Tris-N-alkylpyridinium-functionalised cyclotriguaiacylene hosts as axles in branched [4]pseudorotaxane formation

A series of [4]pseudorotaxanes composed of three-way axle threads based on the cyclotriguaiacylene family of crown-shaped cavitands and three threaded macrocyclic components has been achieved. These exploit the strong affinity for electron-poor alkyl-pyridinium units to reside within the electron-rich cavity of macrocycles, in this case dimethoxypillar[5]arene (DMP). The branched [4]pseudorotaxane assemblies {(DMP)₃?L}³⁺,where L = N-alkylated derivatives of the host molecule (±)-tris-(isonicotinoyl)cyclotriguaiacylene, were characterised by NMR spectroscopy and mass spectrometry, and an energy-minimised structure of {(DMP)₃?(tris-(N-propyl-isonicotinoyl)cyclotriguaiacylene)}³⁺ was calculated. Crystal structures of N-ethyl-isonicotinoyl)cyclotriguaiacylene hexafluorophosphate and N-propyl-isonicotinoyl)cyclotriguaiacylene hexafluorophosphate each show ‘hand-shake’ self-inclusion motifs occurring between the individual cavitands.     

Role of the wall ablation in the operation of a 46.9 nmAr capillary discharge soft x‐ray laser

A capillary discharge pumped soft x‐ray laser operating at 46.9 nm on the 3p–3s transition of the Ne‐like Ar has been realized by pumping the active medium with a relatively slow current pulse (dI/dt ≈ 6 · 10¹¹ A/s). In order to study the role of the ablation in the production of the laser effect, the intensity of the amplified 46.9 nm line has been investigated using the same pumping current pulses in the plastic (polyacetal) and ceramic (Al₂O₃). We showed that the ablation of the capillary walls is unfavorable both for the compression and stability of the plasma and consequently for the soft x‐ray laser production. The amplification and lasing effects are observed only in the ceramic channel. The measurements of the line intensity at 46.9 nm showed the lasing with a gain‐length product of ≈ 9, a laser pulse energy of ≈ 5 μJ, a pulse duration of 1.3 ns and a beam divergence of ≈ 3.5 mrad. In addition, effect of the scaling of the time of lasing with the initial plasma diameter was demonstrated experimentally and compared with a one‐dimensional MHD model.     

Fructose-6-phosphate aldolases as versatile biocatalysts for nitrocyclitol syntheses

Efficient and stereoselective polyhydroxylated nitrocyclitol syntheses were performed via biocatalysed aldol reactions. The key step was based on a one-pot/one-enzyme cascade reaction process where two reactions occur: aldolase-catalysed aldolisation and spontaneous intramolecular nitroaldolisation. The synthetic methodology was investigated using fructose-6-phosphate aldolase A129S for the synthesis of known nitrocyclitols. Improvements were obtained which involved less steps and increased yields. Several new nitrocyclitols were also prepared using hydroxyacetone (HA) as the donor and FSA wt. From nitrocyclitol stereochemical analyses, the intramolecular nitro-Henry reaction stereoselectivity was dependent on the donor substrate used, HA or dihydroxyacetone (DHA). Whereas DHA provided two stereoisomers, four were obtained using HA.     

Enhancing sensitivity and selectivity in the determination of aldehydes in olive oil by use of a Tenax TA trap coupled to a UV-ion mobility spectrometer

A Tenax TA trap was coupled to an ion mobility spectrometer in order to improve basic analytical properties such as sensitivity and selectivity. The analytical performance of this combination was assessed in the determination of volatile aldehydes between 3 and 6 carbon atoms present in olive oil. The aldehydes were extracted and adsorbed into the trap, from which they were thermally desorbed for analysis by UV-Ion Mobility Spectrometry (UV-IMS). Sensitivity was increased by the preconcentration step and selectivity by the combination of temperature programmed thermal desorption and the ability of the ion mobility spectrometer to monitor the desorbed analytes in real time. The limits of detection obtained were lower than 0.3 mg kg(-1) and the relative standard deviation lower than 10%. A one-way analysis of variance (ANOVA) was used to identify significant differences between olive oil grades in terms of peak heights for the target aldehydes.     

