4+ and Fe3+ are the only oxidation states of the particles which can be determined by this technique. Hydrogen reduction of the iron/iron-oxide nanoparticles at 500 degrees C under flowing H2/N2 produces a catalyst, which is active towards formation of carbon nanotubes by a CVD process. Depending on the reaction conditions, the formation of smaller carbon nanotubes inside the interior of larger carbon nanotubes within the alumina pores can be achieved. This behavior can be understood by means of selectively turning on and off the iron catalyst by adjusting the flow rate of the gaseous carbon precursor in the CVD process.     

Symmetry breaking effect in the ferrocene electronic structure by hydrocarbon-monosubstitution: an experimental and theoretical study

We present here the results of a synchrotron radiation-excited UV-photoemission investigation and density functional theory calculations on a structurally related series of organometallic free molecules: ethylferrocene (EtFC), vinylferrocene (VFC), and ethynylferrocene (EFC). This series exemplifies the electronic interactions operating when the C-C substituent group of an aromatic ring is bound to the substrate surface atoms, from a single C-C bond to the double and triple C-C bond pi systems which are still able to preserve substrate-molecule conjugation. A detailed assignment of the gas phase valence photoelectron spectra is discussed, providing new data on the electronic structure of EtFC and EFC and offering a partial reinterpretation of previous assignments on VFC. The broken symmetry of ferrocene caused by the monosubstitution has notable effects on the removal of the molecular orbital (MO) degeneracy which is found to be especially remarkable for the ferrocenelike e(1)' MOs. This effect is ascribed to the interaction between the aromatic cyclopentadyenyl ring and the substituent through sigma/pi hyperconjugation and pi-conjugation mechanisms depending on the nature of the hydrocarbon moiety and its conformational geometry. The vertical ionization energy values of the highest occupied MO for the alkylferrocene and ferrocene free molecules linearly correlate with the redox potential in acetonitrile for ferrocene and the corresponding hybrids obtained by covalently anchoring the free molecule on silicon.     

Thermal decomposition of praseodymium nitrate hexahydrate Pr(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>·6H<Subscript>2</Subscript>O

The hexahydrate of praseodymium nitrate hexahydrate Pr(NO₃)₃·6H₂O does not show phase transitions in the range of 233–328 K when the compound melts in its own water of crystallization. It is suggested that the thermal decomposition is a complex step-wise process, which involves the condensation of 6 mol of the initial monomer Pr(NO₃)₃·6H₂O into a cyclic cluster 6[Pr(NO₃)₃·6H₂O]. This hexamer gradually loses water and nitric acid, and a series of intermediate amorphous oxynitrates is formed. The removal of 68% HNO₃–32% H₂O azeotrope is essentially a continuous process occurring in the liquid phase. At higher temperatures, oxynitrates undergo thermal degradation and lose water, nitrogen dioxide and oxygen, leaving behind normal praseodymium oxide Pr₂O₃. The latter absorbs approximately 1 mol of atomic oxygen from N₂O₅ disproportionation, giving rise to the non-stoichiometric higher oxide Pr₂O_3.33. All mass losses are satisfactorily accounted for under the proposed scheme of thermal decomposition.     

Catalyst‐Dependent Chemoselective Formal Insertion of Diazo Compounds into C−C or C−H Bonds of 1,3‐Dicarbonyl Compounds

A catalyst‐dependent chemoselective one‐carbon insertion of diazo compounds into the C?C or C?H bonds of 1,3‐dicarbonyl species is reported. In the presence of silver(I) triflate, diazo insertion into the C(=O)?C bond of the 1,3‐dicarbonyl substrate leads to a 1,4‐dicarbonyl product containing an all‐carbon α‐quaternary center. This reaction constitutes the first example of an insertion of diazo‐derived carbenoids into acyclic C?C bonds. When instead scandium(III) triflate was applied as the catalyst, the reaction pathway switched to formal C?H insertion, affording 2‐alkylated 1,3‐dicarbonyl products. Different reaction pathways are proposed to account for this powerful catalyst‐dependent chemoselectivity.     

High-performance anion-exchange chromatography coupled with pulsed amperometric detection and capillary zone electrophoresis with indirect ultra violet detection as powerful tools to evaluate prebiotic properties of fructooligosaccharides and inulin

Fructooligosaccharides (FOS) and inulin are food grade non-digestible carbohydrates that exert beneficial nutritional effect. This paper describes the suitability of high-performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) and capillary zone electrophoresis (CZE) to evaluate fermentation properties of FOS and inulin in pure Bifidobacterium cultures; and to study their effects on faecal cultures (microbial population and short-chain fatty acids). Prebiotic effectiveness of FOS and inulin of different degrees of polymerization was evaluated monitoring the changes in their molecular weight distribution during the in vitro growth of selected Bifidobacterium strains. The qualitative analysis of the residual soluble oligosaccharides or polysaccharides from Raftilose Synergy, Raftiline HP and Raftilose P95 was carried out by HPAEC-PAD, using a CarboPac PA 100 column and an appositely optimized gradient elution program. Under the optimized gradient elution conditions, glucose, fructose, sucrose were resolved from each other and from fructans with a DP ranging from 3 (1-kestose) to 60. The chromatographic profiles of the spent broths pointed out that almost every strain presented a different capability to ferment fructan chains of variable DP, indicating wide strain to strain differences. To explore the prebiotic effect of FOS and inulin, related to of short chain fatty acids (SCFAs) accumulation in faecal cultures due to fermentative metabolism of intestinal microflora, analysis of SCFAs, acetic and lactic acid was achieved by co-electroosmotic capillary electrophoresis, where the electrophoretic mobility of the anionic analytes and electroosmotic flow (EOF) were similarly directed. Moreover, the use of UV detection for the analyses of our organic anions required a running electrolyte which allowed indirect detection. The optimization of the capillary electrophoretic conditions was carried out by applying a chemometric study based on the use of the experimental design, the effects of three parameters, i.e. temperature, voltage and percentage of methanol added to the background electrolyte were investigated.