Three-electron auger process from beam-foil excited multiply charged ions

Electron emission from collisions of C3+ ions (22.7 A MeV) with carbon foils (21, 49 and 90 microg/cm(2)) was studied by the time-of-flight method. Two prominent emission patterns can be readily identified as "binary encounter" electrons and "cusp" electrons. With the thinnest target only, a third structure is visible at slightly lower time-of-flight (thus slightly higher energy) than the cusp electrons. The energy of these electrons would correspond to 647(+116)/(-104) eV if they were emitted from the projectile frame of reference. A possible explanation is a rare three-electron-Auger K(2)L(2)L(1) process.     

Phenolic constituents from Ephedra nebrodensis

Two new phenolic glycosides, 4-hydroxy-3-(3-methyl-2-butenyl)phenyl beta-D-glucopyranoside (nebrodenside A) and O-coumaric acid beta-D-allopyranoside (nebrodenside B), were isolated from the aerial parts of Ephedra nebrodensis. In addition, O-coumaric acid glucoside, (-)-epicatechin, and (-)-ephedrine were also isolated. The structures were deduced from extensive 1D and 2DNMR spectroscopy (1H, 13C, DQF-COSY, TOCSY, GHSQC, GHMQC, ROESY) as well as mass spectrometry (EI and HR-MALDI). (-)-Epicatechin showed weak antiviral activity against Influenza A virus and very weak cytotoxicity against MDCK cells.     

Evidence of a borderline region between E1cb and E2 elimination reaction mechanisms: a combined experimental and theoretical study of systems activated by the pyridine ring

We report a combined experimental and theoretical study to characterize the mechanism of base-induced beta-elimination reactions in systems activated by the pyridyl ring, with halogen leaving groups. The systems investigated represent borderline cases, where it is uncertain whether the reaction proceeds via a carbanion intermediate (E1cb, A(xh)D(H) + D(N)) or via the concerted loss of a proton and the halide (E2, A(N)D(E)D(N)) upon base attack. Experimentally, the Taft correlation for H/D exchange, in OD(-)/D(2)O with noneliminating substrates (1-methyl-2-(2-Xethyl)pyridinium iodide), is used to predict the expected values of the rate constants for the elimination reactions with N-methylated substrates and F, Cl, Br as the leaving group. The comparison indicates an E1cb irreversible mechanism with F, but the deviation observed with Cl and Br does not allow a conclusive assignment. The theoretical calculations show that for the N-methylated substrate with a fluoride leaving group the elimination proceeds via formation of a moderately stable carbanion. No stable anionic intermediate is instead found when the leaving group is Cl or Br, as well as for any of the nonmethylated species, indicating a concerted elimination. The methylated substrate with Cl shows however only a moderate increase in reactivity compared to the fluorinated substrate, despite the change in mechanism. Very interestingly, our analysis of the computed two-dimensional potential energy surface for the reaction with a F leaving group indeed evidences the lack of a net distinction between the E1cb and E2 reaction paths, which appear to merge smoothly into each other in these borderline cases.     

A generalization of a theorem by C. Miranda

Summary In this paper we study the well-posedness of the Dirichlet problem for an elliptic non divergence form second order equation. The coefficients are not assumed to be continuous but their derivatives are supposed to belong to a suitable Morrey space hence generalizing a classical result by C. Miranda.This work was partly financially supported by a national project of the Italian Ministero della Pubblica Istruzione and by G.N.A.F.A.-C.N.R.     

Solvent effects on the UV (n --> pi*) and NMR (13C and 17O) spectra of acetone in aqueous solution. An integrated car-parrinello and DFT/PCM approach

The accurate reproduction of ultraviolet and nuclear magnetic resonance spectra of acetone in aqueous solution is used as a test of an integrated computational tool rooted in the density functional theory, the polarizable continuum model, and the Car-Parrinello dynamics. The analysis and solution of several conceptual and practical issues results in a robust and effective approach, which also can be used by nonspecialists and provides a general and powerful complement to experimental techniques.     

Synthesis of α-oxazolinylalkanamides

The synthesis of α-oxazolinylalkanamides 2, based on the reaction of α-chloroalkyloxazolines 1 with hexacarbonyltungsten [W(CO)₆] and lithium amides, has been developed. A plausible mechanism involving the ketene 5 as the intermediate is also proposed.     

On the role of energy convexity in the web function approximation

For a given p > 1 and an open bounded convex set we consider the minimization problem for the functional over Since the energy of the unique minimizer u_p may not be computed explicitly, we restrict the minimization problem to the subspace of web functions, which depend only on the distance from the boundary δΩ. In this case, a representation formula for the unique minimizer v_p is available. Hence the problem of estimating the error one makes when approximating J_p(u_p) by J_p(v_p) arises. When Ω varies among convex bounded sets in the plane, we find an optimal estimate for such error, and we show that it is decreasing and infinitesimal with p. As p → ∞, we also prove that u_p − v_p converges to zero in for all m < ∞. These results reveal that the approximation of minima by means of web functions gains more and more precision as convexity in J_p increases.     

The weathering of natural and artificial stones in the baroque church of S. Pietro in Valle (Fano-Italy)

The church of San Pietro in Valle in Fano is with good reason considered one of the outstanding examples of baroque art in Central Italy. Currently the church is in a serious degradation status. For this reason, and in order to devise a correct conservative restoration project, a scientific study has been carried out, aimed at characterizing mortars used for the application of marble decorations and the different degradation products occurring in the church (i.e. pulverizations, encrustations, salt efflorescences, and condensation water). In the following, results obtained analyzing the different sample typologies by optical microscopy, X-ray diffraction, electron scanning microscopy with energy-dispersion micro-analytical system, ion chromatography, and head-space solid phase microextraction-gas chromatography-mass spectrometry will be reported.