The mechanochemical reactions between CsF and kaolinite

The grinding of a mixture containing kaolinite and CsF was carried out by three different techniques, short manual grinding, Fisher mechanical mortar and Retsch ball mill. In addition to different cesium aluminium silicates which were detected by X-ray powder diffraction, a new type of intercalation complex was identified by FTIR spectroscopy. The X-ray diffractogram of this complex did not show any basal spacing, which may characterize the complex but the 0.715 nm characteristic peak of the untreated kaolinite became very weak. The Retsch ball mill led to a slight destruction of the kaolinite and the formation of small amounts of the new intercalation complex. The delamination of book-like kaolinite assemblages was observed after the manual and Fisher mortar grindings. In the latter grinding techniques the kaolin-like layers persisted and served as the framework for the intercalation complexes. Received: 4 February 1998 Accepted: 11 March 1998     

NMR monitoring of chain-specific stability in heterotrimeric collagen peptides

NMR spectroscopy is used to investigate the heterotrimeric nature of a collagen model peptide. Two distinct peptide chains (A and B) were synthesized to model a site in heterotrimeric basement membrane type IV collagen. For NMR studies, four amino acids in the B chain were labeled with 15N/13C. Circular dichroism spectroscopy and differential scanning calorimetry thermal stability results on a solution with both A and B peptides (molar ratio 2A:1B) are consistent with the presence of one heterotrimeric triple-helical molecular species. Heteronuclear single quantum coherence experiments on homotrimers of the B peptide show trimer peaks which disappear at temperatures higher than 10 degrees C, while the 2A:1B mixture has trimer peaks with increased stability and altered chemical shifts. The reduction in the number of Leu trimer peaks from three to one and the increased stability of trimer resonances confirm the participation of B chains in an AAB heterotrimer molecule.     

Oxaziridine-mediated catalytic hydroxylation of unactivated 3 degrees C-H bonds using hydrogen peroxide

The design, structural characterization, and evaluation of a unique class of 1,2,3-benzoxathiazine-based oxaziridines as potent O-atom transfer agents for catalytic C-H hydroxylation and alkene epoxidation are described. Turnover of this reaction is made possible by employing a diaryl diselenide cocatalyst and urea.H2O2 as the terminal oxidant. Oxidation of saturated hydrocarbons is strongly biased toward 3 degrees C-H bonds even in systems possessing a significantly greater number of methylene groups. In addition, the benzoxathiazine catalyst is effective for epoxidation of terminal and electron-deficient olefins. Collectively, these findings represent an important first step toward the advancement of general methodology for selective C-H oxidation.     

Hadronic wave functions at short distances and the operator product expansion

The operator product expansion, of appropriate products of quark fields, is used to find the anomalous dimensions which control the short distance behavior of hadronic wave functions. This behavior in turn controls the high-Q² limit of hadronic form factors. In particular, we relate each anomalous dimension of the nonsinglet structure functions to a corresponding logarithmic correction factor to the nominal α_S(Q²)/Q² fall off of meson form factors. Unlike the case of deep inelastic lepton-hadron scattering, the operator product necessary here involves extra terms which do not contribute to forward matrix elements.     

Electron Anomalous Magnetic Moment in Basis Light-Front Quantization Approach

We apply the Basis Light-Front Quantization approach to the Hamiltonian field theory of Quantum Electrodynamics in free space. We solve for the mass eigenstates corresponding to an electron interacting with a single photon in light-front gauge. Based on the resulting non-perturbative ground state light-front amplitude we evaluate the electron anomalous magnetic moment. The numerical results from extrapolating to the infinite basis limit reproduce the perturbative Schwinger result with relative deviation less than 0.6%. We report significant improvements over previous works including the development of analytic methods for evaluating the vertex matrix elements of QED.     

Über den Mechanismus der Perkin’schen Reaktion

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