Intense XUV emission generated by a capillary discharge based apparatus

We present the characterization of an apparatus generating XUV radiation by a high peak value (20–40) kA and short rise time (≈ 20 ns) current pulse in a capillary discharge channel (up to 20 cm in length) filled by argon gas. The apparatus has been developed with the purpose of production of an intensive spontaneous emission in the spectral region of (2–50) nm and study of the z-pinch conditions for obtaining the laser generation in the Nelike Ar at 46.9 nm. The current pulses are generated by the direct discharge of a 7 nF water dielectric capacitor resonantly charged up to 400 kV by a six-stages Marx generator. The XUV radiation emitted during the radial compression of the plasma column is measured using calibrated PIN diodes, filters and multilayer mirrors in order to test the z-pinch plasma collapse and to measure the conversion efficiency of the electrical energy into the XUV radiation. This work is supported by the Italian National Institute of Nuclear Physics and in part by the Italian National Institute of Matter Physics.     

Ianus, the three-electrode excimer laser

Received: 2 April 1997/ Revised version: 5 September 1997     

Dual-micro-ESI source for precise mass determination on a quadrupole time-of-flight mass spectrometer for genomic and proteomic applications

A universal dual-electrospray (ESI) source is demonstrated on a quadrupole orthogonal-accelerated time-of-flight mass spectrometer (Q-ToF-MS) for both genomic and proteomic applications. This facile source modification enables internal calibration for consistent mass measurements by a mainstream MS platform and requires no mixing of analyte and calibrant prior to ion formation. In this report, the dual-sprayer is demonstrated in the negative-ion mode for internal calibration of polymerase chain reaction (PCR) amplicons generated from synthetic and genomic templates as well as a proteolytic digest of a naturally phosphorylated protein. For all PCR amplicons, experimentally determined average mass measurements are well within the instrument specifications of better than 0.01%. For the proteolytic fragments of the phosphoprotein, average mass errors of the isotopically resolved peptides are better than 10 ppm.     

Determination of molecular anisotropy in thin films of discotic assemblies using attenuated total reflectance UV-visible spectroscopy

We report here an investigation of absorbance anisotropy in highly ordered, single bilayer (ca. 5.6 nm) Langmuir-Blodgett (LB) thin films of discotic liquid-crystalline phthalocyanines, using a recently introduced broad-band attenuated total reflectance (ATR) spectroscopic technique, capable of measuring dichroism in such films in the UV--visible optical region down to absorbances of ca. 0.003 absorbance units. On the basis of the ATR measurements of LB-deposited films, a thorough treatment was established to determine the ensemble average of the Cartesian components and the associated optical anisotropy of transition dipoles in the molecular film. In an effort to recover order parameters of molecular orientation, those results were interpreted with a circular dipole model, which is the expected model for the isolated molecule based on symmetry properties. We measured a strong dipole component normal to the film plane that cannot be explained in terms of a truly circular model, indicating that the molecular transition dipoles were perturbed upon aggregation. The utility of the experimental approach was further demonstrated by (a) investigating the effect of substrate modifiers (methyl- and phenyl-terminated silanes) on the ordering within the phthalocyanine film and (b) the effect of water immersion and re-annealing of the thin film on molecular ordering and optical anisotropy.     

Mössbauer studies of raw materials from Misti volcano of Arequipa (Peru) for its potential application in the ceramic field

We would like to introduce, the study of two different colour “sillar” samples: white and pink, belonging to the Añashuayco quarry in the Arequipa Region (Peru). The X-ray diffraction (XRD) analysis indicates the presence of several mineralogical phases, such as feldpars and biotite for the both white and pink “sillar” whereas cristobalite and quartz are detected only in the first sample and amorphous phase in the second one. In room temperature, Mössbauer spectroscopy, the presence of hematite (α-Fe₂O₃) was detected as the main phase for both samples, this was not detected in the XRD measurements. Moreover, corresponding doublets in the Mössbauer spectra indicate the presence of iron in the aluminium-silicate minerals. The rates Fe^2?+?/Fe^3?+? are 0.0752 and 0.0526 to the white and pink samples respectively. The minerals composing the white tuff form a heterogeneous aggregate of uniform aspect. Mining of these materials generates a great amount of waste in the form of lumps of varying size and which are raw materials studied in the present work for potential application in the ceramic field.