Gas-phase ion chemistry in the ternary SiH4-C3H6-NH3 system

The gas-phase ion chemistry of propene-ammonia and silane-propene-ammonia mixtures was studied by ion trap mass spectrometry. As far as the binary mixture is concerned, the effect of different molar ratios of the reactants on the trend of ion species formed was evaluated, the ion-molecule reaction processes were identified and the rate constants for the main processes were measured. The results were compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane-propene-ammonia mixture the mechanisms of formation of Si(m)C(n)N(p)H(q)(+) clusters were elucidated and the rate constants of the most important steps were measured. For some species, selected by double isolation (MS/MS), the low abundance of the ions allowed us to determine the reaction paths but not the rate constants. Ternary ions are mainly formed by reactions of Si(m)C(n)H(q)(+) ions with ammonia, whereas a minor contribution comes from reactions of Si(m)N(p)H(q)(+) ions with propene. On the other hand, the C(n)N(p)H(q)(+) ions showed a very low reactivity and no step leading to ternary ion species was identified. The formation of hydrogenated ternary ions with Si, C and N has a basic importance in relation to their possible role as precursors of amorphous silicon carbides doped with nitrogen obtained by deposition from silane-propene-ammonia mixtures properly activated.     

Isolation and purification of lignoperoxidase from the mushroom <Emphasis Type="Italic">Pleurotus ostreatus</Emphasis>

The accumulation dynamics of lignolytic enzymes in culture media of the basidiomycetes Panus tigrinus, Pleurotus ostreatus, Fomes fomentarus, and the micromycete Aspergillus terreus were studied during the incubation period. It was found that Pleurotus ostreatus is the most active producer of lignoperoxidase enzymes among the studied fungi. Gel filtration and ion-exchange chromatography were used to isolate a homogeneous enzyme with lignoperoxidase activity. The maximum activity was found at pH 2.7 and 29°C. Gel electrophoresis determined the molecular weight (44 kDa). __________ Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 564–566, November–December, 2007.     

The chemical state of arsenic in minerals of environmental interest--an XPS and an XAES study

A systematic analytical study using X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) has been carried out to characterize the chemical state of arsenic in complex environmental samples. The conventional approach, which relies on the chemical shift of the core levels As3d, provides ambiguous results in determining the chemical environment of arsenic. A more accurate approach, based on the Auger parameter and on the Wagner (Chemical State) plot, which combines AsLMM kinetic energy and As3d binding energy, was adopted. This novel method for determining the chemical state of arsenic was employed to completely characterize arsenic in complex environmental samples.     

"Stapled" bis(phthalocyaninato)niobium(IV), Pc2Nb: X-ray crystal structure,chemical and electrochemical behavior,and theoretical studies. Perspectives for the use of Pc2Nb (thin films) as an "optically passive electrode" in electrochromic devices

Recrystallization of the previously reported monosolvated bis(phthalocyaninato)niobium(IV), [Pc2Nb].CINP (CINP = 1-chloronaphthalene), has allowed isolation of a single crystal of a new solvated form, i.e. [Pc2Nb]. 3.5CINP, whose structure has been elucidated by X-ray work: space group P2(1)/n (No. 14); a = 16.765(3), b = 23.800(4), c = 19.421(4) A; alpha = gamma = 90 degrees, beta = 92.51(2) degrees; Z = 4. The sandwiched material is a "stapled" molecule, characterized by the presence of two intramolecular interligand C-C sigma bonds and highly strained phthalocyanine units, as formerly observed by crystallographic work for its Ti(IV) analogue, [Pc2Ti], and the +1 corresponding fragment, [Pc2Nb]+, present in the species [Pc2Nb](l3)(l2)0.5.3.5CINP. [Pc2Nb] appears to be reluctant to undergo further oxidation above the +1 oxidation state. Detailed theoretical studies by DFT and TDDFT methods have been developed on [Pc2Nb] and [Pc2Nb]+, also extended for comparison to the Ti(IV) complex [Pc2Ti], and an adequate picture of the ground-state electronic structure of these species has been achieved. Moreover, the excitation energies and oscillator strengths calculated for the closed-shell systems, [Pc2Ti] and [Pc2Nb]+, provide a satisfactory interpretation of their characteristic visible optical spectra and help to rationalize the similar features observed in the visible spectrum of the open-shell "stapled" complex, [Pc2Nb]. Thin solid films (100-250 nm) of [Pc2Nb] deposited on ITO (indium-doped tin oxide) show a reversible redox process in neutral or acidic aqueous electrolytes. The electrochemical and electrochromic properties of the sandwiched complex, combined with impedance and UV/visible spectral measurements, are presented and discussed. The achieved electrochemical information, while substantially in keeping with the observed chemical redox behavior and theoretical predictions, qualifies [Pc2Nb] as an "optically passive" electrode and a promising material for its use in electrochromic devices.     

