Photoreduction de la benzophenone par des thioethers etudiee par pnic

CIDNP (Chemically Induced Dynamic Nuclear Polarization) studies of the photoreduction of benzophenone by R-CH₂-S-R' show evidence for the $\text{formation of vinylic}$ deratives and adducts. The central intermediate in the reaction scheme is the radical pair R-CH-S-R' φ₂-C-OH^t. A study with selenides shows a different behaviour for these compounds.     

Reanalysis of the mass difference ofB_d^0 - \bar B_d^0 within the Minimal Supersymmetric Standard Modelwithin the Minimal Supersymmetric Standard Model

We present a detailed and complete calculation of the loop corrections to the mass difference $\Delta {{m_{B_d^0 } } \mathord{\left/ {\vphantom {{m_{B_d^0 } } {m_{B_d^0 } }}} \right. \kern-0em} {m_{B_d^0 } }}$ . We include charginos and scalar up quarks as well as gluinos and scalar down quarks on the relevant loop diagrams. We include the mixings of the charginos and of the scalar partners of the left and right handed quarks. We find that the gluino contribution to this quantity is important with respect to the chargino contribution only in a small part of phase space: mainly when the gluino mass is small (～100 GeV) and the symmetry-breaking parameterm _S is below 300 GeV. This contribution is also important for very large values of tanβ (～50) irrespective of the other parameters. Otherwise, the chargino contribution dominates vastly and can be roughly as large as that of the Standard Model. We also present the contribution of the charged Higgs to the mass difference $\Delta {{m_{B_d^0 } } \mathord{\left/ {\vphantom {{m_{B_d^0 } } {m_{B_d^0 } }}} \right. \kern-0em} {m_{B_d^0 } }}$ in the casem _b tanβ?m _t cotβ. This last contribution can be larger than the Standard Model contribution for small values of the Higgs mass and small values of tanβ.     

Radiometric detector options to aid in DOE high activity waste tank in situ characterization efforts

Radioactive waste cleanup and subsequent closure of waste storage tanks is currently underway at the Savannah river site, prompting the need to characterize the residual contents (heels) of the tanks. Occasionally, results from laboratory analyses indicate alternative sub-sampling strategies are needed, resulting in repetitive efforts to sample and analyze tank bottoms. The development of a system for in situ tank analyses using a radiometric probe, which could be lowered into a waste tank, could aid in identifying waste structures on tank bottoms requiring further sampling and characterization. Ideally, the probe would provide information for determining which structures were higher in concentrations of actinides and fission products characteristic of DOE high level waste (HLW) heels. Although only a limited set of isotopes can be measured directly without extensive radiochemical separations, the low-energy photon spectra of HLW do offer some intriguing possibilities for characterization using a radiometric probe. One possibility for obtaining a low-energy photon spectrum in the presence of high levels of interfering radiation would be to design a probe primarily based upon recently developed technology from Amptek Inc. Such a detector would be relatively insensitive to the high photon background, which would paralyze conventional gamma probes (i.e. sodium iodide) subjected to the same radiological conditions. The prototype detector is capable of successfully obtaining high resolution measurements at very high count rates (in excess of 500,000 counts per second). An overview of measurements obtained from various HLW samples using the prototype Amptek detector, as well as some additional detector technologies, which could enhance this prototype, will be discussed.     

A Convenient Synthesis of Functionalized α‐Methylidenebutano‐4‐lactams

A concise synthetic approach to functionalized α‐methylidenebutanolactams has been developed. The synthetic strategy is based on the preliminary assembly of the lactam template equipped with appropriate functionalities. Subsequent installation of the methylidene by a metalation/alkylation/elimination sequence completed the elaboration of the racemic title compounds.     

A new total synthesis of porritoxin

A concise and efficient total synthesis of the phytotoxin porritoxin is described. The key step of the synthesis is based upon a Parham cyclization methodology which enables the creation of the lactam unit embedded in the title compound framework with the concomitant formation of the tethered hydroxyakyl chain.     

