2-Aryl and 2-heteroaryl indoles from 1-alkynes and o-iodotrifluoroacetanilide through a domino copper-catalyzed coupling-cyclization process

[reaction: see text] A general method for the synthesis of 2-aryl and 2-heteroaryl indoles from aryl iodides and 1-alkynes through a domino copper-catalyzed process is reported. The best results have been obtained with [Cu(phen)(PPh(3))(2)]NO(3) in the presence of K(3)PO(4) in toluene or dioxane at 110 degrees C. 2-Aryl and 2-heteroaryl indoles can also be isolated in good yields by using catalysts derived from CuI and PPh(3) in dioxane at 110 degrees C.     

Delayed-fluorescence ODMR and EPR studies of triplet excitons in charge-transfer molecular crystals

Triplet excitons in electron donor—acceptor charge-transfer (CT) molecular crystals are generated through the intersystem crossing process by excitation in the CT visible band and give rise to delayed fluorescence. Delayed-fluorescence optically detected magnetic resonance (DF ODMR) in magnetic field is analyzed in terms of microwave-induced transitions between energy levels of either the isolated triplet excitons or the annihilating triplet exciton pair. The spin polarization of the triplet excitons plays an important role in the described phenomena. A comparison between DF ODMR and EPR spectra of the anthracene—tetracyanobenzene and biphenyl—tetracyanobenzene systems is presented. In the former case the microwave transitions occurring between free exciton sublevels are predominantly responsible of the DF ODMR signal, whereas the transitions between energy levels of the exciton pair are the most important for biphenyl—TCNB.     

The Weyl transform and bounded operators on Lp(Rn)

A multiplier theorem for the Weyl transform is proved. This theorem is used to derive sufficient conditions for the boundedness of a general operator on L^p($\text{R}$ⁿ). An application to multipliers of the Hermite expansion is given.     

Transition to stochasticity in a one-dimensional model of a radiant cavity

We make a numerical study of the solutions of the equations of motion for the electromagnetic field in a one-dimensional model of a radiant cavity. Our main results are as follows: (1) There exist Stochasticity thresholds such that below them one has ordered motions without energy exchanges, while chaotic motions with intense energy exchanges occur above them; (2) above thresholds there is a trend toward equipartition of energy (in time average) among the normal modes of the field, but this occurs in the sense of Boltzmann and Jeans, namely, with the higher frequencies requiring longer and longer times in order to be involved in the energy sharing.     

Nuovi criteri per l'esistenza globale in futuro dei moti dei sistemi olonomi scleronomi

Summary By means of the comparison method and an appropriate choice of the Liapunov function, new criteria for the global existence in the future of the motions of several classes of holonomic scleronomic systems are obtained. The main advantage of these criteria respect to those provided in [1], [2]is that the potential energy of the mechanical system need not be bounded from below, as required in the above-mentioned papers, where the total energy of the system is chosen as Liapunov function.     

Influence of fibre coating in headspace solid-phase microextraction-gas chromatographic analysis of aromatic and medicinal plants

Solid-phase microextraction (SPME) is a solvent-free technique, which is well established in headspace analysis since it is sensitive, because of the concentration factor achieved by the fibres, and selective, because of different coating materials which can be used. The performance of eight commercially available SPME fibres was compared to evaluate the recoveries of some characteristic components with different polarities and structures present in the headspace of four aromatic and medicinal plants: rosemary (Rosmarinus officinalis L.), sage (Salvia officinalis L.), thyme (Thymus vulgaris L.) and valerian (Valeriana officinalis L.). The relative concentration capacity of each fibre on the same components of each plant was also determined by comparing their abundance with that obtained by classical static-headspace GC. The partition coefficient, K1, between the headspace gaseous phase and SPME polymeric coating, and the relative concentration factors, of some of the characteristic components of the plant investigated dissolved in dibutyl phtalate, were also determined, under rigorously standardised analysis conditions. The results showed that the most effective fibres were those consisting of two components, i.e., a liquid phase (polydimethylsiloxane) and a porous solid (carboxen or divinylbenzene, or both).     

Carbon nanotubes as reinforcement of styrene-butadiene rubber

This study reports an easy technique to produce cured styrene-butadiene rubber (SBR)/multi-walled carbon nanotubes (MWCNT) composites with a sulphur/accelerator system at 150 °C. Significant improvement in Young's modulus and tensile strength were achieved by incorporating 0.66 wt% of filler without sacrificing SBR elastomer high elongation at break. A comparison with carbon black filled SBR was also made. Field emission scanning electron microscopy was used to investigate dispersion and fracture surfaces. Results indicated that the homogeneous dispersion of MWCNT throughout SBR matrix and strong interfacial adhesion between oxidized MWCNT and the matrix are responsible for the considerable enhancement of mechanical properties of the composite.