Interaction of Cu(+) and Cu(2+) ions with alpha-alanine. A density functional study

The Cu(+) and Cu(2+) preferred binding sites on alpha-alanine and their affinity values for this amino acid were determined at the density functional level using three different hybrid exchange correlation potentials and the 6-311++G** basis set. The results demonstrated that the two ions both give stable complexes with alpha-alanine but the stability order of the metalated species and the coordination sites are different depending on the nature of the cation. In particular, the Cu(+)-alpha-alanine ground-state structure is characterized by an eta(2)-N,O coordination with the nitrogen and oxygen atoms belonging to the amino and carbonyl groups, respectively. In contrast, the most stable complex of the Cu(2+)-alpha-alanine system has an eta(2)-O,O coordination with the cation bonded to the -CO(2) (-) moiety of the zwitterionic form of the amino acid. Comparison with the Cu(+) and Cu(2+) affinity values for glycine, computed at the same levels of theory, demonstrated that the relative values do not change significantly as different hybrid functionals are used, although the absolute affinities are strongly influenced by the choice of the hybrid potential.     

Honeycomb pattern formation by laser-beam filamentation in atomic sodium vapor

We have observed transverse pattern formation leading to highly regular structures in both the near and far fields when a near-resonant laser beam propagates without feedback through an atomic sodium vapor. One example is a regular far-field honeycomb pattern, which results from the transformation of the laser beam within the vapor into a stable three-lobed structure with a uniform phase distribution and highly correlated power fluctuations. The predictions of a theoretical model of the filamentation process are in good agreement with these observations.     

Microelectrode study of single cavitational bubbles induced by 500 kHz ultrasound

Insight is gained into about the processes governing cavitational activity and acoustic streaming induced by high frequency (500 kHz) ultrasound by the use of microelectrodes with short time resolution electrochemical equipment to allow monitoring of the activity of single cavitating bubbles. Current transients are interpreted as showing the flux of solution towards the electrode surface due to microstreaming. In order to explain the current amplitude, a simplified model is produced. Important parameters such as bubble size and shape on the surface as well as the boundary layer thickness for microstreaming are taken into account. This model leads to the amplitude of the oscillations of the cavitating bubble. Introducing realistic bubble sizes, this amplitude is found to be in the order of 1 micron. The conclusions arising from this work allow a further interpretation of previous observations at millimeter scale electrodes.     

A multimode small signal analysis of the single pass free electron laser

We analyze the small signal multimode aspects of the single pass free electron laser and study the operating conditions and the relevant laser parameters.     

Evaluation of hydrogen chemisorption in nanostructured carbon films by near edge X-ray absorption spectroscopy

We have developed a method for the quantitative evaluation of the chemisorbed fraction of hydrogen in nanostructured carbon films using Near Edge X-ray Absorption Spectroscopy (NEXAFS). In the carbon K-edge spectrum the peak related to carbon bonded to hydrogen is assumed to be correlated with the amount of hydrogen bonded to carbon. This assumption is supported by a comparative analysis of gas-phase hydrocarbons obtained via Electron Energy Loss Spectroscopy (EELS). We applied the method to nanostructured carbon (ns-C) films synthesized by supersonic cluster beam deposition. The evaluated quantity of chemisorbed hydrogen in different samples exposed to molecular hydrogen (pressure of 0.12 MPa, for 3 hours at room temperature) is ∼1.5 wt.%.     

Synthesis of substituted quinolines by electrophilic cyclization of N-(2-alkynyl)anilines

Quinolines substituted in the 3-position by an iodo or phenylseleno group are readily prepared in good to excellent yields by the reaction of propargylic anilines with appropriate electrophiles under mild reaction conditions. [reaction: see text]     

Elliptic Problems with Singular Potential and Double-Power Nonlinearity

We prove the existence of positive symmetric solutions to the semilinear elliptic problem

Mapping phosphorylation sites: a new strategy based on the use of isotopically labelled DTT and mass spectrometry

Phosphoproteomics, nowadays, represents a front line in functional proteomics as testified by the number of papers recently appearing in the literature. In an attempt to improve and simplify the methods so far suggested we have set up a simple isotope-coded approach to label and quantitate phospho-Ser/-Thr residues in protein mixtures. First of all, after appropriate oxidation of cysteine/cystine residues followed by tryptic hydrolysis, we have optimised and simplified the beta-elimination reaction to get the corresponding alkene moiety from the phosphate esters. This was achieved by (a) separating the elimination reaction from the addition reaction, (b) the use of Ba(OH)(2) as alkali reagent and (c) its further elimination by the simple addition of solid CO(2) to the peptide mixture. The Michael reaction was then performed, after the removal of BaCO(3) by centrifugation, by adding dithiothreitol (DTT) to the peptide mixture. Finally, the direct purification of the modified phosphopeptides was performed on a thiol-sepharose column. The availability of fully deuterated DTT, introducing a 6 Da difference with respect to the non-deuterated species, allows quantitation of the differential extent of signalling modification when analysed by matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) and liquid chromatography/mass spectrometry. The entire procedure has been set up by using bovine alpha-casein, and resulted in the identification of all the phosphorylated tryptic peptides, including the tetraphosphorylated peptides, which escaped all previously reported procedures     

Synthesis of fused polycycles by 1,4-palladium migration chemistry

Novel palladium migration/arylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement with the idea that these palladium-catalyzed C-H activation reactions parallel electrophilic aromatic substitution.