Kinetics of RAFT homopolymerisation of vinylbenzyl chloride in the presence of xanthate or trithiocarbonate

The RAFT homopolymerisation of vinylbenzyl chloride (VBC, or chloromethyl styrene CMS) in bulk and in acetonitrile initiated by α,α′-azoisobutyronitrile (AIBN) in the presence of two chain transfer agents, O-ethyl-S-(1-methyloxycarbonyl)ethyl xanthate and dibenzyl trithiocarbonate, is presented. The reactions were monitored by ¹H nuclear magnetic resonance spectroscopy in the presence of 1,2-dichloroethane as the internal standard. Such a technique enabled one to assess the evolutions of log ([M]₀/[M]) and VBC conversion vs. time that were shown to be linear. Tobolsky’s law allowed one to determine the square of the propagation rate constant to the termination rate constant, $k_{\text{p}}^2/k_{\text{te}}$, of VBC, that worths about 3 × 10^?3 l mol^?1 s^?1 at 80 °C. On the one hand, the controlled character of the polymerisation involving dibenzyl trithiocarbonate was confirmed by size exclusion chromatography. On the other hand, the molar masses of poly(VBC) polymerised in the presence of the xanthate agent decreased with monomer conversion, as already stated with the macromolecular design via interchange of xanthates (MADIX) polymerisation of styrene.     

Approximate D4d symmetry of the cation site in hexahydrated trichlorides of rare earths and actinides

Many spectroscopic and magnetic properties of the monoclinic hexahydrated chlorides of rare earths have been shown to approximate those of a uniaxial crystal. We explain this approximate symmetry by the shape of the coordination polyhedron of the rare-earth ions which is approximately that of a square antiprism of D_4d symmetry, with an inverse eightfold axis. The directions of this axis and of the spectroscopically or magnetically determined axes agree well. The absence of M_J mixing for some levels, as observed in the Zeeman effect, can be explained by an eightfold axis. As a first approximation, we propose a study of the magnetic ions using a D_4d crystal field hamiltonian with the limited set of even parameters B₀², B₀⁴ and B₀⁶; polarization and intensity spectral data, Zeeman effect, electron paramagnetic resonance and susceptibility measurements can be interpreted in this symmetry. Such remarks also apply to actinide hexahydrated chlorides.     

Reductive photocyclization of benzo[b]furans and their analogs

The UV irradiation of substituted 2,3-diphenylbenzo[b]furans and of 2,3-diphenyl-5-t-butylfuran in n-propylamine gives 1,4-dihydro derivatives of the corresponding aromatic cyclized compounds. This reaction does not involve a photoreduction. It can be concluded from deuterium labelling experiments that H atoms of the alkyl chain of n-propylamine are incorporated in the product. When the solvent is not an unhindered primary amine, only totally aromatic photocyclized products are obtained. It is proposed that hydrogens eliminated during formation of the isolated compounds are released in a reductive form and not as radicals. This is supported by the fact that acenaphthylene is reduced when irradiated in n-propylamine together with 2,3-diphenylbenzo[b]furan under conditions which do not promote, photoreduction. This seems to be a general finding in that the irradiation of stilbene in n-propylamine to acenaphthylene is the same as that of 2,3-diphenylbenzo[b]furan.     

Ligand K-edge X-ray absorption spectroscopy of [Fe4S4]1+,2+,3+ clusters: changes in bonding and electronic relaxation upon redox

Sulfur K-edge X-ray absorption spectroscopy (XAS) is reported for [Fe(4)S(4)](1+,2+,3+) clusters. The results are quantitatively and qualitatively compared with DFT calculations. The change in covalency upon redox in both the [Fe(4)S(4)](1+/2+) (ferredoxin) and the [Fe(4)S(4)](2+/3+) (HiPIP) couple are much larger than that expected from just the change in number of 3d holes. Moreover, the change in the HiPIP couple is higher than that of the ferredoxin couple. These changes in electronic structure are analyzed using DFT calculations in terms of contributions from the nature of the redox active molecular orbital (RAMO) and electronic relaxation. The results indicate that the RAMO of HiPIP has 50% ligand character, and hence, the HiPIP redox couple involves limited electronic relaxation. Alternatively, the RAMO of the ferredoxin couple is metal-based, and the ferredoxin redox couple involves extensive electronic relaxation. The contributions of these RAMO differences to ET processes in the different proteins are discussed.