Densely-packed self-assembled monolayers on gold surfaces from a conformationally constrained helical hexapeptide

A novel hexapeptide was functionalized at the N-terminus by a lipoyl group for binding to gold substrates. Owing to the high content of α-aminoisobutyric acid residues, the peptide adopts a rigid helical conformation despite the shortness of its main chain. Binding of the peptide to gold was investigated by quartz crystal microbalance, cyclic voltammetry, X-ray photoelectron spectroscopy, and scanning tunneling microscopy under ultra-high vacuum conditions. Scanning tunneling microscopy experiments revealed that the peculiar self-assembly properties of this short helical peptide determine the complex morphology of the monolayer, showing ‘stripes’, i.e. peptide aggregates horizontally layered on the gold surface, and ‘holes’, i.e. Au vacancy islands coated by the peptide monolayer.     

Collective modes in a slab of interacting nuclear matter

We consider a slab of nuclear matter and investigate the collective excitations, which develop in the response function of the system. We introduce a finiterange realistic interaction among the nucleons, which reproduces the full G-matrix by a linear combination of gaussian potentials in the various spin-isospin channels. We then analyze the collective modes of the slab in theS=T=1 channel: for moderate momenta hard and soft zero-sound modes are found, which exhaust most of the excitation strength. At variance with the results obtained with a zero range force, new “massive” excitations are found for the vector-isovector channel.     

Two step, hydrolytic-solvothermal synthesis of redispersible titania nanocrystals and their gas-sensing properties

A titanium chloromethoxide solution was prepared by reacting TiCl₄ with methanol, followed by water addition. The starting solutions were characterized by Fourier Transform Infrared (FTIR) spectroscopy, evidencing that the in situ generated water results in early hydrolysis of the chloroalkoxide. The solution was reacted with molten dodecylamine at room temperature, obtaining a white slurry of amorphous titania nanoparticles. Stable, redispersible TiO₂ nanocrystals could be prepared by subsequent solvothermal treatment in oleic acid at 250???C. The use of oleic acid was essential for obtaining crystalline structures, while other surfactants prevented crystallization. The nanocrystals were characterized by X-ray Diffraction and Transmission Electron Microscopy, confirming the formation of anatase TiO₂ nanocrystals with a mean size of 3.3?nm. The TiO₂ nanocrystals were used for fabricating gas-sensing devices, which were tested towards ethanol vapors. The initial small size of the nanocrystals, and the limited size growth during the high-temperature sensor operation, result in remarkable sensing performances if compared with bulk titania sensors.     

Volatile fingerprints of artemisinin-rich Artemisia annua cultivars by headspace solid-phase microextraction gas chromatography/ mass spectrometry

The cultivar Anamed (A3) is a hybrid of Artemisia annua with a high content of the secondary metabolite artemisinin, a well-known antimalarial drug. Here we report for the first time the volatile profile of fresh leaves of this hybrid in comparison with that of Artemisia annua L. wild-type species. Evaluation and comparison of the volatile profiles of A. annua genotypes with different content in artemisinin were carried out by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography/mass spectrometry (GC/MS) that was performed on fresh leaves of the plants under investigation using a polydimethylsiloxane (PDMS) fiber. The chromatograms obtained from hybrids with a high content of artemisinin (A. annua cv. Anamed A3 and A. annua cv. Artemis F2) reveal the total absence of artemisia ketone, one of the major and characteristic compounds of the wild-type A. annua L., along with a significantly lower variety of volatile compounds. In conclusion, HS-SPME coupled with GC/MS is a very useful, non-destructive and efficient method to describe the volatile pattern of Artemisia annua cultivars. It represents a rapid screening method for the evaluation of volatile biomarkers like artemisia ketone, whose absence is typical of artemisinin-rich A. annua cultivars.     

Broadband measurements of acoustic attenuation in water-saturated sands

A method for the measurement of acoustic attenuation in water-saturated granular media as a continuous function of frequency is described. Results for a range of water-saturated sands are presented together with acoustic velocity data and discussed in relation with porosity and grain size variations.     

A simplified,miniature TEA-CO2 laser using a semiconductive pre-ionization technique

Using a pre-ionization system based on a silicon carbide compound and a pulse-forming network using a vacuum relay, we have been able to significantly reduce TEA0-CO₂ laser complexity while maintaining high output energy densities. The design and construction are detailed along with the experimentally obtained laser characteristics.