Headspace solid-phase microextraction-gas chromatography--mass spectrometry analysis of the volatile compounds of Evodia species fruits

In this study the investigation of the aroma compounds of dried fruits of Evodia rutaecarpa (Juss.) Benth. and E. rutaecarpa (Juss.) Benth. var. officinalis (Dode) Huang (i.e. E. officinalis Dode) (Rutaceae family) was carried out to identify the odorous target components responsible for the characteristic aroma of these valuable natural products. To avoid the traditional and more time-consuming hydrodistillation, the analyses were carried out by means of headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS). The SPME headspace volatiles were collected using a divinylbenzene-carboxen-polydimethylsiloxane (DVB-CAR-PDMS) fiber. The extraction conditions were optimized using a response surface experimental design to analyze the effect of three factors: extraction temperature, equilibrium time and extraction time. The best response was obtained when the extraction temperature was around 80 degrees C, equilibrium time near 25 min and extraction time close to 18 min. Analyses were performed by GC-MS with a 5% diphenyl-95% dimethyl polysiloxane (30 m x 0.25 mm I.D., film thickness 0.25 microm) capillary column using He as the carrier gas and a programmed temperature run. The main components of the HS-SPME samples of E. rutaecarpa (concentration >3.0%) were limonene (33.79%), beta-elemene (10.78%), linalool (8.15%), myrcene (5.83%), valencene (4.73%), beta-caryophyllene (4.62%), linalyl acetate (4.13%) and alpha-terpineol (3.99%). As for E. officinalis, the major compounds were myrcene (32.79%), limonene (18.36%), beta-caryophyllene (9.92%), trans-beta-ocimene (6.04%), linalool (5.88%), beta-elemene (7.85%) and valencene (4.62%).     

Fast fluctuations in protein powders: The role of hydration

An elastic neutron scattering investigation of the molecular dynamics of hydrated lysozyme powders has been undertaken for different water contents h (g water/g Lysozyme). The dry sample exhibits a harmonic behaviour in the whole temperature range, while anharmonic motions arise on hydrated samples at a temperature T_d. Both T_d and the magnitude of the anharmonic motions are markedly hydration dependent. On increasing water content the crossing barrier entropy change increases, while the enthalpy change keeps constant. The estimated average rigidity of the protein structure decreases abruptly immediately below the onset of the enzymatic activation at around 0.2h.     

Deprotonations of 5-nitroindole and 5-nitroindole-2-carboxylate ion in zwitterionic surfactants

Deprotonations of 5-nitroindole ( 1 ) and its 2-carboxylate ion 2 at high pH have been examined in solutions of N,N-dimethyl-N-tetradecylglycine (DTG) and N,N-dimethyl-N-hexadecylglycine (DHG). We have compared the surfactant effects with those of single- and twin-tailed ionic surfactants.     

Aza-Michael addition of nosyloxycarbamates to 2-(trifluoromethyl)acrylates

[reaction: see text] The amination of 2-(trifluoromethyl)acrylates, performed by nosyloxycarbamates, gives two different aminated products, the derivatives of alpha-trifluoromethyl beta-amino esters or the aziridines, in high yields by changing the reaction conditions. The aza-Michael addition product was isolated for the first time in this kind of reaction. This finding confirms the aza-MIRC mechanism we previously proposed. Asymmetric induction was also pursued.     

Synthesis of a new series of 8-substituted-2,8-diazaspiro[4.5]decan-3-ones

A new series of 8-substituted-2,8-diazaspiro[4.5]decan-3-ones has been synthesized and tested in in vitro and in vivo assays predictive for cholinergic activity, in comparison with the muscarinic agent RS-86. Preliminary pharmacological data indicate that the compounds are devoid of significant cholinergic properties.     

Nb-Doped PZT Material by Sol-Gel Combustion

Nanocrystalline niobium doped lead zirconate titanate powders (PZTN) were prepared by a citrate-nitrate sol-gel combustion technique. The technique involves three steps: preparation of stable and homogeneous sol, formation of gel, combustion of gel. The sol was prepared by mixing stable solutions of Zr-oxynitrate, Pb-citrate, Nb- and Ti-peroxo-citrate precursors. The heat induced auto ignition leads to the decomposition of precursors and formation of pure perovskite phase after soaking at 400^∘C for 4 h. The particles were found to be irregular aggregates of nanosized primary particles (crystallite size about 30 nm). Different milling treatments were performed in order to improve the sinterability. Ball milled (100 h with PEG) powders were sintered at 1100^∘C for 2 h in air showing 97% relative density at a densification T 100^∘C lower than following the conventional mixed oxide route. The stoichiometry of the system was determined at each stage of the process and no fluctuation was detected.