Degrees of freedom effect on fragmentation in tandem mass spectrometry of singly charged supramolecular aggregates of sodium sulfonates

The characteristic collision energy (CCE) to obtain 50% fragmentation of positively and negatively single charged noncovalent clusters has been measured. CCE was found to increase linearly with the degrees of freedom (DoF) of the precursor ion, analogously to that observed for synthetic polymers. This suggests that fragmentation behavior (e.g. energy randomization) in covalent molecules and clusters are similar. Analysis of the slope of CCE with molecular size (DoF) indicates that activation energy of fragmentation of these clusters (loss of a monomer unit) is similar to that of the lowest energy fragmentation of protonated leucine–enkephalin. Positively and negatively charged aggregates behave similarly, but the slope of the CCE versus DoF plot is steeper for positive ions, suggesting that these are more stable than their negative counterparts. Copyright © 2013 John Wiley & Sons, Ltd.     

Carbon and nitrogen distribution in the sediments of lagoon of Ravenna (Italy)

The distribution and the origin of carbon and nitrogen in sediments of an Italian lagoon--located north-east of Ravenna town--were investigated. From 1957 to 1976, the lagoon had been affected by a strong industrial pollution due to an important petrochemical complex. At present, industrial and domestic waste waters undergo a treatment process before being discharged into the lagoon. Sediment samples from 10 locations throughout the lagoon were analysed, in order to document the spatial and vertical distribution of C and N. Data show a very strong variability (organic carbon content varies between 8.9% and 0.14%) and the highest values were found in the immediate vicinity of the industrial discharge. Sediment organic matter shows allochthonous origin in proximity of industrial discharge and autochthonous origin in the remaining areas.     

Application of B-splines finite basis sets to relativistic two-photon decay rates of level in hydrogenic ions

A theoretical study of the one- and two-photon spontaneous emission rates from the 2 s1/2 state of one-electron ions is presented. High-precision values of the relativistic emission rates for ions with nuclear charge Z up to 100 are obtained through the use of finite basis sets for the Dirac equation constructed from B-splines. Furthermore, we analyze the influence of the inclusion of quantum electrodynamics corrections in the initial and final state energies. Received: 6 January 1998 / Accepted: 31 March 1998     

A novel oxidative rearrangement of 6-methoxypyran-2-ones

As part of our continuing studies of pyrone-containing natural products, a series 6-methoxypyran-2-ones were synthesized. These were found to react with molecular oxygen at 20 degrees C, and this novel reaction yielded a series of highly functionalized alpha,beta-butenolides. [reaction: see text]     

Zero thermal expansion in a Prussian Blue analogue

Isotropic nearly zero thermal expansion (i.e., negligible volume change) is reported in a large temperature range for Fe[Co(CN)6], a member of the Prussian blue family with electronically active metal sublattices and a cubic framework structure built by a cyanide-bridged network of octahedral units. Suitable selection of metal ions and interstitial units could allow such anomalous thermal behavior to be combined with the variety of unusual electronic, optical, and magnetic properties exhibited by Prussian blue analogues.     

Lattice collapse in mixed-valence samarium fulleride Sm(2.75)C(60) at high pressure

Sm(2.75)C(60) displays large negative thermal expansion behaviour in the temperature range 4.2-32 K at ambient pressure as a result of a quasi-continuous valence change from the larger Sm(2+) towards the smaller Sm(2.3+) ion. Here we use the powder synchrotron X-ray diffraction technique at ambient temperature and elevated pressures to study the compression behaviour in the pressure range 0-6 GPa. An abrupt hysteretic phase transition, accompanied by a dramatic volume decrease (approximately =6.0%) and a change in colour from black to golden was found at approximately =4 GPa induced by a sudden Sm valence transition from +2.3 towards +3. Such behaviour is typical of highly correlated Kondo insulators like SmS and makes Sm(2.75)C(60) the first known molecular-based member of this fascinating class of materials.     

Ionic shell and subshell structures in aluminum and gold nanocontacts

Conductance histograms of aluminum and gold nanocontact rupture are studied experimentally and simulated using embedded atom potentials to assess the interplay between electronic and structural properties at room temperature. Our results reveal a crossover from quantized conductance structures to crystalline faceting or geometric shell/subshell structures at 300 K. The absence of electronic shell structure in gold and aluminum is in stark contrast with the behavior of alkaline metal nanowires which emulate their cluster counterparts. Semiclassical arguments suggest why rapid dominance of ionic structures takes place, and possible nanowire architectures are proposed in consistency with both the experimental and simulated nanocontact data.     

First direct observation of coulomb explosion during the formation of exotic atoms

A Doppler broadening of x-ray transitions from pionic nitrogen and muonic oxygen, which is attributed to Coulomb explosion of the molecules, has been observed by using a crystal spectrometer. Large linewidths indicate fast ionization of the molecules and a charge of (3-4)e for the accelerated fragments.     

Symmetry Properties of the Elastic Energy of a Woven Fabric with Bending and Twisting Resistance

A woven fabric can be described as a surface made of two families of fibers: in this work we study how the geometry of the weave pattern affects the symmetry properties of the elastic energy of the surface. Four basic symmetry classes of weave patterns are possible, depending on the angle between the fibers and their material properties. The properties of the pattern determine the material symmetry group of the network, under which the elastic energy is invariant. We derive representations for the energy of a woven fabric that are invariant under the symmetry group of the network, and discuss the relation of these invariants with the curvature and twist of the fibers.      

From favorable atomic configurations to supershell structures: a new interpretation of conductance histograms.

Simulated minimum cross-section histograms of breaking Al nanocontacts are produced using molecular dynamics. The results allow a new interpretation of the controverted conductance histogram peaks based on preferential geometrical arrangements of nanocontact necks. As temperature increases, lower conductance peaks decrease in favor of broader and higher conductance structures. This reveals the existence of shell and supershell structures favored by the increased mobility of Al atoms.