Modulating the Enantiodiscrimination Features of Inherently Chiral Selectors by Molecular Design: A HPLC and Voltammetry Study Case with Atropisomeric 2,2’-Biindole-Based Monomers and Oligomer Films

A family of inherently chiral electroactive selectors based on the 2,2’-biindole atropisomeric scaffold, of easy synthesis and modulable functional properties, is studied in cascade in two enantioselection contexts. They are at first investigated as probes in enantioselective HPLC, studying molecular structure and temperature effects, and achieving very efficient semipreparative enantioseparation. The enantiomers thus obtained, of remarkable chiroptical features (optical rotation as well as circular dichroism), are successfully applied as selectors in chiral voltammetry in different media for discrimination of the enantiomers of chiral electroactive probes, either by conversion into enantiopure electroactive electrode surfaces by electrooligomerization on glassy carbon substrate (the two monomers with shorter alkyl chains), or as chiral additive in achiral ionic liquid (the monomer with longest alkyl chains). Discrimination is conveniently and reproducibly achieved in terms of significant potential differences for the two enantiomers, specularly inverting either probe or selector configuration. In one case successful discrimination is also observed with the two probe enantiomers concurrently present, either as racemate or with enantiomeric excesses, neatly accounted for by the peak current ratios.     

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     

An adiabatic linearized path integral approach for quantum time correlation functions: electronic transport in metal-molten salt solutions

We generalize the linearized path integral approach to evaluate quantum time correlation functions for systems best described by a set of nuclear and electronic degrees of freedom, restricting ourselves to the adiabatic approximation. If the operators in the correlation function are nondiagonal in the electronic states, then this adiabatic linearized path integral approximation for the thermal averaged quantum dynamics presents interesting and distinctive features, which we derive and explore in this paper. The capability of these approximations to accurately reproduce the behavior of physical systems is demonstrated by calculating the diffusion constant for an excess electron in a metal-molten salt solution.     

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.