Magnetically driven growth of anthracene thin films by organic molecular beam deposition

The possible use of a static magnetic field during organic molecular beam deposition of thin molecular films for inducing some preferential growth is discussed and the magnetic properties of diamagnetic molecules and molecular crystals are recalled. Considering prototypical materials, namely anthracene molecules and potassium phthalate substrates, which interact and may give rise to polycrystalline films with specific orientations, we show that in the presence of a magnetic field the films display a macroscopic preferential orientation as a result of minimization of the magnetic energy contribution. A very good agreement between the results of optical spectroscopy, atomic force microscopy, and predictions made on the basis of the anisotropic magnetic susceptibility of anthracene is found.     

Phase Transitions in UHMWPE Fiber Compacts Studied by in situ Synchrotron Microbeam WAXS

Summary: The temperature dependence of the structure of either cross‐linked or non‐cross‐linked ultra‐high‐molecular‐weight polyethylene (UHMWPE) fiber compacts was studied by synchrotron microbeam wide‐angle X‐ray scattering (WAXS), focusing on the fiber‐fiber interface. The phase transition sequence is: melting of the monoclinic phase in the fiber skin, which was completed by 135 °C; melting of the unconstrained orthorhombic phase, by 152 °C; melting of the constrained orthorhombic phase and a orthorhombic‐hexagonal phase transition until 157 °C; and gradual melting of the hexagonal phase, up to 165 °C. Cross‐linking provides additional thermal stabilization.

Histograms of the azimuthally averaged X‐ray intensity as a function of temperature for cross‐linked ultra‐high‐molecular‐weight polyethylene fiber compacts molded at 145 °C.     

Study of organic sulphur compounds (DMS,DMSP and CS2) in lagoon ecosystems: the case of the Venice lagoon

This study of the origin and fate of dimethyl sulphide (DMS) in a particular and complex lagoon ecosystem such as that of the Venice lagoon focuses on the temporal evolutions of DMS concentrations in surface water together with those of dimethylsulphoniopropionate (DMSP), carbon disulphide (CS2), nutrients (nitrate, nitrite, ammonium, phosphate, silicate), sulphate, chlorophyll a, chlorinity, water temperature and phytoplankton (composition and density). Measurements were made from 3 March 1997 to 23 July 1998 at three stations in the central part of the Venice lagoon. The temporal trends of DMS concentration showed an absolute maximum concentration in winter (65 nmol S/l, 19/2/1998, Stn. 1; 119 nmol S/l, 19/2/1998, Stn. 2; 29 nmol S/l, 17/2/1998, Stn. 3) and two relative maxima in the spring-summer period. The spring-summer secondary maxima of DMS concentration were related to the maxima of DMSP and chlorophyll a concentrations and consequently to phytoplanktonic abundance while the winter DMS maximum showed no relation to DMSP or to chlorophyll a suggesting that the production and the fate of DMS could be different for the two periods. According to previous studies the CS2 concentration increased in the spring, achieved its maximum in summer, decreased in autumn and fell to its minimum in winter.     

Organic-organic epitaxy of incommensurate systems: quaterthiophene on potassium hydrogen phthalate single crystals

Hot-wall epitaxy and molecular-beam epitaxy have been employed for growing quaterthiophene thin films on the (010) cleavage face of potassium hydrogen phthalate, and the results are compared in terms of film properties and growth mode. Even if there is no geometrical match between substrate and overlayer lattices, these films are epitaxially oriented. To investigate the physical rationale for this strong orientation effect, optical microscopy, atomic force microscopy, and X-ray diffraction are employed. A clear correlation between the morphology of the thin films and the crystallographic orientation is found. The results are also validated by surface potential calculations, which demonstrate the primary role played by the corrugation of the substrate surface.     

Comparison of two different multidimensional liquid–gas chromatography interfaces for determination of mineral oil saturated hydrocarbons in foodstuffs

This investigation focused on direct comparison of two popular multidimensional liquid–gas chromatography (LC–GC) systems, the Y-interface (retention gap approach) and the syringe-based interface (programmed temperature vaporizer approach). Such transfer devices are structurally very different, and could potentially have a substantial effect on the outcome of a specific application. In this work the application was a topic of much current interest, determination of mineral oil saturated hydrocarbon (MOSH) contamination of a series of food products (rice, pasta, icing sugar, olive oil); the final results were then compared. The two LC–GC methods developed were validated for linearity over the calibration range, analyte discrimination, precision, accuracy, and limits of detection and quantification. No significant differences were found between the two approaches.

Gas-phase synthesis and reactivity of a gold carbene complex

Electrospray ionization tandem mass spectrometry of a phosphonium ylid complex of gold produces an ion whose mass and gas-phase chemical reactivity indicate that it is a gold benzylidene complex. The complex, with a supporting NHC ligand, corresponds to a type of reactive intermediates which have been presumed to act in gold-catalyzed cyclopropanation reactions, but which have not been observed to date in solution or gas-phase experiments. A threshold CID experiment also yields thermochemical information on the formation of the gold carbene from the ylid complex precursor.     

Rapid SPE-HPLC determination of the 16 European priority polycyclic aromatic hydrocarbons in olive oils

Polycyclic aromatic hydrocarbons (PAHs) are a large class of organic compounds. It has been established that the main source of exposure to these compounds for human beings is through food, particularly fats and oils, due to the lipophilic nature of these polycyclic compounds. The aim of this work was to optimise and validate a method involving SPE and HPLC for rapid determination of the 16 European Union (EU) priority PAHs (required by the Recommendation 2005/108/EC) in vegetable oils. Two spectrofluorometric detectors and a UV-Visible detector in series were used to identify and quantify the target compounds. Linearity, recoveries, LOD, and LOQ were found to be in agreement with the performance criteria for benzo[a]pyrene (BaP) analysis as required by the Commission Directive 2005/10/EC, and satisfactory for all the compounds of interest, except for cyclopenta[c,d]pyrene, which presented a very low signal in the UV. Optimised chromatographic conditions for the separation of 25 PAHs, comprising both EPA and EU priority PAHs plus benzo[e]pyrene and benzo[b]chrysene, have been also proposed.     

X-ray scattering study of the phase transitions in crystalline fullerene-biphenyl C 60 [(C 6 H 5 ) 2 ]

The phase diagram of the newly synthesized mixed crystal C₆₀-biphenyl is investigated as a function of temperature by single-crystal X-ray scattering. Diffuse scattering investigations evidencing complex disorder and local order effects are presented. Two phase transitions leading to two different doublings of the high temperature unit cell are observed, at 212 K and 147 K. The first transition is attributed to the ordering of twisted biphenyls, which couples to the orientational ordering of the C₆₀ molecules as the temperature decreases. Full ordering of the C₆₀ molecules is achieved below 100 K only, in the low temperature phase. The rich phase diagram of C₆₀-biphenyl is due to the interplay between fullerene and biphenyl ordering phenomena. Received 31 August 2001 and Received in final form 4 December 2001