Vertical and nonvertical participation by sulfur,selenium, and tellurium

The mechanism of stabilization of positive charge on carbon by sulfur, selenium, or tellurium at the beta-position has been investigated kinetically, by measurement of rate enhancements, and structurally, by variation of the bond strength to the leaving group. Stabilization can occur either nonvertically with formation of a bridged intermediate or vertically through hyperconjugation within an open carbocation. We observed large rate enhancements (10(5) for S, 10(6) for Se) in 97% aqueous trifluoroethanol with trifluoroacetate as the leaving group. These enhancements are consistent with either mechanism. Product structures also are consistent with either mechanism. Nine crystal structures revealed that the bond to the leaving group (C-O) is lengthened by the presence of S or Se at the beta-position, in proportion to the basicity of the leaving group. This lengthening is not accompanied by angle distortions expected for the bridging mechanism. The crystallographic data support vertical (hyperconjugative) character along the reaction coordinate, more so for selenium than sulfur.     

A new approach for the large-scale generation of mature dendritic cells from adherent PBMC using roller bottle technology

Background  

Human monocyte-derived DC (mDC) loaded with peptides, protein, tumor cell lysates, or tumor cell RNA, are being tested as vaccines against multiple human malignancies and viral infection with great promise. One of the factors that has limited more widespread use of these vaccines is the need to generate mDC in large scale. Current methods for the large-scale cultivation of mDC in static culture vessels are labor- and time- intensive, and also require many culture vessels. Here, we describe a new method for the large-scale generation of human mDC from human PBMC from leukopheresis or buffy coat products using roller bottles, never attempted before for mDC generation. We have tested this technology using 850 cm² roller bottles compared to conventional T-175 flat-bottom static culture flasks.     

A bound for

Let denote the largest irreducible character degree of a finite group , and let be a prime. Two results are obtained. First, we show that, if is a -solvable group and if , then . Next, we restrict attention to solvable groups and show that, if and if is a Sylow -subgroup of , then .

     

Photoelectron diffraction study of a catalytically active overlayer: C2H2 on Pd{111}

A quantitative structure determination of a newly discovered (2×2) adsorption phase of acetylene chemisorbed on Pd{111} has been performed by scanned-energy mode photoelectron diffraction: this phase corresponds to the threshold coverage for the catalytic conversion of acetylene to benzene. The carbon atoms in the C₂H₂ molecule are located almost over bridge sites with a C–C bond length of 1.34+0.10 Å, the centre of the molecule being positioned almost over a hollow site. Of the two hollow sites the hcp site (directly above a second layer Pd atom) is favoured, particularly by a subset of the data most sensitive to this aspect of the structure, but the full analysis indicates that the fcc site (above a third layer Pd atom) cannot formally be excluded. The adsorption site adopted by acetylene in the higher coverage phase on Pd{111} is essentially identical. This is the dominant structure in the coverage regime which is catalytically active for the conversion of acetylene to benzene. The implications of these findings for acetylene coupling reactions over Pd{111} are discussed.     

Inelastic neutron scattering study of the ferroelastic phase transition of lead phosphate (PO4)2Pb3

A soft phonon mode is observed above 395°C at zone boundary points of the high temperature β phase. A quasi-elastic scattering exists above the ferroelastic transition at 180°C and progressively vanishes when the temperature is raised. A cross over from 3d to 2d regime is observed in the same temperature range.     

Temperature dependence of the Raman cross section and light absorption in cubic BaTiO3

The temperature dependence of the Raman spectrum in the cubic phase of BaTiO₃ is described. The cross section decreases when the temperature increases, which is contrary to a normal second order effect behaviour. The associated measurements of the optical absorption definitely prove that this variation is intrinsic. The anomalous Raman spectrum is related to the existence in the crystal of anisotropic fluctuation domains.     

Off-energy-shell effects in multiple scattering

The elastic scattering from a two-body bound system is investigated in order to determine what information about the nuclear structure and the projectile-nucleon interaction may be obtained at intermediate energies. Emphasis is placed on the kinematics and the importance of properly treating the overlapping potential region. The kinematics of the “fixed scatterer” and “impulse” approximations result in differences which are still significant at intermediate energies. As far as scattering information is concerned, the overlapping potential region is the interesting one since it requires explicit knowledge of the interaction. Our results suggest that for nucleon scattering at intermediate energies the corrections due to properly taking into account off-energy-shell effects are likely to be comparable with the contributions due to the short-range two-body correlations. The relevance of the above results to various models currently employed in analyzing high- and intermediate-energy nuclear scattering is also discussed.