A Stereoselective Cathodic Coupling of Aryl Styryl Sulfones

Abstract

The cathodic coupling of unsaturated sulfones (title compounds) performed in aprotic media in the presence of lithium salts as electrolyte affords d,l dimers almost exclusively.     

Cathodic modifications of platinum surfaces in organic solvent: reversibility and cation type effects

Cathodic modification of platinum surfaces leads to the formation of iono-platinic phases ([Pt(n-), M+, MX]), which involves the insertion of cations and salts into the platinum electrode. This process was investigated at the local scale by in situ observation of surface electrochemical processes by atomic force microscopy (EC-AFM) techniques as a function of the salt and the injected charge, with special attention about the process reversibility. AFM images recorded in solution after the cathodic modifications of well-defined platinum surfaces [epitaxial platinum deposit on (100) MgO substrate] show drastic modification on the morphology of the surface, confirming previous ex situ studies. The amplitude of the modifications directly depends on both the nature of supporting electrolyte and the quantity of charge injected into the platinum. As long as the injected charge remains small enough to maintain the adhesion of the Pt deposit onto the MgO substrate, the process was found to be fully reversible. Indeed, impressive morphology changes occur under the cathodic treatment (formation of [Pt(n-), M+, MX]) but the initial geometry is totally recovered after reoxidation of the iono-platinic phase. This cycle of reduction-reoxidation can be performed several times without any significant alteration of the recovered surface and of its structural characteristics. It is suggested that the modification starts at the interface solution platinum surface and then its insertion into the platinum surface.     

Nonmagnetic insulator state in Na1CoO2 and phase separation of na vacancies

Crystallographic, magnetic, and NMR properties of a Na1CoO2 single crystal with x approximately = 1 are presented. We identify the stoichiometric Na1CoO2 phase, which is shown to be a nonmagnetic insulator, as expected for homogeneous planes of Co3+ ions with S = 0. In addition, we present evidence that, because of slight average Na deficiency, chemical and electronic phase separation leads to a segregation of Na vacancies into the well-defined, magnetic, Na0.8CoO2 phase. The importance of phase separation is discussed in the context of magnetic order for x approximately = 0.8 and the occurrence of a metal-insulator transition for x --> 1.     

Balance of mass, momentum, and energy in splintering central collisions for 40Ar up to 115 MeV /Nucleon

For central collisions of (17-115)A MeV 40Ar+Cu, Ag, Au, an overall balance is determined for the average mass, energy, and longitudinal momentum. Light charged particles and fragments are separated into forward-focused and isotropic components in the frame of the heaviest fragment. Energy removal by the isotropic component reaches 1-2 GeV. For such high deposition energies, statistical multifragmentation models predict much more extensive nuclear disassembly than is observed.     

Gamow-teller strengths of the inverse beta transition 176Yb-->176Lu for spectroscopy of proton-proton and other sub-MeV solar neutrinos

Discrete Gamow-Teller (GT) transitions 176Yb-->176Lu at low excitation energies have been measured via the ( 3He,t) reaction at 450 MeV and at 0 degrees. For 176Yb, two low-lying states are observed, setting low thresholds Q(nu) = 301 and 445 keV for neutrino ( nu) capture. Capture rates estimated from the measured GT strengths, the simple two-state excitation structure, and the low Q(nu) in Yb-Lu indicate that Yb-based nu detectors are well suited for a direct measurement of the sub-MeV solar electron-neutrino ( nu(e)) spectrum including pp neutrinos.     

The cathodic cleavage of aromatic sulphonamides: an elegant way to produce amino radicals themselves fully characterized by means of the spin marking technique

Sulphonamides may lead, in the course of their cathodic cleavage, to intermediate amino radicals. These radicals may be reduced or trapped rapidly by nitrones added “ in situ ”. The method allows (by means of ESR spectral analysis) elements for establishing cleavage mechanisms to be obtained.     

Solid electrodes modified by Ni–Pd thin layers: Highly efficient and low cost cathodic materials for achieving bond scissions in non-aqueous media

A simple mode of palladization of nickel is described. The obtaining of Ni–Pd surfaces (by means of a rapid redox displacement of Ni⁰ by Pd²⁺) permits the electro-catalytic scission of carbon–halogen linkages in non-aqueous media. This palladized material (presumably an alloy) is found to be quite stable. It affords the cleavage of organic halides (alkyl iodides and bromides, benzylic and aromatic halides) with an important energy gain if compared to reduction potentials already reported at more conventional electrodes such as glassy carbon (GC). This preliminary work focuses on a new class of solid electrodes of modified substrates (like glassy carbon, nickel, platinum, palladium, copper or gold) by a very thin layer (a few tens nm) of Ni–Pd. Presumably, the catalytic effect could be based on the synergetic action of Ni and Pd both involved in their oxidative insertion in the C–X bonds.     

Parity-broken chiral spin dynamics in Ba₃NbFe₃Si₂O₁₄

The spin-wave excitations emerging from the chiral helically modulated 120° magnetic order in a langasite Ba?NbFe?Si?O?? enantiopure crystal were investigated by unpolarized and polarized inelastic neutron scattering. A dynamical fingerprint of the chiral ground state is obtained, singularized by (i) spectral weight asymmetries answerable to the structural chirality and (ii) a full chirality of the spin correlations observed over the whole energy spectrum. The intrinsic chiral nature of the spin waves' elementary excitations is shown in the absence of macroscopic time-reversal symmetry breaking.     

Role of antisymmetric exchange in selecting magnetic chirality in Ba3NbFe3Si2O14

We present an electron spin resonance (ESR) investigation of the acentric Ba(3)NbFe(3)Si(2)O(14), featuring a unique single-domain double-chiral magnetic ground state. Combining simulations of the ESR linewidth anisotropy and the antiferromagnetic-resonance modes allows us to single out the Dzyaloshinsky-Moriya (DM) interaction as the leading magnetic anisotropy term. We demonstrate that the rather minute out-of-plane DM component d(c)=45 mK is responsible for selecting a unique ground state, which endures thermal fluctuations up to astonishingly high temperatures.     

Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.